Dennis C. Flanagan

Landscape benching from tillage erosion between grass hedges

Grass hedges are narrow (1‐2 m wide) parallel strips of stiff, erect, grass planted near to or on the contour of fields but crossing swale areas at angles convenient for farming. They serve as guides for contour cultivation, retard and disperse surface runoff, cause deposition of eroded sediment, and reduce ephemeral gully development. After three years of tilled fallow between mixed-species hedges, the average grade of 18 m wide tilled strips between 1.5 m wide hedges was reduced from 0.068 to 0.052 as a result of surface lowering below hedges and on the shoulders of swale areas combined with increases in elevation above hedges. Annual surveys show progressive lowering of high spots and filling of low spots as contours lines more closely aligned with hedges. Survey data indicated annual erosion rates of nearly 250 t ha ˇ1 year ˇ1 . Both RUSLE and WEPP over-predicted erosion rates, partly because backwater and slope modification affects were not considered. A tillage translocation model predicted enough soil movement to account for 30‐60% of the observed changes. A combination of tillage translocation and water erosion/deposition provides the best explanation for the observed aggradation/degradation patterns. # 1999 Elsevier Science B.V.

Short note: Runoff mapping using WEPP erosion model and GIS tools

Soil erosion, associated with environmental impacts and crop productivity loss, is usually considered the most impacting of surface hydrology processes. Runoff plays a major role in the erosion process, but it is also important by itself as it directly influences several surface hydrologic processes. In this paper, a computer interface (Erosion Database Interface, EDI) is described that allows processing the surface hydrology output database of the Water Erosion Prediction Project (WEPP) erosion prediction model, resulting in a georeferenced estimation of runoff. WEPP output contains non-georeferenced daily information about estimated runoff at the lower end of each Overland Flow Element. EDI, when running with WEPP, allows extracting WEPP-calculated runoff values, transforming them into annual means and relocating them in a georeferenced database readable by Geographic Information Systems (GIS). EDI was applied to a 1990ha watershed in southeast Brazil, with vegetation of mainly sugarcane, forest, and pasture. A 100-year climate simulation was used as input to WEPP, and erosion values were calculated at about six points per hectare and interpolated to a raster format. EDI was successful in preparing the database for automatic calculation of erosion and hydrologic parameters with WEPP and to restore georeferences to mean annual accumulated runoff data that were imported in the GIS as a vector database. Of all the resulting maps, the runoff map is the one that integrates all of the input parameters required for WEPP simulation, thus reflecting not only the physical environment but also crop growth and management and tillage operations. A very small correlation between runoff and erosion shows them to behave independently. Moreover, it is concluded that on analyzing runoff related to agricultural management, georeferenced runoff studies are especially important. In this context, EDI may be a useful tool to assess the effect of tillage and crop management on runoff production.

Assessing Soil Erosion Rates on Manually-Tilled Hillslopes in the Sichuan Hilly Basin Using 137Cs and 210Pbex Measurements

Purple soils are widely distributed in the Sichuan Hilly Basin and are highly susceptible to erosion, especially on the cultivated slopes. Quantitative assessment of the erosion rates is, however, difficult due to small size of the plots of the manually-tilled land, the complex land use, and steep hillslopes. 137Cs and 210Pbex (excess 210Pb) tracing techniques were used to investigate the spatial pattern of soil erosion rates associated with slope-land under hoe tillage in Neijiang of the Sichuan Hilly Basin. The 137Cs and 210Pbex inventories at the top of the cultivated slope were extremely low, and the highest inventories were found at the bottom of the cultivated slope. By combining the erosion rates estimates provided by both 137Cs and 210Pbex measurements, the weighted mean net soil loss from the study slope was estimated to be 3100 t km−2 year−1, which was significantly less than 6930 t km−2 year−1 reported for runoff plots on a 10° cultivated slope at the Suining Station of Soil Erosion. The spatial pattern of soil erosion rates on the steep agricultural land showed that hoe tillage played an important role in soil redistribution along the slope. Also, traditional farming practices had a significant role in reducing soil loss, leading to a lower net erosion rate for the field.

GeoWEPP - The Geo-spatial interface for the Water Erosion Prediction Project

Decision-makers operating at different scales of interest and responsibility have to assess the distribution, extent, and severity of soil erosion and sedimentation. To seek solutions in handling natural and human actions related to this type of nonpoint source pollution, the linkage of distributed assessment models and Geographical Information Systems (GIS) at various spatial and temporal scales is in high demand. The Water Erosion Prediction Project (WEPP) model is a continuous simulation, process-based model that allows simulation of water and sediment balance in small watersheds and on hillslope profiles within those watersheds. This presentation introduces an approach for running WEPP simulations based on using available geo-spatial information through a linkage with GIS. The new Geo-spatial interface for WEPP (GeoWEPP) utilizes readily available digital geo-referenced information from publicly accessible Internet sources such as the U.S. Geological Survey digital elevation models, topographical maps, and land use data as well as Natural Resources Conservation Service soils maps. Together with parameter sets of the WEPP database containing statistical parameter sets from more than 2600 U.S. climate stations, GeoWEPP enables even non-GIS-and-modeling users to derive and prepare valid model input parameters to assess representative conditions in an area of interest. After establishing the main data input for a particular site, various land use scenarios can be evaluated to assist with soil and water conservation planning.

