Hồ và bảo vệ hồ chứa Từ điểm ô nhiễm Các nguồn chính của chất dinh dưỡng và chất hữu cơ cho các suối, hồ, và hồ chứa ở Bắc Mỹ và châu Âu được cho là "điểm" các nguồn như nhà máy xử lý nước thải (WWTP) outfalls. Những đã được rất nhiều nâng cấp (Welch, 1992), dẫn đến cải thiện chất lượng nước ở một số hồ (ví dụ, hồ Washington) vì WWTP thải là nguồn dinh dưỡng chiếm ưu thế của họ. Đối với nhiều hồ, không điểm hoặc khuếch tán chất dinh dưỡng tải, cả bên trong. | 5 Lake and Reservoir Protection From Non-Point Pollution INTRODUCTION The major sources of nutrients and organic matter to streams lakes and reservoirs in North America and Europe were believed to be point sources such as wastewater treatment plant WWTP outfalls. These have been greatly upgraded Welch 1992 leading to water quality improvement in some lakes . Lake Washington because WWTP discharges were their dominant nutrient sources. For many lakes non-point or diffuse nutrient loading both internal and external to the lake is at least as significant as point source loading. This source is difficult to assess and control Line et al. 1999 and water quality in many lakes has not improved rapidly following diversion or treatment of point sources Chapter 4 . The purposes of this chapter are to describe the origins and nature of non-point loading to streams lakes and reservoirs and to discuss certain methods for managing it. Urban and agricultural activities are the major non-point sources of silt and nutrients to streams and ultimately to lakes and reservoirs. Loading from these activities is increasing as urban areas expand food production especially confined animal operations or CAFOs increases and undeveloped land is drained deforested tilled or developed and stored soil nutrients are released. These land uses in the watershed are good predictors of reservoir and lake productivity. More quantitative indices such as the drainage ratio drainage area to lake volume and the cropland area livestock density ratio Pinel-Alloul et al. 2002 Knoll et al. 2003 are being developed and will become more useful with more data. Agriculture is the primary source of non-point loading through erosion of nutrient-rich soil and from livestock activities and also is the largest user of fresh water Novotny 1999 . Demands to increase agricultural yields with fertilizer and manure applications have led to soil nutrient surpluses. For example the average net gain of phosphorus P in .
