Laurel Creek Watershed Monitoring Pilot Study

Benthic Invertebrate Water Quality Component

David R. Barton and Christine M. Boston
Department of Biology
University of Waterloo


Benthic invertebrates are organisms without backbones that live on or in the bed of a stream or lake, including worms, leeches, clams, snails, crayfish and insects. The use of these organisms as monitors of water quality is convenient and economical (Olive et al. 1988) and can improve the interpretation of water quality monitoring that was once based solely on chemical and physical data (Dynes 1960, Lenat et al. 1980). Biological monitoring is especially powerful under conditions of toxic, intermittent or mild organic pollution and habitat alteration where changes in water quality are not easily detected by chemical analyses.

Such simple indices can be very useful, but the amount of information revealed by the benthic fauna increases with sampling effort and closer identification of the animals, so the design of a benthic invertebrate monitoring program depends on the kinds of changes which need to be detected. Discrimination between streams which should be capable of supporting brook trout and those which clearly are not, is simple and inexpensive; assessment of the effects of urban development and any remedial efforts requir ed of developers demands greater effort. Decisions about the final design of a monitoring program must balance costs and objectives, and can best be made if the initial conditions in the watershed are known. A detailed baseline survey will identify areas which have desirable habitat and water quality, those which are degraded and the stream reaches where changes occur. The general nature of any stresses on the system can be described on the basis of the kinds of animals found at individual sites.

Sixteen sampling locations were selected within the western part of the Laurel Creek watershed to document baseline conditions and to determine the overall state or health of the basin (Figure 1). Sites were selected to represent all major sub-basins; det ermine the impact of impoundments; determine the effect of different stages of urban development, establish current conditions in the western portion of the basin; and assess the overall state of the basin. Five additional reference sites were selected on reaches of forested first and third order streams to determine the benthic invertebrate assemblages in "healthy" or undisturbed areas. The data collected from these reference sites were used to augment an existing reference database developed over the pa st 20 years. The results of this baseline survey will be used to design future monitoring programs for the Laurel Creek basin.


When an intensive survey effort is impractical, it is best to conduct the baseline survey during the most stressful season of the year in order to assess the least favourable conditions in the basin. Therefore, sampling took place on 16 August 1996. Sampl es were taken upstream of road crossings, except at Sites 3, 12 and 13. We used qualitative methods described by Barton (1996) which are similar to those of Lenat (1988) and Verdonshot (1992). A kick net (243 µm aperture mesh) was used to collect material from all microhabitats (riffles, pools, margins, macrophytic and trailing vegetation, leaf packs, undercut banks) in proportion to area occurrence. The material was then washed in the net to remove fine sediment and mix the material from each microhabita t. Larger stones and coarse detritus were discarded and a portion (about 400 ml) of the material retained by the net was preserved in 10% formalin. The total time required to collect each sample was about 15 minutes and all samples were taken in one day.

In the laboratory, each sample was emptied into a 100 Am aperture net, washed to remove most of the formalin, then examined under a dissecting microscope and at least the first 200 animals were removed to 70% ethanol for identification. Additional animals were removed until no obviously different taxa were found. Any remaining unsorted residue was scanned for large rare animals which were added to the sorted material. It took, on average, about 3 hours to sort the samples in this manner.

Invertebrates were identified and enumerated at the lowest practical taxonomic level using existing keys and literature. Identification required I to 4 hours per sample, depending on the variety of animals present.

The results were summarized for each station as:

  1. Number of EPT taxa (Lenat 1988),
  2. Score for Hilsenhoff's Biotic Index (BI) (Hilsenhoff 1987), and
  3. Percent Model Affinity (PMA) (Novak & Bode 1992; Barton 1996).

The number of EPT should be high at undisturbed sites and decrease in proportion to increasing stress (e.g. siltation, nutrient enrichment or pesticide inputs). BI is calculated as the weighted average of the "tolerance" scores (based on distributions wit h respect to organic pollution in riffles of Wisconsin streams) of the species in a sample. Higher scores on BI reflect increasing organic loadings.

PMA expresses the degree of similarity between the composition of a sample and that of an expected community (the average composition of samples from physically similar reference sites collected at the same time of year). These expected communities have b een calculated from collections made throughout southern Ontario. In order to decide whether or not a site is significantly impacted, the lower confidence limit about the mean similarity of the samples contributing to the reference community is subtracted from the site PMA. Negative values indicate a significant difference from reference conditions. This also partially standardizes PMA values and facilitates comparisons among physically different streams. PMA is well suited for long-term monitoring becaus e it easily detects change toward, or away from, reference conditions.


The 16 samples from sites on Laurel Creek and its major branches yielded a total of 176 taxa of benthic invertebrates (list available on request). The most diverse group was the Chironomidae (64 taxa); Annelida (25), Ephemeroptera (18), Coleoptera (16),an d Trichoptera (14) were also well-represented. Of the total, 86 could be considered to be rare, occurring at only I or 2 sites; 14 were found at more than half of the sites so could be considered very common. The most commonly collected taxa were the chir onomids Conchapelopia (found in all 16 samples) and Cryptochironomus (15), the caddisfly Cheumatopsyche (13), the snail Physa ( 11) and the riffle beetle Optioservus fastiditus (11). Crayfish are common in Laurel Creek a nd its tributaries, and were collected at 9 sites.

The number of taxa sorted from individual samples ranged from 30 at Site 5 to 60 at Site 10 (Table 1). There was a strong correlation between the numbers of individuals identified and numbers of taxa. This suggests that if more indiv iduals were sorted and identified from any given sample, the number of taxa found there would increase. This is true to some extent, but we stopped sorting at about 200 animals only if no obviously new kinds were being found. The numbers of taxa per sampl e in Table 1 give a good indication of the relative diversity of the fauna among sites, but number of taxa is sensitive to sampling effort and provides no indication of the kinds of animals that are present.

