John A. Morrice

Terminal electron accepting processes in the alluvial sediments of a headwater stream

Chemical fluxes between catchments and streams are influenced by biogeochemical processes in the groundwater–stream water (GW–SW) ecotone, the interface between stream surface water and groundwater. Terminal electron accepting processes (TEAPs) that are used in respiration of organic C in anoxic environments may have a strong effect on nutrient dynamics and water chemistry. Concentrations of oxidized and reduced forms of terminal electron acceptors (dissolved O2, NO3−, Fe2+, SO42−, and CH4) were measured in networks of vertically nested wells installed beneath the surface stream and in the near-stream aquifer of a headwater catchment. Tracer addition experiments were conducted in surface and groundwater environments of a 1st-order montane stream to characterize hydrologic fluxes between the stream and aquifer, and to quantify ecosystem retention of terminal electron acceptors (NO3− and SO42−) in the GW–SW ecotone. Sulfate retention was evident in both hyporheic and groundwater environments. Distribution of important redox sensitive solutes varied predictably with changing hydrologic residence time of water in the GW–SW ecotone. Results suggest a strong hydrologic control of TEAPs and ecosystem retention of biologically important solutes in the GW–SW ecotone related to characteristics of GW–SW mixing and residence time of water in the hyporheic zone.

Water Quality in Great Lakes Coastal Wetlands: Basin-wide Patterns and Responses to an Anthropogenic Disturbance Gradient

ABSTRACT We present water quality data from 58 coastal wetlands, sampled as part of a larger effort investigating effects of nutrient enrichment and habitat disruption in the Laurentian Great Lakes. Our sampling design selected sites from across a gradient of agricultural intensity within combinations of biogeographic ecoprovince and wetland hydromorphic type and captured a large range in water quality. Levels of total nutrients (N and P), and various measures of particulate concentration, water clarity, and ionic strength were strongly associated with agricultural intensity in the watershed, and could be effectively aggregated into an overall principal component-based water quality descriptor. Lake Erie wetlands had the highest nutrient levels and lowest water clarity, while wetlands in Lakes Superior and Huron had the lowest nutrient levels and clearest water. Lake Ontario wetlands had clearer water than would be expected from their nutrient levels and position on the agricultural intensity gradient. Dissolved oxygen, silica, pH, and dissolved organic carbon (DOC) were independent of agricultural intensity but DOC was responsible for low water clarity in some Lake Superior wetlands. Simple classification by hydromorphic type (riverine or protected) did not explain water quality differences among wetlands exposed to similar agricultural intensity levels, so finer hydrologic classification may be desirable. Results are used as a basis for discussing research and information needs underlying development of water quality criteria and monitoring programs for coastal wetlands of the Great Lakes.

Relative Role of Lake and Tributary in Hydrology of Lake Superior Coastal Wetlands

Abstract Despite the documented importance of hydrodynamics in influencing the structure and function of Great Lakes coastal wetlands, systematic assessments of coastal wetland hydrology are lacking. This paper addresses this gap by describing patterns in lake and tributary inputs, water residence times, and mixing regimes for a suite of western Lake Superior wetlands that differ in the amount of tributary and seiche flow they receive. We show that variability in tributary flows among wetlands and over time is far greater than variability in seiche-driven water movements, and that the amount of tributary flow strongly influences wetland hydrology via effects on water mixing and residence times, seiche size, mouth closures, and relative amounts of main and off-channel areas. Wetland seiche amplitudes were reduced in systems with small mouth openings and wetland mouth size was correlated with tributary flow. All wetlands experienced seiche-driven water level oscillations, but there was lake water intrusion only into those wetlands where tributary outflow was small relative to the seiche-driven inflow. Wetlands in settings exposed to long-shore sediment transport exhibited periodic mouth closures when stream flows were low. The absolute and relative size of lake and tributary inputs must be explicitly considered in addition to wetland morphology and landscape setting in studies seeking to understand determinants of coastal wetland structure, function, and response to anthropogenic stressors.

