Author: leahmnel (Page 1 of 3)

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

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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

To learn more about the work that we are doing through ModMon and FerryMon please view our 2022 updates contained in the flyers below!

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

Hi all,

Happy New Year!

Through mid-December river flow continued to be very low. The high salinity record (11.9) that was set at station 0 (Streets Ferry Bridge) in late November was smashed by a 13.4 reading at the bottom on 14 December. The rest of the estuary was really salty too with bottom waters at the mouth near 25. The upper estuary was strongly stratified based on salinity. In the upper estuary (stations 0-30) bottom waters were 3-4 degrees C warmer than surface waters and dissolved oxygen was lowest (~ 4 mg/L) in these warmer, isolated bottom waters. For the rest of the estuary, dissolved oxygen was 8 mg/L or more. Chlorophyll was 10 ug/L or less except near the surface at station 50 where chlorophyll was ~25 ug/L. Microscopic examination revealed the peak in phytoplankton biomass at this station was due to a combination of small cryptophytes and the cool-weather dinoflagellate, Heterocapsa rotundata. These phytoplankton haven’t been associated with fish kills or toxin production. We finally got some rain associated with the strong cold front before Christmas. I imagine that the high salinity upstream of New Bern has probably been pushed downstream. I think we’ll find out next week if the weather cooperates.

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

Dr. Hans Paerl has recently been selected to receive the National Harmful Algal Bloom Committee Lifetime Research and Service Award! This award will be presented at the upcoming HAB Symposium to formally recognize and honor his research achievements, leadership, and extensive service to the HAB community. We are grateful for his many contributions that have advanced the science of HABs, the outstanding mentorship he has provided to many students and early career scientists, and the many other positive impacts that he has had on the field.

Join us in congratulating Dr. Paerl on this amazing achievement!