Spatial Economic–Hydroecological Modelling and Evaluation of Land Use Impacts in the Vecht Wetlands Area

Wetlands provide many important goods and services to human societies, and generate nonuse values as well. Wetlands are also very sensitive ecosystems that are subject to much stress from human activities. Reducing the stress on wetlands requires a spatial matching between physical planning, hydrological and ecological processes, and economic activities. Spatially integrated modelling and evaluation can support this. The present study has developed a triple layer model that integrates information and concepts from social and natural sciences to address the analysis and evaluation of land-use scenarios for a wetlands area in the Netherlands, the Vecht area. This is the floodplain of river Vecht, located in the centre of the Netherlands. The study has resulted in a set of linked spatial hydrological, ecological and economic models, formulated at the level of grids and polders. The main activities incorporated in the system of models are housing, infrastructure, agriculture, recreation and nature conservation. The formulation of alternative development scenarios is dominated by land use and land cover options that are consistent with the stimulation of agriculture, nature or recreation. Two aggregate performance indicators have been constructed from model output, namely net present value of changes and environmental quality. The spatial characteristics of these indicators are retained in a spatial evaluation that ranks scenarios.     

Grinding and sieving soil affects the availability of organic contaminants: a kinetic analysis

Field contaminated soils are often homogenized before application in bioassays and chemical assays that estimate the (bio)availability of their contaminants. The homogenization of the soil might affect the availability, and thereby the outcome of a bioassay might not reflect field situations. In this study, uptake kinetics of polycyclic aromatic hydrocarbons (PAH) by a negligible depletive passive sampler exposed to a ground and non-ground field contaminated soil were tested. The measurements illustrate how freely dissolved pore water concentrations of contaminants can be affected by soil treatment. It took more than a month, and over a year to reach steady state in the passive sampler exposed to the ground and non-ground soil, respectively. The uptake rate seemed to be limited by desorption from the soil, even though the fiber only extracted 0.2% of the soil-sorbed PAH at maximum. If these observations are translated to the field situation, where contaminants are not homogeneously distributed and disappear by (bio)degradation or physical transport processes, it is unlikely that pore water concentrations are solely determined by a thermodynamic equilibrium. Hence, exposure of organisms in these soils cannot always be estimated by sorption studies and an equilibrium partitioning approach.     

Relevant variables to predict macrophyte communities in running waters

In both predictive theoretical and empirical models for aquatic plant communities in running waters, the development and competition are many times explained in terms of nutrients. Minerals necessary for growth are generally not assumed to be limiting, although they influence the important pH-value. At the same time it is known that factors such as oxygen-concentration, solar energy, salinity, dimension of the system and soil characteristics (including river sediments) influence the development of the community, and should be considered in modelling. Effects of water quantity and water quality on macrophytes are reviewed. These conditions are caused by processes in the landscape, characterised by a set of nested variables which explain the distribution of macrophyte species and communities. Relevant variables are described and grouped on three scales: regional, local and site conditions. Case studies with direct and indirect gradient analysis are presented. Statistical tests (stepwise regression with forward selection) reveal that each species distribution is explained by a characteristic set of relevant variables, ranging from soil type and dimension of the system, to nutrient and salinity concentration.