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Lake shoreline and littoral physical habitat structure in a national lakes assessment
Citation:
KAUFMANN, P. R., D. V. PECK, S. G. PAULSEN, C. SEELIGER, R. M. Hughes, T. R. Whittier, AND N. C. Kamman. Lake shoreline and littoral physical habitat structure in a national lakes assessment. LAKE AND RESERVOIR MANAGEMENT. Taylor & Francis Group, London, Uk, 30:192-215, (2014).
Impact/Purpose:
Riparian and littoral habitat components are important to lake biological assemblages, providing refuge from predation, living and egg-laying substrates, and food.
Description:
Riparian and littoral habitat components are important to lake biological assemblages, providing refuge from predation, living and egg-laying substrates, and food. Shoreline structure also affects nutrient cycling, littoral production, and sedimentation rates. Measures of riparian and littoral habitat structure provide information regarding lake ecological condition and potential stresses on biological integrity. We used data collected from 1113 lakes and reservoirs sampled as part of the 2007 USEPA National Lakes Assessment (NLA) to develop and evaluate 4 indices of physical habitat structure: 1) extent and intensity of human disturbance in the riparian zone; 2) riparian vegetation cover and structure; 3) littoral cover complexity, including woody snags and aquatic macrophytes; and 4) a combined index of littoral and riparian habitat structural complexity. We combined the first three to define a 5th index combining habitat complexity and shoreline disturbance. We evaluated the repeatability of the indices using data from lakes sampled twice during the summer field season. We used a combination of modeling and reference site approaches to estimate the distribution of values for each index under least-disturbed conditions and establish criteria for assigning a lake condition class to each lake sampled. Results for the set of sampled lakes were used in the context of the NLA survey design to make inferences about the targeted population of 49,500 lakes in the contiguous US having surface areas > 4 ha). Lack of vegetative cover and littoral habitat complexity were the most important of the physical and chemical stressors evaluated in lakes and reservoirs, both in terms of numbers of lakes affected and relative risk to biota. In the contiguous US, 47% (±3% SE) of lakes had physical habitat complexity and cover at the land-water interface that was comparable to least-disturbed condition (“good”), 20% (±2% SE) were in fair condition, and 32% (±2%) had substantially lower physical habitat complexity ("poor"). Riparian vegetation cover was rated “poor” in 36% (±2% SE) of lakes. A companion study of attributable risk suggested that among the (22 ±2%SE) of lakes with poor biological condition nationwide (based on the loss of expected planktonic taxa), 42% of cases could be attributed to poor condition of lakeshore vegetation. In every region of the US, littoral-riparian cover and structure were negatively related to the level of human disturbance. These results suggest that management of littoral and lakeshore physical habitat should receive emphasis more in line with that traditionally placed on nutrients and acidification.