Wetland Soils Research Articles

Elemental Oxides and Weathering Extent of Wetland Soils Under Different Geological Formations of Ogun State, Nigeria

Elemental Oxides and Weathering Extent of Wetland Soils Under Different Geological Formations of Ogun State, Nigeria

Diel Greenhouse Gas Emissions Demonstrate a Strong Response to Vegetation Patch Types in a Freshwater Wetland

AbstractWetland methane (CH4) fluxes are highly variable over spatial and temporal scales due to variations in CH4 production, oxidation, and transport. While some aspects of temporal variability in CH4 fluxes are well documented, diel variability is poorly constrained, and studies report conflicting findings, making it difficult to generalize. Topographic, geochemical, hydroclimatic, and vegetative variability can result in characteristically different “patches” that likely influence differences in diel patterns. We investigated diel patterns of CH4 fluxes from a large seasonal‐mineral soil wetland in Maryland (USA) across three functionally unique patches: two with vegetation (emergent and submerged aquatic vegetation) and one without (open water) during the summer of 2021. To explore the relationships between vegetation, environmental conditions, and flux patterns, we also measured physiochemical variables (air and water temperature, pH, relative humidity, PAR, dissolved oxygen, and water depth). To our knowledge, this is the first study comparing diel variability using chambers across such distinct vegetation patch types. We found that diel patterns were strongly linked to patch types: CH4 fluxes from the emergent vegetation did not display a consistent diel pattern, while fluxes from the submerged vegetation and no vegetation patches frequently peaked at 13:00 and 05:00, respectively. These differences could be a direct result of vegetation impact on production, oxidation, and/or transport of CH4 or on conditions covarying with patch type. This study contributes to the growing understanding of how CH4 fluxes vary spatially over diel cycles and emphasizes the importance of considering spatially varying diel patterns when estimating fluxes.

Stochastic Processes Dominate the Assembly of Soil Bacterial Communities of Land Use Patterns in Lesser Khingan Mountains, Northeast China

To meet the demands of a growing population, natural wetlands are being converted to arable land, significantly impacting soil biodiversity. This study investigated the effects of land use changes on bacterial communities in wetland, arable land, and forest soils in the Lesser Khingan Mountains using Illumina MiSeq 16S rRNA sequencing. Soil physicochemical properties and enzyme activities were measured using standard methods, while microbial diversity was assessed through sequencing analysis. Our findings revealed that forest soils had significantly higher levels of total potassium (2.62 g·kg−1), electrical conductivity (8.22 mS·cm−1), urease (0.18 mg·g−1·d−1), and nitrate reductase (0.13 mg·g−1·d−1), attributed to rich organic matter and active microbial communities. Conversely, arable soils showed lower total potassium (1.94 g·kg−1), reduced electrical conductivity, and suppressed enzyme activities due to frequent tilling and fertilization. Wetland soils exhibited the lowest values primarily due to water saturation, which limits organic matter decomposition and microbial activity. Land use changes notably reduced microbial diversity, with conversion from forest to arable land leading to habitat loss. Forest soils supported higher abundances of Proteobacteria (37.59%) and Actinobacteriota (34.73%), while arable soils favored nitrogen-fixing bacteria. Wetlands were characterized by chemoheterotrophic and anaerobic bacteria. Overall, these findings underscore the profound influence of land use on soil microbial communities and their functional roles, highlighting the need for sustainable management practices.

Evaluation and risk assessment of heavy metals in wetland soil in the University of Lagos

