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 O 2 m 22 d 21 , spring R ranged from 16 to 110 mmol O 2 m 22 d 21 , and the water column was the most important microhabitat for both GPP and R on average. Summer GPP ranged from 40 to 131 mmol O 2 m 22 d 21 , R ranged from 25 to 155 mmol O 2 m 22 d 21 , and the water column and benthic microhabitats were equally important for GPP and R. Fall GPP ranged from , 1 to 19 mmol O 2 m 22 d 21 , and R ranged from , 1 to 47 mmol O 2 m 22 d 21 , 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.Gross primary productivity (GPP) and respiration (R), collectively referred to as ecosystem metabolism, provide insight into the balance of organic matter production and remineralization in an ecosystem. This balance, or net ecosystem productivity (NEP 5 GPP 2 R), has been used to infer the trophic nature of many aquatic and marine systems, with positive NEP indicating autotrophy and negative NEP indicating heterotrophy (Odum 1956). In lakes, metabolism measurements made in the pelagic zone are often used to characterize the lake as a whole (Cole et al. 2000;Staehr et al. 2010). However, considerable heterogeneity among lake habitats has been observed (Lauster et al. 2006;Van de Bogert et al. 2007). For example, benthic habitats often have much different metabolic conditions than pelagic habitats (Vadeboncoeur et al. 2001(Vadeboncoeur et al. , 2002, and shallow littoral habitats, especially shoreline marshes, can have elevated GPP and R rates relative to deeper pelagic areas (Carter 1988). Despite the recognition that wetlands are important biogeochemical hotspots, there have been markedly few attempts to quantify metabolism or identify its drivers in shoreline wetlands, especially in the Laurentian Great Lakes. This is surprising given that metabolism is an important functional measurement in general (Cole et al. 2000;Staehr et al. 2010) and that wetlands are among the most productive ecosystems globally (Wetzel 2001).Emergent shoreline wetlands support numerous ecosystem services, such as trapping organic matter, nutrients, and sed...

Lakescape connectivity: Mobile fish consumers link Lake Michigan coastal wetland and nearshore food webs

“…This high use of wetland resources is consistent with the characterization of coastal wetlands as energy-rich systems that export resources to adjacent habitats either directly (e.g., physical movement of organic matter via wave action) or indirectly (e.g., through consumer use of multiple habitats; Odum, 1968;Wetzel, 1992). In contrast, wetland-collected perch in our study often had low use of nearshore-derived resources, possibly due to the high natural productivity of wetlands (Cooper et al, 2013). However, the use of nearshore resources by wetland perch at some sites suggests some level of reciprocal exchange of energy between habitats, not solely that wetlands are one-way exporters (Odum, 1968;Wetzel, 1992).…”

Do rivermouths alter nutrient and seston delivery to the nearshore?

“…Some rivermouths also significantly alter the suspended materials being transported from the tributary to the nearshore. Previous studies have suggested rivermouths and coastal wetlands may seed nearshore communities with phytoplankton (Bridgeman et al, 2012;Cooper, Steinman & Uzarski, 2013), and results from this study indicate that production and export of phytoplankton from rivermouths to the nearshore is a common occurrence (at least in summer). During the summer, base-flow period sampled here, 'high-effect' rivermouths appeared to be net sources of a variety of dissolved and particulate nutrients.…”

Microbial community structure and microbial networks correspond to nutrient gradients within coastal wetlands of the Laurentian Great Lakes

“…As such, wave action from the Great Lakes impacted wetlands within the western basin of LE to a lesser degree than other wetlands, thereby reducing sediment export rates into the Great Lakes themselves. Hydrologic energy was found to impact wetland primary productivity and respiration in Lake Huron coastal wetlands, suggesting Great Lakes ecosystems may exert unique environmental forces on wetland microbial communities (Cooper, Steinman and Uzarski 2013). Low carbon export rates or elevated sedimentation rates may exist in the western basin of LE as consequence of low wave action in these wetlands, which may influence the chemical and biological structure (such as vertical microbial community structure) within wetland soils of this region.…”