A review of selected ecosystem services provided by coastal wetlands of the Laurentian Great Lakes

Significant ecosystem services derive from the coastal wetlands of the Laurentian Great Lakes even though two-thirds of the original coastal wetlands have been lost since European settlement, and the remaining 126,000 ha of U.S. coastal wetlands and ≥70,000 ha of Canadian wetlands are affected by anthropogenic stressors. Published information indicates that wildlife habitat, fisheries support, and water quality improvement are significant ecosystem services provided by Great Lakes coastal wetlands that should be strongly considered during management decision making. 30 species of waterfowl, 155 breeding bird species, and 55 species of reptiles and amphibians are supported by coastal wetland habitats across the Basin. Nearly all sport and commercial Great Lakes fish species use coastal wetlands for life-cycle functions, and Great Lakes food webs are supported by wetland export of young sport and forage fish. Biological responses indicate declines in the wildlife and fishery services with increasing levels of anthropogenic disturbance. Extrapolation from a single well-studied system suggests that, Basin-wide, coastal wetlands may retain nearly 4000 tonnes P and 53,000 tonnes N per year, but additional studies are needed to support these estimates and determine stressor effects. Coastal wetlands appear to retain sediments over long time scales, but may either retain or release sediments during storm events. Extrapolation of carbon sequestration from other wetland types suggests that less than 90 g C yr−1 might be retained across the Basin. Wild rice production provides a culturally important ecosystem service, and coastal protection may be locally significant where fringing wetland remain. To support management decisions, quantitative relationships between specific stressors or land use practices and the delivery of ecosystem services are needed, as are ecosystem service indicators to measure those responses.

HYDROMORPHIC DETERMINANTS OF AQUATIC HABITAT VARIABILITY IN LAKE SUPERIOR COASTAL WETLANDS

Despite the recognized importance of wetlands as habitat for fishes and the growing need to assess and manage human impacts on that habitat, there is little information on patterns and variability of habitat within Great Lakes coastal wetlands. Our goal was to describe wetland aquatic habitat patterns and the natural factors that organize them as a step towards developing habitat assessment schemes and identifying experimental design elements for future synoptic surveys. We analyzed data on aquatic vegetation structure, water chemistry, and water movement (inferred from gypsum plug dissolution) in relation to hydrology and morphology in inundated segments of ten relatively un-impacted coastal marshes of western Lake Superior. Spatial differences in aquatic habitat within wetlands were as large or larger than differences among wetlands, and habitat patterns were strongly associated with morphology and hydrology. Back-bay segments tended to have greater vegetation cover and structural complexity and lower levels of water movement, and they were prone to high water temperatures and low dissolved oxygen levels in wetlands having little seiche activity. Increasing seiche inputs tended to homogenize habitat elements among wetland segments, while increasing tributary inputs tended to increase spatial variability. Patterns in emergent vegetation differed from patterns in submerged/floating vegetation, and different assessment metrics may be needed for different plant zones. Segment-scale sampling schemes like those used in this study have the potential to elucidate habitat patterns within inundated portions of wetlands with a reasonable level of effort. Human impacts on coastal wetland fish habitat must be interpreted in the context of natural spatial heterogeneity as structured by wetland morphology and magnitude of seiche and tributary inputs.

Fish-Mediated Nutrient and Energy Exchange between a Lake Superior Coastal Wetland and its Adjacent Bay

Little has been done to quantify fluxes of organisms, nutrients, and energy between freshwater coastal habitats and adjacent offshore waters or to evaluate the ecological implications of these exchanges on a whole-lake basis. To test the hypothesis that fish-mediated transport might play an important role in the flux of nutrients and energy between coastal wetlands and adjacent lake waters, net carbon, nitrogen, phosphorus, and energy fluxes were estimated in forage fish between a Lake Superior coastal wetland and an adjacent bay. This was accomplished by sampling fish at the inlet/outlet of Bark Bay Slough for 1 week per ice-free month in 1995. Average carbon, nitrogen, and phosphorus content of the 20 species analyzed was 45.1, 11.3, and 2.45% of dry-weight, respectively. Estimates of organism, nutrient, and energy movement revealed a net export from the slough to the adjacent Bark Bay, due largely to emigration of YOY yellow perch, Perca flavescens (> 40,000 individuals), YOY northern pike, Esox lucius (> 600 individuals), and yearling emerald shiner, Notropis atherinoides (> 8,000 individuals) in June and July, and YOY brown bullhead, Ameiurus nebulosus (> 500 individuals) in October. Since these fish movements resulted in relatively small fluxes of nutrients (1,376 g carbon, 335 g nitrogen, 73 g phosphorus) and energy (65,100 kJ) from the wetland to the lake, the most significant influence of forage fish emigration on Lake Superior may be through subsequent trophic interactions in nearshore habitats. However, assessment of the significance of the nutrient and energy results awaits a more complete budget for these ecosystems.

