The diversity and composition of benthic macroinvertebrate assemblages in streams in the Mackenzie River system, Northwest Territories

Aquatic ecology;Arctic streams;Aquatic insects;Biology

Scott, Ryan William

University of Waterloo

关键词: Aquatic ecology;    Arctic streams;    Aquatic insects;    Biology;   

Others  :  https://uwspace.uwaterloo.ca/bitstream/10012/4984/1/Scott_Ryan.pdf

瑞士|英语

来源: UWSPACE Waterloo Institutional Repository

【 摘 要 】

Impending natural resources development and concern about the effects of climate change havespurred increased efforts to study and monitor aquatic habitats in the Mackenzie River system. Aspart of Environment Canada’s attempt to survey the system in advance of the construction of theMackenzie Gas Pipeline, benthic macroinvertebrates were sampled at 50 streams spanning thegeographical range of the Mackenzie system in the Northwest Territories, Canada, to assess spatialpatterns in diversity and assemblage structure and the environmental factors driving them. Replicated,quantitative D-net samples were collected during the late summer of 2005 through 2008, mostly atcrossings of the proposed pipeline route.373 macroinvertebrate taxa were recorded, mainly aquatic insects, which were identified tothe genus or species levels; other groups were identified to higher taxonomic levels. Ephemeropteraand Plecoptera diversity declined along a latitudinal gradient, while Trichoptera diversity declined inthe middle of the latitudinal range and rose towards the far north. Chironomidae (Diptera) increasedin diversity and abundance towards the far north, becoming dominant in the northern sub-arctic forestand lowland tundra of the Mackenzie Delta. Diversity, measured as the average generic richness perstream, correlated with a composite environmental variable representing stream size, but not muchelse; spatial trends in local generic richness were only apparent in the far north of the study area.Regional diversity was assessed using rarefaction curves and showed a clear decrease from south tonorth across the study area for most taxa; the major exception was the chironomid subfamiliesOrthocladiinae and Chironomini, the former being diverse throughout the study area and the latterincreasing in diversity on the tundra. Odonata, Hemiptera and Coleoptera were well-represented inthe south of the study area, but decreased sharply in diversity and abundance in the north; anothercommon order, Megaloptera, was entirely absent from the study area, as were crayfish.Community composition varied along a latitudinal gradient, with some species restricted tonorthern latitudes and many more species restricted to the southern areas. Composition varied byregion, as did the environmental factors that control it. Streams in the north of the system areconnected to hundreds of small lakes and tend to freeze in the winter, which increases habitatstability; assemblages in this region were characterized by relatively large chironomids that areusually associated with lentic habitats and by a lack of taxa that are intolerant to freezing. Substratewas the main factor explaining differences in assemblage composition in this region. Just to the south,alluvial streams are more common and permafrost is continuous with very shallow active layers,ivwhich likely results in intense discharge peaks and ice scour in the spring and flashy summerhydrographs. Invertebrates in this region were mainly short-lived, small sized orthoclads, baetids andchloroperlids; the annual disturbance regime seems likely to be an important factor shapingcommunity composition in this region. Many streams in this region received input from salinesprings, resulting in perennial flow, and these streams harboured several taxa that were absent or rarein other streams at similar latitudes, including several stoneflies (e.g. Pteronarcys, Sweltsa); thepresence of flow during the winter was found to be a major factor affecting community compositionin this region, which surrounded the town of Norman Wells, NT. Nutrient dynamics appeared to beimportant in structuring benthic assemblages in the southern portion of the study region, with highnutrientstreams supporting a diverse fauna which included many taxa that were absent in the north,while communities in low-nutrient streams were more similar to the northern alluvial stream fauna.There was no spatial distinction between low- and high-nutrient streams in the southern region, andthe difference may be due to the local conditions of permafrost, which is patchy and discontinuous inthe region.Evidence that winter ice and permafrost conditions are important drivers of benthicinvertebrate diversity and community composition in the Mackenzie system, along with the latitudinalgradients which are consistent with a temperature/climate gradient, raises the possibility that benthicassemblages may be useful as indicators of effects of global climate change on freshwater habitats inthe Canadian north. More immediately, construction of the Mackenzie Gas Pipeline may affect streamhabitat due to sedimentation, and plans for the operation of the pipeline have raised concerns aboutpotential effects on permafrost conditions. Implications for development of a biomonitoring programutilizing benthic invertebrates and their potential as indicators of climate change are discussed.