Abstract
This article presents and tests a new method for the retrospective assessment of ecological status assessment of the lakes in accordance with the Ecological State Macophyte Index (ESMI), which is formally used in biological monitoring in Poland. The proposed method is based on three metrics, the Z colonization index, the average maximum depth of lake vegetation Cmax, and the Secchi disk depth. Mathematical functions of ecological class were developed on the basis of the mean values of these three indicators in summer for different ecological status classes in 88 stratified lakes in northern Poland and the Łęczyńsko-Włodawskie Lake District and five lakes in the catchment area of the Wel River (published data). The new metrics were validated on the basis of literature data—ESMI, Cmax, Z and SD values from 11 lakes near Olsztyn (Poland). The obtained results are similar to those calculated based on macrophyte field surveys and can be an alternative of the Ecological State Macophyte Index (ESMI), which is formally used in biological monitoring in Poland. The proposed method makes it possible to compare long-term changes in the ecological state of lakes, because it enables an analogous assessment on the basis of data calculated from historical bathymetric maps showing the distribution of hydro macrophytes (parameters Z and Cmax) as well as contemporary data, collected, among others, during hydroacoustic research.
Highlights
According to the EU Water Framework Directive (WFD) [1], the quality of inland waters should be evaluated based on biological elements, physicochemical and hydromorphological elements.The systems for assessing aquatic ecosystems should differentiate between the processes that occur naturally and those driven by anthropogenic pressure
The individual equations were developed based on the regression between the indicators (Z, Cmax, Secchi disc visibility (SD)) and classes of the ecological status of lakes were determined with the use of the Ecological State Macophyte Index (ESMI) method [9]
The study presented in this article had to be subject to a number of limitations that were relevant to the discussion of the results obtained
Summary
The systems for assessing aquatic ecosystems should differentiate between the processes that occur naturally and those driven by anthropogenic pressure. Pursuant to the provisions of the WFD, in addition to minimally transformed ecosystems, the reference conditions can be determined based on historical data. Paleolimnological investigations are carried out to assess environmental change, identify the causes of change and determine the current ecological status of aquatic ecosystems, including lakes [7]. Despite their effectiveness, as demonstrated by a study of Lake Pappjärv in Estonia [5], paleolimnological methods can only be applied to selected lakes
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