Influences of Multi-Scale Habitat on Metabolism in a Coastal Great Lakes Watershed

Spatial heterogeneity influences ecosystem structure and function across multiple habitat scales. Although primary production and respiration are fundamental to energy cycling in aquatic ecosystems, we know relatively little about how habitat scale influences metabolism. In this study, we adopted a multi-scale habitat approach to evaluate primary production and respiration in a coastal Great Lakes watershed that is experiencing pressure from past, present, and anticipated future human activities. We divided the watershed into five macrohabitats (stream, river, wetland, drowned-river mouth lake, and Great Lake), two mesohabitats (benthic and water column), and four microhabitats (periphytic substrates: sand/sediment, rock, wood, and plant) for evaluation of spatial patterns and synchrony in metabolism. Factors that influenced patterns of metabolism were scale dependent. Algal biomass strongly influenced spatial patterns in metabolism at the meso- and microhabitat scales; greater algal biomass translated to higher areal-specific and lower chlorophyll-specific metabolism at benthic mesohabitat and sand/sediment and rock microhabitats. Benthic metabolism overwhelmed water column metabolism, irrespective of location or time of year. Watershed position was important at the macrohabitat scale, with greater overall metabolism in macrohabitats located lower in the watershed. Average synchrony in metabolism rates was greatest at the macrohabitat scale, suggesting metabolic patterns that are evident at finer scales may become integrated at coarser scales. Our results (1) show that spatial and temporal patterns in metabolism are shaped by factors that are dependent upon habitat scale; (2) highlight the importance of benthic productivity across habitat and season; and (3) suggest that hydrologic connectivity strongly influences ecosystem processes, although physical factors can affect these responses as evidenced by the low levels of synchrony between Lake Michigan and the other macrohabitats.