Wetland Stream Research Articles

Seasonal Wetlands Make a Relatively Limited Contribution to the Dissolved Carbon Pool of a Lowland Headwater Tropical Stream

AbstractWetlands process large amounts of carbon (C) that can be exported laterally to streams and rivers. However, our understanding of wetland inputs to streams remains unclear, particularly in tropical systems. Here we estimated the contribution of seasonal wetlands to the C pool of a lowland headwater stream in the Australian tropics. We measured dissolved organic and inorganic C (DOC and DIC) and dissolved gases (carbon dioxide—CO2, methane—CH4) during the wet season along the mainstem and in wetland drains connected to the stream. We also recorded hourly measurements of dissolved CO2 along a ‘stream–wetland drain–stream’ continuum, and used a hydrological model combined with a simple mass balance approach to assess the water, DIC and DOC sources to the stream. Seasonal wetlands contributed ∼15% and ∼16% of the DOC and DIC loads during our synoptic sampling, slightly higher than the percent area (∼9%) they occupy in the catchment. The riparian forest (75% of the DOC load) and groundwater inflows (58% of the DIC load) were identified as the main sources of stream DOC and DIC. Seasonal wetlands also contributed marginally to stream CO2 and CH4. Importantly, the rates of stream CO2 emission (1.86 g C s−1) and DOC mineralization (0.33 g C s−1) were much lower than the downstream export of DIC (6.39 g C s−1) and DOC (2.66 g g C s−1). This work highlights the need for further research on the role of riparian corridors as producers and conduits of terrestrial C to tropical streams.

Source, composition and molecular diversity of dissolved and particulate organic matter varied with riparian land use in tropical coastal headstreams

Source, composition and molecular diversity determine the reactivity and stabilization of organic matter (OM, dissolved [DOM]/particulate [POM]), affecting its behavior and fate. Here, multiple spectral and mass spectrometry techniques were applied to examine how riparian land-use shaped the source, composition and molecular diversity of POM and DOM (HDOM) in adjacent headstreams. Compared to HDOM with abundant lignins, microbially-transformed heteroatoms and carboxyl-rich alicyclic acids (CRAMs), POM exhibited higher allochthonous characteristics and more bioactive components, but lower molecular weight and diversity in different land-use-dominated streams. Compared to wetland-dominated headstreams, both POM and HDOM exhibited more terrestrial origin and condensed aromatics/tannins molecules for agriculture-impacted headstreams and bio-labile lipids, proteins and carbohydrates for forest-impacted headstreams. Structural equation mode (SEM) showed that soil-derived DOM (SDOM) showed the most prominent influence on the source, composition and molecular diversity of POM and the source of HDOM. The molecular composition and diversity of HDOM were mainly influenced by soil properties/SDOM and aquatic microorganisms, respectively. Redundancy analysis (RDA) revealed that autochthonous, bio-labile compositions of POM in forest and wetland streams were positively related to aquatic Bacteroidetes/Cyanobacteria, and carbohydrates/biogenic index of SDOM, while that of HDOM were positively linked with aquatic Bacteroidetes/Cyanobacteria, and SDOM molecular diversity. Terrestrial and aromatic POM in agricultural headstreams were associated with aquatic total nitrogen/Actinobacteria, and humification degree, aromatic/phenolic substances of SDOM, while that of HDOM were mainly regulated by aquatic nitrate/total nitrogen/Actinobacteria, and aromatic/carboxylic-containing moieties of SDOM. Noteworthily, the molecular diversity of agricultural OM increased along the soil-stream continuum due to the input of soil condensed aromatics and tannins. The opposite trend was observed in forest and wetland streams due to the input of bioactive carbohydrates and the microbial-degradation in-stream. These results are helpful to predict the behavior and fate of OM and determine effective management strategies in tropical coastal regions undergoing intense anthropogenic alterations.

