Effects of road salt on zooplankton : - a freshwater experiment in oligotrophic and eutrophic waters

Pollution or changes in abiotic factors can be stressful if they exceed a species tolerance level, it can for example prevent the species ability to reproduce and disperse. High nutrition- and salt levels may be limiting for species in higher concentrations and affects all species since indirect, interactive and additive effects of high nutrient or salt levels lead to changes in the community structures. Algae blooms are a major problem in many lakes around the world and a reduced population of zooplankton had contributed to faster growth in phytoplankton and therefore eutrophication. The purpose of the study is to investigate species composition of zooplankton in a eutrophic- and oligotroph nutrient levels with different salt concentration and how it changes over time. Three salt concentrations (15, 250 and 1000 mg Cl-/L) along with the two nutritional levels resulted in six possible combinations replicated four times each, a total of 24 units. Zooplankton samples were taken from all units on day 19 and 78. A total of 51 different species were found throughout the study, of which a total of 34 species was found in the first sample and a total of 36 species in the second sample. The result showed an increase in Nauplii and Philodina spp. and a decrease in Daphnia pulex and Daphnia rosea. In the first sample a significant difference in the number of species was found between the salt concentrations 1000 mg Cl-/L and 15 mg Cl-/L and also between 1000 mg Cl-/L and 250 mg Cl-/L, where the total number of species decreased. There was also a significant difference in the species community between the nutrient levels from the first to the second sample, where a more even community was found between the first and second sample. The reduction in the number of species from the first to the second sampling may have been the reason why the species turned into communities that looked more like each other at the second test occasion, while the higher nutritional level may be what contributed to a community with higher evenness and similarity due to a greater opportunity to utilize food resources for the zooplankton without competition. The conclusion is that the salt concentration reduced the number of species, although the results show that salt concentrations with oligotrophic nutrient levels were more similar and had a greater similarity in amount of different species. Preserving lakes together with protective efforts is needed to reduce the ecological consequences of road salt, to be able to preserve species diversity and biodiversity in freshwater ecosystem