Fragmentation and seed dispersal in freshwater wetlands


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Title Fragmentation and seed dispersal in freshwater wetlands
Period 07 / 2005 - 05 / 2012
Status Completed
Dissertation Yes
Research number OND1317415
Data Supplier Website Sense


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.

Abstract (NL)

Het proefschrift van Hester Soomers toont aan dat het transport van plantenzaden die zich aan de wind hebben aangepast, grotere afstanden afleggen via sloten dan via wind. Voor de biodiversiteit is het dus van belang dat bestaande oeverpopulaties en geschikte gebieden waar nog geen populatie aanwezig is, verbonden zijn via een netwerk van oppervlaktewater. Verlies van biodiversiteit Naast het verlies of achteruitgang van de kwaliteit van het leefgebied van een plantensoort, zorgt ook verandering in landgebruik vaak voor het versnipperen van het leefgebied van een plantensoort. Het opsplitsen van het gebied waar de plantensoort voorkomt, kan tot een grotere uitsterftekans leiden, omdat onder andere de isolatie van plantenpopulaties toeneemt. Effectieve zaadverspreiding is dan van groot belang om dit proces tegen te gaan. Slotennetwerk Zaadverspreiding kan plaatsvinden via wind, water, dieren of door de plant zelf. Modelsimulaties lieten zien dat verspreidingsafstanden via water voor zaden die zich hebben aangepast aan verspreiding via wind gelijkwaardig zijn aan die voor zaden die zijn aangepast aan verspreiding via water. Zo kunnen deze zaden een afstand van honderden meters overschrijden in een slotennetwerk. Het zaadtransport in sloten wordt, in tegenstelling tot in rivieren, bepaald door windrichting en -snelheid.

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Supervisor Prof.dr. J.T.A. Verhoeven
Supervisor Prof.dr. M.J. Wassen
Co-supervisor Dr. P.A. Verweij
Doctoral/PhD student H. Soomers


A12000 Surfacewater and groundwater
D22400 Ecology

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