Characterizing seston in the Penobscot River Estuary

Area of Science:

• Estuarine ecology
• Aquatic chemistry
• Fish biology

Background:

• The Penobscot River Estuary supports the largest population of Atlantic salmon in the USA.
• Limited knowledge exists regarding the chemical and biological properties of seston in this vital estuary.
• Understanding seston composition is crucial during spring when river discharge and fish migration peak.

Purpose of the Study:

• To characterize the chemical and biological aspects of seston in the Penobscot River Estuary during high river discharge and fish migration.
• To identify the sources and composition of suspended particles in the estuary.
• To assess potential risks posed by seston to diadromous fish populations.

Main Methods:

• Estuarine transects were used to collect seston samples in spring 2015.
• Analyses included phytoplankton identification, total suspended matter (TSM), organic TSM, chlorophyll a, particle size, particulate carbon and nitrogen, and stable isotopes.
• Limited fish samples were analyzed for pathological gill damage post-algal bloom.

Main Results:

• Total suspended matter (TSM) exhibited non-conservative behavior, with a net gain in the estuary.
• Phytoplankton comprised a minimal fraction (1/1000) of the total particles, indicating non-phytoplankton sources for TSM.
• Particulate carbon and nitrogen ratios, along with stable isotope data, revealed a dominant terrestrial (allochthonous) signal in the seston.
• The toxic phytoplankton Heterosigma akashiwo was detected, coinciding with fish samples showing gill damage.

Conclusions:

• The seston in the Penobscot River Estuary is largely composed of non-detrital, terrestrial-derived particles.
• The presence of ichthyotoxic algae like Heterosigma akashiwo poses a potential threat to resident and migratory fish.
• Further research is warranted to investigate the impacts of seston composition and algal blooms on fish health in the estuary.