Wetlands最新文献

Riparian vegetation varies along hydrologic gradients, along which inundation and drought tend to be inversely correlated. Differentiating effects of inundation and drought on plant distributions is critical for predicting impacts of changes to baseflows and designing flow patterns to achieve vegetation objectives in regulated river systems. To this end, we conducted a greenhouse experiment where we decreased, increased, or maintained constant water levels experienced by a suite of riparian plant species. We related changes in new root growth and stomatal conductance under experimental conditions to species hydrologic niches in the field, specifically the median elevation at which they occur above the channel, along the regulated Colorado River in Grand Canyon. We found a significant negative relationship between root growth response to experimental inundation with increasing elevation above the channel in the field, and a negative response of stomatal conductance to inundation among the most xeric-adapted species. Drought responses were idiosyncratic with respect to hydrologic niche, and instead seemed to vary in relation to clonality and rooting depth. Several Salicaceae tree species that are uncommon along regulated rivers exhibited consistently negative responses to both drought and inundation relative to other species, which may explain their rarity. The results of this study suggest that riparian plant distributions along hydrologic gradients have been shaped primarily by current and past levels of inundation. However, future anticipated declines in the water table are likely to produce species-specific responses based on drought tolerance that may in part be predicted from the results of this experiment.

Freshwater ecosystems are of great importance but increasingly threatened by human land uses such as intensive livestock production. We investigated the influence of cattle grazing in floodplains on the zooplankton community during a period of water retraction. We hypothesized that cattle activity in surrounding shallow lakes acts as an environmental filter for zooplankton, with its effect depending on the hydrological conditions. Accordingly, we analyzed changes in the taxonomic and functional diversity metrics in three lakes characterized by different grazing management (no-cattle; short grazing period with high stocking rates; and long grazing period with low stocking rates) over a nine-month period into three periods of water retraction (flood, early low water, and late low water). Functional diversity indexes (FRic, FEve, FDis) were influenced by grazing management and the periods of water retraction, without interactive effects, while taxonomic indices (H’, J’, D’) did not show significant relationships with any of these variables. The FRic and FDis indices decreased in lakes subjected to cattle activity, whereas FEve and FDis increased during lower water periods. Functional and taxonomic composition exhibited different patterns among lakes according to grazing management and the periods of water retraction. Overall, a similar composition was found during the flood period but it diverged in the subsequent periods of water retraction. Besides, cattle activity reduced the functional and taxonomic composition in the late low water phase. Our findings suggest that cattle activity acts as an environmental filter for zooplankton altering the functional diversity and composition through the progress of water retraction.

Wetlands constructed primarily for the treatment of wastewaters have been shown to have a role in enhancing biodiversity. However, while most biodiversity studies of constructed wetlands focus on the larger, more iconic animal groups, there is a paucity of information on the aerial phases of wetland invertebrate species associated with constructed wetlands. This study compares Sciomyzidae (Diptera) assemblages, established indicators of wetland dipteran communities, in Irish constructed and natural wetlands, in addition to determining the impacts of water quality and surrounding habitats on Sciomyzidae community structure. Natural wetlands had significantly greater species richness, abundances and diversity (measured as Shannon’s entropy) of sciomyzid flies than constructed wetlands. Nevertheless, although concentrations of nitrogen and phosphorus in waters were significantly greater in constructed wetlands, seven of the eight constructed wetlands examined hosted species of Sciomyzidae listed as scarce or threatened in Britain. In addition, sciomyzid species richness increased as areas of semi-natural habitat immediately surrounding constructed and natural wetlands increased. Composition of Sciomyzidae assembalges in both natural and constructed wetlands were analysed. The results of this study demonstrate that constructed wetlands can be important contributors to biodiversity particularly in the context of current losses of natural wetlands worldwide. The importance of habitats immediately surrounding constructed wetlands also highlights the need for relatively simple design recommendations (e.g. wet grassland creation or judicious planting of wetland trees) that could enhance the biodiversity of existing and future constructed wetlands.

