Identification of phosphorus index improvements through model comparisons across topographic regions in a small agricultural watershed in Vermont

Many U.S. states require farmers to evaluate the risk of P loss from farm fields using P site assessment tools, such as the Phosphorus Index (P-Index). The simplicity of the P-Index allows for users with various backgrounds to utilize the tool; however, the P-Index may be limited in its ability to reliably predict P losses across variable farm terrain, for instance where saturation-excess runoff generation dominates. The objective of this study was to identify potential improvements that could be made to the Vermont P-Index (VT P-Index) by comparing VT P-Index predictions of P loss with those of a model that considers topographic controls on P transport. Scenarios with varying P management strategies were developed and modeled for corn (Zea mays L.) silage production fields in a small agricultural watershed (360 ha) located in Vermont using both the VT P-Index and a modified version of the Soil and Water Assessment Tool (SWAT). Modeled outputs from both the VT P-Index and SWAT were aggregated based on topographic index (TI) class and compared for the directional agreement of P risk assessments and relative annual average dissolved and particulate P losses. The P-Index nutrient management recommendations gave higher P loss risk ratings than SWAT for 94% of the 120 unique scenario combinations simulated. Results from this study suggest that the VT P-Index could improve its ability to support farm nutrient management planning by incorporating topographic controls on runoff production into its estimation of P transport

Evaluation of CFSR, TMPA 3B42 and ground-based rainfall data as input for hydrological models, in data-scarce regions: The upper Blue Nile Basin, Ethiopia

Accurate prediction of hydrological models requires accurate spatial and temporal distribution of rainfall. In developing countries, the network of observation stations for rainfall is sparse and unevenly distributed. Satellite-based products have the potential to overcome this shortcoming. The objective of this study is to compare the advantages and the limitation of commonly used high-resolution satellite rainfall products (Climate Forecast System Reanalysis (CFSR) and Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA) 3B42 version 7) as input to hydrological models as compared to sparsely and densely populated network of rain gauges. We used two (semi-distributed) hydrological models that performed well in the Ethiopian highlands: Hydrologiska Byråns Vattenbalansavdelning (HBV) and Parameter Efficient Distributed (PED). The rainfall products were tested in two watersheds: Gilgel Abay with a relatively dense network of rain gauge stations and Main Beles with a relatively scarce network, both are located in the Upper Blue Nile Basin. The results indicated that TMPA 3B42 was not be able to capture the gauged rainfall temporal variation in both watersheds and was not tested further. CFSR over predicted the rainfall pattern slightly. Both the gauged and the CFSR reanalysis data were able to reproduce the streamflow well for both models and both watershed when calibrated separately to the discharge data. Using the calibrated model parameters of gauged rainfall dataset together with the CFSR rainfall, the stream discharge for the Gilgel Abay was reproduced well but the discharge of the Main Beles was captured poorly partly because of the poor accuracy of the gauged rainfall dataset with none of the rainfall stations located inside the watershed. HBV model performed slightly better than the PED model, but the parameter values of the PED could be identified with the features of the landscape

Simulating hydrological and nonpoint source pollution processes in a karst watershed: A variable source area hydrology model evaluation

AbstractAn ecohydrological watershed model can be used to develop an efficient watershed management plan for improving water quality. However, karst geology poses unique challenges in accurately simulating management impacts to both surface and groundwater hydrology. Two versions of the Soil and Water Assessment Tool (SWAT), Regular-SWAT and Topo-SWAT (which incorporates variable source area hydrology), were assessed for their robustness in simulating hydrology of the karstic Spring Creek watershed of Centre County, Pennsylvania, USA. Appropriate representations of surface water – groundwater interactions and of spring recharge – discharge areas were critical for simulating this karst watershed. Both Regular-SWAT and Topo-SWAT described the watershed discharge adequately with daily Nash-Sutcliffe efficiencies (NSE) ranging from 0.77 to 0.79 for calibration and 0.68–0.73 for validation, respectively. Because Topo-SWAT more accurately represented measured daily streamflow, with statistically significant improvement of NSE over Regular-SWAT during validation (p-value=0.05) and, unlike Regular-SWAT, had the capability of spatially mapping recharge/infiltration and runoff generation areas within the watershed, Topo-SWAT was selected to predict nutrient and sediment loads. Total watershed load estimates (518t nitrogen/year, 45t phosphorus/year, and 13600t sediment/year) were within 10% of observed values (−9.2% percent bias for nitrogen, 6.6% for phosphorous, and 5.4% for sediment). Nutrient distributions among transport pathways, such as leaching and overland flow, corresponded with observed values. This study demonstrates that Topo-SWAT can be a valuable tool in future studies of agricultural land management change in karst regions

Economics and Policy Context For the Biological Management of Soil Fertility (BMSF) in Ethiopia