Heterogeneity in habitat and nutrient availability facilitate the co-occurrence of N2 fixation and denitrification across wetland–stream–lake ecotones of Lakes Superior and Huron

Heterogeneity in habitat and nutrient availability facilitate the co-occurrence of N2 fixation and denitrification across wetland–stream–lake ecotones of Lakes Superior and Huron

Response of size-dependent chemical composition of dissolved organic and inorganic species to land use types in tropical coastal headstreams

Land-use types dramatically affect the source, composition, behavior and fate of headstream chemical species. However, the influence of land-use types on the size-dependent composition of dissolved organic matter (DOM) and dissolved inorganic matter (DIM) is still unclear. Here, we evaluated the size-dependent concentration, composition and relationship of chemical species from 9 coastal headstreams (i.e. forested, agricultural and wetland headstreams) using multiple spectroscopic techniques including absorbance, excitation-emission matrix, near-edge X-ray absorption fine structure spectroscopy (NEXAFS), X-ray diffraction (XRD), scanning electron microscopy combined with energy dispersive spectroscopy (SEM-EDS) and synchrotron-based micro-X-ray fluorescence (μ-XRF). Results showed that 68.57%-85.78% of dissolved organic carbon (DOC) with abundant humic/fulvic-like substances were distributed in the <1 kDa fraction in all samples, with a higher percentage in wetland samples. Agricultural land-use increased the export of aluminosilicate minerals in >1 kDa fractions and terrestrial fulvic/humic-like substances from land to stream. Forested streams showed high DOC in the 1 kDa-0.2 μm fraction, predominance of autochthonous DOM rich in amides, amines, carboxyl and O-alkyl groups, and abundance whitlockite and ferromanganese oxides. Wetland streams were characterized by abundant halite, sylvite, and microbially-transformed humic-like DOM rich in aromatic and phenolic groups. Morphology and correlation analysis implied DIM was closely combined with fluorescent DOM (FDOM) and colored DOM (CDOM), resulting in more irregular organo-inorganic complexes in forested and agricultural streams, and more halite and sylvite crystal blocks encapsulating by smooth and close organic–inorganic complexes in wetland streams. Redundancy analysis (RDA) analysis suggested that land-use types (17.20%) and molecular weight (14.29%) were the prominent factors impacting the composition and relationship of DOM and DIM. Land-use types altered the sources and transport patterns of chemical species in headstreams, influencing their size-dependent compositions and associated biogeochemical processes. Such information is imperative for monitoring and developing land-use policies in coastal regions undergoing intense anthropogenic alterations.

Energy from Salinity Gradient of Wetland Saline Water Using Reverse Electrodialysis Membrane

Reverse electrodialysis (RED) membrane is an emerging renewable energy which harvest electricity from mixing two streams on different salinities. In real practice is still not clearly defined for the effectiveness of salinity gradient power (SGP)-RED due to the limitation of artificial saline water. Generally, South Kalimantan Indonesia is rich by wetland and coastal area. Due to that wetland saline water is potential as saline water sources for collection the SGP. This experiment aims to investigate the impact of natural feed stream wetland saline water was collected from Muara Halayung South Kalimantan-Indonesia to demineralized (WSW),artificial brackish (ABW) (0.35 wt %NaCl), and artificial seawater (ASW) (3.5 wt % NaCl) in terms of power density measured on a lab-scale RED membrane stack prototype 12 x 12 cm. Ion exchange membrane (IEM) was used in this work consisted from cellulose modified Anion Exchange Membrane (AEM) by EDTA-quaternization (EDC) process. Whereas, Cation Exchange Membrane (CEM) was employing Nafion NR-212 with thickness 0.002 in. Lab-scale RED tests operated 3 hours into area system has 121cm2; AEM and CEM area have 100cm2; uses spacer nylon a pair between membranes; and two electrodes by stainless-steal and copper. Feed water was into RED system then measured power density as an electrical energy potential that from separate ions by AEM and CEM. The result among of this experiment, characteristic of wetland saline water naturally had electro conductivity (EC) 135.6 µS/cm; TOM 15.2 ppm; and has ionic compound higher in Na+ and Cl- which is Cl- compound as one of potentially formed salinity on that wetland water and become potential uses one of natural feed water in RED system. The highest energy power density on RED process obtained by mixed WSW:ASW was 1.43 W/m2. While ratio of the gradient salinity WSW:ABW to ABW:ASW were increasing 86% which has 1:5 to 1:30 as the effect of stream mixing by two natural feed water.