A study was conducted to evaluate the concentration of heavy metals, and the physicochemical and microbiological properties of wetland soils at the University of Lagos. Soil samples were randomly collected from the Faculty of Science (FSC), Lagoon Front, and Distance Learning Institute areas at depths of 5 cm, 10 cm, 15 cm, and 20 cm using a soil auger. The samples were stored in sterile nylon bags, appropriately labelled, and transported to the University of Lagos Central Research Laboratory for chemical analysis. The physicochemical characteristics measured included soil pH, determined using a pH meter, and moisture content, assessed through the oven-drying method. Heavy metal concentrations were analyzed using an Atomic Absorption Spectrophotometer. Microbial population diversity was examined using the disc diffusion method. Statistical analysis was performed using SPSS version 20, and mean values were evaluated using Tukey’s multiple comparison test at a probability level of P < 0.05. The results revealed that soil pH ranged from 7.20 to 8.81, with the highest value (8.81) recorded near the Faculty of Science (FSC-3). Eight heavy metals, including Pb, Ni, Cr, Cd, Fe, Cu, Mn, and Zn, were analyzed. Lead concentrations ranged from 0.02 to 0.29 ppm, followed by nickel, which ranged from 0.01 to 0.13 ppm. Chromium ranged from 0.0 to 0.25 ppm, cadmium from 0.03 to 0.08 ppm, iron from 1.02 to 2.96 ppm, copper from 3.31 to 4.60 ppm, manganese from 3.31 to 5.16 ppm, and zinc from 1.67 to 9.17 ppm. Lead and zinc concentrations were found to be below the permissible limit at all locations, while chromium and cadmium were within permissible limits. However, Zn, Mn, Cu, Fe, and Ni exceeded the permissible limits. Correlation analysis revealed a significant correlation (P < 0.05) between Pb and Zn, likely due to effluents from human waste and seepage from nearby dumpsites into the lagoon, streams, or beaches. The isolated microbial flora included three bacterial genera, Bacillus megaterium, Bacillus spp, and Enterobacter spp, as well as four fungal genera, Aspergillus, Penicillium, Aspergillus flavus, and Fusarium. Bacterial counts were lower than fungal counts in polluted soils, likely due to the nutrient status of the soil. The isolates were found to be tolerant to slightly alkaline pH and heavy metal pollutants, with microbial variation attributed to the impact of pH and heavy metals on the microbial population.

Determination of geochemical stability of swamp ecosystems of the taiga zone of Western Siberia to anthropogenic impact

Relevance. The need for scientifically based regulation of impacts on wetland ecosystems taking into account their specificity and geochemical stability. Aim. To determine the geochemical stability of wetlands in the taiga zone of Western Siberia to pollutants for two typical cases associated with: 1) operation of sludge pits; 2) discharge of domestic and industrial wastewater. Methods. Mathematical modeling, statistical methods. Results and conclusions. The authors have carried out the analysis of the results of studies of the chemical composition of wetland waters and extracts from peat and mineral soils of wetlands in the taiga zone of Western Siberia (mainly in the Tomsk region, as well as in the adjacent territories of the Khanty-Mansiysk Autonomous Okrug, Novosibirsk and Omsk regions). They obtained the estimates of the average values of geochemical indicators of wetland waters and peat by the depth of the peat deposit in peat bogs with varying degrees of anthropogenic impact. The paper introduces the method for assessing the anthropogenic impact of wastewater discharge and geomigration on swamps in areas where oil and gas facilities are located (permissible concentrations in wastewater entering swamp ecosystems), taking into account the «geochemical background» and sorption capacity of peat. In particular, the authors substantiated and tested the method for assessing the values of permissible concentrations, which should be considered as a «relatively safe» level of impact on swamp ecosystems, at which secondary pollution of swamp waters is not expected. It is shown that anthropogenic changes are mainly limited vertically by the upper layer of the peat deposit up to 1–2 m, and horizontally (within the active horizon of the peat deposit) – by areas up to 100–200 m.

Technical note: Comparison of radiometric techniques for estimating recent organic carbon sequestration rates in inland wetland soils

Abstract. For wetlands to serve as natural climate solutions, accurate estimates of organic carbon (OC) sequestration rates in wetland sediments are needed. Dating using cesium-137 (137Cs) and lead-210 (210Pb) radioisotopes is commonly used for measuring OC sequestration rates in wetland sediments. 137Cs radioisotope dating is relatively simple, with calculations based on a single point representing the onset (1954) or peak (1963) of the 137Cs fallout. 210Pb radioisotope dating is more complex, as the calculations are based on multiple points. Here, we show that reliable dating of sediment cores collected from wetlands can be achieved using either 137Cs or 210Pb dating or their combination. However, 137Cs and 210Pb profiles along the depth of sediment cores need to be screened, analyzed, and interpreted carefully to estimate OC sequestration rates with high precision. To this end, we propose a decision framework for screening 137Cs and 210Pb profiles into high- and low-quality sediment profiles, and we compare dating using the 1954 and 1963 time markers, i.e., the rates of sedimentation and, consequently, OC sequestration over the past ∼ 60 years. Our findings suggest that 137Cs- and 210Pb-based OC sequestration rates are comparable, especially when using the 1963 (vs. 1954) time marker.

