Cumulative Effects of Headwater Degradation on Downstream Ecosystems in Urbanizing Landscapes

Session: 58. - Cities on the Shore: Urbanization as a Growing Threat to Nearshore Ecosystem Health

Brian Kielstra, University of British Columbia, [email protected]
Lenka Kuglerova, University of British Columbia, [email protected]
Les Stanfield, Ecohealth Solutions, [email protected]
John Richardson, University of British Columbia, [email protected]

Abstract

Headwater streams contribute important material to downstream habitats including exported sediment, nutrients, organic matter, and organisms. As upstream components of dendritic stream networks, they occupy a substantial proportion of total network length and watershed area. Despite well-established functional linkages between up- and downstream habitats and biota, less research focuses on predicting cumulative effects of headwater degradation on downstream ecosystems. These effects are likely complex, non-linear, and interact across scales. They are also of interest in urbanizing regions since individual headwaters can be small, intermittent, considered less important, and consequently have less legislated protections than larger streams. Therefore, headwater streams are often modified and/or degraded. Predicting downstream responses requires a multiscale understanding of headwater stream variability. We examined a spatially extensive dataset (>1000 headwater streams) across an urbanized region to determine spatial structure of headwater conditions and their relationship to land use. We then examined a satellite image time series to determine how threats to headwaters have changed. We found that predictive capacity of headwater condition increases when both land use and spatial structure are incorporated. We also found that headwaters are under greater threat as urban regions expand. Understanding these interactions allows for predicting cumulative effects of headwater degradation downstream.

1. Keyword
urban watersheds

2. Keyword
Spatial analysis

4. Additional Keyword
cumulative effects