Enhancing soil health and nutrient availability for Carrizo citrange (X Citroncirus sp.) through bokashi and biochar amendments: An exploration into indoor sustainable soil ecosystem management.

This study investigated the efficacy of organic soil amendments: bokashi (Bok), biochar (BC), and their combination (Bok_BC) in promoting soil health, nutrient availability, and growth of Carrizo citrange (X Citroncirus sp. Rutaceae, Parentage Citrus sinensis × Poncirus trifoliata) under indoor greenhouse settings. Results indicate significant alterations in soil parameters like total carbon (C), total nitrogen (N), and C:N ratio due to Bok, BC, and Bok_BC treatments. BC treatments boosted total C, while Bok increased total N, compared to controls. A note-worthy 25 % average decrease in C:N ratio was observed with Bok and Bok_BC, nearing the optimal 24:1 C:N for microbial growth. This highlights the potential of waste by-products in balancing nutrient release to benefit soil health and plant development. Analysis of nitrite (NO2-), nitrate (NO3-), and ammonium (NH4-N) levels revealed a dynamic relationship between soil treatments and time. Bok and Bok_BC amendments combined with both fertilizer doses [700 and 1400 Electrical Conductivity, EC] showed an initial NH4-N spike (averaging 1513 and 1288 µg N/g dry, respectively), outperforming control soils (average 503 µg N/g dry). Other key elements like phosphorus, potassium, calcium, and chlorine also experienced initial surges in Bok and Bok_BC soils before declining, suggesting a gradual nutrient release. The concentration of potentially toxic elements remained mostly stable or inconclusive, warranting further exploration. Bok, BC, and Bok_BC treatments considerably influenced germination rate and plant growth. The germination rate averaged 24.2 %, 23 %, and 22.5 % for Bok, BC, and Bok_BC, compared to the 15.9 % control. Plant height increased with Bok, BC, and Bok_BC to 18.4 cm, 18.7 cm, and 16.4 cm, respectively, from the 14.8 cm control. The results remained consistent across fertilizer doses, emphasizing the soil amendments' role in bolstering soil and plant health. In summary, the research underscores the potential of carbon-based amendments like bokashi and biochar in enhancing soil health, reducing reliance on synthetic fertilizers, and fostering sustainable soil ecosystems. The insights are pivotal for advancing sustainable agriculture in indoor greenhouse settings for nursery plant production.

Depth-dependent responses of soil organic carbon under nitrogen deposition.

Emerging evidence points out that the responses of soil organic carbon (SOC) to nitrogen (N) addition differ along the soil profile, highlighting the importance of synthesizing results from different soil layers. Here, using a global meta-analysis, we found that N addition significantly enhanced topsoil (0-30 cm) SOC by 3.7% (±1.4%) in forests and grasslands. In contrast, SOC in the subsoil (30-100 cm) initially increased with N addition but decreased over time. The model selection analysis revealed that experimental duration and vegetation type are among the most important predictors across a wide range of climatic, environmental, and edaphic variables. The contrasting responses of SOC to N addition indicate the importance of considering deep soil layers, particularly for long-term continuous N deposition. Finally, the lack of depth-dependent SOC responses to N addition in experimental and modeling frameworks has likely resulted in the overestimation of changes in SOC storage under enhanced N deposition.

Draft genome sequence of a black yeast fungus Exophiala xenobiotica isolated from La Brea Tar Pits.

A 30.28 Mb draft genome sequence was assembled and annotated for the melanized ascomycetous fungus Exophiala xenobiotica NRRL_64630 (Pezizomycotina; Chaetothyriales) isolated from La Brea Tar Pits, Los Angeles, California. Species identification was made by phylogenetic assessment of the Internal Transcribed Spacer. This is the first isolated fungal species from this historic space.

Small Community Water Systems Have the Highest Prevalence of Mn in Drinking Water in California, USA.

