Search

In Chesapeake Bay in the United States, decades of management efforts have resulted in modest reductions of nutrient loads from the watershed, but the corresponding improvements in estuarine water quality have not consistently followed. Generalized additive models were used to directly link river flows and nutrient loads from the watershed to nutrient trends in the estuary on a station-by-station basis, which allowed for identification of exactly when and where responses are happening. Results show that Chesapeake Bay's total nitrogen and total phosphorus conditions are mostly improving after accounting for variation in freshwater flow. Almost all of these improving nutrient concentrations in the estuary can be explained by reductions in watershed loads entering through 16 rivers and 145 nearby point sources, with the nearby point source reductions being slightly more effective at explaining estuarine nutrient trends. Overall, these two major types of loads from multiple locations across the watershed are together necessary and responsible for the improving estuarine nutrient conditions, a finding that is highly relevant to managing valuable estuarine resources worldwide.

This study compared four different statistical methods, involving six estimation procedures, for addressing censored left data in measuring temporal trends of eight different pyrethroids measured in sediment from a 10-year data set in a residential California stream (Pleasant Grove Creek). The statistical methods used were: the Kaplan–Meier (km) method; the robust regression on order statistics (ros using normal and log normal distributions rosln); the maximum likelihood estimation (mlen using normal and log normal distributions mleln); and a substitution method (sub) using ½ the detection limit. For five of the eight pyrethroids (bifenthrin, cyfluthrin, cypermethrin, lambda-cyhalothrin, and permethrin), the six statistical methods generally agree, with one exception, that the data set exhibit significant declining trends. In the case of bifenthrin, the slight disagreement among statistical methods only occurred for the mleln estimate that did not show a significant declining trend, whereas the other five methods did. For deltamethrin, esfenvalerate, and fenpropathrin, all six statistical methods were in agreement showing no significant trends. Possible reasons for declining sediment concentrations of pyrethroids in Pleasant Grove Creek are urban label changes effective in 2012–2015 that reduced residential use, variable annual rainfall, and more responsible homeowner use based on outreach/education programs.

Traveling water screens (TWSs) modified for fish protection can be used at power plant cooling water intakes to reduce the injury to and mortality of impinged fish. Existing biological efficacy data show that postimpingement survival is highly variable by species and has improved over time as screen designs have incorporated more fish-friendly features. Data with the improved screen designs were largely absent for many freshwater species prior to this evaluation. The mortality, injury, and scale loss rates of 10 species of freshwater fish impinged and recovered with a modified Ristroph-style TWS were evaluated in a laboratory flume. Fish were impinged at a 0.3-, 0.6-, or 0.9-m/s approach velocity. Over 13,000 fish were tested in more than 100 replicates during the study. Mortality rates did not exceed 5% for any species and velocity tested. Despite a general trend toward increasing mortality at higher velocities, velocity was only a significant factor in the mortality of Bluegills Lepomis macrochi...

The Ohio River fish community was sampled three times (June, August, and October) in 2005 by electrofishing near 17 power plants encompassing nearly the entire length of the Ohio River (river kilometer 82–1,527). Six 500-m zones were electrofished at each plant. Using a generalized additive model, we examined this data set of 306 electrofishing samples to determine how the abundance of 31 taxa varied over the length of the river. We also looked for trends in several measures of community health (catch rate, species richness, index of biotic integrity, and modified index of well-being). Of the 31 taxa examined, all but three showed longitudinal differences over the course of the river. Based on the patterns for the 31 taxa and 5 community measures, we assigned each taxon or measure to one of seven classes. The largest class included 10 taxa that declined steadily in abundance from upriver to downriver. All community measures followed a similar pattern except that each measure increased near the do...

To reduce ballast water-borne aquatic invasions worldwide, the International Maritime Organization and United States Coast Guard have each proposed discharge standards specifying maximum concentrations of living biota that may be released in ships’ ballast water (BW), but these regulations still lack guidance for standardized type approval and compliance testing of treatment systems. Verifying whether BW meets a discharge standard poses significant challenges. Properly treated BW will contain extremely sparse numbers of live organisms, and robust estimates of rare events require extensive sampling efforts. A balance of analytical rigor and practicality is essential to determine the volume of BW that can be reasonably sampled and processed, yet yield accurate live counts. We applied statistical modeling to a range of sample volumes, plankton concentrations, and regulatory scenarios (i.e., levels of type I and type II errors), and calculated the statistical power of each combination to detect noncompliant discharge concentrations. The model expressly addresses the roles of sampling error, BW volume, and burden of proof on the detection of noncompliant discharges in order to establish a rigorous lower limit of sampling volume. The potential effects of recovery errors (i.e., incomplete recovery and detection of live biota) in relation to sample volume are also discussed.

