Effect of hydrologic management on marsh surface sediment deposition in coastal Louisiana

High rates of coastal land loss in Louisiana have prompted efforts to maintain or restore coastal wetland habitats, and structural management of marsh hydrology is one of a number of approaches that has been adopted. The aim of this study was to determine the effect of hydrologic management measures on marsh-surface sediment deposition in the Mississippi deltaic plain. Four impoundments, ranging in size from 50 ha to 177 ha and similarly sized control sites were included in the study. At each site, marsh-surface sediment traps were collected approximately biweekly for 3.5 yr to measure changes in sediment deposition. There was no significant difference in sediment deposition between any of the impoundment and control sites during the premanagement period. The results show no significant difference in marsh-surface sediment deposition between management year 1992–1993 and management year 1994–1995, but management year 1993–1994 had significantly lower sediment deposition than either the first or the last year of the study. Management year 1992–1993 showed the highest sediment deposition when it was assessed across all basins, areas, and sites, and this high rate of deposition is accounted for by the impact of Hurricane Andrew. For all management years there were significant differences between impoundment and control sites, with control sites showing higher rates of marsh surface sediment deposition than impoundments. No clear pattern was identified concerning the influence of various types of hydrologic management on rates of sediment deposition. This reduction in sediment deposition indicated that the areas under management in this study are receiving insufficient inorganic sediment deposition to keep pace with sea-level rise.     

Carbon dioxide concentration and atmospheric flux in the Hudson River

We made direct measurements of the partial pressure of CO₂ (P_{CO 2}) in the tidal-freshwater portion of the Hudson River Estuary over a 3.5-yr period. At all times the Hudson was supersaturated in CO₂ with respect to the atmosphere. P_{CO 2} in surface water averaged 1125±403 (SD) μatm while the atmosphere averaged 416±68 μatm. Weekly samples at a single, mid-river station showed a pronounced and reproducible seasonal cycle with highest values (～2000 μatm) in mid-to-late summer, and lowest values (～500 μatm) generally in late winter. Samples taken along the length of the 190-km section of river showed a general decline in CO₂ from north to south. This decline was most pronounced in summer and very slight in spring. Diel and vertical variation were small relative to the standing stock of CO₂. Over six diel cycles, all taken during the algal growing season, the mean range was 300±114 μatm. CO₂ tended to increase slightly with depth, but the gradient was small, about 0.5 μmol m^?1, or an increase of 190 μatm from top to within 1 m of the bottom. For a large subset of the samples (n=452) we also calculated CO₂ from measurements of pH and total DIC. Calculated and measured values of CO₂ were in reasonably good agreement and a regression of calculated versus measured values had a slope of 0.85±0.04 and an r₂ of 0.60. Combining our measurements with recent experimental studies of gas exchange in the Hudson, we estimate that the Hudson releases CO₂ at a rate of 70–162 g C m^?2 yr^?1 from the river to the atmosphere.     

Filtration of Hudson River water by the zebra mussel (Dreissena polymorpha)

Zebra mussels (Dreissena polymorpha) graze on phytoplankton, and decreased phytoplankton concentrations have been associated with zebra mussels in lakes. It is not known, however, how the zebra mussel will affect phytoplankton in turbid systems such as rivers and the freshwater portions of estuaries. To determine whether zebra mussels can effectively remove phytoplankton in these turbid systems, and to determine what components of the suspended material are removed and at what rates, we conducted a series of grazing and size-selection experiments using ambient Hudson River water and its natural phytoplankton community. Zebra mussels removed both phytoplankton and total suspended weight (TSW) at comparable rates (～115 ml mussel^?1 h^?1). Variation in filtration rates were not correlated with TSW or chlorophylla (chla) concentration, and did not appear to depend on relative proportions of either component. Mussels removed particles with approximately equal efficiency in all particle size classes measured (0.4 μm to >40 μm). Zebra mussels appear to remove Hudson River phytoplankton effectively in the presence of suspended sediment and do so at rapid rates. Based on our measurements and unpublished estimates of the size of the population, zebra mussels filter a volume equivalent to the entire volume of the tidal freshwater portion of the Hudson River about every 2 d.     

Predicting spatio-temporal concentrations of PM<Subscript>2.5</Subscript> using land use and meteorological data in Yangtze River Delta,China

The prediction of PM_2.5 concentrations with high spatiotemporal resolution has been suggested as a potential method for data collection to assess the health effects of exposure. This work predicted the weekly average PM_2.5 concentrations in the Yangtze River Delta, China, by using a spatio-temporal model. Integrating land use data, including the areas of cultivated land, construction land, and forest land, and meteorological data, including precipitation, air pressure, relative humidity, temperature, and wind speed, we used the model to estimate the weekly average PM_2.5 concentrations. We validated the estimated effects by using the cross-validated R² and Root mean square error (RMSE); the results showed that the model performed well in capturing the spatiotemporal variability of PM_2.5 concentration, with a reasonably large R² of 0.86 and a small RMSE of 8.15 (μg/m³). In addition, the predicted values covered 94% of the observed data at the 95% confidence interval. This work provided a dataset of PM_2.5 concentration predictions with a spatiotemporal resolution of 3 km × week, which would contribute to accurately assessing the potential health effects of air pollution.     

Extreme storm surge modelling in the North Sea

This study shows that storm surge model performance in the North Sea is mostly unaffected by the application of temporal variations of surface drag due to changes in sea state provided the choice of a suitable constant Charnock parameter in the sea-state-independent case. Including essential meteorological features on smaller scales and minimising interpolation errors by increasing forcing data resolution are shown to be more important for the improvement of model performance particularly at the high tail of the probability distribution. This is found in a modelling study using WAQUA/DCSMv5 by evaluating the influence of a realistic air-sea momentum transfer parameterization and comparing it to the influence of changes in the spatial and temporal resolution of the applied forcing fields in an effort to support the improvement of impact and climate analysis studies. Particular attention is given to the representation of extreme water levels over the past decades based on the example of the Netherlands. For this, WAQUA/DCSMv5 is forced with ERA-Interim reanalysis data. Model results are obtained from a set of different forcing fields, which either (i) include a wave-state-dependent Charnock parameter or (ii) apply a constant Charnock parameter (α _{C h} =?0.032) tuned for young sea states in the North Sea, but differ in their spatial and/or temporal resolution. Increasing forcing field resolution from roughly 79 to 12 km through dynamically downscaling can reduce the modelled low bias, depending on coastal station, by up to 0.25 m for the modelled extreme water levels with a 1-year return period and between 0.1 m and 0.5 m for extreme surge heights.     

The effect of decrease in salinity on the dynamics of abundance and the cell size of <Emphasis Type="Italic">Corethron Hystrix</Emphasis> (Bacillariophyta) in laboratory culture

Effect of salinity on abundance dynamics and cell size of microalga Corethron hystrix Hensen (Bacillariophyta) were studied. C. hystrix can normally grow within a rather narrow salinity range between 32 and 28‰. The viable cells of this microalga change their morphological characters at a salinity of 24‰. This salinity level probably marks the beginning of cell division restriction, because the general number of cells by the end of the experiment was lower than in the control. The decrease of salinity to 16‰ caused pronounced irreversible morphological changes: cell height increased, chloroplasts compressed, protoplasm became granular, cytoplasm retracted, and spines shortened.