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

The Paerl Lab welcomes Madison as our Science Communication Intern for the summer of 2022! Madison is a rising junior at NC State studying marine science. She will be assisting Haley in disseminating scientific information to the public, especially regarding Asphyxiation by Algae. Welcome Madison!

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

Dr. Hans Paerl recently presented on current eutrophication and related habitat problems in NC’s Albemarle-Pamlico Sound system.

To see the full presentation & learn more, visit the link below:

Eutrophication along NC Continuum

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