Methodology for Topographic Survey of Carbon Absorption Sources in Stream Wetland Using Industrial Drone

As the increase of carbon dioxide in atmospheric accelerates climate change, various efforts have been performed to reduce carbon worldwide. Recently, as the concept of green carbon stored and sequestrated through photosynthesis by land plants has been emphasized to reduce carbon content from environments, the importance of carbon absorption survey for plant groups analysis of terrestrial ecosystems such as forests and river wetlands is increasing. Carbon absorption sources in terrestrial ecosystems exist in various forms of plant, soil, and topography, and represent various carbon absorption through physical, chemical and biological reactions between each other depending on the location and height of the plant groups. In this study, an industrial RTK drone capable of taking high-resolution images was used for efficient carbon absorption survey in Damyang stream wetland. Based on the global navigation satellite system by RTK, the location could be corrected in real time, and ecosystem surveys could be conducted on the height of the terrain with RTK drone. The point cloud technique of the high-density surface model was used to analyze the three-dimensional topography of areas that are difficult to access. Using the photo survey function of the RTK drone, it is expected to play an important role in understanding the total amount of green carbon of terrestrial ecosystems and carbon circulation of the land ecosystem by enabling the creation of topographic maps of stream wetlands, and riparian vegetation with complex terrain.

Effects of bulk degradation and boundary absorption on dispersion of contaminant in wetland flow

The paper presents transport phenomena of solute in a shallow wetland channel considering the effects of the bulk degradation and boundary absorption at both the channel banks. A piece-wise uniform mesh on the finite difference implicit scheme is adopted to investigate the present problem. The current solution has achieved an excellent agreement with the existing experimental and numerical results. It is seen that the transport of contaminant in the width dominated wetland stream is influenced by various parameters such as boundary absorption, bulk degradation, vegetation parameter, tortuosity and dispersion time. The significant effects of the bulk degradation and boundary reactions are observed on the contaminant emission. The work measures the dispersion of contaminant in both longitudinal and transverse directions. Also, the transversal and longitudinal mean concentration distributions are shown in the shallow wetland flow. The results of this study may be used to control the water degradation, flood mitigation and coastal protection.

Numerical study on dispersion of fine settling particles in a depth dominated wetland flow

Wetlands were long considered a nuisance because they were not suitable for growth of many agriculture products. Nowadays, owing to it’s importance in agriculture engineering, wetlands are invaluable to the mankind. Wetlands due to their commanding influences on ecosystem, benefited people and the environment in terms of water supply, climate regulation, biodiversity conservation and contaminant erosion are very useful in water resources. This investigation presents a numerical approach to detect the environmental dispersion of the fine particles with settling velocity in a wetland flow. A finite difference implicit scheme with layer-adapted mesh is employed to find the solution of the problem. The consequences of the various relevant parameters on the flow and concentration profiles are illustrated graphically. The computed concentration profiles agreed well with the existing experimental data as well as with the numerical solution. The vertical concentration profiles of fine settling particles are presented in different downstream stations with various settling velocities. It is found that the mixing of tracers into the wetland stream significantly influenced by settling velocity, dispersion time, damping factor, porosity, tortuosity, and mass dispersivity. This study finds great importance in understanding and organizing the elementary methods of wastewater treatment and flood damage control in natural and manufactured wetland flows.

Anionic nanoparticle and microplastic non-exponential distributions from source scale with grain size in environmental granular media

Nanoparticle and microplastic (colloid) transport behaviors impact strategies for groundwater protection and remediation. Complex colloid transport behaviors of anionic nano- and micro-sized colloids have been previously elucidated via independent experiments in chemically-cleaned and amended granular media with grain sizes in the range of fine to coarse sand (e.g., 200–1000 μm). Such experiments show that under conditions where a repulsive barrier was present in colloid-collector interactions (unfavorable conditions), the distribution of retained colloids down-gradient from their source deviates from the exponential decrease expected from compounded loss across a series of collectors (grains). Previous experiments have not examined the impact of colloid size or granular media grain size on colloid distribution down-gradient from their source, particularly in streambed-equilibrated granular media. To address this gap, a field transport experiment in constructed wetland stream beds to distances up to 20 m were conducted for colloids ranging in size from micro to nano (60 nm–7 μm) in streambed-equilibrated pea gravel and sand (4200 and 420 μm mean grain sizes, respectively). All colloid sizes showed non-exponential (hyper-exponential) distributions from source, over meter scales in pea gravel versus cm scales reported for fine sand. Colloids in the ca. 1 μm size range were most mobile, as expected from mass transfer to surfaces and interaction with nanoscale heterogeneity. The distance over which non-exponential colloid distribution occurred increased with media grain size, which carries implications for the potential mechanism driving non-exponential colloid distribution from source, and for strategies to predict transport.

