Raised Water Table Research Articles

Effects of dynamic redox zonation on the potential for natural attenuation of trichloroethylene at a fire-training-impacted aquifer

Hydrogeochemical and microbiological methods were used to characterize temporal changes along a transect of an aquifer contaminated by mixed hydrocarbon and solvent wastes from fire training activities at Wurtsmith Air Force Base (Oscoda, MI). Predominant terminal electron accepting processes (TEAPs) as measured by dissolved hydrogen indicated reoxygenation along the transect between October 1995 and October 1996, possibly because of recharge, fluctuations in water table elevation, or microbial activity. Microbiological analyses using universal and archaeal probes revealed a relationship between groundwater hydrogen concentration, TEAP, and predominant bacterial phylogeny. Specifically, a raised water table level and evidence of methanogenesis corresponded to an order of magnitude increase in archaeal 16S rRNA relative to when this zone was unsaturated.Spatial microbial and geochemical dynamics did not result in measurable differences in trichloroethylene (TCE) mineralization potential in vadose, capillary fringe, and saturated zone soils during a 500-day microcosm experiment using unprocessed contaminated soil and groundwater. Aerobic systems indicated that methane, but not toluene, may serve as a cosubstrate for TCE cometabolism. Anaerobic microcosms demonstrated evidence for methanogenesis, CO2 production and hydrogen consumption, yet dechlorination activity was only observed in a microcosm with sulfate-reduction as the dominant TEAP. Mass balance calculations indicated less than 5% mineralization, regardless of redox zone or degree of saturation, at maximum rates of 0.01–0.03 μmol/g soil·d. The general lack of dechlorination activity under laboratory conditions corroborates the limited evidence for natural dechlorination at this site, despite abundant electron donor material and accumulated organic acids from microbial degradation of alkylbenzenes. Thus, the short-term temporal dynamics in redox conditions is unlikely to have measurable effects on the long-term natural remediation potential of the aquifer.

Physical effects of site disturbance on peatlands

Forest harvesting on peatland sites during the frost-free season often creates water-filled ruts and transfers more humified layers of peat to the surface. Foresters have generally assumed that such disturbance has negative consequences related to proliferation of graminoid vegetation, disruption of surface drainage leading to raised water tables and, possibly, reduced site productivity. An experiment was established during 1996 near Cochrane, Ontario to examine the physical impacts of site disturbance on peatlands. Summer traffic by forest harvesting equipment was imposed at three intensities on a Black Spruce–Speckled Alder site type. The fractional area of surface disturbance increased with the amount of traffic, but disturbance effects on the thickness of the aerated zone, depth to the water table, and microtopography were not significant. However, the consistency of the effects produced by the most intense disturbance treatment suggests that it reduced average elevations and aerobic layer thicknesses, and increased water levels, by 2 to 6 cm. The hydrological effect of site disturbance in this study was small compared with the typical effect of forest canopy removal on water levels. Key words: Forest harvesting; peat; peatlands; site disturbance; hydrology

Effects of wetland excavation on avian communities in eastern Washington

Despite having an arid climate, the Columbia River Basin of eastern Washington is one of the most important areas for breeding, migrating, and wintering wetland birds in the Pacific Northwest. Extensive farmland irrigation near the O’Sullivan Reservoir and other areas has raised water tables, resulting in closed canopies of emergent vegetation in what are now permanent, shallow wetlands. During 1994–95, we found that avian communities on vegetation-filled wetlands excavated to create open water had greater mean densities of dabbling and diving ducks (Anatidae), shorebirds, American coots (Fulica americana), and terns (Sterna spp.) than untreated control wetlands. Densities of yellow-headed blackbirds (Xanthocephalus xanthocephalus) were greater on excavated wetlands, while the densities of red-winged blackbirds (Agelaius phoeniceus), Sora (Porzana carolina), and Virginia rails (Rallus limicola) were greater on unaltered sites. Densities of marsh wrens (Cistothorus palustris) and other passerines were similar among excavated and control wetlands. Zooplankton biomass was greater on altered wetlands and generally greater in older excavations. We suggest that managers may design constructed wetland basins to improve population management of diverse wetland bird species by creating an appropriate mix of wetland habitats at the landscape level.

