tailieunhanh - RESTORATION AND MANAGEMENT OF LAKES AND RESERVOIRS - CHAPTER 8

Nở hoa tảo phiền toái có thể được giảm hoặc loại bỏ phốt pho (P) nồng độ thấp hơn để hạn chế mức tăng trưởng bởi sự chuyển tải bên ngoài, bằng cách pha loãng, hoặc sự kết hợp của những phương pháp này. Trong trường hợp tải giảm có ý nghĩa quan trọng, tốc độ xả nước hồ là tương đối nhanh chóng, và nơi tái chế từ trầm tích là không quan trọng, trong hồ P có thể được giảm và tình trạng dinh dưỡng được cải thiện đáng kể và nhanh chóng. Trường hợp của hồ Washington. | Q Phosphorus Inactivation and Sediment Oxidation INTRODUCTION Nuisance algal blooms can be reduced or eliminated if phosphorus P concentrations are lowered to growth-limiting levels by diversion of external loading by dilution or a combination of these methods. In cases where loading reduction is significant where the lake flushing rate is relatively fast and where recycling from sediments is unimportant in-lake P can be reduced and trophic state significantly and rapidly improved. The case of Lake Washington Edmondson 1970 1994 is probably the most recognized example of this response Chapter 4 . For many lakes however internal P release prolonged the lake s enriched state and supported continued algal blooms even though diversion removed a significant fraction of external loading Cullen and Forsberg 1988 Sas et al. 1989 Jeppesen et al. 1991 Welch and Cooke 1995 Scheffer 1998 . Lakes that experience significant internal loading of P to their water columns are the rule rather than the exception. Lakes with extensive littoral and wetland areas Wetzel 1990 close proximity between the epilimnion and anoxic sediments Fee 1979 or shallow lakes with enriched sediments from a history of high external loading Jeppesen et al. 1991 will have extensive P recycling. In those lakes additional in-lake steps may be necessary following nutrient diversion to prevent a prolonged eutrophic state. For example Shagawa Lake Minnesota MN did not respond as rapidly as expected to the reduction of a large fraction of external loading and it is predicted to require decades to reach equilibrium Larsen et al. 1981 Chapra and Canale 1991 Chapter 4 . In some lakes even without reduction of external loading the major input of P and cause for summer algal blooms is from sediments Welch and Jacoby 2001 . In-lake treatments have been effective in such lakes. Phosphorus inactivation is an in-lake technique designed to lower the lake s P content by removal of P from the water column P .