Many developing countries implement programs and policies to increase or maintain soil fertility, with the objectives of increased crop yields and decreased poverty. However, few countries give emphasis to the biological management of soil fertility (BMSF) compared to more traditional approaches. Ethiopia emphasizes the use synthetic fertilizers to increase food security and reduce poverty, with little attention to BMSF. This paper examines the long term fertilizer consumption and agricultural productivity response trend and discusses the potential for BMSF to promote agricultural productivity and reduce poverty in Ethiopia. The paper also discusses the Economics and Policy Context for BMSF for the well functioning of the ecosystem. To do so, we used long-term fertilizer consumption and crop productivity national data as well as data from several studies carried in Amhara Region near Bahir Dar. The methods include analysis of soil chemical properties for various land uses (crops, pastures, and forest) household surveys, focus group discussions and a review of pertinent literature. Aggregate data indicate increasing fertilizer use but stagnant crop yields. The lowest carbon and nitrogen levels in soil are for crop land, followed by grassland and forest. Continuous cultivation, removing crop residue and using cow dung for cooking rather than fertilization probably are responsible for the low values on cropland. At 1.49 percent threshold of carbon content, crop yields cannot be optimized through use of synthetic fertilizer alone. The household survey and focus group discussions suggest that farmers use of synthetic fertilizer to be minimal due to many and complicated factors. Surveys also indicated that all productive land in surveyed watershed was under cultivation, limiting the potential to increase crop production through expanding cultivated area. Thus, technologies and practices to increase yield per ha are needed. BMSF should be investigated further for its potential to increase agricultural production in Ethiopia, to reduce poverty and to achieve food security

I4. Irrigation Area Suitability Mapping by Multi-criteria Evaluation Technique for the Case of Lake Tana Basin, Upper Blue Nile, Ethiopia

The study was carried out in the Lake Tana Basin, the upper portion of the Blue Nile Basin in Ethiopia. It has a total catchment area of around 15,000 km2, of which the lake covers approximately 3,060 km2 at an average altitude of 1786 m amsl. Although the lake has developmental potential, until recently, there has been only one water resource development situated at the mouth of the lake to control the outflow for harnessing hydroelectricity down stream on the Blue Nile River. Besides hydroelectric power, expansion of surface irrigation is of great interest to the basin farmers whose livelihoods are heavily dependent on cereal and other rainfed crop production. Therefore, in this study, the suitability of surface irrigation within the lake basin was evaluated by employing a GIS-based Multi Criteria Evaluation (MCE) analysis of available spatial data. The main objective was to identify suitable medium scale (between 200 and 3000ha) and large scale (greater than 3000ha) irrigation areas in the basin by considering factors, such as meteorological information (temperature, humidity, rainfall etc), river proximity, soil type, land cover, topography/slope and market outlets. Using the daily metrological data from 1992 to 2006, the long-term average rainfall and potential evapotranspiration raster map was computed through interpolation based on Thiessen polygons. The monthly rainfall deficit map (rainfall-evaporation) was aggregated to the annual rainfall deficit map. The major perennial river network segment map and slope raster map was derived from an SRTM DEM of the basin, and then the drainage network map was interpolated using the Euclidian distance tool in ArcGIS. Major potential marketing towns and the main paved road were digitized manually from Google Earth and interpolated. The interpolated maps were reclassified into four groups of suitability by an equal interval ranging technique. The soil and land use map collected from the Ethiopian Ministry of Water and Energy (EMWE) was reclassified to four major classes of FAO land suitability. Weighting of the decision factors was accomplished by comparing three approaches: ranking technique, pairwise comparison and equal weighting. Approximately 10%, 7% and 5% of the basin was suitable for surface irrigation according to the pairwise, equal weighting and ranking technique, respectively

Eco-hydrological impacts of Eucalyptus in the semi humid Ethiopian Highlands: the Lake Tana Plain

Abstract: Eucalyptus is the tree of choice for wood production by farmers in Ethiopia. Although there are many claims about its harmful effect on ecology and water availability, little actual research exists. The main objective of this study was, therefore, to study the extent of harm of Eucalyptus on the ecosystem. This study was conducted at the Koga Watershed near Lake Tana in Ethiopia. Twenty-five farmers were interviewed and a field experiment with three replications was carried out to quantify the effect of Eucalyptus on various soil physical and chemical properties and maize crop measurements and to compare bulk density, soil moisture contents, maize crop counts and shading effects in fields bordered by Eucalyptus and Croton macrostachyus. Our results show that Eucalyptus decreased both soil nutrients and maize yields within 20 m of the trees. Although moisture content was not affected during the monsoon, it decreased faster within 30 m of the Eucalyptus trees than elsewhere. Soils become water repellent, too. Local farmers ’ perception agreed with our experimental findings and indicated that Eucalyptus trees are exhausting the once productive land. They also reported that Eucalyptus dries up springs. Despite this, the growers insist on planting Eucalyptus because of its cas

