Allen P. Wiens

Effects of sediment addition on macrobenthic invertebrates in a Northern Canadian River

Two channels built into the Harris River, Northwest Territories were used to study responses of invertebrates to sediment addition. Sediment was added to one channel continuously for approximately 5 h. The other channel was used as a control. In August, 28.27 kg of sediment or 1.38 kg m−2 of channel bottom were added. Values for September were 35.88 kg or 1.53 kg m−2. As a result of sediment addition, numbers of macrobenthos drifting from the sediment addition channel (S) increased significantly over those drifting in the control (C) in August (= summer) and September (= fall). Total drift from S was > 3 times higher in August and > 2 times higher in September than from C. Significantly higher numbers of macrobenthos drifted in fall than summer. Numbers of macrobenthos drifting during sediment addition were significantly related to time in September but not in August, indicating a seasonal difference in temporal response to sediment addition. Two explanations are proposed for the response of the September community, as indicated by shape of a polynomial regression curve, to sediment addition. No significant difference existed in standing crops of macrobenthos in the substrate in C and S after sediment addition. Sediment addition caused (1) higher numbers of Oligochaeta and Simuliidae to drift in August and September; (2) higher numbers of Plecoptera and Ephemeroptera to drift in September but not in August; and (3) higher numbers of Hydracarina and Chironomidae to drift in August but not September. We suggest that future work try to relate amounts of settled rather than suspended sediments to quantitative responses of stream macrobenthos. We recommend that highway and pipeline construction undertaken in watersheds of Mackenzie Valley streams during the open-water period, resulting in sediment addition to these streams, should be done during summer rather than spring or fall, providing river discharge is adequate to transport the added sediment.

A method for subsampling unsorted benthic macroinvertebrates by weight

A simple method for subsampling unsorted benthic macroinvertebrates by weight is described for different types of samples obtained from lentic and lotic environments. It is especially useful for samples containing large amounts of filamentous algae that preclude the use of conventional subsampling methods. The method provided random dispersions of individuals in the original samples. Overall variability of the subsamples was low for artificial substrate and catastrophic drift samples. Variability was higher for regular drift samples, which had the lowest numbers of individuals of the three sample types. The method produced considerable savings in time spent sorting. Subsampling approaches for community level studies are discussed.

Effects of Crude Oil Contamination on Ephemeroptera in the Trail River, Northwest Territories, Canada

Artificial substrates were soaked in crude oil and placed in the Trail River, N.W.T. for periods up to almost 1 year. Ephemeroptera nymphs usually occurred in lower numbers, fewer taxa and lower diversity on oiled substrates than on unoiled substrates. Communities of nymphs were significantly different except for the substrates left in the river for the longest period (335 days). Numbers of Heptagenia (flavescens Walsh?), Stenonema vicarium (Walker), Ameletus sp. 1, and Baetis spp. decreased in response to the oil while numbers of Pseucdocloeon sp. 1 and Ephemerella aurivillii Bengtsson increased. Numbers of E. (bicolor Clemens?) and E. simplex McDunnough were unaffected. H. (flavescens?) should be the best indicator (reduced numbers) of low level contamination of aquatic systems by oil and petroleum products although S. vicarium (reduced numbers) and E. aurivillii (increased numbers) may also be useful. Responses of these three species to oil contamination are related to the presence of food and to quality of the substrate.

Peatland Chironomidae (Diptera): effects of flooding on emergence from Lake 979, Experimental Lakes Area, Ontario*

The experimental flooding of Lake (L) 979, a small wetland lake at the Experimental Lakes Area (ELA) in northwestern Ontario, provided an opportunity to study effects on the chironomid fauna emerging from the surrounding peatland. Nearby L632 was used as a reference system. The nature of the peatland chironomid fauna in L979 changed dramatically. Most true peatland species were eliminated by the flooding. They were quickly replaced by lacustrine species whose numbers emerging from the flooded peatland increased substantially. In contrast, qualitative and quantitative changes in emergence were minimal from the open-water zone of the lake and from L632. Intensive study of L979 and L632 revealed 12 species of true peatland chironomids in common with other peatlands at the ELA, and added another 18 species to the 37 peatland species already identified from previous studies at the ELA. Most of the 55 species have wide zoogeographic distributions, and probably occur in peatlands all across the boreal zone of Canada, but confirmatory studies are needed.