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Posts Tagged ‘WATERSHEDS’

Impacts of long-term soil and water conservation on agricultural productivity: the case of anjenie watershed, ethiopia






Abstract: Over the last three decades, many soil and water conservation projects have been implemented in various parts of eastern and southern Africa to control land degradation, and improve land productivity, especially under ‘catchment approach’ initiatives of the 1980s. In Ethiopia, many of these soil conservation projects were implemented following the severe drought of 1974. To capture long-term impacts of these initiatives, a study was conducted in Anjenie Watershed of Ethiopia, assessing fanya juu terraces and grass strips constructed in a pilot project in 1984, and which are still functional 25 years later. Data were collected from government records, field observations and questionnaire surveys administered to 60 farmers. Half of the respondent had terraced farms in the watershed former project area (with technology) and the rest were outside the terraced area (without technology). The crops assessed were teff, barley and maize. Cost–benefit analyses were used to determine the economic benefits with and without terraces, including gross and net profit values, returns on labour, water productivity and impacts on poverty. The results indicated that soil and water conservation had improved crop productivity. The average yields on terraced fields for teff, barley and maize were 0.95tha−1 (control 0.49), 1.86tha−1 (control 0.61), and 1.73tha−1 (control 0.77), respectively. The net benefit was significantly higher on terraced fields, recording US$ 20.9 (US$ −112 control) for teff, US$ 185 (US$ −41 control) for barley and US$ −34.5 (US$ −101 control)ha−1 yr−1 for maize, respectively. The returns on family labour were 2.33, 1.01 and 0.739US$man-day−1 for barley, teff and maize grown on terraced plots compared to US$ 0.44, 0.27 and 0.16man-day−1 for without, respectively. Using a discount rate of 10%, the average net present value (NPV) of barley production with terrace was found to be about US$ 1542 over a period of 50 years. In addition, the average financial internal rate of return (FIRR) was 301%. Other long-term impacts of terracing included farmers’ growing of maize on terraced fields as a result of water conservation. Currently, farmers also grow barley on terraced fields for two crop seasons per year unlike the experiences on farms without terraces. Household incomes and food security had improved and soil erosion drastically reduced. Many farmers had adopted terracing doubling the original area under the soil conservation pilot project and consequently improving environmental conservation in the watershed. [Copyright &y& Elsevier]


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Assessment of effects of best management practices on agricultural non-point source pollution in xiangxi river watershed

Abstract: Agricultural non-point source pollution (ANSP) is considered a major contributor to local water degradation in the Three Gorges Reservoir Area (TGRA) of China. The Xiangxi River, which is a first level anabranch of the Yangtze River, was selected for investigation of the effectiveness of selected best management measures (BMPs) to alleviate water pollution through analysis of several scenarios by SWAT (Soil and Water Assessment Tool). Specifically, changes in land use, fertilizer management and tillage management measures were simulated in SWAT because they were shown to be the primary factors influencing non-point source (NPS) pollution in the Xiangxi River watershed. The results revealed that when farmland was returned to forests, both runoff and NPS pollution loads showed a clear downward trend and the NPS pollution loads in the Xiangxi River watershed decreased by 20% or more when compared with the status of 2007. Furthermore, conservation tillage and contour farming can help reduce runoff by 15.99% and 9.16%, total nitrogen (TN) by 8.99% and 8%, and total phosphorus (TP) by 7% and 5%, respectively. Conservation tillage has a greater effect in controlling the losses of soil, water and nutrients than contour farming. Based on the fertilizer conditions of 2007, changing the fertilizer application resulted in little change in local runoff; however, for NPS pollution loads, various forms of nitrogen (N) and phosphorus (P) pollution loads were directly proportional to the amount of chemical fertilizer applied. Overall, the results of this study can facilitate development of environmental friendly land use plans by local managers, and enable farmers to manage agriculture and fertilizer more efficiently, ultimately achieve the goal of reduce water pollution. [Copyright &y& Elsevier]

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Road-deposited sediments in an urban environment: a first look at sequentially extracted element loads in grain size fractions

