What Is Salinity?

The concentration of dissolved salts in water is referred to as salinity. The water in the oceans, which is about 3.5% salt by its weight, is extremely salty compared to fresh waters. For comparison, Otisco Lake, a lake also located in Onondaga County, has a salt content of about 0.03%, nearly 120 times lower than the ocean. Before the Solvay Process Company (later Allied-Signal) closed in 1986, the salt content of Onondaga Lake was unusually high, averaging 0.30%. This was 10-times greater than Otisco Lake.

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“Natural” Salt Contributions

Some Central New Yorkers may believe that most of the lake’s salt concentration results from natural inputs from nearby salt formations. This may seem plausible considering that the eastern and southern shores of Onondaga Lake supported a flourishing salt mining industry in the 1800’s. Scientific measurements of the salt concentrations in the lake and tributaries following the closure of the soda ash facility established that earlier assessments of “natural” salt contributions to Onondaga Lake were greatly overestimated. However, it is important to understand that the salt mined in Syracuse during the 19th century was taken from springs and wells located near the lakes shore, not from the lake water. Approximately 6 million pounds of salty wastes, made up of sodium, chloride and calcium were discharged daily to Onondaga Lake from the soda ash facility before it closed.

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Salinity Decrement

The chloride concentration, the most important component of salinity to Onondaga Lake, has decreased from 1600 milligrams per liter to less than 400 milligrams per liter since the closure of the Allied soda ash facility. The salt content of the lake is presently about 0.10% by weight, a three-fold reduction since the soda ash facility closed.

Solvay Waste Beds

The salinity level of the lake is still artificially high because salty wastes are still entering Onondaga Lake from the Solvay waste beds located along Nine Mile Creek. The waste beds contain by-products of the company’s soda ash production. Elimination of continued salt pollution inputs from waste beds would result in reductions in the chloride concentrations of the lake to less than 250 milligrams per liter. Without this loading, the total salt content of Onondaga Lake could approach 0.05%, which is much closer to the levels of other freshwater lakes in the area.

Impacts of High Salinity

The discharge of salt and other wastes associated with the production of soda ash has had far-reaching impacts on Onondaga Lake and the adjoining Seneca River system. The lake’s elevated salinity undoubtedly reduced the diversity of its aquatic life. High concentrations of calcium discharged to the lake from soda ash production caused massive quantities of calcium carbonate to accumulate on the lake bottom. The Seneca River, a moving body of water that ordinarily should not stratify throughout the year, also experiences chemical stratification as a result of receiving denser, salty water from Onondaga Lake.

These deposits have accelerated the rate at which Onondaga Lake is filling in and eliminated habitats suitable to support a normal near-shore biological community. Because salty water is denser than fresh water, high salt loadings also altered the natural stratification cycle in Onondaga Lake. The stratification in both the lake and the river contributes to a decline in the oxygen levels in both bodies of water.