COASTAL EUTROPHICATION IN NORTHEAST U.S. ESTUARIES: DINOFLAGELLATE CYSTS AS BIOINDICATORS

Relationships between nutrient inputs and biological responses in estuaries are useful to determine how much nitrogen is too much. Nutrient concentrations in coastal waters do not always reflect the total amount of nutrients entering a water body, as they can be rapidly taken up by phytoplankton and aquatic vegetation. One method to estimate nutrient input is nutrient loading models, such as the SPARROW model. Coupling nutrient loading models with biological indicators that act as early warning signs in water quality degradation can be used to quantify the level of nutrient inputs that may be harmful to estuaries. We are investigating the use of dinoflagellate cysts (the fossilizable life stage of planktonic dinoflagellates) from sediments as a means to evaluate and monitor levels of eutrophication. Dinoflagellate cyst assemblages are known to reflect sea-surface conditions and are used in paleoenvironmental reconstructions to provide information on past sea-surface temperature, salinity, productivity, and nutrient availability. Previous studies have noted the impact of eutrophication on species, abundances and diversity of cysts in sediments, but no study has yet compared empirical values of nutrient loading to cyst taxa. In this study our main objective is to determine if cyst assemblages correlate to nitrogen levels as estimated from nutrient loading models. Our second objective is to determine if there is a relationship between cysts of heterotrophic taxa and biogenic silica (a sedimentary proxy for the abundance of diatoms), as diatoms are important prey for many heterotrophic dinoflagellates. Lastly, as samples encompass four main estuary types (riverine, lagoon, coastal embayment, and fjord) we can determine if the cyst response varies by estuary type. A total of 61 sediment samples from 20 different estuaries from Maine to Delaware collected by the EPA were analyzed for dinoflagellate cysts and biogenic silica. Over 60 dinoflagellate cyst taxa were identified, and assemblages were found to vary by biogeographic zone. Using canonical correspondence analysis (CCA) results thus far indicate nitrogen loading and tidal range as important variables influencing the cyst signal.