Wetlands

Methane Cycling Contributes to Distinct Patterns in Carbon Stable Isotopes of Wetland Detritus Abstract Increasing global temperatures are changing the balance between carbon sequestration and its microbial processing in wetlands, making the tracking of these processes important. We used detrital carbon stable isotopes (δ13C) to trace aerobic decomposition and CH4 production in two experiments conducted in Alaskan wetlands. In laboratory bottle incubations, larger decreases in detritus δ13C corresponded to higher net CH4 and CO2production rates. Because net CH4 production was the stronger predictor and its effect was negative, we hypothesize that decreases in δ13C trace concurrent CH4 production and oxidation. In a field experiment, decreases in detritus δ13C were not correlated with aerobic decomposition rates, but were positively correlated with CH4 production potentials as estimated from bottle incubations. We hypothesize that the positive relationship reflects only CH4 production, rather than concurrent production and oxidation. Although CH4 production rates were correlated with changes in detrital δ13C in both experiments, the direction of this relationship differed between laboratory and field with important consequences for the scale of ecological experiments. Our study demonstrates that CH4 cycling can create distinct patterns in δ13C of wetland detritus. Future studies should conduct explicit mass balance experiments to clarify mechanisms and determine the importance of scale in shaping isotopic patterns.

Paleoecological assessment of cladoceran community dynamics in two subarctic peatlands Abstract Crustacean community structure and dynamics are very well studied in lakes, rivers and oceanic systems but wetlands, where moisture conditions fluctuate, have not received equal attention in research. For example, cladoceran communities in peatland systems in the subarctic region have not been fully investigated. We used paleolimnological and paleoecological methods to study plant and cladoceran assemblages and the community dynamics in two subarctic peatlands, which differ in their hydrological characteristics. At the first site, Iitto, river floods introduce planktonic species to fen pools and the steep topography of the catchment induces rapid but relatively short flooding periods. Fluctuating environmental conditions result in a high amount of cladoceran resting stages in the samples. At the other site, Kaamanen, the cladoceran assemblage goes through clear directional changes, which could be attributed to changes in fen hydrology and ultimately to climatic changes during the past two millennia.

Rising Tides: Assessing Habitat Vulnerability for an Endangered Salt Marsh-Dependent Species with Sea-Level Rise Abstract Salt marsh-dependent species are vulnerable to impacts of sea-level rise (SLR). Site-specific differences in ecogeomorphic processes result in different SLR vulnerabilities. SLR impacts to Ridgway’s rail (Rallus obsoletus) of Southern California (SC) and San Francisco Bay (SF), U.S.A. could foreshadow SLR effects on other coastal endemic species. Salt marsh vulnerabilities to SLR were forecasted across 14 study sites using the Wetland Accretion Rate Model of Ecosystem Resilience, which accounts for changes in above and belowground marsh processes. Changes in suitable habitat for rail were projected with MaxEnt. Under a high (166 cm/100 yr) SLR scenario, current extent of suitable habitat is projected to increase by 34% across the combined area of 14 sites by 2050, but by 2100, total habitat suitability is projected to decrease by 83%, with six salt marshes losing over 95% of suitable habitat. Under a high SLR scenario, SF’s suitable habitat is predicted to increase by 35% at mid-century, and SC’s current suitable habitat extent will increase by 24%. However, by 2100, SF is forecasted to lose 84% of suitable habitat and SC to lose 80% of its current habitat extent. If accretion rates cannot keep pace with SLR, salt marsh obligate species are in danger of being extirpated from their habitat.

