The response of salt marsh vegetation to tidal reduction caused by the Oosterschelde storm-surge barrier

In 1986 a sluice gate barrier was completed in the mouth of the Oosterschelde estuary. The barrier has been partially or completely closed during 1986 and the first months of 1987. Consequently the high tides were reduced to such a level that the salt marshes were scarcely flooded. Since April 1987 the barrier has been closed on average during two out of 706 high tides a year. Although the barrier allows tidal exchange the tidal flow has been restricted as a result of the reduced width of the mouth of the estuary. This restriction of the tidal flow caused a 26 cm decrease of mean high water in the eastern part of the estuary. As a result the inundation frequencies of the salt marshes decreased.The response of salt-marsh vegetation to this tidal reduction was analyzed using annual records (1982 till 1990) of species composition in 57 permanent plots in two marshes at the southern shore of the estuary. Analysis of the response of individual species to marsh elevation in the pre and the post-barrier situation revealed that most species moved down the marsh elevation gradient. The first axis of an ordination (DCA-1) was significantly negatively related to inundation frequency. Between 1984 and 1990 all plots were displaced towards a significantly higher ordination score, indicating a trend towards a species composition from higher up the marsh. The position of most plots along DCA-1 remained stable until 1985 and started to increase in 1986 or 1987. The vegetation in plots dominated either by Halimione portulacoides or by Spartina anglica, started to change in 1985. This premature change was attributed to frost damage in January 1985. The initially high rate of change along DCA-1 decreased in 1989 and 1990. This would suggest that the vegetation re-equilibrated with the newly established tidal conditions. Further analysis revealed no significant difference in the relation between inundation frequency and sample score along DCA-1 between 1984 and 1990. This corroborates the view that species composition had re-equilibrated with the tidal conditions. Along DCA-2 the samples were displaced towards a significantly higher score as well. The change was attributed to an increase of the perennial Halimione and the annual Suaeda maritima. The annual Atriplex hastata displayed an increase from 1986 till 1988, but strongly declined in 1990. The transient response of this annual was described by DCA-3.During the pre-barrier phase several attempts had been made to predict the vegetation response to tidal reduction. We developed a multivariate model (CCA) with inundation frequency as a constraining factor to describe the relation between inundation frequency and species composition in the pre-barrier phase in 1984. Next we used this model to predict the score of the samples along CCA-1 in the post-barrier phase from the inundation frequencies in 1990. The actual ordination score in 1990 was calculated from the observed species composition. The predicted ordination scores did not differ significantly from the observed ones. In retrospect it is concluded that the response of the vegetation to the reduction of the tides, as far as the fraction of species composition which is related to inundation frequency is concerned, could have been predicted by our model.

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Domestic Water Use in the United States: A Life-Cycle Approach

Water and energy are two primary natural resources used by building occupants. A life-cycle assessment (LCA) is performed for water-consuming plumbing fixtures and water-consuming appliances during their operational life for four different building types. Within the cycle studied, water is extracted from the natural environment, subjected to water treatment, pumped to buildings for use, collected for wastewater treatment, and discharged back to the natural environment. Specifically, the impacts of water use, electricity and natural gas generation, energy consumption (for water and wastewater treatment, and for water heating), and the manufacture of water and wastewater treatment chemicals are evaluated both quantitatively and qualitatively on a generalized national level in the United States of America.
It is concluded that water use and consumption within buildings have a much larger impact on resource consumption than the water and wastewater treatment stages of the life cycle. To study this more specifically, the resource consumption of four different building types-an apartment building, a college dormitory, a motel, and an office building-is considered. Of these four building types, the apartment has the highest energy consumption (for water and wastewater treatment, and for water heating) per volume of water used, whereas the office building has the lowest. Similarly, the calculated LCA score for the apartment building is typically greater than those of the other three building types.     

Daily Fish and Zooplankton Abundances in the Littoral Zone of Lake Texoma,Oklahoma-Texas,in Relation to Abiotic Variables

Many studies have shown the effects of yearly or monthly environmental conditions on the structure of fish and zooplankton communities. Environmental conditions can also vary greatly on much shorter time scales. We tested the effects of abiotic conditions on the daily abundance of fish and zooplankton in the littoral zone of Lake Texoma, Oklahoma-Texas. After date was removed statistically from the analysis, no environmental variables were particularly important in determining the daily abundance of zooplankton, whereas, numbers of fish in the littoral zone were related to changes in wind velocity and wave height. Regressions of daily fish abundance against wave height showed that the response differed among species and among life-history intervals within species. Numbers of juvenile Dorosoma petenense, Notropis atherinoides, and Morone chrysops were positively correlated with wave height, whereas juvenile Menidia beryllina were negatively correlated with wave height. We suggest that changes in the abundance of particular species may be associated with (1) avoidance of inshore areas to escape possible physical damage by wave induced turbulence, (2) attraction to inshore areas to feed on prey organisms suspended in the water column by wave induced turbulence, and (3) avoidance of inshore areas to escape high predator abundance and increased possibility of being eaten due to turbulence.