Identification of key factors and mechanism determining arsenic mobilization in paddy soil-porewater-rice system.

Arsenic (As) mobilization in paddy fields poses significant health risks, necessitating a thorough understanding of the controlling factors and mechanisms to safeguard human health. We conducted a comprehensive investigation of the soil-porewater-rice system throughout the rice life cycle, focusing on monitoring arsenic distribution and porewater characteristics in typical paddy field plots. Soil pH ranged from 4.79 to 7.98, while porewater pH was weakly alkaline, varying from 7.2 to 7.47. Total arsenic content in paddy soils ranged from 6.8 to 17.2 mg/kg, with arsenic concentrations in porewater during rice growth ranging from 2.97 to 14.85 µg/L. Specifically, arsenite concentrations in porewater ranged from 0.48 to 7.91 µg/L, and arsenate concentrations ranged from 0.73 to 5.83 µg/L. Through principal component analysis (PCA) and analysis of redox factors, we identified that arsenic concentration in porewater is predominantly influenced by the interplay of reduction and desorption processes, contributing 43.5 % collectively. Specifically, the reductive dissolution of iron oxides associated with organic carbon accounted for 23.3 % of arsenic concentration dynamics in porewater. Additionally, arsenic release from the soil followed a sequence starting with nitrate reduction, followed by ferric ion reduction, and subsequently sulfate reduction. Our findings provide valuable insights into the mechanisms governing arsenic mobilization within the paddy soil-porewater-rice system. These insights could inform strategies for irrigation management aimed at mitigating arsenic toxicity and associated health risks.

A landscape limnology approach to assessing controls on soluble reactive phosphorus in sediment porewater and internal loading risk.

Sediment nutrients can be mobilized to overlying water via internal loading, which can be important to aquatic productivity. Using data from 143 Canadian lakes, we show high (~2400-fold) variation of soluble reactive phosphorus (SRP) concentrations in surficial sediment porewater, with results suggesting internal phosphorus loading (IPL) is also likely to vary widely. Consistent with past work at smaller scales, we show that lake depth, pH, trophic status, and bulk sediment Al:P and Fe:P influence porewater SRP, and IPL. Median porewater SRP concentration in lakes with high Al:P (molar ratios >10) were 4.8-fold smaller than in lakes with lower Al:P. In lakes where bulk sedimentary Fe:P molar ratios were >10 porewater SRP was 3.9-fold lower than in lakes with lower Fe:P. High pH (>7.8), along with hyper-eutrophic lakes were associated with higher porewater SRP. Finally, shallow lakes (<4 m depth) had median porewater SRP concentration 6-fold higher than deep lakes (>9 m depth). Important regional differences emerged, linked to regional variation in pH, soils, lake depth and trophic status, and paralleling areas of poor water quality. For example, median porewater SRP in lakes from the Boreal Plains and Prairies ecozones (dominated by Chernozems/Mollisols) was 64-fold and 44-fold higher than in the Boreal Shield (dominated by Podzols/Spodosols) (respectively), although we note that IPL risk is likely important across many ecozones. Using national data, we found in-lake measurements (particularly pH, and salinity) showed strong capacity in predicting porewater SRP (explaining 60-72 % of the variance in the data). Importantly, watershed predictors showed good predictive power, explaining ~50 % of variance in porewater SRP using variables including soil types, and % agriculture. Porewater SRP can be predicted with reasonable accuracy using easily measured variables, as can estimates of internal phosphorus loading, suggesting that landscape limnology holds strong potential in helping to inform lake management by informing understanding of in-lake nutrient sources.

Uptake of Typical Hydrophobic Organic Contaminants in Vegetables: Evidence From Passive Samplers.

