After ModMon sample collections, Dr. Nathan Hall (UNC-IMS) summarizes the data collected via sonde and any visual observations. Profiles are also created along the sampling stations.

2024

The freshening effect of Hurrican Debby is still apparent. The surface layer salinity was completely fresh downstream to station 70. Along the bottom, the salt wedge reached upstream of station 30. Stratification was intense with surface to bottom salinity differences of about 10 in the upper estuary between stations 30 and 120 and salinity differences greater than 5 in the lower estuary. The temperature profiles showed an interesting pattern at the upstream stations with cool river flowing between a warmer, freshwater surface layer, and similarly warm, salty bottom layer. Strong stratification and warm temperatures led to hypoxic bottom water from station 30 to 140. A broad zone of elevated chlorophyll (20-30 ug/L) occurred from stations 100 to 160. Microscopic examination of surface water from station 140 showed a mixed community of small centric diatoms and two large dinoflagellates, Levandarina fissa and Polykrikos hartmannii. These two dinoflagellates can conduct photosynthesis but also eat other phytoplankton including small diatoms. There’s probably a lot of phytoplankton eating phytoplankton called mixotrophy going on out there. None of these phytoplankton are toxic or are known to cause fish kills.

The Neuse basin received a lot of rain in late July. By the end of July flows were already about 4 times the seasonal norm. Then, in early August Hurricane Debby dumped 5-10 additional inches and flows in the Neuse peaked above 20,000 CFS. That’s about ten times the normal flow but less than half of what was observed during the super floods following Hurricanes Floyd and Matthew. The salinities in the estuary clearly show the impact of the flood pulse with surface salinities less than 2 extending downstream to station 120. The bottom waters were still very salty and surface to bottom salinity differences of greater than 10 extended from station 50 to 160. Water temperatures ranged from 24 upstream to 26 downstream. Despite warm waters and intense stratification, bottom waters were not hypoxic. Perhaps this stems from aeration due to intense wind mixing in the days prior to sampling. I bet bottom waters rapidly became hypoxic in the days after the 12 August sampling trip. Chlorophyll a was low (< 15 ug/L) throughout the estuary with highest values generally downstream of station 120. Elevated turbidity (10-20 NTU) was observed in the fresh flood waters at the head of the estuary.

River flows in mid July were near the seasonal average. The tip of the salt wedge was between stations 20 and 30. Bottom water salinity ranged from ~13 at station 30 to over 20 at station 180. Water temperatures ranged from 26 to 28 C and the combination of warm waters and strong stratification led to hypoxic bottom water conditions from stations 30 to 140. Chlorophyll was mostly < 15 ug/L but near surface peaks > 40 and 20 ug/L were observed at stations 30 and 140, respectively. Microscopic examination of the surface water from station 30 showed that the high biomass was caused by a small cryptophyte. Cryptophytes are nutritious food for zooplankton and haven’t been associated with fish kills.

The estuary looks very similar on 8 July to how it looked on 26 June. The upper estuary was moderately stratified from stations 30 to 100 with surface to bottom salinity differences of 2-3 ppt. The lower estuary was again impacted by intrusion of high salinity water from the Intercoastal Waterway which formed a high salinity bottom water layer with salinity greater than 20 from stations 120 to 180. Unlike on 26 June, bottom waters were hypoxic (< 2 mg/L) or nearly hypoxic (~ 3 mg/L) from the tip of the salt wedge at station 30 to station 180. No blooms were observed and Chla was less than 15 ug/L throughout the estuary. Surface water turbidity was less than 5 NTU throughout the estuary.

On 26 June the upper estuary was only moderately stratified with surface to bottom salinity differences generally less than 2. Weather records at Havelock (station KNKT) show sustained 15+ mph winds on June 24 and 25 which likely mixed the water column. Only the lower estuary was strongly stratified and that was due to intrusion of high salinity (~30 ppt) water from the Intercoastal Waterway. Moderate stratification and likely recent mixing produced normoxic bottom waters in the upper and mid-estuary. Bottom water hypoxia only occurred in the salty bottom waters downstream at stations 120 to 180. Water temperature ranged from 29 upstream at the surface to 26 C downstream. Part of this apparent temperature gradient is likely a sampling artifact due to the downstream stations being sampled in the early morning when waters are at their daily minimum and the upstream stations being sampled in the early afternoon when temperature is near its daily max. The chlorophyll probe malfunctioned on this trip. So no chlorophyll fluorescence data is reported. Turbidity in the upper half of the water column was less than 5 NTU throughout the estuary.  Stay cool.

In the two weeks leading up to the sampling on 10 June, the Neuse basin received very little precipitation and river flows decreased to about a quarter of the seasonal median. Salinity in the upper estuary showed a noticeable increase with measurable salinity at station 20. The upper estuary was strongly stratified with surface to bottom salinity differences greater than 5 and the lower estuary was moderately stratified with surface to bottom salinity differences of 2-3. Surface water temperature ranged from about 26 C in the incoming river water to about 25 C in the lower estuary. Bottom waters were about 2 degrees cooler throughout much of the estuary and reinforced salinity based stratification. Hypoxic (< 2 mg/L) bottom water occurred from station 30 downstream to station 100 and bottom water dissolved oxygen of the lower estuary was only 3-4 mg/L. Chlorophyll ranged from 5-20 ug/L with the higher values occurring in the incoming river water and near surface from stations 30 to 140. Turbidity was approximately 10 NTU in the incoming river water but was generally less than 5 NTU downstream in the estuary.

On 22 May 2024, the estuary was a little saltier than on 23 April with surface salinity in the upper estuary (stations 0-100) ranging from 0 to 12 and salinity in the lower estuary (stations 120-180) ranging from 13 to 16. The upper estuary was strongly stratified with surface to bottom salinity differences from 4-9. Stratification in the lower estuary was weaker with surface to bottom salinity differences of about 2. As on 23 April, dissolved oxygen was normoxic except for hypoxic conditions at the tip of the salt wedge in the bottom water of station 30. Chlorophyll was generally about 10 ug/L with isolated near surface peaks of ~15 ug/L at stations 30, 50 and 160. Turbidity of the incoming river water was ~20 NTU but decreased to below 5 NTU downstream of station 30.

On 23 April 2024, salinities were near average for spring with surface salinity in the upper estuary (stations 0-100) ranging from 0 to 8 and salinity in the lower estuary (stations 120-180) ranging from 9 to 15. The estuary was moderately stratified from stations 30 to 180 with surface to bottom salinity differences of ~3. Temperature ranged from about 17 C upstream to about 16 C downstream. Oxygen conditions were normoxic except for at the tip of the salt wedge at station 30 where bottom waters were hypoxic. A localized region of elevated chlorophyll (30-40 ug/L) was observed in the surface waters at stations 30 and 50. Microscopic examination of station 50 surface water revealed ​​​​​​a mixed community of diatoms, cryptophytes, and dinoflagellates with no species of concern regarding toxicity or association with fish kills. Turbidity was elevated (~ 6 NTU) in the incoming freshwater at stations 0 and 20 and in the bottom waters of stations 160 and 180 but was otherwise less than 5 NTU.

The conditions in the estuary on Apr. 8 were very similar to those on Mar. 26. The depth averaged salinity ranged from about 10 to 18 in the lower estuary downstream of station 120. However, the estuary was more strongly stratified with surface to bottom salinity differences in the lower estuary of 4 to 7 and in the upper estuary 7 to a max of about 12 near the tip of the salt wedge at station 30. The zone of subsaturated bottom water oxygen near the tip of the salt wedge expanded downstream to include the bottom waters from stations 30 downstream to station 70. At stations 30 and 50, the bottom waters were hypoxic (< 2 mg/L) which is unusual for this early in the season and for water temperatures that were only 13-14C. The rates of oxygen consumption at these temperatures would be low which means that the strong stratification observed during late March was probably maintained through the time of sampling on 8 April. Chlorophyll was generally less than 5 throughout the estuary with the exception of a broad zone of elevated surface chlorophyll (> 15 ug/L) from stations 50 to 100. Within this area, maximum biomass was observed near the surface at stations 60 and 70. Microscopic examination of station 70 surface water showed a community primarily composed of the dinoflagellate, Levanderina fissa, a cryptophyte, and a small raphidophyte. The small raphidophyte was most likely Heterosigma akashiwo and has been associated with fish kills in estuaries worldwide. Despite this global association with fish kills, high densities of Heterosigma akashiwo are pretty common in the Neuse and New Rivers and have rarely been associated with fish kills here. It’s a species to keep an eye on though. Elevated turbidity (> 10 NTU) at the upstream stations 0 and 20 was related to high river flow. Turbidity decreased to less than 3 NTU in the estuary below station 70.

River flow in the couple weeks leading up to the March 26 sampling event was slightly higher than the seasonal norm. On March 26, salinity in the lower estuary (station 120 and downstream) ranged from about 10 to 18. These salinities are  typical for this time of year and an indication that the strong river flow is bringing down the above average salinity that has been in place for over a year now. Water temperatures were cool, ranging from ~11 to 13 C. Stratification was moderate in the lower estuary but strong upstream of station 120 where surface to bottom salinity differences were ~ 7. There was no hypoxia in the estuary but there was a zone of subsaturated bottom water with a DO concentration of ~4 mg/L at station 30 near the tip of the salt wedge. Chlorophyll was generally less than 10 ug/L throughout the estuary with the exception of a zone of elevated surface biomass at stations 50 and 60 and a subsurface maximum along the pycnocline at about 2 m depth at stations 30 and 50. Microscopic examination of station 50 surface water revealed a phytoplankton community dominated by a cryptophyte. Their high biomass is no cause for concern.  In fact, cryptophytes are readily grazed, and nutritious prey for zooplankton.

