Bước đầu tiên trong việc khôi phục hoặc nâng cao chất lượng của hồ và các hồ chứa eutrophic hoặc phì đại là để loại bỏ hoặc điều trị các yếu tố đầu vào trực tiếp của nước thải, nước mưa, hoặc cả hai. Nguồn như vậy thường có nồng độ tương đối cao của P và N. Trừ khi đầu vào bên ngoài đó (tải) được giảm, bất kỳ lợi ích lâu dài từ phương pháp điều trị trong hồ thường không được thực hiện. Trong một số trường hợp, giảm đầu vào bên ngoài là đủ để khôi. | 4 Lake and Reservoir Response to Diversion and Advanced Wastewater Treatment GENERAL The first step in restoring or improving the quality of eutrophic or hypertrophic lakes and reservoirs is to remove or treat direct inputs of wastewater stormwater or both. Such sources usually contain relatively high concentrations of P and N. Unless such external inputs loading are reduced any long term benefits from in-lake treatments will usually not be realized. In some cases reduction of external inputs is sufficient to restore the water body . Lake Washington Edmondson 1978 1994 but in others where internal loading of nutrients is significant in-lake treatments may be necessary to achieve lake quality improvement . Lake Trummen Bjork 1974 see Chapter 20 . Diversion is expected to have similar effects to P removal through advanced wastewater treatment AWT . Either P is already the most limiting nutrient or in the case of highly eutrophic or hypertrophic lakes where N is often limiting P can be made to limit if its concentration is sufficiently reduced. To cause P to limit in enriched N-limited lakes usually requires a substantial reduction in external loading. However if internal loading from sediments is sufficiently high so that N is still limiting after external load reduction there could be more benefits from diversion than AWT since incoming N is also removed. Nevertheless lakes would probably still remain highly eutrophic even if benefits resulted from N reduction. This was the case in Lake Norrviken Sweden as will be discussed later Ahlgren 1978 . Benefits have also been documented from diluting inflow nitrate concentration Welch et al. 1984 Chapter 6 . Both N and P removal from wastewater may be necessary if background P loading is naturally high Rutherford et al. 1989 . The important question is usually not whether lakes or reservoirs will recover or improve following external nutrient load reduction but when and to what extent Lake P concentrations have .
