1 Department of Biology, Faculty of Science, SDU2 Faculty of Science, SDU3 CLEAR, Department of Biology, Faculty of Science, SDU4 University of Southern Denmark5 Department of Biology, Faculty of Science, SDU
Lake Hampen is representative of a group of lakes called Lobelia lakes. These are oligotrophic, clear water lakes which tend to have a low alkalinity. These lakes are termed “Lobelia lakes” due to the characteristic isoetid species which thrive in these conditions. Isoetids are small, evergreen aquatic plants whose leaves grow in a rosette form and have a large root base. The large root system enables the plants to better assimilate nutrients from the sediments, and the uptake of CO2 which is used for photosynthesis, and to release O2 into otherwise anoxic sediments. Lake Hampen is situated high up in the Jylland ridge and lies close to the groundwater boundary. This means that the groundwater flow between the aquifer and the lake is not constant, sometimes the groundwater flows from the aquifer into the lake (discharge) and other times it flows from the lake into the aquifer (recharge). Discharge and recharge areas may also be geographically separated. This variable groundwater pattern combined with only minor surface inlets and outlets provides good conditions for studying the interactions between groundwater and Littorella uniflora. Studies have shown that this dynamic seepage correlates hydrology to the lake shore ecosystem; in that highly productive areas coincide with seepage sites in the littoral zone. The changes in seepage flux will affect the pore water biogeochemistry by altering the transport of gases and dissolved substrates, these changes will in turn affect the rooted vegetation. The macrophytes themselves can also affect the biogeochemistry by changing the concentration of the dissolved CO2, O2 and nutrients in the sediment. The main objective of this project is to investigate how plant growth in Lobelia lakes is influenced by the inlet and outlet of groundwater; and which role the plants have in the cycling of the nutrients in these lakes. To fulfil these objectives several smaller studies are to be carried out, these include the determination of the groundwater flow pattern, the determination of the Littorella uniflora coverage within the lake and to establish how this coverage relates to the seepage patterns. It is also the intention of this study to determine the nutrient input around the lake and how this relates to the plant coverage; as well as investigate the nutrient assimilation processes for Littorella uniflora. Preliminary results from the ongoing investigation will be presented, including data on plant biomass and morphology; and on pore water chemistry.