Manganese (Mn) is currently regulated as a secondary contaminant in California, USA; however, recent revisions of the World Health Organization drinking water guidelines have increased regulatory attention of Mn in drinking water due to increasing reports of neurotoxic effects in infants and children. In this study, Mn concentrations reported to California's Safe Drinking Water Information System were used to estimate the potentially exposed population within California based on system size. We estimate that between 2011 and 2021, over 525,000 users in areas with reported Mn data are potentially exposed to Mn concentrations exceeding the WHO health-based guideline (80 µg L-1), and over 34,000 users are potentially exposed to Mn concentrations exceeding the U.S. Environmental Protection Agency health-advisory limit (300 µg L-1). Water treatment significantly decreased Mn concentrations compared to intake concentrations for all system sizes. However, smaller water systems have a wider range and a higher skew of Mn concentrations in finished water than larger systems. Additionally, higher Mn concentrations were found in systems above the maximum contaminant levels for chromium and arsenic. The treatment of these primary contaminants appears to also remove Mn. Lastly, data missingness remains a barrier to accurately assess public exposure to Mn in very small, small, and medium community water system-delivered water.

Disparities in Drinking Water Manganese Concentrations in Domestic Wells and Community Water Systems in the Central Valley, CA, USA.

Over 1.3 million Californians rely on unmonitored domestic wells. Existing probability estimates of groundwater Mn concentrations, population estimates, and sociodemographic data were integrated with spatial data delineating domestic well communities (DWCs) to predict the probability of high Mn concentrations in extracted groundwater within DWCs in California's Central Valley. Additional Mn concentration data of water delivered by community water systems (CWSs) were used to estimate Mn in public water supply. We estimate that 0.4% of the DWC population (2342 users) rely on groundwater with predicted Mn > 300 µg L-1. In CWSs, 2.4% of the population (904 users) served by small CWSs and 0.4% of the population (3072 users) served by medium CWS relied on drinking water with mean point-of-entry Mn concentration >300 µg L-1. Small CWSs were less likely to report Mn concentrations relative to large CWSs, yet a higher percentage of small CWSs exceed regulatory standards relative to larger systems. Modeled calculations do not reveal differences in estimated Mn concentration between groundwater from current regional domestic well depth and 33 m deeper. These analyses demonstrate the need for additional well-monitoring programs that evaluate Mn and increased access to point-of-use treatment for domestic well users disproportionately burdened by associated costs of water treatment.

Vanadate Retention by Iron and Manganese Oxides.

Anthropogenic emissions of vanadium (V) into terrestrial and aquatic surface systems now match those of geogenic processes, and yet, the geochemistry of vanadium is poorly described in comparison to other comparable contaminants like arsenic. In oxic systems, V is present as an oxyanion with a +5 formal charge on the V center, typically described as H x VO4 (3-x)-, but also here as V(V). Iron (Fe) and manganese (Mn) (oxy)hydroxides represent key mineral phases in the cycling of V(V) at the solid-solution interface, and yet, fundamental descriptions of these surface-processes are not available. Here, we utilize extended X-ray absorption fine structure (EXAFS) and thermodynamic calculations to compare the surface complexation of V(V) by the common Fe and Mn mineral phases ferrihydrite, hematite, goethite, birnessite, and pyrolusite at pH 7. Inner-sphere V(V) complexes were detected on all phases, with mononuclear V(V) species dominating the adsorbed species distribution. Our results demonstrate that V(V) adsorption is exergonic for a variety of surfaces with differing amounts of terminal -OH groups and metal-O bond saturations, implicating the conjunctive role of varied mineral surfaces in controlling the mobility and fate of V(V) in terrestrial and aquatic systems.

Oxidation of V(IV) by Birnessite: Kinetics and Surface Complexation.

