The Pacific Northwest (PNW) is currently experiencing some of the fastest human population growth within the United States with another 1.5 million residents expected in the Puget Sound Region by 2040. The expanding population is also predicted to result in a 40% increase in demand for travel, which will in turn lead to higher deposition of heavy metal pollutants through brake and tire attrition. As metal contaminant loads increase, PNW ecosystems also face the added stress of increased temperatures due to anthropogenic climate change, which is exacerbated by urban heat island effects. We sought to quantify the interactive effects of metal pollutants and temperature on forest ecosystems of the PNW using moss-dwelling microarthropod communities as an indicator. We reared the temperate springtail Folsomia candida under laboratory conditions for comparison with wild springtail populations collected from Seattle city parks and the Hoh Rainforest on the Olympic Peninsula. We examined the role of copper and zinc, both of which are components of vehicular pollution, on springtail mortality, and under different temperature regimes projected under IPCC climate change scenarios.
Results/Conclusions
We observed that lab-reared Collembola (springtails) were significantly less susceptible to copper and zinc than wild populations. Moreover, despite the greater quantities of copper and zinc deposition in the city of Seattle relative to the Hoh Rainforest, rates of mortality in field-collected springtails from these locations were not significantly different. In experiments where we exposed lab-reared springtails to different concentrations of copper, and under different temperature regimes (ambient, +1.8 °C, +3.4 °C), we observed that increases in temperature for several days prior to exposure to copper solutions significantly increased mortality. Since the lab population (F. candida) is often used as an indicator species in ecotoxicology studies, and given that it appears to be less susceptible to copper than wild springtail populations, studies that rely on F. candida could be under-estimating the true effects of pollutants on microarthropod communities and their associated ecosystems. This research enhances our understanding of the role of both increased vehicular pollution, owing to increased urbanization, and climate change on urban ecosystem health and sustainability.