Riparian Wetlands Research Articles

Hydrology as a Determinant of Riparian Habitat Structure in Lowland River Floodplains

The objective of the study was to determine the relationship between the structure of phytocenoses in riparian wetland ecosystems and the hydrologic regime in a lowland river floodplain. The hydrobotanical study was conducted over three years—2017, 2018, and 2019—which differed in hydrological conditions (wet, average, and dry) in a middle section of the Supraśl floodplain (NE Poland) as a case study. The results showed that the structure and pattern of phytocenoses in the floodplain are primarily controlled by the hydrological regime of the river and the geomorphological features of the area. The reach and duration of the flood contributed to a specific pattern of riparian vegetation. Based on the plant community structure and riparian habitat indicators such as soil moisture, fertility, reaction pH, soil granulometry, and organic matter content, four habitat types were identified and supported by linear discriminant analysis (LDA): wet, semi-wet, semi-dry, and dry zones. The indicator species analysis (ISA) revealed species characteristic of the zones with the dominance of reed rush, reed canary grass, anthropogenic or partially natural herbaceous communities along watercourses or riparian meadows, respectively. Natural inundation of the river water is an important driver of site-specific vegetation elements and habitat types and determines habitat availability, biodiversity, and ecosystem functions of wetlands. This knowledge can serve as the basis for conservation efforts, sustainable management practices, and decision-making processes aimed at maintaining the biodiversity and ecological integrity of riparian ecosystems in similar regions.

Leaves stimulate aquatic phosphorus uptake by dark‐grown but not by light‐grown microbial communities in sediments: A laboratory study

Abstract It is a widely discussed topic in restoration ecology to use organic carbon (OC) management to increase nutrient uptake in chronically loaded agricultural streams. However, although nitrate uptake has been shown to correlated closely with the availability of dissolved OC, this relationship is less clear for phosphate. Likewise, the role of particulate OC (POC) on stimulating nutrient uptake has to be clarified. We aimed at investigating the effects of leaf additions on the net uptake of soluble reactive phosphorus and nitrate‐nitrogen from the water column by benthic biofilms in combined laboratory flume and batch experiments. Fine sediments were colonised under nutrient‐enriched conditions in the dark (dark‐grown heterotrophic biofilms) and under a 12/12‐hr dark/light cycle (light‐grown photoautotrophic biofilms) in flumes. In each light treatment, half of the biofilms were grown under strong OC‐limitation, the other half under near‐optimal C:N:P ratios. For the uptake experiments, the colonised sediments were incubated in nutrient‐enriched water to which (1) fresh alder leaves, (2) pre‐leached leaves, or (3) no leaves were added. Net nutrient uptake (or release) rates were determined via the change in nutrient concentrations in the water column over time. Net phosphorus uptake by dark‐grown biofilms was significantly increased by the addition of leaves. Despite their high initial nutrient leaching, fresh leaves showed stronger stimulating effects on the net P uptake than leached leaves over the entire experiment. Furthermore, biofilms grown under near‐optimum C:N:P ratios responded stronger to the POC supply than biofilms grown under C‐limited conditions. In contrast to dark‐grown biofilms, leaf additions had no significant effects on the net P uptake by light‐grown biofilms. We also found no effects of leaf additions on net nitrate uptake. Our study shows that an increased POC supply in nutrient‐impacted streams may boost heterotrophic phosphate uptake. However, the stimulating effect of the POC addition depends on a variety of POC‐dependent (e.g. respiration, heterotrophic assimilation, denitrification) and independent (e.g. adsorption, photoautotrophic assimilation) processes, making nutrient control via POC management challenging. We suggest application of management approaches that focus on restoration of riparian areas and wetlands to increase the amount of natural, complex POC with a moderate degradability, thus keeping the heterotrophic metabolism low but potentially stimulating in‐stream N and P retention.