Improving denitrification in an aquaculture wetland using fish waste - a case study

Cost-efficient, end-of-pipe, nitrate removal techniques are called for by the commercial aquaculture industry. This case study examined how simple flow manipulations improved the denitrification performance of a 19,007 m2 (13,305 m3) constructed, free water surface (FWS) wetland treating aquaculture effluent. The wetland consisted of two separate streams with a common outlet: one stream treating nitrate-rich but carbon deficient effluent from the production unit at a hydraulic retention time (HRT) of 1.5 days (wetland stream 1); and a second stream treating carbon-rich, fish sludge-based effluent at a HRT of 41.0 days (wetland stream 2). During the course of the study (May–July 2017), three increasing proportions (40, 49 and 56%) of nitrate-rich effluent were re-directed from wetland stream 1 to the sludge-fed wetland stream 2 aiming at improving heterotrophic denitrification conditions in wetland stream 2 and consequently nitrogen removal in the wetland as a whole. Inlet C/N ratio in wetland stream 2 decreased from 1086 ± 57 to an average of 234 ± 56 (p < .05), and the area-based, total nitrogen (TN) removal rate in this wetland section increased significantly from 0.1 ± 0.01 to 8.4 ± 1.4 g/m2/d at the highest manipulated flow. In comparison, the flow manipulations had no effect on TN removal rates in wetland stream 1 averaging 1.4 ± 0.2 g/m2/d throughout the study. For the wetland as a whole, the TN removal rate increased from 1.4 ± 0.2 to 3.9 ± 0.8 g TN/m2/d. The flow manipulations furthermore improved the removal rates of total phosphorous and dissolved organic matter in the wetland as a whole. The study demonstrates that denitrification in a constructed aquaculture wetland may be improved by combining sludge-based and nitrogen-rich effluents in right proportions and leading it through an anoxic section of the wetland.

Controls on soil carbon dioxide and methane fluxes from a peat swamp vary by hydrogeomorphic setting

AbstractCarbon dynamics of temperate peat swamps are a largely understudied component of wetland carbon cycling. Under a changing climate, hydrometeorological conditions may change, and understanding how peat swamps may be impacted is important. We investigated the importance of hydrogeomorphic setting on controlling soil carbon dioxide (CO2) and methane (CH4) fluxes from a temperate peat swamp in southern Ontario, Canada over a 3‐year period. We chose three different hydrogeomorphic settings: (a) a site with strong wetland‐stream interactions (i.e., an unconfined stream channel; unconfined), (b) a site with limited wetland‐stream interactions (confined), and (c) an interior site (no wetland–stream interaction). The differing hydrogeomorphic conditions between the sites resulted in differences in carbon fluxes. The unconfined site maintained a higher water table across all three study years, providing conditions that are not favourable to CO2 production. The confined and interior sites sustained a much lower water table, with conditions more conducive to CO2 efflux. The unconfined site also had the highest CH4 emissions due to the increased anoxic conditions favourable for CH4 production as a result of the higher water table position. Hydrogeomorphic setting was found to be important for understanding within site variation, suggesting the sites may respond differently to longer‐term shifts in environmental conditions. This may change relationships between sites if the responses are strong enough to significantly alter carbon fluxes, decomposition, and potential peat accumulation rates. It is important to understand the locally specific responses to environmental conditions within peat swamp ecosystems, in order to make future predictions about whole ecosystem function under changing conditions.

Differential Response of Greenhouse Gas Evasion to Storms in Forested and Wetland Streams