Habitat edge effects can have profound impacts on biodiversity throughout terrestrial and aquatic biomes. Yet, few studies have examined how habitat edge effects impact the spatial patterning of sediment properties and microbial communities, especially in coastal ecosystems. Coastal salt marshes throughout the world are being transformed by sea level rise; high-marsh, flood-intolerant species, such as Spartina patens, are being fragmented and replaced by low-marsh, flood-tolerant species, such as Spartina alterniflora. The consequences of these habitat transformations on fungal communities remain unclear. Thus, we sought to identify how habitat edge effects, alongside changing plant community dynamics, impact the spatial patterning of fungal communities associated with ubiquitous Spartina species. We analyzed 26 Spartina patens patches: 13 pure monocultures and 13 mixed patches with Spartina alterniflora infiltration. We measured patch characteristics, plant characteristics, sediment physicochemical properties, and sediment fungal communities. We found that habitat edge effects structured sediment and plant properties in both pure and mixed patches. However, habitat edge effects only structured fungal community composition in mixed patches, counter to expectations. These results indicate that changing plant community dynamics driven by sea level rise can exacerbate habitat edge effects in coastal ecosystems. Least discriminant analysis and co-occurrence networks further revealed unique taxa and network structures between pure and mixed patches and between interiors and edges. In sum, we found that habitat transformation of coastal salt marshes driven by global change impacts the spatial dynamics of sediment and fungal properties.

To understand patterns in CO₂ partial pressure (P_CO2) over time in wetlands’ surface water and porewater, we examined the relationship between P_CO2 and land–atmosphere flux of CO₂ at the ecosystem scale at 22 Northern Hemisphere wetland sites synthesized through an open call. Sites spanned 6 major wetland types (tidal, alpine, fen, bog, marsh, and prairie pothole/karst), 7 Köppen climates, and 16 different years. Ecosystem respiration (R_eco) and gross primary production (GPP), components of vertical CO₂ flux, were compared to P_CO2, a component of lateral CO₂ flux, to determine if photosynthetic rates and soil respiration consistently influence wetland surface and porewater CO₂ concentrations across wetlands. Similar to drivers of primary productivity at the ecosystem scale, P_CO2 was strongly positively correlated with air temperature (T_air) at most sites. Monthly average P_CO2 tended to peak towards the middle of the year and was more strongly related to R_eco than GPP. Our results suggest R_eco may be related to biologically driven P_CO2 in wetlands, but the relationship is site-specific and could be an artifact of differently timed seasonal cycles or other factors. Higher levels of discharge do not consistently alter the relationship between R_eco and temperature normalized P_CO2. This work synthesizes relevant data and identifies key knowledge gaps in drivers of wetland respiration.

Wetlands concentrate biodiversity, particularly in arid regions. Chott Ech Chergui (Algeria), one of the biggest wetlands of the north African desert, presents extreme temperatures and salinity conditions. We initiated a physico-chemical and microbiological survey at seven sites encompassing various conditions (salt lakes, freshwater lakes and hot springs), through a one-year monthly sampling campaign. Four sites under the influence of the spring showed little temporal physio-chemical variation. Three sites displayed higher variation and the aridity level, high from late spring until autumn, was a strong predictor of water chemistry. We evidenced extremophile bacteria. Among 320 bacterial isolates tested for thermo-, acido- and alcalino- tolerance, 39, affiliated to Firmicutes and Proteobacteria, were successfully maintained and underwent physiological, biochemical and molecular characterizations. Thermotolerance was recorded up to 100 °C for a water isolate affiliated to Geobacillus stearothermophilus. Halotolerance was recorded up to 30% NaCl (w:v) for soil isolates affiliated to Salinicola zeshunii, Chromohalobacter beijerinckii and Virgibacillus halodenitrificans. Acido- and alcalo- tolerance were recorded for a pH range from 5 to 11 for several soil and water isolates affiliated to Exiguobacterium, Bacillus, Salinicola and Chromohalobacter genus. Our results comfort the interest of studying extremophile diversity in wetlands of the highly arid Sahara region.