Quantifying the root uptake of hydrophobic organic contaminants (HOCs) by plants remains challenging due to the lack of data on the freely available fractions of HOCs in soil porewater. We therefore hypothesized that a passive sampler could act as a useful tool to evaluate the root uptake potential and pathways of HOCs by plants in soil. We tested this hypothesis by exploring the uptake of polybrominated diphenyl ethers (PBDEs) and organophosphate esters (OPEs) by carrot and lettuce with the codeployment of passive samplers in a contaminated soil system. The results showed that the amounts of PBDEs enriched in carrot and lettuce were positively correlated with those in a passive sampler (r2 = 0.46-0.88). No concentration correlation was observed for OPEs between lettuce and passive samplers, due to possible degradation of OPEs in lettuce. The root-to-porewater ratios of PBDEs and OPEs, respectively, were 6.2 to 11 and 0.05 to 0.88 L g-1 for carrot, and 8.8 to 130 and less than reporting limits to 1.2 L g-1 for lettuce. The ratios were negatively correlated with log KOW values for carrot, but increased with increasing log KOW values over a range of 1.97 to 6.80, and then decreased with log KOW values greater than 6.80 for lettuce. This finding indicated that passive transport and partition were the accumulation pathways of PBDEs and OPEs in carrot and lettuce, respectively. Overall, passive samplers performed adequately in assessing the available fractions of persistent HOCs in plants, and can serve as a viable tool for exploring the pathways for plant root uptake of HOCs. Environ Toxicol Chem 2024;00:1-12. © 2024 SETAC.

Unravelling the salinity origins in the coastal aquifer/aquitard system of the Volturno River (Italy).

To counteract the ongoing salinization of coastal aquifers, which poses a significant environmental and socioeconomic challenge to local communities, it is necessary to first understand the origin and mechanisms of this phenomenon. This study investigates the origins of salinity in the Volturno River lowland in Southern Italy and reveals that the primary source in the area is paleo-seawater entrapped within sediments that were subject to evapoconcentration processes. By systematically collecting sediment samples at variable depths and locations and extracting porewaters, a comprehensive understanding of the interplay between freshwater and saline water was gained, including complex patterns of vertical stratification of groundwater salinity. The study highlights the limitations of traditional methods that rely on salinity monitoring via integral depth sampling, particularly in capturing the vertical redox and salinity gradients characteristics of layered aquifer/aquitard systems. On the contrary, environmental tracers, like chloride and bromide, provide valuable insights into the sources of groundwater salinity, distinguishing between current seawater intrusion and other causes, such as paleo-seawater and return flow from drained agricultural land. Results suggest that the majority of salinity does not originate from modern seawater intrusion or recent evaporation. Instead, it can be attributed to paleo-seawater affected by evapoconcentration processes. This study has broader implications for the sustainable management of coastal aquifers and the safeguarding of freshwater resources. While our findings are specific to the Volturno River coastal area, the methodologies and insights here presented can be reproduced in every coastal region facing similar salinity challenges.

The stability of natural and man-made unsaturated slopes influenced by different rainfall patterns.

Many slope failures have been recorded in Malaysia in recent times, particularly during the rainy season. An irregular rainfall is a change in rainfall patterns that is found to affect the slope stability with the infiltration of rainfall. The objective of this research is to investigate variations in the pattern of rainfall and their effect on the stability of natural and man-made unsaturated slopes in two separate site locations. Case A is located near a student's hall in Universiti Kebangsaan Malaysia (UKM), and another is located at the main entrance of UKM. Both cases are simulated with current and projected rainfall. The behaviour of the slopes with applied rainfall is analyzed with generated pore-water pressure, displacement and factor of safety. The first case was conducted by including the rainfall records from January 2011 to January 2021 and future-oriented data in January 2050. The software package used for this case is Plaxis2D. The results indicate that the highest factor of safety captured for 2021 was 1.156, while the lowest factor of safety was 1.11. It is observed that the obtained safety factor decreased with increasing rainfall intensity. Moreover, the displacement obtained was 0.1761 m. In Case B, the capillary barrier system was used consisting of two layers of soil with different hydraulic properties as slope cover. A parametric study was performed to investigate the effect of several variables, including the hydraulic conductivity of soil and the rate of infiltration. By using SEEP/W from the GeoStudio, the results obtained show that the pore-water pressure in the initial slope is higher than the slope with the capillary barrier system. In addition, the factor of safety was calculated in SLOPE/W, indicating that the slope with a capillary barrier system has a high factor of safety than the original slope. The capillary barrier system was seen to improve slope stability by reducing the rainwater infiltration. These two cases were investigated in regard to the behaviour of unsaturated slopes within the changing rainfall and the unsaturated soil conditions.

