The influence of mussel beds on nutrients in the Western Wadden Sea and Eastern Scheldt estuaries

The uptake and release of materials by intertidal mussel beds were directly measured in two cultivated Dutch estuaries. Generally, chlorophylla, seston, and particulate organic carbon were taken up, while ammonium, orthophosphate, and silicate were released. The observed rates were higher than values computed from organismic observations and similar to those observed for intertidal oyster reefs in South Carolina. Specific estuarine material turnover rates varied from 1 week to 38 weeks when calculated with mussel bed fluxes. The fastest turnover rates were for chlorophylla and ammonium. These results support the idea that dense assemblages of bivalves are major components in the recycling of nutrients in estuaries.     

Eutrophication—The future marine coastal nuisance?

Increased inputs of nutrients to marine coastal areas over the last decades have created a basis for eutrophication of the waters surrounding Sweden. In combination with relatively low water exchange in these vertically stratified and almost non-tidal waters, local and regional effects of increased macro-algal biomass, and decreased oxygen concentrations in bottom water leading to mortalities of benthic animals and decreased fish catches have at times been observed. The effects were first noted in the Baltic, but are now obvious also in Swedish and Danish coastal areas in the Kattegat and the Belt Sea. Similar symptoms have recently also been recorded off the Danish North Sea coast. Other shallow coastal and shelf areas, where stratification occurs, can be regarded as potentially eutrophic risk areas.     

Spectra of the earthquake sequence February-March, 1981, in south-central Sweden

On February 13, 1981 a relatively strong earthquake occurred in the Lake Vänern region in south-central Sweden. The shock had a magnitude ofM_L = 3.3 and was followed within three weeks by three aftershocks, with magnitudes 0.5 ≤ M_L ≤ 1.0. The focal mechanism solution of the main shock indicates reverse faulting with a strike in the N-S or NE-SW direction and a nearly horizontal compressional stress. The aftershocks were too small to yield data for a full mechanism solution, but first motions of P-waves, recorded at two stations, are consistent for the aftershocks. Dynamic source parameters, derived from Pg- and Sg-wave spectra, show similar stress drops for the main shock (2 bar) and the aftershocks (1 bar), while the differences in seismic moment (1.5·10²⁰ resp. 4·10¹⁸dyne cm), fault length (0.7 resp. 0.2 km) and relative displacement (0.15 resp. 0.03 cm) are significant.     

The effects of annealing and concentration on the hysteresis properties of magnetite around the PSD-MD transition

Hysteresis parameters H_cr, H_c, J_rs, J_s, and their ratios H_cr/H_c, J_rs/J_s have been measured for a large number of accurately prepared grain size fractions of magnetite in the range between 5 and 150 μm. For several grain size fractions three different concentrations of magnetite are used: 100, 0.1, and 0.002 vol.%. Most of the measurements were repeated after annealing the specimens to 600°C. For some specimens in the pseudo-single (PSD) and multidomain (MD) range H_c and H_cr have been measured as functions of temperature. Plots of the results from H_c, H_cr/H_c and J_rs/J_s versus the grain size reveal curves with a convex and a concave part. Concentration and annealing affects the values of the hysteresis parameters, especially for grains coarser than 25 μm but the shape of the curves remains the same. The inflection point from convex to concave for all curves occurs at 25 μm and it appears to be independent of concentration and annealing. It is therefore proposed to define the transition from PSD to MD as the inflection point of these curves.     

Effects of dredging operations on estuarine benthic macrofauna

Dredging operations in a Swedish estuary reduced the number and diversity of benthic species. The larval recruitment in the vicinity of the dredged area was strongly affected. An overall increase in concentrations of Hg, Cd, Zn, Cu, Pb and Ni were recorded in benthic fauna. One and a half years after termination of dredging, the benthic community structure was nearly restored and the high concentrations of heavy metals had decreased considerably.     

Marine quality assessment by use of benthic species-abundance distributions: a proposed new protocol within the European Union Water Framework Directive

The aim of this study is to develop a new method for classification of marine benthic quality according to the European Union Water Framework Directive. Tolerance values to environmental disturbance were determined in an objective analysis for benthic species along the Swedish west coast by using 4676 samples from 257 stations. Based on a combination of the species tolerance values, abundance and diversity, a benthic quality index (BQI) was calculated for the assessment of environmental status at a particular station. The qualification of BQI was evaluated in relation to known spatial and temporal gradients of disturbance.     

Differences in flood hazard projections in Europe – their causes and consequences for decision making

This paper interprets differences in flood hazard projections over Europe and identifies likely sources of discrepancy. Further, it discusses potential implications of these differences for flood risk reduction and adaptation to climate change. The discrepancy in flood hazard projections raises caution, especially among decision makers in charge of water resources management, flood risk reduction, and climate change adaptation at regional to local scales. Because it is naïve to expect availability of trustworthy quantitative projections of future flood hazard, in order to reduce flood risk one should focus attention on mapping of current and future risks and vulnerability hotspots and improve the situation there. Although an intercomparison of flood hazard projections is done in this paper and differences are identified and interpreted, it does not seems possible to recommend which large-scale studies may be considered most credible in particular areas of Europe.

EDITOR D. Koutsoyiannis

ASSOCIATE EDITOR not assigned     

Alternative water management options to reduce vulnerability for climate change in the Netherlands

Urbanization, land subsidence and sea level rise will increase vulnerability of the urbanized low-lying areas in the western part of the Netherlands. In this article possibilities are explored to reduce vulnerability of these areas by implementing alternative water management options. Two main water management fields are distinguished, water supply and flood control. A four-component vulnerability framework is presented that includes threshold capacity, coping capacity, recovery capacity, and adaptive capacity. By using the vulnerability framework it is shown that current water supply and flood control strategies in the Netherlands focus on increasing threshold capacity by constructing higher and stronger dikes, improved water storage and delivery infrastructure. A complete vulnerability decreasing strategy requires measures that include all four capacities. Flood damage reduction, backup water supply systems and emergency plans are measures that can contribute to increasing coping capacity. Recovery capacity can be increased by multi-source water supply, insurance, or establishing disaster funds. Adaptive capacity can be developed by starting experiments with new modes of water supply and urbanization. Including all four components of the vulnerability framework enables better understanding of water and climate related vulnerability of urban areas and enables developing more complete water management strategies to reduce vulnerability.