Vanadium is a redox-active metal that has been added to the EPA's Contaminant Candidate List with a notification level of 50 µg L-1 due to mounting evidence that VV exposure can lead to adverse health outcomes. Groundwater V concentration exceeds the notification level in many locations, yet geochemical controls on its mobility are poorly understood. Here, we examined the redox interaction between VIV and birnessite (MnO2), a well-characterized oxidant and a scavenger of many trace metals. In our findings, birnessite quickly oxidized sparingly soluble VIV species such as häggite [V2O3(OH)2] into highly mobile and toxic vanadate (HnVO4(3-n)-) in continuously stirred batch reactors under neutral pH conditions. Synchrotron X-ray absorption spectroscopic (XAS) analysis of in situ and ex situ experiments showed that oxidation of VIV occurs in two stages, which are both rapid relative to the measured dissolution rate of the VIV solid. Concomitantly, the reduction of birnessite during VIV oxidation generated soluble MnII, which led to the formation of the MnIII oxyhydroxide feitknechtite (ß-MnOOH) upon back-reaction with birnessite. XAS analysis confirmed a bidentate-mononuclear edge-sharing complex formed between VV and birnessite, although retention of VV was minimal relative to the aqueous quantities generated. In summary, we demonstrate that Mn oxides are effective oxidants of VIV in the environment with the potential to increase dissolved V concentrations in aquifers subject to redox oscillations.

Effects of residual disinfectants on the redox speciation of lead(ii)/(iv) minerals in drinking water distribution systems.

This study investigated the reaction kinetics on the oxidative transformation of lead(ii) minerals by free chlorine (HOCl) and free bromine (HOBr) in drinking water distribution systems. According to chemical equilibrium predictions, lead(ii) carbonate minerals, cerussite PbCO3(s) and hydrocerussite Pb3(CO3)2(OH)2(s), and lead(ii) phosphate mineral, chloropyromorphite Pb5(PO4)3Cl(s) are formed in drinking water distribution systems in the absence and presence of phosphate, respectively. X-ray absorption near edge spectroscopy (XANES) data showed that at pH 7 and a 10 mM alkalinity, the majority of cerussite and hydrocerussite was oxidized to lead(iv) mineral PbO2(s) within 120 minutes of reaction with chlorine (3 : 1 Cl2 : Pb(ii) molar ratio). In contrast, very little oxidation of chloropyromorphite occurred. Under similar conditions, oxidation of lead(ii) carbonate and phosphate minerals by HOBr exhibited a reaction kinetics that was orders of magnitude faster than by HOCl. Their end oxidation products were identified as mainly plattnerite ß-PbO2(s) and trace amounts of scrutinyite α-PbO2(s) based on X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopic analysis. A kinetic model was established based on the solid-phase experimental data. The model predicted that in real drinking water distribution systems, it takes 0.6-1.2 years to completely oxidize Pb(ii) minerals in the surface layer of corrosion scales to PbO2(s) by HOCl without phosphate, but only 0.1-0.2 years in the presence of bromide (Br-) due the catalytic effects of HOBr generation. The model also predicts that the addition of phosphate will significantly inhibit Pb(ii) mineral oxidation by HOCl, but only be modestly effective in the presence of Br-. This study provides insightful understanding on the effect of residual disinfectant on the oxidation of lead corrosion scales and strategies to prevent lead release from drinking water distribution systems.

Firing Increases Arsenic Leaching from Ceramic Water Filters via Arsenic and Iron Phase Transformations.

Ceramic water filters (CWFs) are produced globally using local clay sources and can effectively remove bacterial pathogens during point-of-use water treatment. The ceramic production process involves firing clay mixed with burnout material at temperatures of 800-1100 °C, which induces mineralogical changes leading to increased arsenic (As) leaching from CWF material compared to source clay. Unfired clay and fired CWFs from Cambodia, Canada, and Mexico, CWF from Laos, and test-fired clay from the United States were analyzed to determine the extent of As leaching from CWFs that range in As (<1 to 16 mg kg-1) and iron (Fe) (0.6 to 5%) content. Deionized water, NaOH, HCl, and oxalate extractions showed that firing increased As solubility and decreased Fe solubility compared to unfired clay, with up to 8 mg kg-1 of water-soluble As in Cambodian CWFs. X-ray absorption spectra of the Cambodian clay and CWF showed a decrease in the Fe-O distance from 2.01 to 1.91 Å and decreased Fe coordination number from 6.3 to 4.6 after firing, indicating a decrease in Fe-O coordination. Arsenic(V) was the dominant species in Cambodia clay and CWF, existing primarily as a surface complex with average As-Fe distance of 3.28 Å in clay while in CWF As was either an outer-sphere As(V) phase or a discrete arsenate phase with no significant As-Fe scattering contribution within the resolution of the data. Improved understanding of molecular-scale processes that cause increased As leaching from CWFs provides a basis for assessing As leaching potential prior to CWF factory capital investment as well as engineered solutions (e.g., modified firing temperature, material amendments, and leaching prior to distribution) to mitigate As exposure from CWFs.

