Implications For Water Quality Research Articles

Serra da Canastra National Park: Influence of forest fires on the RUSLE C factor and its impact on water erosion

The adverse impacts of soil degradation and nutrient loss resulting from water erosion are significant environmental concerns that have profound implications for both water quality and biodiversity. This study aims to evaluate the impact of forest fires on soil loss through water erosion in the Serra da Canastra National Park, in Minas Gerais state, Brazil. Using the Revised Universal Soil Loss Equation (RUSLE), which considers rainfall erosivity, soil erodibility, slope length and slope and vegetation cover, the C factor (vegetation cover) values were obtained from data from literature and methods based on the Normalized Differential Vegetation Index (NDVI). Validation was carried out using data on total sediment, water flow and daily runoff from the hydrosedimentological station and the InVEST software. The results highlight the significant impact of wildfires on soil loss through water erosion and indicate that areas recently affected by wildfires, especially on steep slopes and with more erodible soils, are subject to the highest rates of soil loss. Soil loss rates varied from 0.75 to 12.55 Mg ha-1 yr-1, in part due to the different ways of obtaining factor C. The research emphasizes the need to conserve vegetation cover to prevent soil erosion, particularly in regions impacted by forest fires. This study offers valuable insights that can contribute to enhancing the sustainable environmental management of the Serra da Canastra National Park.

Taxonomic and functional dynamics of nirS denitrifiers along a salinity gradient in the Pearl River Estuary

Understanding the factors that shape the diversity, distribution, and function of denitrifying microbes is vital for managing nitrogen cycling in these ecosystems. This study explores the diversity, biogeographic distribution, assembly processes, interaction, and denitrification potential of the nirS-encoding microbial community (nirS denitrifier) in the Pearl River Estuary based on high-throughput and metagenomics sequencing dataset. The results of this study show that salinity is a crucial regulatory environmental factor that determines the spatial distribution, phylogenetic turnover, and co-occurrence patterns of nirS denitrifiers. Additionally, the dissolved organic carbon (DOC), suspended sediment concentration (SSC), and dissolved oxygen (DO) in water also significantly impact the biodiversity and abundance of nirS denitrifiers. Furthermore, our findings demonstrate that, in comparison to environmental factors, the ecological and evolutionary characteristics of nirS denitrifiers play a more prominent role in regulating their denitrification potential, suggesting that alterations in the microbial community within dynamic changes in estuarine water can profoundly affect its denitrification function. Our results indicate the significant roles of denitrification microbial structure and phylogenetic characteristics in maintaining their ecological functions. Future studies should continue to explore the interactions between microbial communities and environmental factors to further elucidate the denitrification process in estuaries and its implications for ecosystem health and water quality.

Design, Synthesis, and Mode of Action of Thioacetamide Derivatives as the Algicide Candidate Based on Active Substructure Splicing Strategy.

Lakes and reservoirs worldwide are experiencing a growing problem with harmful cyanobacterial blooms (HCBs), which have significant implications for ecosystem health and water quality. Algaecide is an effective way to control HCBs effectively. In this study, we applied an active substructure splicing strategy for rapid discovery of algicides. Through this strategy, we first optimized the structure of the lead compound S5, designed and synthesized three series of thioacetamide derivatives (series A, B, C), and then evaluated their algicidal activities. Finally, compound A3 with excellent performance was found, which accelerated the process of discovering and developing new algicides. The biological activity assay data showed that A3 had a significant inhibitory effect on M. aeruginosa. FACHB905 (EC50 = 0.46 μM) and Synechocystis sp. PCC6803 (EC50 = 0.95 μM), which was better than the commercial algicide prometryn (M. aeruginosa. FACHB905, EC50 = 6.52 μM; Synechocystis sp. PCC6803, EC50 = 4.64 μM) as well as better than lead compound S5 (M. aeruginosa. FACHB905, EC50 = 8.80 μM; Synechocystis sp. PCC6803, EC50 = 7.70 μM). The relationship between the surface electrostatic potential, chemical reactivity, and global electrophilicity of the compounds and their activities was discussed by density functional theory (DFT). Physiological and biochemical studies have shown that A3 might affect the photosynthesis pathway and antioxidant system in cyanobacteria, resulting in the morphological changes of cyanobacterial cells. Our work demonstrated that A3 might be a promising candidate for the development of novel algicides and provided a new active skeleton for the development of subsequent chemical algicides.

