ZIPLAS: Zooplankton Index for Polish Lakes' Assessment: a new method to assess the ecological status of stratified lakes

Zooplankton is widely recognized as a key component of pelagic ecosystems and forms the basis for major trophic webs. Although zooplankton has often been used as an indicator of trophic state, it has not been included as an obligatory element of the water assessment systems compliant with the Water Framework Directive. This article introduces the Zooplankton Index for Polish Lakes' Assessment (ZIPLA(S)) as a new method to assess the ecological status of stratified lakes based on the zooplankton community. The ZIPLA(S) evaluates three aspects of zooplankton communities, namely, taxonomic composition and abundance, diversity of the zooplankton community, and stressor-sensitive species, which are combined into a multimetric index. Following are the metrics used to compose multimetric ZIPLA(S): percentage share of the Rotifer species indicative of high trophy in the indicative group's number (IHTROT; %), ratio of Calanoida to Cyclopoida individual numbers (CA/CY), percentage of tecta form in the population of Keratella cochlearis (TECTA; %), Margalef's index (d), and zooplankton abundance (NZOL; ind./L). ZIPLA(S) responds clearly to eutrophication indicators-the strongest with Secchi disc visibility (Spearman's rank correlation R = 0.86) and slightly weaker with the expressed by total phosphorus (R = -0.74), total nitrogen (R = 0.68) and the catchment pressure expressed by the nutrient loads generated by different types of land use (R = -0.58).