Landscape indicators as a tool for explaining heavy metal concentrations in urban streams

Abstract

In urban watersheds, the toxicity and persistence of metals found in urban runoff has serious consequences for aquatic organisms. Landscape indicators - measures of the amount and arrangement of land cover - have been widely used as proxies for monitoring stream water quality. Yet, landscape indicators of heavy metal concentrations remain largely unexamined. Here, we investigated the utility of landscape indicators for explaining spatio-temporal trends of heavy metal concentrations in 58 streams throughout the Greater Vancouver Region in British Columbia, Canada. We asked: 1) How effective are landscape indicators in explaining instream heavy metal concentrations over different spatio-temporal scales? 2) Does explanatory power differ for landscape composition versus configuration indicators? We developed landscape indicators using a high resolution (5-m) land cover map and then used these landscape indicators to develop statistical models explaining Copper (Cu), Lead (Pb), Zinc (Zn), Cadmium (Cd) and Iron (Fe) concentrations in streams. Overall, riparian indicators explained 5–11% more variation of wet season metals than dry season, whereas watershed indicators only explained more variability in Pb during the dry season. Combining indicators mapped across multiple scales improved explanatory power of models, explaining >60% of the variability in heavy metal concentrations, regardless of season. When considering spatial arrangement of land cover, edge contrast between deciduous patches and impervious surroundings explained as much as 39% of the variability in Cu concentrations. Our approach is cost-effective, transportable, and especially useful in cities where high resolution land cover is readily available yet resources for in-stream monitoring are scarce.