Constructed treatment wetlands provide habitat for zooplankton communities in agricultural peat lake catchments

Zooplankton are an essential component of healthy functioning lake and wetland ecosystems. Despite this, zooplankton communities within constructed treatment wetlands (CTWs) in agricultural landscapes remain unstudied. Taxa richness, total abundances and community composition were evaluated for zooplankton assemblages from three habitat types (lakes, CTWs and drainage ditches) within five intensive agricultural peat lake catchments in New Zealand. Relationships to water quality, physicochemical and biotic habitat variables were examined. Zooplankton were dominated by cladocerans, copepods, ostracods and rotifer taxa, representing a range of communities typical of lake and pond habitats. CTWs supported species otherwise absent from lake and drain habitats, increasing the overall biodiversity of the highly-modified peat lake catchments. Taxa richness of CTWs was higher than that of drains, and a few CTWs had greater diversity than several lakes. The morphological variables area and depth contributed to the greatest differences between habitats, followed by pH, inorganic nitrogen, conductivity and temperature. Correspondingly, zooplankton communities were significantly influenced by habitat area, depth and pH, as well as ammonium, phosphate, water temperature, dissolved oxygen, and macrophyte cover. Opportunities were explored for refining CTW designs to enhance zooplankton biodiversity and potentially improve treatment efficiency through increasing the complexity and diversity of CTW habitat niches.