Modeling is a very important tool for developing nonpoint source (NPS) pollution control plans. Current NPS models were developed for temperate conditions and, thus, do not appropriately represent tropical conditions. The objective of this research was to develop or adapt a nonpoint source pollution model to simulate transformations and losses of nitrogen (N) and phosphorus (P) in leachate and runoff from crop fields under humid tropical conditions. An extensive literature synthesis identified appropriate relationships for representing hydrologic and NPS processes in the tropics, as well as soil and climate conditions that differ from temperate conditions and impact NPS pollution. The GLEAMS model was selected for adaptation. Changes to the model included calculation of potential evapotranspiration (ET); changes in initial and default values of N and P pools, C:N ratio of soil organic matter, and soil P sorption; changes in simulation of transformations between N and P pools, along with the effect of temperature; and inclusion of a nitrate retardation factor (Ncrit) and pH in the calculation of N transformation and movement. The adapted model, called TROPGLEAMS, was evaluated through model verification, application, and sensitivity analysis. Model verification comprised a mass balance of nutrients and analysis of the variation of variable values in time. Model validation included application of the GLEAMS and TROPGLEAMS to three sites in Brazil: a set of lysimeters planted with sugarcane in Piracicaba, SP; a set of plots planted with sugarcane in Piracicaba; and a set of plots planted in a wheat-soybean rotation in Lages, SC. Model sensitivity to temperature, Ncrit and pH were evaluated in the sensitivity analysis. Model evaluation indicated that TROPGLEAMS is more accurate than GLEAMS in simulating fate and transport of nutrients under tropical conditions. Prediction of actual ET, effect of tillage on losses of N and P in runoff, and N and P kinetics was improved with TROPGLEAMS compared to GLEAMS. However, based on data from the Lages study, TROPGLEAMS did not simulate losses of nutrients in runoff well. Improvements in the model, especially related to losses in runoff, and application of TROPGLEAMS to different areas of the humid tropics are recommended. / Ph. D.

ANSWERS-2000, a continuous simulation, distributed parameter nonpoint source model for simulating runoff, sediment, and nutrients from disturbed watersheds was updated to include a critical-shear rill detachment subroutine, an improved interrill detachment subroutine, and a channel scour subroutine. The existing version of ANSWERS-2000 did not simulate channel scour. The original detachment equations used in the model were developed through regression analysis of data from a northeast Indiana watershed, and were not directly applicable to other watersheds. The new detachment equations are based on process-oriented equations developed for the WEPP model and they can be applied to ungaged watersheds with a wide variety of soils and land use conditions. The new model (ANSWERS-2000) was evaluated on three watersheds and its predictions were compared with the previous version of ANSWERS. On the largest watershed (2070 hectares), both models appeared to predict sediment loss adequately. On the second watershed (1053 hectares), ANSWERS-2000 improved sediment yield predictions compared to the original model. Neither model adequately described sediment loss from the smallest watershed (1.2 ha) used for validation. The sediment prediction errors were caused by errors in runoff prediction, despite an attempt to increase runoff prediction accuracy by calibration. The channel scour subroutine was evaluated by comparison with observed channel erosion data from the largest watershed. The new model appeared to consistently over predict scoured depth. However, more research is required to determine if the channel scour component is flawed or if the uncertainty in the observed channel scour data was large as suspected. Ultimately, the erosion prediction accuracy of the ANSWERS-2000 model was improved in two of the three upland evaluation data sets. The channel scour data set was not successfully validated. Model input parameter requirements increased significantly as a result of the new erosion and channel scour submodels. / Master of Science

The objective of this study is to evaluate the costs of reducing pesticide, nitrogen, phosphorus, and sediment losses of a representative risk-neutral and risk-averse peanut-cotton farmer in Southeast Virginia. Five currently popular rotations and eight alternative conservation rotations are evaluated for the representative farm. The Erosion-Productivity Impact Calculator (EPIC) model is used to simulate pesticide, nitrogen, phosphorus, and soil loss from each rotation using actual rainfall and temperature data from the study area. A Target-MOTAD mathematical programming model, REPVAFARM, is developed and solved with GAMS. The objective of the farmer is to maximize expected net return, while meeting a target income with certain allowable expected shortfall from the income target. The farmer is also constrained by land, labor, peanut quota, and levels of pesticide, nitrogen, phosphorus, and soil losses. Major findings of this study are: reducing pesticide, nitrogen, phosphorus, and soil losses imposes costs to the farmer regardless of his risk attitude, with costs ranking from high to low in the order of reducing all pollutant losses, reducing nitrogen losses, reducing phosphorus losses, reducing soil losses, and reducing pesticide losses. Costs of reducing pollutant losses are higher for more risk-averse farmers than for less risk-averse and risk-neutral farmers implying that risk-aversion is an obstacle to the adoption of alternative conservation practices. Reducing pesticide losses has little impact on other pollutants. Reducing pesticide and nitrogen losses simultaneously achieves similar reductions in soil loss and phosphorus loss. / Master of Science

