Abstract
Lakes hold most of the world’s fresh surface water resources. Safeguarding these resources from water quality degradation requires knowledge of the relationship between lake morphometry and water quality. The 3046-km2 Lake Tana in Ethiopia is one of the water resources in which the water quality is decreasing and water hyacinths have invaded. The objective of this study is to understand the interaction between the lake morphometry and water quality and specifically the phosphorus dynamics and their effect on the water hyacinths. A bathymetric survey was conducted in late 2017. Various morphometric parameters were derived, and both these parameters and sediment available phosphorus were regressed with the dissolved phosphorus. The results show that, with a wave base depth that is nearly equal to a maximum depth of 14.8 m, the bottom sediments were continuously suspended in the water column. As a result of the resuspension mixing, we found that the dissolved phosphorus in the water column decreased with lake depth and increased with sediment available phosphorus (R2 = 0.84) in the northern half of the lake. This relationship is not as strong in the south due to a large flow of Gilgel Abay to the outlets. Water hyacinths were found where the lake was shallow and the available phosphorus was elevated. The large reservoir of sediment phosphorus will hamper any remedial efforts in removing the water hyacinths.
Highlights
Lakes are important ecosystems whose environments are continuously changing due to natural and human factors [1,2]
The objective of the study was to determine the effect of lake morphometry on the sediment and phosphorus dynamics of Lake Tana
Morphometric characteristics were derived from a bathymetric survey conducted in late 2017
Summary
Lakes are important ecosystems whose environments are continuously changing due to natural and human factors [1,2]. The rate of change depends in part on the morphometric characteristics [1,3,4] For this reason, Lake Tanganyika and Lake Malawi, which are deep, have been less affected by the degradation of the watershed and increased fertilizer use [5,6] than shallow lakes such as Lake Chad and Lake Tana [7,8]. The difference is that deep lakes are stratified [9,10] and shallow lakes are mixed by the wind and waves [2,11]. Another morphometric characteristic that affects water quality is the shape of the lake. Many scholars have developed empirical models for defining lake morphometry in relation to water quality [1,4,12,13,14]
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