The influence of raised water table levels on carbon dioxide and methane production in ditch-dissected peat grasslands in the Netherlands

The impact of hydrological manipulation on the mineralisation rates, measured as carbon dioxide and methane production rates, in the soil of the land-water transition zone of an unfertilised, Dutch peat grassland area was studied. The hydrological manipulation involved raising the ditch and groundwater levels by admitting nutrient-poor, Ca-rich groundwater in the trial area. An adjacent, fertilised, field served as a control. On an annual basis the CO 2 production rate was usually highest in the parcels, intermediate in the ditch banks and lowest in the ditch bottoms, ranging from 2496 to 598 kg C ha −1 year −1 in the wet field and from 2918 to 421 (kg C) ha −1 year −1 in the control field. The CH 4 production rate was negligible in the parcels, low in the ditch banks and substantial in the ditch bottoms, ranging from 0 to 1175 (kg C) ha −1 year −1 in the wet field and from 2 to 241 (kg C) ha −1 year −1 in the control field. The CO 2 production rate was significantly affected by pH, C:N ratio and by moisture content. It tended to be highest at pH 5.8, at a C:N ratio of 12, at a moisture content of 50% and at a temperature of 20°C. The CH 4 production rate was significantly affected by pH, organic matter content and C:N ratio. It tended to be highest at pH 6.7, at an organic matter content of > 40% and at a C:N ratio of 17. A temperature effect was not apparent. It was estimated that the COZ and CH, production rates of typical Dutch peat grasslands are 2824.3 and 6.1 (kg C) ha −1 year −1 when used for agriculture, but 2435.5 and 20.8 (kg C) ha −1 year −1 when rewetted with nutrient-poor, Ca-rich artesian water. Thus, rewetting, e.g. for nature conservation purposes, may cause the production of CO 2 to decrease by 14% but that of CH 4 to increase 3.4-fold. Circumstances in which these gases are emitted were discussed. This study indicates that hydrological manipulation of typical Dutch peat grassland areas in which fertilisation has ceased has profound effects on the production of CO 2 and CH 4 of these systems and may lead to increased emission of methane to the atmosphere.

A Program to Calculate Ground‐Water Mound Heights

AbstractMounding of the ground‐water table beneath recharge sources may be of concern where the raised water table approaches too closely to near‐surface facilities or features. Because of its high accuracy and wide range of applicability, the method of Hantush is probably the most widely used to calculate the time‐varying heights of ground‐water mounds on extensive and near‐horizontal saturated zones. Use of that method entails a number of inconveniences, however, including function evaluations and two‐dimensional interpolations between tabulated values, which must be performed iteratively. A FORTRAN computer program was developed to rapidly perform the necessary iterations and to evaluate some rather long and complex equations. These equations avoid the need for interpolation or other approximation procedures, and they provide accurate calculations for all conditions. Comparison of results from the computer program with results from approximation procedures indicates the areas and extents of the unreliability of the approximation procedures.

EXPERT SYSTEM-BASED COUPLING OF SOYGRO AND DRAINMOD

ABSTRACT A combined crop growth (SOYGRO 5.4) and water management (DRAINMOD 3.4) modeling system was developed using an expert system shell to coordinate input and output between the models. An iterative simulation procedure was used to keep the models intact and modular for inclusion of additional crop growth, pest, economic, and environmental impact models in the future. DRAINMOD 3.4 was modified to accept evapotranspiration and effective rooting depths from SOYGRO and allow feedback control. The feedback control system performed satisfactorily. SOYGRO 5.4 was enhanced to accept from DRAINMOD water movement due to upward flux from a water table. In addition, the model was modified to account for the crop stress due to oxygen deprivation caused by a water table extending into the rooting zone. Simulated soybean yields and root length densities were greatly affected by a raised water table and by climatic variations for the tested conditions. However, if the water table was maintained within 90 cm of the soil surface during the entire growing season, weather patterns had only a minor influence on root length densities and yield.

METAMORPHOSIS OF SOUTH PLATTE AND ARKANSAS RIVERS, EASTERN COLORADO

The Arkansas and South Platte Rivers in eastern Colorado have changed dramatically during the past 150 years. Earlier, they were relatively straight, wide, braided, intermittent streams. However, percolation of irrigation water into and through valley alluvium has raised water tables, and flow regulation has produced more uniform flow into the rivers. As a result new floodplains formed, and bank and floodplain vegetation became denser, as if a climatic change to more humid conditions had occurred. The rivers became narrower and more sinuous due to perennial stream flow, abstraction of sediment with irrigation water, and a decrease in discharge during drought. Three reaches of these rivers responded differently to the changes. The South Platte River and a reach of the Arkansas River narrowed and developed a single thalweg. In contrast, a reach of the Arkansas River at Bent's Old Fort began to meander as a result of an increase of suspended sediment load. All of the reaches are near a pattern threshold.

Effects of irrigation on mosquito populations and mosquito‐borne diseases in man, with particular reference to ricefield extension

The modification by man of his environment, particularly for large‐scale irrigation and ricefield extension, often results in increased incidence of mosquito‐borne disease in associated human populations. Habitat modification leads to changes in the species composition of mosquitoes and thus the variety of disease agents to which man is exposed. Increased acreage of water attracts birds which act as hosts of arboviruses while a raised water table leads to marginal marshy areas and humid peripheral vegetation. These two aspects of the environment favour extended breeding and survival respectively. Higher atmospheric humidity enhances mosquito survival and the transmission of disease. Associated urban resettlement encourages domestic mosquito species and effects the distribution and abundance of vertebrates which may act as hosts of disease agents.