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.

2022

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