Erosion database interface (EDI): a computer program for georeferenced application of erosion prediction models

The multidisciplinary approach of soil erosion research often requires erosion to be treated as spatial georeferenced information. This condition is essential so as to be compatible with information analyzed via Geographic Information Systems (GIS). The original versions of important soil erosion prediction models such as the Universal Soil Loss Equation (USLE) and Water Erosion Prediction Project (WEPP) do not operate on a georeferenced basis. The Erosion Database Interface (EDI) is a computer program for georeferenced application of USLE and WEPP. EDI uses, as input, a text format database with points defined by coordinates (x, y and z) representing hillslopes, each point associated to soil type and land use. Such input data can be provided by different methods. Exclusive field work with ordinary topographic equipment and GIS procedures are examples of methods that can be used for this purpose. Flexibility in the methods adopted for providing input data is an important prerequisite for erosion prediction in tropical and developing regions, where soil erosion is a major concern and the availability of digital data is usually restricted. Hillslopes for EDI were defined as straight line segments beginning at the upper slope and ending down at runoff output. This restricts EDI as a complete erosion-prediction method for areas where runoff deflecting features predominate or where channel or gully erosion is to be considered. As output, EDI provides georeferenced soil erosion values in another text format database. This database can be used directly for statistical or geostatistical analysis or imported into a GIS for further processing. A practical example representative of a sugarcane-growing area located at the southeastern part of Brazil is used to illustrate EDIs performance. In this example, soil erosion maps were produced from GIS data using EDI as interface for erosion calculations for WEPP and USLE.

Development of a GIS Interface for WEPP Model Application to Great Lakes Forested Watersheds

This presentation will highlight efforts on development of a new online WEPP GIS interface, targeted toward application in forested regions bordering the Great Lakes. The key components and algorithms of the online GIS system will be outlined. The general procedures used to provide input to the WEPP model and to display model output will be demonstrated.

Application of polyacrylamide to reduce phosphorus losses from a Chinese purple soil: a laboratory and field investigation.

Use of anionic polyacrylamide (PAM) to control phosphorus (P) losses from a Chinese purple soil was studied in both a laboratory soil column experiment and a field plot experiment on a steep slope (27%). Treatments in the column study were a control, and PAM mixed uniformly into the soil at rates of 0.02, 0.05, 0.08, 0.10, and 0.20%. We found that PAM had an important inhibitory effect on vertical P transport in the soil columns, with the 0.20% PAM treatment having the greatest significant reduction in leachate soluble P concentrations and losses resulting from nine leaching periods. Field experiments were conducted on 5m wide by 21m long natural rainfall plots, that allowed collection of both surface runoff and subsurface drainage water. Wheat was planted and grown on all plots with typical fertilizer applied. Treatments included a control, dry PAM at 3.9 kg ha(-1), dry PAM at 3.9 kg ha(-1) applied together with lime (CaCO(3) at 4.9 t ha(-1)), and dry PAM at 3.9 kg ha(-1) applied together with gypsum (CaSO(4).2H(2)O at 4 t ha(-1)). Results from the field plot experiment in which 5 rainfall events resulted in measurable runoff and leachate showed that all PAM treatments significantly reduced runoff volume and total P losses in surface runoff compared to the control. The PAM treatments also all significantly reduced water volume leached to the tile drain. However, total P losses in the leachate water were not significantly different due to the treatments, perhaps due to the low PAM soil surface application rate and/or high experimental variability. The PAM alone treatment resulted in the greatest wheat growth as indicated by the plant growth indexes of wheat plant height, leaf length, leaf width, grain number per head, and dried grain mass. Growth indexes of the PAM with Calcium treatments were significantly lesser. These results indicate that the selection and use of soil amendments need to be carefully determined based upon the most important management goal at a particular site (runoff/nutrient loss control, enhanced plant growth, or a combination).