AbstractGreenhouse gas evasion from inland waters is a globally significant yet highly uncertain flux, especially in regard to effects of wetlands and hydrologic variability. We sampled five first‐order and two second‐order streams with variable wetland influence during storm events for dissolved CO2, CH4, and N2O. We also calculated gas evasion rates. In first‐order streams, pCO2 and pN2O were significantly higher in the stream with the most wetland influence (mean ± 1 std: 3,965 ± 1,504 and 1.18 ± 0.37 μatm, respectively) than the forested stream (2,927 ± 439 and 0.47 ± 0.08 μatm, respectively). In second‐order streams, pCO2, pCH4, and pN2O were higher in the 14% wetland stream (3,274 ± 825, 501 ± 207, and 1.37 ± 0.43 μatm, respectively) than in the 2% wetland stream (1,858 ± 423, 137 ± 53, and 0.37 ± 0.08 μatm, respectively). In first‐order streams, pCO2 in streams with wetland influence increased during rain events, while pCO2 in streams with little to no wetland influence decreased or remained constant. Generally, pCH4 and pN2O followed the same trend, except in one stream with intermediate wetland influence. Gas transfer velocity increased in all streams during storm events. However, the forested streams had higher gas transfer velocities than the wetland streams due to steeper topography. CO2, CH4, and N2O evasion peaked in one of the intermediate wetland streams at high flow (maximum: 66 g C·m−2·day−1, 177 mg C·m−2·day−1, and 9.7 mg N·m−2·day−1, respectively). These findings suggest that gases are shunted downstream in flatter, wetland streams, while gases are evaded closer to their source in steeper, forested streams.

Hydrological dynamics of prairie pothole wetlands: Dominant processes and landscape controls under contrasted conditions

AbstractNumerous studies have examined the impact of prairie pothole wetlands on overall watershed dynamics. However, very few have looked at individual wetland dynamics across a continuum of alteration status using subdaily hydrometric data. Here, the importance of surface and subsurface water storage dynamics in the prairie pothole region was documented by (1) characterizing surface fill–spill dynamics in intact and consolidated wetlands; (2) quantifying water‐table fluctuations and the occurrence of overland flow downslope of fully drained wetlands; (3) assessing the relation (or lack thereof) between intact, consolidated or drained wetland hydrological behaviour, and stream dynamics; and (4) relating wetland hydrological behaviour to landscape characteristics. Focus was on southwestern Manitoba, Canada, where ten intact, three consolidated, seven fully drained wetlands, and a nearby creek were monitored over two years with differing antecedent storage conditions. Hourly hydrological time series were used to compute behavioural metrics reflective of year‐specific and season‐specific wetland dynamics. Behavioural metrics were then correlated to wetland physical characteristics to identify landscape controls on wetland hydrology. Predictably, more frequent spillage or overland flow was observed when antecedent storage was high. Consolidated wetlands had a high degree of water permanence and a greater frequency of fill–spill events than intact wetlands. Shallow and highly responsive water tables were present downslope of fully drained wetlands. Potential wetland–stream connectivity was also inferred via time‐series analysis, while some landscape characteristics (e.g., wetland surface, catchment area, and storage volume) strongly correlated with wetland behavioural metrics. The nonstationarity of dominant processes was, however, evident through the lack of consistent correlations across seasons. This, therefore, highlights the importance of combining multiyear high‐frequency hydrometric data and detailed landscape analyses in wetland hydrology studies.

Effects of conservation wetlands on stream habitat, water quality and fish communities in agricultural watersheds of the lower Mississippi River Basin

Wetland conservation programs (e.g., Wetland Reserve Program and Conservation Reserve Program) have been implemented throughout the Mississippi River Basin to reduce environmental impacts from agricultural activities. However, there is limited information on the overall effectiveness of these programs on improving stream ecological conditions. To address this issue, replicate streams from southeastern Arkansas draining watersheds containing predominately croplands (n=4, termed “cropland”) and created wetlands (n=4, termed “wetland”) were monitored monthly from August 2012 through July 2013. Although repeated-measures analyses of variance (ANOVA) detected many significant time×stream type interactions, several habitat parameters and total habitat scores exhibited a general improvement in wetland streams. Some water quality conditions were better in wetland streams (e.g., lower turbidity, total suspended solids, and nutrient) compared to cropland streams. The time (season) effect was significant (p<0.05) for 13 of the 14 water quality parameters measured, meaning that water quality varied seasonally. Among the water quality parameters measured, three (water temperature, pH, and turbidity) exhibited significant (p<0.05) time×stream type interaction, meaning that the stream type effect was not consistent through time (seasons). Fish community sampling collected 6543 specimens from 12 species during the study period; 4410 and 2133 fish specimens were collected from cropland and wetland streams, respectively. Fish community metrics such as species diversity, species evenness, and species richness index were not significantly (p>0.05) greater in wetland streams. Overall, the conservation wetlands in the Lower Mississippi River Basin appear to have significantly improved stream habitat and moderately improved water quality, though no significant fish community effect was detected.

