Abstract
Lake restoration is a part of geoengineering, which is a useful tool for landscape management. The phosphorus inactivation method is one of the most popular lake restoration methods. Using chemical compounds for P binding is leading to the creation of sediment “active layer”, which should show higher P adsorption abilities, compared to non-modified sediment. Howewer, it provides rather little information, how long the modified sediment remains active, and whether it is effective in continuous P binding. Lake meromixis is not commonly observed phenomenon, and sediment located in monimolimnion area is subjected long term anoxia. Therefore, observation of “active layer” in a meromictic lake can give very important data about durability of restoration effects. The object of our study was meromictic Starodworskie Lake (5.57 ha, max. depth 24.5 m), located in Olsztyn Lakeland, Poland. In the past the analyzed lake was subjected to various restoration methods, and phosphorus inactivation method by alum use (1994–1995) was the last used treatment type. The mixing regime of this lake had changed from bradimictic (before and during restoration time) into durable meromictic (post-restoration period). The research made two decades after implementing of P inactivation showed the presence of “active” sediment layer 10–15 cm below sediment surface. This sediment layer showed much higher content of P bound to aluminum, compared to surficial sediment layer. P binding molar ratio was assessed and amounted to 16.1 straightly after restoration and 6.1 after 21 years. This fraction amounts were higher that the values noted before restoration (ca. 358% higher than in 1994) and during restoration (ca. 86% higher than in 1995), which was probably the effect of continuous phosphorus adsorption by “active layer” in post-restoration period.
Highlights
Excessive eutrophication of surface water bodies is a common phenomenon worldwide [1,2,3]
The aim of this study was the analysis of changes in the profundal watersediment interface of meromictic Starodworskie Lake, which were induced by restoration treatment with alum use
Phosphorus inactivation method using alum, which was implemented on Starodworskie Lake in Olsztyn in the 1994 and 1995 years, created an “active layer” in sediment of profundal zone, which was able to bind phosphorus in the post-restoration period, despite of long-term permanent anoxia in monimolimnion zone
Summary
Excessive eutrophication of surface water bodies is a common phenomenon worldwide [1,2,3]. In the situation of rising water pollution, deep lakes with slow mixing regime (bradimictic) can form permanent meromixis, in which deep water layer (monimolimnion) has higher density, than water column above. This density difference is a factor blocking effectively the possibility of lake water full mixing. Negative symptoms of excessive eutrophication make water usage difficult, or even impossible, necessitating many types of geoengineering actions in the drainage basins as well as directly in the lake bowl, aiming to improve water quality [9,10]. Taking actions, which could help to improve and maintain good water quality of water bodies, is an important part of proper landscape management
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