National Assessment of Pulp and Paper Environmental Effects Monitoring Data: Findings from Cycles 1 through 3

Three primary benthic invertebrate community response patterns were observed in Cycle 2 (Lowell et al. 2003). These are illustrated in Figure 9, which shows expected changes in abundance, taxon richness and community structure with changing effluent quality (pulp mill effluent effects on invertebrates reviewed in Lowell et al. 1995, 2000; Chambers et al. 2000; Culp et al. 2000; Lowell and Culp 2002). In this context, “effluent quality” refers to that experienced by organisms exposed in the field, as distinguished from effluent effects measured under controlled conditions in the laboratory. The x-axis progresses from better quality effluent and less deleterious effects on the left to poorer quality effluent and more deleterious effects on the right. More deleterious effects may also be associated with past historical effects (such as the smothering effects of fibre mats generated over many years of mill operation).

Figure 9 : Predicted response patterns for benthic invertebrate communities (Lowell et al. 2003).

In general, nutrient enrichment (or eutrophication) increases from left to right, along with increasing toxicity or smothering effects (Fig. 9). Nutrient enrichment can often be measured at lower effluent concentrations than toxicity, and toxic effects are often masked by eutrophication at low to medium concentrations. Mild eutrophication is typified by increases in both total abundance and taxon richness. Progressing to the right, moderate eutrophication is typically associated with lessened increases in taxon richness, although further increases in abundance may still occur. More pronounced eutrophication is commonly associated with decreases in taxon richness, even while abundance is still greater than that found in reference areas. Finally, decreases in both taxon richness and abundance are typically a sign of overall inhibitory effects, such as toxicity or smothering.

In the EEM program, changes in invertebrate community composition are measured by changes in the Bray-Curtis index of dissimilarity. The value of this index usually increases with poorer quality effluent, reflecting changes in community structure (particularly community composition). This is illustrated at the bottom of Figure 9. Evenness similarly measures changes in community structure and typically decreases (or sometimes increases) with poorer quality effluent. However, it should be emphasized that changes in community composition are not always tied to changes in total abundance and taxon richness, as there are many different ways in which benthic communities may be affected in the field. Due to complex direct and indirect effects (e.g., substitution of more sensitive species by less sensitive species), effluent exposure may lead to pronounced effects on community composition without large effects on abundance or taxon richness, and vice versa.

The national average response pattern in Cycle 2 was consistent with one of mild to moderate eutrophication, as indicated by increases in abundance and no national average change in taxon richness (although subgroups of mills showed either significant increases or significant decreases in taxon richness) (Fig. 10; Lowell et al. 2003). Note that Figure 10 focuses on control/impact mill data, the most commonly used design in the EEM program. This allowed direct comparisons among all four endpoints (calculation of the Bray-Curtis endpoint for gradient mills requires highly site-specific information that was not readily available at a national scale; Lowell et al. 2003).

Figure 10 : Control/impact grand means for Cycles 2 (n = 62) and 3 (n = 55). Error bars represent 95% confidence intervals.

In Cycle 3, the national average response pattern was similar to that observed in Cycle 2, although some shifts in the degree of response were also observed (Fig. 10; grand means averaging data across habitats on a national basis). Average abundance showed no change between cycles. In Cycle 3, however, there was a significant decrease in taxon richness in exposure areas relative to reference areas, indicative of a possible shift toward more pronounced eutrophication relative to Cycle 2 (mostly due to a response shift in freshwater depositional habitats; see below). As with abundance, there was also a high degree of overlap between cycles for the evenness and Bray-Curtis endpoints, particularly for the control/impact mills. Including data (not shown) from the lower number of mills using the gradient design had little effect on the overall response patterns shown in Figure 10, except for a shift in evenness slightly to the right in Cycle 2 and slightly to the left in Cycle 3. A decrease in evenness in exposure areas relative to reference areas (significant for gradient mills in Cycle 3, but not observed in Cycle 2) is a fairly commonly observed effect of stressors on benthic invertebrate communities.

In Cycle 2, distinct differences in response patterns were observed among habitat types, and similar differences were also seen in Cycle 3 (Fig. 11). The control/impact and gradient data are combined in Figure 11, given that the Bray-Curtis endpoint is not included and in order to provide a larger number of comparisons for the less commonly used habitat types. In both cycles, erosional river habitats exhibited increases in abundance and at least a tendency towards increases in number of taxa, indicative of mild to moderate eutrophication.

Figure 11: Abundance and taxon richness, by habitat, for Cycles 2 (C2) and 3 (C3). Error bars represent 95% confidence intervals. Number of studies for: river-erosional (C2 = 34; C3 = 21), river-depositional (C2 = 21; C3 = 23), Lake (C2 = 7; C3 = 9), estuary (C2 = 8; C3 = 10), marine (C2 = 13; C3 = 12).

In marine and estuarine habitats, taxon richness exhibited significant decreases during both cycles (Fig. 11). In marine habitats, abundance showed a significant decrease in Cycle 2, but was not significant in Cycle 3. A similar slight shift to the right was seen in estuarine habitats, perhaps reflecting a lessening of effects measured in marine-type habitats in Cycle 3. The high degree of overlap between cycles makes any firm conclusions premature, however.

In freshwater depositional habitats (river-depositional and lakes), abundance showed similar increases during both cycles. In Cycle 3, however, taxon richness was significantly decreased in exposure areas relative to reference areas in these habitats (this was not the case in Cycle 2). This is suggestive of a shift toward more pronounced eutrophication in these habitats during Cycle 3. This also led to the overall shift in the taxon richness grand mean in Figure 10.

As was also found for the fish survey, the overall benthic response patterns were fairly similar between Cycles 2 and 3. The abundance, Bray-Curtis and (for control/impact mills) evenness grand means all showed a high degree of overlap. There were, however, some shifts in the degree of response in some habitat types that may have resulted from a number of possible causes, as discussed in section 8.