EPT scores suggest that Clair Creek at site 16 is the most degraded stream reach that we sampled (Table 1). Sites 12 (Monastery Creek), 3 (Laurel Creek below Columbia Lake), 8 and 9 (Beaver Creek) also yielded small numbers of EPT, w hile large numbers were found at Sites 10, 6, 7, 14 and 1. It is worth emphasizing that no stoneflies were found at any site in the Laurel Creek basin.

The absence of stoneflies suggests at least some environmental degradation has occurred at all sites. This agrees with the assessment based on HilsenhoffÕs Biotic Index: the lowest score at any site, 5.03, would be evaluated as "good water quality with so me organic pollution" (Hilsenhoff 1987). The score of 8.58 at site 16 indicates very poor water quality. It should be emphasized, however, that the values of HBI reported here are not strictly comparable with those listed by Hilsenhoff (1987) because of d ifferences in sampling methods and the inclusion of molluscs and worms in calculating the index for the Laurel Creek survey. (When HBI was calculated using only arthropods (toe original method for this index), the worst sites appeared to be slightly less polluted and water quality ranged from "good"' to "fairly poor".) HBI scores were highest at sites 16, 12 and

The level to which animals are identified influences PMA scores, as shown in Table 1. In general, the sensitivity of PMA decreases as taxonomic categories are broadened. That is, the accuracy of site assessments increases with increa sing effort in identifying the organisms. However, accurate identification of many aquatic organisms to species is not possible with the taxonomic information available today, so identification to genus may be satisfactory.

In most cases the relative impact at a site was similar whether assessed at the level of species or genus, but overall water quality appeared to be somewhat better at the genus level. Exceptions were Beaver Creek site 9, Monastery Creek site 12 and Clair Creek site 13. Sites 5,7, 14 and 15 appeared to be in substantially better condition when assessed at the level of genus rather than species. Samples from the mainstream of Laurel Creek above Columbia Lake were not significantly different from reference c ommunities, nor were those from sites 7, 8 (Beaver Creek), 14 (Monastery Creek) and 15 (Clair Creek). The negative PMA score for Beaver Creek site 9 is somewhat surprising and deserves further investigation. The apparent improvements at the most downstream sites on Clair and Laurel Creeks are very encouraging.

Table I

Summary of the results of the benthic invertebrate survey of Laurel Creek
and major tributaries conducted 16 August 1996.

Site# Animals# of TaxaEPTBiotic Index PMA - SpeciesPMA - GenusPMA - Order

Overall Assessment

All of the indices used in this study suggest that conditions in Laurel Creek are fairly good upstream of Columbia Lake. However, the complete absence of stoneflies (Plecoptera) is cause for concern as this group should be present, and was well represented at site 6 only a few years ago. The fauna at site 5, just below Laurel Creek Reservoir, is strongly influenced by the reservoir (as shown by the greater abundance of filter-feeding caddisflies and blackflies) and may be expected to be more negatively impacted in warmer, drier years. Columbia Lake and the smaller reservoirs on the University of Waterloo campus appear to be major contributors of suspended material and organic enrichment, the effects of which are clearly evident at sites 2 and 3. The relative improvement downstream at site I is very encouraging: the benthic fauna included a substantial proportion of mayflies and filter-feeding caddisflies, but also a relatively large number of pollution tolerant worms and isopods. This is consistent with moderate organic enrichment, most of which is probably attributable to waterfowl and runoff of fertilizer from lawns.

Of the major tributaries, Beaver Creek appears to be in the best condition. Site 9 deserves closer scrutiny. The physical appearance of the stream at this point gives no evidence of recent disturbance but the sediment in the streambed is very loose and the benthic fauna is quite different from the expected community. Casual observations during several visits to Beaver Creek suggest that there are significant inputs of sediment downstream of site 7.

Monastery Creek in the vicinity of site 12 appears to be significantly degraded. The fauna is characteristic of areas where substantial amounts of fine sediments have been trapped. Most of the animals are also very tolerant of low oxygen, so there is also a possibility of organic pollution. Future monitoring should reveal whether this is a temporary result of recent construction in the immediate area, or an ongoing problem.

Evidence of the potential for recovery from disturbance during residential development can be seen in Clair Creek. Most of Clair Creek appears to be significantly degraded, especially adjacent to the newly developed area above Fischer-Hallman Road (site 16), but a much more balanced benthic community was found at Westmount Road.

figure 1


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Hilsenhoff, W.L. 1987. An improved biotic index of organic stream pollution. Great Lakes Entomologist 20: 31-39.

Hynes, H.B.N. 1960. The Biology of Polluted Waters. Liverpool University Press, Liverpool, UK.

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Lenat, D.R., L.A. Smock and D.L. Penrose. 1980. Use of benthic macroinvertebrates as indicators of environmental quality. In: D.L. Worf (ed.), Biological Monitoring for Environmental Effects. Lexington Books, Lexington, MA: p.97- 112.

Novak M.A.. and Bode R.W. 1992. Percent model affinity: a new measure of macroinvertebrate community composition. Journal of the North American Benthological Society 11: 80-85.

Olive, J.H., J.L. Jackson, J. Bass, L. Holland, and T. Savisky. 1988. Benthic macroinvertebrates as indexes of water quality in the Upper Cuyahoga River. Ohio

Journal of Science 88:91-9X. Verdonshot P.F.M. 1992. Macrofaunal community types of ditches in the province of Overijssel (The Netherlands). Archiv fur Hydrobiologie, Supplement 90: 133-158.

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