Hi all,

 
February was generally dry and river flows were running at 50-100% below the seasonal average. The estuary is still saltier than normal, particularly for late winter. The saltwedge was above New Bern and bottom water salinty at New Bern (station 30) was about 10. Salinity was 18 at the mouth. The lower estuary downstream of station 120 was weakly stratified with surface to bottom salinity differences less than 2, but the upper estuary was highly stratified with vertical salinity differences greater than 5. Water temperature ranged from 11 C downstream to about 14 C in the upstream surface waters. Oxygen conditions were above 4 mg/L throughout the estuary though bottom waters at stations 30 and 50 were close to 4 mg/L. Dissolved oxygen was supersaturated near the surface at stations 50 and 60. Fluorescence profiles showed a bloom in this area with Chla greater than 40 ug/L at the surface of station 50. I looked at the surface water sample from station 50 and it was dominated by the same cool-season dinoflagellate, Heterocapsa rotundata, that was prominent in February. There were also a bunch of another winter dinoflagellate, Heterocapsa triquetra, and the euglena, Eutreptia sp. None of these are known to be toxic or linked to fish kills. 
 
Best,
Nathan

Hi all,
River flow in late January was about twice the seasonal average and it significantly freshened the estuary. On 8 Feb. 2024, surface salinity was less than ten all the way down to station 120. The lower estuary, however, was still very salty with salinity near 20 at the mouth. The estuary was highly stratified with surface to bottom salinity differences of more than 5 from station 20 to 160. Water temperature ranged from 7-9 C with the warmest water along the bottom at station 30 near the tip of the salt wedge. Chlorophyll was generally less than 20 ug/L but there was a near surface peak of about 20 ug/L at station 50 and a bottom water maximum of about 25 ug/L at stations 60 and 70. I looked at the surface water sample from station 50 and it was a mix of the cool-season dinoflagellate, Heterocapsa rotundata, cryptophytes, and diatoms.  None of these are known to be toxic. Turbidity was elevated (>10 NTU) near the estuary head, a likely response to the prior elevated river flow.
Best,
Nathan

Starting Christmas Eve, several strong cold fronts produced significant rainfall in the Neuse River watershed and river flows peaked over 8000 CFS prior to sampling on 16 January 2024. The high river flow completely freshened the estuary upstream of New Bern (stations 0 and 20) and surface waters were fresh downstream to station 60. Surface water at station 180 was only about 15 where it had been about 20 a month earlier. The estuary was strongly stratified with surface to bottom salinity differences of 5-7 along the estuary from New Bern to the mouth. Water temperature was 8-10 C throughout the estuary. Chlorophyll was less than 15 ug/L throughout the estuary with highest levels of ~ 15 ug/L occurring as a broad surface maximum from stations 60 to 140. High river flows caused high turbidity (>20 NTU) at the upper stations (stations 0-30).

2023

A few rain events in late November increased river flow at Kinston from less than 400 CFS in mid-November to 2400 CFS by Thanksiving, a value near the seasonal average. On 6 December 2023, the estuary was still very salty but surface waters above New Bern were significantly freshened and bottom water salinity at station 0 was back to its normal freshwater condition. The estuary was strongly stratified with surface to bottom salinity differences of 13 to 5 from above New Bern to the Mouth. Cooler (10-14 C) water temperatures prevented bottom water hypoxia. Chlorophyll was less than 15 ug/L throughout the estuary.

Other than a decline of water temperature by another 2-3 C down to 15-16C, conditions on 6 November 2023 were very similar to those on 9 and 24 October. The estuary was very salty and moderately stratified. Bottom water salinity at the head of the estuary increased to 10, ranking in the top 5 of salinity measurements at that location. Chlorophyll was generally less than 10 ug/L but again there was a small zone of elevated chlorophyll (30-40 ug/L0 at the surface at station 20. Microscopy revealed it was the same non-toxic dinoflagellate, Levandarina fissa, that had been observed blooming at station 20 on 9 and 24 October. The bloom was positioned at the leading edge of the freshwater plume and highest biomass was just slightly below the surface. The combination of consistently low flows (400-800 CFS from 9 October to 6 November 2023) and the ability of the motile dinoflagellate to take advantage of the riverine nutrients and minimize downstream advection through vertical migrations probably had something to do with its persistence at this upstream location over the past month.

Conditions on Oct 24th were very similar to those on Oct. 9. The estuary as a whole was still unusually salty and bottom waters at station 0 still had a salinity of 8. Water temperatures were a couple of degrees cooler with surface temperatures ranging from about 16 to 18 and bottom waters a couple of degrees warmer (18-19). Surface to bottom salinity differences ranged from 8 at the head of the estuary to about 4 at the mouth. The most upstream stations (0 and 20) had hypoxic bottom water. Again, chlorophyll values were generally less than 15 ug/L with the exception of a bloom at station 20 where chlorophyll was greater than 40 ug/L.  The bloom was still dominated by the non-toxic, warm weather bloom forming dinoflagellate, Levandarina fissa (a.k.a. Gyrodinium instriatum).

On Oct. 9, the estuary was still very salty with downstream salinity greater than 20. Bottom water at station 0 (usually freshwater) had a salinity of 8 which is in the top ten highest ModMon salinity measurements. Temperature ranged from about 19-22 C with warmer and saltier waters along the bottom. The upper estuary above New Bern and near the bend (stations 100 and 120) had hypoxic bottom waters. Chlorophyll concentrations were less than 15 ug/L except a small surface bloom at station 20 where chlorophyll fluorescence was greater than 40 ug/L. Microscopic examination of surface water from station 20 revealed a phytoplankton community dominated by the warm season dinoflagellate, Lavanderina fissa (a.k.a. Gyrodinium instriatum). It’s the most common bloom former during the warmer months in the Neuse and is not known to produce toxins.

High salinity continued on 25 September 2023 with downstream salinity near 25. The estuary was moderately stratified and water temperatures were much cooler (20-24 C) due to the passage of our first early fall cold front. Bottom water dissolved oxygen conditions were much improved from earlier in September with the only zone of hypoxia confined to the region near New Bern (station 30). Chlorophyll values were generally less than 10 throughout the estuary with the exception of a small zone of elevated (15-30 ug/L) at stations 30 and 50.

On 11 September 2023 the estuary continued to be extremely salty. Bottom water salinity at station 180 in the lower estuary was 28, the fourth saltiest salinity measurement in the 28 year record for that station. Surface waters greater than 15 extended upstream to about where the estuary widens at stations 60 and 70. Water temperatures ranged from about 30 C at the surface upstream in the estuary to about 25 C in the bottom waters near the mouth. The estuary was strongly stratified and bottom waters were hypoxic from above New Bern at station 20 to the mouth at station 180. A zone of elevated surface chlorophyll (30-40 ug/L) was observed from stations 30 to 70. Microscopic observation of station 60 surface water indicated that the bloom was composed of a mixed assemblage of cryptophytes, dinoflagellates, and diatoms. The icthyotoxic dinoflagellate Karlodinium veneficum was abundant (~500 cells/mL) but fish kills usually aren’t observed until concentrations reach about ten thousand cells/mL.

Hi all,
The summer is humming along and it’s finally gotten hot. Water temperatures ranged from 27-30 throughout the estuary. Since the last sampling in July, river flow has averaged only about half of the seasonal median. These periods of low discharge are maintaining high salinity conditions that resulted from last year’s low discharge. Surface water salinity at station 180 was 23, about 8 higher than normal for August, and the tip of the salt wedge extended upstream of station 0. The lower estuary downstream of station 100 was moderately stratified and bottom water oxygen levels were 4 or greater. The upper estuary was strongly stratified with surface to bottom salinity differences of 5-10. Bottom waters in the upper estuary were hypoxic from stations 20 to 100. Based on visual observations, it appears that these bottom waters contained high concentrations of dissolved iron that rusted upon contact with the atmosphere to produce a dark orange color. The high bottom water turbidity in this region may be the result of these precipitates forming in situ as dissolved, reduced iron is mixed upward and oxidized by more oxygen rich waters near the pycnocline. A broad zone of elevated chlorophyll (~25 ug/L) was observed in the lower estuary at stations 120 and 140. Microscopic examination of station 140 surface water revealed dominance by the dinoflagellates, Gyrodinium instriatum, Pheopolykrikos hartmannii, and another large athecate dinoflagellate that was not identified. Gyrodinium instriatum and Pheopolykrikos hartmannii are common this time of year and haven’t been associated with fish kills. 
 
I hope everyone enjoys the last few weeks of summer.
 
