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Sử dụng đất thay đổi và thực tiễn quản lý đất trên một quy mô đầu nguồn thường gây ra sự mất cân bằng phốt-pho (P) đi xe đạp, dẫn đến các vấn đề về chất lượng nước cả bên trong và ngoài lưu vực trong câu hỏi. Một số mô hình quy mô lưu vực sông đã được phát triển để theo dõi chuyển động của P từ các khu vực tập trung để tiếp nhận nước cơ quan (Cơ quan Bảo vệ Môi trường Hoa Kỳ năm 1992, năm 1997) | 11 Watershed Ecosystem Nutrient Dynamics-Phosphorus WeNd-P Models Robert L. Kort U.S. Department of Agriculture Natural Resources Conservation Service Colchester VT E. Alan Cassell University of Vermont Burlington VT Stefanie G. Aschmann U.S. Department of Agriculture Natural Resources Conservation Service Portland OR CONTENTS 11.1 Introduction.261 11.2 History and Development.262 11.3 Purpose.263 11.4 The Modeling Framework.263 11.5 Phosphorus Processes.268 11.6 Case Studies.269 11.7 Model Availability.275 11.8 Conclusions.275 References.275 11.1 INTRODUCTION Changing land uses and land-management practices on a watershed scale often cause an imbalance in phosphorus P cycling resulting in water-quality problems both inside and outside the watershed in question. A number of watershed-scale models have been developed to trace movement of P from areas of concentration to receiving water bodies U.S. Environmental Protection Agency 1992 1997 . These models primarily 261 2007 by Taylor Francis Group LLC 262 Modeling Phosphorus in the Environment focus on hydrologic and soil chemical processes to predict the likelihood of water contamination due to land-based P loading. Watershed Ecosystem Nutrient Dynamics-Phosphorus WEND-P differs markedly from most of these models. Instead of focusing on hydrologic mechanisms of P movement WEND-P examines the long-term storage process and cycling mechanisms by which the mass balance of P can change in various land uses and under various management scenarios throughout a specified watershed. This approach when combined with the hydrologic approach provides a more complete picture of P within a watershed and helps land managers devise strategies for addressing P pollution considering short-term economic social and environmental goals as well as long-term watershed ecosystem health. 11.2 HISTORY AND DEVELOPMENT WEND-P is a watershed-scale modeling process that uses dynamic simulation technology integrated with mass balance concepts to .