E. de Deckere

Interplay between biology and sedimentology in a mudflat (Biezelingse Ham, Westerschelde, The Netherlands)

Abstract The aim of this research was to investigate the importance of biological processes on the sediment characteristics and the morphology of a mudflat in the Westerschelde (The Netherlands). For this purpose, a transect in the Biezelingse Ham mudflat was sampled on a monthly basis. In spring, the muddy part of the mudflat was dominated by a biofilm of microphytobenthos that altered the morphology of the mudflat and resulted in a two-fold increase in sediment stability. The biofilm also bound fine-grained sediment that was deposited. From June onwards, wind generated waves dominated the conditions at the mudflat which resulted in the disappearance of diatom biofilms, and caused a gradual erosion of the mudflat. During this period, meio- and macrofauna densities increased from which it was concluded that the hydrodynamic forces did not have a big impact on these communities. Spatial variations in sediment characteristics, morphology and biology were observed between stations 1 and 2 on the one hand and station 3 on the other. This resulted in different responses to the changing conditions on the mudflat. In general, the results from this field study indicate that sedimentology and biology, interact in a complex manner with the hydrodynamic regime both on a temporal as well as on a spatial scale.

Toxicity assessment of sediments from three European river basins using a sediment contact test battery

The toxicity of four polluted sediments and their corresponding reference sediments from three European river basins were investigated using a battery of six sediment contact tests representing three different trophic levels. The tests included were chronic tests with the oligochaete Lumbriculus variegatus, the nematode Caenorhabditis elegans and the mudsnail Potamopyrgus antipodarum, a sub-chronic test with the midge Chironomus riparius, an early life stage test with the zebra fish Danio rerio, and an acute test with the luminescent bacterium Vibrio fischeri. The endpoints, namely survival, growth, reproduction, embryo development and light inhibition, differed between tests. The measured effects were compared to sediment contamination translated into toxic units (TU) on the basis of acute toxicity to Daphnia magna and Pimephales promelas, and multi-substance Potentially Affected Fractions of species (msPAF) as an estimate for expected community effects. The test battery could clearly detect toxicity of the polluted sediments with test-specific responses to the different sediments. The msPAF and TU-based toxicity estimations confirmed the results of the biotests by predicting a higher toxic risk for the polluted sediments compared to the corresponding reference sediments, but partly having a different emphasis from the biotests. The results demonstrate differences in the sensitivities of species and emphasize the need for data on multiple species, when estimating the effects of sediment pollution on the benthic community.

Distribution of extracellular carbohydrates in three intertidal mudflats in Western Europe

In this study, the spatial distribution of two operationally defined extracellular carbohydrate fractions (water- and EDTA-extractable carbohydrates) were examined in three intertidal mudflats in Western Europe (Dollard, the Netherlands; Marennes, France; Humber, UK). The three mudflats were sampled along cross-shore transects and sediment cores were sliced to a depth of 5 cm. In these mudflats, diatoms were the dominant component of the microphytobenthos. Carbohydrate content showed little variation with depth, but it varied along transects within each mudflat. Carbohydrate contents were also significantly different between the mudflats, and the carbohydrate contents of the stations within a mudflat grouped together resulting in separate clusters. This was also observed when the Marennes mudflat was investigated on a temporal scale. These results suggest that processes that act on the scale of whole mudflats determine the variations in extracellular carbohydrate contents. In the surface 0.5 cm of the sediment, water-extractable carbohydrates showed a correlation with both chlorophyll a content and median grain size, while EDTA-extractable carbohydrates were only correlated with median grain size. Incubation experiments also showed the importance of microphytobenthos as a source of extracellular carbohydrate, especially when subjected to the light. Analyses of the monosaccharide distribution of the carbohydrate fractions revealed that the carbohydrate composition was largely similar between the areas investigated. Structurally, the carbohydrates found in these sediments seem to represent a biorefractory part of the freshly produced carbohydrates that remained after rapid degradation of the more labile component [KEYWORDS: Extracellular carbohydrate; Microphytobenthos; Grain size distribution; Tidal flats; Monosaccharide distribution; Marennes-Oleron Bay; Ems-Dollard estuary; Humber estuary]

Characterizing field sediments from three European river basins with special emphasis on endocrine effects - A recommendation for Potamopyrgus antipodarum as test organism

The assessment of endocrine disrupting potentials of field sediments has until now been mostly limited to classical chemical analysis, in vitro assays and in vivo bioassays performed with vertebrates. There is an urgent need for easy, cheap and reproducible invertebrate tests which may be applied in certain monitoring activities. Since the mudsnail Potamopyrgus antipodarum is known to be tolerant to natural stressors, but also sensitive to endocrine disrupting chemicals, it is very likely that this organism could be suitable for the assessment of endocrine effects of e.g. field sediments. Within this study the endocrine potential of sediments in three European river basins was assessed. The yeast estrogen screen (YES) and a sediment contact test with P. antipodarum were performed. Furthermore, analyses of physico-chemical properties and concentrations of heavy metals, PAHs, organotins, natural steroids and alkylphenols were done. In the sediment contact test, the reproduction of the snail was promoted by a part of the sediments. This phenomenon could not be explained by their physico-chemical properties. However, at some of those sites a high estrogenic activity was detected in the YES, leading to the assumption that endocrine disrupting compounds could be responsible for those effects. This assumption could be confirmed to some extent with partially high concentrations of xeno-estrogens (e.g. nonylphenol) at the certain sites. Our study demonstrates the applicability of the test with P. antipodarum for a variety of sediments and once again points out the need of suitable in vivo biotests for the risk assessment of field sediments.

Assessing the impact of chemical pollution on benthic invertebrates from three different European rivers using a weight-of-evidence approach.