Thesis (M.S.)--University of Hawaii at Manoa, 2007. / Includes bibliographical references (leaves 124-131). / xv, 131 leaves, bound ill. (some col.) 29 cm

Thesis (M.E.S.)--The Evergreen State College, 2007. / Title from title screen viewed (1/17/2008). Includes bibliographical references (leaves 67-68).

Agricultural nonpoint source pollution is recognised as a major cause of water pollution. The characteristics of nonpoint source pollution suggest that an efficient approach should focus on a source control and hence land-use management. Recently, the concept of Payments for Ecosystem Services (PES) has been advanced as an efficient market-based approach to protect in-stream water quality, while simultaneously supporting agriculture. Farmers can be rewarded for the adoption of certain ‘Best Management Practices’ (BMPs) in farming systems. But little is known about the adoption of BMPs in the context of Thai agriculture. This thesis examines the adoption of twelve BMPs on citrus farms in the Ping river basin in northern Thailand. In the context of potential PES development, three studies were undertaken using frameworks from economics and psychology. The first study used a bottom-up engineering approach to estimate economic costs of twelve BMPs at the farm-scale. The total annualised costs, including installation, maintenance, and land opportunity costs of each BMP were compared. The results indicated that land opportunity cost was the largest proportion of total costs. These estimates provided a basis for discussion on how the farmers’ perception of cost may influence their stated adoption intention. The second study used the Theory of Planned Behaviour (TPB), to investigate farmers’ intentions on adoption of twelve BMPs. A survey of 218 citrus farmers was undertaken in the application. Descriptive statistics and frequency of BMP selection were presented. The results showed that soil analysis was the most preferred BMP. A graphical analysis of other preferred measures suggested that these were not always consistent with the known cost information derived (above) and thus farmers’ perceived costs might not be the most important factor influencing adoption decisions. Further analysis based on TPB investigated other factors thought to be significant in farmers’ decision-making. Other potential external and psychological factors influencing adoption were investigated using a multinomial logistic model. The results indicated that the probability of adopting BMPs was associated with other psychological factors and external factors, rather than perceived costs. The significant psychological factors were farmers’ attitudes towards consumers and perception about farm returns, while the significant external factors were, for example, access to information and contribution of family labour to farm workload. The third study was based on the application of Q-Methodology, and aimed to obtain a deeper understanding of farmers’ perception towards BMPs. Seventy two participants were purposively selected from the 218 TPB observations. The results revealed four distinctive farmer groups holding different perceptions towards BMPs. The four groups were conservationist, traditionalist, disinterested, and risk-averse. These provided a specific segmentation to guide policy towards influencing attitudes and behaviours. The results suggested that farmers were not motivated solely by a profit maximisation goal. Overall, key findings from these three studies revealed some fundamental requirements for developing a water-related PES programme. These were: i) factors affecting eligibility to participate; ii) factors affecting desire to participate; and iii) factors affecting ability to participate. This information provided the basis for a set of recommendations addressing the development of the water-related PES programme in the Ping river basin.

