We tend to think positively about productivity. When viewing ourselves as individuals, or our national economy, or our cornfields, hayfields or apple orchards, we aim for high productivity. The higher the productivity, the more impressed we are.
There is a part of nature, though, where high productivity has a definite down side. The negative aspects of high productivity show up at times in our aquatic ecosystems - our streams, ponds, lakes, and even our oceans. The problem is caused by too much plant growth (i.e., algae and rooted aquatic plants) due to an excess of nutrients.
The outcome can be disastrous for fish and many other aquatic animals living in the water body. When the large amount of plant life dies, it is decomposed by microbes. The microbes multiply exponentially as they feed on the rich food supply of dead plant life, and in the process, use up the available oxygen that is dissolved in the water. The unfortunate outcomes are the deaths of fish and other animal species that are dependent upon this oxygen. While the process and outcome might not be as easy to envision as poisoning by a slug of toxic chemical that enters a stream in a chemical spill, suffocation due to oxygen depletion likely accounts for more annual fishkills than all of the toxic chemical spills combined.
The problem with oxygen depletion is widespread, and stems from too much nitrogen and phosphorus running off our land and entering our streams. We simply over-fertilize! We seek to achieve maximum yields in our corn and soybean fields, to have lush green lawns, and to have attractive golf courses. Unfortunately, some of the fertilizer that is applied to achieve these goals washes off into our streams, ponds and lakes. Some of it from the Corn Belt states even makes its way to the Gulf of Mexico, creating a "Dead Zone" there.
In the upper Midwest, the deaths generally occur silently during the winter months, often after a thick snow layer has developed on the ice. The ice prevents the normal exchange of gases between the air and water, and the snow reduces light penetration into the water, thereby reducing the amount of photosynthesis that might still be occurring. Photosynthesis produces oxygen, so this source of oxygen production becomes very limited or nonexistent. The whole problem and drama that has occurred becomes evident in the spring when the ice thaws, and dead fish float to the surface.
The problem of excessive nutrients and oxygen depletion is a challenging one to remedy, and will likely take some time. For the most part, think in terms of years rather than a single season. Some steps to take follow. First, we must learn to live with lower application rates of fertilizer. In other words, we should strive for maximum crop yields and attractive lawns with "just the right amount" of fertilizer, but not too much where some washes away each year. This might require a new mindset, with some experimentation and "risk-taking." If we can achieve this "right" level, it will save money for us as individuals, homeowners, farmers, and municipalities.
Secondly, aeration of small water bodies could prevent or reduce the severity of the problem. This step might actually show immediate results. Small windmill-powered aerators may serve to reduce the use of nonrenewable energy here.
Thirdly, if the water body is fairly small and the sources of nutrient inputs are known and limited, sediment dredging will remove nutrients, especially phosphorus, that are stored in the mud.
And fourthly, unmowed buffer strips of native grasses, flowers, and shrubs along the banks of streams, ponds, and lakes will capture the nutrients in runoff so that less will enter the water body.
Water bodies within city limits are tremendous resources for recreation and enjoyment by the public. Efforts to reduce the problem of winter fishkills will likely be very well received. Young and old will appreciate the efforts to have a healthy lake!