Peat swamp hydrological connectivity and runoff vary by hydrogeomorphic setting: Implications for carbon storage

AbstractDespite their importance in carbon cycling and catchment runoff dynamics, the hydrology of temperate peat swamps in response to changing hydrometeorological conditions is largely understudied. We examined the importance of hydrogeomorphic settings in controlling hydrological connectivity and runoff in a temperate peat swamp in southern Ontario, Canada over two consecutive growing seasons with contrasting conditions (dry and wet years). We chose two different small‐scale hydrogeomorphic settings to investigate: (i) a site with strong wetland‐stream interactions (i.e., an unconfined stream channel; unconfined) and (ii) a site with limited wetland‐stream interactions (confined).During the wet year, the confined site exhibited a consistently gaining stream, maintaining lateral hydrological connectivity and yielding high runoff ratios, while during the dry year, the confined site lost water and experienced low runoff ratios during storm events. Overland flow at the unconfined site maintained a longitudinal hydrological connectivity delivering water to its sub‐catchment outflow, as reinforced by hydrochemical observations. This connectivity was maintained in the wet year but ceased in the dry year despite consistent upstream sub‐catchment water inflow due to high depression storage. Runoff ratios were reduced because of this hydrological disconnection.We highlight the importance of small‐scale hydrogeomorphic setting on peat swamp carbon storage as facilitated by the variation of within‐site hydrological connectivity and runoff, which also has important implications for downstream water quality. The unconfined site maintained a higher water table position in both years and has much greater peat carbon stocks. We suggest peat swamp channelization either naturally or through drainage decreases carbon stocks.

Assessing the resilience of stormwater ponds under climate change: A case study on Grace Lake, Florida, unveiling flood control and water quality implications

Stormwater ponds have emerged as a crucial solution in Florida to accommodate excess runoff from new developments and mitigate environmental pollution. Climate change affects rainfall and evapotranspiration, likely altering the hydrologic process. It is unclear how effective stormwater ponds will be in a changing climate, especially where surface water and groundwater interaction is highly expected. To address these concerns, this study employs a fully coupled surface water and groundwater model that was calibrated for the Grace Lake, located in central Florida. Utilizing the Multi-Model Ensemble method and GCM data, future rainfall projections were generated for the mid-century (2040–2070). The results indicate a projected 13 % increase in rainfall for the mid-century under the Representative Concentration Pathway 4.5 (RCP 4.5). This increase led to a rise of 13 cm in the seasonal high water elevation of Grace Lake, reducing its reliability as a flood control mechanism by 13 %. Moreover, downstream areas from the lake are expected to experience higher flood stages in the future, with the duration of road flooding extending from less than three days (base period) to approximately seven days (future period). This increase in surface runoff raises concerns for water quality, with nitrogen and phosphorus loads projected to surge up to 67 % in the future period.

The Effects of Annual Compost Addition to Agricultural Green Roofs on Runoff Water Quality

Space availability is one of the largest barriers to urban agriculture. One way around this issue that urban farmers in some parts of the world are exploring is moving their farming activities to building rooftops. One method of rooftop farming in use is row agriculture using green roof technology. Vegetable crop plants, which typically require more water and more nutrients than the ornamental species found on green roofs, require irrigation and the use of fertilizers. One nutrient management practice that some rooftop farmers are using is the addition of compost, which could lead to changes over time in the water-holding capacity, organic matter content, and weight of green roof media. This practice and its long-term implications have not been well-studied. Green roof platforms were created to examine how the annual additions of compost in quantities of 0, 0.33, 0.66, and 1 kg/m2 affect runoff water quality and green roof media properties. Runoff water samples were collected and analyzed for pH, conductivity, color, turbidity, and nitrate nitrogen, ammonia nitrogen, total phosphorus, and potassium contents. Compost treatment had no effect on any water quality metric except for color, which had slightly different changes over time in the different compost treatments. The lack of difference among the treatments may be attributed to the low nutrient content of the compost and continued use of fertilizers to provide nutrients. Most samples observed in this study exceeded the US Environmental Protection Agency water quality guidelines for nitrate nitrogen and phosphorus and were similar to values observed in the green roof literature regarding agricultural and ornamental green roofs. This has potential implications for surface water quality and eutrophication, especially as green roof agriculture increases.