The impact of organic carbon mineralization on pollution and toxicity of toxic metal in sediments: Yellow Sea and East China Sea study.

Organic carbon mineralization is the main driving force of metal migration and transformation in sediments, greatly influencing the distribution, pollution degree, and toxicity of toxic metals. However, relevant research on this subject is still limited. In this study, the concentration of toxic metals (Cr, Cd, Cu, Pb, Zn, Co, Fe, Mn, Ni, As) in the solid and liquid phase (porewater) of sediments were measured, toxic metal pollution degree and toxicity of the Yellow Sea (YS) and the East China Sea (ECS) were assessed. Combined with the rate of organic carbon mineralization, the impact of organic carbon mineralization was analyzed. The results showed that Ni was slightly enriched and posed a certain ecological risk, and As was moderately enriched in the studied area, Pb was at a moderate pollution level in the studied area. Zn, Co, Mn, and Fe were at a moderate pollution level in the mud area of SYS and the west coastal area of ECS. Additionally, the total organic carbon mineralization rate (TCMR) in the ECS (5.12-18.04 mmol C m-2 d-1) was slightly higher than that in the YS (3.29-14.46 mmol C m-2 d-1) during spring. Moreover, organic carbon mineralization promotes metal enrichment, and the TCMR was significantly correlated with the pollution load index. Thus, TCMR can be used as an indicator to predict the degree of metal pollution. Furthermore, organic carbon mineralization promotes the mobilization of Cu from the solid phase to the liquid phase, while facilitating the transfer of Cr, Pb, Co, Ni, and Fe from the liquid phase to the solid phase. This process increases the potential risks of Cu and reduces the toxicity of Cr, Pb, Co, Ni, and Fe. Therefore, the impact of organic carbon mineralization should be considered in future assessments and predictions of toxic metal pollution and toxicity.

Assessment of toxicity potential of freely dissolved PAHs using passive sampler in Kentucky Lake and Ohio River.

Polycyclic aromatic hydrocarbons (PAHs) are characterized with high KOW values, which lead to their recalcitrant nature, bioaccumulation, and biotoxicity, adversely affects the environment. Passive samplers (PS) have proven effective in measuring bioavailable PAH concentrations for toxicity assessments. In this study, we used low-density polyethylene (LDPE) to measure freely dissolved PAH concentrations (Cfree) in Kentucky Lake (KL) and Ohio River (OH), USA. PAHs toxicity potential in sediment was assessed using equilibrium partitioning sediment benchmarks toxic units (ESBTUs) and the interstitial water toxic units (IWTUs) that were derived from OC-normalized concentration (COC) and Cfree, respectively. The Cfree in April and June were 127 and 97 times higher in OH than in KL, respectively. Moreover, ESBTUs were higher in both the KL and OH compared to the IWTUs, suggesting that ESBTUs overestimate the toxicity potential to organisms. These results indicate that PS provides a reliable method for assessing the toxicity potential in sediments.

A User-Friendly Kinetic Model Incorporating Regression Models for Estimating Pesticide Accumulation in Diverse Earthworm Species Across Varied Soils.

