Refining aquatic macroinvertebrate community metrics for the assessment of headwater streams in New York State

The River Continuum Concept describes the structural and functional shift that occurs from sensitive headwater streams to the lowest reaches of large, non-wadeable rivers. New York State (NYS) maintains a long-established biological monitoring program using macroinvertebrate community assemblages for water quality assessment. However, headwater streams are rarely assessed, and no reference models are available, except those calibrated for lower-continuum wadeable streams and rivers. Current patterns of rural landuse change emphasize the need for more accurate assessment of previously neglected headwaters, in order to set natural reference standards for more accurate assessments of water quality. Ecoregion, drainage area (DA), elevation (elev.), and wetland landcover were found to be the most influential variables and were used to define headwater conditions. Results indicate at least four biologically distinct headwater regions within NYS, each with a unique combination of watershed characteristics. New metric thresholds based on models of community structure and function were developed for headwaters in the Catskills (DA 1200 ft) and Allegheny Plateau (DA1200 ft). Unique conditions in the Croton headwaters (DA<16 km 2) and Adirondack wetland headwaters (DA5%) necessitated alternate interim approaches that require further assessment. Defining and assessing headwater streams will bring NYS in line with other northeastern states and provide greater protection for its high-quality water resources.