Multivariate Analyses of Phytoplankton Pigment Fluorescence from a Freshwater River Network.

Monitoring phytoplankton classes in river networks is critical to understanding phytoplankton dynamics and to predicting the ecosystem response to changing land-use and seasons. Applicability of phytoplankton fluorescence as a quick and effective ecological monitoring approach is relatively unexplored in freshwater ecosystems. We used multivariate analyses of fluorescence from pigment extracted in 90% acetone to assess the variability in phytoplankton classes, herbivory, and organic matter quality in a freshwater river network. A total of four models developed by the parallel factor analysis (PARAFAC) of fluorescence excitation and emission matrices identified six components: Model 1 (pheophytin-A and chlorophyll-A), Model 2 (chlorophyll-B and chlorophyll-C), Model 3 (pheophytin-B), and Model 4 (pheophytin-C). Redundancy analyses revealed that in the summer, urban and agricultural streams were abundant in chlorophylls, fresh organic matter, and organic nitrogen, whereas in winter, streams were high in phaeopigments. A slow-moving, light-limited wetland stream was an exception as high phaeopigment abundance was observed in both seasons. The PARAFAC components were used to develop a partial least-squares regression-based model (r2 = 0.53; Nash-Sutcliffe efficiency = 0.5; n = 147) that successfully predicted chlorophyll-A concentrations from an external subset of river water samples (r2 = 0.41; p < 0.0001; n = 75). Thus, combining multivariate analyses and fluorescence spectroscopy is useful for monitoring and predicting phytoplankton dynamics in large river networks.

Design and assessment of stream–wetland systems for nutrient removal in an urban watershed of China

Constructed wetlands are typical best management practices (BMPs) often used to reduce nutrient loads in streams. Evaluating the effectiveness of wetland design on nutrient removal is essential to assist watershed managers in optimal design of BMP dimensions and placement. In this study, we assess performance of two constructed wetland systems (comprising of nine wetlands) installed in downstream of Longhongjian Stream in Hangzhou City, China. These wetland systems are monitored and evaluated for their effects on nutrient removal, particularly TN, NO3-N, TP, and PO4-P. Based on wetland input–output metrics, removal efficiency (RE) is used to quantify wetland system. Results show that both wetland systems effectively removed nutrients, with RE as high as 45% of TN, 57% of NO3-N, 78% of TP, and 86% of PO4-P. In general, nutrient removal efficiency is seasonally dependent, with better removal efficiency occurring during warmer seasons than others. Macrophyte uptake is a primary removal process in these wetlands. We observe that more wetlands working concurrently can provide a greater level of control on nutrients in lotic environments. Wetland design parameters play an important role in removal of nutrients in streams. Increasing flow volume and surface area of wetland, designing curvilinear shoreline, and longer flow paths can be used as design criteria for wetland systems aimed at nutrient removal.

Temporal variability in hydrology modifies the influence of geomorphology on wetland distribution along a desert stream

Summary Both geomorphic setting and dynamic environmental variables influence riverine wetland vegetation distributions. Most studies of species distributions in riverine systems emphasize either hydrological variability or geomorphic controls, but rarely consider the interaction between the two. It is unknown whether and to what extent the relationship between the geomorphic template and species distribution is modified by fluctuating environmental conditions. This study examines how spatial patterns of riverine wetlands in a desert stream change in response to environmental shifts brought about by interannual variability in the hydrologic regime. We surveyed wetland spatial distribution and measured its abundance every June over 5 years (2009–2013) by recording patch size and presence/absence of five wetland plant species along the 12‐km main stem of Sycamore Creek, Arizona, U.S.A. The study period encompassed a very large flood in January 2010, a wet year (2010), two average years (2009 and 2013) and two extremely dry years (2011 and 2012). We used a Bayesian statistical approach to analyse the relationship between geomorphic variables and wetland distribution under different hydrological conditions. The geomorphic variables provided much greater explanatory power in dry years than in average to wet years. Hydrological conditions modified the interactions between geomorphic template and species distribution. Annual hydrological conditions affected the direction (i.e. positive or negative effect) and magnitude (i.e. the size and significance level of an effect) of these interactions, both of which gave rise to spatial patterns of wetlands. Ecosystem temporal variability, such as inter‐annual and multi‐year hydrological variability and longer‐term ecosystem state changes, triggered complex species responses. Synthesis. The effect of geomorphic setting on stream wetland plant distribution in this desert system is conditioned on the temporal variability in hydrology among years. Temporal transferability of the relationship between geomorphology and species distributions is therefore questionable.

