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With the advancements in lithium-ion battery technology, lithium has been extensively used in many electronic products. Lithium usage is expected to increase in the coming decades. Elevated levels of lithium in the environments, including source water and biota, have been recently reported. Lithium can cause soil dispersion and aggerate swelling and can be readily taken up by plants and filter-feeders, potentially causing toxicity to plants, organisms, and human. As learnt from the reactive approach of the Clean Water Act, many emerging pollutants have not been recognized until they have been widespread and reached dangerous levels in the environments. Aftermath cleanup costs are huge, and many of these damages are irreversible. To avoid lithium being the next global contaminant of emerging concern, environmental agencies shall implement proactive regulation and education soon.

High-intensity wildfires alter the chemical composition of organic matter, which is expected to be distinctly different from low-intensity prescribed fires. Herein, we used pyrolysis gas chromatography/mass spectrometry (Py-GC/MS), in conjunction with solid-state 13C nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectroscopy, to assess chemical alterations from three wildfires and a long-term frequent prescribed fire site. Our results showed that black ash formed under moderate intensity burns contained less aromatic (ArH), polyaromatic hydrocarbon (PAH), and nitrogen-containing compounds (Ntg) but more lignin (LgC) and phenol compounds (PhC), compared to white ash formed under high intensity burns. Both 13C NMR and FT-IR confirmed a higher relative percentage of carboxyl carbon in white ash, indicating the potential for higher water solubility and more mobile carbon, relative to black ash. Compared to wildfires, ash from low-intensity prescribed fire contained less ArH, PAH, and Ntg and more LgC and PhC. Controlled laboratory burning trials indicated that organic matter alteration was sensitive to the burn temperature, but not related to the fuel type (pine vs fir) nor oxygen absence/presence at high burn temperatures. This study concludes that higher burn temperatures resulted in higher (poly)aromatic carbon/nitrogen and lower lignin/phenol compounds.

Wetlands are widely regarded as biogeochemical hotspots of highly toxic methylmercury (MeHg), mainly mediated by sulfate-reducing bacteria. In low-lying coastal wetlands, sea level rise, a phenomenon caused by global climate change, is slowly degrading numerous healthy freshwater forested wetlands into salt-degraded counterparts with a nickname "ghost forests", and eventually converting them to saltmarshes. However, little is known about the changes of mercury (Hg) methylation, bioaccumulation, and biomagnification along the forest-to-saltmarsh gradient. Here, we conducted extensive field sampling in three wetland states (healthy forested wetlands, salt-degraded forested wetlands, and saltmarsh) along a salinity gradient (from 0 to 9.4 ppt) in Winyah Bay, South Carolina, USA. We found that in our study wetland systems the saltmarshes had the lowest levels of both total Hg and MeHg in sediments and biota, as compared to healthy forested wetlands and saltwater-degraded ghost forests. Our results suggest that the slow conversion of forested wetland to saltmarsh could reduce net MeHg production in our study wetland systems, which we hypothesized that could be attributed to increased sulfate reduction and excessive buildup of sulfide in sediment that inhibits microbial Hg methylation, and/or reduced canopy density and increased photodegradation of MeHg. However, it should be noted that biogeochemical MeHg responses to salinity changes may be site-specific and we urge more similar studies in other wetland systems along a salinity gradient. Therefore, long-term salinization of coastal wetlands and the slow conversion of forests to marshes could decrease long-term exposure of toxic MeHg levels in coastal food webs that are similar to our system, and ultimately reduce human exposure to this neurotoxin.

While impervious surface expands with global urbanization, understanding the quality and quantity changes of soil organic carbon (SOC) under impervious surfaces is essential to assess the impacts o...

