Trophic Status of Conesus Lake 2014: Long-term Trends in Lake Chemistry and the Plankton Community

Abstract

Conesus Lake, considered a eutrophic lake in the late 1960s (Mills, 1975) and one of the smaller of the Finger Lakes of western New York, is used for recreation and fishing and is a source of municipal water for several local communities. The shoreline area is densely populated with residences, primarily year-round homes. The upstream area is a mixture of agricultural land and mixed deciduous hardwood forests encompassing an area of 16,714 ha. In 1999 about half of the entire land use within the Conesus Lake watershed was and continues to be in agriculture. Much of the agriculture (~70%) is concentrated in the western subwatersheds of the lake (SOCL, 2002). In general, the watershed is characterized by slight slopes at the northern outlet and southern inlet areas and steeper slopes along the flanks and southern portion of the lake. There are numerous tributaries and rivulets that enter the lake (Forest et al., 1978) and account for large amounts of erosion and sediment that enter the lake system. For example, in August 2005, Stantec Consulting Services (2005) indicated that most of the 12 stream reaches visited were in an unstable state due to the heavy sediment supplies of the past and the related geomorphic adjustment. The New York State Department of Environmental Conservation (NYSDEC) listed Conesus Lake on its Priority Waterbody List (303d)(NYSDEC, 2013) due to elevated phosphorus levels and high oxygen demand. The DEC identified the lake as impaired for boating and bathing purposes, stressed relative to fishing and aesthetics, and threatened as a water supply. The Livingston County Planning Department reported the following problems as being critical to the degraded health of Conesus Lake: 1) weed growth and invasive species, 2) increased algae from phosphorus loading, 3) pathogens from animal waste, 4) pesticides from residential and agricultural sources, 5) increasing salts from deicing chemicals on impervious surfaces, and 6) erosion from various landuse practices and developments (SOCL, 2002). Since then, monitoring and management plans for land use have been recommended and/or updated (Makarewicz et al., 2008, 2012a,b; Makarewicz and Lewis 2009; CLWC, 2011) A major achievement 7 of long-term monitoring on Conesus Lake is the creation of a database that can be used as a tool to assess the trophic health of the lake over time. Measuring selected chemicals, such as phosphorus, and the transparency of water and determining the amount of algae (chlorophyll measured) in the water allow us to answer whether management practices have had any effect on the lake. The goal of this project was to update information on the water chemistry of Conesus Lake to determine if any progress has been made in improving water quality.