Zooplankton shifts from headwater to lowland streams: Insights into the role of water quality to assist the protection and restoration of agricultural waterways.

GUTIERREZ M.F.; MAYORA G.; LICURSI M.; MICHLIG M.; REPETTI M.R.; NEGRO L.

ECOHYDROLOGY

JOHN WILEY & SONS INC

Lugar: New York; Año: 2022

1936-0584

Despite the critical importance of zooplankton for many ecological processes, knowledgeof its structure and distribution patterns in small streams subject to intensiveland uses remains limited. Here we analysed changes in zooplankton community andcomposition in 10 sites located in streams from first-order to sixteenth-order,according to Shreve´s classification, in a small catchment influenced by intensive agriculture.Using univariate and multivariate methods, we investigated the extent towhich local scale environmental factors explained the spatial patterns of zooplanktoncommunity. We found that environmental conditions of headwaters differed markedlyfrom those of lowland streams, especially with respect to nutrient levels, whichwere higher in the former than the latter. Zooplankton community was mainly composedby microphagous rotifers, and the overall species composition differed withthe stream order. While zooplankton diversity and evenness increased with streamorder and correlated negatively with nutrient level, zooplankton abundance and biomassshowed the opposite trend. The mechanistic processes creating these patternsremain unknown but are likely linked to the effects of greater water mixing and dilutionin lowland streams, as well as ecological processes such as predation andresource diversification. No clear pattern was found for presence or concentrationsof pesticides in relation to the stream order. However, water quality seemed to be animportant factor influencing zooplankton assemblages, which were significantly associatedwith pesticides and trophic state variables. Our findings suggest that agriculturalpollution is impacting the zooplankton community, which may have implicationsfor the food webs and overall health of the stream systems.