Best,
Nathan

On 25 July, water temperatures throughout the estuary were in the high 20s which is normal for late July. The estuary was still strongly stratified and bottom waters were hypoxic from station 30 to the mouth. A zone of elevated chlorophyll (25-30 ug/L) was detected in the bottom waters of stations 60 and 70. Elevated bottom water chlorophyll a is common in winter and spring but less so in summer, prompting further examination. A look under the microscope at station 60 bottom water showed high concentrations of the mixotrophic (eats other phytoplankton) dinoflagellate, Pheopolykrikos hartmannii. It’s a huge cell packed with pigments which explains the peak in chlorophyll. It is not known to cause any problems.

I hope everyone has a safe end to the summer, and that we’re spared from storms.

Best,

Nathan

By 10 July, surface water temperatures were in the high 20s and bottom waters were 26-28 C. Salinity based stratification was strong with surface to bottom differences that ranged from greater than 10 from stations 20 to 70 to about 5 further downstream. Bottom waters were hypoxic from stations 20 to the mouth at station 180. Chlorophyll was mostly less than 10 ug/L with a few zones up to 15 ug/L between stations 30 and 140. Turbidity was less than 5 NTU except on the bottom at station 0 where turbidity was ~10 NTU.

By 28 June, water temperatures had climbed into the mid 20s throughout most of the estuary. Again, there was only moderated salinity-based stratification. Bottom waters were not hypoxic and chlorophyll concentrations were low (5-15 ug/L). Elevated turbidity (>10 NTU) at the head of the estuary was caused by elevated river flows. Turbidity was also elevated at the bottom along the entire transect but the cause isn’t clear.

We had an unusually cool June and that was reflected in water temperatures that were still mostly in the low 20s on 13 June. Stratification was again moderate with surface to bottom differences that ranged from 1-4. Bottom water oxygen was about 4 mg/L throughout most of the estuary and only station 60 had hypoxic bottom water conditions. Chlorophyll a was less than 15 ug/L throughout the estuary.

On May 30, salinity-based stratification was moderate with top to bottom differences of about 5. Water temperatures were still less than 20 C throughout most of the estuary and bottom waters were well oxygenated. A zone of elevated chlorophyll extended from station 50 to 100 with a surface peak at station 50 that was about 40 ug/L. Microscopic examination showed a community dominated by a euglena, Eutreptia lanowii I believe, and a mix of diatoms and cryptophytes. None of these are known problem makers.

Hi all,

I hope everyone is enjoying the start of summer. River flow over the month prior to the 11 May 2023 sampling trip was about twice the seasonal norm. The tip of the salt wedge was near New Bern and the lower estuary is still saltier than normal at a salinity of ~20. Strong salinity based stratification was reinforced by temperature gradients with bottom water temperature 2-4 degrees cooler than the surface. Bottom water dissolved oxygen was 4-6 mg/L along most of the transect but dipped to near hypoxic (<2 mg/L) near the tip of the salt wedge at stations 30 and 50. Chlorophyll was less than 10 ug/L throughout the estuary and only approached 10 ug/L within a broad mid-estuary maximum between stations 60 and 140. High river flows caused elevated turbidity (~10 NTU) in the river water entering the estuary.

Best,
Nathan

 

Hi all,

The winter and early spring saw flows that were always below normal and usually only about half of the seasonal norm. That changed starting on 10 April when flows began to rapidly increase. By the time of sampling 19 April, flows peaked at nearly twice the seasonal norm. Dumping that much freshwater into a really salty estuary caused very strong salinity based stratification with surface to bottom salinity differences of ~15 in the upper estuary from station 30 to station 120 and ~10 further downstream. Bottom waters were cool (< 15 C) and certainly the low temperatures helped prevent bottom water hypoxia. High turbidity (>10 NTU) flood water penetrated downstream to station 60 and turbidity was < 5 NTU throughout the rest of the estuary. A large mid-estuary chlorophyll maximum (> 20 ug/L) was observed from station 60 to 140 and was concentrated vertically just above the pycnocline at ~1.5 m depth. Microscopic examination of station 100 surface water revealed that small solitary centric diatoms and chain-forming centric diatoms were the dominant taxa. There was a relatively high concentration (~1000 cells/mL) of the toxic dinoflagellate, Karlodinium veneficum. Although 1000 cells/mL is higher than normal, Karlodinium doesn’t usually cause fish kills until the concentrations reach about 10,000 cells/mL.

-Nathan

 

Hi all,

Despite a few rain events, river flows in late March and the first few days of April were still only about half their seasonal norm. The recent freshwater inputs lowered surface salinity values to less than 2 upstream of station 70. The tip of the salt wedge was still upstream of New Bern and bottom waters of the lower estuary were still greater than 20. The estuary was strongly stratified with vertical salinity differences greater than ~5 and temperature differences greater than ~3 C along most of the estuary. A small zone of very salty and hypoxic water occurred at the very bottom at station 160 and likely resulted from saltwater intrusion from the intercoastal waterway. A subsurface maximum of chlorophyll up to ~ 30 ug/L occurred along the pycnocline from station 50 to 160. No samples were collected at these depths to determine the dominant organisms but previous sampling events found an ongoing bloom of the dinoflagellate, Prorocentrum minimum, which has been commonly observed to form subsurface maxima. Turbidity was < 5 NTU except for at the head of the estuary where river inputs had turbidity of ~ 10 NTU.

Best,

Nathan

Hi all,

Not much has changed since the last report. A spring cold front cooled temperatures by about 5 degrees and now temperature are near their seasonal norm. River flow has been low all March at about half its seasonal norm. Salinity at the mouth was about 17 at the surface and above 20 at the bottom. The tip of the salt wedge is still upstream of New Bern (station 30). Supersaturated oxygen levels at stations 60 and 70 were produced by a dense surface bloom (chl > 40) at those stations. The bloom extended upstream as a subsurface bloom to above station 50. I looked at station 60 under the microscope and saw a near monoculture of the dinoflagellate Prorocentrum minimum, the same dinoflagellate species that’s been blooming in this region of the Neuse for the past two months. Colleagues, Drs. Rick Stumpf and Alexandria Hounshell, at NOAAs National Centers for Coastal Ocean Science have provided us a bird’s eye view of bloom with their chlorophyll a product derived from Copernicus Sentinel-3 satelite imagery. It shows the highly concentrated nature of the bloom with maximum biomass just where the estuary starts to widen and residence time increases. It also shows an extension of the bloom along the north shore of the estuary down stream to Beard Cr. P. minimum hasn’t been associated with fish kills or toxin production. If history is a good predictor, the P. minimum bloom will be gone in the next few weeks. The satellite derived chlorophyll also shows other co-occurring blooms in the Pamlico River, Pungo River, and on Lake Mattamuskeet. I wouldn’t be surprised if the Pamlico River and Pungo River blooms were also P. minimum. I’ve sampled Mattamuskeet recently and its bloom is a 50:50 mix of diatoms and cyanobacteria.

Best,

Nathan

Hi all,

Late winter has been unusually warm and water temperatures in the estuary are about 5 C warmer than normal. High salinity conditions are still in place with salinity near 20 at the estuary mouth. The tip of the salt wedge is still upstream of New Bern. No hypoxic bottom waters were observed. Super saturated oxygen conditions were observed near the surface at station 60 where high chlorophyll (>40 ug/L) indicated a bloom. The intense surface bloom at station 60 was part of a broad region with high (~25 ug/L) subsurface chlorophyll that stretched from station 50 to 120. Microscopic examination of station 60 surface water revealed a mix of the winter/spring bloom forming dinoflagellate, Prorocentrum minimum, and a Euglena sp. These are the same two species that were found blooming in the same area in February. Neither is thought to be problematic in regards to toxins and fish kills.

Best,

Nathan

Hi all,

The Neuse River basin had several significant rainfall events prior to the 7 February sampling event and salinity in the upper estuary responded strongly. Surface salinity was < 5 downstream to station 60 and the tip of the salt wedge was between stations 20 and 30. Salinity in the lower estuary dropped about 5 units since January also. The freshwater pulse also caused high turbidity (>10 NTU) at the head of the estuary. Temperature was seasonably cool (8-10 C). Dissolved oxygen was well above levels required for the health of fish and other animals. However, the bottom water dissolved oxygen at station 30 was atypically low (~ 5 mg/L) for this time of year. Strong suppression of mixing caused by the > 10 salinity difference from the surface to bottom layer led to the oxygen sag even though respiration rates were surely very slow in at such cold water temperatures. A localized surface bloom at station 60 was caused primarily by very high densities of a Euglena sp. and secondarily by the dinoflagellate, Prorocentrum minimum. Neither have been linked to fish kills or other toxicity issues in North Carolina.

-Nathan

Hi all,

Here’s an update on the conditions during the first trip in 2023. The estuary was still extremely salty with surface salinity near the mouth well above 20. An oyster farmer friend measured a salinity of 28 in a creek near Bay River. We did have a little rain associated with a strong Christmas time cold front. The salt wedge still extends upstream of New Bern but higher flows have pushed the salt wedge downstream of Streets Ferry Bridge. The water is seasonably cold, < 10C. Dissolved oxygen conditions were normoxic throughout the estuary. Elevated turbidity (>10 NTU) at the head of the estuary likely resulted from higher flows. A subsurface chlorophyll maximum extended from station 30 to station 120 at ~1.5 m depth. Examination of station 50 surface water revealed numerous Prorocentrum minimum cells. Prorocentrum minimum is a shade adapted species that commonly forms subsurface maxima at low light levels. I bet that the observed subsurface chl-a maximum is the beginning of the nearly annual late winter/early spring bloom of Prorocentrum minimum. P. minimum isn’t known to produce toxins/ kill fish but it has been shown to cause problems with oysters. Fortunately, the area where it tends to bloom is too fresh for oysters anyway. The crew plans to be out again later this week and we’ll see how the bloom’s developed.

