The primary production in wetland ecosystems is greatly enhanced by hydrological fluxes, which leads to high biomass, primary production, and accretion rates. The carbon (C) is either fixed stored in standing biomass, released by soil decomposing microorganisms, or stored in soil sediments. With the continual destruction of wetlands worldwide, more of this sequestered C is released to the atmosphere. The protection of wetlands will preserve the amount of C already stored in these ecosystems.

Wetlands are highly complex ecosystems subjected to a variety of hydrologic regimes, climatic conditions, soil formation processes, and geomorphologic settings. They include swamps, bogs, marshes, mire, fens, salt marshes, mangroves, and other types of ecosystems saturated by water during all or part of the growing season. They are found on every continent, except Antarctica, and in various climes, from the tropics to the tundra. The extent of the world's wetland is generally estimated to be from 7 to 9 million km2 or about 4–6% of the Earth. The variety of seasonal and perennial wetlands provides environmental conditions for highly distinctive fauna and flora.

Wetlands are the largest natural source of methane to the atmosphere, but factors controlling methane emissions from wetlands are a major source of uncertainty in greenhouse gas budgets and projections of future climate change. We conducted a controlled outdoor mesocosm experiment to assess the effects of plant community structure (functional group richness and composition) on potential methane production and potential iron reduction in freshwater emergent marshes. Four plant functional groups (facultative annuals, obligate annuals, reeds, and tussocks) were arranged in a full-factorial design and additional mesocosms were assigned as no-plant controls. Soil samples from the top 10 cm were collected three times during the growing season to determine potential methane production and potential iron reduction (in unamended soils and in soils amended with 200 mM formate). These data were compared to soil organic matter, soil pH, and previously published data on above and belowground plant biomass. We found that functional group richness was less important than the presence of specific functional groups (reeds or tussocks) in mediating potential iron reduction. In our mesocosms, where oxidized iron was abundant and electron donors were limiting, iron reducing bacteria outcompeted methanogens, keeping methane production barely detectable in unamended lab incubations. When the possibility of re-oxidizing iron was eliminated via anaerobic incubations and the electron donor limitation was removed by adding formate, potential methane production increased and followed the same patterns as potential iron reduction. Our findings suggest that in the absence of abundant oxidized iron and/or the presence of abundant electron donors, wetlands dominated by either reeds or tussocks may have increased methane production compared to wetlands dominated by annuals. Depending on functional traits such as plant transport and rhizospheric oxygenation capacities, this could potentially lead to increased methane emissions in some wetlands. Additional research examining the role these plant functional groups play in other aspects of methane dynamics will be useful given the importance of methane as a greenhouse gas.

Biodiversity and ecosystem functioning experiments have demonstrated that plant biomass of species grown in mixtures is often greater than plant biomass of monocultures (i.e., mixtures over yield). While we understand that plant species utilize resources differently, how a combination of species increases resource use and productivity is not well known, especially in wetland ecosystems. Here, we used a mesocosm experiment to explore diversity effects on plant biomass production and to examine the role of N partitioning as a mechanism for overyielding in wetland ecosystems. Plant functional groups (FGs) represented the unit of diversity, and we included five levels of diversity (0-4 FGs). To test for N partitioning, we used a stable isotope technique to determine niche breadth and proportion similarity of inorganic N use (NO3- and NH4-) for individual FGs as well as mixtures containing 3 and 4 FGs. We found that total plant biomass increased in the first season from an average of 290 +/- 60 SE g ash-free dry mass (AFDM) m(-2) at the 1 FG level to 490 +/- 70 g AFDM m(-2) at the 4 FG level and in the second season from an average of 560 +/- 80 g AFDM m(-2) at the 1 FG level to 1000 +/- 90 g AFDM m(-2) at the 4 FG level indicating overyielding. Plant species comprising the majority of mesocosm biomass demonstrated preferential uptake of (NO3-)-N-15, while species with relatively less biomass (e.g., Acorus calamus and Carex crinita) preferred (NH4+)-N-15. Concentrations of N-15 in biomass increased with FG richness, but only in the 15NO(3)(-) treatment. Niche breadth did not vary among levels of FG richness. We observed a greater niche overlap with an increase of FGs, with species taking up greater proportion of (NO3-)-N-15 than (NH4+)-N-15. Our results indicate that plant overyielding in wetland mesocosms is not the result of niche partitioning of N chemical forms, but is associated with greater uptake of NO3. (C) 2011 Elsevier B.V. All rights reserved.

