Measure Amount of sediment and other runoff constituents within surface waters that flow from headwaters to coastal wetlands in the coastal watersheds of the Great Lakes Basin.

Purpose This metric assesses the sediment and nutrient load to coastal wetlands and its potential impact on wetlands.

Features This metric offers information on the presence, location, and predominance of land cover types that may provide information about the flow of sediment to coastal wetlands (e.g., agriculture and wetlands), as demonstrated by the use of remote-sensing data and GIS data. Field-based collection of land cover and surface water data can also be accomplished by: surveys (using global positioning systems); sketches; personal interviews; or record analyses at local, county, or state offices.

Limitations To conduct such measures at a broad scale, the relationships between land use, surface water quality, and coastal wetland impacts need to be verified. This metric will need to be validated fully with thorough field sampling data and sufficient a priori knowledge of endpoints and the mechanisms of impact. The development of this metric as an indicator of wetland condition is an important goal, and requires uniform measurement of field parameters across a vast geographic region to determine accurate information to calibrate such models.

Interpretation A thorough exploration of the relationships between hydrodynamic, biochemical, and ecological functions of affected coastal wetlands is essential for the proper interpretation of these analyses. Human impact measures may be strongly correlated with this landscape metric (e.g., percent agriculture), and the pattern of such human impacts may exert a substantial influence on the results and interpretation of this metric. Because land cover is temporally variable and is non-linear in spatial and temporal patterns, this metric is complex. Thus, multiple-scale, multiple-season, multiple-year analyses of land cover are required to develop a robust indicator of this kind. Additionally, this metric may perform better with greater specificity of land cover or other parameter types, and may be most useful when contemporaneous remote sensing data is used. Contemporary and more specific data are currently under development by EPA/ORD to improve this metric.

Comments A thorough field-sampling protocol, properly validated geographic information, and other remote-sensing-based data could lead to successful development of this metric as an accurate indicator of coastal wetland function and ecological vulnerability. Such an indicator could be applied to select coastal wetland sites, but would be most effective if used at a regional or basin-wide scale.

Metric Maps The impact of surface water runoff in the Great Lakes Basin is mapped for relevant coastal areas using remote-sensing-based geographic information. In the examples, the estimated risk of surface water export of sediment throughout the entire Great Lakes Basin is demonstrated using several associated parameters. These measures could be fine-tuned to focus solely on loading to coastal wetland regions, or be calibrated using field-based data and/or other finer scale GIS data (e.g., topographic or soil data).