Sewers and lake health: What is the connection?

From Cazenovia Town Councilor Moran

The importance of the plant nutrient phosphorus is well-established as the single most important factor affecting the quality of the lake; algae will grow until the supply of phosphorus in the water is used up. Most rooted aquatic plants, including Eurasian watermilfoil, draw their nutrition from the lake’s bottom muds. Consequently, any long-term strategy for lake management must focus on phosphorus.

Sources of phosphorus

There are three main pathways for phosphorus to reach Cazenovia Lake. First, about one-third of the annual phosphorus input washes into the lake from the watershed (the lands surrounding the lake where water flows toward the lake). The town and village have been working to reduce this source — by banning phosphorus-containing lawn fertilizers and by requiring better controls of runoff during construction. The town is working with the Madison County Soil and Water Conservation District to identify “hot spots” of erosion in the watershed and design preventative measures to keep the soils on the landscape.

The second major source of phosphorus is seepage of groundwater containing effluent from on-site wastewater disposal systems (septic systems). The lake soils have a finite capacity to bind phosphorus and other materials in wastewater. We estimate that about one-half of the lake’s phosphorus input comes from shoreline septic systems. Water testing has confirmed that groundwater affected by septic tank leachate is reaching Cazenovia Lake.

In addition, indicators of wastewater impacts (salts and optical brighteners from detergents) are not present in the lake in areas served by sanitary sewers. Bacteria levels are variable, depending on weather and waterfowl, but are elevated adjacent to regions with a high density of septic tanks.

The third significant source of phosphorus is internal-phosphorus that entered the lake long ago and is continually recycled from the bottom muds back into the water column during the summer. Eventually, this source will diminish as the external sources (from the watershed and septic leachate) are reduced. Some lake communities have turned to a chemical treatment to help seal the bottom sediments and prevent this flux. This remedial measure works best once the external sources have been reduced to the extent possible.

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