Role of Fe dynamic in release of metals at Rio Doce estuary: Unfolding of a mining disaster.

The role of Fe oxyhydroxides dynamic on metal bioavailability was studied in the Rio Doce estuary after the largest mining disaster in the world. Soon after the disaster in 2015, metals were associated with Fe oxyhydroxides under a redox-active estuarine environment. Our results indicate that organic matter inputs from plant colonization on deposited tailings over estuarine soils led to a reductive dissolution of Fe oxyhydroxides within two years. Soil pseudo-total Fe content decreased by 70% between 2015 and 2017, while the total metal contents (Cr, Cu, Ni, Pb, and Zn) decreased by 79% in the soil. The losses of Fe and metals coupled to changes in Fe oxides crystallinity reveal a future ephemeral control of Fe oxyhydroxides over metal immobilization. Our results suggest a potential chronic contamination at the estuary and points to an aggravating scenario for the following years due to the increasing dominance of poorly crystalline Fe oxyhydroxides.

Retention of thallium by natural minerals: A review.

Though thallium (Tl) is usually present in trace amounts in natural environments, its biotoxicity is extremely high. With the development of mining, the metallurgy industry, and the growing application of Tl in high-tech fields, the threat of Tl to ecological environments and human health is increasing. Natural minerals, such as clay minerals, iron oxides, and manganese oxides, are natural Tl adsorbents due to their mineralogy and crystal structures. In this review, we discuss the mechanisms of Tl adsorption by various natural minerals, compare the adsorption capacities of common soil minerals for Tl, and describe the limitations of traditional sequential extraction methods for identifying the chemical states of Tl on minerals and source of Tl. We also provide suggestions on future directions needed in Tl research including a) additional in-depth studies on the competitive adsorption of Tl by minerals; b) more direct comparison of Tl adsorption behavior from lab-based experiments with field observations to clarify the mechanisms of Tl adsorption by minerals under environmental conditions; c) more research data are needed to support the establishment and improvement of relevant research methods based on modern leading-edge technologies such as synchrotron radiation. Further, we suggest further research is needed in adsorption technologies used for Tl treatment. This is the first review on the research progress of Tl adsorption by natural minerals with the purpose of helping understanding the mechanisms of Tl migration and transformation controlled by natural minerals, and providing theoretical supports for the development of Tl adsorbents and the treatments of Tl pollution.

Mobilization of Arsenic and Other Naturally Occurring Contaminants during Managed Aquifer Recharge: A Critical Review.

