| Introduction: Extraction of drinking water, intensive agriculture and the intake of Rhine water in the polder area have caused a decline of natural ecosystems and a loss of biodiversity in wetlands in the Netherlands. This decline in quality and quantity in habitat for wetland plant species is most evident in nutrient poor and groundwater dependent ecosystems such as species rich fens. The Vechtsteek in the province of Utrecht is a good example of this phenomenon. The fragmented distribution of ecosystems in the Vecht river plain is caused by hydrological fragmentation, which is mainly caused by drinking water extractions and drainage to the lower-lying polders. Fragmentation of regional groundwater seepage systems leads to a decrease of seepage of non-acidic nutrient-poor fresh groundwater that enters the root zone of plants, leading to changes in site factors and subsequent disappearance of species depending on the original conditions. Loss and fragmentation of habitat of species depending on seepages sites causes, besides the loss of total (sub)populations, a decrease in size of the remaining subpopulations and a decrease in connectivity between these subpopulations. This will decrease the viability of the species concerned. Aim: The aim of this project is to disentangle the accumulating effects of abiotic and biotic factors that decrease the distribution and viability of rare groundwater dependent fen plant species. This will be done by developing and integrating hydrological and ecological mechanistic models. A decision support system will be created to evaluate the effects of different management options. The relatively undisturbed fen area Biebrza in Poland will be used as a reference area. The project is devided into three subprojects executed by PhD students. Arnaut van Loon will focus on the hydrology, Yuki Fujita on plant competition and the decision support system and Hester Soomers on plant dispersal. Research: The plant dispersal research will focus on rare, species-rich, groundwater dependent vegetation types such as quagfens (Scorpidio-Caricetum diandrae). To gain more insight in the key-factors that determine the presence and abundance of the selected species, a multiple regression analysis will be carried out. For this purpose, several large datasets will be combined and new independent variables such as patch size, connectivity and management will be added. Aditionally, water dispersal of seeds will be modelled mechanistically. Modelling seed dispersal by water in a semi-natural anthropogenic environment with its canals, ditches, polders and sluices is challenging and innovative. To parameterize the model, seed buoancy will be determined experimentally and other seed characteristics, such as size and weight, will be measured. The model will be validated by assessing the dispersal potential of water dispersing seeds by the catchment of seeds in aquatic habitats by for example drift nets or Astroturf mats. This model can be used to answer questions about colonization capacity of different plant species, the meta-population structure of these species and the effect of different management options. It is hypothesised that in the less fragmented area Biebrza, where flooding occurs more regularly than in the Vechtstreek, connectivity between subpopulations is higher. This hypothesis will be tested by model simulations and genetic analyses. For a few selected species, subpopulations in both the Vechtstreek and the Biebrza will be sampled for determining DNA profiles using microsatellites. Microsatellites can be used to address questions concerning degree of relatedness of individuals or groups and to assess the magnitude and direction of gene flow between populations. |
