Search

Vegetative treatment areas (VTAs) are commonly being used as an alternative method of agricultural process wastewater treatment. However, it is also apparent that to completely prevent discharge of pollutants to the surrounding environment, settling of particulates and bound constituents from overland flow through VTAs is not sufficient. For effective remediation of dissolved agricultural pollutants, VTAs must infiltrate incoming wastewater. A simple water balance model for predicting VTA soil saturation and surface discharge in landscapes characterized by sloping terrain and a shallow restrictive layer is presented and discussed. The model accounts for the cumulative effect of successive rainfall events and wastewater input on soil moisture status and depth to water table. Nash–Sutcliffe efficiencies ranged from 0.65 to 0.81 for modeled and observed water table elevations after calibration of saturated hydraulic conductivity. Precipitation data from relatively low, average, and high annual rainfall years were used with soil, site, and contributing area data from an example VTA for simulations and comparisons. Model sensitivity to VTA width and contributing area (i.e. barnyard, feedlot, silage bunker, etc.) curve number was also investigated. Results of this analysis indicate that VTAs should be located on steeper slopes with deeper, more-permeable soils, which effectively lowers the shallow water table. In sloping landscapes (>2%), this model provides practitioners an easy-to-use VTA design and/or risk assessment tool that is more hydrological process-based than current methods. [Copyright &y& Elsevier]

Manure fertilization of soil significantly impacts the level of nitrous oxide (N2O) emission. Despite their short duration, periods of significant N2O emissions during soil thaws in winter and spring are an important portion of the total annual emissions from agricultural lands. The goal of this study was to understand the effects of tillage, moisture content and manure application on N2O emissions from agricultural soils at low temperatures. We summarize here both field and laboratory experiments. The field chamber study was focused on quantification of N2O flux from a field (Hudson clay loam: fine, illitic, mesic Glossaquic Hapludalf) growing corn (Zea mays L.) located in upstate New York. The field was moldboard plowed in the fall and then fertilized with liquid dairy manure. Intact soil cores were collected from the site both before and after field treatments for subsequent laboratory incubation that included freeze¿thaw cycles. The results demonstrated that tillage reduced N2O emissions in non-manured soils by 20¿30% in the 35¿50 days following the tillage event, attributed to improved aeration resulting from reduced bulk densities and pore space saturation. The maximal emission of 200¿gNm¿2 h¿1 was found at soil temperatures greater than 5°C and at WFPS between 40 and 70%. Subsequent application of liquid manure caused an increase in the total intensity of N2O emission. The emission of N2O from manure-amended soils was not limited to thawing events: emissions began at soil temperatures below 0°C and continued even after complete soil freezing. The tillage history prior to manure application was found to have a significant influence on N2O emission during freezing/thawing cycles following manure application. The subsequent total winter N2O emissions were greater from the field areas that were tilled earlier in the fall, particularly in the first few freeze¿thaw cycles, during which the maximum N2O fluxes occurred.Increasing soil saturation in a wet area formed during a spring thaw caused increasing N2O emissions up to a maximum of 200¿gNm¿2 h¿1 at ¿60¿70% saturation. However, emissions dropped dramatically with further increases in soil moisture, decreasing to 50¿gNm¿2 h¿1 in the most saturated areas (90% saturated). Overall, maximal emissions were found at temperatures greater than 5°C and at water filled porosities between 40 and 70%. [Copyright &y& Elsevier]

Planners advocate best management practices (BMPs) to reduce loss of sediment and nutrients in agricultural areas. However, the scientific community lacks tools that use readily available data to investigate the relationships between BMPs and their spatial locations and water quality. In rural, humid regions where runoff is associated with saturation-excess processes from variable source areas (VSAs), BMPs are potentially most effective when they are located in areas that produce the majority of the runoff. Thus, two critical elements necessary to predict the water quality impact of BMPs include correct identification of VSAs and accurate predictions of nutrient reduction due to particular BMPs. The objective of this research was to determine the effectiveness of BMPs using the Variable Source Loading Function (VSLF) model, which captures the spatial and temporal evolutions of VSAs in the landscape. Data from a long-term monitoring campaign on a 164-ha farm in the New York City source watersheds in the Catskills Mountains of New York state were used to evaluate the effectiveness of a range of BMPs. The data spanned an 11-year period over which a suite of BMPs, including a nutrient management plan, riparian buffers, filter strips and fencing, was installed to reduce phosphorus (P) loading. Despite its simplicity, VSLF predicted the spatial distribution of runoff producing areas well. Dissolved P reductions were simulated well by using calibrated reduction factors for various BMPs in the VSLF model. Total P losses decreased only after cattle crossings were installed in the creek. The results demonstrated that BMPs, when sited with respect to VSAs, reduce P loss from agricultural watersheds, providing useful information for targeted water quality management. [Copyright &y& Elsevier]