Silicate coprecipitation reduces green rust crystal size and limits dissolution-precipitation during air oxidation

Green rusts (GR) are mixed-valence iron (Fe) hydroxides which form in reducing redox environments like riparian and wetland soils and shallow groundwater. In these environments, silicon (Si) can influence Fe oxides’ chemical and physical properties but its role in GR formation and subsequent oxidative transformation have not been studied starting at initial nucleation. Green rust sulfate [GR(SO4)] and green rust carbonate [GR(CO3)] were both coprecipitated from salts by base titration in increasing % mol Si (0, 1, 10, and 50). The minerals were characterized before and after rapid (24 h) aqueous air-oxidation by x-ray diffraction (XRD), scanning electron microscopy (SEM), Fe extended x-ray absorption fine structure spectroscopy (EXAFS), and N2-BET surface area. Results showed that only GR(SO4) or GR(CO3) was formed at every tested Si concentration. Increasing % mol Si caused decreased plate size and increased surface area in GR(CO3) but not GR(SO4). GR plate basal thickness was not changed at any condition indicating a lack of Si interlayering. Air oxidation of GR(SO4) at all % mol Si contents transformed by dissolution and reprecipitation into lepidocrocite and goethite, favoring ferrihydrite with higher % Si content. Air oxidation of GR(CO3) transformed into magnetite and goethite but increasing Si caused GR to oxidize while retaining its hexagonal plate structure via solid-state oxidation. Our results indicate that Si has the potential to cause GR to form in smaller particles and upon air oxidation, Si can either stabilize the plate structure or alter transformation to ferrihydrite.Graphical

Analysis of coupled wetland soil–plant ecological stoichiometric characteristics of carbon, nitrogen, and phosphorus under different disturbance intensities

Analysis of coupled wetland soil–plant ecological stoichiometric characteristics of carbon, nitrogen, and phosphorus under different disturbance intensities

Root-Driven Soil Reduction in Wadden Sea Salt Marshes

The soil redox potential in wetlands such as peatlands or salt marshes exerts a strong control over microbial decomposition processes and consequently soil carbon cycling. Wetland plants can influence redox by supplying both terminal electron acceptors (i.e. oxygen) and electron donors (i.e. organic matter) to the soil system. However, quantitative insight into the importance of plant effects on wetland soil redox and associated plant traits are scarce. In a combined mesocosm and field study we investigated the impact of plants on soil reduction using IRIS (Indicator of Reduction in Soils) sticks. Vegetated plots were compared to non-vegetated plots along an elevational gradient in a salt marsh of the Wadden Sea and along an artificially created gradient in a tidal tank mesocosm experiment. Our findings from the mesocosm experiment demonstrated that vegetation both enhanced and suppressed soil reduction relative to non-vegetated control pots. The direction of the plant effect (i.e., net oxidizing or net reducing) was inversely correlated with background redox conditions. Insights from high-resolution oxygen profiling via planar optode imaging corroborated these findings. In the field study, vegetation consistently reduced the comparatively well-aerated Wadden Sea salt marsh soil. Reduction correlated positively with soil organic matter content and belowground biomass, indicating that greater availability of plant-derived electron donors, in the form of organic matter, increased soil reduction. Challenging the dominant paradigm that wetland plants primarily act as soil oxidizers, our study reveals their potential to exert a net reducing effect. The documented impact of these plant-induced changes in soil redox conditions suggests a previously overlooked role in shaping the stability of soil organic carbon stocks in wetland ecosystems with variable water tables.

Impacts of plastic pollution on soil–plant properties and greenhouse gas emissions in wetlands: A meta-analysis

Plastic pollution in wetlands has recently emerged as an urgent environmental problem. However, the impacts of plastic contamination on soil-plant properties and greenhouse gas (GHG) emissions in wetlands remain unclear. Thus, this study conducted a meta-analysis based on 44 study sites to explore the influence of plastic pollution on soil physicochemical variables, soil microorganisms, enzyme activity, functional genes, plant characteristics, and GHG emissions (CO2, CH4, and N2O) in different wetland types. Based on the collected dataset, the plastic pollution significantly increased soil organic matter and organic carbon by on average 28.9 % and 34.2 %, respectively, while decreased inorganic nutrient elements, bacteria alpha diversity and enzyme activities by an average of 5.9 −14.2 %. The response of bacterial abundance to plastic pollution varied depending on phylum classes. Plant biomass and photosynthetic efficiency were decreased by an average of 12.8 % and 18.4 % due to plastic pollution. The concentration and exposure time of plastics play a key role in influencing the soil and plant properties in wetlands. Furthermore, plastic exposure notably increased the abundance of the functional genes related to C degradation and the ammonia oxidizing microorganisms, and the consequent CO2 and N2O emissions (with effect sizes of 2.10 and 1.94, respectively). We also found that plastic concentrations and exposure duration affected the wetland soil–plant system. Our results might be helpful to design further investigations on plastic effects and develop appropriate measures for mitigating plastic pollution in wetlands.

