Effects of nutrient enrichment on primary and secondary productivity in a subtropical floodplain system: an experimental approach

Abstract

In this study, we evaluated the effects of nutrient enrichment on primary and secondary productivity, the relationship between these ecosystem processes, and the relationship between the resources of zooplankton community in response to ecosystem processes, experimentally. The experimental design was randomized, with three levels of nutrient replicated three times, giving a total of nine experimental units, for a period of 30 days (November–December, 2013). We measured primary productivity, secondary productivity, and zooplankton community structure, at the beginning and after every seven days of the experiment. Primary and secondary productivity increased with nutrient enrichment. Secondary productivity was supported by a few dominant species with ecologically selected traits, especially large-bodied zooplankton (copepods and large cladocerans). Nutrient enrichment turned the relationship between primary and secondary productivity from positive to negative and intensified the biotic process of competition because of exploitation by zooplankton populations, favoring an increase in the dominance of large microcrustaceans. This reflects the initial effects of a moderate eutrophication. At a larger temporal scale and at higher nutrient concentrations, effects of higher magnitude are expected, which may disrupt the whole community, resulting in the loss of ecosystem processes.