Part One: Lake Turbidity
Every Coves resident knows that the water in our ponds is murky at best. But what is the source of this problem? Is agricultural runoff the culprit? What about the carp who dig holes in the sediment to lay their eggs? To begin to understand this complicated issue, we must first explore the differences between lakes that are cloudy due to suspended sediment (i.e. turbid lakes) versus lakes that are cloudy as a result of an overgrowth of algae (i.e. eutrophic lakes).
Ponds that are turbid have relatively high amounts of suspended sediment floating in the water. Usually, the particles that float throughout the water column are made up of mud and clay. However, suspended materials may also include sand, algae, plankton, microbes and other substances. As pond water becomes more turbid, several changes may occur to the water. Because suspended particles absorb more heat, the water may become warmer, resulting in a lower concentration of dissolved oxygen (i.e. DO) in the water. This phenomenon occurs because warm water holds less DO than cold. Low concentrations of DO can lead to the death of aquatic life because (almost) all animals breathe oxygen.
Another change that may occur with increasing turbidity is that the suspended particles may block sunlight from penetrating the water. Without sunlight, plants and plant-like organisms cannot convert sunlight and carbon dioxide to oxygen. This reduces the DO even more and can lead to the collapse of food webs. Turbid water can also harm fish by clogging their gills, reducing their resistance to disease, lowering their growth rates, and affecting egg and larvae development. When these particles finally settle, they can smother fish eggs and benthic invertebrates.
By now you may have guessed that the water in the Coves is very turbid. In general, sources of turbidity include soil erosion, waste discharge, urban runoff, eroding stream banks, large numbers of bottom feeders which stir up bottom sediments, and excessive algal growth. In our next post, we will explain how this excessive algal growth can lead eutrophication, the second cause of cloudy water.