Development and application of seasonal indices of coastal-zone eutrophication

Ryan, S. A., Roff, J. C., and Yeats, P. A. 2008. Development and application of seasonal indices of coastal-zone eutrophication. – ICES Journal of Marine Science, 65: 1469–1474.Indices of coastal-zone eutrophication were developed based on combined values of nitrogen, phosphorus, and phytoplankton biomass (measured as Chl a). Measurements of nitrate, ammonia, phosphate, Chl a, and total phosphorous were taken at a series of inlets (bays and estuaries) along the Atlantic coast of Nova Scotia and the north shore of Prince Edward Island in summer 2006. Reference data from offshore sites and measured data are displayed on a N (nitrogen):P (phosphorus) nutrient–space diagram, which clearly indicates thresholds between impacted and unimpacted inlets. The problem of seasonal variability in nutrient levels and phytoplankton concentrations is accounted for by using an amalgamation of the Redfield nutrient ratios and the coastal carbon–Chl a ratio and allowing for sedimentary losses. This amalgamated ratio allows for the inverse seasonal relationship between labile nutrient levels and Chl a, permitting the collection, comparison, and interpretation of seasonally variable data. Measured concentrations of phosphate were adjusted from measured Chl a and were compared with measured levels of total phosphorous for the Nova Scotian sites to assess the accuracy of conversions. Given regional calibration, these indices should be applicable to all coastal waters.