Existing models for estimating pesticide bioconcentration in earthworms exhibit limited applicability across different chemicals, soils and species which restricts their potential as an alternative, intermediate tier for risk assessment. We used experimental data from uptake and elimination studies using three earthworm species (Lumbricus terrestris, Aporrectodea caliginosa, Eisenia fetida), five pesticides (log Kow 1.69-6.63) and five soils (organic matter content = 0.972-39.9 wt %) to produce a first-order kinetic accumulation model. Model applicability was evaluated against a data set of 402 internal earthworm concentrations reported from the literature including chemical and soil properties outside the data range used to produce the model. Our models accurately predict body load using either porewater or bulk soil concentrations, with at least 93.5 and 84.3% of body load predictions within a factor of 10 and 5 of corresponding observed values, respectively. This suggests that there is no need to distinguish between porewater and soil exposure routes or to consider different uptake and elimination pathways when predicting earthworm bioconcentration. Our new model not only outperformed existing models in characterizing earthworm exposure to pesticides in soil, but it could also be integrated with models that account for earthworm movement and fluctuating soil pesticide concentrations due to degradation and transport.

Spatiotemporal variations of domoic acid: New findings in the sedimentary environment of a typical nearshore mariculture bay, China.

Domoic acid (DA) is a neurotoxin produced by marine microalgae. It tends to accumulate in marine shellfish and fish, posing a threat to aquaculture and seafood consumers' health. In this study, DA in the surface and bottom seawater, sediment, and porewater of the Jiaozhou Bay, a typical mariculture bay in China, was systematically investigated for the first time over different seasons. Surprisingly, a high concentration of DA was discovered in the marine sediment porewater (maximum detected concentration: 289.49 ng/L) for the first time. DA was found to be extensively distributed in the water body and sedimentary environment of the Jiaozhou Bay. DA in the surface and bottom seawater of Jiaozhou Bay in spring was uniformly distributed, whereas DA showed obvious spatial variations in summer and winter. The high concentration areas of DA are located in the north of Jiaozhou Bay and decreased to the south areas. DA was also distributed in the sediment (spring mean: 316.57 ng/kg; summer mean: 10.22 ng/kg; winter mean: 237.08 ng/kg) and porewater (spring mean: 129.70 ng/L; summer mean: 53.54 ng/L; winter mean: 19.90 ng/L) of Jiaozhou Bay. The DA concentrations in the surface sediment and porewater were higher in the spring than in the winter and summer, contrary to the seasonal variation pattern observed in the surface and bottom seawater. The DA concentration in porewater was significantly higher than in the surface and bottom seawater, indicating that the risk of pollution contamination from DA to benthic fishery organisms may be underestimated. Overall, DA is widely distributed in the seawater and also in the benthic environment of Jiaozhou Bay and exhibited potential harm to fishery organisms varied greatly with seasons. It is an important discovery for marine algae toxins and has important guiding significance and important indicative role for the routine monitoring and management of DA pollution in water and benthic environment.

Unraveling the impact of Spartina alterniflora invasion on greenhouse gas production and emissions in coastal saltmarshes: New insights from dissolved organic matter characteristics and surface-porewater interactions.

Saltmarshes along the Chinese coast are threatened by the invasion of Spartina alterniflora (S. alterniflora). This study was carried out in the Andong Shoal, Hangzhou Bay, China, with the aim of comprehending the intricate impacts of S. alterniflora invasion on greenhouse gases (GHG) production and emissions. To address this issue, we thoroughly examined the chemistry of dissolved organic matter (DOM) and the rate of surface water-porewater interaction. Porewater and surface water samples were collected from farm land, S. alterniflora invaded areas, and Scirpus mariqueter (S. mariqueter) dominated areas. The findings indicated that the invasion of S. alterniflora impeded the interaction between surface water and porewater, resulting in reduced porewater exchange rates within its affected region (0.015-0.440 cm d-1), in contrast to areas dominated by S. mariqueter (9.635-18.232 cm d-1). The invasion also increased dissolved organic carbon concentration in porewater and created a stable and closed soil environment that resulted in DOM with smaller molecule sizes and higher humification levels. The presence of high tryptophan-like fluorescent DOM caused an increase in the production of methane and carbon dioxide in S. alterniflora invaded area. However, both limited surface-porewater exchange and significant differences in GHG concentrations between porewater and surface water suggested that the aerenchyma tissues of S. alterniflora may play an important role in transporting GHG from soil to the atmosphere.

Straw removal reduces Cd availability and rice Cd accumulation in Cd-contaminated paddy soil: Cd fraction, soil microorganism structure and porewater DOC and Cd.