Long-term trends in climate and hydrology in an agricultural, headwater watershed of central Pennsylvania, USA

AbstractStudy regionThe WE-38 Experimental Watershed, which is a small (7.3 km2) basin in the Ridge and Valley physiographic region of east-central Pennsylvania.Study focusWe used non-parametric Mann-Kendall tests to examine long-term (1968 to 2012) hydroclimatic (precipitation, temperature, streamflow) trends in WE-38 in the context of recent climate change across northeastern US.New hydrological insights for the regionAnnual mean temperatures in WE-38 increased 0.38°C per decade, leading to an expansion of the growing season (+2.8 days per decade) and a contraction of frost days (-3.6 days per decade). Consistent with increased temperatures, annual actual evapotranspiration rose significantly (+37.1mm per decade) over the study period. Precipitation also trended upward, with October experiencing the most significant increases in monthly total rainfall (+8.2mm per decade). While augmented October precipitation led to increased October streamflow (+5.0mm per decade), the trend in WE-38 streamflow was downward, with the most significant declines in July (-1.2mm per decade) and February (-7.5mm per decade). Declines in summertime streamflow also increased the duration of hydrological droughts (maximum consecutive days with streamflow < 10th percentile) by 1.9 days per decade. While our findings suggest some challenges for producers and water resource managers, most notably with increased fall rainfall and runoff, some changes such as enhanced growing seasons can be viewed positively, at least in the near term

A6. A Simple Hillslope Erosion Model for Saturation Excess Runoff Tested in the Ethiopian Highlands

A simple hillslope erosion model is developed and tested for watersheds ranging from 100 ha to 180,000 km2 in Ethiopian Highland. The erosion model is a simplification of Hairsine and Rose (1992) in which sediment concentration is a linear function of velocity and it has only two parameters to be calibrated. The model is coupled with a saturation excess water balance model that divides the watershed into three regions: two runoff producing areas (saturated and degraded) and a hillslope region with shallower soils where water infiltrates and is the source of the baseflow and interflow. The hydrology model has nine parameters consisting of the relative portion in the watershed and the water holding capacity for each of the regions and three subsurface flow parameters. Only surface flow generates sediment. Baseflow and interflow dilutes the concentration in the surface flow. This model was simulated in two upland watersheds (Anjeni and Debre Mawi with a size of 1Km2) in Blue Nile Basin dominated by agricultural activity and the Blue Nile Basin (180,000km2). The daily sediment concentration simulation for the two upland wa-tersheds and the 10-day model simulation for Blue Nile basin compares well with the measured data with Nash Sutcliffe efficiency in the range of 0.64 to 0.8 while the hydrology model was in the range of 0.7 to 0.9. The result suggested that sediment producing areas are only 20% and the higher parameter parameters in Debre Mawi and Anjeni might be because of agricultural activities, higer slope and gullies. The analysis also suggests that identifying the runoff source areas and predicting the surface runoff correctly is an important step in predicting the sediment concentration

Predicting phosphorus dynamics in complex terrains using a variable source area hydrology model

Phosphorus (P) loss from agricultural watersheds has long been a critical water quality problem, the control of which has been the focus of considerable research and investment. Preventing P loss depends on accurately representing the hydrological and chemical processes governing P mobilization and transport. The Soil and Water Assessment Tool (SWAT) is a watershed model commonly used to predict run-off and non-point source pollution transport. SWAT simulates run-off employing either the curve number (CN) or the Green and Ampt methods, both assume infiltration-excess run-off, although shallow soils underlain by a restricting layer commonly generate saturation-excess run-off from variable source areas (VSA). In this study, we compared traditional SWAT with a re-conceptualized version, SWAT-VSA, that represents VSA hydrology, in a complex agricultural watershed in east central Pennsylvania. The objectives of this research were to provide further evidence of SWAT-VSA’s integrated and distributed predictive capabilities against measured surface run-off and stream P loads and to highlight the model’s ability to drive sub-field management of P. Thus, we relied on a detailed field management database to parameterize the models. SWAT and SWAT-VSA predicted discharge similarly well (daily Nash–Sutcliffe efficiencies of 0.61 and 0.66, respectively), but SWAT-VSA outperformed SWAT in predicting P export from the watershed. SWAT estimated lower P loss (0.0–0.25 kg ha^-1) from agricultural fields than SWAT-VSA (0.0–1.0+ kg ha^-1), which also identified critical source areas – those areas generating large run-off and P losses at the sub-field level. These results support the use of SWAT-VSA in predicting watershed-scale P losses and identifying critical source areas of P loss in landscapes with VSA hydrology

Intricacies of an effective global "rooted" collaboration in soil and water research

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