Effects of pulp and paper mill effluent on fish: a temporal assessment of fish health across sampling cycles.

The Canadian environmental effects monitoring (EEM) program is a regulated, cyclical, industry-funded program designed to determine whether receiving water impacts exist when a mill is in compliance with its discharge limits. The results from three cycles of the fish monitoring program (1992 to 2004) are available from over 200 surveys of fish compared between sites located upstream and downstream of pulp and paper mill effluent outfalls. Previous meta-analyses have shown a national average response pattern across cycles characterized by an increase in endpoints measuring energy storage and growth and a decrease in a reproductive endpoint, consistent with a response of nutrient enrichment in combination with some form of metabolic disruption. Although the national average pattern of effects was temporally consistent, there was some variability in the magnitude of effects among cycles. Questions were raised as to whether the intercycle variability was due to changes in effluent quality or due, at least in part, to other factors. The present study compares responses over the first three cycles, and shows that the choice of sentinel species is likely to be a major contributing factor to the variability in observed effects. Subset analyses using studies from mills that used the same sentinel species across cycles reveal fairly uniform responses and little evidence of significant improvements in overall fish health from cycles one to three. However, a meta-analysis using 1991 data collected from 10 mills before the implementation of the EEM program and data from the same mills collected during cycles one to three of the program reveal significantly reduced effects on relative liver weight and potential improvements in other endpoints.

Dealing with heterogeneous regression slopes in analysis of covariance: new methodology applied to environmental effects monitoring fish survey data.

Analysis of covariance (ANCOVA) is a powerful statistical method which incorporates one or more covariates into the analysis to reduce error associated with measurement. ANCOVA (modeling response as a function of fish size) is frequently used to analyze environmental effects monitoring (EEM) fish survey data. In approximately 12% of fish survey data sets taken from cycles 1 to 3 of Environment Canada's EEM database for pulp and paper mills, the standard assumption of parallel regression slopes is not met. For the first three cycles of the EEM program, these data sets were classified as indicating a mill effect, but for the most part were excluded from subsequent analyses aimed at quantifying the effect. We present two different methods for initially dealing with data sets that exhibit heterogeneous slopes so that they can be analyzed using the parallel slope model. The first method identifies data sets where heterogeneous slopes are forced by a few high-influence observations. The second approach identifies data sets where a model with heterogeneous slopes is statistically, but not practically, significant: with a high coefficient of determination for the parallel slope model. These new methodologies are applied to EEM pulp and paper data sets and about 55% of cases with heterogeneous slopes can be described by a parallel slope model. We also discuss a third method that can be used to describe mill effects when regression slopes remain heterogeneous even after applying the above two methods, enabling comparison with a critical effect size. These new methodologies could benefit the EEM program by enabling more data sets to be incorporated into meta-analyses and be used to make more equitable mill monitoring decisions in the future.

A review of potential methods of determining critical effect size for designing environmental monitoring programs.

The effective design of field studies requires that sample size requirements be estimated for important endpoints before conducting assessments. This a priori calculation of sample size requires initial estimates for the variability of the endpoints of interest, decisions regarding significance levels and the power desired, and identification of an effect size to be detected. Although many programs have called for use of critical effect sizes (CES) in the design of monitoring programs, few attempts have been made to define them. This paper reviews approaches that have been or could be used to set specific CES. The ideal method for setting CES would be to define the level of protection that prevents ecologically relevant impacts and to set a warning level of change that would be more sensitive than that CES level to provide a margin of safety; however, few examples of this approach being applied exist. Program-specific CES could be developed through the use of numbers based on regulatory or detection limits, a number defined through stakeholder negotiation, estimates of the ranges of reference data, or calculation from the distribution of data using frequency plots or multivariate techniques. The CES that have been defined often are consistent with a CES of approximately 25%, or two standard deviations, for many biological or ecological monitoring endpoints, and this value appears to be reasonable for use in a wide variety of monitoring programs and with a wide variety of endpoints.

Effects of arsenic speciation and low dissolved oxygen condition on the toxicity of arsenic to a lotic mayfly.