Anthropogenic impacts on lake and stream water quality are well established but have been much less studied in wetlands. Here we use data from the 2016 National Wetland Condition Assessment to characterize water quality and its relationship to anthropogenic pressure for inland wetlands across the conterminous USA. Water samples obtained from 525 inland wetlands spanned pH from < 4 to > 9 and 3 to 5 orders of magnitude in ionic strength (chloride, sulfate, conductivity), nutrients (total N and P), turbidity, planktonic chlorophyll, and dissolved organic carbon (DOC). Anthropogenic pressure levels were evaluated at two spatial scales – an adjacent scale scored from field checklists, and a catchment scale indicated by percent agricultural plus urban landcover. Pressure at the two spatial scales were uncorrelated and varied considerably across regions and wetland hydrogeomorphic types. Both adjacent- and catchment-scale pressure were associated with elevated ionic-strength metrics; chloride elevation was most evident in road-salt using states, and sulfate was strongly elevated in a few sites with coal mining nearby. Nutrients were elevated in association with catchment-scale pressure but concomitant changes were not seen in planktonic chlorophyll. Acidic pH and high DOC occurred primarily in upper Great Lakes and eastern seaboard sites having low anthropogenic pressure, suggesting natural organic acid sources. Ionic strength and nutrients increased with increasing catchment-scale pressure even in Flats and closed Depression and Lacustrine sites, which indicates connectivity to rather than isolation from upland anthropogenic landuse even for wetlands lacking inflowing streams.

Thirty-five years post-harvest, effects of harvest disturbances upon tree composition and aboveground biomass were evaluated in a water-tupelo (Nyssa aquatica)- baldcypress (Taxodium distichum) bottomland. The forested wetland, along the Tensaw River, is within the Mobile-Tensaw River Delta in southwest Alabama. Nine replications of four disturbances were evaluated: no harvest reference (REF), clearcutting with helicopter removal (HELI), HELI combined with skidder extraction simulation (SKID), and HELI combined with broadcast herbicide application (glyphosate) to sprouts and seedlings for two years (GLYPH). Thirty-five years post-treatment, species, diameter at breast height (DBH; 1.37 m or above swell) and tree height were measured within treatments and converted to aboveground dry weight biomass. Clip plots were installed for herbaceous and woody stems < 1.37 m. Density and biomass results indicate HELI and SKID are on a trajectory to produce species, densities and biomass similar to REF. GLYPH coppice and seedlings were removed, so GLYPH regenerated from seedbanks and flood disseminated seed. GLYPH has transitioned from an herbaceous freshwater marsh to an open woodland/savanna community. GLYPH exemplifies advantages of coppice for rapid tree regeneration and growth on sites with long hydroperiods. This research demonstrates the capacity for long-term recovery of forested wetland ecosystems following harvest where multiple site/stand factors favored recovery. Adequate stocking of flood tolerant species capable of stump sprouting favored survival of original species. Floods provided annual sediment deposits to offset rutting. Compaction was additionally ameliorated by shrink-swell clays. Finally, nearby forests provided seed sources for areas. Collectively, these factors favored rapid recovery from disturbances.

The partitioning patterns and retention turnover of soil organic carbon (SOC) in peat bogs are closely related to vegetation, hydrology and soil factors. Research on SOC partitioning patterns in peat bogs in alpine regions in relation to vegetation and soil factors can contribute to the understanding of carbon sequestration mechanisms in peat bogs. In this paper, the Gahai Wetland of international importance on the Qinghai-Tibet Plateau was selected as the experimental site. Three inundation gradient sample plots, SI (heavily inundated zone), SII (moderately inundated zone) and SIII (lightly inundated zone), were established along the vertical shoreline of the lake as the starting point to study the distribution characteristics of the SOC content of peat bogs at different profile depths. The results showed that, horizontally, the SOC content in the three inundation gradients were as follows: SI > SII > SIII, vertically, the SOC content was the highest in the surface layer and showed a decreasing trend from the surface layer to the deep layer with increasing soil depth. All soil factors except bulk density and pH showed a decreasing trend and were significantly different (P < 0.05). The results of the path analysis showed that the effect on SOC content was in the order of soil water content > alkaline nitrogen > total nitrogen > bulk weight, indicating that these four soil factors were the dominant factors affecting the variation in SOC content, their combined effect also played a major role in regulating the SOC content (P < 0.01).