Temporal Dynamics of Nutrients (N and P) and Hydrology in a Lake Superior Coastal Wetland

Abstract Coastal wetlands on Lake Superior are hydrologically complex ecosystems situated at the interface of upland catchments and the oligotrophic lake. Little is known about nutrient dynamics within coastal wetlands or their role in modifying or contributing to nutrient fluxes from watersheds to Lake Superior. We conducted an intensive study of Lost Creek Wetland (LCW) near Cornucopia, WI, with the objective of determining influences of temporal variability in hydrology on dynamics and retention of N and P. We measured hydrologic inputs and distributions of inorganic and organic forms of nitrogen and phosphorus within LCW under hydrologic conditions ranging from summer base flow to spring snow melt. Our study confirms that the interrelationship between hydrologic connections to lake and tributary and seasonal variations in hydrology can regulate internal nutrient dynamics of coastal wetlands. The strength of hydrologic linkage of LCW to Lake Superior and tributary varied greatly among seasons, resulting in shifts in the relative importance of these nutrient sources and influencing spatial distribution of nutrients within the wetland. Ratios of inorganic nitrogen and phosphorus in the wetland were consistently low (

Benthic Versus Planktonic Foundations of Three Lake Superior Coastal Wetland Food Webs

Abstract The structure of aquatic food webs can provide information on system function, trophic dynamics and, potentially, responses to anthropogenic stressors. Stable isotope analyses in a Lake Superior coastal wetland (Allouez Bay, WI, USA) revealed that the food web was based upon carbon fixed by phytoplankton. We report analyses of two Lake Superior coastal wetland food webs not based upon plankton, indicating that Allouez Bay is not the prototype. In Lost Creek and West Fish Creek wetlands (WI, USA), upper trophic levels appear to be supported by benthic, rather than planktonic, food web pathways. Also, zooplankton in Lost Creek and West Fish Creek wetlands are enriched in 13 C relative to periphyton, rather than 13 C-depleted as reported in most other systems. This appears to be a consequence of zooplankton feeding on detrital seston that is 13 C-enriched relative to phytoplankton. We suggest possible causes for the observed differences in food web structure among these wetlands, including hydrologic differences among the systems, and responses to nutrient enrichment among the dominant forms of primary producers, similar to those described in lakes.

Determining Sources of Water to Great Lakes Coastal Wetlands: A Classification Approach

Water and associated nutrients can enter freshwater and marine coastal wetlands from both watershed and offshore sources. Identifying the relative contribution of these potential sources, and the spatial scale at which sources are influenced by anthropogenic activities, are critical steps in wetland protection and restoration. We developed a hydrology-based classification scheme for Great Lakes coastal wetlands for the purpose of identifying dominant hydrologic influences and water sources. Classes were determined through analysis of data quantifying hydrologic linkages to lake (seiche) and watershed (watershed area, tributary discharge) in 57 wetlands distributed along the U.S. shoreline of the Laurentian Great Lakes. Wetlands were partitioned into four classes of hydrology that were predicted to differ in sources of water. Source water predictions were tested by comparing Chloride (Cl-) concentrations in wetland, lake, and tributary waters of the wetlands in each class. Results confirmed that classification based on quantitative hydrology data was successful in identifying groups of wetlands with similar water sources. Correlations between wetland Cl-, an indicator of anthropogenic disturbance, and agricultural and urban land uses suggest that differences among classes in water sources resulted in differences in the scale at which wetlands were connected to and influenced by landscapes.