The impacts of straw removal on rice Cd absorption, behaviour of Cd and microbial community in rhizosphere soil were investigated in paddy fields over two consecutive seasons. The results of the experiments in two fields revealed that straw removal promoted the transformation of soil Cd from acid-extractable and oxidisable fraction to residual fraction and reduced soil DTPA-Cd content with the reduction in DOC and Cd ions in soil porewater, thereby decreasing Cd content in rice. Specifically, the Cd content in brown rice was below 0.2 mg·kg-1 when all rice straw and roots were removed in the slightly Cd-contaminated soils. The α-diversity of soil microbial communities was less influenced by continuous straw removal, ß-diversity was altered and the relative abundances of Anaeromyxobacter, Methylocystis and Mycobacterium microbes were increased. Redundancy analysis and network analysis exhibited that soil pH predominantly influenced the microbial community. Path analysis revealed that the Cd content in brown rice could be directly influenced by the soil Total-Cd and DTPA-Cd, as well as soil pH and OM. Straw removal, including roots removal, is an economical and effective technique to reduce Cd accumulation in rice plants.

Potential Hazards of Polycyclic Aromatic Hydrocarbons in Great Lakes Tributaries Using Water Column and Porewater Passive Samplers and Sediment Equilibrium Partitioning.

The potential for polycyclic aromatic hydrocarbon (PAH)-related effects in benthic organisms is commonly estimated from organic carbon-normalized sediment concentrations based on equilibrium partitioning (EqP). Although this approach is useful for screening purposes, it may overestimate PAH bioavailability by orders of magnitude in some sediments, leading to inflated exposure estimates and potentially unnecessary remediation costs. Recently, passive samplers have been shown to provide an accurate assessment of the freely dissolved concentrations of PAHs, and thus their bioavailability and possible biological effects, in sediment porewater and overlying surface water. We used polyethylene passive sampling devices (PEDs) to measure freely dissolved porewater and water column PAH concentrations at 55 Great Lakes (USA/Canada) tributary locations. The potential for PAH-related biological effects using PED concentrations were estimated with multiple approaches by applying EqP, water quality guidelines, and pathway-based biological activity based on in vitro bioassay results from ToxCast. Results based on the PED-based exposure estimates were compared with EqP-derived exposure estimates for concurrently collected sediment samples. The results indicate a potential overestimation of bioavailable PAH concentrations by up to 960-fold using the EqP-based method compared with measurements using PEDs. Even so, PED-based exposure estimates indicate a high potential for PAH-related biological effects at 14 locations. Our findings provide an updated, weight-of-evidence-based site prioritization to help guide possible future monitoring and mitigation efforts. Environ Toxicol Chem 2024;43:1509-1523. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Effects of catchment land use on temperate mangrove forests.

Human land use changes are threatening the integrity and health of coastal ecosystems worldwide. Intensified land use for anthropogenic purposes increases sedimentation rates, pollutants, and nutrient concentrations into adjacent coastal areas, often with detrimental effects on marine life and ecosystem functioning. However, how these factors interact to influence ecosystem health in mangrove forests is poorly understood. This study investigates the effects of catchment human land use on mangrove forest architecture and sedimentary attributes at a landscape-scale. Thirty sites were selected along a gradient of human land use within a narrow latitudinal range, to minimise the effects of varying climatic conditions. Land use was quantified using spatial analysis tools with existing land use databases (LCDB5). Twenty-six forest architectural and sedimentary variables were collected from each site. The results revealed a significant effect of human land use on ten out of 26 environmental variables. Eutrophication, characterised by changes in redox potential, pH, and sediment nutrient concentrations, was strongly associated with increasing human land use. The δ15N values of sediments and leaves also indicated increased anthropogenic nitrogen input. Furthermore, the study identified a positive correlation between human land use and tree density, indicating that increased nutrient delivery from catchments contributes to enhanced mangrove growth. Propagule and seedling densities were also positively correlated with human land use, suggesting potential recruitment success mechanisms. This research underpins the complex interactions between human land use and mangrove ecosystems, revealing changes in carbon dynamics, potential alterations in ecosystem services, and a need for holistic management approaches that consider the interconnectedness of species and their environment. These findings provide essential insights for regional ecosystem models, coastal management, and restoration strategies to address the impacts of human pressures on temperate mangrove forests, even in estuaries that may be relatively healthy.