Best,

Nathan

2022

Hi all,

Overall, river flow during the fall has been very low and high salinity is still firmly in place. On 29 November, salinity still exceeded 20 in the lower parts of the estuary. The estuary was weakly stratified except in the upper estuary where the difference between surface and bottom salinity was approximately 10. At the head of the estuary at Streets Ferry Bridge (station 0), bottom water salinity set an all time ModMon record of 11.95 beating the previous record of 11.27 set in Dec. 2007. Dissolved oxygen was > 8 mg/L except in the highly stratified wates at Streets Ferry Bridge where bottom water dissolved oxygen was ~ 3 mg/L. Chlorophyll was generally less than 10 ug/L throughout the estuary with the exceptoin of a near surface maximum at station 30. Microscopic examination of station 30 surface water revealed a phytoplankton community dominated by the dinoflagellate, Prorocentrum minimum. P. minimum is the most common cool-weather, bloom-forming dinoflagellate in the Neuse. It’s not toxic and hasn’t been associated with fish kills. Turbidity was less than 5 NTU throughout the estuary. The monitoring crew is on the Neuse again today, so we’ll provide one more summary of conditions before the holiday break.

Best,

Nathan

Hi all,

Overall, river flow during the fall has been very low and high salinity is still firmly in place. On 29 November, salinity still exceeded 20 in the lower parts of the estuary. The estuary was weakly stratified except in the upper estuary where the difference between surface and bottom salinity was approximately 10. At the head of the estuary at Streets Ferry Bridge (station 0), bottom water salinity set an all-time ModMon record of 11.95 beating the previous record of 11.27 set in Dec. 2007. Dissolved oxygen was > 8 mg/L except in the highly stratified wates at Streets Ferry Bridge where bottom water dissolved oxygen was ~ 3 mg/L. Chlorophyll was generally less than 10 ug/L throughout the estuary with the exceptoin of a near surface maximum at station 30. Microscopic examination of station 30 surface water revealed a phytoplankton community dominated by the dinoflagellate, Prorocentrum minimum. P. minimum is the most common cool-weather, bloom-forming dinoflagellate in the Neuse. It’s not toxic and hasn’t been associated with fish kills. Turbidity was less than 5 NTU throughout the estuary. The monitoring crew is on the Neuse again today, so we’ll provide one more summary of conditions before the holiday break.

Best,

Nathan

Hi all,

So far, the second half of hurricane season had done little to end the low flow, high salinity conditions in the Neuse River Estuary.

On Sep 6, surface water salinity at the mouth of the Neuse was 25 and bottom water salinity was about 29. Surface to bottom salinity differences were approximately 5 along the length of the estuary. The upper most stations were not accessible due to the railroad bridge being closed just above New Bern. Water temperatures were very warm, 26-30C. The bottom 2 meters of the water column were hypoxic from the mouth to station 100. The membrane on the dissolved oxygen probe failed after data from station 100 were collected. Phytoplankton biomass was generally less than 10 ug/L chlorophyll a except for a small zone of elevated (20-30 ug/L) chlorophyll a in surface waters and even higher chlorophyll a levels along the bottom from station 30 to station 70. Surface and bottom water samples from station 50 were microscopically examined and revealed that in both the surface and bottom there was a mixed assemblage of cryptophytes, dinoflagellates, diatoms, and a euglena. The euglena was likely the dominant species biomass-wise, followed by the dinoflagellates Levandarina fissa, and Scrippsiella trochoidea. The toxic dinoflagellate, Karlodinium veneficum, was also present, but at concentrations that are unlikely to cause fish kill problems (< 1000/mL). The main diatom was Leptocylindrus minimum.

On 19 September 2022, the salinity regime was similar to that on 6 September but the lower estuary was less stratified. Water temperatures were ~25 C, cooler by 4-5 degrees compared to 6 September. At station 50, high surface water temperatures (~28 C) also coincided with high dissolved oxygen, chlorophyll a, and pH, all conditions indicative of a bloom. I think what we’re seeing here is that high light attenuation caused by a bloom increased the solar warming of the surface layer. Bottom water dissolved oxygen conditions downstream of station 140 were normoxic but hypoxic bottom water conditions extended from station 120 upstream to the tip of the salt wedge above station 20. Bottom waters at stations 20 and 30 were truly anoxic and smelled strongly of hydrogen sulfided. The high turbidity along the halocline at these stations is likely due to the formation of mineral precipitates as dissolved iron forms iron hydroxides when it meets oxygenated waters along the halocline. Microscopic examination of station 50 surface water showed that the bloom was dominated by the same euglena observed on 6 September, the dinoflagellate Levandarina fissa, and the autotrophic ciliate, Myrionecta rubra. None of these are know to produce toxins or cause fish kills.

The Neuse River basin got several inches of rain in late September from Hurricane Ian. The resultant increased river flow decreased salinity a little. Surface salinity near the mouth was still > 20 and the salt wedge still extended upstream of New Bern. An early October cold front significantly cooled the water to less than 20C. Dissolved oxygen conditions were normoxic along the length of the estuary. There were no areas of high (>20 ug/L chlorophyll a) phytoplankton biomass observed. High turbidity (> 20 NTU) was observed at the most upstream station and probably reflects continued moderate river flows after Hurricane Ian.

On 20 October, the tip of the salt wedge extended beyond our sampling stations. Bottom water salinity at station 0 (Streets Ferry Bridge) was 4.6. That’s in the 99th percentile of bottom water salinity at station 0. Despite cool water temperatures (<20 C), hypoxic conditions (< 2mg/L) occurred at stations 20 and 30. A subsurface zone of elevated biomass occurred at ~1 m depth from stations 20 to 50. Examination of surface water from station 20 showed that the community was dominated by Cryptomonas sp. All cryptomonads are generally considered nutritious phytoplankton that rarely cause any kind of habitat/water quality issues.

Take care,

Nathan

Hi all,

Flows on the Neuse River have increased some and have fluctuated around the seasonal norm since the beginning of August. The estuary is still really salty though. Surface water salinity at station 180 was 24.2, a 99% value for the ModMon dataset. The recent modest freshwater inputs haven’t changed that situation much but they are helping to maintain strong stratification in the upper parts of the estuary. From station 20 to 70, surface to bottom salinity differences are about 10 and the bottom waters are anoxic. The crew reported a strong sulfide smell and the water in sample bottles was bright orange from oxidation of free dissolved iron. There was a broad zone of elevated chlorophyll from station 30 to station 120. Throughout most of this zone, the chlorophyll maximum occurred at 1 to 2 m depth. At station 120, the maximum was at the surface. I examined samples from station 50 and 120. Station 120 had a typical mixed bag of cryptophytes, small diatoms, and several medium to large dinoflagellates including Scrippsiella trochoidea, Levandarina fissa (aka Gyrodinium instriatum), and Pheopolykrikos hartmannii. Station 50 was dominated by tiny, ~4 um diameter centric diatoms, but also had a few Levandarina fissa, cryptophytes, and small chlorophytes. Turbidity at the head of the estuary was about 7 NTU. At station 30 and 50 there was a zone of elevated bottom water turbidity with a subsurface turbidity maximum > 10 NTU along the pycnocline. This happens occasionally when the bottom waters are truly anoxic. I think it results from chemical precipitation of reduced iron as oxic and anoxic waters mix.

I hope everyone enjoys a safe Labor Day weekend.

-Nathan

Hi all,

The high flows of mid July were short lived and there was hardly any rainfall in the basin in the 2 weeks prior to sampling on 3 August. Conditions on August 3 were nearly identical to those on June 15. Surface salinity at station 60 was about 10 and surface salinity at the mouth was greater 20. Bottom water salinity at the mouth exceeded 25. Stratification was strong upstream near New Bern and moderate in the mid and lower estuary. Hypoxic conditions (< 2 mg/L) occurred in the upper estuary from station 20 to 50. The only area of high chlorophyll was the subsurface patch of high biomass that has apparently persisted at stations 30 and 50 all summer.  The sample was again dominated by the dinoflagellate Levanderina fissa but it also contained a diverse mix of diatoms, cryptophytes, chlorophytes, and other dinoflagellates. None of the mixed assemblage are known to be problematic with regard to toxins and fish kills.

I hope everyone enjoys the rest of the summer and stays cool.

Best regards,

Nathan

Prior to sampling on July 12, the Neuse basin had some substantial rain and river peaked on July 12 and 13 at about 4 times the seasonal average. On July 12, the main impact seen on the estuary was freshening of the upper estuary where low salinity water <5 extended downstream to stations 60 and 70. On the previous sampling on June 15, surface water salinity at these stations was ~10. High turbidity, 10 -15 NTU also resulted from the high flow. The estuary was stratified from New Bern to the mouth and bottom waters were hypoxic along that distance. As on June 15, there was a small subsurface maximum of chlorophyll a occurred along the pycnocline at stations 30 and 50. Microscopic examination of station 50 surface water showed the dominant organism was the same as on June 15, the dinoflagellate Levanderina fissa.

