Thinking outside the lake: Multiple scales of amphipod recovery
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Tracking recovery in disturbed environments requires the consideration of many spatial and temporal scales. A sensitive indicator organism, Hyalella azteca, was used to assess lake recovery at multiple scales in the region of Sudbury, Canada. A 40-lake presence-absence survey was conducted over a period of 23 years to track colonization history and chemical factors that limit this typically ubiquitous organism. A six-lake study was used to investigate the importance of spatially varying watershed characteristics within lakes, which could provide habitat hot spots for colonization during early stages of recovery. An intensive single-lake study examined the effects of local-scale chemistry (e.g., bioavailable metals, waterborne organic matter) and adjacent subcatchment terrestrial features on the availability of suitable habitat for colonizing amphipods. At the regional scale, presence-absence models suggested that colonization probability increased with lake water conductivity and alkalinity. Within lakes, subcatchment confluence sites appeared to be important habitats in the early stages of colonization. Site-specific features, such as macrophyte and woody debris cover, increased and decreased H. azteca abundance, respectively, and yet these relationships were influenced by adjacent terrestrial subcatchment characteristics. For example, with more terrestrial vegetation, the relative increase in abundance due to macrophyte cover was further increased. Within the intensively-studied lake, larger subcatchments with more terrestrially-derived waterborne organic matter had higher abundances of H. azteca. Using H. azteca as an indicator of aquatic ecosystem health, these relationships suggest that as lakes recover, subcatchment confluence sites can be hot-spots for colonization, and their suitability improves with interactions between local habitat characteristics and terrestrial characteristics.