Decomposing foliar litter organic matter (LOM) in forested watersheds is an essential terrestrial source of dissolved organic matter (DOM) to aquatic ecosystems. To evaluate the relationship of chemical composition between LOM and DOM, we collected freshly fallen leaves of white oak (Quercus alba) and conducted an 80-week field decomposition experiment along a small elevation gradient in a floodplain within the Congaree National Park, South Carolina. Foliar litters were collected for water extraction and instrumental analyses using pyrolysis GC/MS, UV/VIS and fluorescence spectrophotometry. Factor analyses of pyrolysates showed that fresh LOM was mainly composed of lignin compounds (LgC), phenolic compounds (PhC), and carbohydrate (Carb), and the change in composition was relatively small throughout the decomposition process. In contrast, there were two distinct chemical compositions of DOM in early (between 0–8 weeks) and late phases (between 16–80 weeks). The early phase had a higher percentage of PhC, but the late phase contained higher percentages of Carb, unsaturated hydrocarbon (UnSaH), aromatic hydrocarbon (ArH), and nitrogen-containing compounds (Ntg). The fluorescence emission-excitation matrix showed there was an increasing trend in humic and fulvic-like fractions in DOM over time, matching well with increases of UnSaH and ArH fractions from the results of pyrolysis GC/MS. Our study illustrated that the changes of chemical components in LOM and water extractable DOM were not parallel during the decomposition process and the degradation of lignin and phenolic compounds was one of the controlling factors on the production of DOM.

The byproducts of anaerobic biogeochemical processes, many mediated at the sediment–water interface, can degrade water quality in the bottom of reservoirs. Using both experimental sediment–water chambers and field monitoring, this study assessed nutrient and metals cycling in the profundal zone of hypereutrophic Hodges Reservoir, San Diego (maximum depth = 29.1 m; maximum surface area = 6.0 km2). A focus of the study was methylmercury (MeHg), a toxic form of mercury that bioaccumulates in aquatic food webs. Results confirmed that oxic conditions repressed release of redox-sensitive compounds (e.g., MeHg, ammonia, phosphate, manganese) from profundal sediment, though high sediment oxygen demand complicated experimental efforts to maintain a well-oxygenated sediment–water interface. In both experimental chambers and in the reservoir, patterns of MeHg cycling correlated with manganese cycling, suggesting that moderately low redox conditions that stimulate reductive dissolution of manganese also enhance net Hg methylation. Sediment MeHg flux was tightly coupled with sulfate uptake under moderately reduced conditions, reinforcing the link between sulfate-reducing bacteria and Hg methylation. Results highlight the fact that hypolimnetic oxygenation in Hodges Reservoir using pure oxygen gas, which is planned for spring 2020, must maintain high oxygen concentrations at the profundal sediment–water interface. In addition, results indicate that the presence of manganese in surface water can be used as an indicator of oxygenation’s effectiveness in lowering rates of internal nutrient and MeHg loading.

Releases of hydrogen sulphide (H

Climate change is driving an increase in catastrophic wildfires; consumers see, smell, and taste the effects in their water. Water utilities must prepare for worse times ahead.

Considerable recent research has confirmed that anthropogenic materials including microplastics and nanomaterials have been integrated into soil and dissolved organic matter in the environment. These pools of organic matter could be geochemically processed through different pathways and have different chemical and physical characteristics than the pools of natural organic matter (NOM). However, environmental scientists and engineers currently refer to any organic matter collected in soil, water, and sediments as NOM. Since "real" NOM pools are rapidly dissipated due to losses in natural landscapes, the shift from NOM to human influenced-organic matter (Hi-OM) pools could have huge ecological impacts on the environment. Future environmental quality research should highlight the differences between Hi-OM from NOM.

Severe wildfires often have dramatic short-term effects on water quality, although there is increasing evidence that in some catchments their effects can persist for many years. Forest recovery after the 2002 Hayman Fire burned catchments that supply drinking water to over a half million users in Denver, CO, has been extremely slow and has caused persistent water quality concerns. To evaluate whether postfire water quality changes increase the potential to form undesirable by-products of water disinfection, we compared stream water from eight burned catchments within the Hayman Fire and five adjacent unburned catchments. We tested dissolved organic carbon (DOC) concentrations and the formation of disinfection byproducts (trihalomethanes [THMs], haloacetonitriles [HANs], chloral hydrate [CHD, and haloketones [HKTs]) in stream water monthly during 2014 and 2015. Stream DOC, THMs, and CHD and specific ultraviolet absorbance at 254 nm (SUVA254) were elevated in catchments with a moderate extent of high-severity wildfire (8-46% of catchment area) relative to catchments that were unburned and those that burned more extensively (>74% of catchment area) 14 yr after the fire. In contrast, formation of highly toxic but unregulated nitrogenous HANs increased linearly with wildfire extent. Although these findings should not raise concern regarding drinking water safety, they highlight the long-term influences of high severity wildfire on source water C content, composition, and treatability.

