Phytoplankton metrics response to the increasing phosphorus and nitrogen gradient in shallow lakes

Abstract

A new phytoplankton-based method (the Phytoplankton Metric for Polish Lakes – PMPL) for the ecological status assessment of lakes has been developed in Poland. This method has not been validated and tested on independent data, hence the aim of the study was to check the applicability of this method and the sensitivity of different phytoplankton metrics along pressure gradient. Phytoplankton data were collected from 33 Polish lowland lakes (20 stratified, 13 non-stratified), during the growth season in the period from 2005 to 2009. The biomass of phytoplankton was calculated from cell volume measurements and chlorophyll a concentration was determined spectrophotometrically by the alcohol method. Total nitrogen and total phosphorus concentrations were determined by standard methods (PN-EN ISO 6878:2006p.7 and PN-EN 25663:2001, respectively) and water transparency was measured using a Secchi disk. For comparability, an ecological status was determined according to three phytoplankton-based methods: Polish, German and Hungarian. Polish metrics showed a strong correlation with the other metrics (German, Hungarian), which are broadly and successfully used for assessment in Europe. However, a statistically significant correlation was found between all the metric values and the main parameters: total phosphorus, total nitrogen and Secchi disk visibility. The metrics based on quantitative phytoplankton features were more sensitive to the growth of eutrophication than others, based on indicator taxa. Total phosphorus demonstrated a stronger relationship with the tested metrics than total nitro