Wetlands provide many important services throughout the world, with an estimated economic value that, in comparison to other ecosystems, far exceeds their relatively small global extent. In recognition of their importance, both national and international regulations exist to protect the world's remaining wetlands. Of growing interest is the "no-net-loss'' policy which permits unavoidable destruction of wetlands if compensated by restoration of degraded wetlands or creation of new wetlands. The fundamental assumption of no-net-loss is that wetlands can be created which function equivalently to natural wetlands. One integral function that wetlands perform is cycling of carbon, nitrogen and phosphorus. Here we demonstrate that loss of this nutrient-related function is not being mitigated by creation or restoration of wetlands. We compare indicators of plant-and microbial-mediated functions, as well as abiotic (e. g., soil character, hydrology) and biotic (e. g., plant community composition) structure, between 10 created or restored and 5 natural freshwater depressional wetlands in central Ohio, USA. Nutrient stocks were generally smaller and transformations slower in created wetlands than in natural wetlands, with little development over time. Of particular concern were differences in C-and N-related function. Created wetlands stored 90% less C within litter and 80% less C within soil and processed 60% less N through denitrification, on average compared to natural wetlands. Our study suggests that subversion of natural wetlands into restored or created wetlands could have large-scale environmental consequences such as reduced capacity for nitrate removal and C sequestration.

Changes in the world’s species composition and the loss of biodiversity have prompted a closer investigation of the importance of biodiversity and community composition to ecosystem functioning. However, few studies have explored this relationship outside of controlled experiments. Here, we examined the relationship between plant diversity, primary production, and methane efflux in freshwater wetlands in an across-site field study and assessed the applicability of experimental findings to natural wetlands. Four wetland sites in central Ohio (USA) were divided into two plant communities, one dominated by clonal species and one dominated by non-clonal species. We found that plant diversity was negatively correlated with aboveground biomass in both the clonal and non-clonal communities. Overall, plant community composition was a stronger predictor than diversity of the response variables and in certain instances a stronger predictor than environmental factors such as soil organic matter content, moisture content, and pH. Thus, plant community composition is an important driver of ecosystem functioning in depressional wetlands beyond the well-known environmental factors. Additionally, our work indicates that results from experimental wetland studies of the relationship among diversity, biomass and methane emission are not applicable to the wetland ecosystems included in our study.

The current U.S. wetland mitigation policy of “no net loss” requires that a new wetland be created to replace any natural wetland destroyed under development pressures. This policy, however, may be resulting in a net loss of carbon‐based wetland functions. We evaluated the ability of created wetlands to accumulate carbon and to mitigate loss of carbon‐based functions in natural wetlands with variable hydrology. Potential limiting factors to carbon accumulation within created systems included soil aggregation, texture, and bulk density. Rates of soil development and the time required for created wetlands to accumulate the amount of carbon found in natural wetlands were estimated by an exponential model. Soils collected from five created (ages 3–8 years) and four natural freshwater marshes, located in central Ohio, USA, were analyzed for soil organic carbon (SOC), mineralizable soil carbon ( C min ), water‐stable aggregates (WSA), particle‐size fractions (PSD), and bulk density. Peak‐standing aboveground plant biomass was also quantified. Created wetlands contained significantly less plant biomass, SOC, and C min than natural wetlands (α ≤ 0.05; false discovery rate). Soil physical properties also differed significantly between created and natural wetlands, with fewer macroaggregates, more microaggregates, more silt–clay (0–5 cm only), and higher bulk density in created wetlands (α ≤ 0.05; false discovery rate). Carbon content was positively correlated with macroaggregate content and negatively correlated with microaggregate content, silt‐clay fraction, and bulk density. Fit of SOC data to the exponential model indicated that a newly created wetland would require 300 years to sequester the amount of SOC contained in a natural wetland. At this rate of carbon accumulation, a mitigation ratio of 2.7:1 (area) would be necessary for successful mitigation over a 50‐year time period. However, other trajectories fit the data equally well and suggested area mitigation ratios of 2.2:1 (logistic) to 4.4:1 (linear regression) to 5.1:1 (exponential regression). Whether created wetlands are on a trajectory toward natural wetland carbon function, however, remains uncertain. Until gaps in the data are filled and a trajectory verified, the best mitigation policy will be a conservative one, with a restrictive permitting process and high mitigation ratios (5.1:1 minimum).

