THE EFFECTS OF MOTORWAY RUNOFF ON FRESH-WATER ECOSYSTEMS .1. FIELD-STUDY

The effects of motorway runoff on the water quality, sediment quality, and biota of small streams were investigated over a 12-month period. Downstream of motorway runoff discharges there was an increase in the sediment concentrations of total hydrocarbons, aromatic hydrocarbons, and heavy metals and an increase in the water concentrations of heavy metals and selected anions. Hydrocarbon contamination of sediments was positively correlated with potential contaminant loading (i.e., lengt h of road drained/stream size). The greatest effect was observed at Pi geon Bridge Brook, a small stream receiving drainage from a 1,500-m st retch of the M1 motorway. The dominant PAHs in contaminated sediment a t this site were phenanthrene, pyrene, and fluoranthene, whereas the d ominant metals were zinc, cadmium, chromium, and lead. Differences bet ween the station upstream and downstream of discharges in the diversit y and composition of the macroinvertebrate assemblages were detected i n four out of the seven streams surveyed. However, there was no eviden ce of an effect on either the diversity or abundance of epilithic alga e. The diversity of the aquatic hyphomycete assemblage was only affect ed at the most impacted site. Reductions in macroinvertebrate diversit y were associated with reductions in the processing of leaf litter and a change from an assemblage based on benthic algae and coarse particu late organic matter to one dependent upon fine particulate organic mat ter.