Rapid Increases in Bat Activity and Diversity after Wetland Construction in an Urban Ecosystem Abstract Wetland construction can mitigate the biodiversity and water quality losses associated with reduced natural wetland coverage. While beneficial effects of wetland construction for bats have been observed in natural and rural settings, the effects of wetland construction on bats in an urban ecosystem are less understood. We used passive acoustic monitoring to measure bat activity levels and diversity at two constructed wetlands and two control sites on the University of North Carolina Greensboro campus, in Greensboro, North Carolina, USA. We monitored all 4 sites before and after wetland construction. Pre-wetland construction, there were few differences in bat activity and community structure at our sites. After wetland construction, we observed greater activity, attributable to all species we recorded, at wetland sites compared to control sites. Species diversity and species richness were also higher at wetland sites compared to control sites. When comparing the same sites before and after wetland construction, both bat activity and species richness increased after construction, but the effects were seen in Winter and not Spring. Our results demonstrate that bats use constructed wetlands in urban ecosystems similarly to other habitat settings. Increases in bat activity, diversity, and species richness occurred within one year of wetland construction.

Landscape Indicators and Ecological Condition for Mapped Wetlands in Pennsylvania, USA Abstract Although landscape indicators are widely used to assess wetland ecological condition, how they capture the spatial arrangement of land cover is not well addressed. We conducted a Level 1 Landscape Assessment to revise strengths and weaknesses of landscape indicators when links to ecological conditions are strong. Wetland sites mapped by the National Wetlands Inventory were defined as 1-km radius circles around centroid points. Forest fragmentation type, road density, Landscape Development Intensity (LDI) index, and percentage of impervious surface were quantified at each site by integrating land cover and road network information. Based on forest cover, 6% of wetland sites scored in the highest ecological category while 45% fit into the lowest one. Results showed high dispersion of data for the impervious surface indicator in the lowest condition category. When comparing LDI and impervious surface under different landscape compositions and configurations, LDI better described disturbance in agricultural areas where road density was low. Impervious surface better reflected the occurrence of fragmented landscapes at forested areas with high percentage of edge forest cover. In addition, a significant proportion of freshwater wetlands (60%) in the lowest condition category was associated with first-order streams, indicating a wide range of disturbance at some headwater watersheds.

Mathematical Formulations for Three Components of Hydroperiod in Tidal Wetlands Abstract Hydroperiod has numerous ecological function and effective methods for calculating hydroperiod would be valuable for different ecological or biological studies. However, accurate computation of hydroperiod remain challenging mainly due to absence of accurate mathematical formulation. Additionally, computing hydroperiod is complex due to the daily fluctuating water levels from tides, wind, river flows, and other meteorological events. This research presents quantitative formulations for three components of hydroperiod (flooding depth, frequency, and duration) directly from the physical dynamics of water surface movement in a tidal wetland. A set of National Oceanic and Atmospheric Administration (NOAA) tide gauges along the U.S. West, East, and Gulf coasts are selected to demonstrate the application of the new formulations. The computational results in terms of duration are compared with Morris non-dimensional depth (D) of hydroperiod. The comparison indicates that D is a linear-triangular approximation of sinusoid tide curve and it would generally be a good estimate of the duration component of hydroperiod within the tidal range and the accuracy of D depends on geographic location of the stations that determine the tidal regimes. Whereas the proposed formulation is not limited to variations in tide regimes and can be used as a powerful tool to determine hydroperiod.

Quantifying Functional Increases Across a Large-Scale Wetland Restoration Chronosequence Abstract Over 300,000 ha of forested wetlands have undergone restoration within the Mississippi Alluvial Valley region. Restored forest successional stage varies, providing opportunities to document wetland functional increases across a large scale restoration chronosequence using the Hydrogeomorphic (HGM) approach. Results from >600 restored study sites spanning a 25 year chronosequence indicate that: 1) wetland functional assessment variables increased toward reference conditions; 2) restored wetlands generally follow expected recovery trajectories; and 3) wetland functions display significant improvements across the restoration chronosequence. A functional lag between restored areas and mature reference wetlands persists in most instances. However, a subset of restored sites have attained mature reference wetland conditions in areas approaching or exceeding tree diameter and canopy closure thresholds. Study results highlight the importance of site selection and the benefits of evaluating a suite of wetland functions in order to identify appropriate restoration success milestones and design monitoring programs. For example wetland functions associated with detention of precipitation (a largely physical process) rapidly increased under post restoration conditions, while improvements in wetland habitat functions (associated with forest establishment and maturation) required additional time. As the wetland science community transitions towards larger scale restoration efforts, effectively quantifying restoration functional improvements will become increasingly important.

