ZOOMIX · Zooplankton Generated Mixing in Stratified Lakes

The aims of this work are to directly measure turbulence from vertical migrations of zooplankton, quantify how much mixing the migrations cause, and determine the importance of this mechanism in lakes. Answering these questions will help us better understand the physical drivers of water quality in lakes, environments upon which society depends for many key ecosystem services.Summer time stratification in lakes suppresses vertical mixing of dissolved substances such as oxygen, nutrients, or pollutants. This can lead to adverse water quality affects such as anoxic bottom waters that result in fish kills, trapping of nutrient-laden waters in the photic zone creating ideal conditions for nuisance algal blooms, and reduced dilution of wastewaters and nonpoint source pollution.Processes that generate turbulence below the water surface increase the mixing of the stratified waters. Recent work in the ocean has suggested that daily vertical migrations of zooplankton might be a significant source of mixing comparable with winds and tides. Zooplankton, which are significant elements of lake ecosystems as well, swim between deeper darker regions of the water column, where they stay during daylight to avoid predation, and the phytoplankton-rich surface layer, where they go to feed during the nighttime.Because the background mixing in lakes is less than in the ocean and migrations happen twice daily, vertical migrations of zooplankton may be a significant source of turbulence and mixing in the lake environment. The work proposed here would be the first in situ measurements of zooplankton-generated turbulence in lakes. In addition to tackling recent issues of debate in the science community, this work will enhance understanding of mixing in lakes, a key issue in managing our water resources for public health and recreation.