Ecohydrology of groundwater dependent wetland ecosystems: groundwater discharge, age and hydrochemistry
Batelaan, O.; De Becker, P.; Huybrechts, W. (2005). Ecohydrology of groundwater dependent wetland ecosystems: groundwater discharge, age and hydrochemistry. [S.n.]: [s.l.]. 52 pp.
The position of an area within the hydrological and landscape system is an important factor in the ecology of valley wetlands. However, the regional context is often not explicitly taken into account in the ecohydrological analyzes of these wetlands, which hampers the identification and quantification of regional dependent abiotic factors for ecohydrological site modelling. Therefore, the relationship between groundwater fed valley wetlands and the quantitative and qualitative aspects of the regional groundwater flow is investigated. This is done by mapping and analyzing the vegetation of three groundwater dependent ecosystems, measuring and modelling groundwater levels and seepage zones, measuring and analyzing hydrochemical patterns, and simulating groundwater ages. The ‘figure of merit’ is used to compare spatial patterns of measured and simulated groundwater discharge locations, and it is shown that the occurrence of phreatophytic vegetation is clearly corresponding to groundwater discharge locations. However, the groundwater discharge zones derived from the occurrence of phreatophytic plant species are not synonymous to hydrologically derived groundwater discharge locations. The spatial distribution of the recharge in these humid study areas did not appear to have an important influence on the simulated groundwater ages. We quantify and map the spatial variation in groundwater ages in groundwater discharging wetlands, at a level not observed before. It is shown that the convergence of flow paths as well as the groundwater ages have a high spatial variability within the wetland. However, the two are spatially not corresponding. Important consequences for ecohydrological understanding of vegetation patterns, as well as for groundwater sampling methodology in these wetlands is that very different groundwater fluxes and qualities can be expected at very short distances. Since in groundwater dependent wetlands groundwater availability is generally not a discriminating factor, the hydrochemistry of the discharging groundwater as a consequence of the geochemistry of the feeding aquifer and the convergence of flow paths is determined as the most important factor in the explanation of the occurrence of vegetation types in and between the study areas. Groundwater discharge conditions in valley areas will strongly mask groundwater pollution, due to convergence of water of different contributing regions as well as from hydrogeochemical different reactive parts of aquifers.
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