Hi all,

As I’m sure you’re all aware, it’s still really dry. The Neuse River flow is less than half its seasonal norm. Salinity is still high along the estuary and salinity is >20 in the surface waters near the mouth. The tip of the salt wedge is still upstream of New Bern. The estuary is moderately stratified with surface to bottom salinity differences of ~8 at station 30 to ~ 2 at station 180. Warm bottom water temperatures (> 25 C) and stratification promoted hypoxia (< 2 mg/L) from stations 30 to 120 and even the lower stations had bottom water DO < 4 mg/L. A small subsurface maximum of chlorophyll a occurred along the pycnocline at ~ 1.5 m depth at stations 30 and 50. Microscopic examination of station 50 surface water revealed a phytoplankton community dominated by the summer bloom forming dinoflagellate, Levandarina fissa (formerly known as Gyrodinium instriatum). Its not known to produce toxins and hasn’t been associated with fish kills.

-Nathan

Hi all,

We finally got some rain in the basin on 26 May that sent river flows to nearly twice their seasonal norm. On May 31, the estuary was still really salty though. The salt wedge was upstream of New Bern and bottom water at New Bern (station 30) was ~ 10. Surface salinity at the mouth of the estuary was ~20. Water temperatures ranged from low 20s C in the bottom waters to nearly 30 C at the surface. The strong temperature gradient reinforced the vertical density gradient caused by salinity. Surface to bottom salinity differences ranged from about 10 upstream to 2 at the mouth. Hypoxic bottom water conditions were observed from the tip of the salt wedge at station 30 downstream to station 160. A subsurface zone of elevated chlorophyll (~40 ug/L) occurred at ~ 1 m depth at station 50. Microscopic observation of station 50 surface water indicated the phytoplankton community was dominated by small centric diatoms and cryptophytes. Generally, both small centric diatoms and cryptophytes are highly edible fuel for the estuarine food web. Elevated turbidity (15-20 NTU) at the freshwater head of the estuary is indicative of the elevated discharge conditions.

-Nathan

Hi all,

Conditions on 17 May 2022 were very similar to the previous sampling in April. The estuary is very salty with surface salinity almost 20 at the mouth. The tip of the salt wedge was upstream of New Bern which usually only happens during summer and fall drought. The estuary was normoxic with the exception of near the tip of the salt wedge at station 30 where dissolved oxygen was low < 4 mg/L but still sufficient for most estuarine fish. A small zone of elevated chlorophyll a (~25 ug/L) was observed at station 50. Microscopic analyses showed dominance by small centric diatoms and a few cryptophytes.

-Nathan

River flow has been below normal for most of the spring but there were some high flows in late March. On April 5, the upper estuary was freshened by those high flows with surface salinity < 5 downstream to station 70. Surface salinity at the mouth was ~18 which is unusually salty for spring. Despite cool water temperatures (< 20 C), low bottom water dissolved oxygen (< 4 mg/L) was observed in the upper estuary at stations 30 and 50 and within the high salinity intrusion of bottom water from the intercoastal waterway at station 160.

A subsurface zone of high chlorophyll a was observed along the pycnocline at ~ 2 m depth at stations 60 and 70. Microscopic analysis of surface water from station 60 showed a mixed bag of spring dinoflagellates, Prorocentrum minimum, Heterocapsa rotundata, Heterocapsa triquetra, small centric diatoms, and cryptophytes. These dominant species are not known to produce toxins. Karlodinium veneficum, a toxic fish killing dinoflagellate, was present in low numbers. Turbidity was highest (8-10 NTU) at the head of the estuary. Throughout the rest of the estuary turbidity mainly ranged from 2-3 NTU except at stations 60 and 70 within the zone of high phytoplankton biomass where turbidity was ~5 NTU.

-Nathan

 

Hi all,

Since the last trip on 8 March, river flow has gone from about a quarter of the seasonal norm to well above average. The freshwater pulse resulted in a plume of highly turbid freshwater (>10 NTU) downstream to station 30, and strong salinity-based stratification from the tip of the saltwedge at station 30 to the mouth. Despite cool water temps (~15C), bottom water dissolved oxygen was depressed (2-4 mg/L) in the upper estuary from station 30 to station 70. The unusually salty and warm bottom water at station 140 is due to intrusion from the intercoastal waterway.

Two subsurface layers of elevated chlorophyll, one at 1-2 m and the other along the bottom, were observed at stations 50 and 60. The surface water sample from station 60 was examined microscopically and contained a mixed assemblage of the two dinoflagellates that have been blooming for the past 6 weeks, Prorocentrum minimum and Heterocapsa triquetra, and also several species of cryptophytes, and small diatoms. None of the major taxa were concerning, fish-kill/toxin wise.

Stay well,

– Nathan

Hi all,

The crew managed to catch a brief break in northeast winds to do the March 8 run. The upper stations weren’t sampled due to steering problems on the boat. River flow for the weak prior to sampling was about 25% of the seasonal norm. As a result of the low flow, salinity is unusually high for late winter and ranged from 5 at station 50 to 20 in the bottom near the mouth. Vertical stratification was very weak due to prior wind mixing and low flow. There was a subsurface patch of high chlorophyll a at stations 60 and 70. I looked at the bottom water sample from station 70 and it was co-dominated by the dinoflagellates, Prorocentrum minimum and Heterocapsa triquetra. These are the two typical bloom winter/spring bloom formers in the Neuse and haven’t been shown to cause problems (e.g. toxins/fish kills etc.).

Stay well,

– Nathan

Hi all,

It was a calm day yesterday and the crew got out on the Neuse. We’ve had cold weather and several inches of rain/wintery mix in the past couple of weeks and the river flow is near its seasonal average. Water temperatures ranged from about 10C upstream to only about 6C at the mouth. The tip of the salt wedge was still upstream of New Bern, and the upper estuary from station 20 to station 120 was strongly stratified with surface to bottom salinity differences greater than 5. A  pronounced subsurface maximum of chlorophyll with maximum concentrations near 40 ug/L occurred at depths ranging from 1.5 to 2 m from stations 30 to 140. The surface water sample from station 60 was dominated by the dinoflagellate Prorocentrum minimum which commonly forms these subsurface maxima in the Neuse, Chesapeake Bay, and other estuaries. The subsurface bloom also generated subsurface maxima of dissolved oxygen and even showed up as elevated turbidity.

We can expect the bloom to hang around through mid April before it mysteriously disappears. I say mysteriously because (as far as I know) the actual fate of all that biomass has never been completely worked out. Sediment trap studies have been conducted during blooms in the Neuse and the Chesapeake but they mainly catch diatoms even during dinoflagellate blooms. So, maybe the bloom is either passed up the food chain or eaten up by protist grazers within the microbial food web in the water column rather than settling to the sediments. It’s interesting, and probably has important implications for the role these late winter/ early spring dinoflagellate blooms play in summer hypoxia. If anybody sees any recent papers on this, I’d love to read them.

Stay well,

-Nathan

Hi all,
Happy New Year! I hope everyone is having a good one so far and staying healthy.
After a progressively dryer fall and early winter, rains in the first week of the year have put Neuse River flows at near normal levels (at least based on flows at Kinston, the USGS gage at Fort Barnwell is still not reporting). The salt wedge had been upstream of station 0 at Streets Ferry Bridge back in December but is now somewhere just upstream of New Bern between stations 20 and 30. This location for the tip of the salt wedge is still unusually far upstream for January, and the estuary in general is still much saltier than normal with downstream salinity at about 20. Suspended sediment from the high river flow is apparent as a region of elevated turbidity (> 20 NTU) at the upstream, freshwater stations that gradually diminishes in the surface waters downstream to station 70. Dissolved oxygen conditions were normoxic or supersaturated throughout most of the estuary. A slight dissolved oxygen sag was evident in the bottom water at the tip of the saltwedge at station 30 but the levels of ~6 mg/L are sufficient for estuarine animals. Generally, chlorophyll fluorescence was low (<10 ug/L) but a subsurface zone of elevated chlorophyll (~20 ug/L) occurred at stations 60 and 70 at ~ 1 m depth. It’s likely that this is the beginning of the annual Prorocentrum minimum bloom, a dinoflagellate that is considered harmful to some shellfish but hasn’t been shown to cause problems in the Neuse. With the recent nutrient inputs from elevated flows, the bloom size and intensity will likely increase over the next couple of months. Next time I’ll look at samples and take some pictures.
-Nathan

