The Ithaca Journal
April 12, 1999
Guest Columnist Nelson Hairston, Jr.
Frank H. T. Rhodes Professor of Environmental Science
College of Arts and Sciences Cornell University
The origins of Cayuga Lake's problems
BACK TO THE TOPThe New York Sate Department of Environmental Conservation has added southern Cayuga Lake to the, now famous, 303d list.
Although the legal and environmental significance of this listing that has been debated at length in this newspaper and elsewhere, the reasons for the designation are well known and relate to levels of nutrients and sediments present in the lake water.
While nutrients have received considerable discussion, the turbidity caused by sediments (particles of silt and clay suspended in the lake water) has received much less attention. It is the sediment that creates such unattractive murky brown water after storms and runoff from spring snowmelt.
It is also sediment accumulation in the near-shore region at Stewart Park that has long-time residents lamenting what they perceive as the worsening conditions in the lake. What are the origins of this problem?
The south end of Cayuga Lake, the area now occupied by Stewart, Treman and Cass Parks, was originally and naturally a large marsh. The shallow, muddy sediments that formed the substrate upon which marsh vegetation grew came from the silt and clay particles carried by the tributaries that flowed across the land surrounding the Ithaca area and into the lake: Fall Creek, Cascadilla Creek, and Sixmile Creek.
These particles came from a naturally eroding landscape and were trapped in the marsh where they accumulated. This process led very slowly to an addition of dry land at the shore - much of it now supporting the homes and business of Ithaca.
At the same time the deposited sediments extended the marsh edge out into the lake.
The southern Cayuga Lake marsh was filled in by Ithacans early in this century, first to make land for industrial development, and then later converted into the parks that we who live in the Ithaca area enjoy so much. But, the filling of the marsh did not stop the sediment from flowing down the creeks to the lake.
Indeed, farming and land development in the watershed no doubt substantially increased the rate of erosion. With no marsh remaining to trap the sediments, the particles now flow largely uninhibited into the lake.
When the velocity of the creek water is slowed by mixing with lake water, the sediments fall to the lake bottom, building up near the shores of Stewart and Treman Parks, and creating a large shallow shelf of mud.
Many long-time residents of the Ithaca area recall a wonderful period in the past when swimming was possible at Stewart Park.
There is an understandable tendency for these residents to think that swimming at this site was somehow the natural state, that the current condition is unnatural, and that this change must be someone's fault.
In reality, all that is occurring is the inexorable action of natural processes that began when the glaciers receded from the region some ten millennia ago: a marsh is being deposited at the south end of Cayuga Lake - by an accumulation of shallow sediments that will eventually, without our intervention, be occupied by aquatic vegetation such as sedges, rushes and cattails.
The erosion that is depositing these sediments is an accelerated version of the process that formed our beautiful gorges and waterfalls. Those who enjoyed swimming at Stewart Park were lucky.
They lived during the period of a few decades between the filling of the natural marsh and the point at which sediment accumulation at the edge of the park became so great that swimming was no longer possible.
The marsh is the natural condition. If the residents of Ithaca and Tompkins County don't like the marsh that is building off the shore at Stewart Park, then it will be necessary to fight back the forces of nature.
It is a decision that should be considered only with the knowledge that this really is the action that is being proposed: to keep the lake shoreline in an unnatural state that we as users of the resource prefer.
There is no question that unnaturally high erosion in and along the tributaries should be curtailed by good land-management practices. This will reduce but not stop the rate at which the marsh is being built.
We cannot, however, and I assume do not wish to halt farming, building new homes, schools and recreation sites in Tompkins County; some human accelerated erosion will always occur.
Natural erosion can be reduced by better watershed and channel management practices. Whatever our decision as a community, gravity will continue to make water flow down hill, natural erosion will continue, and sediments will continue to enter the lake and accumulate along the shore.
We can influence the rates, but at some level we have no choice but to accept the process.