Effect of Abiotic Factors on the Mercury Reduction Process by Humic Acids in Aqueous Systems

As a global pollutant process, the reduction of mercury (Hg) is especially important. One pathway is through an abiotic reduction with humic acids (HAs), which is controlled by different factors, including initial Hg and HA concentrations, pH, temperature and light. In this study, three humic acids were selected to illustrate the Hg2+ abiotic reduction mechanisms by HAs, and to identify the key limiting factors for reduction rates and amounts. In addition, the initial status of the HAs as a solid or in an aqueous solution were also compared, to help explain why HAs show different dominant characteristics (e.g. complexation or reduction) in the reaction process with Hg. Results indicated that HAs were able to reduce Hg abiotically. Higher initial Hg, higher HA concentrations and either high (8.1) or low (3.6) solution pH decreased the HA reduction capacity. In addition, Hg0 production rates increased with increasing temperature, and the same trend was observed with light exposure. Humic acids added as an aqueous solution resulted in significantly greater Hg0 production than addition as a bulk solid. Finally, the Hg reduction rate and capacity varied significantly (P < 0.05) with HAs from different sources. These findings helped to explain why HAs showed different dominant characteristics (e.g. complexation or reduction) in the reaction process with Hg, and evidentially demonstrated the existence of a possible pathway of Hg2+ reduction, which indicated that humic substances in natural environments, especially in water bodies, could act either as a sink or a source for Hg.

The development of U. S. soil erosion prediction and modeling

Soil erosion prediction technology began over 70 years ago when Austin Zingg published a relationship between soil erosion (by water) and land slope and length, followed shortly by a relationship by Dwight Smith that expanded this equation to include conservation practices. But, it was nearly 20 years before this works expansion resulted in the Universal Soil Loss Equation (USLE), perhaps the foremost achievement in soil erosion prediction in the last century. The USLE has increased in application and complexity, and its usefulness and limitations have led to the development of additional technologies and new science in soil erosion research and prediction. Main among these new technologies is the Water Erosion Prediction Project (WEPP) model, which has helped to overcome many of the shortcomings of the USLE, and increased the scale over which erosion by water can be predicted. Areas of application of erosion prediction include almost all land types: urban, rural, cropland, forests, rangeland, and construction sites. Specialty applications of WEPP include prediction of radioactive material movement with soils at a superfund cleanup site, and near real-time daily estimation of soil erosion for the entire state of Iowa.

Development of a Combined Wind and Water Erosion Model (WWEM) for the Object Modeling System

The USDA Natural Resources Conservation Service (NRCS) is currently re-evaluating its need for erosion prediction technology from the USDA Agricultural Research Service (ARS). While the exact technology required has not yet been determined, the NRCS has proposed in the past to collaborate with the ARS to build a single process-based model to simulate both rainfall induced rill and interrill erosion as well as perform computations for wind erosion prediction. An additional priority within the NRCS is to incorporate any natural resource modeling technology (e.g., science module code and databases) for use by the agency within the Object Modeling System (OMS) being developed by the ARS Agricultural Systems Research Unit (ASRU) in Fort Collins, Colorado. The OMS is a modeling framework that uses an open-source software component-based approach to enable members of the scientific community to collaboratively address the many complex issues associated with the design, development, and application of natural resource models. The ARS has the lead in OMS design and development; however, strong collaborative support in terms of financial resources and personnel involvement has been provided by the NRCS and other federal agencies. OMS 3.0 represents a major milestone towards an easier to use, more transparent and scalable implementation of an environmental modeling framework. The main goal of OMS3 development is an easier integration of component-based model source code while being accommodating and flexible towards adopting existing legacy models. In OMS3, the internal complexity of the framework itself is reduced, while allowing models to implicitly scale from multi-core desktops to clusters to clouds, without burdening the model developer with complex technical details. This paper describes the development and application of a component-based, standalone, combined water and wind erosion model (WWEM) running under the OMS3 framework. Because OMS3 fully embraces multi-threading as the default execution model of simulation components, WWEM component execution is controlled by synchronization on objects passed from and to components, i.e., the components run in parallel without explicit programming by the component developer. The model (Figure 1) consists of both FORTRAN and Java-based components for hydrology (infiltration, water balance/redistribution and kinematic wave overland flow routing), plant cover (evapotranspiration), water erosion (sediment detachment, deposition, enrichment, and routing), and wind erosion (wind detachment). The components were adapted and modified primarily from the WEPP, WEPS, and RZWQM2 models and have been engineered for modularity and substitutability (e.g., the FORTRAN simulation components do not contain any common blocks). WWEM hydrology (surface runoff) and erosion (sediment loading) predictions were evaluated using data obtained from rainfall simulator studies on experimental plots in Colorado. Results show that the model was able to accurately capture runoff and erosion dynamics for discrete rainfall events at the plot-scale. Additional evaluation of the model is planned at the field scale. This study demonstrates the feasibility of using OMS3 as a modeling platform for enhancing open source component design through re-use of legacy code and improved model interoperability. Work is currently underway to add additional WWEM modeling components (e.g., the WEPS-based Unified Plant Growth Model being developed by ASRU scientists) and to improve existing model components (e.g., the WEPP-based hillslope water erosion modules). In conclusion, the component-oriented and modular approach of OMS3 and the erosion modules/models implemented in it will provide the basis for more efficient and internationally collaborative erosion model development in the future.