An impingement survival study was conducted to determine 48-h survival of fish impinged on a modified rotary disk screen equipped with fish protection features. The rotary disk screen was installed for a technology evaluation at the cooling-water intake structure of the North Omaha Station located on the Missouri River in Omaha, Nebraska. Hatchery-raised fish and native fish collected from the Missouri River were released in batches into the rotary disk screen bay and collected with a system that was constructed to recover fish from the screen's vacuum system. That system was designed to remove fish from the rotary disk screen and return them to the river. Screen performance was assessed in April and August, representing spring and summer environmental conditions. The 48-h survival rates of hatchery-raised fathead minnow Pimephales promelas, channel catfish Ictalurus punctatus, and bluegills Lepomis macrochirus and a group of mixed native species approached 100%. Survival rates were not statistic...

Impingement abundance monitoring was conducted at 15 Ohio River power plants as part of the Ohio River Ecological Research Program. Impingement rates were compared with environmental, power plant design, and operational factors that varied within and among the power plants, including water temperature, river flow and stage, change in flow and stage during the sampling events, volume of cooling water pumped, design pumping capacity, approach velocity, location of the intakes along the river, intake type, and intake configuration. The study demonstrated similarities in species composition, size distributions, and seasonal patterns over nearly 1,400 river kilometers of the Ohio River, results that were consistent with studies conducted nearly 30 years earlier. Dramatic annual differences in impingement rates during the 2-year study indicated that impingement is largely a function of the recruitment levels of juvenile gizzard shad Dorosoma cepedianum, threadfin shad D. petenense, and freshwater drum ...

We examined the influence of landscape alteration and in situ stream habitat variables on brook trout Salvelinus fontinalis by using a landscape-scale, space-for-time substitution analysis and a smaller data set that tracked long-term changes in land use over time. Forested land cover within a catchment was the overall best landscape-scale predictor of brook trout occurrence at a given site; measures of impervious land cover and urbanization were also important predictors. Brook trout were almost never found in watersheds where impervious land cover exceeded 4%, as assessed from the 2001 National Land Cover Dataset (2001 NLCD); the single exception was in a stream that displayed consistently low water temperatures. Landscape-scale analyses indicated that increases in water temperature and erosion were associated with increasing percentages of urbanization and imperviousness and decreasing percentage of forested land cover. Three of six brook trout populations that were followed over time were ext...

We examined methods for verifying whether or not ships have performed mid-ocean ballast water exchange (BWE) on four commercial vessels operating in the Pacific and Atlantic Oceans. During BWE, a ship replaces the coastal water in its ballast tanks with water drawn from the open ocean, which is considered to harbor fewer organisms capable of establishing in coastal environments. We measured concentrations of several naturally occurring chemical tracers (salinity, six trace elements, colored dissolved organic matter fluorescence and radium isotopes) along ocean transects and in ballast tanks subjected to varying degrees of BWE (0-99%). Many coastal tracers showed significant concentration changes due to BWE, and our ability to detect differences between exchanged and unexchanged ballast tanks was greatest under multivariate analysis. An expanded dataset, which includes additional geographic regions, is now needed to test the generality of our results.

Cooling water intake systems have the potential to adversely impact aquatic organisms though entrainment and impingement (impacts referenced under 316(b) of the Clean Water Act), yet the loss of individual fish does not necessarily mean that a population will suffer a significant decrease in number. The results of utility sponsored studies on Ohio River fish populations provide strong evidence of positive changes in the fishery due to water quality improvements. Despite these improvements, a simulation is needed to determine if a reduction in 316(b) fish losses would result in higher or similar fish population levels. Electrofishing data collected at seven power plant locations from 1981 to 1998 will be used for the population assessments. Potential 316(b) impacts on Ohio River fish populations will be modeled using site specific 316(b) data and a Leslie matrix model. The theoretical maximum population for various fish species, with and without 316(b) impacts, will be compared and the probabilistic risk that fish populations will fall below the threshold for species survival will be assessed. Historically, EPA has allowed 316(b) to be implemented on a case-by-case basis, however, the utilities believe that the first step in assessing potential adverse environmental impacts is to assess the condition of the affected fish populations.

