Bierkens reported in late 2022 that a new study explains why the arsenic that has accumulated in lake bottom sediments is more harmful to the lake ecosystems in shallow lakes. A schematic of the mechanism that explains why shallow lakes are more sensitive to shallow water pollution with Arsenic than deep lakes. During the warm season, a warmer layer develops on top of a cold layer. The cold layer becomes depleted of oxygen as it is cutoff from the atmosphere by the warm layer. This leads to the mobilization of arsenic. During episodic mixing events that can occur under night-time cooling of the upper layer, the Arsenic is transported to the lake surface where it is taken up by the organisms living there.
A schematic of the mechanism that explains why shallow lakes are more sensitive to shallow water pollution
with arsenic than deep lakes. During the warm season, a warmer layer develops on top of a cold layer.
The cold layer becomes depleted of oxygen as it is cutoff from the atmosphere by the warm layer.
This leads to the mobilization of arsenic. During episodic mixing events that can occur under night-time
cooling of the upper layer, the arsenic is transported to the lake surface where it is taken up by the
organisms living there.
Lakes in urbanized areas accumulate arsenic in their bottom sediments as a result of human activities, such as mining, smelting, and the application of arsenic-containing pesticides. If this arsenic ends up in the water column close to the surface, it can endanger lake ecosystems and human health. Shallow lakes are more susceptible to high arsenic concentrations in their waters than deep lakes, but the cause of this was unknown.
Fung et al. [2022] found the explanation by using a combination of dedicated observations of lake turbulence intensity, temperature, and concentrations of dissolved oxygen and arsenic. Understanding this mechanism will be highly beneficial in guiding measures to keep arsenic concentrations in shallow lakes at bay.
Arsenic, a toxic pollutant found in many urban lakes, can get taken up into the food web and make its way into fish and other animals consumed by humans. Arsenic has a larger impact on the food web in shallow lakes compared to deep lakes. To understand why this is the case, the authors carried out a 17-month field study in Lake Killarney, a shallow, urban lake in Washington, USA. In this paper, we examine the processes that control the movement of arsenic from the bottom to the surface of contaminated lakes. They found that more arsenic moved out of lake sediments into bottom waters when the lakebed sediment was warm and the lake was separated into layers of different density.
The frequency of lake mixing changed throughout the year and controlled how arsenic was distributed in the lake water. Highest arsenic concentrations in lake surface water occurred when the lakebed sediment temperature was elevated and the lake mixed frequently. This work clarifies the mechanisms that contribute to arsenic transport in shallow lakes and provides information needed to identify systems with conditions that lead to high levels of surface water arsenic.
The original working URL: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022WR032564
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