How do nutrients control the productivity of brownified freshwater and coastal ecosystems?

Summary

Anthropogenic drivers lead to unwanted loading of nutrients to freshwater and marine ecosystems, potentially causing eutrophication and loss of biodiversity and fish stocks. The ability to predict these ecological responses is limited by the current understanding of nutrient bioavailability, i.e. the degree to which nutrients can be assimilated by biota. Traditionally, coastal water management has focused on inorganic nutrients, but recent evidence suggests that also organic forms of nitrogen (N) and (P), especially in the form of brown-pigmented organic compounds, can be both highly abundant and bioavailable. Scientists and managers lack the conceptual framework and toolkit required to make biologically meaningful assessments of nutrient bioavailability, necessary to understand and predict the consequences of anthropogenic loading to aquatic habitats. We here apply a new, simple, and inexpensive tool to simultaneously determine N, P and organic carbon bioavailability in surface waters. We use this tool to characterize patterns of bioavailable nutrient loading from land, and to explain spatial and temporal variability in nutrient limitation of primary production and bacterioplankton production in inland and coastal waters. We also address the physical transformation of bioavailable organic nutrients that happens in the mixing zone between fresh and salt water.

bioavailability nutrients dissolved organic matter