Impacts of irrigation development on water quality in the San Salvador watershed (Part 1): Assessment of current nutrient delivery and transport using SWAT

The development of irrigation involves a change in land use and management and has implications for water quality and quantity. It is critical to design conservation practices and best management practices consistent with sustainable agricultural intensification. The objective of this work was to understand and characterize key processes affecting hydrology, nutrient export and transport, and quantify impacts in the San Salvador watershed. For such purpose, the Soil & Water Assessment Tool (SWAT) was implemented, calibrated for water quantity, and water quality was adjusted using soft calibration techniques. The model reproduces water quantity and nutrient balance, and aids in characterizing the nutrient delivery and transport in the watershed. The magnitude of runoff affects the balance of nutrients. In high flows, diffuse sources are more prevalent, while in low flows, point sources and direct livestock manure to the river are more significant. The main outcomes of this work contribute to the design of strategies to achieve sustainable agricultural intensification. It also describes a new modeling tool freely available that could be used in further studies.

Exploring the Complex Effects of Wildfire on Stream Water Chemistry: Insights From Concentration‐Discharge Relationships

AbstractWildfires are a worldwide disturbance with unclear implications for stream water quality. We examined stream water chemistry responses immediately (<1 month) following a wildfire by measuring over 40 constituents in four gauged coastal watersheds that burned at low to moderate severity. Three of the four watersheds also had pre‐fire concentration‐discharge data for 14 constituents: suspended sediment (SSfine), dissolved organic and inorganic carbon (DOC, DIC), specific UV absorbance (SUVA), major ions (Ca2+, K+, Mg2+, Na+, Cl−, , , F−), and select trace elements (total dissolved Mn, Fe). In all watersheds, post‐fire stream water concentrations of SSfine, DOC, Ca2+, Cl−, and changed when compared to pre‐fire data. Post‐fire changes in , K+, Na+, Mg2+, DIC, SUVA, and total dissolved Fe were also found for at least two of the three streams. For constituents with detectable responses to wildfire, post‐fire changes in the slopes of concentration‐discharge relationships commonly resulted in stronger enrichment trends or weaker dilution trends, suggesting that new contributing sources were surficial or near the surface. However, a few geogenic solutes, Ca2+, Mg2+, and DIC, displayed stronger dilution trends at nearly all sites post‐fire. Moreover, fire‐induced constituent concentration changes were highly discharge and site‐dependent. These similarities and differences in across‐site stream water chemistry responses to wildfire emphasize the need for a deeper understanding of landscape‐scale changes to solute sources and pathways. Our findings also highlight the importance of being explicit about reference points for both stream discharge and pre‐fire stream water chemistry in post‐fire assessment of concentration changes.

How the catchment-river-lake continuum shapes the downstream water quality

Lakes play a crucial role in the nutrient cycling of Earth, despite covering only a small fraction of the planet’s surface. Their interactions with their surrounding catchment areas significantly impact ecosystems and regulatory services. The connection between a lake and its catchment, especially the drainage ratio (catchment area to lake surface area), shapes the characteristics of lakes and their response to catchment processes. Within the catchment area, geological, land cover, and land use factors influence the composition of stream water that flows into the lake. These factors play a role in transporting various substances, both organic and inorganic, to the streams. Lakes act as dynamic filters, altering the chemical composition of water that flows through them. This study aims to investigate how a large, shallow lake impacts the quality of the river water as it passes through. It builds on an analysis of nutrient (carbon, nitrogen, phosphorus, silicon) fluxes into Lake Võrtsjärv, using six years of monthly monitoring data from five main inflows and the outflow. The research explores how catchment characteristics and hydrology affect nutrient concentrations and loadings into the lake, as well as the retention or release of substances by the lake. Findings reveal that catchment characteristics, such as land use and forest cover, significantly influence water quality parameters. Different inflows showed variations in water quality, and annual variations were observed, largely correlated with precipitation and discharge. Võrtsjärv plays a critical role in retaining or releasing nutrients, with varying impacts depending on the water budget of the lake. In years with a positive water balance, the lake retains all nutrients, whereas in dry years only inflowing N and P loads exceed their outflow. Overall, this study underscores the importance of lakes as integral components of catchment ecosystems, shedding light on their complex interactions with the environment and the implications for water quality. It emphasizes the need for careful consideration of land use and hydrological factors in managing and preserving these vital aquatic systems.