Screening and quantification of pesticides in wetland water, ice, sediment and soil: Occurrence, transport and risk assessment

Current researches on pesticides in wetlands are limited in terms of screening and quantification of many types of pesticides. Understanding the spatial and temporal dynamics, distribution patterns, and environmental risks of pesticides in multiple media is important for wetland ecological conservation. In this study, 222 pesticides were determined in multimedia samples collected simultaneously from the Songhua Wetland during four seasons. Concentrations of target pesticides in water, ice, sediment and soil ranged from 94.1 to 7445 ng/L, 62.6–953 ng/L, 0.82–50.2 ng/g dw, and 4.32–146 ng/g dw. Large spatial differences (p < 0.05) in pesticide concentrations in ice were found. However, there were no significant differences in the spatial and temporal distribution of pesticides in water, sediment, and soil (p > 0.05), suggesting that there were no correlation between the spatial and temporal use of pesticides. The dynamic exchange of pesticides between water-ice indicated that most pesticides were more enriched in water. However, there were still some pesticides (Dichlorvos and Biphenyl) that showed a stronger tendency to transfer from water to ice. Sediment-water exchange suggested that sediment is a source of secondary releases of most pesticides in wetland ecology, but is a sink for Biphenyl and Oxadiazon. The correlation between concentration ratios and fugacity fraction supported this finding. Most individual pesticides in wetland water and ice had shown low or moderate ecological risk conducted using risk quotient. The cumulative toxic effects of multiple pesticides had a high potential to pose a threat to wetland aquatic organisms.

Sugarcane straw biochar: effects of pyrolysis temperature on barite dissolution and Ba availability under flooded conditions

AbstractReductive dissolution of barium (Ba) sulfate in wetland soils may increase Ba bioavailability in the environment, yet no information is available regarding Ba remediation using biochar. This study investigated the effectiveness of sugarcane (Saccharum officinarum) straw biochar pyrolyzed at 350 °C (BC350), 550 °C (BC550), and 750 °C (BC750) in inhibiting barite dissolution and, consequently, Ba availability in a soil artificially spiked with barite and flooded for 365 days. Increasing pyrolysis temperature alters the carbon structure, and increases dehydration and depolymerization, resulting in more stable biochar that releases less DOC (8.6-fold decrease from BC350 to BC750). Additionally, high-temperature biochar (BC750) had 1.7 times higher carbon (C) content, 2.4 times higher ash content, and a 13.1 times greater specific surface area (SSA) than low-temperature biochar (BC350). Amending soil with BC750 increased pH but did not promote reducing conditions, and thus did not promote barite dissolution. Conversely, greater DOC in low-temperature biochar, particularly BC350, favored reducing conditions and increased barite dissolution by 23%, with BC550 also showing an 18% increase. This enhancement led to a greater pool of Ba sorbed into more labile exchangeable sites. In summary, pyrolysis temperature affects biochar attributes, which in turn influences the soil geochemical environment and Ba speciation. Low-temperature biochar (BC350) shows potential as an amendment to increase the bioavailable Ba pool in assisted remediation programs, such as biochar-assisted phytoremediation. Graphical Abstract

Molecular-chemical characterization of soil organic matter in wetlands by pyrolysis-gas chromatography/mass spectrometry