Population growth and climate variability highlight the need to enhance freshwater security and diversify water supplies. Subsurface storage of water in depleted aquifers is increasingly used globally to alleviate disparities in water supply and demand often caused by climate extremes including floods and droughts. Managed aquifer recharge (MAR) stores excess water supplies during wet periods via infiltration into shallow underlying aquifers or direct injection into deep aquifers for recovery during dry seasons. Additionally, MAR can be designed to improve recharge water quality, particularly in the case of soil aquifer treatment and riverbank filtration. While there are many potential benefits to MAR, introduction of recharge water can alter the native geochemical and hydrological conditions in the receiving aquifer, potentially mobilizing toxic, naturally occurring (geogenic) contaminants from sediments into groundwater where they pose a much larger threat to human and ecosystem health. On the basis of the present literature, arsenic poses the most widespread challenge at MAR sites due to its ubiquity in subsurface sediments and toxicity at trace concentrations. Other geogenic contaminants of concern include fluoride, molybdenum, manganese, and iron. Water quality degradation threatens the viability of some MAR projects with several sites abandoning operations due to arsenic or other contaminant mobilization. Here, we provide a critical review of studies that have uncovered the geochemical and hydrological mechanisms controlling mobilization of arsenic and other geogenic contaminants at MAR sites worldwide, including both infiltration and injection sites. These mechanisms were evaluated based on site-specific characteristics, including hydrological setting, native aquifer geochemistry, and operational site parameters (e.g., source of recharge water and recharge/recovery cycling). Observed mechanisms of geogenic contaminant mobilization during MAR via injection include shifting redox conditions and, to a lesser extent, pH-promoted desorption, mineral solubility, and competitive ligand exchange. The relative importance of these mechanisms depends on various site-specific, operational parameters, including pretreatment of injection water and duration of injection, storage, and recovery phases. This critical review synthesizes findings across case studies in various geochemical, hydrological, and operational settings to better understand controls on arsenic and other geogenic contaminant mobilization and inform the planning and design of future MAR projects to protect groundwater quality. This critical review concludes with an evaluation of proposed management strategies for geogenic contaminants and identification of knowledge gaps regarding fate and transport of geogenic contaminants during MAR.

Manganese: The overlooked contaminant in the world largest mine tailings dam collapse.

Manganese (Mn) is an abundant element in terrestrial and coastal ecosystems and an essential micronutrient in the metabolic processes of plants and animals. Mn is generally not considered a potentially toxic element due to its low content in both soil and water. However, in coastal ecosystems, the Mn dynamic (commonly associated with the Fe cycle) is mostly controlled by redox processes. Here, we assessed the potential contamination of the Rio Doce estuary (SE Brazil) by Mn after the world's largest mine tailings dam collapse, potentially resulting in chronic exposure to local wildlife and humans. Estuarine soils, water, and fish were collected and analyzed seven days after the arrival of the tailings in 2015 and again two years after the dam collapse in 2017. Using a suite of solid-phase analyses including X-ray absorption spectroscopy and sequential extractions, our results indicated that a large quantity of MnII arrived in the estuary in 2015 bound to Fe oxyhydroxides. Over time, dissolved Mn and Fe were released from soils when FeIII oxyhydroxides underwent reductive dissolution. Due to seasonal redox oscillations, both Fe and Mn were then re-oxidized to FeIII, MnIII, and MnIV and re-precipitated as poorly crystalline Fe oxyhydroxides and poorly crystalline Mn oxides. In 2017, redox conditions (Eh: -47 ± 83 mV; pH: 6.7 ± 0.5) favorable to both Fe and Mn reduction led to an increase (~880%) of dissolved Mn (average for 2015: 66 ± 130 µg L-1; 2017: 582 ± 626 µg L-1) in water and a decrease (~75%, 2015: 547 ± 498 mg kg-1; 2017: 135 ± 80 mg kg-1) in the total Mn content in soils. The crystalline Fe oxyhydroxides content significantly decreased while the fraction of poorly ordered Fe oxides increased in the soils limiting the role of Fe in Mn retention. The high concentration of dissolved Mn found within the estuary two years after the arrival of mine tailings indicates a possible chronic contamination scenario, which is supported by the high levels of Mn in two species of fish living in the estuary. Our work suggests a high risk to estuarine biota and human health due to the rapid Fe and Mn biogeochemical dynamic within the impacted estuary.

Enzymes, Manganese, or Iron? Drivers of Oxidative Organic Matter Decomposition in Soils.