A redução dos impactos da poluição difusa é ainda pouco explorada no Brasil, havendo ausência de critérios legais quanto à sua mitigação. Contudo, na esfera científica o seu impacto é reconhecido. Seguindo evidências de que há uma carência no tratamento de poluição difusa no país, este trabalho se propõe a analisar wetlands construídas como medidas de controle de poluição difusa, através de modelagens, para 4 áreas na bacia do córrego do Mineirinho. A exploração dessa proposta se deu por três abordagens paralelas. Na primeira, as wetlands foram projetadas para tratar o escoamento superficial de uma chuva crítica, de 61 minutos. Na segunda abordagem, foi utilizada uma chuva crítica de 24 horas de duração. Na terceira, utilizou-se o índice de precipitação anual. O escoamento superficial foi calculado conforme os coeficientes de runoff. Atribuíram-se valores de concentrações médias de evento para DBO e Fósforo aos tipos de uso e ocupação, obtendo-se concentrações médias nas águas pluviais a serem tratadas. O modelo P-k-C* foi empregado na primeira e terceira abordagens, para dimensionar os sistemas com base no desempenho de remoção de cargas. Os resultados obtidos demonstraram a aptidão dos sistemas em reduzir cargas e/ou concentrações na bacia, apresentando como principal limitação técnica o espaço demandado para sua implantação. Houve influência majoritária da infiltração na remoção de cargas, que agiu em conjunto com o decaimento de poluentes ao longo dos sistemas. Na primeira abordagem, o modelo P-k-C* apresentou limitações em prever o desempenho dos sistemas por não comportar vazões variáveis. A segunda abordagem foi a mais simples, baseada apenas no armazenamento do evento crítico, entretanto, há uma carência de relações empíricas traçadas experimentalmente para prever seu desempenho. A terceira abordagem se mostrou a mais adequada ao modelo P-k-C*, podendo ser aprimorada de duas formas: adaptações nas constantes cinéticas ou vazões equivalentes, a fim de descrever uma média anual de desempenho. Concluiu-se que wetlands construídas demonstram potencial para o tratamento de poluição difusa, porém há uma necessidade de estudos a fim de se adaptar as ferramentas de modelagem disponíveis. / Nonpoint source pollutions impacts are still a rarely explored theme in Brazil, in which there are no legal criteria for its treatment. Although, in the scientific sphere its impacts are well known. Following evidence that there is a lack of nonpoint source pollution treatment in Brazil, this study proposes to analyze constructed wetlands as a nonpoint source pollution control measure, through modelling, for four different areas in the Mineirinho stream watershed. This proposal was explored through three different approaches. At first, the wetlands were designed to threat a critic rainfall for flood estimation, with detailed hydrographs. On the second approach, the wetlands were design to fully contain a 24-hour critic rainfall. On the third approach, the wetlands were designed to treat the average annual rainfall. The runoff volumes were estimated by runoff coefficients, and event mean concentrations for BOD and TP were assigned to each source area, resulting in the stormwater quality estimation. The P-k-C* model was applied to calculate systems performance on the first and third approaches. The results showed the aptitude of the systems for reducing loads and concentrations in the watershed, although mainly limited by the availability of areas. Infiltration had a major hole in reducing loads, although there were also significant amounts of pollutant removed by the systems. At the first approach, the P-k-C* model presented limitations on describing stormwater treatment, because of its unsteady and intermittent characteristics. The second approach was the simplest, based on containing the whole runoff volume, but it also showed a lack of studies stablishing empiric relations to estimate its performance. The third approach was the most adequate to the P-k-C* model, which usage could be improved by two adaptations in its parameters: kinetic coefficient adaptations or the adoption of equivalent steady flows, to describe the annual wetland performance. The study concluded that constructed wetlands show great promise for treating nonpoint source pollution in the watershed, but there is a need of more studies to regionalize empiric solutions available in the scientific literature, to apply the designing techniques with greater precision.

The water quality in the United States has greatly improved since the implementation of the Clean Water Act (CWA) in the early 1970s. Unfortunately, the Clean Water Act only addresses one kind of water pollution, point source pollution. The major problem that is present in the degradation of todays water quality has to deal with nonpoint source pollution. Agriculture is commonly regarded as the leading contributor to nonpoint source pollution in the United States. This study uses two analytical tools to try to determine the significant factors in the transport of pollutants in the Lower Kentucky Watershed, located in central Kentucky. Spatial analysis (GIS) coupled with the statistical analysis (SAS), allowed for significant factors to be identified within a small proximity of sampling sites throughout the watershed. The results suggest that although agriculture is commonly regarded as the largest contributor to nonpoint source pollution, other factors outside of agriculture were also found to be significant, such as resident land use and rainfall. The results generated from this study suggest that land managers in communities throughout the watershed should analyze agricultural factors, as well as, factors outside of agriculture, in an effort to protect their communities water quality.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 193-217).

Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references (leaves 154-161). Also available on the Internet.