More than half of the drinking water supply in the United States originates from forest watersheds, where terrestrial dissolved organic matter (DOM) is known as an important disinfection byproduct (DBP) precursor. Throughfall-derived DOM, a significant portion of terrestrial DOM, has seldom been evaluated for its formation potential of DBPs. Here, we collected throughfall and leaf extracts of an evergreen (loblolly pine, Pinus taeda L.) and a deciduous tree species (turkey oak, Quercus cerris L.) in South Carolina to explore their seasonal DOM quantity, optical properties, and DBP formation potential. Elevated dissolved organic carbon (DOC) from rainwater (1.2 ± 0.4 mg/L) to pine (26.0 ± 19.7 mg/L) and oak throughfall (38.8 ± 37.8 mg/L) indicated canopy can be a significant DOM source. DOM aromaticity (indicated by specific ultraviolet absorbance at 254 nm) was higher in oak than pine throughfall and higher in throughfall than leaf extracts. The throughfall DOM characteristics were seasonally more stable ...

Subaqueous wetland sediments (SWSs) and banana peels (BPs), respectively used as anaerobic inoculums and raw materials, were valorized for electricity generation in membrane-less and biocathode-containing microbial fuel cells (MLBC-MFCs). The maximum current density was 78.2 mA/m2 for banana peel extracts (BPE) and 91.3 mA/m2 for anaerobically fermented banana peel extracts (ABPE). The polarization data indicated that Ohmic resistances were high that were 3.5, 4.2 and 9.3 kΩ when MLBC-MFCs were fed with ABPE, BPE and sodium acetate (SA), respectively. The ultraviolet-visible absorption spectroscopy coupled with three-dimensional fluorescence spectroscopy was used to explore the mechanisms of generating electricity. Results showed that SWSs provided functional microorganisms and a source of organic matter, while BPs were more helpful for the growth of microorganisms than SA and the microorganisms attached on the cathode primarily functioned as biocatalysts. Overall, this study highlights the simplicity and scalability of MLBC-MFCs equipped with SWSs and BPs.

Wildfires are expected to become more frequent and intensive at the global scale due to climate change. Many studies have focused on the loss of mercury (Hg) from burned forests; however, little is known about the origins, concentration, reactivity, and bioavailability of Hg in residual ash materials in postfire landscapes. We examine Hg levels and reactivity in black ash (BA, low burn intensity) and white ash (WA, high burn intensity) generated from two recent northern California wildfires and document that all ash samples contained measurable, but highly variable, Hg levels ranging from 4 to 125 ng/g dry wt. ( n = 28). Stable Hg isotopic compositions measured in select ash samples suggest that most Hg in wildfire ash is derived from vegetation. Ash samples had a highly variable fraction of Hg in recalcitrant forms (0-75%25), and this recalcitrant Hg pool appears to be associated with the black carbon fraction in ash. Both BA and WA were found to strongly sequester aqueous inorganic Hg but not gaseous elemental Hg under controlled conditions. During anoxic ash incubation with natural surface water, we find that Hg in most ash samples had a minimal release and low methylation potential. Thus, the formation of wildfire ash can sequester Hg into relatively nonbioavailable forms, attenuating the potentially adverse effects of Hg erosion and transport to aquatic environments along with eroded wildfire ash.

