WATER QUALITY IMPACTS AND INDICATORS OF METABOLIC ACTIVITY OF THE ZEBRA MUSSEL INVASION OF THE SENECA RIVER1

ABSTRACT: The conspicuous shifts in summertime values of common measures of water qualify that have persisted for 10 years (1993 to 2002) in the Seneca River, New York, as a result of the zebra mussel invasion are documented. Resolution of patterns in time and space is supported by water quality monitoring that extends back to the late 1970s. Patterns are evaluated to describe the stability of impacts and quantify metabolic activity of the invader. The water quality impacts that have persisted unabated for 10 years since the invasion are the most severe documented for a river in North America. Changes in summer median conditions since the invasion include: (1) a 16‐fold decrease in chlorophyll concentration (Chi), (2) a 2.5‐fold increase in Secchi disc transparency, (3) a 17‐fold increase in soluble reactive phosphorus concentration, (4) a 3.7‐fold increase in total ammonia concentration, (5) a greater than 25 percent decrease in dissolved oxygen (DO) concentration, and (6) a decrease in pH of 0.55 units. The strength of these signatures has been driven by anthropogenic influences that include upstream nutrient loading and morphometric modifications of the river, and the functioning of Cross Lake, through which the river flows. This hypereutrophic lake sustains dense zebra mussel populations and related water quality impacts in the river downstream of the lake outflow by acting as a source of veligers and suitable food for this bivalve. Evidence is presented that levels of metabolic activity of the zebra mussel in this river have been resource limited, manifested through increased consumption of Chl and DO with increased delivery of these constituents in the lake's outflow.     

The use of algae to control heavy metals in the environment

Aqueous effluents from a lead mining and milling operation located in southeastern Missouri, USA, caused a degradation of stream quality despite treatment by a large tailings pond. The receiving stream was choked with algal mats which accumulated unexpectedly large amounts of manganese, lead and zinc. A wastewater treatment system was designed to utilize algae and benthic macrophytes to remove metals from the tailings pond effluent. The system has proved successful and water quality in the receiving stream has been improved to drinking water standards.Experiments were conducted to understand more fully the phenomenon of heavy metal accumulation by algae. Radionuclides (²¹⁰Pb,²⁰³Hg,⁶⁵Zn,¹⁰⁹Cd) were used in conjunction with commercially available microculture apparatus to screen several species of algae for heavy metal accumulation. It was found that all species of algae studied concentrated mercury, green algae were more efficient accumulators of cadmium than blue-green algae, one alga (Chlamydomonas) proved best at removing lead from solution and no alga studied removed zinc.     

Effects of food-level acclimation on digestive enzyme activities and feeding behavior of Calanus pacificus

A recent hypothesis in the zooplankton literature states that zooplankton acclimate to ambient food concentrations such that higher digestive enzyme activities and, consequently, higher maximum ingestion rates are achieved at higher food levels. To test this hypothesis, adult female Calanus pacificus, collected from the main basin of Puget Sound, Washington, USA, in August 1979 and May 1982, were conditioned for 2 wk at different concentrations of the diatom Thalassiosira weissflogii (=fluviatilis). Ingestion rates and the activity of the digestive enzymes laminarinase, maltase, and cellobiase were measured periodically during acclimation and in a block-designed feeding experiment at the end of acclimation. Consistent with the hypothesis, maximum ingestion rate and digestive enzyme activity were positively correlated. However, in contrast to the hypothesized mechanism, this result arose because both maximum ingestion rate and digestive enzyme activity were negatively correlated with food concentration during acclimation. The enhanced ingestion of copepods following long-term (12 to 14 d) acclimation to low food is similar to that previously described for short-term (e.g. 1 d) starvation. It might be energetically optimal for copepods experiencing a patchy food environment to maintain higher levels of digestive enzymes at low food concentrations in order to exploit high concentrations of food when encountered.     

Differences in accumulation of PAHs and metals on the leaves of Tiliaxeuchlora and Pyrus calleryana

The accumulation of substances associated with PM2.5 [polycyclic aromatic hydrocarbons (PAHs) and metals] on leaves of Pyrus calleryana (pear) and Tiliaxeuchlora (linden) along an urban road was investigated. These species have similar leaf morphology and were exposed to the identical environmental conditions. The accumulation of both PAHs and metals per leaf area was significantly higher on linden leaves than on pear leaves.     

Testing the field of dreams hypothesis: functional responses to urbanization and restoration in stream ecosystems

As catchments become increasingly urban, the streams that drain them become increasingly degraded. Urban streams are typically characterized by high-magnitude storm flows, homogeneous habitats, disconnected riparian zones, and elevated nitrogen concentrations. To reverse the degradation of urban water quality, watershed managers and regulators are increasingly turning to stream restoration approaches. By reshaping the channel and reconnecting the surface waters with their riparian zone, practitioners intend to enhance the natural nutrient retention capacity of the restored stream ecosystem. Despite the exponential growth in stream restoration projects and expenditures, there has been no evaluation to date of the efficacy of urban stream restoration projects in enhancing nitrogen retention or in altering the underlying ecosystem metabolism that controls instream nitrogen consumption. In this study, we compared ecosystem metabolism and nitrate uptake kinetics in four stream restoration projects within urban watersheds to ecosystem functions measured in four unrestored urban stream segments and four streams draining minimally impacted forested watersheds in central North Carolina, U.S.A. All 12 sites were surveyed in June through August of 2006 and again in January through March of 2007. We anticipated that urban streams would have enhanced rates of ecosystem metabolism and nitrate uptake relative to forested streams due to the increases in nutrient loads and temperature associated with urbanization, and we predicted that restored streams would have further enhanced rates for these ecosystem functions by virtue of their increased habitat heterogeneity and water residence times. Contrary to our predictions we found that stream metabolism did not differ between stream types in either season and that nitrate uptake kinetics were not different between stream types in the winter. During the summer, restored stream reaches had substantially higher rates of nitrate uptake than unrestored or forested stream reaches; however, we found that variation in stream temperature and canopy cover explained 80% of the variation across streams in nitrate uptake. Because the riparian trees are removed during the first stage of natural channel design projects, the restored streams in this study had significantly less canopy cover and higher summer temperatures than the urban and forested streams with which they were compared.     

Estimating the grazing impact of marine micro-zooplankton

This paper describes a dilution technique for estimating the micro-zooplankton grazing impact on natural communities of marine phytoplankton. Experiments performed in coastal waters off Washington, USA (October, 1980), yield estimates of micro-zooplankton impact equivalent to 6 to 24% of phytoplankton standing biomass and 17 to 52% of production per day. Indirect evidence suggests that most of this impact is due to the feeding of copepod nauplii and tintinnids; in contrast, non-loricate ciliates, comprising 80 to 90% of numerical abundance, appeared to contribute little to phytoplankton mortality.Contribution No. 1237 from the School of Oceanography, University of Washington, Seattle, Washington 98195, USA