Using foliar δ13C from high‐Andean plants (Silala River basin) as a measure of potential evapotranspiration through water use efficiency

AbstractThe water‐dependent nature of arid ecosystems is closely related to the coupling between energy input through photosynthesis and the loss of water through transpiration (Tr), which can be expressed as water use efficiency (WUE). The relationship, however, between environmental factors and plant physiology in controlling evapotranspiration is not well understood in high‐altitude arid environments. Here, we review the use of carbon isotope fractionation (δ13C) to indirectly track fluctuations in WUE and the use of the portable chamber method to partition landscape actual evapotranspiration (ETa) into Tr and bare soil evaporation (Ebs) in the alluvial deposits of the Silala River, a high elevation watershed located in northern Chile. Landscape ETa was also measured with Eddy covariance (EC) systems in the basin's riparian wetland and alluvial hillslope deposits. Carbon isotope results were consistent with what is known from the literature regarding these high‐elevation ecosystems. WUE, as estimated by carbon isotope discrimination values, decreased in summer (the wet season), and increased in winter at all sites. These results were consistent with the EC measurements. Changes in WUE were much greater in the valley wetlands than along the hillslopes, most likely due to a large drop in available soil moisture along the valley bottom during the dry season. Portable chamber results obtained during summer and winter field campaigns showed that at the landscape scale, hillslope ETa was mainly dominated by bare soil evaporation; and ETa partitioning into Tr and Ebs had a seasonal change.This article is categorized under: Engineering Water > Methods Science of Water > Hydrological Processes

Identification of sulfamethazine degraders in swine farm-impacted river and farmland: A comparative study of aerobic and anaerobic environments

Sulfonamides (SAs) are extensively used antibiotics in the prevention and treatment of animal diseases, leading to significant SAs pollution in surrounding environments. Microbial degradation has been proposed as a crucial mechanism for removing SAs, but the taxonomic identification of microbial functional guilds responsible for SAs degradation in nature remain largely unexplored. Here, we employed 13C-sulfamethazine (SMZ)-based DNA-stable isotope probing (SIP) and metagenomic sequencing to investigate SMZ degraders in three distinct swine farm wastewater-receiving environments within an agricultural ecosystem. These environments include the aerobic riparian wetland soil, agricultural soil, and anaerobic river sediment. SMZ mineralization activities exhibited significant variation, with the highest rate observed in aerobic riparian wetland soil. SMZ had a substantial impact on the microbial community compositions across all samples. DNA-SIP analysis demonstrated that Thiobacillus, Auicella, Sphingomonas, and Rhodobacter were dominant active SMZ degraders in the wetland soil, whereas Ellin6067, Ilumatobacter, Dongia, and Steroidobacter predominated in the agricultural soil. The genus MND1 and family Vicinamibacteraceae were identified as SMZ degrader in both soils. In contrast, anaerobic SMZ degradation in the river sediment was mainly performed by genera Microvirga, Flavobacterium, Dechlorobacter, Atopostipes, and families Nocardioidaceae, Micrococcaceae, Anaerolineaceae. Metagenomic analysis of 13C-DNA identified key SAs degradation genes (sadA and sadC), and various of dioxygenases, and aromatic hydrocarbon degradation-related functional genes, indicating their involvement in degradation of SMZ and its intermediate products. These findings highlight the variations of indigenous SAs oxidizers in complex natural habitats and emphasize the consideration of applying these naturally active degraders in future antibiotic bioremediation.

Flooding drives tropical dry forest tree community assembly in Southeast Brazil

In this study, we characterized and compared vegetation types associated with geomorphological units susceptible to distinct flooding levels. Differences in vegetation are related to landform variations. We aimed to 1) characterize the vegetation structure and quantify community compositional differences among landforms and 2) compare landforms soil characteristics and how these correlate with the tree vegetation. The study area is located in the Brazilian Caatinga domain, near the Verde Grande river, a tributary of São Francisco river (14°54′38ʺS, 43°42′53ʺW). We allocated six plots in each of the five landforms sampled (from wettest to driest sites): 1) marginal dike (RF – riparian forest), 2) upper terrace (RWF – riparian wetland forest), 3) lower terrace (WF – wetland forest), 4) lower plain (OFF – occasionally flooded forest) and 5) upper plain (UF – unflooded forest). We ran a non‐metric multidimensional scaling, produced a Venn diagram, and performed a principal component analysis (PCA) on the soil data (compared through a Tukey test at 5% significance after a significant ANOVA). A total of 1422 individuals, 26 families, 70 genera and 89 species were recorded. The NMDS revealed two distinct floristic groups: one group is associated with landforms with assumed higher flood frequency (RF, RWF, WF) and one with less frequently flooded landforms (OFF and UF). The RF, OFF, and UF landforms contained exclusive species (that only occurred in the plots of a particular landform). The species Geofroea spinosa (Fabaceae) was responsible for 70% of the total biomass recorded in the landforms RWF and WF. The soil analysis showed a gradient of soil acidity and fertility related to water saturation, whereby the most frequently flooded plots had the highest acidity values and highest fertility. We found that flood‐related conditions significantly influence tree community structure and species distribution in this floodplain in the Brazilian Caatinga domain.