The Efficacy of Constructed Stream-Wetland Complexes at Reducing the Flux of Suspended Solids to Chesapeake Bay.

Studies documenting the capacity of restored streams to reduce pollutant loads indicate that they are relatively ineffective when principal watershed stressors remain intact. Novel restorations are being designed to increase the hydraulic connectivity between stream channels and floodplains to enhance pollutant removal, and their popularity has increased the need for measurements of potential load reductions. Herein we summarize input-output budgets of total suspended solids (TSS) in two Coastal Plain lowland valleys modified to create stream-wetland complexes located above the head-of-tide on the western shore of Chesapeake Bay. Loads entering (input) and exiting (output) the reconfigured valleys over three years were 103 ± 26 and 85 ± 21 tons, respectively, and 41 ± 10 and 46 ± 9 tons, respectively. In both cases, changes in loads within the reconfigured valleys were insignificant relative to cumulative errors. High variability of TSS retention among stormflow events suggests that the capacity of these systems to trap and retain solids and their sustainability depend on the magnitude of TSS loads originating upstream, design characteristics, and the frequency and magnitude of large storms. Constructed stream-wetland complexes receiving relatively high TSS loads may experience progressive physical and chemical changes that limit their sustainability.

Legacy source of mercury in an urban stream–wetland ecosystem in central North Carolina, USA

In the United States, aquatic mercury contamination originates from point and non-point sources to watersheds. Here, we studied the contribution of mercury in urban runoff derived from historically contaminated soils and the subsequent production of methylmercury in a stream–wetland complex (Durham, North Carolina), the receiving water of this runoff. Our results demonstrated that the mercury originated from the leachate of grass-covered athletic fields. A fraction of mercury in this soil existed as phenylmercury, suggesting that mercurial anti-fungal compounds were historically applied to this soil. Further downstream in the anaerobic sediments of the stream–wetland complex, a fraction (up to 9%) of mercury was converted to methylmercury, the bioaccumulative form of the metal. Importantly, the concentrations of total mercury and methylmercury were reduced to background levels within the stream–wetland complex. Overall, this work provides an example of a legacy source of mercury that should be considered in urban watershed models and watershed management.

Surface Hydrologic Connectivity Between Delmarva Bay Wetlands and Nearby Streams Along a Gradient of Agricultural Alteration

Although recent U.S. Supreme Court rulings indicate surface hydrologic connectivity (SHC) between geographically isolated wetlands and nearby streams may be used, in part, to determine wetland jurisdictional status, and ecologic implications are considerable regardless of policies, wetland–stream SHC has rarely been quantified. Furthermore, the impact of cultivation and restoration on wetland–stream SHC is largely unknown. To help fill these knowledge gaps, we recorded SHC patterns during water year 2010 in non-perennial streams connecting Delmarva bay wetlands, which are commonly considered geographically isolated, and nearby perennial streams. We also evaluated how hydrologic wetland restoration impacts SHC relative to historical wetlands and native forested wetlands. Cumulative connection duration, number of connectivity transitions, mean connection duration, and maximum individual connection duration (D max-c ) were quantified. Forested wetlands were connected to perennial streams for a greater cumulative duration but exhibited fewer connectivity transitions relative to both historical and restored wetlands. SHC between historical and restored wetlands and nearby perennial streams did not differ with respect to any of the calculated metrics. Forested wetland-stream SHC was seasonally intermittent, exhibiting stream outflow from mid-fall to late-spring during periods of low evapotranspiration and elevated groundwater levels but lacking connectivity during summer months when evapotranspiration and groundwater were at an annual high and low, respectively. Historical and restored wetland-stream SHC was largely ephemeral, occurring in response to antecedent rainfall, particularly during winter and spring. Stepwise regression models describe cumulative connection duration and D max-c as a function of wetland, watershed, and non-perennial stream metrics including watershed relief, non-perennial stream slope, non-perennial stream length, and soil saturated hydraulic conductivity. Wetland–stream SHC has potential ecological implications, including provision of dispersal corridors for biota, biogeochemical processing of nutrients, and downstream delivery of energy, matter, and organisms, and is currently tied to wetland regulatory status in the U.S.