Protecting Connecticut Lakes
Gregory J. Bugbee
Department of Soil and Water; The Connecticut Agricultural Experiment Station
123 Huntington St.; P.O. Box 1106; New Haven,. CT 06504
Plant Science Day. August 5, 1998
Lakes and ponds are one of Connecticut’s most important natural resources. There are over 2000 lakes and ponds in the state. These bodies of fresh water provide recreation, wildlife habitat, drinking water, irrigation supplies, scenic vistas, and tranquil escapes. The major threat to our lakes and ponds is a process called eutrophication. Eutrophication is the gradual buildup of nutrients in surface water from natural and manmade sources. Unlike gardens and lawns, where nitrogen usually limits plant growth, the limiting nutrient in bodies of fresh water is usually phosphorus. Connecticut’s lakes and ponds are relatively young. Most were created during a retreat of the glacier which covered the area about 10,000 years ago. Since then, all have evolved to their current state through eutrophication. The presence of nutrients leads to the growth of aquatic plants and algae. Aquatic plants are not necessarily bad because they often provide habitat for wildlife. However, excessive aquatic vegetation becomes unsightly, interferes with recreation, and gradually turns the lake into a swamp. Our current peat bogs are ponds that filled in naturally without human intervention. Natural eutrophication can be accelerated with manmade nutrient inputs from industries, homes and agriculture.
In the mid 1970’s, The Connecticut Agricultural Experiment Station undertook a comprehensive study of the major lakes in the state. In all, 70 lakes were tested for a wide range of characteristics including clarity, alkalinity, phosphorus, and nitrogen. This data was correlated to land use in each lake’s watershed, and it was found that the least eutrophic lakes occurred where the watersheds were primarily forested whereas the most eutrophic lakes were situated in areas with greater urbanization. The critical nutrient responsible for the eutrophication was thought to be phosphorus.
In recent years my interest has focused on utilizing the information obtained in our past work to help solve problems in lakes and ponds brought to us by Connecticut residents. Dense areas of rooted aquatic plants and floating mats of algae are the most frequent problems I encounter. Because these organisms need nutrients to grow, the first step in trying to achieve long term reductions in aquatic vegetation is to determine if nutrients moving into the body of water can be reduced. Sources of nutrients can be municipal or industrial discharges, septic systems, fertilizers, decaying leaves, and even natural rainfall. Environmental legislation has resulted in a dramatic reduction of municipal and industrial discharges. I can say that I have yet to visit a lake or pond where these so called "point sources" were the likely problem. Most lakes and ponds in Connecticut are found in suburban environments. Homes along the lakeshore are common, and many were built prior to today’s strict zoning standards. Most homes on lakes are on small lots with substandard septic systems. It is therefore easy to assume that much of the eutrophication we see today is caused by leachate from septic systems and fertilizers used around the home. Of the dozens of lakes and ponds I visit each year I can rarely find a failing septic system. In fact, many lake associations and towns have required all lakefront homes to have their septic systems tested using colored dye. If leachate from the system is reaching a lake a plume of dye becomes visible. I have yet to see a septic system fail this test. Fertilizers are considered sources of nutrients and care must be given to not only minimizing their use, but maintaining unfertilized buffer zones near watercourses.
Although reducing nutrient inputs help in the long term, most lake owners desire quicker acting alternatives. Mechanical methods include hand or machine harvesting, and dredging. Dredging is the only alternative that can deepen a shallow lake and remove the nutrient rich sediment. I will be discussing research I have done on dredging later. Certain rooted weeds can be controlled biologically. A plant-eating fish called grass carp can be introduced into the lake, and good weed control can be achieved. Permits from the Connecticut Department of Environmental Protection (CTDEP) are needed because uncontrolled releases could jeopardize desirable aquatic plant habitats. A common technique for reducing weeds and algae is the use of aquatic herbicides such as copper sulfate. All applications of aquatic herbicides into water within the state are regulated by the CTDEP through permits. When used carefully these materials can minimize outbreaks of weeds and algae, however they do little to reduce the eutrophic state of the lake or pond. Some of my work involves helping lake owners choose the best herbicide, making sure it is applied properly and determining if an application can be effective for more than one year.
So the question I ask myself is what makes the lakes and ponds with problem vegetation different from those without problems. The most obvious difference is that waters with problems are shallow and generally have mucky bottoms. The muck is composed of the remains of the previous year’s aquatic vegetation and leaves from deciduous trees that fall on the surface water and sink to the bottom. As the muck decays, nutrients may be liberated into the water. I decided in 1994 to undertake research to compare the nutrient level of a eutrophic lake that had been dredged of all it’s muck to that of a similarly sized undredged lake. The first lake, Clear Lake, is typical of a small Connecticut lake with a mucky bottom. The second lake, Malleys Pond, was similar, however, the lake owners decided to have it drained and dredged in the 1980’s. In 1994, when the dredging was completed, the pond had an average depth of about 20 feet and a sandy bottom. I started testing the water from both lakes. We have tested the lakes every two weeks during the spring, summer and fall, from 1994 to present. Results of these tests were somewhat surprising. The clarity of the dredged Malleys Pond was better than the undredged Clear Lake, but only moderately so. The phosphorus level averaged lower in Malleys Pond than in Clear Lake by 6 parts per billion (ppb). In addition, Malleys Pond has had no problematic algal blooms or excessive rooted plants. The question arises, did the removal of nutrients by dredging result in the better water quality observed in Malleys Pond? Unfortunately, no water tests were done on Malleys Pond prior to the dredging, thus we have nothing to which we can compare the current test results. We know that the aquatic vegetation was so dense that nutrients must have been abundant. One clue to what is going on in the lakes is to look at the phosphorus (P) in the streams going in and the streams going out of each lake. We tested the stream going into Malleys Pond and found it to have an average P concentration of 24 ppb, while the P levels within the lake averaged 16 ppb. Because the water in the lake had lower levels than the inflow stream, the lake was probably accumulating P. The same trend occurred in Clear Lake, however, both the P level in its inflow stream and the P level in the lake water was on average 6 ppb higher than the levels in Malleys Pond. Thus, I could not conclude that dredging had appreciably reduced the level of P in Malleys Pond, but rather that the P level in the lakes is governed more by P level in their inflow streams. This suggests that particular attention has to be paid to reducing nutrients in the watershed that feeds our streams.
Please feel free to contact me if you desire assistance with your problems with lakes and ponds.