Solute transport by groundwater flow to wetland ecosystems : the environmental impact of human activities

This thesis deals with solute transport by groundwater flow and the way in which solute transport is affected by human activities. This in relation to wetland ecosystems. Wetlands in the eastern part of the Vecht river plain in The Netherlands are historically renown for their great variety of aquatic and fen vegetation. Over the past decades a marked deterioration of wetland vegetation has been observed. In particular species of the alliance Caricion davalianae disappeared. It is generally believed that the Caricion davalianae are dependent on rather nutrient-poor (mesotrophic) calcium-rich groundwater. In the Vecht river plain this type of water naturally originates from the adjacent sandy ice-pushed ridge 'Het Gooi'. Upward seepage of ridge water in the river plain has decreased over the past decades as an effect of increasing groundwater extraction for public water supply on the ridge. The resulting water shortages on the Vecht river plain in summer are met by import of external polluted surface water. This eutrophic water has negative effects on the mesotrophic aquatic and fen vegetation. Provincial groundwater management is therefore directed towards regeneration of upward seepage of groundwater from the ridge. At the same time groundwater pollution on the ridge has increased. In time this may affect the vegetation on the river plain through solute transport by groundwater flow. Increased upward seepage from the ridge may thus have adverse effects. Specific research questions related to the vegetation on the river plain are: - to what extent is the groundwater under the ridge polluted? - are pollutants transported towards the river plain? - are pollutants retarded or chemically altered during flow? - is regeneration of upward seepage a good restoration measure; are there alternatives