Unravelling the signatures of submarine groundwater discharge and seawater intrusion along the coastal plains of Odisha, India: a multi-proxy approach.

Submarine Groundwater Discharge (SGD) and Seawater Intrusion (SWI) are two contrary hydrological processes that occur across the land-sea continuum and understanding their nature is essential for management and development of coastal groundwater resource. Present study has attempted to demarcate probable zones of SGD and SWI along highly populated Odisha coastal plains which is water stressed due to indiscriminate-exploitation of groundwater leading to salinization and fresh groundwater loss from the alluvial aquifers. A multi-proxy investigation approach including decadal groundwater level dynamics, LANDSAT derived sea surface temperature (SST) anomalies and in-situ physicochemical analysis (pH, EC, TDS, salinity and temperature) of porewater, groundwater and seawater were used to locate the SGD and SWI sites. A total of 340 samples for four seasons (85 samples i.e., 30 porewater, 30 seawater and 25 groundwater in each season) were collected and their in-situ parameters were measured at every 1-2 km gap along ~ 145 km coastline of central Odisha (excluding the estuarine region). Considering high groundwater EC values (> 3000 µS/cm), three probable SWI and low porewater salinities (< 32 ppt in pre- and < 25 ppt in post-monsoons), four probable SGD zones were identified. The identified zones were validated with observed high positive hydraulic gradient (> 10 m) at SGD and negative hydraulic gradient (< 0 m) at SWI sites along with anomalous SST (colder in pre- and warmer in post-monsoon) near probable SGD locations. This study is first of its kind along the Odisha coast and may act as initial basis for subsequent investigations on fresh-saline interaction along the coastal plains where environmental integrity supports the livelihood of coastal communities and the ecosystem.

Pockmarks and associated fresh submarine groundwater discharge in the seafloor of Puck Bay, southern Baltic Sea.

This is the first well-documented report on the occurrence of pockmarks in Puck Bay. Pockmarks in the seafloor of Puck Bay were discovered during a hydroacoustic survey carried out in 2020. They are located at a depth of 25-27 m in the southwestern part of the bay. Significant depletion of chloride (Cl-) concentrations in sediment pore water was found within the depressions. Most likely, the formation of pockmarks was due to groundwater flow through the Miocene-Pleistocene system of aquifers, which extends from land to the bay area. One-dimensional modeling of vertical Cl- concentration profiles in pore water revealed the upward flow of freshened groundwater within the pockmarks. The magnitude of submarine groundwater discharge (SGD) was estimated to vary from 1.53·10-2 to 18·10-2 L·m-2·h-1. The effect of groundwater seepage was also observed at 3 cm above the seafloor within the pockmarks, which was identified as a decrease in salinity of approximately 0.12 PSU compared to reference sites. Furthermore, due to the effect of water advection, SGD can be detected even several meters above the seafloor as a decrease in salinity values within the thermocline layer.

PFAS Porewater concentrations in unsaturated soil: Field and laboratory comparisons inform on PFAS accumulation at air-water interfaces.