Plant–plant interactions vary greatly along a flooding gradient in a dam-induced riparian habitat

Plant–plant interactions under extreme environmental stress are still controversial. The stress gradient hypothesis (SGH) proposes that facilitation prevails under extreme environmental stresses, while an alternative view states that facilitation collapses or even switches back to competition at the extreme end of stress gradients. However, how the relationship between plant–plant interaction and periodic extreme flooding stress varies and its underlying mechanism are still unclear in a dam-regulated riparian ecosystem. We established a controlled experiment using two dominant species pairs (Cynodon dactylon–Cyperus rotundus and C. dactylon–Xanthium sibiricum) in the water level fluctuating zone of the Three Gorges Dam to examine their growth responses to the periodic extreme flooding stress. The results showed that as flooding stress increased, the competitive effect of C. dactylon on X. sibiricum shifted to facilitation, whereas the effect of X. sibiricum on C. dactylon maintained a strong inhibition. The plant height of X. sibiricum was the most important driver of the interaction between X. sibiricum and C. dactylon along the flooding gradient. The net effect of C. dactylon on C. rotundus shifted from neutral to negative, and the inhibitory effect of C. rotundus on C. dactylon became stronger at the extreme end of flooding stress. The root biomass of the two species was the key trait regulating their interaction with increasing flooding stress. Overall, the SGH was partially supported along our periodic extreme flooding stress gradient. Aboveground resource (light) might be the dominant factor driving the response of the interaction between annual plants and perennial clonal plants to periodic flooding stress, whereas belowground resource (water and nutrients) was probably the dominant factor for perennial clonal plants. Our study will help to further understand the environmental responses of plant–plant relationships and their regulatory mechanism, and the succession of riparian plant communities under extreme environmental changes, providing a basic theoretical basis and data support for the ecological restoration and management of riparian wetland vegetation.

Integrating Tracers and Soft Data Into Multi‐Criteria Calibration: Implications From Distributed Modeling in a Riparian Wetland

AbstractCalibrating distributed hydrological models often leads to equifinality due to complex model structures, which can be further exacerbated in wetlands due to spatio‐temporal heterogeneity in ecohydrological processes. Here, step‐wise calibrations of the physically‐based distributed model EcH2O‐iso was conducted in a data‐rich wetland by minimizing a weighted average of the errors on discharge, stream isotopes, groundwater (GW) isotopes, and soil moisture. Results showed multi‐criteria calibration outperformed single‐criterion calibration as it strongly increased the overall performance, yet only marginally degraded performance of each calibration target. Isotopes were highlighted as appropriate auxiliary data as they effectively constrained the model with relatively small weights (0.1). However, those parameter sets that minimize the errors could still lead to physically implausible simulations of uncalibrated internal states or fluxes. This was further demonstrated by an approach developed to check internal fluxes based on soft data (transpiration and lateral flow), suggesting 54% of optimized models gave “right answers for the wrong reasons.” By excluding those models against soft data, such an approach further constrained equifinality, and unraveled potential inconsistencies between observations and calibration. Modeling represented the wetland as a slow‐draining system mainly fed by GW, but also influenced by near‐surface flow during winter or summer convectional events. Further, heterogeneity in hydrological functioning was partly attributed to distinct evapotranspiration patterns between contrasting vegetation communities. Therefore, this study not only provided insights into wetland functioning, but also revealed potential equifinality even with abundant data for calibration, and potential solutions based on the integration of isotopes and soft data.