The carbon cycle in ecosystems is fundamentally controlled by the composition and transformation of organic molecules. Alpine wetland soils have enormous carbon storage, but they are sensitive to climate change, and can easily shift from carbon sink to carbon source. However, we currently lack understanding in molecular-chemical composition of soil organic matter (SOM) in alpine wetlands. In this study, we tried to decipher molecular-chemical features of SOM in typical alpine wetlands using the pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Results indicated that nitrogen-containing compounds were the most abundant moieties among pyrolytic products of SOM. More than 83 % of pyrolytic moieties had a molecular weight of no more than 200 Daltons and a H/C ratio of no more than 2.0. O/C ratio of most pyrolytic products were less than 0.5. A van Krevelen diagram potentially indicated that SOM in wetlands might consist of massive heterogeneous molecules where aromatic compounds and their derivatives served as the core, with aliphatic hydrocarbon molecules of varying carbon chain lengths attached externally. About 72.25 % of variances in SOM were explained by 50 pyrolytic products, of which toluene was the most important. A significantly negative relation was observed between molecular weight (MW) and abundance of pyrolytic products, while positive relations were found between H/C, O/C, and abundance of pyrolytic products. Our work implied that SOM in wetlands was mainly composed of molecules with low MW and aromatic function groups.

Functional effects of subsidies and stressors on benthic microbial communities along freshwater to marine gradients.

Leaf litter in coastal wetlands lays the foundation for carbon storage, and the creation of coastal wetland soils. As climate change alters the biogeochemical conditions and macrophyte composition of coastal wetlands, a better understanding of the interactions between microbial communities, changing chemistry, and leaf litter is required to understand the dynamics of coastal litter breakdown in changing wetlands. Coastal wetlands are dynamic systems with shifting biogeochemical conditions, with both tidal and seasonal redox fluctuations, and marine subsidies to inland habitats. Here, we investigated gene expression associated with various microbial redox pathways to understand how changing conditions are affecting the benthic microbial communities responsible for litter breakdown in coastal wetlands. We performed a reciprocal transplant of leaf litter from four distinct plant species along freshwater-to-marine gradients in the Florida Coastal Everglades, tracking changes in environmental and litter biogeochemistry, as well as benthic microbial gene expression associated with varying redox conditions, carbon degradation, and phosphorus acquisition. Early litter breakdown varied primarily by species, with highest breakdown in coastal species, regardless of the site they were at during breakdown, while microbial gene expression showed a strong seasonal relationship between sulfate cycling and salinity, and was not correlated with breakdown rates. The effect of salinity is likely a combination of direct effects, and indirect effects from associated marine subsidies. We found a positive correlation between sulfate uptake and salinity during January with higher freshwater inputs to coastal areas. However, we found a peak of dissimilatory sulfate reduction at intermediate salinity during April when freshwater inputs to coastal sites are lower. The combination of these two results suggests that sulfate acquisition is limiting to microbes when freshwater inputs are high, but that when marine influence increases and sulfate becomes more available, dissimilatory sulfate reduction becomes a key microbial process. As marine influence in coastal wetlands increases with climate change, our study suggests that sulfate dynamics will become increasingly important to microbial communities colonizing decomposing leaf litter.

Dredged Canals, Wetland Loss, and Legacy

AbstractThe direct effects of converting coastal wetlands to open water by dredging them can be magnified by indirect effects. For example, dredged canals allow for recovery of mineral fluids 1000 s of m belowground which may induce geological subsidence or faulting; the dredged material deposited at the surface creates levees that redirect overland water flows. These indirect factors may stress wetland plants enough so that additional wetland habitat is converted to open water as a result of longer intervals of wetland soil waterlogging and drying, sulfide toxicity, less organic matter and sediment accumulation, and greater erosion. We quantified the indirect effects by demonstrating a robust dose–response relationship between coastal land loss and canal density in the Mississippi and Niger river deltas over 5 decades. Importantly, the ratio of land loss to canal area increases with time—a legacy effect. Surface impediments to water movements rather than belowground subsidence are the dominant causal factor. We also found that flood protection levees on the main river channel did not significantly magnify the effect of dredging on wetland loss. The cumulative effect of these direct and indirect consequences in coastal Louisiana is enormous and continuing, equaling many tens of billions dollars annually. Understanding these effects supports the rejection of a hypothesis that regional river channel flood protection levees or fluid withdrawal is of greater importance than the local changes in wetland hydrology. Wetland restoration/mitigation of dredging impacts on these two coasts can be implemented at a relatively low cost and quickly if this paradigm of the causes of coastal wetland losses is adopted.

