Document of bibliographic reference 229042

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Bibliographic resource

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Book chapters

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Summary

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AM

Title

A regime shift in a freshwater estuarine ecosystem recovering from hypereutrophication?

Abstract

After decades of hypereutrophication, with strong hypoxia and elevated ammonia concentrations, water quality in the freshwater part of the Schelde estuary changed rapidly. Average May-Sep oxygen concentrations more than quintupled, from 8% of saturation (1996) to 51% (2007). Ammonium concentrations decreased from a 296 µM May to Sep average (1996) to 16 µM (2007). Average May-Sep chlorophyll a concentrations increased from 15 µg/l (1996) to 178 µg/l (2007). From 2006 oversaturated oxygen concentrations are occasionally observed, caused by algal primary production. We hypothesise that inhibition of primary production and algal growth due to anoxia and/or ammonia toxicity prevented the build-up of algal biomass until a decade ago. We study the steady states and dynamics of a simple mathematical model, including this algal growth inhibition. It displays a regime shift from a heterotroph state to an autotroph state, when ammonia load is reduced below a threshold. At intermediate loads it predicts fluctuations in oxygen concentration in response to discharge peaks. Data and model results are consistent, and thus indicate a possible regime shift from heterotrophy to autotrophy in this ecosystem.

Bibliographic citation

Cox, T.; Maris, T.; Soetaert, K.; Conley, D.; Van Damme, S.; Meire, P.; Struyf, E. (2009). A regime shift in a freshwater estuarine ecosystem recovering from hypereutrophication?, in: ASLO Aquatic Sciences Meeting 2009: A Cruise Through Nice Waters, 25-30 January 2009, Nice, France. pp. 56

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