PARENT SESSION
Oral Session # 74: Riparian Ecology I: Nutrient Cycling; Decomposition.
Presiding: K Bushaw-Newton
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 205.

Detecting disturbance in aquatic ecosystems in theory and in the field: Matching variance and experimental design.

Irvine, Robyn^*,1, ¹ University of Calgary, Calgary, Alberta, Canada

ABSTRACT- The magnitude and structure of temporal and spatial variance have direct ecological importance for how clearly community patterns in nature can be seen, and how large perturbations have to be to move systems beyond background variation. Here, I examine the spatial and temporal variability of benthic communities in montane stream ecosystems and consider the implications of the communities' variance to the detection of disturbance. Benthic invertebrates inherently vary through space and time, so I pose two questions: 1) what size of disturbance can be reliably detected using changes in invertebrate community structure? and 2) does the spatial and temporal structure of the variance in the benthic community make one experimental design more sensitive to detecting a change than another? I conducted my study in the headwaters of the McLeod River, Alberta, Canada. Benthic community data were collected from the five streams that comprise the headwaters in 1985, 1993, 1995, 1999, and 2000 to estimate the spatial and temporal structure of the variance in the benthic community. I contrast three experimental designs to assess each design's ability to detect changes in these streams given the variance inherent in the systems and using a disturbance effect size drawn from the literature. Specifically, I compare a BACI design (Before After Control Impact), a paired Control-Treatment design, and a multiple treatment (4), one contro1 design. The results of my work have direct management implications, because these streams sit on a site slated for an open-pit coal mine. Benthic invertebrates are a key indicator of water quality employed in Canada's Environmental Impact Assessment (EIA) procedures.

Key words: stream ecology, Spatial and temporal variance, disturbance , experimental design