Choosing the best 316(b) mitigation option is a daunting task. Decision analysis (DA) provides an objective framework that can be used to choose among several mitigation strategies where there are multiple objectives and numerous uncertainties. This paper has two objectives: (1) to illustrate the use of the DA framework for making a 316(b) decision (using the Chalk Point Power Station as a case study); and (2) to show that DA is also useful for quantifying the benefits of a previous decision. The Chalk Point case, resolved in 1990, centered around the mitigation of adverse environmental impacts of a cooling water intake structure (CWIS) as a result of fish and blue crab losses associated with impingement and entrainment. Barrier nets and fishery enhancement programs were used to mitigate the losses. We compare the costs and benefits of the mitigation options actually employed to those of other options. The costs and benefits were estimated numerically using standard DA methods. Valuations and probabilities were derived largely by professional judgment based upon the original Chalk Point 316(b) studies and ongoing monitoring. DA indicated that the optimal strategy and expected utility were functions of the weighting of environmental benefits relative to cost.

The objectives of this study were to use both parametric and probabilistic approaches to analyze water column concentrations of both salinity (24,845 measurements) and boron (13,028 measurements) from numerous investigations conducted in the San Joaquin River watershed from 1985 to 2002 to assess spatial and temporal trends and determine the probability of exceeding regulatory targets during both the irrigation and non-irrigation season. Salinity and boron concentrations from 26 mainstem and tributary sites were highly correlated based on this 17 yr data set. Generally, salinity and boron concentrations were higher in winter/spring and lower in summer/fall; higher concentrations of both constituents were reported in tributary sites when compared with the mainstem San Joaquin River. Approximately half the sites showed showed a negative correlation between flow and both constituents. Concentrations of both salinity and boron were somewhat variable with flow conditions for the other sites. Both linear and curvilinear trends were inconsistent over time. The salinity 90th centiles for the 26 sites ranged from 143 to 7,559 micros cm(-1) with the highest 90th centiles in tributary sites. Probabilistic analysis of salinity 90th centiles by year for five sites with extensive data showed a significant decrease over time at two sites and no significant trend for the other three sites. The probability of exceeding the salinity targets during either the irrigation (700 microm cm(-1)) or non-irrigation (1,000 micros cm(-1)) season was greater than 19% for all but three sites. The boron 90th centiles for the 26 sites ranged from 0.41 to 13.6 mg L(-1) with the highest 90th centiles from tributary sites. Probabilistic analysis of the boron 90th centile values by year for the five sites with the most extensive data showed a significant decrease over time at two sites and no significant trend for the other three sites. The probability of exceeding the boron target during the irrigation season (0.80 mg L(-1)) and non-irrigation (1.0 mg L(-1)) season was greater that 18% for all but three sites. Results from this analysis have important regulatory implications as targets for both salinity and boron are frequently exceeded at various sites in the San Joaquin River watershed.

Provisional physical habitat indices were developed and validated for Maryland Coastal and Non-Coastal Plain streams using variables (commonly called metrics) that best discriminated reference and degraded conditions based on biological, chemical and land use data from the 1994-97 Maryland Biological Stream Survey (MBSS). These habitat indices contained variables that described structural, hydrological, vegetative and aesthetic components of stream habitat. Variables with the best discriminatory power for Coastal Plain streams were: instream habitat, velocity/depth diversity, pool/glide/eddy quality, embeddedness, maximum depth and aesthetic rating. Physical habitat variables with the best discriminatory power for Non-Coastal Plain sites were: instream habitat, velocity/depth diversity, riffle/run quality, embeddedness, number of rootwads and aesthetic rating. The overall classification efficiency for index validation was 76% for both indices pooled over both strata. Scaled physical habitat index values (0-100) for both strata identified nearly twice as many good sites (31%) as very poor sites (16%). More than half the Maryland sites were in the poor to fair range (53%).

To assess the possible impacts caused by cooling-water intake system entrainment and impingement losses, populations of six target fish species near power plants on the Ohio River were modeled. A Leslie matrix model was constructed to allow an evaluation of bluegill, freshwater drum, emerald shiner, gizzard shad, sauger, and white bass populations within five river pools. Site-specific information on fish abundance and length-frequency distribution was obtained from long-term Ohio River Ecological Research Program and Ohio River Sanitation Commission (ORSANCO) electrofishing monitoring programs. Entrainment and impingement data were obtained from 316(b) demonstrations previously completed at eight Ohio River power plants. The model was first run under a scenario representative of current conditions, which included fish losses due to entrainment and impingement. The model was then rerun with these losses added back into the populations, representative of what would happen if all entrainment and impingement losses were eliminated. The model was run to represent a 50-year time period, which is a typical life span for an Ohio River coal-fired power plant. Percent changes between populations modeled with and without entrainment and impingement losses in each pool were compared to the mean interannual coefficient of variation (CV), a measure of normal fish population variability. In 6 of the 22 scenarios of fish species and river pools that were evaluated (6 species × 5 river pools, minus 8 species/river pool combinations that could not be evaluated due to insufficient fish data), the projected fish population change was greater than the expected variability of the existing fish population, indicating a possible adverse environmental impact. Given the number of other variables affecting fish populations and the conservative modeling approach, which assumed 100% mortality for all entrained fish and eggs, it was concluded that the likelihood of impact was by no means assured, even in these six cases. It was concluded that in most cases, current entrainment and impingement losses at six Ohio River power plants have little or no effect at the population level.

