The Aging Of Lakes (1971)

man's interference with his environment is causing critical changes in our valuable Water Resources one major pollution problem is the increasing nutrient content in freshwater lakes when first formed Lakes are usually nutrient poor or oligotrophic the water is clear as it contains little suspended material or algae But as time passes natural aging occurs and Lakes become nutrient-rich or utopic lakes become choked with sediment and living and decaying plants as layers of sediment and dead plants increase in depth The Edge Community gradually encroaches out into the shallow water over thousands of years Lakes evolve into bogs or marshes then into Meadows and even forests there are two main causes of Lake aging one is sediment washed into a lake from its tributaries as well as from the Lake's own Banks this erosion and deposit of sediment goes on continuously even this clearl looking water is carrying some sediment the second factor is an increase in dissolved nutrients such as phosphorus nitrogen and carbon these nutrients cannot be seen But the plant life they nourish can this increase in the amount of nutrient in a lake is called nutrification the green yellow or brown tint in water is caused by algal blooms when these plants die they contribute to Lake aging nutrients are continuously recycled so that more plants grow die and decompose using more and more of the oxygen in bottom Waters consequently species of fish with higher oxygen requirements are unable to survive they are replaced by species with lower oxygen requirements as the amount of dissolved oxygen continues to decrease carp and other rough fish replace more desirable species slow urif can be beneficial in increasing the productivity of a lake but in many cases urif is accelerating at an alarming rate this can be detected by measuring transparency and dissolved oxygen content as ufic progresses transparent Y lessens and dissolved oxygen decreases in the bottom Waters Blooms of algae cause taste odor water filtration and other problems the increased rate of urif seems to be directly related to the growth of man's population around Lakes this graph shows that the population around Lake Michigan has steadily increased since 1840 there has been a corresponding increase in dissolved solids in the lake a similar correlation exists in the other Great Lakes the conclusion is obvious man substantially contributes to and speeds up the natural aging process domestic sewage contributes large amounts of nutrients such as phosphorus detergents have been a major source additional phosphates come from far Farm wastes and fertilizers washed from [Applause] Fields utopic conditions caused by industrial pollution are being reported worldwide in large cities where most land has been paved or built on little rain soaks into the ground raindrops pick up dust soot pollen and gases from the atmosphere oil grease animal wastes and other debris as well are washed away in most large cities the same sewer that carries raw sewage from homes and offices to the sewage treatment plant is also used to carry off storm water when heavy rains occur sewage treatment plants cannot handle the extra load so raw sewage is Ed to lakes or Rivers along with the [Applause] rainwater The Accelerated input of nutrients speeds up urif foration and upsets the ecological balance algae and other plants grow profusely bacteria and chemicals flushed into the water use up dissolved oxygen fish and other animal life die a lake transformed into a smelly unsanitary mess is often said to be biologically dead in truth this water is very much alive biologically there are astronomical numbers of algae and a wide variety of decomposers some fish that can tolerate low oxygen levels still survive a tragic result of accelerated aging is the loss of one of man's most valuable [Applause] resources many communities and government agencies are turning their efforts to reducing nutrification to slow down the aging process here a lake is being dredged to remove nutrient-rich sediments which have clogged its use the sediment and other debris are pumped onto land where they are used as landfill some nutrients can be removed from a lake by cutting and removing the weeds in which they are contained after harvesting the weeds might be a future source of fertilizer or cattle food this lake is being pumped out and the highly nutritive waters are being spread out on the surrounding land the lake will refill itself from underground Springs thus getting a fresh start in another effort artificial irration is being tried to increase dissolved oxygen content compressors furnish the air which is piped to several underwater Outlets far out in the lake turbulence caused by The Escape of air increases the dissolved oxygen content of the bottom Waters this community's lake is small but highly prized here people are contributing their time to clean out years of accumulated debris later the lake will be drained so that its bottom can be covered with black plastic sheeting weighted with gravel this will help keep the nutrients trapped [Applause] below all of these efforts should help slow ufic but they are treating its symptoms not its causes the only long range solution is preventing man-made pollutants from entering our Lakes commonly used secondary treatment of sewage removes only part of the nutrients until treatment methods are improved the best solution would be to divert sewage away from Lakes as early as 1900 to reduce the problem of waterborne disease such as typhoid from contaminating its water supply Chicago constructed Lux to reverse the flow of the Chicago River this diverted sewage wastes from Lake Michigan and has kept Lakefront Waters relatively clean treated sewage and storm drainage now flow into a natural and artificial river system where Continuous Flow and mixing can better handle the incoming wastes Seattle Washington and surrounding towns dumped sewage into Lake Washington for many years the nutrient Rich sewage caused a tremendous growth of slimy algae the lake became unsafe to swim in and unpleasant for boating beginning in 1957 new networks of pip P lines and sewage treatment plants were built to divert the waste water away from the lake and into the offshore Waters of the ocean Lake Washington is a good example of how even a very large lake can be rehabilitated from high utopic conditions but even though the treated wastewaters of Chicago Seattle and most other cities are piped elsewhere they still carry high concentrations of nutrients into rivers and oceans a third stage of sewage treatment is needed to correct cor this condition in this tertiary treatment plant solids that remain after regular secondary treatment are removed by Sand Filtration and micro strainers various means can be used to remove dissolved nutrients oxygen is put back in the Water by bubbling air through it the treated water now ready for discharge from the plant meets the standards of the federal water quality Act of 1965 five sludge a byproduct of sewage treatment plants cannot be dumped into streams but it can be used as a natural fertilizer this land reclamation project demonstrates how nutrients contained in sludge can convert unused land into fertile crop bearing Farm areas flood control reservoirs are a way of retaining storm Waters until they can be released on a regulated basis following the storm deep underground tunnels such as this one being built in Chicago will be able to hold back millions of gallons of storm water that would otherwise flood basements and wash untreated wastes into Lake Michigan much needs to be learned about how man's activities affect ufic here are sites of nuclear power plants built or proposed on Lake Michigan alone how will the discharge of heated water thermal pollution from these plants affect Lake aging while all lakes are destined to age and die natural nutrification is a slow process usually taking thousands of years for even the shallow small lakes we can reduce man's contribution to ufic by applied research and Technology if we will expend the effort and money what works in one Lake and its surrounding area might not work elsewhere each lake has its own problems Lakes are a prized resource of man but each lake is an entity with its own ecology its problems must be dealt with accordingly for