Improved understanding of vegetation dynamics and wetland ecohydrology via monthly UAV‐based classification

AbstractVegetation classification is an essential prerequisite for understanding vegetation‐water relations at a range of spatial scales. However, in site‐specific applications, such classifications were mostly based on a single Unmanned Aerial Vehicle (UAV) flight, which can be challenging in grasslands and/or herbaceous‐dominated systems, as those communities are small in size and highly mixed. Here, we conducted monthly UAV flights for two years in a riparian wetland in Germany, with acquired imagery used for vegetation classification on a monthly basis under different strategies (with or without auxiliary information from other flights) to increase understanding in ecohydrology. The results show that multi‐flight‐based classification outperformed single‐flight‐based classification due to the higher classification accuracy. Moreover, improved sensitivity of temporal changes in community distribution highlights the benefits of multi‐flight‐based classification ‐ providing a more comprehensive picture of community evolution. From reference to the monthly community distribution, we argue that a combination of two or three flights in early‐ and late‐summer is enough to achieve comparable results to monthly flights, while mid‐summer would be a better timing in case only one flight is scheduled. With such detailed vegetation mapping, we further interpreted the complex spatio‐temporal heterogeneity in NDVI and explored the dominant areas and developmental progress of each community. Impacts from management (mowing events) were also evaluated based on the different responses between communities in two years. Finally, we explored how such vegetation mapping could help understand landscape ecohydrology, and found that the spatio‐temporal distribution of minimal soil moisture was related to NDVI peaks of local community, while grass distribution was explained by both topography and low moisture conditions. Such bi‐directional relationships proved that apart from contributing to an evidence base for wetland management, multi‐flight UAV vegetation mapping could also provide fundamental insights into the ecohydrology of wetlands.

Late Holocene riparian vegetation dynamics, environmental changes, and human impact in the Harapan forest of Sumatra, Indonesia

Riparian wetland ecosystems provide important ecological services but are also vulnerable to climate change and human activities. To understand the influence of natural factors (e.g. climate change, flooding, drought) and human activities (e.g. agriculture) as well as to support management strategies, reconstructions of past vegetation and environmental changes are needed. To achieve this, we conducted a multi-proxy paleoecological analysis, including pollen and spores, macro-charcoal and radiocarbon dating, on a sediment core taken from a riparian area in the Harapan forest of Sumatra. Three distinct periods were identified: i) AD 1100 – 1400: Upland and swamp forest with riparian and herbaceous vegetation, possibly part of a riparian buffer zone (e.g. riverbank), was present in the study area under a stronger dry season regime; ii) AD 1400 – 1870: freshwater swamps expanded to the study site; iii) later, from AD 1870 to present, upland forests dominated in the study area with a strong dry season. The presence of cereal cultivation from AD 1300 – 1450, and oil palm (Elaeis guineensis) since the mid-19th century AD indicates the presence of small-scale agriculture in the study area. This study of riparian vegetation dynamics and environmental changes in the Harapan forest of Sumatra shows the development from a riparian forest to a freshwater swamp and upland forest under the impact of climate change and human activities.

Effects of substrate improvement on winter nitrogen removal in riparian reed (Phragmites australis) wetlands: rhizospheric crosstalk between plants and microbes.

