Cạn kiệt oxy hòa tan (DO) trong hypolimnia hồ eutrophic phân tầng là một trong những dấu hiệu đầu tiên của hiện tượng phú dưỡng. Anoxia xảy ra nếu hô hấp của vật chất hữu cơ trong nước và trầm tích hypolimnetic là đủ để thải hầu hết hoặc tất cả các hypolimnetic DO trước khi destratification mùa thu. Anoxia sản xuất thay đổi không mong muốn trong hồ chất lượng, bao gồm cả tái chế nội bộ tăng tốc của chất dinh dưỡng hòa tan của các kim loại không mong muốn trong các nguồn cung cấp nước và. | 1 8 Hypolimnetic Aeration and Oxygenation INTRODUCTION Depletion of dissolved oxygen DO in the hypolimnia of stratified eutrophic lakes is one of the first signs of eutrophication. Anoxia occurs if respiration of organic matter in hypolimnetic water and sediments is sufficient to exhaust most or all of the hypolimnetic DO before autumn destratification. Anoxia produces undesirable changes in lake quality including accelerated internal recycling of nutrients solubilization of metals that are undesirable in water supplies and limitation of fish distribution especially cold-water species. Chapter 2 describes the expected seasonal changes in temperature and DO in stratified lakes and reservoirs. Hypolimnetic aeration used first in Lake Bret Switzerland Mercier and Perret 1949 is a lake management technique designed to counteract hypolimnetic anoxia and its associated problems. The specific objectives of hypolimnetic aeration are threefold. The first and usually most attainable is to raise the oxygen content of the hypolimnion without destratifying the water column or warming the hypolimnion. The second which is largely dependent on the first is to provide an increased habitat and food supply for coldwater fish species. The third if sediment-to-water exchange of P is controlled by iron redox is to reduce sediment P release by establishing oxic conditions at the sediment-water interface. Other constituents that reach high and possibly undesirable concentrations under anoxic conditions such as NH4 Mn and Fe should also be diminished by hypolimnetic aeration. This technique and its effects were described by Pastorak et al. 1981 1982 . However many device modifications and improvements have occurred since that review. DESCRIPTION AND OPERATION OF UNITS There are several designs for hypolimnetic aerators. Fast and Lorenzen 1976 reviewed 21 designs and grouped them into three categories 1 mechanical agitation involving removal treatment and return of the .