2021

Hi all,

The dry conditions continue and flows on the Neuse are still very low, about a third of median levels for this time of year. Over Thanksgiving break, I noticed that I could see the bottom of the river from bank to bank while crossing the bridge in Kinston. It’s definitely a lot clearer and shallower than normal in the upstream freshwaters.
The estuary is very salty. There was measurable (a couple tenths of part per thousand) in the surface and 8.5 salinity in the bottom waters at Streets Ferry. Those values are in the top 1% of values measured over the last 25 years. Salinity at New Bern was greater than 10 and salinity at the mouth was near 20. In the upstream section above New Bern, the salty bottom waters also had low (<4 mg/L) dissolved oxygen but otherwise the bottom waters had high (>7 mg/L) dissolved oxygen. There was a small zone of elevated phytoplankton biomass at the surface at station 30 that extended as a subsurface maximum downstream to station 60. Microscopic examination of surface waters from station 30 determined that the bloom was caused by a dinoflagellate but more detailed examination will be required to make a positive identification.
I hope the holidays are good to everyone.
-Nathan
Hi all,
River flow has still been below normal and salinity in the Neuse is showing it. Near the mouth, salinity was ~20 and the tip of the salt wedge was upstream of New Bern, somewhere between station 20 and 0. Cool water temperatures, ~14 C, occurred throughout most of the estuary. Cool temperatures causing low oxygen demand likely explain the lack of hypoxia despite strong stratification in the upper estuary. Chla was unusually low (<10 ug/L) throughout most of the estuary and there was only a small zone of elevated phytoplankton biomass at station 50 where Chla was approximately 15 ug/L. Since 11 November, river flows have continued to decline. We’ll see how the Neuse responds after the Thanksgiving Holidays.
I hope everyone enjoys a healthy and safe Thanksgiving break.
-Nathan

Hi all,
River flows are still low and salinity in the Neuse is still high. The salt wedge still extends upstream of New Bern and salinity near the mouth is 16 at the surface and near 20 on the bottom. Vertical stratification was moderate and there was a zone of hypoxic water in the upper estuary that extended from the tip of the salt wedge at station 20 downstream to station 70. An unusual chlorophyll maximum with chla ~ 35 ug/L was observed in the freshwater at Streets Ferry Bridge (station 0). Freshwater blooms are unusual but their development is promoted by low flow conditions like we’ve had recently. Microscopic examination indicated the bloom was caused by Planktothrix, a non-heterocystous, filamentous cyanobacteria. This genus is known to produce cyanotoxins including microcystins. A lesser-intensity peak of phytoplankton biomass at stations 60 and 70 was caused primarily by the dinoflagellate, Levandarina instriatum which is not known to produce toxins or cause ecological problems. We’ll keep an eye on the freshwater bloom.
-Nathan

Hi all,Fall is here. The estuary has cooled significantly with temperatures ranging from 22-24 C. Although we’ve had some local rainfall along the coast, not much has fallen in the watershed and flows on the Neuse have been well below seasonal norms for the month prior to sampling on Oct. 11. Salinity is unusually high throughout the estuary. Station 180 wasn’t sampled due to high winds but salinity at station 160 was 17. Bottom water salinity was 3.4 at Streets Ferry Bridge (station 0), and that’s in the 97th percentile of measurements made at the head of the estuary. Vertically, strong winds resulted in a well-mixed estuary and there were no areas of bottom water hypoxia. Chlorophyll was low (<10 ug/L) throughout the estuary with the exception of a small zone of elevated chlorophyll (​~ 25 ug/L) at the surface at station 20. Microscopic examination of station 20 surface waters showed the high biomass was caused by the marine dinoflagellate, Levandarina instriatum. This dinoflagellate species commonly blooms in the Neuse during warmer months. It isn’t a known toxin producer and hasn’t been associated with fish kills. -Nathan

Hi all,
Heavy rains in early June sent Neuse flow up to about 5 times its seasonal norm. Consequently, on June 7, the estuary was much fresher than normal with surface salinity near the mouth only about 8. The estuary was moderately stratified with top to bottom salinity differences ranging from about 2 at station 50 to almost 10 station 180. There was a high salinity blob in the bottom waters at 160 that is likely from the intercoastal waterway. Dissolved oxygen of the bottom waters was < 4 mg/L from station 60 to the mouth. There was a broad region of elevated, ~15 ug/L chlorophyll a extending from station 50 to station 160.
 On 29 June, the lower estuary was a little saltier than on 7 June with surface salinity at station 180 greater than 10. The upper estuary from station 50 to station 140 was strongly stratified but the estuary was more mixed downstream. A thin layer of hypoxia was apparent at station 60 and from station 100 to 140. A surface chl-a peak of ~ 30 ug/L was observed at station 50, and a broad subsurface peak of 30->40 ug/L chl-a occurred from stations 60 to 120. High productivity of these blooms was evidenced by super saturated dissolved oxygen and elevated pH in the bloom area.
-Nathan

2020

Hi all,
Despite funding uncertainty, ModMon sampling has continued and I am catching up on relaying what we’ve seen in the data. Conditions during late fall (19 Nov and 10 Dec 2020) were typical with moderately depressed due to the generally high rainfall of late summer early fall. For example, on 19 November surface salinity at station 120 near the bend in the estuary was ~2 compared to a long-term average of ~8. High river flow also caused elevated turbidity (> 15 NTU)  in the upper estuary above New Bern. Patches of elevated surface chlorophyll a were observed at stations 100 and 140 on 19 November. A water sample from station 100 was examined and the bloom organism was identified as Gyrodinium instriatum, the same dinoflagellate observed during blooms on 27 October and not considered a HAB forming species. On Nov 19, the water column was highly stratified with cool freshwater overlying much warmer and saltier bottom water from station 60 to the mouth. Hypoxic bottom waters were observed at stations 60, 70 and 140. The fish kills that were observed from late September through October were not observed in November.
Conditions on 10 December 2020 were similar to November. Flows were reduced compared to November. The estuary was fresher than normal but saltier than in November and turbidity near the head of the estuary was much lower than in November. A patch of high chlorophyll was observed at station 160 and was identified as Gyrodinium instriatum. Water temperature was ~10 degrees C and dissolved oxygen was normoxic throughout the estuary.
The Holiday break in eastern NC was a washout, and the rain didn’t seem to stop until late February. By January 11, 2021 surface salinity dropped to ~3 at the mouth though the salt wedge still penetrated to the HWY 17 bridge near New Bern. The strong stratification led to a dissolved oxygen sag from station 50 to 120 but not to hypoxic (< 2 mg/L) levels. As during November, the upper estuary had elevated turbidity (>15 NTU). A patch of high surface chlorophyll was observed at stations 160 and 180 and was again caused by Gyrodinium instriatum. G. instriatum is normally abundant during the warmer parts of the year and seeing it so abundant in December and January is unusual to me.
On 8 February 2021, salinity had recovered a little but the estuary was still much fresher than normal. Turbidity from station 100 upstream was moderately elevated (>10 NTU). There were no observed blooms but there was a strong longitudinal gradient with highest chlorophyll a (~15 ug/L) observed at the most downstream stations. This is likely the result of rapid flushing suppressing biomass development in the upper estuary. The water column most mostly well mixed and oxygen was normoxic.
The extreme rainfall during February caused salinity to fall to very low levels by early March. On March 3, the tip of the salt wedge was off Oriental at station 140. Surface salinity at station 180 was 2.5 and only 7 at the bottom. Elevated turbidity (>10 NTU) occurred from station 120 upstream and was >15 NTU throughout the water column at stations 100 and 120. It’s unclear what caused this localized region of high turbidity. As during February, no blooms were observed but chlorophyll a was highest at downstream stations.
On 17 March 2021, the estuary was still very fresh with surface salinity at station 180 < 3 and bottom salinity less than 5. Vertically, the estuary was well mixed with only a small zone of stratified waters where the Neuse empties to Pamlico Sound. There were no observed blooms and chlorophyll a increased from ~0 near New Bern to ~ 15 ug/L at the mouth.
-Nathan

Hi all,
Our crew was out Tuesday, 13 October 2020. The estuary was stratified with pockets of hypoxic water observed near New Bern at station 30 and near the bend at stations 100 and 120. The fluorescence probe that measures chl-a failed mid-cast at station 140 and all chl-a data upstream of 140 was removed due to meaningless, negative values. A bloom at station 70, however, was indicated by the high near surface DO, observation of brown water color, and clogging of filters back in the lab. The crew observed fish actively dying south of Fairfield Harbor (our station 70) and fish dead on the surface from there to mid-channel north of Slocum Cr. (our station 100). The dominant species in the bloom, the dinoflagellate Gyrodinium instriatum aka Levanderina fissa)  is not known to be toxic. G. instriatum is the most common bloom former in the Neuse during the summer and early fall and hasn’t previously been associated with a fish kill. This fish kill appears to have been ongoing since 30 September.
Best,
Nathan

Hi all,
I’m playing catch up again.
Conditions on 18 August were about as stratified as they get in the Neuse. From New Bern to the mouth bottom water salinities were more than 10 ppt greater than at the surface. The pycnocline increased in depth from about 2 meters at New Bern to 5 m at the mouth, and waters below the pycnocline were hypoxic/anoxic along that whole stretch. Overall, chl-a levels were low but there was a broad zone of moderate 10-20 ug/L at the surface that extended from station 60 to station 140. A subsurface, thin layer of chl-a > 40 ug/L was observed at station 70.
After ~20 kt winds from 14-15 Sep. and continued ~15 kt winds on 16 Sep, the estuary was much more mixed on 16 Sep. There were pockets of stratification and hypoxia near New Bern and near the bend at stations 100 and 120. These pockets of hypoxia were associated with waters that were warmer than surface waters and saltier than downstream bottom waters. It’s not unusual for bottom waters to be warmer than surface waters during the fall as the surface loses heat to a cooling atmosphere. It is weird to see higher salinity upstream, and may reflect cross channel variability that isn’t being captured by our down-channel transect.  Chl-a was moderate (10-20 ug/L) from New Bern to the mouth.
On Monday 28 Sep, the estuary was highly stratified again. Bottom waters were 2 mg/L or less from New Bern to about station 70 and were ~4 or less from station 70 to the mouth. A broad zone of elevated surface chl-a was observed from station 60 to station 140, with a surface maximum of ~40 ug/L at station 100. Downstream of station 100, maximum biomass occurred as a subsurface maximum at 1 to 2 m depth. Two days later on 30 Sep., a fish kill was reported on Flanners Beach. Water from the location of the kill contained high concentrations of the potentially harmful raphidophyte species, Heterosigma akashiwo. Microscopic observation of surface water from station 100 contained very few Heterosigma akashiwo cells. The community was primarily cryptophytes, dinoflagellates, and small diatoms that are typical for this time of year and not known to harm fish. During an unrelated sampling trip on 2 Oct., I observed an ongoing fish kill near the mouth of Slocum Cr. There was a mix of actively dying and menhaden that had been dead for a day or two. I microscopically examined water samples collected from the fish kill area and from the Neuse outside the fish kill area. Low concentrations of Heterosigma akashiwo were present but the low observed concentrations have not been previously related to fish kills.
Stay well,
Nathan