With continued anthropogenic inputs of nitrogen (N) into the environment, non-point source N pollutants produced in winter cannot be ignored. As the water-soil interface zones, riparian wetlands play important roles in intercepting and buffering N pollutants. However, winter has the antagonistic effect on the N removal. Substrate improvement has been suggested as a strategy to optimize wetland performance and there remain many uncertainties about the inner mechanism. This study explores the effects of substrate improvement on N removal in winter and rhizospheric crosstalk between reed (Phragmites australis) and microbes in subtropical riparian reed wetlands. The rates of wetland N removal in winter, root metabolite profiles, and rhizosphere soil microbial community compositions were determined following the addition of different substrates (gravel, gravel + biochar, ceramsite + biochar, and modified ceramsite + biochar) to natural riparian soil. The results showed that the addition of different substrates to initial soil enhanced N removal from the microcosms in winter. Gravel addition increased NH4+-N removal by 8.3% (P < 0.05). Gravel + biochar addition increased both TN and NH4+-N removals by 8.9% (P < 0.05). The root metabolite characteristics and microbial community compositions showed some variations under different substrate additions compared to the initial soil. The three treatments involving biochar addition decreased lipid metabolites and enhanced the contents and variety of carbon sources in rhizosphere soil, while modified ceramsite + biochar addition treatment had a greater impact on the microbial community structure. There was evidence for a complex crosstalk between plants and microbes in the rhizosphere, and some rhizosphere metabolites were seen to be significantly correlated with the bacterial composition of the rhizospheric microbial community. These results highlighted the importance of rhizospheric crosstalk in regulating winter N removal in riparian reed wetland, provided a scientific reference for the protection and restoration of riparian reed areas and the prevention and control of non-point source pollution.

A Comparison of Saturated Hydraulic Conductivity (Ksat) Estimations from Pedotransfer Functions (PTFs) and Field Observations in Riparian Seasonal Wetlands

Accurate saturated hydraulic conductivity (Ksat) predictions are critical for precise water flow estimations. Pedotransfer functions (PTFs) have been used to estimate Ksat based on soil structural and textural properties. However, PTF accuracy must be validated with observed Ksat values to improve confidence in model predictions. A study was conducted in the seasonal wetlands of a representative mixed land-use watershed in West Virginia (WV), USA. The observed data included soil characteristics and observed piezometric Ksat using slug tests. Soil texture was predominantly sandy, and the observed average Ksat ranged from 35.90 to 169.64 m/d. The average bulk dry density (bdry) increased, while porosity and volumetric water content decreased significantly with a depth to 45 cm (p &lt; 0.05). The degree of saturation varied significantly between monitoring sites (p &lt; 0.05). A Pearson correlation matrix and Principal Component Analysis (PCA) revealed that Ksat was more connected to soil textural properties, specifically clay. Single parameter PTFs that estimated Ksat as a function of clay content performed better (ME = −90.19 m/d, RMSE = 102.87 m/d) than the PTFs that used silt or sand percentages (ME= −96.86 m/d, RMSE = 108.77). However, all five PTFs predicted Ksat with low accuracy (RMSE &gt; 100 m/d), emphasizing the need to calibrate existing PTFs with observed data or develop site-specific PTFs. These results provide valuable insights into Ksat estimation in riparian wetlands of mixed land-use watersheds and are a helpful reference for land managers and future work.

Mapping the Late Miocene Pyrenean Forests of the La Cerdanya Basin, Spain

The Late Miocene palaeofloras of the La Cerdanya Basin represent a unique look into the Pyrenean Miocene forested areas of the Iberian Peninsula at a time when the European warm and humid climate was experiencing progressive cooling and aridification. Macrofossils (leaves, seeds, fruits and cones) and miospores from several outcrops revealed the composition and abundances of the different plant species present in the area during the Tortonian and early Messinian geological stages (ca. 11.1–5.7 Ma). These fossils were found in the sediment deposits of an ancient lake system situated in the southwestern part of the basin. Previous studies indicated the presence of highly diversified mixed mesophytic forests with broadleaved evergreen and deciduous trees and conifers. However, the spatial structure and distribution of these forest types remains unknown. In the present work, the biomization method was used to infer the different late Miocene vegetation types from the basin. The extent of these vegetation types was calculated using a methodology for mapping vegetation units from fossil and biome data. While previous attempts at mapping Miocene vegetation units had a broad geographical scale, the present work aimed to map the extent of the vegetation units at a small scale, recreating local and specific vegetation changes in an abrupt basin. Results showed similarly high scores between for four biome types, which represent the different types of vegetation that coexisted in the basin during the Tortonian and the early Messinian: warm-temperate evergreen broadleaf and mixed woodlands (WTEM biome), temperate deciduous forests (TEDE) and cool conifer forests (COMX and COEG). Their extent was depicted in two vegetation maps, which account for differences in palaeoaltitude and palaeoclimate. These forests occupied different vegetation belts, which shifted upwards and downwards with climatic variations and the progressive uplift of the Pyrenees during the late Miocene. Azonal riparian forests and wetland vegetation occupied the more humid areas in the centre of the basin. Nonetheless, dry conditions during the early Messinian and decrease in the lake area degraded the wetland environments, which were partially replaced by broadleaved evergreen mixed woodlands.