Poly- and perfluoroalkyl substance (PFAS) leaching from unsaturated soils impacted with aqueous film-forming foams (AFFFs) is an environmental challenge that remains difficult to measure and predict. Complicating measurements and predictions of this process is a lack of understanding between the PFAS concentrations measured in a collected environmental unsaturated soil sample, and the PFAS concentrations measured in the corresponding porewater using field-deployed lysimeters. The applicability of bench-scale batch testing to assess this relationship also remains uncertain. In this study, field-deployed porous cup suction lysimeters were used to measure PFAS porewater concentrations in unsaturated soils at 5 AFFF-impacted sites. Field-measured PFAS porewater concentrations were compared to those measured in porewater extracted in the laboratory from collected unsaturated soil cores, and from PFAS concentrations measured in the laboratory using batch soil slurries. Results showed that, despite several years since the last AFFF release at most of the test sites, precursors were abundant in 3 out of the 5 sites. Comparison of field lysimeter results to laboratory testing suggested that the local equilibrium assumption was valid for at least 3 of the sites and conditions of this study. Surprisingly, PFAS accumulation at the air-water interface was orders of magnitude less than expected at two of the test sites, suggesting potential gaps in the understanding of PFAS accumulation at the air-water interface at AFFF-impacted sites. Finally, results herein suggest that bench-scale testing on unsaturated soils can in some cases be used to inform on PFAS in situ porewater concentrations.

Impact of freshwater river reconnection on porewater salinity and ammonium availability in coastal brackish marsh soils.

Restoring freshwater flows to wetland ecosystems is an increasingly common tool for reversing saltwater intrusion/chronic salinization. Hydrologic restoration projects can deliver large volumes of sediment and fresh water to coastal basins, episodically exposing brackish and salt marsh vegetated soils to low surface water salinities. Yet little is known about the impacts of river reconnection/diversions to porewater salinity of the active root zone (0-30 cm) and salinity dependent soil biogeochemical processes like sorption. Intact soil cores from a brackish marsh site in mid-Barataria Basin, LA were subjected to a simulated river diversion opening to examine how porewater salinity and ammonium (NH4+) availability change with depth and time. Quadruplicate soil cores were inundated with continuously flowing fresh (0 salinity) water for 0, 7, or 28 d then measured for porewater salinity and NH4+ partition coefficient (exchangeable NH4+:porewater NH4+) every 2 cm for the top 10 cm of soil. Porewater salinity decreased in the 0-4 cm interval between 0 and 7 d of the simulated river diversion and increased in the 8-10 cm interval between 7 and 28 d. Overall, depth-averaged porewater salinity of the top 10 cm did not significantly change between 0 and 28 d of the simulated river diversion. Ammonium partition coefficients increased only in the 0-2 cm interval between 0 and 7 d of the simulated river diversion, likely due to freshening-induced NH4+ adsorption. These results indicate that the physicochemical environment of brackish marsh soils is relatively resistant to a single surface water freshening over one month. Models utilized by the state of Louisiana may be overpredicting freshening of the marsh soil porewater in Mid-Barataria Basin in response to the episodic operation of the Mid-Barataria Sediment Diversion. This study demonstrates the importance of measuring diffusive-adsorptive flux of major cations and anions when modeling vertical salt transfer in brackish marsh soils.

Commercial compost amendments inhibit the bioavailability and plant uptake of per- and polyfluoroalkyl substances in soil-porewater-lettuce systems.

Compost is widely used in agriculture as fertilizer while providing a practical option for solid municipal waste disposal. However, compost may also contain per- and polyfluoroalkyl substances (PFAS), potentially impacting soils and leading to PFAS entry into food chains and ultimately human exposure risks via dietary intake. This study examined how compost affects the bioavailability and uptake of eight PFAS (two ethers, three fluorotelomer sulfonates, and three perfluorosulfonates) by lettuce (Lactuca sativa) grown in commercial organic compost-amended, PFAS spiked soils. After 50 days of greenhouse experiment, PFAS uptake by lettuce decreased (by up to 90.5 %) with the increasing compost amendment ratios (0-20 %, w/w), consistent with their decreased porewater concentrations (by 30.7-86.3 %) in compost-amended soils. Decreased bioavailability of PFAS was evidenced by the increased in-situ soil-porewater distribution coefficients (Kd) (by factors of 1.5-7.0) with increasing compost additions. Significant negative (or positive) correlations (R2 ≥ 0.55) were observed between plant bioaccumulation (or Kd) and soil organic carbon content, suggesting that compost amendment inhibited plant uptake of PFAS mainly by increasing soil organic carbon and enhancing PFAS sorption. However, short-chain PFAS alternatives (e.g., perfluoro-2-methoxyacetic acid (PFMOAA)) were effectively translocated to shoots with translocation factors > 2.9, increasing their risks of contamination in leafy vegetables. Our findings underscore the necessity for comprehensive risk assessment of compost-borne PFAS when using commercial compost products in agricultural lands.