Hi all,
August 5th was a couple days after Hurricane Isaias made landfall and tracked across the Neuse River watershed.  On August 5th, stratification was much weaker than two week’s prior. It appears that the major impact of Isaias was wind mixing. Hypoxic/ anoxic bottom waters were not observed. There wasn’t a lot of precipitation associated with Isaias and that’s reflected in the moderate salinity levels and the salt wedge extending upstream all the way to New Bern. There were moderate intensity (chl a ~30 ug/L) subsurface peaks in chlorophyll a at stations 60 and 120.
Since, August 5th the Neuse flow has steadily increased to near flood stages. Part of this may be due to Isaias but most is likely due to a rash of high precip. thunderstorms centered over the upper Neuse basin. We’ll see how the estuary responds to the flow increase during the next sampling.
Stay well,
Nathan

Hi all,
The recent dry conditions have allowed salinity to creep up to New Bern in the bottom waters. The estuary is still highly stratified from New Bern downstream to station 120. True anoxic conditions occurred from New Bern to station 100, just upstream of the bend at Minnesott/ Cherry Branch. Bottom waters in this area smelled strongly of sulfur indicating that there was essentially no oxygen present. Elevated chlorophyll a occurred at the surface at station 50, and as a subsurface chlorophyll maximum downstream to station 120. Microscopic observation of surface water from station 50 indicated the bloom was a mix of small centric diatoms and nanoflagellates. The nanoflagellates were hard to identify but their morphology wasn’t consistent with any types of particular concern, e.g. toxin producing dinoflagellates.
Stay well,
Nathan

Hi all,
The estuary is extremely well stratified from New Bern to the mouth. The salinity difference is the major driver of the stratification, but a temperature difference of ~4 degrees C is playing an unusually strong role in reinforcing the stratification. Bottom waters were hypoxic from New Bern to the mouth. There were no reports of rotten egg smell from the bottom waters. So the bottom waters were probably hypoxic rather than anoxic. A zone of high surface chlorophyll occurred from New Bern (station 30) to where the estuary widens at stations 60 and 70. From there downstream there was also a subsurface chlorophyll maximum along the pycnocline. I haven’t looked to see what was blooming.
Nathan

Hi all,
The estuary looks almost exactly like it did two weeks ago. The upper region above New Bern is very turbid as flows are still much higher than normal for this time of year.  Surface waters are basically fresh to near the bend at Cherry Branch. The tip of the salt wedge is at station 50 just downstream of the HWY 17 bridge and the estuary is highly stratified ,and bottom waters were hypoxic from station 50 to the mouth. A broad zone of elevated chlorophyll a occurred from stations 100 to 160. Depth-wise the high phytoplankton biomass was maximum at about 1 m depth. This vertical patchiness is a tell-tale sign that the phytoplankton producing the peak is likely a flagellate seeking optimum light levels for photosynthesis. Our surface sample is collected at 0.2 m and missed the peak. I suspect it’s probably still an ongoing bloom of Gyrodinium instriatum.
Best regards,
Nathan

Hi all,
The estuary continues to freshen with the 2020 spring deluge. Surface water salinity at station 140 near Oriental is only about 5. The tip of the salt wedge is still just below New Bern at station 50, and the estuary is highly stratified from there to the mouth. Bottom waters were hypoxic from station 50 to 140. A broad surface bloom extended from station 60 to 120. This is likely the same dinoflagellate bloom of Gyrodinium instriatum from two weeks ago. I’ll take a look when I’m in the lab next and will post a correction with the next report if I’m wrong. With the rain still falling, the estuary will likely stay very fresh, and the hypoxic zone may expand without some serious wind mixing.
Best regards,
Nathan

Hi all,
The estuary is fresher now due to all the rain from Arthur and Bertha but the tip of the salt wedge still extends almost to New Bern. A strong pycnocline occurred at about 4 m depth at stations upstream of station 120 and at about 5 m at the lower stations. Bottom waters were hypoxic (< 2 mg/L) at station 50 -120, and were <4 mg/L at the lower stations. There was a zone of high surface chlorophyll from stations 70 to 120. Microscopic examination of station 120 surface water where chlorophyll was greatest showed that the bloom was dominated by the dinoflagellate, Gyrodinium instriatum (more correctly known as Lavanderina fissa). This dinoflagellate is our most common summer-time bloom former in the Neuse and is not known to produce toxins. The other phytoplankton in the sample were a mix of cryptophytes, small diatoms, and smaller dinoflagellates.
Nathan

Hi all,
Since I’ve last reported on conditions in the Neuse River Estuary our world has changed a lot more than it has. Nothing exceptional to report water quality-wise. The high chl-a at stations 120 and 140 during March were likely remnants of the dinoflagellate bloom noticed in February. I’ll find out once I’m able to get back to the lab. Y’all stay safe and well.
Best,
Nathan

Hi all,
That line of strong storms with torrential rains on Feb 6 and 7th has increased Neuse River flows to about five times their average for this time of year. The turbid (>20 NTU) flood waters are clearly evident upstream of New Bern (stations 0-30).  Downstream of New Bern, the estuary was highly stratified. Waters are quite warm for this time of year and bottom water DO was well below saturation from station 50 to 100. A near surface zone of elevated chl-a (~30 ug/L) occurred at station 160.
Best regards,
Nathan

Hi all,
Happy New Year.
The Neuse has kicked off the new decade with an impressive bloom of Prorocentrum minimum. We saw the beginnings of this bloom a month ago in December but it’s a lot more dense now. The surface water at station 100 was actually scummy (see attached photo taken by Melissa LaCroce) and the YSI measured 200 ug/L chl-a at 0.3 m depth. The bloom extended throughout the water column at station 100. Upstream to station 50, the bloom was concentrated just below the surface, and downstream at station 120 the bloom was concentrated along the pycnocline. Subsurface aggregations are really common for Prorocentrum minimum, but in my experience such dense surface scums are less common. However, there is a nice photo from an airplane of a Neuse River P. minimum bloom in Springer et al. (Harmful Algae 2005). P. minimum is not know to be toxic, and despite the high biomass levels there aren’t reports of problems associated with these blooms (e.g. hypoxia, fish kills, etc.). While we await further laboratory measurements, I think it’s safe to assume that such high biomass levels are at least partly the result of physical concentration of highly motile cells along a frontal zone.  Other than the bloom, the river is about 4-6 degrees warmer than normal for this time of year. The river is also quite salty with salinity near 20 at throughout the water column at the lower stations.
Best regards,
Nathan

2019

Hi all,
I’ve really fallen behind but have attached the figures for the fall. Dorian freshened things up a little in early September but afterwards the Neuse has looked very average. An bloom of the dinoflagellate Gyrodinium instriatum occurred at stations 60 and 70 on 23 Sep.  An unusual euglenoid bloom (probably a species of Eutreptia) occurred at station 50 on 4 Nov. and a typical late fall/winter/early spring bloom of the dinoflagellate Prorocentrum minimum occurred at station 50 on 9 Dec 2019. None of these bloom organisms have been know to cause problems related to toxins/fish kills etc.
Best,
Nathan

Hi all,
Catching up again. Attached are the three figures showing conditions from mid-July to the end of August. Up until the last Neuse run conditions were typical for summertime under low/moderate flows. Salinity was 5ish around New Bern and 15-20ish at the mouth. Stratification was strong and bottom water hypoxia was present throughout much of the estuary. Conditions looked very different on 27 Aug following three days of brisk NE winds and cooler temperatures associated with an offshore subtropical low. Waters throughout the estuary were mixed up and cooled significantly. A small pocket of warm, hypoxic bottom water remained in the upstream area around New Bern that was sheltered from the NE winds (my guess). There were no significant bloom events.
Best,
Nathan

Hi all,

I’m a little behind but here are the results from the last Neuse run on 9 July. It’s crazy how things have changed since spring when the estuary was basically a river. Salinities in the bottom waters of the lower estuary are as high as I remember seeing. The only other time that bottom waters at 180 have been this high was on 5 Oct 2002. Neuse river flows do not indicate that we are in as significant of a drought as in 2002. So, I think something on the ocean-side of the estuary might be playing a role in the high salinities and plan to see what our physical oceanographers think. The estuary was strongly stratified from New Bern to the mouth. Bottom waters were anoxic along much of the transect as evidenced by a strong sulfide smell. The crew will be out again next week.