In agricultural landscapes restoring riparian forest patches along streams is a watershed management priority. There are questions, however, as to the degree to which aquatic food webs are supported by inputs from small and often isolated forested riparian patches in agricultural landscapes. To examine these contributions we compared the plant communities and stream food webs between forested and non-forested riparian patches in an agricultural landscape and used stable isotope analyses to determine whether the primary source of energy for different levels of aquatic food webs were derived from terrestrial or aquatic sources. We observed no differences in the δ 13 C signatures of consumers between forested and non-forested riparian areas. Similarly, we also observed few differences in δ 15 N signatures between forested and non-forested sites for different trophic levels. This suggests that there may be other mechanisms driving the structure of aquatic food webs than basal resources alone.

Agricultural drainage can contribute excess N to aquatic ecosystems. The objective of our study was to investigate the capacity of agricultural ditches to remove NO3- via denitrification in maintained 1-stage and naturalized 2-stage agricultural ditches. We hypothesized that maintenance of ditches limits the potential for denitrification by removing in-stream and riparian vegetation and excavating fine sediments. We quantified denitrification rates in the sediments collected from ten 1-stage and ten 2-stage headwater ditches with 2 methods (sediment static core and denitrification enzyme activity) and over 4 sampling periods. We also measured water, plant, and sediment characteristics. With both methods, denitrification rates from sediments collected inside the channel (i.e., not along the slope and the bench) did not differ between the 2 types of ditch. We used a series of enrichment treatments of sediment slurries with C and NO3- to determine that denitrification was limited by NO3- on the bench of the 2-stage ditches and by both NO3- and C on the slope of the 1-stage ditches. We hypothesize that greater denitrification rates measured with the static core method in the slope might have been linked to greater % fine sediments in the slope of the 1-stage ditches and, thus, more developed anaerobic conditions in the sediment cores. Accumulation of organic matter in the benches that form in unmaintained ditches is favorable to denitrification, as shown by greater denitrification measured in the sediment slurries unamended with C.

Background/Question/Methods The loss of biodiversity worldwide has prompted a close investigation of the link between diversity and ecosystem functions. Most experimental studies have looked at the relationship between grassland plant diversity and aboveground productivity. Less is known about other ecosystems or how diversity affects belowground processes. Our objective was to investigate the link between plant community (diversity and composition) and key belowground processes such as root biomass production and CH4 dynamics in wetland ecosystems. We hypothesized that 1) root biomass would increase with functional group diversity due to complementarity and 2) the sediment pool of CH4 would decrease with diversity due to increased CH4 oxidation facilitated by root biomass. Four plant functional groups (facultative annuals, obligate annuals, reeds and tussocks) were planted in controlled mesocosms to represent five levels of functional diversity and every combination of functional groups at each diversity level. Unplanted mesocosms served as the zero diversity treatment. At peak biomass in 2007, porewater samplers were used to extract water at 5, 15, and 25 cm. The samples were frozen prior to headspace analysis of CH4 and CO2. Porewater was also analyzed for DOC. Afterward, we took soil cores from each mesocosm at 0-10 cm, 10-20 cm and 20-30 cm to determine the root biomass in each depth. Results/Conclusions Root biomass increased with functional diversity (F 3, 71 = 2.78, P < 0.05), however only the lowest diversity treatment had significantly lower root biomass than the highest diversity level; 150.6 ± 24.94 (SE) g DW m-2 and 307.2 ± 49.9 g DW m-2, respectively. At each depth, root biomass increased with diversity (P < 0.01), and root biomass at 0-10 cm >10-20 cm >20-30 cm. The facultative annual and obligate annual functional groups had significantly less root biomass than the other functional groups and combinations (P < 0.001). Porewater concentrations of CH4 did not significantly differ between functional group combinations or diversity levels (P > 0.05). However, CH4 was positively correlated with depth (F 1, 194 =19.75, P < 0.001), CO2 concentration (F 1, 194 = 42.94, P < 0.001) and DOC (F 1,194 = 4.98, P < 0.001) and was not correlated with root biomass (P > 0.05). Since this data is from the first year of sampling following mesocosm establishment, the insignificant relationship between root biomass and CH4 in the sediment pool may indicate that the microbial processes were influenced more by starting soil conditions than plant-mediated conditions.