Microplastics (MPs) are widespread in natural ecosystems and have attracted considerable attention from scientists all over the world because they are believed to threaten every life form. In addition to their potential physical and chemical effects on organisms, MPs may act as a carrier for transferring many micropollutants including antibiotics, heavy metals and others. Over the last 10-15 years, extensive research has been carried out on MPs in marine environment, its sources, fate and toxicity. However, studies concerning their accumulation in soil ecosystem, uptake, internalization and impacts on photosynthetic components of the terrestrial ecosystem, and risk assessment have been scanty. Thus, there is a large knowledge gap on the extent to which terrestrial environments, especially agroecosystems are affected by MPs, and their subsequent risks to human health. This review summarizes up-to-date findings about MPs on terrestrial environments and would provide some guidelines for future studies regarding the phytotoxic effects of MPs on plants, mechanism of uptake and translocation in plant tissues, detection tools for MPs in plants, impacts on plant growth, development and agricultural productivity, and most importantly the future prospects of MPs interaction and accumulation in plants. This article is protected by copyright. All rights reserved.

Globally, prescribed fire, harvesting, and understory mastication, alone and in combination, are common forest management practices. Timber commodities, wildlife habitat, wildfire fuel reduction, soil conservation, and water quality are frequently targeted and assessed as these practices are utilized. In the 1960s, a study of paired, first-order watersheds was established in coastal South Carolina, USA, to evaluate the long-term impacts of forest management (i.e. prescribed fire, thinning, mastication of understory vegetation) on water quantity and quality. Following Hurricane Hugo in 1989, this included salvage logging on one watershed, but not the other. In 2015, these watersheds were comprehensively evaluated to determine differences in forest species composition, fuels, and soil chemistry. Softwood basal area was greater in the managed watershed than in the unmanaged watershed and hardwood basal area was greater in the unmanaged watershed than in the managed watershed. Total fuel mass did not differ between the two watersheds, but 1-hr and 1000-hr rotten fuel mass were greater on the unmanaged watershed. Ten-hr fuel mass was greater on the managed watershed. Calcium, nitrogen, magnesium, phosphorus, potassium, and pH differed between the litter (Oi horizon) and duff (Oe + Oa horizons) of both watersheds, but carbon only differed in the duff. Mineral soil (Ultisols, 0-10 and 10-20 cm depths) calcium and phosphorus differed between the watersheds, but pH and the other chemicals did not. Collectively, these results indicated that: (1) forest management and natural disturbance on these watersheds altered long-term forest structure; (2) different species compositions and the inclusion or exclusion of salvage logging after Hurricane Hugo produced different fuel compositions that may potentially impact potential wildfire hazard and fire behavior; (3) organisms as a primary soil-forming factor were impacted by long-term management, therefore, some soil chemical properties were affected. Collectively, these analyses highlighted the broad, long-term impacts to ecosystem properties and processes that might directly and indirectly result from active forest management and natural disturbance and the scale of site-specific assessment that might be considered when landowner objectives are targeted in forest management plans and practices. Public domain – authored by a U.S. government employee

Torrential rain and extreme flooding caused by Atlantic hurricanes mobilize a large pool of organic matter (OM) from coastal forested watersheds in the southeastern United States. However, the mobilization of toxic metals such as mercury (Hg) that are associated with this vast pool of OM are rarely measured. This study aims to assess the variations of total Hg (THg) and methylmercury (MeHg) levels and the isotopic compositions of Hg in a blackwater river (Waccamaw River, SC, U.S.A.) during two recent extreme flooding events induced by Hurricane Joaquin (October 2015) and Hurricane Matthew (October 2016). We show that extreme flooding considerably increased filtered THg and MeHg concentrations associated with aromatic dissolved organic matter. During a 2-month sampling window each year (October-November), we estimate that about 27% (2015) and 78% (2016) of the average amount of Hg deposited atmospherically during these 2 months was exported via the river. The isotopic composition of Hg in the river waters was changed only slightly by the substantial inputs of runoff from surrounding landscapes, in which mass-dependent fractionation (as delta Hg-202) decreased from -1.47 to -1.67 parts per thousand and mass-independent fractionation (as increment Hg-199) decreased from -0.15 to -0.37 parts per thousand. The slight variations in Hg isotopic composition during such extreme flooding events imply that sources of Hg in the river are nearly unchanged even under the very high wet deposition of Hg derived from the intensive rainfall. The majority of Hg exported by the river (74-85%) is estimated to have been derived from dry deposition to the watersheds. An increase in frequency and intensity of Atlantic hurricanes is expected in the next few decades due to further warming of ocean surface waters. We predict that increased hurricanes will mobilize more dry-deposited Hg and in situ produced MeHg from these coastal watersheds where MeHg can be extensively bioaccumulated and biomagnified in the downstream aquatic food webs.

