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SPATIAL AND TEMPROAL RELATIONSHIPS BETWEEN TOTAL NITROGEN AND PALNKTONIC CHLOROPHYLL IN LONG ISLAND SOUND: HOW STABLE ARE THEY?
Citation:
Dettmann, E H. AND L. B. Mason. SPATIAL AND TEMPROAL RELATIONSHIPS BETWEEN TOTAL NITROGEN AND PALNKTONIC CHLOROPHYLL IN LONG ISLAND SOUND: HOW STABLE ARE THEY? Presented at EPA Region 1 Risk Assessors Meeting, Boston, MA, May 5-7, 2004.
Description:
Our purpose is to examine seasonal and year-to-year variability of relationships between concentrations of total nitrogen and chlorophyll in the water column of an estuary. Understanding this variability gives guidance to those developing methods to assess risk of eutrophication as a result of nutrient loading. We used data collected by the Connecticut Department of Environmental Protection's Long Island Sound Water Quality Monitoring Program to examine spatial and temporal trends in concentrations of total nitrogen and chlorophyll in the water column and in the relationship between these two variables. Concentrations of both nitrogen and chlorophyll showed similar spatial gradients in Long Island Sound, with peak concentrations in the western Sound, and much smaller concentrations in the eastern Sound. Chlorophyll concentrations increased more steeply with increasing total nitrogen in spring and summer than in autumn and winter. Summertime concentrations of total nitrogen declined modestly from 1995 to 2001. During this same period, summertime concentrations of chlorophyll showed much stronger temporal trends, with concentrations declining substantially in 1997?1999, compared to previous summers, followed by a large increase in 2000 and 2001. The spatial relationship between chlorophyll and total nitrogen reflected these changes. The slope of this relationship declined substantially from 1995-1999, only to increase dramatically in 2000. The summers of 1997?1999 were preceded by winters with somewhat warmer water temperatures than in the preceding two and following two years. Other environmental variables examined (incident light intensity, river inflow, wind speed, total suspended solids) did not show patterns that correlated with the observed chlorophyll to nitrogen relationship. We will discuss mechanisms that could cause these temporal trends and implications of the observed year-to-year variability for risk assessment.