Influence of geomorphic setting on the metabolism of Lake Huron fringing wetlands

Abstract

We measured gross primary productivity (GPP) and respiration (R) seasonally in benthic, water column, and epiphytic microhabitats of Lake Huron fringing wetlands. Spring areal GPP ranged from 33 to 103 mmol O2 m-2 d-1, spring R ranged from 16 to 110 mmol O2 m-2 d-1, and the water column was the most important microhabitat for both GPP and R on average. Summer GPP ranged from 40 to 131 mmol O2 m-2 d-1, R ranged from 25 to 155 mmol O2 m-2 d-1, and the water column and benthic microhabitats were equally important for GPP and R. Fall GPP ranged from, 1 to 19 mmol O2 m-2 d-1, and R ranged from, 1 to 47 mmol O2 m-2 d-1, with the benthic and water column microhabitats being equally important. Net metabolism (the difference between GPP and R) was close to zero at most wetlands, but when macrophyte productivity was accounted for, most wetlands appeared autotrophic. Both GPP and R were highest in deep wetlands protected from hydrologic energy and declined with increasing wave exposure. With increasing exposure, wetlands were restricted to shallower water and benthic GPP and R increased relative to water column GPP and R. This pattern persisted to intermediate levels of exposure, beyond which benthic GPP and R declined as a result of physical disturbance to the sediment. Coastal wetlands are hotspots of productivity in Lake Huron and hydrologic energy is an important driver of total metabolism rates, as well as the distribution of GPP and R among microhabitats. © 2013, by the Association for the Sciences of Limnology and Oceanography, Inc.