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.
This image was sent to us by Jim Cloern, showing his collection of Paerl Lab t-shirts from over the years! Thanks for sharing with us, Jim!
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!
The Paerl Lab was back in the Bay Delta, CA last week! Hans Paerl, Leah Nelson, Alex Sabo, and Haley Plaas were working to continue Haley’s dissertation research which focuses on assessing the linkage between nutrient enrichment, phytoplankton community composition, cyanobacterial harmful algal bloom toxin production, and aerosol formation in the Sacramento-San Joaquin River/Bay Delta estuarine ecosystem. This research was accomplished by completing a combination of aerosol measurements and a nutrient addition bioassay experiment. For this trip, an additional nutrient was added to the bioassay: NH4 and NH4 + P! We will be sure to keep you updated as we analyze the data from these experiments.
Special thanks to all of our collaborators at CA-DWR, USGS, and Restore the Delta (and more)!
Dr. Hans Paerl recently gave a talk for the Morehead City fieldsite’s ‘Seminar in Marine Issues’ course. He spoke on the global proliferation of harmful cyanobacterial blooms and what can be done to control them. A recording of his talk can be found here.
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!
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.
Meg McCartney Madison Milotte (they/them)
The Paerl Lab welcomes two Field Site students, Madison and Meg, from UNC main campus for the 2022 Fall Semester! These students will work on independent projects in order to learn more about coastal environmental microbiology. We are very excited to work with them this semester!
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.
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.
The Paerl Lab took a lab photo last week in front of IMS’s brand-new mural!
Pictured from left to right:
Maxfield Palmer, Hans Paerl, Jeremy Braddy, Haley Plaas, Nathan Hall, Mingying Chuo
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