Application of a portable ion chromatograph for real-time field analysis of nitrite and nitrate in soils and soil pore waters.

Real-time monitoring of nitrite and nitrate is crucial for maintaining soil health and promoting plant growth. In this study, a portable ion-chromatograph (IC, Aquamonitrix) analyser, coupled with a field-applicable ultrasonic-assisted extraction method, was utilised for in-field determination of nitrate and nitrite in soils. This is the first application of this type of analyser to soil nutrients. On-site analysis of soil from a local sports field showed 94.8 ± 4.3 µg g-1 nitrate, with LODs of 32.0 µg g-1 for nitrate and 5.4 µg g-1 for nitrite. The results were in close agreement with those obtained using a conventional lab-based IC. Relative standard deviations (%RSDs) for soil analysis using Aquamonitrix were consistently below 10%. The obtained average recoveries of samples spiked with nitrite were 100% and 104% for the portable IC and conventional IC, respectively. Furthermore, to assess the suitability of portable IC for samples with high organic matter content, various natural organic fertilisers were extracted and analysed. The results showed 16.2 ± 0.7 µg g-1 nitrite and 28.5 ± 5.6 µg g-1 nitrate in sheep manure samples with LODs of 2.0 µg g-1 for nitrite and 12.0 µg g-1 for nitrate. The portable IC system was further demonstrated via real-time on-site analysis of soil pore-water acquired using a portable battery-based ceramic pore-water sampler. A continuous increase in nitrate concentration over time was observed (from 80 to 148 µg mL-1) in the soil pore-water in a vegetable garden four days after heavy rain. Unlike conventionally sampled natural waters, 7-day storage of the studied pore water samples revealed no changes in nitrate concentrations. An average of 558 ± 51 µg mL-1 nitrate was detected in the soil pore-water samples analysed on a spinach farm, immediately after irrigation.

A preliminary study on benthic nutrient exchange across sediment-water interfaces in a shallow marine protected area of the Northwestern Arabian Gulf.

Sedimentary processes are expected to play a crucial role in macronutrient cycling of the shallow Arabian Gulf. To investigate this aspect, sediment cores were collected from the shallow intertidal and subtidal expanses of the first Marine Protected Area (MPA) of Kuwait in the Northwestern Arabian Gulf (NAG). Porewater nutrient profiling and whole core incubation experiments were conducted to measure the nutrient fluxes, both with and without the addition of the nitrification inhibitor allylthiourea (ATU). The porewater data confirmed the potential of sediments to host multiple aerobic and anaerobic pathways of nutrient regeneration. The average (±SD) of net nutrient fluxes from several incubation experiments indicated that ammonium (NH4+) predominantly fluxed out of the sediment (3.81 ± 2.53 mmol m-2 d-1), followed by SiO44- (3.07 ± 1.21 mmol m-2 d-1). In contrast, the average PO43- flux was minimal, at only 0.06 ± 0.05 mmol m-2 d-1. Fluxes of NO3- (ranged from 0.07 ± 0.005 to 1.16 ± 0.35 mmol m-2 d-1) and NO2- (0.03 ± 0.003 to 0.71 ± 0.21 mmol m-2 d-1) were moderate, which either reduced or reversed in the presence of ATU (-0.001 ± 0.0001 to 0.01 ± 0.0001 mmol m-2 d-1 and -0.001 ± 0.0003 to 0.006 ± 0.001 mmol m-2 d-1 for NO3- and NO2- respectively). Thus, this study provides preliminary experimental evidence that nitrification can act as a source of NO3- and NO2- as well as contribute towards the relatively high concentrations of NO2- (>1 in the gulf waters.