Impact of yeast extract and basal salts medium on 1,4-dioxane biodegradation rates and the microorganisms involved in carbon uptake from 1,4-dioxane

Conventional physical and chemical treatment technologies for 1,4-dioxane can be ineffective and consequently attention has focused on bioremediation. Towards this, the current research investigated the impact of basal salts medium (BSM) and yeast extract on 1,4-dioxane biodegradation rates in microcosms with different soil or sediment (agricultural soil, wetland sediment, sediment from an impacted site). Phylotypes responsible for carbon uptake from 1,4-dioxane were determined using stable isotope probing (SIP), both with and without BSM and yeast extract. Further, putative functional genes were investigated using 1) soluble di-iron monooxygenase (SDIMO) based amplicon sequencing, 2) qPCR targeting propane monooxygenase (large subunit, prmA) and 3) a predictive approach (PICRUSt2). The addition of BSM and yeast extract significantly enhanced 1,4-dioxane removal rates the agricultural soil and impacted site sediment microcosms. The phylotypes associated with carbon uptake varied across treatments and inocula. Gemmatimonas was important in the heavy SIP fractions of the wetland sediment microcosms. Unclassified Solirubacteraceae, Solirubrobacter, Pseudonocardia and RB4 were dominant in the heavy SIP fractions of the agricultural soil microcosms. The heavy SIP fractions of the impacted site microcosms were dominated by only two phylotypes, unclassified Burkholderiaceae and oc3299. SDIMO based amplicon sequencing detected three genes previously associated with 1,4-dioxane. The predicted functional gene analysis suggested the importance of propane monooxygenases associated with Solirubrobacter and Pseudonocardia. Overall, more microorganisms were involved in carbon uptake from 1,4-dioxane in both the wetland and agricultural soil microcosms compared to the impacted site sediment microcosms. Many of these microorganisms have not previously been associated with 1,4-dioxane removal.

High salinity restrains microplastic transport and increases the risk of pollution in coastal wetlands

Microplastics (MPs) pollution in coastal wetlands has attracted global attention. However, few studies have focused on the effect of soil properties and structure on MP transport in coastal wetlands. Salinity is one of the most pivotal environmental factors and varies in coastal wetlands. Here, we conducted column experiments and employed fluorescent labeling combined with Derjaguin–Landau–Verwey–Overbeek (DLVO) theoretical calculations to reveal the vertical transport behavior of MPs. Specifically, we investigated the influence of five salinity levels (0, 0.035, 0.35, 3.5, and 35 PSU) on MP transport in different coastal wetlands soils and a sand through the X-ray photoelectron spectroscopy and nondestructive computed tomography technique. The results indicated that the migration capability of MPs in soils is significantly lower than in quartz sand, and that the migration capability varies depending on the soil type. This variability may be due to soil minerals and microporous structures providing numerous attachment sites for MPs and may be explained by the DLVO energy barrier of MP-Soil (6568–7767 KT) and MP-sand (5250 KT). Salinity plays a crucial role in modifying the chemical properties of pore water (i.e., zeta potential) as well as altering the soil elemental composition and pore structure. At 0 PSU, the maximum C/C0 of MPs through the sand, Soil 1, and Soil 2 transport columns were 37.86 ± 2.36 %, 23.96 ± 1.71 %, and 3.94 ± 0.68 %, respectively. When salinity increased to 3.5 PSU, MP mobility decreased by over 20 %. Additionally, a salinity of 35 PSU may alter the soil pore distribution, thereby changing water flow paths and velocities to constrain the migration of MPs in soils. These findings could provide valuable insights into understanding the environmental behavior and transport mechanisms of MPs, and lay a solid scientific basis for accurately simulating and predicting the fate of MPs in coastal wetland water–soil systems. We highlight the effect of salinity on the fate of MPs and the corresponding priority management of MPs risks under the background of global climate change.

Consequences of intense drought on CO2 and CH4 fluxes of the reed ecosystem at Lake Neusiedl

