Invasion of Onondaga Lake, New York, by the zebra mussel (Dreissena polymorpha) following reductions in N pollution

Abstract

An initial failed invasion by the zebra mussel, followed by an abrupt shift to dense populations, is documented for polluted, hypereutrophic Onondaga Lake. The Lake is located in a region of New York subject to high infestation rates by the zebra mussel. Our analysis was supported by: 1) monitoring of multiple life stages of the zebra mussel, including veligers, pediveliger deposition, and adults in the lake and an adjoining source river over a 4-y interval, 2) a quantitative substrate survey of the lake’s nearshore zone, 3) in situ growth-rate experiments, and 4) long-term water-quality monitoring data for the lake. Despite the availability of appropriate substrate and food, near-optimal temperature and primary water chemistry requirements, and continuing inputs of veligers since the early 1990s, veliger concentrations (<0.2 individuals/L) and adult densities in the nearshore zone (<1 individual/m2) remained extremely low in the lake through 1998. This failure was caused by the toxic effects on early life stages from high lake concentrations of forms of N, particularly total ammonia (T-NH3) and free (unionized) ammonia (NH3), associated with discharges of a domestic wastewater-treatment plant (WWTP). The abrupt shift from extremely low to high densities in the summer of 1999 continued through 2000 (maximum of ∼65,000 individuals/m2), coincident with abrupt decreases in concentrations of T-NH3 and NH3 associated with increased treatment at the WWTP. Water-quality monitoring data suggested that summertime T-NH3 and NH3 concentrations of ∼2 and 0.05 mg/L, respectively, were adequate to prevent the development of dense zebra mussel populations in the lake. The establishment of dense populations of zebra mussels in Onondaga Lake may complicate the resolution of impacts/benefits of an ongoing rehabilitation program to remediate domestic waste inputs in the lake.