Soil edaphic factors and climate seasonality explain the turnover of methanotrophic communities in riparian wetlands

Aerobic CH4-oxidizing bacteria (methanotrophs) represent a biological model system for the removal of atmospheric CH4, which is sensitive to the dynamics of water tables. However, little attention has been given to the turnover of methanotrophic communities across wet and dry periods in riparian wetlands. Here, by sequencing the pmoA gene, we investigated the turnover of soil methanotrophic communities across wet and dry periods in typical riparian wetlands that experience intensive agricultural practices. The results demonstrated that the methanotrophic abundance and diversity were significantly higher in the wet period than in the dry period, probably owing to the climatic seasonal succession and associated variation in soil edaphic factors. The co-occurrence patterns of the interspecies association analysis demonstrated that the key ecological clusters (i.e., Mod#1, Mod#2, Mod#4, Mod#5) showed contrasting correlations with soil edaphic properties between wet and dry periods. The linear regression slope of the relationships between the relative abundance of Mod#1 and the carbon to nitrogen ratio was higher in the wet period than in the dry period, whereas the linear regression slope of the relationships between the relative abundance of Mod#2 and soil nitrogen content (i.e., dissolved organic nitrogen, nitrate, and total nitrogen) was higher in the dry period than in the wet period. Moreover, Stegen's null model combined with phylogenetic group-based assembly analysis demonstrated that the methanotrophic community exhibited a higher proportion of drift (55.0%) and a lower contribution of dispersal limitation (24.5%) in the wet period than in the dry period (43.8% and 35.7%, respectively). Overall, these findings demonstrate that the turnover of methanotrophic communities across wet and dry periods were soil edaphic factors and climate dependent.

Spatio-temporal sensitivity analysis of the wetland modules of a semi-distributed hydrological model

Hydrological models offer the opportunity to evaluate wetland conservation networks as nature-based solutions to mitigate hydrological extremes. To optimize the replication of a hydrological model response (i.e., stream flows), the models rely on input data (land cover, hydrographic network, soil types, topography, meteorological data) and parameters. However, the effect of parametric uncertainty on the simulated variables and the spatio-temporal variability of this sensitivity are insufficiently documented. This study presents an application of the novel global sensitivity analysis method, the Variogram Analysis of Response Surface, to the isolated and riparian wetland modules of HYDROTEL, a semi-distributed, process-based, deterministic model, on two watersheds located in the province of Quebec, Canada. The analysis accounted for: (i) the spatial variability by assessing the sensitivity at various locations in the watersheds and by compiling sensitivity indices for wetland networks discretized following the Strahler order classification which quantifies the structure of hydrographic networks and (ii) the temporal variability of the sensitivity using the Generalized Global Sensitivity Matrix. The results indicate that the parameters defining the geometry of wetlands (area, depth) are the most sensitive for both isolated and riparian wetlands, and for all Strahler orders. The temporal assessment of sensitivity highlights the seasonal controlling processes, including a peaking sensitivity of the maximum water depth in wetlands during spring snowmelt, whereas the sensitivity of the evapotranspiration parameter increases during summer, but is null during winter. Results also indicate that the parameters of the isolated modules are more sensitive for wetlands located on lower stream order (upstream/headwaters) while those of the riparian modules display a greater sensitivity when wetlands are located on higher Strahler orders (downstream/main channel). These findings deepen our understanding of the impact of wetland features on stream flows and provide guidelines to plan future data acquisition campaigns in wetlandscapes.