Reed (Phragmites australis) dominated wetlands are commonly known as strong carbon (C) sinks due to the high productivity of the reed plant and C fixation in the wetland soil. However, little is known about the effects of drought on reed-dominated wetlands and the possibility of Pannonian reed ecosystems being a source of greenhouse gases (GHG). The drought at Lake Neusiedl had a particular impact on the water level, but also had consequences for the reed belt. Therefore, we investigated the drought-influenced C fluxes and their drivers in the reed ecosystem of this subsaline lake over a period of 4.5 years (mid-2018 to 2022). We applied eddy covariance technique to continuously quantify the vertical turbulent GHG exchange between reed belt & atmosphere and used vegetation indices to account for reed growth. Methane emissions decreased by 76% from 9.2 g CH4-C m-2a-1 (2019) to 2.2 g CH4-C m-2 a-1 (2022), which can be explained by the falling water level, the associated drying out of the reed belt and its consequences. Carbon dioxide emissions initially decreased by 85% from 181 g CO2-C m-2 a-1 (2019) to 27 g CO2-C m-2 a-1 (2021), but then increased to twice the 2019 level in 2022 (391 g CO2-C m-2 a-1). Due to the drying reed belt, the reed initially grew into formerly water-covered areas within the reed belt, especially in 2021, leading to higher photosynthesis through 2021. This development stopped and even reversed in 2022 as a consequence of the sharp decrease in sediment water content from about 65 to 32 Vol-% in mid-2022. Overall, drought led to a decoupling of the reed ecosystem from the open lake area and developed the wetland into a strong C source.

Spatio-temporal Dynamics of Land Use/Cover Change and Associated Carbon Stocks in Kanyabaha Wetland in Rukiga District, Uganda

Wetlands play an important ecological function of sequestering atmospheric carbon dioxide and thereby moderating adverse impacts of climate change. It is therefore important to understand the dynamics of carbon stocks in wetland vegetation and soils. This study investigated the spatio-temporal dynamics of aboveground, belowground, and total carbon stocks in Kanyabaha Wetland, located in Rukiga District, Uganda, spanning from 1990 to 2021. Through field sampling and laboratory analysis, aboveground carbon stocks were assessed by harvesting vegetation biomass and converting it to carbon stock using established conversion factors. Soil samples collected at different depths (0-20cm, 20-50cm, 50-100cm) were analyzed for soil organic carbon content to determine belowground carbon stocks. The study reveals variable spatio-temporal patterns of carbon stocks across land use types, with papyrus-dominated areas exhibiting the highest aboveground carbon stocks (49.66 tC/ha), followed by small-scale farmlands (33.73 tC/ha) and tree plantations (23.01 tC/ha). Conversely, built-up areas exhibit the lowest carbon stocks (1.29 tC/ha). Temporal analysis reveals fluctuating patterns in carbon stocks, with increases observed in built-up areas and small-scale farmlands, and decreases in grasslands and tree plantations that could be due to changes in hydrological cycle. Belowground carbon stocks follow similar trends, with papyrus areas maintaining the highest stocks (39.96 tC/ha), particularly at deeper soil depths that exhibit the highest carbon accumulation due to its extensive network of papyrus rhizome. Changes in land use, especially reclamation of the wetlands for farming and settlements affected carbon capture and storage in the wetland ecosystem. These findings highlight the importance of targeted conservation of natural wetlands and sustainable land management strategies in the Kanyabaha Wetland catchment for enhanced carbon sequestration. Further, in depth studies in the variability of carbon stocks due to various eco-climatic factors and anthropogenic activities are necessary to support sustainable wetland land management practices in Uganda.

Bridging ecological processes to diversity formation and functional profiles in belowground bacterial communities

Revealing the generation and maintenance of biodiversity is a central goal in ecology, but how dispersal, selection, and regional taxon pool size shape soil microbial communities is not well understood. Here, we examined how dispersal and environmental selection affected soil bacterial diversity and their related metabolic functions by leveraging large-scale cross-biome soil surveys of ∼1400 samples from diverse ecosystems across China, including agricultural, forest, grassland, and wetland soils. Our results showed that high dispersal increased α-diversity and decreased β-diversity, whereas strong selection generated the opposite pattern in various ecosystems. This is likely due to dispersal enabling species access to otherwise unreachable habitats, and environmental selection excluding non-adapted species from communities. The α-diversity increased with γ-diversity, whereas β-diversity did not covary. We also showed that bacterial phylotypes positively associated with dispersal and selection exhibited distinct metabolic diversity. Dispersal-induced phylotypes, which were abundant in agricultural soils, exhibited more metabolic diversity in fructose and mannose, starch and sucrose, and nitrogen metabolism. Conversely, selection-induced phylotypes, dominated in wetland soils, were primarily associated with sulfur and methane metabolism. In addition, the complexity of taxon associations increased when communities had higher selection increasing β-diversity. Our study establishes the predictive links of ecological processes to microbial diversity, metabolic functions, and taxon coexistence, thus facilitating a better understanding of the mechanisms underlying biodiversity generation and conservation.