Yazar "Isenhart, Thomas M." seçeneğine göre listele

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    High stage events and stream bank erosion on small grazed pasture stream reaches in the rathbun lake watershed, southern IOWA, USA
    (Health & Environment Assoc, 2019) Tüfekçioğlu, Mustafa; Isenhart, Thomas M.; Schultz, Richard C.
    Stream bank erosion in agricultural landscapes is a major pathway for non-point source sediment and phosphorus loading of receiving waters. Previous studies have shown direct and indirect effects of land use on stream bank erosion, and identified high erosion rates within riparian pastures. One potential impact of agricultural land-use on stream bank erosion is the alteration of stream stage characteristics, including an increase in frequency of high-stage events over short periods of time (forming flash hydrographs). The objective of this study was to assess the relationship between the number of high stream stages and corresponding stream bank soil erosion. The study was conducted in six grazed pasture stream reaches within the Rathbun Lake Watershed, a reservoir on the Chariton River located within the Southern Iowa Drift Plain. The erosion pin method was utilized to measure the change in stream bank erosion in response to differences in the number of high stream-stage events, which were monitored by pressure transducers. The measured seasonal bank erosion rates were correlated with the different stream stages data to assess their impact on stream bank erosion. Based on the different model assumptions, there were generally strong linear relationships between high stage and bank erosion. Approximately 75% of the variability in stream bank erosion rates was directly linked to the number of high stages/erosive stream flow depths. Conservation practices that reduce these erosion rates will be those that increase soil-water infiltration, reduce the frequency of high stream flow events and increase bank stability through perennial vegetation cover or reducing disturbance within the riparian zone.
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    Riparian land-use, stream morphology and streambank erosion within grazed pastures in southern lowa, USA: A catchment-wide perspective
    (MDPI, 2020) Tüfekçioğlu, Mustafa; Schultz, Richard C.; Isenhart, Thomas M.; Kovar, John L.; Russell, James R
    Factors influencing streambank erosion at the field/reach scale include both watershed andriparian land-uses, stream hydrology and channel morphology at the catchment scale. This studyassesses the relationship of riparian land-uses, stream morphologic characteristics and catchmentscale variables to streambank erosion within grazed riparian pastures in the Southern Iowa DriftPlain. Thirteen cooperating beef cow–calf farms and their catchments ranging from 2.5 to 12.9 km2in the Rathbun Lake watershed in South Central Iowa (USA) were chosen to conduct this study.Results suggest that the integration of stream morphologic characteristics and riparian land-uses atboth the reach and catchment scale are necessary to explain the current level of streambank erosionmeasured at the reach scale. Larger catchment size or catchments with more total channel lengthwere found to experience more bank erosion at the reach scale. A significant positive relationshipbetween percent sand-and-silt in the bank soil and bank erosion rates implies that bank soils with lesscohesiveness are more erodible. Catchment-scale assessments of the thirteen watersheds showedthat within the 50 m corridor on both sides of the stream, 46 to 61% of riparian area was devoted toagricultural use and only 6 to 11% was in ungrazed perennial vegetation, much of it enrolled in theUSDA Conservation Reserve Program. Overall, this and previous Rathbun watershed studies haveshown that intensive agricultural use of riparian areas over such extents of time and scale could bedirectly (in field scale) and/or indirectly (watershed scale) related to excessive amounts of streambankerosion (ranging from 8.6 to 38.3 cm/yr) to receiving streams and lakes leading to their impairmentand reduction in ecological services. Exclusion of cattle grazing in the riparian areas along bufferedstream lengths (2.1% of the total watershed area) of the Rathbun watershed would reduce this impact.This approach could also be applicable to other similar watersheds with extensive land-use undergrazed management.
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    Stocking rate and riparian vegetation effects on physical characteristics of riparian zones of midwestern pastures
    (Soc Range Managment, 2012) Bear, Douglas A.; Russell, James R.; Tüfekçioğlu, Mustafa; Isenhart, Thomas M.; Morrical, Daniel G.; Kovar, John L.
    Grazing at high stocking rates may increase sediment and nutrient loading of pasture streams through transport in precipitation runoff and bank erosion. A 3-yr (2007-2009) grazing study was conducted on 13 cool-season grass pastures to quantify effects of stocking rate and botanical composition on forage sward height, proportions of bare and manure-covered ground, and bank erosion adjacent to streams. Pastures ranged from 2 ha to 107 ha with stream reaches of 306 m to 1 778 m that drained watersheds of 253 ha to 5 660 ha. Bare and manure-covered ground were measured at a 15.2-m distance perpendicular to the stream at 30.5-m intervals at up to 30 locations on each side of the stream by the line transect method in May, July, September, and November of each year. At the midpoint of the 15.2-m line, forage sward height was measured with a falling plate meter (4.8 kg . m(-2)) and plant species identified. In November 2006, fiberglass pins (1.6 x 76.2 cm) were driven 73.7 cm into the stream bank at 1-m intervals from the streambed to the top of the bank along 10 equidistant transect locations on each side of the stream to measure bank erosion during spring, summer, and fall of each year. Increasing pasture stocking rates increased manure-covered ground and decreased sward height, but did not affect proportions of bare ground. The greatest, intermediate, and least net soil erosion rates occurred during the winter/early spring, late spring/early summer, and late summer/fall seasons. Stocking rates between measurements, expressed as cow-days . m(-1) stream, were not related to bank erosion. Increasing stocking rates per unit of stream length will increase manure cover and decrease forage sward height, but not affect proportions of bare ground or bank erosion rates adjacent to pasture streams. Therefore, managing stocking rates may reduce nutrient loading of pasture streams.