The aim of this study was to combine different lines of evidence on the impact of chemical pollution on benthic invertebrate communities in three European river basins (Elbe, Scheldt, and Llobregat). The study integrates chemical analyses, a battery of different sediment toxicity tests, and field data from soft-sediment meio- and macrobenthic fauna within a sediment-quality triad in which chironomids, oligochaetes, and nematodes are identified on the species level. The use of TU (toxic units) and msPAF (multi-substance potentially affected fraction) in an approach assessing the chemical impact as well as the integration of sediment toxicity tests with bacteria (Vibrio fischeri), benthic invertebrates (Caenorhabditis elegans, Potamopyrgus antipodarum, Lumbriculus variegatus, Chironomus riparius), and fish embryos (Danio rerio), together with univariate and non-parametric multivariate statistical analyses of the biological data revealed significant differences between unpolluted and polluted sites in all three river basins. To combine the different results obtained in the sediment-quality triad, a scoring system was successfully developed based on a simple algorithm. This system provides an easily understandable scheme for non-experts among decision makers and water managers.

Arsenic in drinking water wells on the Bolivian high plain: field monitoring and effect of salinity on removal efficiency of iron-oxides-containing filters.

In the rural areas around Oruro (Bolivia), untreated groundwater is used directly as drinking water. This research aimed to evaluate the general drinking water quality, with focus on arsenic (As) concentrations, based on analysis of 67 samples from about 16 communities of the Oruro district. Subsequently a filter using Iron Oxide Coated Sand (IOCS) and a filter using a Composite Iron Matrix (CIM) were tested for their arsenic removal capacity using synthetic water mimicking real groundwater. Heavy metal concentrations in the sampled drinking water barely exceeded WHO guidelines. Arsenic concentrations reached values up to 964 μ g L−1 and exceeded the current WHO provisional guideline value of 10 μ g L−1 in more than 50% of the sampled wells. The WHO guideline of 250 mg L−1 for chloride and sulphate was also exceeded in more than a third of the samples, indicating high salinity in the drinking waters. Synthetic drinking water could be treated effectively by the IOCS- and CIM-based filters reducing As to concentrations lower than 10 μ g L−1. High levels of chloride and sulphate did not influence As removal efficiency. However, phosphate concentrations in the range from 4 to 24 mg L−1 drastically decreased removal efficiency of the IOCS-based filter but had no effects on removal efficiency of the CIM-based filter. Results of this study can be used as a base for further testing and practical implementation of drinking water purification in the Oruro region.

The seasonal dynamics of benthic (micro) organisms and extracellular carbohydrates in an Intertidal mudflat and their effect on the concentration of suspended sediment

The Ems-Dollard estuary, situated in the north of the Netherlands near to the German border, is covered for a large part by intertidal flats. Currents and wind- induced waves exert a shear stress on these flats, resulting in resuspension of the sediment. Fluctuations of the suspended sediment concentration in the Dollard are strongly affected by erosion due to wind-induced waves and by settling during calm weather conditions. However it is believed that benthic processes influence the amount of sediment that can be resuspended from the intertidal flats. Therefore suspended sediment concentration above the Heringsplaat, an intertidal flat in the Ems-Dollard estuary, was measured during two seasons and related to the dominant benthic biological features. The benthos and the abiotic sediment characteristics were monitored from 1995 till 1997, at two stations. At both stations a peak of chlorophyll-α concentration was found in spring, caused by a diatom bloom. Meiobenthos was dominated by nematodes, macrobenthos by the polychaete Marenzelleria viridis and the amphipod Corophium volutator. The seasonal pattern was studied most intensively during 1996. Monthly sampling was done on the Heringsplaat. The flat was covered with ice during March. This period was followed by a clear water phase during spring and an increase of the silt content at the edge of the Heringsplaat. During this period an increase was found of chlorophyll-α concentration and of the carbohydrate concentration. This carbohydrate secretion stabilized the sediment. This finally resulted in a stable diatom mat at the end of the spring and a two-centimeter thick layer of silt. During June a high increase of nematodes and Corophium volutator was found. Nematode density was about 5000 ind per 10 cm 2 during June and July and Corophium density reached almost 100.000 per m 2 . The diatom population decreased rapidly during June. It is assumed that this is caused by high grazing pressure of the nematodes and of Corophium. The reduced diatom concentration and the increased bioturbation activity of Corophium resulted in reduced sediment stability. The silt content of the sediment surface at the edge of the Heringsplaat reduced and at the same time the turbidity in the water column increased.

Mathematical Models of Water and Solute Transport in Soil

Improved understanding of water flow and solute transport through the unsaturated zone is important for the sustainable management of soils. As soils are complex and heterogeneous systems, quantification of the transport processes is difficult. More knowledge on the relationship between solute transport process, soil structure, hydrologic initial and boundary conditions, and observation scale is needed here.Modeling unsaturated flow and transport with mathematical or numerical methods is an important tool for predicting the infiltration and redistribution of soil water and the transport of solutes in the unsaturated zone. Flow and transport models are commonly used to support the decision making process in agricultural management, environmental impact assessment, toxic waste control, remediation design, and subsurface cleanup monitoring. The movement of contaminants through porou media describs by the combination of advection, diffusion-dispersion and chemical retardation. The most common model that describes solute transport by convection and dispersion is the convection-dispersion equation (CDE). This equation describes the change in concentration at any point along the flow path as a function of time. This paper is mainly dedicated to a discussion of basic processes for modelling of water flow and contaminant transport in saturated and unsaturated soils. After a brief description of the classical approach for simulating water flow and solute transport in porous media, issues related to water and solute trasport equation in soil.