Location: Water Quality and Ecology Research2007 Annual Report
1a. Objectives (from AD-416)
Develop and refine conservation technologies for implementation within agricultural watersheds that improve water quality and ecosystem function, contribute to TMDL and nutrient criteria development, and conserve natural resources by (1) evaluating farm and land management systems in Beasley Lake Conservation Effects Assessment Project (CEAP) watershed that are intended to reduce erosion, conserve soil, improve receiving water quality, and protect ecological resources; (2) determining the effectiveness of conservation practices for improving water and soil quality within the Yazoo River Basin to meet Total Maximum Daily Load criteria; (3) developing a database for Beasley Lake CEAP watershed that contains water, soil, ecological, and land management results from research conducted at field, farm, and watershed scales for assessment of conservation practices applicable to the Yazoo River Basin; (4) validating and quantifying uncertainties of model predictions for Beasley Lake CEAP watershed; (5) determining essential abiotic and biotic relationships required to effectively restore streams impaired by physical habitat degradation as defined by Total Maximum Daily Load criteria; and (6) assessing effects of conservation practices on off-site water quality for improved TMDL and nutrient criteria decision-making in agricultural watersheds impaired by non-point source pollution.
1b. Approach (from AD-416)
There is extensive literature on agricultural conservation practices aimed at protecting water quality and ecological integrity. Most of this work, however, is based on small-scale studies, and findings often are not easily scaled up due to complex interactions at the whole-farm, watershed, and landscape scales. Therefore, effects of widespread implementation of conservation measures (i.e. BMPs) have not been demonstrated. Continued work is needed on assessing individual innovative BMPs. Furthermore, realistic ecological restoration experiments require additional work at the prototype scale. To address these issues, natural resource (water, soil, and biological quality) responses to conventional and innovative conservation measures will be studied across a range of scales to provide support for the goals of the Clean Water Act of 1972 (and its amendments) and the Farm Security and Rural Investment Act of 2002. This research will focus on quantifying and assessing impacts associated with conservation practice implementations in an economically efficient manner to reduce nutrient, pesticide, and sediment loadings to the nation's surface waters necessary to produce sustainable ecosystems. This plan calls for a set of complementary experiments dealing with physical, chemical, and ecological processes at a range of scales from the laboratory bench to the watershed.
1. Stream restoration that works. Over $1 billion is expended annually on stream restoration, but few projects are monitored, and scientists disagree about the most effective approaches. Streams in watersheds treated with standard erosion control practices were monitored for ten years. Two stream reaches were treated with special features to restore habitat quality, while others were not. Habitat restoration produced major shifts in the types and sizes of fish that did not occur in the other stream sections. These findings show that even watershed-scale application of traditional erosion control measures is not adequate to restore stream ecological integrity, but projects that address specific habitat deficiencies can be effective. NP201, Problem area 5, product 2. 2. Sediment yields from cotton drastically reduced. Standard approaches for growing cotton on sloping lands produce rates of erosion and sediment yield several times greater than the 7t/ha tolerance value. A four-year study was conducted that included measuring water runoff and sediment yield from plots cultivated for cotton with conventional approaches and three innovative approaches involving combinations of narrow row spacing, no-till, and grass hedges. Sediment yield from no-till plots with grass hedges was reduced 94% relative to conventional tillage, and yielded an average of 0.2 t/ha of cotton more than conventional tilled plots. These results will be guide future research on field-sized areas and are potentially useful to extension personnel, action agencies involved in water quality planning, and to farmers. NP201, Problem area 4, product 5. 3. Index developed for targeting pollution hotspots. Often only a relatively small area is responsible for a disproportionate fraction of the fine sediment and associated chemical load leaving the watershed. Control efforts may be targeted at these hotspots if they can be identified. A sediment production index was developed using data from the Walnut Gulch Experimental Watershed at Tombstone, AZ, that showed that the greatest potential for sediment production was on the south facing slopes with steepness between 13% and 20%. This ability to identify primary sediment source areas in watersheds will improve the design of best management practices and provides direction for future research in sediment source identification. NP201, Problem area 4, product 4. 4. Channel sizing procedures refined. There is currently much debate among engineers and scientists about the appropriate way to determine the average width and depth of a stream channel that is being restored or otherwise modified. By applying the three most popular methods to four channels with widely varying hydrologic and geologic conditions it was shown that one of the three (the effective discharge method) is preferred for alluvial channels, particularly those in disturbed watersheds with flashy hydrology. These findings are useful to design engineers, but also contribute to the ongoing professional debate regarding selection of stream restoration approaches. NP201, Problem area 5, product 2. 5. Rotating crops encourages bacterial degradation of pesticides. Ideally, pesticides applied to crops would rapidly degrade after destroying pests, but factors that promote such ideal behavior are largely unknown. Instead, some portion of applied pesticide often ends up in aquatic ecosystems. Conditions (bacterial populations and carbon and nitrogen levels) were compared in soils supporting continuous cotton farming, continuous corn or a corn and cotton rotation. Conditions under continuous corn and a corn-cotton rotation were more favorable for accelerated degradation of atrazine, a widely used herbicide, than those under continuous cotton. This discovery has prompted initiation of new studies to ascertain the effect of accelerated atrazine degradation on weed control potential. NP201, Problem area 5, product 6. 6. Conditions in constructed wetlands used for treating agricultural runoff documented. Constructed wetlands may be used as a buffer between agricultural fields and nearby water sources. However, pollutants in runoff may harm organisms living in the treatment wetland. Live, caged mussels were placed in a constructed wetland receiving insecticide in an artificial runoff event. Although all of the mussels survived the event, long-term growth effects were observed. These findings will be used to refine plans for subsequent constructed wetland research. NP201, Problem area 6, product 6. 7. Pesticides may leave sediments and harm animals. Agricultural pesticides are often removed from streams, lakes and wetlands by becoming attached to sediments and settling to the bottom. The subsequent fate of these pesticides is often unknown. By mixing sediment sampled from a wide range of aquatic environments adjacent to cultivated fields with water and then exposing aquatic insects to this mixture for 28 days, it was shown that the compounds moved from the sediments into the animals’ tissues. These findings will guide future studies of the movements and fate of such liberated pesticides in aquatic ecosystems. NP201, Problem area 5, product 6. 8. Wetland plants release nutrients when they die back in winter. Degradation of water quality due to excessive nutrient pollution is of growing concern globally. Some control strategies involve using wetland plants to remove nutrients from surrounding waters. However, studies of a common wetland plant species exposed to elevated levels of nitrogen and phosphorus documented elevated releases of phosphorus during winter die off. This research will allow more informed decisions regarding nutrient best management practices. NP201, Problem area 6, product 2.
5. Significant Activities that Support Special Target Populations
Shields Jr, F.D., Knight, S.S., Cooper, C.M. 2007. Can warmwater streams be rehabilitated using watershed-scale standard erosion control measures alone? Environmental Management 40:62-79. DOI 10.1007/s00267-006-0191-0.