Oxidative decomposition of soil organic matter determines the proportion of carbon that is either stored or emitted to the atmosphere as CO2. Full conversion of organic matter to CO2 requires oxidative mechanisms that depolymerize complex molecules into smaller, soluble monomers that can be respired by microbes. Current models attribute oxidative depolymerization largely to the activity of extracellular enzymes. Here we show that reactive manganese (Mn) and iron (Fe) intermediates, rather than other measured soil characteristics, best predict oxidative activity in temperate forest soils. Combining bioassays, spectroscopy, and wet-chemical analysis, we found that oxidative activity in surface litters was most significantly correlated to the abundance of reactive Mn(III) species. In contrast, oxidative activity in underlying mineral soils was most significantly correlated to the abundance of reactive Fe(II/III) species. Positive controls showed that both Mn(III) and Fe(II/III) species are equally potent in generating oxidative activity, but imply conventional bioassays have a systematic bias toward Fe. Combined, our results highlight the coupled biotic-abiotic nature of oxidative mechanisms, with Mn-mediated oxidation dominating within Mn-rich organic soils and Fe-mediated oxidation dominating Fe-rich mineral soils. These findings suggest microbes rely on different oxidative strategies depending on the relative availability of Fe and Mn in a given soil environment.

Manganese, Arsenic, and Carbonate Interactions in Model Oxic Groundwater Systems.

Manganese and arsenic both threaten groundwater quality globally, but their chemical behavior leads to both co-contamination and separation of these contaminants from individual well to regional scales. Here we tested manganese and arsenic retention under conditions commonly found within aquifer redox fluctuating and transition zones where both arsenic and iron phases are present in oxidized forms, but manganese persists as reduced and soluble Mn(II). Analysis of column aqueous breakthrough data and characterization of solid-phase products using X-ray photoelectron (XPS) and absorption spectroscopies (XAS) show that the addition of bicarbonate increased manganese retention but decreased arsenic retention, while the presence of manganese and arsenic together increased both arsenic and manganese retention. In the presence of O2 arsenic remained oxidized as arsenate under all conditions measured; however, reduced Mn(II) was oxidized to an average Mn oxidation state of ∼3 in the absence of arsenate. The presence of arsenate partially inhibited Mn(II) oxidation likely by blocking ferrihydrite surfaces needed to catalyze Mn(II) oxidation by O2 and by stabilizing Mn(II) via ternary complex formation. These results highlight the interactions between reduced and oxidized contaminants that can contribute to the co-occurrence or physical separation of manganese and arsenic in groundwater systems under changing or stratified redox conditions.

Long-term nitrogen loading alleviates phosphorus limitation in terrestrial ecosystems.

Increased human-derived nitrogen (N) deposition to terrestrial ecosystems has resulted in widespread phosphorus (P) limitation of net primary productivity. However, it remains unclear if and how N-induced P limitation varies over time. Soil extracellular phosphatases catalyze the hydrolysis of P from soil organic matter, an important adaptive mechanism for ecosystems to cope with N-induced P limitation. Here we show, using a meta-analysis of 140 studies and 668 observations worldwide, that N stimulation of soil phosphatase activity diminishes over time. Whereas short-term N loading (≤5 years) significantly increased soil phosphatase activity by 28%, long-term N loading had no significant effect. Nitrogen loading did not affect soil available P and total P content in either short- or long-term studies. Together, these results suggest that N-induced P limitation in ecosystems is alleviated in the long-term through the initial stimulation of soil phosphatase activity, thereby securing P supply to support plant growth. Our results suggest that increases in terrestrial carbon uptake due to ongoing anthropogenic N loading may be greater than previously thought.

Assessment of reactive oxygen species production and genotoxicity of rare earth mining dust: Implications for public health and mining management.

