Comparative Analysis of Bioenergy Crop Impacts on Water Quality Using Static and Dynamic Land Use Change Modeling Approach

Researchers and federal and state agency officials have long been interested in evaluating location-specific impact of bioenergy energy crops on water quality for developing policy interventions. This modeling study examines long-term impact of giant miscanthus and switchgrass on water quality in the Cache River Watershed (CRW) in Arkansas, United States. The bioenergy crops were simulated on marginal lands using two variants of a Soil and Watershed Assessment Tool (SWAT) model. The first SWAT variant was developed using a static (single) land-use layer (regular-SWAT) and for the second, a dynamic land-use change feature was used with multiple land use layers (location-SWAT). Results indicated that the regular-SWAT predicted larger losses for sediment, total phosphorus and total nitrogen when compared to location-SWAT at the watershed outlet. The lower predicted losses from location-SWAT were attributed to its ability to vary marginal land area between 3% and 11% during the 20-year modeling period as opposed to the regular-SWAT that used a fixed percentage of marginal land area (8%) throughout the same period. Overall, this study demonstrates that environmental impacts of bioenergy crops were better assessed using the dynamic land-use representation approach, which would eliminate any unintended prediction bias in the model due to the use of a single land use layer.

On-Farm Irrigation Reservoirs in Two Arkansas Critical Groundwater Regions: A Comparative Inventory

Arkansas, which ranks third in the nation in terms of irrigated cropland, relies heavily on the Mississippi River Valley alluvial aquifer for irrigation. Two critical groundwater areas have been identified, with one in the Grand Prairie in central Arkansas and the other along the Cache River in northeast Arkansas. Thus, there has been a call to develop surface water resources for irrigation, and as a result, on-farm irrigation reservoirs have been constructed to capture and store surface water. To assess the current state of surface water development, a remote-sensing survey using National Agricultural Imagery Program data was conducted to provide an inventory of the locations and surface area of on-farm reservoirs in the two critical groundwater areas. Expert consultation and on-site inspections were used to confirm the remote sensing results. In the larger Grand Prairie area, where aquifer decline was recognized earlier, 632 reservoirs were identified for a total surface area of 9,300 ha. In the Cache River area, 143 reservoirs were identified for a total surface area of 2,000 ha. Average reservoir size in both regions was 14.6 ± 20 ha and ranged from 1 to 265 ha. Reservoir area comprised approximately 3% and 1% of the areas of potentially-irrigated cropland in Grand Prairie and Cache River regions, respectively. Keywords: Aquifer depletion, Irrigation, On-farm reservoirs, Surface water.

Stauroneis kingstonii sp. nov. (Bacillariophyta: Naviculales), a new diatom species from the Black Swamp, Arkansas, USA

A freshwater diatom species, Stauroneis kingstonii sp. nov., is described from cypress-tupelo wetlands of the Cache River, Arkansas, USA. Stauroneis kingstonii can be distinguished from other Stauroneis species by its narrow lanceolate shape, high length:breadth ratio, coarse areolae and striae, and lateral raphe bounded by a broad axial area and straight proximal raphe ends. The diatom is currently known only from the Cache River Watershed and found living benthic or epiphytic on submerged bald cypress and water tupelo tree bark, in slightly acidic, and fresh to slightly brackish waters.