Effects of hypolimnetic aeration on the quantity and quality of settling material in a eutrophied dimictic lake

Juha Niemistö,Soila Silvonen,Jukka Horppila

doi:10.1007/s10750-019-04160-6

Juha Niemistö, Soila Silvonen + Show 1 more

Open Access

https://doi.org/10.1007/s10750-019-04160-6

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Abstract

Effects of hypolimnetic aeration (pumping of epilimnetic water into the hypolimnion) on the quantity of settling material in eutrophied Lake Vesijärvi, Finland were studied by comparing spatially comprehensive gross sedimentation rates as dry and organic matter prior to aeration activity and during two aerated years. Possible changes in the organic matter (as loss on ignition, LOI), carbon (C) and nitrogen (N) contents and changes in the C/N ratio of the settling material and surface sediment were quantified. Thermal stratification broke up earlier due to aeration and was followed by sedimentation peaks. The absolute amount of dry and organic matter as well as C and N settling to the lake bottom were significantly higher in the aerated years. Increased sedimentation rates were especially pronounced in the deep zones indicating enhanced sediment focusing. Increased sedimentation of C and N reflected higher primary production during the aerated years, which most likely was associated with increased temperature and turbulence and the subsequent regeneration and recycling of nutrients in the water body. Aeration seemed to slightly enhance degradation, but contrary to its ultimate aim, it failed to decrease the phosphorus content of the water column and deposits of organic material in the deep zones of the lake.

Highlights

Eutrophication of water bodies results in excess production of organic material and increased sedimentation rates (Harper, 1992)
The sedimentation rate of organic material significantly increased (1.4-fold) in the deep zones of the lake and oxygen deficit was not avoided due to increased oxygen consumption
Intensifying the treatment is not a relevant option, since in a cooler summer, mixing aeration caused destratification in the middle of the growth season and resulted in three times higher sedimentation rates of organic material compared with the reference year

Summary

Introduction

Eutrophication of water bodies results in excess production of organic material and increased sedimentation rates (Harper, 1992). Organic material accumulates on the lake bottom and leads to increased oxygen demand of bottom sediments. Increased oxygen supply may enhance mineralisation of organic matter of sediments and subsequently decrease the long-term oxygen demand (Engstrom & Wright, 2002). This target is often set for an aeration measure, but rarely quantified

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