This study examined if riparian land use (forested vs agricultural) affects hydraulic transport in headwater streams located in an agriculturally fragmented watershed. We identified paired 50‐m reaches (one reach in agricultural land use and the other in forested land use) along three headwater streams in the Upper Sugar Creek Watershed in northeast Ohio, USA (40° 51′42″N, 81° 50′29″W). Using breakthrough curves obtained by Rhodamine WT slug injections and the one‐dimensional transport with inflow and storage model (OTIS), hydraulic transport parameters were obtained for each reach on six different occasions (n = 36). Relative transient storage (AS:A) was similar between both reach types (As: A = 0·3 ± 0·1 for both agricultural and forested reaches). Comparing values of Fmed200 to those in the literature indicates that the effect of transient storage was moderately high in the study streams in the Upper Sugar Creek Watershed. Examining travel times revealed that overall residence time (HRT) and residence time in transient storage (TSTO) were both longer in forested reaches (forested HRT = 19·1 ± 11·5 min and TSTO = 4·0 ± 3·8 min; agricultural HRT = 9·3 ± 5·3 min and TSTO = 1·7 ± 1·4 min). We concluded that the effect of transient storage on solute transport was similar between the forested and agricultural reaches but the forested reaches had a greater potential to retain solutes as a result of longer travel times. Copyright © 2009 John Wiley & Sons, Ltd.

The determinination of an adequate collection protocol for protists is critical in the examination of their distribution and composition in temperate headwater streams. The objective of this study was to test which sampling design/sample gear combination would yield a cost-effective, site-representative protist assemblage. Defining parameters included greatest taxa richness, abundance, morphological diversity, taxa overlap, and cell-size diversity. Two sample designs (i.e., transect and mesohabitat design) and two sample gears (i.e., benthic grab sample, and a colonizing device [polyurethane foam unit, PFU]) were tested in three 100-m reaches representing the predominant environmental conditions (i.e., fragmented woodlots and agriculture) in the study area. A two-way ANOVA was used to evaluate abundance taxa richness and abundance of the protist assemblage (fixed effects) across the three reaches (random effects). The mesohabitat sampling design had the highest mean in both taxa richness (n = 72, P = 0.0012) and abundance (n = 72, P = 0.0004). The highest mean was reported with the benthic grab sampler (39.89 ± 1.1) in the abundance count only (n = 72, P < 0.0001). There was no difference in the design and gear interaction. Morphological diversity, cell-size diversity and percent taxa overlap between sampling design/sample gear combinations also were examined. A higher taxa overlap of the top 10% most abundant taxa was observed with the benthic grab sampler (43–100%) versus the PFU (25–69%); however, the greatest morphological and cell-size diversity was produced by the transect design/PFU combination. We conclude a “hybrid” of the two sample designs will account for “patchy” distributional patterns of protists and use of the PFU, because of the highest yield in morphological and cell-size diversity, will provide the most cost-effective, site-representative protist assemblage in temperate headwater streams.