Municipal Solid Waste (MSW) and its Impact on Soil Properties in and around the Achan Dump Site in Srinagar, Jammu & Kashmir

Abstract: Solid waste disposal may result in soil pollution with implications for ground water quality. Deteriorating soil quality and decrease in vegetation are grave consequences of open waste dumping which have resulted in growing public concern. The effect of waste disposal on soil quality of Achan, Srinagar was studied. The objective of the study was to determine the physical and chemical properties of the soil samples collected from all the sides of the dumping site and at different distances. The results of the physical properties showed that bulk density was lower at the dumpsite and increased with increase in distance. Soil moisture content, pH, EC, OC, organic matter, CEC were higher at the dump site and decreased with increase in distance. Exchangeable cautions (Ca, Mg, and Na), DTPA micro nutrients and heavy metal concentration were higher at the dumpsite and decreased with the increase in the distance. All the parameters were found to be significantly different in different sampling sites except soil pH and nitrogen

Increases in trade secret designations in hydraulic fracturing fluids and their potential implications for environmental health and water quality

Hydraulic fracturing is an increasingly common method of oil and gas extraction across the United States. Many of the chemicals used in hydraulic fracturing processes have been proven detrimental to human and environmental health. While disclosure frameworks have advanced significantly in the last 20 years, the practice of withholding chemical identities as “trade secrets” or “proprietary claims” continues to represent a major absence in the data available on hydraulic fracturing. Here, we analyze rates of trade secret claims using FracFocus, a nationwide database of hydraulic fracturing data, from January 1, 2014 to December 31, 2022. We use the open-source tool Open-FF, which collates FracFocus data, makes it accessible for systematic analysis, and performs several quality-control measures. We found that the use by mass of chemicals designated as trade secrets has increased over the study time period, from 728 million pounds in 2014 to 2.96 billion pounds in 2022 (or a 43.7% average yearly increase). A total of 10.4 billion pounds of chemicals were withheld as trade secrets in this time period. The water volume used (and therefore total mass of fracturing fluid) per fracturing job has shown a large increase from 2014 to 2022, which partly explains the increase in mass of chemicals withheld as trade secrets over this time period, even as total fracturing jobs and individual counts of proprietary records have decreased. Our analysis also shows increasing rates of claiming proppants (which can include small grains of sand, ceramic, or other mineral substances used to prop open fractures) as proprietary. However, the mean and median masses of non-proppant constituents designated as trade secrets have also increased over the study period. We also find that the total proportion of all disclosures including proprietary designations has increased by 1.1% per year, from 79.3% in 2014 to 87.5% in 2022. In addition, most disclosures designate more than one chemical record as proprietary: trade secret withholding is most likely to apply to 10–25% of all records in an individual disclosure. We also show the top ten reported purposes that most commonly include proprietary designations, after removing vague or multiple entries, the first three of which are corrosion inhibitors, friction reducers, and surfactants. Finally, we report the top ten operators and suppliers using and supplying proprietary chemicals, ranked by mass used or supplied, over our study period. These results suggest the importance of revisiting the role of proprietary designations within state and federal disclosure mechanisms.

