The actual role of oxygen deficit in the linkage of the water quality and benthic phosphorus release: Potential implications for lake restoration.

Human activities in watersheds have resulted in huge accumulations of phosphorus (P) in sediments that have subsequently hindered restoration efforts of lake water quality managers worldwide. Much controversy exists about the factors that control the release of P from sediments (internal P loading). One of the main debates concerns the role of oxygen deficit (anoxia) in the regulation of water quality. Our results based on a comprehensive set of lakes worldwide demonstrate that internal P loading (IP) plays a significant role in water quality regulation. Internal P loading due to anoxia (IP) contributes significantly to the IP. However, this contribution is insufficient to significantly increase the chlorophyll a (Chl a) concentration in stratifying lakes. In the lakes of the north temperate and boreal zone, this is because the IP reaches surface water layer in the end of the growing season. Observed water quality implications of IP are most likely caused by the sedimentary P that actually originates from the shallow areas. These findings suggest limitations for the use of aeration (improvement of the oxygen conditions in the hypolimnion) in lake water quality restoration. Moreover, lake ecosystem managers can benefit from our model that enables to predict anoxia triggered sedimentary P release from the combination of lake characteristics. The final decision on the use of aeration is indeed unique to each lake, and lake specific targets should be considered.