Current methods of wetland assessment rely on the use of ecological indicators such as vegetation and amphibians, but often lack an in-depth analysis of soil parameters. The objective of this study was to determine whether the Ohio Rapid Assessment Method (ORAM) can be used to predict soil quality in forested wetlands. Soil cores were taken from six wetlands ranging in ORAM scores. The soil samples were analyzed for key soil parameters (aggregate stability, bulk density, organic matter, C, N, S, P, microbial biomass, and enzyme activity). Some of these soil parameters (i.e., microbial biomass, soil C, N and S, bulk density, soil moisture) were correlated with the ORAM scores, while others (i.e., P, pH, aggregate stability) showed no correlation. Enzyme activity was correlated with the ORAM score for one of the four sampling events. When analyzed together by a principal component analysis, the soil parameters did not separate the wetland sites along a gradient of ORAM scores. Our results indicate that the ORAM reflects some of the key soil quality conditions, but not all. We further discuss whether some of the soil parameters we selected are appropriate indicators of the quality of wetland soils.

Plant-based systems, such as wetlands and other ecological treatment systems, are promising, sustainable alternatives to conventional wastewater treatment. One of the biggest drawbacks of these systems when compared with conventional wastewater treatment systems is a large land area requirement; thus greater efficiency is needed to reduce land requirements and consequent costs. This research identified plant species that promote greater nitrogen removal, and whose use could lead to increased efficiency of ecological treatment systems. Potential nitrification and denitrification rates of bacteria associated with the roots of herbaceous species (Cyperus papyrus, Colocasia esculentus), and woody species (Hibiscus moscheutus and Salix nigra) were measured in the lab. Potential nitrification rates were determined from the rate of NO 3 − accumulation in microcosms containing wastewater and live plants. Potential denitrification was measured using the acetylene inhibition technique on microcosm incubations of filtered wastewater and plant roots. Significantly more NO 3 − (mg 1−1 hr−1) was produced by bacteria associated with S. nigra and C. papyrus roots than in microcosms containing only wastewater, or H. moscheutus, (P < 0.001). Potential denitrification rates were significantly greater in H. moscheutos and S. nigra root microcosms than in C. esculentus and C. papyrus root microcosms on dry weight, wet weight and root area bases (P < 0.001). These results demonstrate that the efficiency of ecological treatment systems treating wastewater high in NH 4 + would be improved with a mix of herbaceous and woody species, whereas wastewater high in NO 3 − would be most efficiently treated with woody species. Thus, a diversity of species is needed to optimize ecological treatment system function.

The objective of this project was to assess in‐stream nitrogen removal capacity in a fragmented agricultural landscape and to compare removal capacities in streams with agricultural or residential (hereafter referred to as agricultural streams) and forested riparian land use. We also identified what stream characteristics control nitrogen removal in these systems. We examined paired reaches (one agricultural and one forested reach) along five headwater streams in an agricultural watershed (Upper Sugar Creek Watershed) in northeast Ohio. Although denitrification rates were high (<0.1‐17.2 mg N m−2 h−1), annual nitrogen removal was most likely low because during spring and fall, when in‐stream nitrogen loads were high, removal was low, and during summer when instream nitrogen loads were low, removal was high. Between the agricultural and forested reaches removal rates were similar in terms of loss rate and uptake velocity. Removal capacities were similar despite forested reaches having higher hydraulic residence times. Using a redundancy analysis we identified temperature, in‐stream nitrate concentration, and relative transient storage as stream characteristics that affect nitrogen removal. Further analysis suggests that nitrogen removal via denitrification in these headwater streams was not limited by the availability of nitrate. In this fragmented agricultural watershed in‐stream nitrogen removal was low and riparian land use had no effect on this process, most likely because of nitrate saturation.