The influence of site-specific conditions on contaminant bioavailability and toxicity to benthic invertebrates is a key consideration in the environmental risk assessment process. This is particularly relevant for contaminants with complex speciation chemistries, such as arsenic. The present study addressed uncertainties regarding arsenic toxicity to a mayfly (Baetis tricaudatus) under low dissolved oxygen (DO) conditions characteristic of many contaminated sites. Arsenic toxicity (arsenite, As(III); arsenate, As(V)) to mayfly nymphs was assessed under two DO scenarios (68 and 84% saturation). Arsenic speciation ratios were determined during testing to confirm the nature of arsenic exposure. The present study found that As(III) was more lethal and bioaccumulated to a greater degree in B. tricaudatus compared to As(V), but the sublethal toxicities of the two arsenic species were similar. Nymph growth and development were significantly inhibited after 12 d of exposure to both 1 mg/L of As(III) and As(V). Exposure to arsenic under low DO conditions (6.5 mg/L, 68% saturation) did not significantly affect As(III) or As(V) toxicity and bioaccumulation over 12 d. The DO level of 6.5 mg/L, however, appeared to be marginally lethal to B. tricaudatus. Results indicate that the Canadian arsenic criterion for the protection of aquatic life (5 microg/L) is protective of B. tricaudatus and is low enough to accommodate differences in arsenic toxicity because of the interconversions between As(III) and As(V). These findings provide insight regarding the toxicity and speciation of arsenic under DO conditions considered to be low for this lotic mayfly species and representative of existing conditions at mine sites in northern Canada.

SAFETY FACTORS OF TROPICAL VERSUS TEMPERATE LIMPET SHELLS: MULTIPLE SELECTION PRESSURES ON A SINGLE STRUCTURE.

A comparison of the safety factors of tropical and temperate limpet shells in the eastern Pacific yielded two results of significance. A safety factor was defined as shell strength/maximum tenacity, where maximum tenacity (force required to detach foot) determines the maximum prying force that a crab or bird predator can exert on the shell. 1) On average, shell strength and foot tenacity for the tropical limpets were twice those for the temperate limpets. In contrast, the average safety factors for the two groups were approximately equal. This comparatively narrow range of safety factors was due to a highly significant association of greater shell strengths with greater foot tenacities. The implication of this result is that selection has acted to closely link the mechanical performances of these two rather independent structures, the shell and the foot. 2) The presence of an additional class of predators which feed on the tropical limpets was reflected in the safety factors of their shells. Whereas the shells of both tropical and temperate limpets are exposed to predator-induced prying forces, the shells of the tropical group are also exposed to lateral crushing forces generated by fish predators. This additional selection pressure was associated with several deviations from a regression of safety factor versus variability in shell strength which had been calculated previously for the temperate limpets. As predicted, the magnitudes of these deviations were correlated with the degree of exposure to this additional selection pressure. Hence, the presence of more than one selection pressure appears to have influenced the precision with which the shells of these species have become adapted to a single selection pressure. The use of safety factor analysis provides a very useful methodology for identifying additional selection pressures or adaptive constraints on biological structures.

CRAB PREDATION ON LIMPETS: PREDATOR BEHAVIOR AND DEFENSIVE FEATURES OF THE SHELL MORPHOLOGY OF THE PREY.

The feeding behavior of rocky intertidal crabs in the tropical and temperate eastern Pacific was studied in relation to specific mechanical properties of the shells of their limpet prey. A series of laboratory experiments, involving direct observations, records of shell remains, and measurements of the forces generated by a feeding crab, showed that by far the most common feeding technique was to pry the margin of the limpet shell away from the substratum. The pattern of deformation in models of limpet shells subject to a similar prying force indicated (1) that the greatest stress on the shell was at the point of force application at the shell margin and (2) that the thickness of the shell margin contributed more to shell strength than did thickness in more apical regions of the shell. Measurements of the strength of real shells provided further support for this latter conclusion. In addition, the strength of foot attachment, which sets the maximum prying force that the shell can experience, closely paralleled shell strength. This linkage between foot tenacity and shell strength appeared to be maintained via the degree of allometry between foot area and the thickness of the shell margin. The potential for a particular predator feeding behavior to lead to selection for a defensive feature in shell morphology should be a function, not only of the frequency of occurrence of attacks, but also of the frequency of successful attacks. In particular, for selection to occur, some individuals must survive an attack so that they may pass on to their off spring the defensive feature that enabled survival. Compared to other crab feeding techniques, prying attacks on limpets occurred frequently and with low success. These data support the hypothesis that selection to resist prying forces has been an important feature in the evolution of limpet shell morphology.