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Ecological links between emergent macrophytes and associated periphyton and benthic communities in a coastal reservoir littoral zone Wilson, Sandra Joan


A study conducted in Stave Reservoir, near Mission British Columbia, examined the linkages between flooded shoreline vegetation and associated periphyton and benthic communities in a coastal reservoir drawdown zone. Two native perennial species, woolgrass (Scirpus cyperinus) and lenticulate sedge (Carex lenticularis), and an annual agronomic species, fall rye (Secale cereale L.) were used in the study. A total of 108 pots containing either one of the plant species or barren substrate (i.e. no vegetation) were installed within three elevation bands in the inundated reservoir drawdown zone in June 2000. Samples were retrieved monthly over the period of inundation, with the final samples being removed in early September 2000. The effects of planting elevation, vegetation species and time on endpojnts including plant biomass and nutrient composition, periphyton density and biovolume, and benthos abundance were examined. Fall rye decomposed quickly, losing approximately 80% of its foliar biomass after one month of submergence. Woolgrass and sedge foliage decomposed much more slowly, losing only 30% and 55%, respectively, of their aboveground biomass by the final sample date. There was evidence that nitrogen was translocated from shoots to roots fairly quickly upon inundation in all three plant species. Phosphorus was lost rapidly from the fall rye foliage with no concurrent increase in the roots, suggesting that rather than being translocated to the roots, phosphorus was leached from the plant material. No trends were noted for phosphorus for the perennial species. The periphyton communities associated with all plants types were dominated by diatoms. The maximum diatom density was approximately 112,000 cells/m2 observed in the final sample period. Oligochaetes and chironomids were the most dominant benthic taxa, accounting for 63% of all benthic organisms. The presence of vegetation increased the number of benthic organisms by 3 times, and benthic taxa by 1.7 times in comparison to barren substrate. There was no significant difference in total benthos abundance between the three plant species; however, distinct groupings of benthic community composition associated with the control, fall rye and perennial plant species were noted using the nonmetric multidimensional scaling (NMS) ordination technique.

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