Microtopography Alters Hydrology, Phenol Oxidase Activity and Nutrient Availability in Organic Soils of a Coastal Freshwater Forested Wetland Abstract Hummock-hollow microtopography is a unique feature of wetland ecosystems, but our understanding of its effects on soil carbon and nutrient cycling is limited. We investigated effects of microtopography on hydrology, phenol oxidase activity (POX) and nutrient availability in a freshwater forested wetland of coastal North Carolina. Water table depth (WTD) was measured from September 2012 to August 2013. Ion exchange probes were used to measure nutrient concentrations prior to soil sample collection in August 2013. WTD fluctuated seasonally with maximum and minimum WTD resulting in 92% (September 2012) to 8% (June 2013) of the site in flooded and non-flooded conditions, respectively. Hummocks had greater POX activity (12 ± 2.8 μmol g−1 h−1) compared to hollows (4 ± 0.7 μmol g−1 h−1) and greater concentrations of potassium and sulfur, but lower concentrations of calcium, iron, zinc, boron, and lead. POX was negatively correlated with soil water content. Higher enzyme activity in hummocks likely drives greater rates of carbon and nutrient cycling compared to hollows, consistent with observations that hummocks are hotspots for CO2 fluxes. Microtopography altered site-level hydrologic conditions, phenol oxidase activity and nutrient availability with important implications for understanding carbon and nutrient cycling in forested wetlands and response to changes in hydrology.

Morphology of Drained Upland Depressions on the Des Moines Lobe of Iowa Abstract An algorithm developed to derive the morphology of depressional landscape features was applied to the Iowa portion of the Des Moines Lobe using high-resolution hydrologically corrected digital elevation models. In total, 173,171 topographically intact, drained upland depressions were identified, and their individual morphologies determined. The frequency distributions of maximum area of inundation, maximum depth, and maximum storage volume of depressions were described by a power-law function. Maximum storage volume was strongly related to maximum inundation area through a power-law model, the parameters of which differ from those reported for other areas of the North American Prairie Pothole Region. The spatial distributions, densities, and bulk morphological attributes of upland depressions within the DML-IA tend to be coincident with the region's distinctive glaciated sub-regions.

Effects of Nutrient-Limitation on Disturbance Recovery in Experimental Mangrove Wetlands Abstract Coastal wetlands are exposed to high-energy storms that influence plant and soil structure. To understand how nutrient availability interacts with storm-induced plant stress, we tested how defoliation interacts with nutrient enrichment to affect carbon (C) and nutrient (nitrogen, N; phosphorus, P) cycling and storage within soils and plants. In outdoor experimental mesocosms, we defoliated red mangrove saplings (Rhizophora mangle), added 30 g of inorganic P to peat soils, and quantified plant [elemental stoichiometry (C:N, C:P, N:P), leaf count, and above- and below- ground biomass] and soil responses [C:N, C:P, N:P, litter breakdown rate (k), soil CO2 efflux] during a 42-d recovery period. Mangroves rapidly regrew all removed leaves and recovered nearly 30% of leaf biomass. Mangrove biomass %P increased by 50% with added P; however, soil stoichiometry remained unchanged. Defoliation reduced Soil CO2 efflux by 40% and root litter k by 30%. Phosphorus was quickly incorporated into mangrove biomass and stimulated nighttime soil CO2 efflux. This work highlights the importance of testing interactions of nutrient availability and plant stress on plant and soil biogeochemical cycling and suggests that plants quickly incorporate available nutrients into biomass and defoliation can lead to reduced soil C losses.