Looking at the Mirror, by Margaret H. Murphy, Ph.D.
Certified Fisheries Professional
Watersheds and Lake Health
Mirror Lake, the Chubb River, and the West Branch Ausable are all important waterbodies for the Village of Lake Placid and Town of North Elba and provide us and visitors places to fish, swim, and boat. Mirror Lake is the heart and soul of Village of Lake Placid. How often have you forgotten about the importance of this lake to our village and the surrounding area?
Watersheds
We all live in a watershed. What exactly does that mean? A watershed is the entire area of land that directs waterflow from rain and snowmelt to creeks, streams, rivers and eventually lakes and the ocean. Size can vary and watersheds can be defined at different levels depending on the specific area of interest. For example, if we look at the Mirror Lake watershed, from the outlet (near the beach), the watershed size is relatively small at 1.2 square miles. However, if we extend our boundary to where the Mirror Lake Outlet flows into the Chubb River less than half a mile downstream, we now encompass the Lake Placid lake watershed and the Chubb River watershed upstream of that point – 37.7 square miles. Finally, if we move that boundary to the mouth of the Ausable River at Lake Champlain we encompass 512 square miles. Why does this matter? Water flows downhill; what we do to our land within that watershed can add contaminants and pollutants, both solids and dissolved, to that waterbody. Maintaining the watershed in a natural condition allows for natural filtration, reducing what ultimately gets to the downstream point – for us – that is Mirror Lake.
Trees are Important in Watersheds
Part of maintaining the natural conditions in a watershed includes maintaining the vegetation, especially adjacent to streams and lakes. Trees provide many functions in a watershed such as:
- Shading along streams, rivers, lakes and maintaining cooler water temperatures
- Tree roots provide more stability to soils which reduces erosion along the lakeshore or streambank, as well as providing cover for fish and aquatic organisms
- Providing nutrients to water bodies in both leaf litter and organisms that fall into the water
- Filtering sediment from streams during storm events
- Removal of nitrogen and phosphorous leaching from adjacent land uses
- Habitat for many aquatic and wildlife species
- Reducing stream velocity and downstream flooding
As we lose trees and forest cover, by roads, parking lots, driveways, homes, and businesses, we are creating more impervious surfaces. An increase in the amount of impervious surfaces in a watershed leads to more runoff during rain events – what we call stormwater runoff. The volume of water in runoff is higher in watersheds with more impervious surfaces. Runoff moves the water faster, decreasing the amount of time it takes to get to the water body, and carrying more pollutants with it from the impervious surfaces (including nutrients and salt).
Stormwater Runoff
Increased peak flows, due to both impervious surfaces and climate changes, can lead to more flooding, stream bank erosion, a decline in water quality, and decreased fish habitat. Trees and forests can reduce storm water and protect water quality. Within a forested watershed, the tree canopy intercepts precipitation so less falls to the ground. Some of that water is evaporated and some is taken up by the tree. The average interception of rainfall by a forest canopy ranges from 10-40%, depending on the species, time of year, and rate of precipitation in each storm event. A single deciduous tree in an urban or suburban area can intercept 500-760 gallons of water per year; a mature evergreen tree can intercept more than 4,000 gallons per year. Leaf litter on the ground also can intercept water, with some of that evaporating. Rainfall can then be absorbed into the ground – which acts like a sponge – and helps recharge ground water. One study found the mean infiltration rate to the ground was reduced from 12.4 inches per hour to 4.4 inches per hour when a site was converted from forest to suburban turf (Kays 1980). Plants, especially woody plants, also protect water quality, by removing nutrients (nitrates and phosphates) and contaminants (such as metals, pesticides, solvents, oils and hydrocarbons) from soil and water. Limiting the amount of excess nutrients from reaching a water body reduces the potential for algal blooms, including harmful cyanobacteria (aka blue-green algae) blooms.
It’s important that we all remember we live in a watershed. What we do with our onsite water management can affect the entire watershed. We should be thinking about how to manage our own rainwater and snowmelt – and not sending it downstream for our neighbors to worry about. There are many technologies available including rain barrels and rain gardens. Other options include planting native trees and shrubs along shorelines and propery borders, reducing or eliminating fertilizers on lawns and gardens, and using permeable (e.g., stones, permeable pavers) driveway and road surfaces. The Mirror Lake Watershed Association is committed to maintaining the high water quality of Mirror Lake and the Chubb River, we welcome you to our meetings, held the second Monday of each month at 5:00 pm in the David Ackerman Room at the Beach House.