Land Use Change Detection and Evaluation in a Watershed: The Implications for Ofu River Water Quality in Anyigba, Kogi State, Nigeria

This paper examined visible land use changes in Ofu River watershed. Supervised and unsupervised classification of land use types were adopted. Geographical Information System (GIS) software, ArcGIS was used handling and analyzing geographic information by visualizing land use change characteristics or spatio-temporal variability of land use in the study area. The results shows built-up in 2000, 2010, 2020, and 2030 projection were analyzed to be (18.931km2, 30.891km2, 81.280km2 and 112.455km2) respectively, water body (7.491km2, 7.491km2, 7.450km2 and 7.428km2), wetlands (105.637km2, 81.713km2, 61.590km2 and 39.564k2), scattered agriculture (1381.057km2, 1,460.415km2, 1,58.560km2 and 1,662.313km2) and vegetated land (415.428km2, 348.033km2, 209.660km2 and 106.783km2) respectively. Tested hypothesis revealed that p< .05. This study recommends proper monitoring of land uses and workable land use policies be put in place in the study area.

Systematic Review of Contaminants of Emerging Concern (CECs): Distribution, Risks, and Implications for Water Quality and Health

The introduction of contaminants of emerging concern (CECs) into the environment has raised concerns due to the significant risks they pose to both ecosystems and human health. In this sys-tematic review, we investigate research trends on CECs worldwide over the past 10 years, focus-ing on four critical aspects: (i) the identification and distribution of typical CECs across various media, (ii) the sources and environmental behavior of CECs, (iii) the implications of CECs expo-sure on human health, and (iv) risk assessment and control measures for CECs. The review re-veals a comprehensive understanding of the typical types and distribution of CECs in different environmental media, shedding light on their prevalence and potential impact on ecosystems. Furthermore, insights into the sources and behavior of CECs provide crucial information for de-vising effective strategies to mitigate their release into the environment. By examining the health effects of EC exposure, we highlight the importance of considering potential risks to human well-being. This aspect of the review emphasizes the significance of monitoring and managing CECs to safeguard public health. The review also synthesizes the advancements in risk assessment methodologies and control measures for CECs, which are essential for developing comprehensive regulations and guidelines to manage these contaminants effectively. Drawing from the findings, we identify future research directions for CECs in aquatic environments.

Effects of drying-rewetting cycles on colloidal phosphorus composition in paddy and vegetable soils

The impact of drying-rewetting (DRW) cycles on soil phosphorus (P) behavior is well-established; however, its impact on the different-sized colloidal P (CP) in agricultural soils is still unclear. To investigate the effect of DRW events on the mobilization of CP in agricultural soils, and to understand how this impact varies with different DRW cycles and drought intensities, the study explored the role of soil type, CP fractions, and compositions. The concentration of CP was measured in paddy soil and vegetable soil after 3, 6, and 9 DRW cycles of varying intensities. The CP was then fractionated into fine-sized colloids (FC-P; 1–220 nm), medium-sized colloids (MC-P; 220–450 nm), and coarse-sized colloids (CC-P; 450–1000 nm) through soil supernatant filtration. CP accounted for 71.1 % and 55.6 % of water-dispersible colloidal P (<1000 nm) in paddy and vegetable soils, with FC-P constituting the greatest proportion at 50 % and 44 % of CP respectively. The colloidal fraction correlated with organic carbon, aluminum, and iron. DRW cycles did not change the overall distribution of the three CP size fractions. However, they affected the concentration and composition of CP. This study concluded that DRW can have significant implications for nutrient release and water quality in agricultural soils and that maintaining soil moisture at 50 % to 70 % of water-holding capacity could alleviate CP accumulation resulting from DRW cycles.

The effect of novel aquaculture mode on phosphorus sorption-release in pond sediment

The emergence of aquaculture modes has brought considerable changes to the aquaculture landscape and profoundly influenced environmental processes. However, there is limited research on nutrient cycling in emerging aquaculture modes. This study investigated the characteristics and mechanisms of sediment phosphorus (P) sorption-release in traditional earthen pond culture (TEP) and pond-tank culture mode (PTC), which represents novel aquaculture modes. The results showed that under higher nutrient load, the PTC did not show significant differences in nutrient concentration in water and sediments compared to TEP. Although there are no significant differences in overlying water P concentration between the modes throughout the entire aquaculture period, the trends of its variation over time are different, which significantly affected the P sorption-release characteristics of sediment. Additionally, correlation analysis suggested that calcium-bound P and hot NaOH-extractable organic P may affect the sorption-release characteristics of sediment as active P fractions. The change in redox condition caused by enzyme-mediated organic matter decomposition (such as protein and lipids) is also an important reason for sediment P release. However, the P fractions and organic matter content showed no significant differences between the two modes. Sediment microbial analysis showed that TEP exhibited a significant dominance of inorganic P-solubilizing bacteria, especially Actinobacteria and Bacilli classes. PTC had a higher proportion of organic P-solubilizing bacteria, primarily in the Bacteroidia class. The quantitative results of the key functional gene phoD in organic P decomposition also showed that the abundance in PTC was significantly higher than that in TEP. This suggested that microbial differences may be another reason for differences in P sorption-release behavior. This study revealed the differences in P sorption-release characteristics and mechanisms between the TEP and PTC, which holds positive implications for water quality and pollution management in novel aquaculture modes.