Abstract: Sediments stored in urban drainage basins are important environmental archives for assessing contamination. Few studies have examined the geochemical fractionation of metals in individual grain size classes of solid environmental media. This is the first study of road sediments to quantify the mass loading of Al, Cu, Pb, and Zn in individual grain size classes (<63μm to 1000–2000μm) and partition contributions amongst four sequentially extracted fractions (acid extractable, reducible, oxidizable, and residual). The optimized BCR sequential extraction procedure was applied to road sediments from Palolo Valley, Oahu, Hawaii. Road sediments from this non-industrialized drainage basin exhibited significant enrichment in Cu, Pb, and Zn. Metal mass loading results indicate that the <63μm grain size class dominated almost all fraction loads for a given element. The residual fraction dominated the Al loading for this geogenic element. The reducible fraction, associated with Fe and Mn oxides, was the most important component for Cu, Pb, and Zn loading. These results have direct implications for environmental planners charged with reducing sediment-associated contaminant transport in urbanized drainage basins. [Copyright &y& Elsevier]

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On calibration data selection: the case of stormwater quality regression models

Abstract: A stormwater quality model should be calibrated and verified against available data before it can be confidently used. This paper mainly examines two questions: how do the size and selection of calibration data sets affect model performances and how should the calibration data sets be selected. Regression models are used to simulate stormwater quality (TSS and COD) with variables characterizing rainfall and flow characteristics. Based on large databases of three catchments in France, several models are calibrated and verified with different data subsets. It is confirmed that the selection of calibration data sets leads to significant uncertainty in model performance. The information content in the calibration data sets is also important in addition to their size. Generally model performances can be improved by using a large size of calibration data sets and by selecting calibration data that are representative of all data. Three methods endeavoring to improve model performance by selecting calibration data either according to model outputs or model inputs are developed based on the principle of choosing calibration data that are representative of the whole data set. The effectiveness of the three selection methods is demonstrated by their application on databases of the three catchments. Model performances can be generally improved by selection methods. The selection methods based on model inputs that consider multi-dimension information perform better than the method with one-dimension information consideration. [Copyright &y& Elsevier]

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The relative importance of land use and climatic change in alpine catchments

Carbon storage and catchment hydrology are influenced both by land use changes and climatic changes, but there are few studies addressing both responses under both driving forces. We investigated the relative importance of climate change vs. land use change for four Alpine catchments using the LPJ-GUESS model. Two scenarios of grassland management were calibrated based on the more detailed model PROGRASS. The simulations until 2100 show that only reforestation could lead to an increase of carbon storage under climatic change, whereby a cessation of carbon accumulation occurred in all catchments after 2050. The initial increase in carbon storage was attributable mainly to forest re-growth on abandoned land, whereas the stagnation and decline in the second half of the century was mainly driven by climate change. If land was used more intensively, i.e. as grassland, litter input to the soil decreased due to harvesting, resulting in a decline of soil carbon storage (1.2−2.9 kg C m) that was larger than the climate-induced change (0.8-1.4 kg C m). Land use change influenced transpiration both directly and in interaction with climate change. The response of forested catchments diverged with climatic change (11-40 mm increase in AET), reflecting the differences in forest age, topography and water holding capacity within and between catchments. For grass-dominated catchments, however, transpiration responded in a similar manner to climate change (light management: 23-32 mm AET decrease, heavy management: 29-44 mm AET decrease), likely because grassroots are concentrated in the uppermost soil layers. Both the water and the carbon cycle were more strongly influenced by land use compared to climatic changes, as land use had not only a direct effect on carbon storage and transpiration, but also an indirect effect by modifying the climate change response of transpiration and carbon flux in the catchments. For the carbon cycle, climate change led to a cessation of the catchment response (sink/source strength is limited), whereas for the water cycle, the effect of land use change remains evident throughout the simulation period (changes in evapotranspiration do not attenuate). Thus we conclude that management will have a large potential to influence the carbon and water cycle, which needs to be considered in management planning as well as in climate and hydrological modelling. [ABSTRACT FROM AUTHOR]

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