Biological responses to liming in boreal lakes: an assessment using plankton, macroinvertebrate and fish communities

P>1. Biological responses to liming of acidified surface waters are equivocal and limit the overall assessment of food web responses. In this study, we analysed community structure in limed, acidified and circumneutral lakes, based on the analyses of phytoplankton, zooplankton, macroinvertebrates (littoral, sublittoral, profundal) and fish between 2000 and 2004. We also studied associations between functional feeding groups in food webs. 2. Most univariate metrics of structure and function revealed similar community attributes among lake types, suggesting that community responses to natural recovery from acidification and liming management converge with those observed in circumneutral lakes. These trends were less clear in the multivariate analyses which showed significant community differences among lake types. For phytoplankton, these patterns were partly mediated by the invasive raphidophycean flagellate Gonyostomum semen. 3. The associations between functional feeding groups indicated less connectivity and food web complexity in limed lakes relative to the other lake types. We speculate that repeated lime applications comprise frequent pulse disturbances which offset the establishment of stable trophic relationships in the food webs of limed lakes. 4. Synthesis and applications. The limited structural and functional food web similarity among lake types supports the argument that liming constitutes an ecosystem-level disturbance. Managers should be aware of the ecosystem impacts of altered disturbance regimes when designing their management schemes because this can influence the success of restoration programmes. Furthermore, the lack of recovery, mediated in part by species invasions, suggests that impacts derived from global change are likely to lead to novel environmental situations. This calls for adaptive management strategies where managers are challenged to tackle multiple forms of anthropogenic stress simultaneously.