Plasticiser leaching from polyvinyl chloride microplastics and the implications for environmental risk assessment

Microplastics in aquatic environments is a growing concern, particularly due to the leaching of chemical additives such as plasticisers. To develop comprehensive environmental risk assessments (ERAs) of high-concern polymers and plasticisers, an understanding of their leachability is required. This work investigated diethylhexyl phthalate (DEHP) and bisphenol A (BPA) leaching from polyvinyl chloride (PVC) microplastics (average diameter = 191 μm) under simulated marine conditions. Leaching behaviours were quantified using gel permeation chromatography (GPC) and thermal gravimetric analysis (TGA), and the polymer's physiochemical properties analysed using differential scanning calorimetry (DSC), Fourier Transform-Infrared Spectroscopy (FT-IR) and optical microscopy. Experimental data were fitted to a diffusion and boundary layer model, which found that BPA leaching was temperature-dependent (diffusion-limited), whereas DEHP leaching was controlled by surface rinsing. Model predictions also highlighted the importance of microplastic size on leaching dynamics. These data contribute towards greater accuracy in ERAs of microplastics, with implications for water quality and waste management, including decommissioning of plastic infrastructure.

Biofilm community composition is changing in remote mountain lakes with a relative increase in potentially toxigenic algae

Mountain lakes provide clear drinking water to humankind but are strongly impacted by global change. Benthic biofilms are crucial for maintaining water quality in these oligotrophic lakes, yet little is known about the effects of global change on mountain biofilm communities. By combining analyses of metabarcoding data on 16S and 18S rRNA genes with climatic and environmental data, we investigated global change effects on the composition of biofilm prokaryotic and micro-eukaryotic assemblages in a five-year monitoring program of 26 Pyrenean lakes (2016–2020). Using time-decay relationships and within-lake dissimilarity modelling, we show that the composition of both prokaryotic and micro-eukaryotic biofilm communities significantly shifted and their biodiversity declined from 2016 to 2020. In particular, analyses of temporal trends with linear mixed models indicated an increase in the richness and relative abundance of cyanobacteria, including potentially toxigenic cyanobacteria, and a concomitant decrease in diatom richness and relative abundance. While these compositional shifts may be due to several drivers of global change acting simultaneously on mountain lake biota, water pH and hardness were, from our data, the main environmental variables associated with changes for both prokaryotic and micro-eukaryotic assemblages. Water pH and hardness increased in our lakes over the study period, and are known to increase in Pyrenean lakes due to the intensification of rock weathering as a result of climate change. Given predicted climate trends and if water pH and hardness do cause some changes in benthic biofilms, those changes might be further exacerbated in the future. Such biofilm compositional shifts may induce cascading effects in mountain food webs, threatening the resilience of the entire lake ecosystem. The rise in potentially toxigenic cyanobacteria also increases intoxication risks for humans, pets, wild animals, and livestock that use mountain lakes. Therefore, our study has implications for water quality, ecosystem health, public health, as well as local economies (pastoralism, tourism), and highlights the possible impacts of global change on mountain lakes.