We measured the salinity tolerance of eggs and larvae of yellow perch, Perca flavescens, from three Coastal Plain stream populations in Maryland and a Pennsylvania lake population during a series of continuous flow-through laboratory experiments. Fertilized eggs were incubated in freshwater (mean total hardness of 39.8 mg/liter as CaCO,) and three salinities (7-129o or parts per thousand) until hatching (15-17 days) or death. Yolk-sac larvae were exposed to freshwater and nine salinities (2-139k) for test periods of 5-8 days. The exposures were ramped; salinities were increased from freshwater to treatment conditions at an average rate of 2.7%o/h. Mean cumulative mortalities for Maryland eggs were 4.0% (freshwater), 16.7% (7%o), 28.5% (9%o) and 100% (129/,). The LT50 value for eggs exposed to 129o salinity was 139 h. Mean cumulative mortalities for Maryland larvae was 21.3% (freshwater), 0.0% (2%o), 2.0% (4 and 600), 4.0% (700), 0.0% (8 and 9%o), and 100% (12 and 13%o). Mean LT50 values for larvae exposed to the 12 and 139o salinity treatments were 73 and 50 h. Abnormal behavior was observed in groups of larvae exposed to salinities of 8-1300. Larvae from the Pennsylvania lake population exhibited cumulative mortalities of 18.0% (freshwater, 4 and 6%o) and 100% (8 and 10oo). LT50 values were 158 and 71 h for the Pennsylvania larvae exposed to the 8 and 10 oo salinity treatments. Abnormal behavior was observed in groups of Pennsylvania larvae exposed to salinities of 6-10%o. Pennsylvania larvae were slightly more sensitive to salinity changes than Maryland larvae; LC50 values were 6.3 and 9.1/, respectively. Our laboratory results suggest that yellow perch populations in Maryland Coastal Plain streams can tolerate a relatively wide range of salinities during the egg and early larval stages at mean temperatures of 10-13 C. These populations should be capable of successful reproduction in habitats that range from 0 to 6 or 7%o salinity.

Exponentially growing cultures of Thalassiosira fluviatilis Hustedt and Dunaliella tertiolecta Butcher were exposed to 4 min temperature shocks of 5° to 20°C above ambient (20°C). Photosynthetic carbon fixation, changes in in vivo fluorescence and fluorescence on the addition of the herbicide DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) were measured over the subsequent 24 h. The fluorescence ratio (R, DCMU-enhanced fluorescence/in vivo fluorescence) paralleled changes in photosynthesis over this period; both were significantly reduced (P < 0.05) by temperature shocks of +15° and +20° C, but +5° and +10° C treatments had no inhibitory effect on either relative to the control. The instantaneous response obtained with the fluorescence ratio indicates that the technique might be applicable to routine bioassay procedures and thus replace the time consuming methods now used for the estimation of 14C-incorporation and growth rates.

Fathead minnow ( Pimephales promelas ) 1-d post-hatch larvae, 12-d post-hatch larvae, and 4-wk post-hatch juveniles were exposed to combinations of acid and inorganic aluminum (Al) for 96 h in the laboratory. Life stages were exposed, under flow-through conditions, to four nominal pH levels: 4.5, 5.5, 6.5, 7.5 (control) and five nominal Al concentrations: 0 (control), 50, 100, 200, 400 μg/l in fresh water with a total hardness of 20–24 mg/l as CaCO 3 . Theoretical speciation of the measured total dissolved monomeric Al was performed in order to estimate the toxic forms of Al. The ranking of life stage sensitivities to acid alone was 1-d larvae, most sensitive, followed by 12-d larvae and juveniles. At pH 4.5, all three stages exhibited 100% mortality in all Al treatments and controls. At pH 5.5, 90–100% mortality occurred in all but the 50 μg/l Al treatment and the no Al control. At that pH, hydroxoid species of Al were the predominate forms of the total dissolved monomeric aluminum. At pH 6.5 and 7.5, Al was not toxic to the 1-d larvae and juveniles, but the mortality of 12-d larvae exposed to Al (predominately hydroxy species) ranged from 18 to 68% with no clear dose response.