Natural attenuation of uranium in a fluvial Wetland: Importance of hydrology and speciation

A nuclear fuel fabrication facility released 43,500 kg of uranium into a riparian wetland located on the Savannah River Site between 1955 and 1988. Studies were undertaken to evaluate hydrological and geochemical processes influencing uranium accumulation in the wetland. Gamma-radiation-mapping surveys were conducted by systematically walking over the contaminated wetland with backpacks equipped with global positioning systems and NaI gamma detectors. Based on maps compiled from >700,000 gamma spectra and eight sediment uranium depth profiles, it was determined that 94% of the released uranium remained in the wetland. The uranium in the wetland is concentrated in five multi-hectare areas along the stream, accounting for ∼11% of the land area adjacent to the stream. While land type (upland or wetland) and topography provided a reasonable first approximation of where much of the uranium was deposited, hydrological watershed modeling revealed that the stream velocity was especially slow through many of the hot spots. Using autoradiography combined with SEM/EDX measurements of contaminated sediments, surprisingly few hot particles were detected. Instead, uranium was evenly distributed throughout the sampled sediment, suggesting that dissolved uranium had bound to sediment particles that became suspended and later deposited in low energy (low flow velocity) portions of the stream. EXAFS suggested that U atoms were present as individual ions in disordered complexes within the sediment. Furthermore, linear combination analyses suggested that the predominant component of the U(VI) was adsorbed to sediment minerals (∼70%) and a minor component (∼30%) was associated with organic matter phases. These studies show that wetlands can be extraordinarily effective at binding and retaining uranium, thereby providing a natural barrier to the transport of uranium out of a watershed. However, significant anthropogenic or climatic changes to wetlands, such as those associated with flooding, forest fires, or land use, may disrupt the complex hydrological and biogeochemical balance necessary to maintain long-term immobilization of uranium.

EEAGER: A Neural Network Model for Finding Beaver Complexes in Satellite and Aerial Imagery

AbstractBeavers are ecosystem engineers that create and maintain riparian wetland ecosystems in a variety of ecologic, climatic, and physical settings. Despite the large‐scale implications of ongoing beaver conservation and range expansion, relatively few landscape‐scale studies have been conducted, due in part to the significant time required to manually locate beaver dams at scale. To address this need, we developed EEAGER—an image recognition machine learning model that detects beaver complexes in aerial and satellite imagery. We developed the model in the western United States using 13,344 known beaver dam locations and 56,728 nearby locations without beaver dams. Performance assessment was performed in twelve held out evaluation polygons of known beaver occupancy but previously unmapped dam locations. These polygons represented regions similar to the training data as well as more novel landscape settings. Our model performed well overall (accuracy = 98.5%, recall = 63.03%, precision = 25.83%) in these areas, with stronger performance in regions similar to where the model had been trained. We favored recall over precision, which results in a more complete catalog of beaver dams found but also a higher incidence of false positives to be manually removed during quality control. These results have far‐reaching implications for monitoring of beaver‐based river restoration, as well as potential applications detecting other complex landforms.

The Contribution of Anammox to Nitrogen Removal Is Greater in Bulk Soils Than in Rhizosphere Soils in Riparian Wetlands Along the Yangtze River

AbstractThe importance of denitrification and anaerobic ammonium oxidation (anammox) in removing nitrogen (N) from upland runoff has been well documented in riparian wetlands. However, the relative contributions of denitrification and anammox to N removal in the rhizosphere and non‐rhizosphere soils of riparian zones remain unclear. Here, we explored the denitrification and anammox rates in the rhizosphere and bulk soils (0–5 and 10–15 cm) of 39 riparian wetlands along the Yangtze River using the 15N isotope pairing technique. Additionally, we used a quantitative polymerase chain reaction assay to determine the abundance of soil denitrifying and anammox bacteria using nosZ and hzsB genes, respectively. The results showed that both denitrification and anammox rates were significantly higher in rhizosphere soils than in bulk soils, suggesting that the rhizosphere environment is favorable for N removal. The contribution of anammox constituted over half (62.53% ± 1.49%) of the N loss and was greater in bulk soils (68.57% ± 1.42%) than in rhizosphere soils (55.64% ± 2.42%). Higher nosZ and hzsB gene abundances were also observed in rhizosphere soils than in bulk soils. Denitrification and anammox rates were significantly regulated by edaphic properties, microbial abundance, and plant biomass. The structural equation model further revealed that soil pH and N availability could affect denitrification and anammox rates both directly and indirectly by altering nosZ and hzsB gene abundance. Overall, this study highlights that the rhizosphere is a control point for N removal and harbors more functional microbes than bulk soils. Therefore, revegetation may effectively enhance the N removal function of riparian wetlands along the Yangtze River.

