Anne M. Cotter

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.

Effects of agricultural activities and best management practices on water quality of seasonal prairie pothole wetlands

Long-term effects of within-basin tillage can constrain condition andfunction of prairie wetlands even after uplands are restored. Runoff wassignificantly greater to replicate wetlands within tilled basins with orwithoutvegetated buffer strips as compared to Conservation Reserve Program restorationcontrols with revegetated uplands (REST). However, mean water levels for nativeprairie reference sites were higher than for REST controls, becauseinfiltrationrates were lower for native prairie basins, which had no prior history oftillage. Nutrient dynamics changed more in response to changes in water leveland vegetation structure than to increased nutrient inputs in watershed runoff.Dissolved oxygen increased between dry and wet years except in basins or zoneswith dense vegetation. As sediment redox dropped, water-column phosphatedeclined as phosphate likely co-precipitated with iron on the sediment surfacewithin open-water or sparsely vegetated zones. In response, N:P ratios shiftedfrom a region indicating N limitation to P limitation. REST sites, with densevegetation and low DO, also maintained high DOC, which maintains phosphate insolution through chelation of iron and catalysis of photoreduction. Referencesites in native prairie and restored uplands diverged over the course of thewet-dry cycle, emphasizing the importance of considering climatic variation inplanning restoration efforts.

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 (

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.

Rapid stable isotope turnover of larval fish in a Lake Superior coastal wetland: Implications for diet and life history studies

Trophic linkages of larval fish in Lake Superior coastal habitats can be identified using naturally occurring differences in the stable isotope ratios of nitrogen (15N:14N, δ15N) and carbon (13C:12C, δ13C). We measured 13C and 15N values in common fish larvae weekly during spring run-off (late-April to mid-July) in the hydrologically complex drowned river mouth of the St. Louis River, the second largest tributary to Lake Superior. For all species, δ13C was increasingly negative with increasing weight as the fish developed from the yolk-sac stage, during which they possess a maternally-derived isotopic signature, to an exogenously feeding larvae. Trends in δ15N with increasing weight varied among species; an increase, decrease, and no change in δ15N were observed. A weight-based stable isotope turnover function modeled well the observed changes in δ13C and δ15N. In general, fish obtained a constant signature after a 10-fold gain in body mass, implying their tissue was at isotopic equilibrium with their diet. Difference between yolk-sac and larvae δ13C and δ15N revealed distinct patterns in larval origin and settlement. Based on the species analyzed, we identify two specific Lake Superior coastal wetland-dependent fish early life histories that incorporate habitat use, movement, and trophic dynamics. This study thus provides a methodological approach that can potentially help resolve interactions between watershed character, coastal productivity, and Lake Superior that are of significance to the lakes fisheries.

Fish tissue lipid-C:N relationships for correcting δ(13) C values and estimating lipid content in aquatic food-web studies.

RATIONALE Normalizing δ(13) C values of animal tissue for lipid content is necessary to accurately interpret food-web relationships from stable isotope analysis. To reduce the effort and expense associated with chemical extraction of lipids, various studies have tested arithmetic mass balance to mathematically normalize δ(13) C values for lipid content; however, the approach assumes that lipid content is related to the tissue C:N ratio. METHODS We evaluated two commonly used models for estimating tissue lipid content based on C:N ratio (a mass balance model and a stoichiometric model) by comparing model predictions to measure the lipid content of white muscle tissue. We then determined the effect of lipid model choice on δ(13) C values normalized using arithmetic mass balance. To do so, we used a collection of fish from Lake Superior spanning a wide range in lipid content (5% to 73% lipid). RESULTS We found that the lipid content was positively related to the bulk muscle tissue C:N ratio. The two different lipid models produced similar estimates of lipid content based on tissue C:N, within 6% for tissue C:N values <7. Normalizing δ(13) C values using an arithmetic mass-balance equation based on either model yielded similar results, with a small bias (<1‰) compared with results based on chemical extraction. CONCLUSIONS Among-species consistency in the relationship between fish muscle tissue C:N ratio and lipid content supports the application of arithmetic mass balance to normalize δ(13) C values for lipid content. The uncertainty associated with both lipid extraction quality and choice of model parameters constrains the achievable precision of normalized δ(13) C values to about ±1.0‰.

Extraction and analysis of low concentrations of DDT, DDE and DDD in small volumes of sediment pore water

Abstract As a result of effluent discharges by a previous chemical manufacturer, sediments in the Huntsville Spring Branch-Indian Creek (HSB-IC) near Huntsville, AL are contaminated with DDT and its metabolites. This area was selected as a field location at which to evaluate equilibrium partitioning theory (EqP) to predict the bioavailability of nonionic organic chemicals associated with sediments. An important component of the evaluation of EqP features determination of contaminant concentrations in the sediment interstitial (pore) water. The objective of our study was to develop an analytical method to measure o,p′- and p,p′-DDE, DDD and DDT at low concentrations (

Landscape-Scale Food Webs of Fish Nursery Habitat Along a River-Coast Mixing Zone

We used carbon and nitrogen stable isotope ratios to identify changes in organic matter (OM) sources supporting fish larvae along the river–lake mixing zone in three Lake Superior coastal tributaries. We used a stable isotope mixing model to quantify how the number and origin of OM sources supporting fish larvae changed with respect to the relative fraction of tributary and lake water along the coastal mixing zone. Fish stable isotope ratios, after adjusting for trophic fractionation, generally were intermediate between the measured OM sources, indicating widespread nutritional support from multiple OM sources. Mixing model results indicated that more OM sources supported fish larvae in river and mixed regions than in the lake; however, the number of OM sources did not change linearly with respect to tributary water fraction. Contributions from allochthonous OM were highest in the mixed and lake regions; most fish larvae obtained some energy from food sources originating outside the region where the fish larvae were collected. At the species level, principal component analysis revealed that the number of OM sources was positively correlated with percent terrestrial OM contribution and greatest in demersal fish larvae that were captured in the mixed region. Our findings demonstrate that these coastal habitats do function as a “mosaic”, wherein proximal and some more distal habitats and ecosystems contribute to fish growth during a critical life stage. By extension, the findings suggest the need for conservation measures to consider upland, wetland, and coastal habitat, whether or not fish directly occupy all of those habitats.