Mining rare earth elements (REEs) can release large amounts of metal(loid)-rich dust, which can pose significant health risks to local residents. However, compared to other types of particulates, toxicity of mining dust has been largely overlooked. To provide experimental evidence on toxicity of REE mine dust, the study assessed the oxidative stress potential and genotoxicity of inhalable particles collected in a REE mining area, and associated toxicological response with source compositions. Both source types (i.e., mine and tailing area) and distances from source (i.e., industrial and residential areas) were considered when selecting the 44 sampling sites. The particle samples contained 2.3-3.5 folds higher concentrations of tested metal(loid)s than background concentrations in soil. Specially, elevated Fe, REEs, Cd, Pb were found. In spite of low cytotoxicity in lung epithelial A549 cells, there was increased cellular ROS production by of particle exposure. Samples with higher mining-originated source contributions (Provenance Index <0.3) had higher cellular ROS production (1.72 fold, 95%CI: 1.66-1.79 fold) than samples with lower mining contributions (1.58 fold, 95%CI: 1.52-1.65 fold). The factors soil (~46%), mine (~22%), and heavy metal (~20%) sources were recognized by source apportionment analysis as the main contributors to cellular ROS production; importantly, mine and heavy metal sources counted more in industrial samples. While samples generated genotoxicity, there were no differences in DNA damage between the location groups of sampling. Collectively, the results indicate that particles in mining areas may cause ROS production and DNA damage in lung cells depending on mine dust. Coupled with the long-range transportation potential of mine dust, safety measures on open pit and dust disposal sites should be adopted.

Dust Sources in the Salton Sea Basin: A Clear Case of an Anthropogenically Impacted Dust Budget.

The Salton Sea Basin in California suffers from poor air quality, and an expanding dry lakebed (playa) presents a new potential dust source. In 2017-18, depositing dust was collected approximately monthly at five sites in the Salton Sea Basin and analyzed for total elemental and soluble anion content. These data were analyzed with Positive Matrix Factorization (PMF). The PMF method resolved seven dust sources with distinct compositional markers: Playa (Mg, SO42-, Na, Ca, Sr), Colorado Alluvium (U, Ca), Local Alluvium (Al, Fe, Ti), Agricultural Burning (K, PO43-), Sea Spray (Na, Cl-, Se), Anthropogenic Trace Metals (Sb, As, Zn, Cd, Pb, Na), and Anthropogenic Copper (Cu). All sources except Local Alluvium are influenced or caused by current or historic anthropogenic activities. PMF attributed 55 to 80% of the measured dust flux to these six sources. The dust fluxes at the site where the playa source was dominant (89 g m-2 yr-1) were less than, but approaching the scale of, those observed at Owens Lake playas in the late 20th century. Playa emissions in the Salton Sea region were most intense during the late spring to early summer and contain high concentrations of evaporite mineral tracers, particularly Mg, Ca, and SO42-.

Distribution, pollution status, and source apportionment of trace metals in lake sediments under the influence of the South-to-North Water Transfer Project, China.

In an effort to combat the threat of drought, China constructed the South-to-North Water Transfer Project (SNWTP), the biggest water transfer project in terms of volume with the largest beneficiary population in the world. Reports have shown that massive water diversion projects have had detrimental environmental consequences including water quality decline and freshwater habitat degradation. However, few reports have assessed the impact of the transfer project on sediment quality, which is highly susceptible to allogenic and local anthropogenic pollution. We examined the distribution characteristics of Cd, Cr, Cu, Ni, Pb and Zn in surface sediment of the largest reservoir along the East Route of SNWTP, Nansihu Lake, followed by positive matrix factorization (PMF) to determine their potential sources. We utilized enrichment factor, multiple sediment quality guidelines (SQGs), and potential ecological risk index (RI) to determine metal accumulation or pollution risk. The results show the mean concentrations of Cr, Cu, Pb, Zn were slightly lower than in samples collected in 2003, 2010 and 2012, while the mean concentrations of Cr and Ni were significantly higher than samples from previous years. Among the six metals, Cr, Cu and Ni are of higher ecological risk according to SQGs; but Cd is of higher ecological risk according to RI. PMF analysis shows that industrial production and shipping are important sources of Cr, Cu, and Ni. PMF analysis also shows that a considerable amount of trace metals, especially Cd, Cr, Pb and Zn, mainly comes from the use of pesticide fertilizers and biomass sources in farmland, and may partly enter Nansihu Lake from SNWTP. This study reveals the possible sources of trace metals to the Nansihu Lake which is part of SNWTP; the results of the study may serve as a reference for better understanding the impact of future water diversion projects on metals distribution.