Ecological Indicators of Effects of Changing Air Quality

Christine Negra
The Heinz Center,
Washington, DC USA

Measurement of atmospheric composition, pollutant deposition and ecological condition are essential for monitoring the influence of changing air quality on terrestrial and aquatic ecosystems. Focusing on nitrogen, sulfur, mercury and ozone, a suite of indicators has been developed to track air pollution induced ecological impairment and to document improvements resulting from air pollution reductions. Twenty-nine experts from public and private institutions reviewed 30 broad categories of ecological endpoints in 11 major ecosystem types and produced a refined list of 28 potential indicator metrics, sorted by level of scientific development. These potential metrics encompass four major types of ecological effects: (1) acidification in terrestrial and freshwater ecosystems; (2) nitrogen enrichment in terrestrial, freshwater and coastal systems; (3) mercury methylation and bioaccumulation in aquatic systems; and (4) ozone-induced plant damage.

To develop useful indicators, a number of challenges must be addressed. Across time and space, terrestrial and aquatic systems vary considerably in their exposure and response to air pollutants. Exposure may vary seasonally or interannually and may be characterized by acute episodes or chronically elevated concentrations. Ecological alteration may reflect contemporary or historical deposition. Indicator metrics, and the spatial and temporal scale of reporting, should be designed to enable tracking of slow and fast responses across affected ecosystems. In addition to air pollution, ecological systems are affected to varying degrees by a wide range of stressors (e.g., climate change, land use change, fire and other disturbances, extractive uses). To document ecological changes that result primarily from air pollutant exposure or air quality management strategies, indicators should optimally be designed to parse out confounding factors. Finally, ecological response may be initially chemical and secondarily biological, yet parameters of greatest management and public interest tend to be biological. To the greatest degree possible, indicators should reflect scientific understanding of linkages across air pollutant exposure/ deposition, primary ecological responses and secondary effects on organisms, species and biological communities.

This presentation will report on recommended indicators for tracking the ecological effects of atmospheric deposition of nitrogen, sulfur and mercury and elevated ambient ozone. Findings will be presented for: (1) specific indicator metrics; (2) stratified reporting strategies to account for heterogeneity in ecological response; (3) optimal temporal and geographic scales of indicator reporting; and (4) available and needed data sources.