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Evaluating physical habitat condition in the National Lakes Assessment (NLA)
Citation:
KAUFMANN, P. R. Evaluating physical habitat condition in the National Lakes Assessment (NLA). Presented at Seventh National Monitoring Conference, Denver, CO, April 25 - 29, 2010.
Impact/Purpose:
The NLA and other lake survey and monitoring efforts increasingly rely upon biological assemblage data to define lake condition.
Description:
The NLA and other lake survey and monitoring efforts increasingly rely upon biological assemblage data to define lake condition. Information concerning the multiple dimensions of physical and chemical habitat is necessary to interpret this biological information and meaningfully assess ecological condition. The controlling influence of littoral structure and complexity on lake biota has been long recognized, and recent research highlights the roles of littoral woody debris in providing refuges from predation and affecting nutrient cycling and littoral production. NLA field crews characterized lake depth, water surface characteristics, bank morphology and evidence of lake level fluctuations, littoral and shoreline substrate, fish concealment features, aquatic macrophytes, riparian vegetation cover and structure, and human land use activities. These littoral and riparian physical habitat measurements and visual observations were made in a randomized array of 10 littoral plots (10m x 15m) with adjoining riparian plots (15m x 15m) systematically spaced along the shoreline of each sample lake. Metrics describing a rich variety of lake characteristics were calculated from this raw data, and many of these were determined with moderate precision in the national dataset. For the NLA, we summarize this information with four integrative measures of lake condition: RipDist, incorporating measures of the extent and intensity of human land use activities; RipVeg, incorporating the structure and cover in three layers of riparian vegetation, including inundated vegetation; LitCvr, a combined biotic cover complexity measure including large woody snags, brush, overhanging vegetation, aquatic macrophytes, boulders, and rock ledges; and LitRipCvr, which combines RipVeg and LitCvr.. Compared with riparian and littoral conditions in lesser disturbed reference lakes throughout the U.S.A, lakes with moderate or high human disturbances in the same region have reduced cover and extent of multi-layered riparian vegetation or natural wetlands. Those with moderate or high disturbance generally also have reduced snag, brush and emergent aquatic macrophyte cover. Our general expectation is that wetland and multi-layered riparian vegetation and abundant, complex fish concealment features foster native fish, macroinvertebrate, and avian assemblage diversity, whereas extensive and intensive shoreline human activities that reduce natural riparian vegetation and reduce littoral cover complexity are probably detrimental to native biota.