As a result of increased anthropogenic nitrogen (N) loading in surface waters of agricultural watersheds, there is enhanced interest to understand and quantify N removal mechanisms. Denitrification, an important N removal mechanism in aquatic systems, may contribute to reducing N pollution in agricultural headwater streams. However, the key factors controlling this process in lotic systems remain unclear. The objective of our study was to examine the factors regulating rates of denitrification in the sediments of agricultural headwater streams in the mid-western USA. Denitrification rates were variable among streams and treatments (<0.1–28.0 μg N g AFDM−1 h−1) and on average, were higher than those reported for similar headwater streams. Carbon quantity and quality, and pH had no effect on denitrification, while temperature and nitrate (\( {\text{NO}}^{ - }_{{\text{3}}} \)) concentrations had a positive effect on rates of denitrification. Specifically, \( {\text{NO}}^{ - }_{{\text{3}}} \) controlled denitrification following Michaelis-Menten kinetics. We calculated a value of km (1.0 mg \( {\text{NO}}^{ - }_{{\text{3}}} \)-N L-1) that was comparable to other studies in aquatic sediments but was well below the median in-stream \( {\text{NO}}^{ - }_{{\text{3}}} \) concentrations (5.2–17.4 mg \( {\text{NO}}^{ - }_{{\text{3}}} \)-N L−1) observed at the study sites. Despite high rates of denitrification, this removal mechanism is most likely \( {\text{NO}}^{ - }_{{\text{3}}} \) saturated in the agricultural headwater streams we examined, suggesting that these systems are not effective at removing in-stream N.

A watershed-based assessment of wetland impacts and compensatory mitigation was conducted for the Cuyahoga River Watershed (CRW) in northeastern Ohio, USA, to explore the effectiveness of wetland mitigation regulations and any resulting cumulative changes to wetland and landscape structure. Mitigation projects from 23 Section 401 certifications and Ohio Isolated Wetland permits were evaluated for permit compliance, wetland structure, and landscape context. Although there was a net gain in wetland area as a result of the 23 permits, the CRW experienced a net loss of wetland acreage due to the exportation to mitigation banks located outside the watershed. The majority of projects (67%) that restored or created wetlands independently (not at a mitigation bank) were not successful at meeting permit requirements in terms of wetland area. The comparison of impacted and mitigation wetland vegetation types revealed an increase in open-water/emergent wetland area and a decrease in area of scrub/shrub and forested wetlands, along with a decrease in the number of wetlands from 134 impacted wetlands to 65 mitigation wetlands. Impacted wetlands were significantly smaller than replacement wetlands. Landscape composition surrounding the wetlands was highly variable, varying from 17%–75% natural land uses and from 18%–82% human land uses. We suggest that an improvement in compliance with permit requirements is necessary. Current wetland policy allows for the exportation of wetlands for mitigation purposes, which can result in the loss of wetlands from some hydrologic units. The consideration of wetland structure needs to be incorporated into the regulatory process to avoid a shift in wetland types that are present. Finally, instead of reviewing projects on a site-by-site basis, a landscape approach should be taken in order to avoid the loss of upland-wetland heterogeneity and the placement of mitigation wetlands in degraded landscapes.

Soil gas flux is commonly measured by monitoring the change in headspace gas concentration over time within a sealed compartment at the soil surface. Often, more than one trace gas is monitored at a time (e.g., CO 2 and CH 4 ), but the data fit separately. Flux estimates for CO 2 and CH 4 were obtained simultaneously by minimizing a weighted sum‐of‐squares error. The approximation of one model parameter for CH 4 , through theoretical relationship to the respective CO 2 parameter, reduced the total parameter count by one and allowed for the joint estimation of one parameter using the combined CO 2 and CH 4 datasets. The method of joint optimization was compared with separate optimization for two nonlinear models, using both real and simulated data. The datasets were best fit with the jointly optimized models. Furthermore, the jointly optimized models more accurately estimated initial soil–air fluxes (simulated data only). The method of joint optimization is recommended as a means to apply better‐fitting nonlinear models to typically small gas sample sets. This method is applicable to any number of trace gases monitored simultaneously.