| Tile drainage is a commonly used water management practice in over 80% of agricultural land in southern Ontario. While it is widely known that tile drainage improves conditions for agriculture, subsurface drains play an important role in the transfer of bacteria, sediment and pollutants to receiving streams. However, impacts of tile drain effluent on benthic ecology in receiving streams are relatively unknown. This thesis examines the effects of tile drain effluent on benthic macroinvertebrate community structure in four agricultural headwater streams in southern Ontario. An Ekman Grab Sampler was used to collect benthic macroinvertebrates in run sequences above (reference site) and below (two sites) tile drain outlets to examine the spatial effect of tile drain effluent on benthic macroinvertebrate community structure in agricultural headwater streams. Benthic macroinvertebrates were sampled (May 20, 2005 and July 1, 2005) in order to assess temporal variability of tile drain effluent impacts on benthic macroinvertebrate community structure. Nine summary indices were determined (abundance, taxa richness, EPT taxa richness, Hilsenhoff's Biotic Index, percent dominant taxon, relative abundance of Chironomidae, Oligochaeta, Isopoda, and a multimetric summary index). The data are compared to technical and management criteria to evaluate the utility of benthic macroinvertebrates as an indicator of environmental change. (Abstract shortened by UMI.)... |