Evaluation of Legacy Forest Harvesting Impacts on Dominant Stream Water Sources and Implications for Water Quality Using End Member Mixing Analysis

Forests are critical water supply regions that are increasingly threatened by natural and anthropogenic disturbance. Evaluation of runoff-generating processes within harvested and undisturbed headwater catchments provides insight into disturbance impacts on water quality and drinking water treatability. In this study, an extensive hydrologic dataset collected at the experimental Turkey Lakes Watershed (TLW) located on the Canadian Shield was used to quantify sources of stormflow in legacy clear-cut (24-years post harvesting) and forested (control) headwater catchments using an end member mixing analysis (EMMA) model. Stream water, groundwater, soil water, and throughfall water quality were evaluated during spring snowmelt, stormflow, and fall wet-up. Groundwater chemistry was similar to stream water chemistry in both catchments, suggesting that groundwater is a major contributor to stream flow. The water chemistry in small wetlands within the study catchments was comparable to stream water chemistry, suggesting that wetlands are also important contributors to stream flow. Differences in wetland position between the legacy clear-cut and control catchments appeared to have a greater influence on source contributions than legacy harvesting. Results from this study provide insight into runoff-generation processes that reflect event/seasonal flow dynamics and the impacts on water quality.

Influence of soil drying followed by flooding on micronutrient solubilization

AbstractFlooding is known to solubilize soil nutrients, particularly those associated with redox‐sensitive metals (Fe/Mn). Both soil flooding and drying are becoming more common due to climate change, but it is not clear how soil drying prior to flooding influences nutrient solubilization in soils, compared with flooding of already moist soils. This study was designed to examine how soil drying followed by extended flooding might influence solubilization of micronutrient metals (Fe, Mn, Cu, Co, Zn and Ni). A series of laboratory mesocosm experiments was carried out by flooding samples of two contrasting grassland soils, which had each been either dried (40°C for 10 days) or kept at field moisture conditions (25%, w/w). The flooding of dried soils generally resulted in higher concentrations of the micronutrients (Mn, Co, Ni and Cu) in the water columns relative to their moist‐flooded counterparts. The results demonstrate that the flooding‐induced variations in pH and redox potential influence solubilization of micronutrients in the soils. The mobilization of Co and Ni appeared to be controlled by redox‐driven reductive dissolution of Fe/Mn minerals. This was supported by significant (p &lt; .001) negative correlations between redox and metals: Co (r = −.712), Ni (r = −.784) and the positive correlations between Fe and metals: Co (r = .763) and Ni (r = .714) and between Mn and other metals: Co (r = .909) and Ni (r = .811). However, there were no significant correlations of Zn and Cu with Fe and Mn. The results suggest that soil drying followed by flooding has the potential to promote greater solubilization of soil micronutrients compared with flooding of moist soils, with potential implications for soil fertility and catchment water quality under future changes in weather patterns driven by climate change.

Effects of burn severity on organic nitrogen and carbon chemistry in high-elevation forest soils

Fire frequency and severity have increased in recent decades in the western United States, with direct implications for the quantity and composition of soil organic matter (SOM). While the effects of wildfire on soil carbon (C) and inorganic nitrogen (N) have been well studied, little is known about its impacts on soil organic N. Since organic N is the most abundant form of soil N in conifer forests and dominant source of plant N facilitated by symbiotic mycorrhizae and mineralization, better understanding of post-fire organic N chemistry will help address a critical gap in our understanding of fire effects on SOM. Here, we characterized changes to organic N chemistry across fire severity gradients resulting from two wildfires that burned lodgepole pine (Pinus contorta) forest along the Colorado/Wyoming border, USA. One representative gradient was selected for high-resolution analysis based on results from bulk data (total C and N, and pH). Mineral soils were collected from two depths in low, moderate, and high severity burned areas and adjacent, unburned locations one year following the Ryan and Badger Creek fires. Nuclear magnetic resonance spectroscopy and 21 tesla ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry analysis showed that N content and aromaticity of water-extractable SOM (0–5 ​cm depth) increased with burn severity, while minimal changes to 5–10 ​cm depth were observed. Heterocyclic N species are generally higher in toxicity compared to their non-nitrogenated counterparts, which prompted soil toxicity measurements. Complementary Microtox® analysis revealed a positive relationship between increased fire severity and increased soil toxicity to Aliivibrio fischeri (microbial test species). These findings add to our molecular-level understanding of organic C and N responses to wildfire severity, with likely implications for nutrient cycling, forest recovery and water quality following severe wildfire.