Copper-based algaecides are usually used for controlling algae bloom triggered by the elevated levels of nutrients after wildfires, resulting in the promoted reactivity of dissolved organic matter (DOM) in forming disinfectant byproducts (DBPs). To identify the best strategy for handling this source water, we employed Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to characterize the DBPs precursors after 4-d Microcystis aeruginosa bloom cultured with black (BE) and white (WE) ash water extracts under 0, 0.5, and 1.0 mg-Cu/L. The disappeared DOM during disinfections, primarily composed of O1-14, N1O1-14 and N2O1-14, had a higher average molecular weight (MW) and double-bond equivalent (DBE), relative to DOM after incubation, regardless of disinfects and Cu2+. This result suggests assigned features with larger MW and more double bonds/rings as preferable DBP precursors. We observed a larger number of disappeared assigned features with low DBE of 1-10 in control without Cu2+ addition, possibly explaining lower DOM chlorine reactivity in forming carbonaceous and oxygenated DBPs, relative to the treatments with Cu2+ addition. We found a larger number of O1-14 and N1O1-14 with DBE=5-16 in the treatments, potentially explaining higher DOM chloramine reactivity in forming N-nitrosodimethylamine (NDMA), compared to the control. Our study suggests removing oxygen- and nitrogen-containing organic compounds with more double bonds/aromatic rings as a preferable strategy for handling source water after controlling post-fire algae blooms with copper sulfate.

We investigated the effects of two California wildfires (Rocky and Wragg Fires, 2015) compared to an unburned reference watershed on water quality, dissolved organic matter (DOM), and precursors of disinfection by-products (DBPs) for two years' post-fire. The two burned watersheds both experienced wildfires but differed in the proportion of burned watershed areas. Burned watersheds showed rapid water quality degradation from elevated levels of turbidity, color, and suspended solids, with greater degradation in the more extensively burned watershed. During the first year's initial flushes, concentrations of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), ammonium (NH4+/NH3), and specific ultraviolet absorbance (SUVA(254)) were significantly higher (67 +/- 40%, 418 +/- 125%, 192 +/- 120%, and 31 +/- 17%, respectively) in the more extensively burned watershed compared to the reference watershed. These elevated values gradually declined and finally returned to levels like the reference watershed in the second year. Nitrate concentrations were near detection limits (0.01 mg-N/L) in the first year but showed a large increase in fire-impacted streams during the second rainy season, possibly due to delayed nitrification. Changes in DOM composition, especially during the initial storm events, indicated that fires can attenuate humic-like and soluble microbial by-product-like (SMP) DOM while increasing the proportion of fulvic-like, tryptophan-like, and tyrosine-like compounds. Elevated bromide (Br-) concentrations (up to 8.7 mu M]) caused a shift in speciation of trihalomethanes (THMs) and haloacetic acids (HAAs) to brominated species for extended periods (up to 2 years). Wildfire also resulted in elevated concentrations of N-nitrosodimethylamine (NDMA) precursors. Such changes in THM, HAA, and NDMA precursors following wildfires pose a potential treatability challenge for drinking water treatment, but the effects are relatively short-term (

Forested land plays an essential role in water supply across the United States (US). Smoldering commonly existing in wildfires contributes significantly to biomass consumption and gas emission, but its influence on source water quality has been rarely studied. Here, we investigated the impact of smoldering temperature (i.e., no burn, 250, 400, and 600 °C) on the nutrients, elements, and dissolved organic matter (DOM) of water extracts from the residues of the leaf needles and woody trunks of pine (Pinus jeffreyi) under the lab-simulated smoldering fire. Results showed the increase of pH and the yields of the dominated exchangeable cations of K