Effect of land use conversion on heavy metals and magnetic minerals on water reservoir riparian soils

Spatial hydrological alterations seem to influence the variability of soil-bound magnetic particles and heavy metals in water reservoir riparian wetlands (RW). To date, applying geochemical analysis with magnetic techniques to assess heavy metal pollution is rarely practiced in RW soils. We studied the magnetic properties and heavy metals, including Cu, Cr, and Zn, of topsoils in RW and the adjacent upland regions (UR, as control) in the Three Gorges Reservoir, China. Potentially elevated low-frequency mass magnetic susceptibility (χLF), anhysteretic remanent magnetization susceptibility (χARM), isothermal remanent magnetism, and all selected heavy metals were found in RW. The grain size of the magnetic minerals was coarser in RW than that in UR. The pollution load index (PLI) of the studied samples was 1.18 ± 0.12 and 1.04 ± 0.21 in RW and UR, respectively. PLI and concentrations of Cu, Cr, and Zn were positively correlated with χLF, χARM, and isothermal remanent magnetism in RW, whereas no clear linkages were observed between PLI and isothermal remanent magnetism in UR. This finding reveals that hydrological alterations increased the magnetic enhancement and heavy metal enrichment in RW. We find that magnetic proxies of soils could trace the concentration of selected anthropogenic heavy metals and their pollution level in RW.

Bacterial Communities Structure and Diversity in Rhizosphere Soil of Dominant Plants in Riparian Wetlands of Reservoir in Zhejiang Province, China

Soil bacterial play special roles in the maintenance and stabilization of wetland ecosystem. To investigate bacterial community structure and diversity in rhizosphere soils of four dominant plants in riparian wetlands of mountain reservoir in Zhejiang province, the V4+V5 areas of 16S rDNA gene of bacteria were sequenced and analyzed by the Illumina HiSeq 2500 high-throughput sequencing technology. The results indicated that 27 phylums, 70 classes, 144 orders, 218 families, and 370 genuses of bacteria were achieved, with Proteobacteria, Acidobacteria,Actinobacteria and Bacteroidetes being the dominant phylum and Gammaproteobacteria, Deltaproteobacteria, Acidobacteria, Actinobacteria, Betaproteobacteria and Thermoleophilia being the main class in the soils of riparian wetlands in this areas. The Shannon index and chao1 index of the rhizosphere soil bacteria of Salix babylonica were 8.64 and 585.58, respectively, which were the highest among the four plants, and that of Pterocarya stenoptera were the lowest, with 7.71 and 289.63, respectively. Soil pH, total nitrogen and organic matter were the main factors affecting the soil bacterial community structure in the soil rhizosphere of four dominant plants species in wetlands of riparian zone of reservoir in Zhejiang province.

Restoring a First Order Stream and Adjacent Riparian Wetlands In West Virginia: Integrating Lessons from Science and Practice

Stream and wetland mitigation knowledge and understanding are rapidly evolving. However, the objectives of mitigation are wide-ranging. In 2021, a branch of Deckers Creek (Preston Co., West Virginia, USA) was restored by bank recontouring, reconnecting the incised channel to the constructed bankfull bench floodplain, creating small wetlands, and planting native riparian vegetation. Our research objectives were to 1) provide annual biodiversity and abundance data before, during, and after mitigation efforts and 2) assess woody-vegetation growth (height and diameter) and survivorship of a 10% biochar and 90% compost mixture. The complexity of mitigation warrants discussing challenges before, during, and after mitigation occurs. During restoration efforts, we encountered several challenges that were overcome through perseverance and collaboration. We incorporated ideas and practices from academia and the private sector to provide a detailed list of challenges encountered during our mitigation efforts, the solutions enacted, and future management implications to streamline mitigation planning.