| Popis: |
According to the Water Framework Directive of the European Union, macrophytes should be used as indicators in the ecological and environmental monitoring of lakes. In the member state Sweden the Environmental Protection Agency has elaborated assessment criteria for determining lake status based on macrophytes. The main focus of this thesis is to evaluate the efficiency of the assessment criteria for macrophytes. In addition the concordance between the ecological status classes of the four quality factors included was analysed. The assessment criteria for macrophytes are based on the total phosphorus preference of the respective species. The focus is thus mainly on the nutrient level of the investigated lakes and the environmental problem monitored is eutrophication. Macrophytes are one of the five biological quality factors used for lakes. The others are phytoplankton, diatoms, benthic fauna and fish. The two latter were included in this thesis. In addition to the biological factors the chemical factor, nutrients in lakes, i.e. the total phosphorus, was included. The macrophyte composition was investigated in two eutrophic Uppland lakes: Lake Trehörningen and Lake Edasjön. Since the assessment criteria were launched in 2007 there have been problems reported regarding the outcome of the methods. The results are sometimes inconclusive for eutrophicated lakes and especially for lakes with naturally high levels of nutrients. In this study the macrophyte species composition was compared with the nutrient level of different lakes. Some species were found in equal shares in oligotrophic lakes as in eutrophic, e.g. Nymphaea candida and Nuphar lutea. Hence they were considered less suitable as elements in the method evaluated. A couple of species were present in predominantly oligotrophic (e.g. Lobelia dortmanna) or eutrophic (e.g. Hydrocharis morsus-ranae) lakes, respectively. They were regarded as better indicators since they ”preferred” lakes either poor or rich in nutrients. It is important to point out that all the other biological quality factors used, except for macrophytes, are multimetric. I conclude that more parameters are needed for evaluation of macrophytes in lakes. Tentatively, the degree of coverage of the plants and algae, the presence and degree of coverage of invasive nonnative species, lake lowerings and the consequent composition and abundance change, all should be tested as additional parameters. A high level of concordance was verified for the status classifications of the four quality factors in lakes of oligotrophy as well as in lakes of eutrophy, i.e. no particular pattern based on trophy level was found. The macrophyte inventories of the two Uppland lakes both resulted in a moderate ecological status for macrophytes. |