Best,

Nathan

Hi all,

Salinity in the lower estuary is average for this time of year but the upstream section is a little fresher than normal. The basin saw quite a bit or rain in the second week of June and river flows are about four times higher than the seasonal average.  The salt wedge penetrated upstream to station 50 just downstream of the HWY 17 bridge. Bottom water dissolved oxygen was low from the tip of the salt wedge through the length of the estuary but was only below 2 mg/L (acutely lethal to fish) at stations 50-70. A subsurface peak in chlorophyll a at about 1 meter depth occurred from stations 60 -100. Microscopic examination of the surface water sample from station 60S revealed high concentrations of the dinoflagellate, Gyrodinium instriatum. This dinoflagellate is a common bloom former during the warmer months in the Neuse and is not known to produce toxins or negative food web related impacts.  Photosynthesis produced a zone of supersaturated dissolved oxygen at the stations with high chlorophyll. pH data are not shown due to probe failure.

Happy 25th Birthday ModMon!

Hi all,

For two and a half decades, ModMon has provided valuable information on water quality and habitat conditions in the Neuse River Estuary and Pamlico Sound. These data are crucial for evaluating how conditions are changing in response to human and climatic pressures. ModMon has also served as a platform to support research projects aimed at figuring out how estuaries work from ecological, geological, physical, and biogeochemical perspectives.

Conditions on 4 June 2019 were pretty typical for this time of year. Salinities ranged from zero above New Bern to a maximum of about 15 in the bottom waters near the mouth.  Stratification was not particularly intense except at station 160 which was influenced by saltier bottom water likely from the Intracoastal Waterway. Hypoxic conditions occurred throughout most of the length of the estuary but were confined to a thin, ~1 m thick, layer near the bottom. A zone of high DO, high pH, and high chlorophyll a was observed at station 30 near New Bern. Microscopic examination of surface waters from station 30 revealed a high concentration of cryptophytes that are generally good food for higher trophic levels, and don’t cause problems.

Best,

Nathan

Hi all,

A couple of weeks without rain and the estuary is looking almost normal. The salt wedge is at New Bern and surface water salinity near the mouth was about 10. Most of the estuary was strongly stratified and bottom waters were hypoxic from stations 60 to 160. There was a peak in DO at station 50 that was likely due to high phytoplankton production. Microscopic observation of the station 50 surface sample showed a high concentration of small (3-5 um) centric diatoms. Chlorophyll data are not shown due to a failed probe. During the previous trip on 7 May, the chlorophyll probe of the YSI data sonde started to malfunction but the malfunction was not noticed until this trip on 21 May 2019. The bloom level chlorophyll a concentrations observed at station 50 on 7 were an artifact of this malfunction. The probe has been replaced and in vivo chlorophyll a data from both dates have been flagged in the data set.

A fish kill was observed a few days following this trip on 21 May, but no dead fish were noticed during a boat run from New Bern to station 100 on yesterday, 28 May. Based on the reports that I saw, the dead fish were mostly menhaden and had sores consistent with ulcerative mycosis caused by Aphanomyces invadans. This fungus is most virulent when salinities are low and temperatures are in the low to mid 20’s C; conditions observed during the fish kill. Fish that are already stressed, e.g. due to hypoxia, are more likely to suffer from the infection. I’ve attached a couple good papers for those interested.

Best,

Nathan

Hi all,

The Neuse is an estuary again, a strongly salinity, stratified estuary with hypoxic bottom waters. The hypoxic zone stretched from just downstream of New Bern to the mouth. A zone of high chlorophyll with a subsurface maximum at ~1 m depth was detected from stations 20 to 70. Microscopic examination of surface waters from station 50 revealed a community dominated by freshwater diatoms, primarily Aulacoseira.

Until the next trip,

Nathan

Hi all,

Not much has changed on the Neuse. It’s still much fresher than normal. There is a small bolus of high salinity bottom water at station 160, but that’s likely intruding from the intercoastal waterway. High chlorophyll (~30 ug/L) and turbidity  occurred near the surface at station 100, and microscopy identified high concentrations of the diatom Aulacoseira sp., and a high concentrations of several cryptophyte species. These phytoplankton are non-toxic and considered “good” phytoplankton that tend to contribute energy to higher trophic levels.

Best regards,

Nathan  Hall

Hi all,

For the first time since Hurricane Florence, the estuary has some salt upstream of the bend at Cherry Point (station 120). The lower estuary is moderately stratified but the water is still cool and dissolved oxygen is > 8 mg/L throughout the estuary. There was a front between stations 60 and 70 with strong downstream gradients of temperature, pH, Chlorophyll fluorescence, and a spike in turbidity at station 70.

Best,

Nathan

Hi all,

With flows just above average, the Neuse is starting to look more like an estuary, a really fresh estuary but at least with some salt at all the lower stations. Moderate chlorophyll values of ~20 were patchily distributed throughout the mid/lower estuary.

Best regards,

Nathan

Hi all,

Unbelievably, the estuary is fresher now than what we measured ten days after Hurricane Florence. Temperatures are cool and DO is high throughout the estuary. chl-a was generally les than 20 throughout the estuary except for a thin aggregation along the pycnocline at the lower stations. The dinoflagellate, Prorocentrum minimum, is famous for this and has been abundant for the last few trips.

Best,

Nathan

Hi all,

It’s still really fresh and the bloom downstream has gotten more dense. I looked at a sample from station 180S and the bloom is mostly Heterocapsa triquetra with lesser abundances of Prorocentrum minimum and Heterocapsa rotundata.  Again, these dinoflagellates don’t typically cause problems.

Best,

Nathan

 

Hi all,

The Neuse is still really fresh and it looks like the winter/spring bloom may be starting near the mouth. I looked at station 180 surface waters and the phytoplankton biomass was dominated by the dinoflagellate, Heterocapsa triquetra. There were also a bunch of cryptophytes, and small diatoms; nothing to worry about toxin or fish kill wise.

Best,

Nathan

2018

Hi all,

The Neuse River Estuary continues to be fresher than normal but the salt wedge has crept back up to near the HWY 17 bridge. Temperatures have cooled a little since late November. Dissolved oxygen is greater than 9 mg/L throughout the estuary with the exception of bottom waters at stations 60 and 70 where oxygen levels were around 7 mg/L. Turbidity was generally less than 10 NTU throughout the estuary but was approximately 10 near the surface at station 120 and along the bottom in the lower estuary. There were no strong peaks in chlorophyll.

Happy Holidays!

Nathan

Hi all,

With all the rain in the past two weeks the estuary is really fresh. Salinity at the surface near the mouth was only 6. The estuary has also cooled a lot with the latest cold fronts. Dissolved oxygen was high ((8 – 12 mg/L)and chlorophyll levels were low to moderate (< 20 ug/L) throughout the estuary.

Best,

Nathan

Hi all,

Salinity is slowly rising with measureable salinity intruding in the bottom waters as far upstream as station 50 and surface water salinity near 10 at station 180 near the mouth. Water temperature cooled by 5-6 degrees since mid October and there were no stations with hypoxic bottom water conditions. Phytoplankton biomass as measured by chlorophyll fluorescence was highest near the surface at stations 120 and 140. I looked at surface water from station 120 under the microscope and saw mainly small centric diatoms and small cryptophytes. I didn’t see any known harmful algal bloom species.

Stay tuned.

Nathan

 

Hi all,

Here are the latest conditions on the Neuse River Estuary. It’s still much fresher than normal but saltier than a couple weeks ago. Water temperatures have cooled by 3 or 4 degrees and dissolved oxygen has increased throughout the estuary. Bottom water hypoxia was only observed at stations 140 and 160, and then only just above the bottom.

Best,

Nathan

Hi all,

Here are the latest conditions. River flows are slowing down and the salt wedge has crept back up to near New Bern despite very low surface salinities. Stratification is strong and dissolved oxygen is basically zero in the bottom waters from New Bern to the mouth. Residence time is increasing in the mid estuary to the point that chlorophyll levels are starting to rebound after having been flushed out by Florence.

Best,

Nathan

Hi all,

The Neuse was sampled again yesterday. It looks very similar to last week with hypoxic river water entering the estuary and bottom water hypoxia and strong salinity stratification in the lower estuary. pH values of the river water have increased from 5.5 to about 6.5. No algal blooms were observed. Another trip is planned for next week.

Best,

Nathan

 

Hi all,

Not surprisingly, most of the estuary is completely fresh after parts of the watershed received 20+ inches of rain. Surface salinity near the mouth at station 180 were about 2. Some folks have asked when the last time salinity got this low at station 180. Surface salinity at the mouth was actually a little lower after Matthew in 2016, and was likely lower after Floyd in 1999 (don’t know for sure because station 180 wasn’t sampled after Floyd). Bottom waters near the mouth are still high. The intense stratification is accompanied by bottom water hypoxia at the downstream stations. All the upstream stations also have relatively low oxygen levels due to decomposition of all the organic matter that has been washed out of the watershed. The upstream pH values were also among the lowest on reThe field crew noted that the whole river smelled bad. There were no phytoplankton blooms.

Best,

Nathan