The biology of the zebra mussel is reviewed as it relates to water‐quality problems in rivers. A relationship between population densities of the zebra mussel and their respiration demands for oxygen is developed, which can be used to support the analysis of the impact of zebra mussel infestation on the oxygen resources of streams and rivers. Dramatic changes in the water quality of the Seneca River, N.Y., a major tributary to Lake Ontario, have been brought about by zebra mussel infestation. These changes are documented from 3 years of monitoring data. The infestation converted the Seneca River from a turbid, phytoplankton‐rich, nutrient‐depleted system, with nearly saturated oxygen concentrations, to a river with high clarity, low‐phytoplankton concentrations, enriched in dissolved nutrients, with greatly undersaturated oxygen concentrations. The degradation of oxygen resources was severe enough to cause violations of New York State standards for daily minimum and daily average concentrations for a number of days in the late summer of 1993. The associated loss in the waste assimilative capacity of the river is confounding waste discharge management and planning efforts in the river basin. This form of degradation is expected for other systems as the zebra mussel infestation spreads. The impact is expected to be greatest in rivers and streams with high concentrations of phytoplankton, large areas of rock substrate, and limited reaeration capacity.

Phosphorus release rates were measured on intact sediment cores collected from the major depositional basin of Onondaga Lake, a dimictic, calcareous, hypereutrophic system in Syracuse, N.Y., U.S.A. Release experiments were conducted under a matrix of redox and pH conditions to investigate the importance of Ca- and Fe-related physicochemistry on sediment cores collected seasonally, i.e., during the spring, summer, fall, and winter periods. Strong seasonal variation in P release was observed, with rates ranging from ~3 to 38 mg P·m-2·day-1. This variation is attributed to changes in redox status and P concentration gradients at the sediment-water interface. An oxidized microlayer at the sediment-water interface partially inhibits sediment P release under isothermal, well-mixed conditions in the spring and fall. Phosphorus trapped in the oxic microlayer (sorption) is freed when the microlayer is chemically reduced at the onset of anoxia and high P release rates are observed. The oxidized microlayer serves to regulate seasonality in rates of sediment P release but does not influence long-term sediment-water exchange. It is proposed that the long-term P release process is best represented by a time-weighted annual average rate, calculated here to be ~10 mg P·m-2·day-1.

SMITH, M. E., DRISCOLL, C. T., WYSKOWSKI, B. J., BROOKS, C. M., and COSENTINI, C. C. 1991. Modification of stream ecosystem structure and function by beaver (Castor canadensis) in the Adirondack Mountains, New York. Can. J. Zool. 69: 55-61. Stream ecosystem structure and function were studied in an acidic second-order Adirondack Mountain stream system with current beaver activity. Acid-neutralizing capacity, pH, dissolved organic carbon, ~e~+ , and ~n~+ values were elevated and SO$-, Aln-, and dissolved oxygen concentrations were decreased following water transport through the beaver impoundment. Upstream acidity was primarily ameliorated by SO$-and Fe retention in the impoundment during the low-flow summer period. High Fe and Al sediment concentrations were present during low-flow periods immediately downstream of the beaver dam. During the high-flow period, Fe and A1 concentrations were highest 0.25 km downstream of the dam, owing to slow metal hydrolysis-oxidation kinetics during spring snowmelt. The immediate downstream site exhibited significantly lower invertebrate richness and diversity and collector-filterer, Plecoptera, and Trichoptera densities, but significantly higher total invertebrate, Diptera, Ephemeroptera, predator, and collector-gatherer densities. Significant differences were noted primarily during April and July. Our results indicate that beaver dams modify stream ecosystems longitudinally and temporally and ameliorate stream acidity. Current lotic ecosystem paradigms like the river continuum concept should incorporate "patch" occurrences such as those created by beaver.

Nitrite (NO−2) concentrations in the upper waters of N polluted Onondaga Lake, New York, are documented for the April through October interval for a 10‐yr (1989–1998) period. Inputs of NO−2 from a domestic waste treatment facility (METRO) and tributaries (4) to the lake are quantified for four of the years (1991–1994). The NO−2 concentrations measured in Onondaga Lake (e.g., annual maxima in the range 200–1000 mg N m 3) are some of the highest reported for lakes and rivers in the literature. These levels represent severe violations of toxicity standards. Annual average concentrations in the METRO effluent ranged from 412 to 1097 mg N m−3. The METRO load represented >90% of the total external NO−2 load to the lake. A mechanistic mass balance model for NO−2 and NO−3 is developed and applied for the lake to identify occurrences, and quantify the rates, of the first and second stages of nitrification. Nitrite is found to behave in a nearly conservative manner in the upper waters of the lake over the April to July interval. The progressive increases in concentrations over this interval have been largely in response to inputs from METRO. Major deviations from conservative behavior occurred for NO−2 in most years over the July to October interval as a result of the irregular operation of the two stages of the nitrification process. This has been manifested as large and abrupt changes in NO−2 concentration in the July to October interval. Potential factors responsible for the observed dynamics in nitrification and the NO−2 pool are considered.

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