Author: leahmnel (Page 1 of 2)

Neuse River Estuary Conditions – 6 Sept, 19 Sept, 6 Oct & 20 Oct, 2022

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,


Congratulations Dr. Paerl!

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!

IE Student Projects Kickoff!

Today the Paerl lab kicked off a third bioassay in collaboration with the Zhao Research Group at NC A&T, which is focused on determining the water quality impacts of landfill leachates (to learn more about this project click here). IE student Meg will be building off of this bioassay for her Independent Research Project and will be determining the effects that these leachates have on algal communities and their composition over a longer period of time. We are looking forward to seeing the results of her project!

Neuse River Estuary Conditions – 24 August 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.


Paerl Lab Photo

The Paerl Lab took a lab photo last week in front of IMS’s brand-new mural!

Pictured from left to right:

Back Row

Maxfield Palmer, Hans Paerl, Jeremy Braddy, Haley Plaas, Nathan Hall, Mingying Chuo

Front Row

Madison Sholes, Alex Sabo, Karen Rossignol, Leah Nelson, Randy Sloup 

The Hall Lab, who we often collaborate on projects with, also got a lab photo.

Pictured from left to right: Maxfield Palmer, Nathan Hall, Mingying Chuo

Investigating Associations between Air and Water Quality in Eastern North Carolina

This past week PhD student Haley Plaas and intern Madison Sholes deployed PurpleAir Sensors at pre-established sites along the Chowan River, where Cyanobacterial Harmful Algal Blooms (CHABs) are known to occur. In recent years, communities in northeastern North Carolina surrounding the Chowan River and Albemarle Sound have faced degraded water and air quality tied to a suite of environmental issues, including increased incidences of toxin-producing harmful algal blooms. Previous work done by Plaas et al. found that several aquatic cyanobacterial genera were detected in sampled particulate matter (PM), including two toxin-producing strains, Dolichospermum and Microcystis. These findings suggested a need for further research on the link between HABs and HAPs, i.e., the presence of Harmful Air Pollutants, in this region. The goal of this project is to investigate the association between indicators of CHABs and corresponding PM mass concentrations via the deployment of several PurpleAir sensors throughout the Chowan River and Albemarle Sound basin.

Haley and Madison deploying sensors in the field:


Photos taken by: Tom Brennan

Neuse River Estuary Conditions 15 June, 2022

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.


Neuse River Estuary conditions 31 May, 2022

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.


Neuse River Estuary conditions 17 May, 2022

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.


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