Catchment land-use effects on littoral macroinvertebrates in response to local habitat structure and trophic state

Lake habitat alteration is a major stressor for lakes worldwide, and physical habitat alteration is likely the biggest threat to aquatic ecosystems, exceeding all other anthropogenic pressures. This study sought to elucidate which group of variables was the most important for describing Swedish macroinvertebrate community structure: trophic status, substrate variables or riparian variables. We also investigated what influence each of these groups of variables has on the other. The impact of large scale land use patterns was also investigated, to determine if macroinvertebrates responded differently in two different catchment land use types: impaired and unimpaired. Partial canonical ordination analysis showed that substrate variables were the most important for describing macroinvertebrate community variation in both catchment land use classes, followed by riparian descriptors, with the trophic signal only becoming clear when lakes were more strongly stratified for coarseness of substrate. This trophic effect was only evident in the impaired lakes, as the trophic gradient was much shorter in the lakes with an unimpaired catchment. Our results suggest that trophic effects on benthic invertebrates are nested within substrate habitat effects, and were masked by local habitat heterogeneity. This indicates that, at least in the Swedish situation, greater care needs to be taken in stratifying the substrate sampled in order to see this nutrient pressure-macroinvertebrate response relationship. The macroinvertebrate community composition was also responding to changes in riparian vegetation, specifically the presence of riparian trees and canopy cover. These variables, or lack of, are possible proxies for anthropogenic alteration of lake shores. Therefore, although macroinvertebrates may not be strong indicators of trophic pressure in all cases or habitats, they may be useful indicators for other anthropogenic pressures (e.g. hydromorphology) on lake shores.