The membrane-less and biocathode-containing microbial fuel cells (MLBC-MFCs) were used for the electrical energy production from different wetlands, and the corresponding mechanisms were explored based on the characteristics of dissolved organic matters (DOM) in this study. The average voltage output on indoor MLBC-MFCs was 60 mV for the saltmarsh wetland water (SWW), 48 mV for the forest wetland water (FWW) and 71 mV for the FWW supplemented with sodium chloride (FWWS). For the field experiments, as high as 800 mV was obtained from the MLBC-MFCs installed in the forest wetland and the voltage output varying between 200 mV and 800 mV maintained approximately for half a year except for a few days with an extremely low temperature, while the voltage output from the MLBC-MFCs installed in the saltmarsh wetland went down to below 10 mV within 37 days likely due to the tide. The DOM before and after MFCs treatment was analyzed using the ultraviolet–visible absorption spectroscopy (UV–Vis) and the fluorescence excitation-emission matrix (EEM). Results showed that both carbon sources and anaerobic microorganisms included in subaqueous wetland sediments (SWSs) were vital for the electricity generation, and the food used to produce electrical energy mainly came from SWSs instead of wetlands water.

Pyrolysis gas chromatography/mass spectrometry is a potent tool for studying the molecular fingerprints of natural organic matter (NOM). With advances in analytical techniques, a pyrogram generally consists over a hundred pyrolysates, which increases the difficulty of interpreting the associated data. Here, we propose a systematic approach that includes an automatic peak identification and quantification pipeline and statistical techniques for the analysis of NOM. White oak (Quercus alba) and forest floor litter samples from a 48-week field decomposition study including sites along a soil moisture gradient were used to evaluate the applicability. An analysis of variance of the chemical classes indicated that the composition differed among sites, although a trend following the moisture gradient was not observed. Factor analysis of the pyrolysates clearly identified two decomposition stages in both types of decomposition. For the oak litter, 2,6-dimethoxy-phenol originating from syringyl lignin was dominant in the early stage, whereas for the forest floor litter, 2-methoxy-4-vinylphenol was enriched in the early stage, while 4-ethyl-2-methoxyphenol and 3-allyl-6-methoxyphenol were dominant in the later stage. These compounds originated from guaiacyl lignin, which suggested that guaiacyl lignin was relatively constant. The proposed approach provides a convenient and effective way to study the chemical composition of NOM.

In this study, we report for the first time the effect of prescribed fires on the export of dissolved organic matter (DOM) and precursors of disinfectant by-products (DBPs) from periodically (every 2-3 years) and seasonally (i.e., dormant and growing) burned forest fuel materials (i.e., live vegetation, woody debris, and detritus [litter and duff]) and treatability of its rainwater leachate. Periodically applied (every 2-3 years for 40 years) prescribed fires decreased total fuel load (62 10%), primarily detrital mass (75 +/- 2%). How-ever, functional groups (i.e., phenolic compounds, proteins, carbohydrates, aromatic [1-ring], polycyclic aromatic hydrocarbons [PAHs], and lipids) attached to DOM of ground solid materials did not change significantly. Outside rainwater leaching (from forest fuel materials) experiments showed that the leaching capacity of dissolved organic carbon (DOC) from burned litter samples decreased by 40 +/- 20% regardless of burning season when compared to unburned litter samples. The leaching of total dissolved nitrogen (TDN), dissolved organic nitrogen (DON), ammonium (NH4+), and reactive phosphorus (PO43-) from burned materials decreased between 40 and 70% when compared to unburned materials. Also, DOM composition was affected by prescribed fire, which partially consumed humic-like substances based on fluorescence analyses. Thus, periodically applied prescribed fires also resulted in a reduction of trihalomethane (THM) (42 +/- 23%) and haloacetic acid (HAA) (42 +/- 20%) formation potentials (FPs), while DOC normalized reactivity of THM and HAA FPs did not change significantly. Additionally, the leaching of Nnitrosodimethylamine (NDMA) precursors, bromide ion (Br-), and selected elements (K, Ca, Mg, Mn, Fe, S, Na, B, and Al) were not significantly affected by prescribed fires. Finally, coagulant (i.e., alum and ferric) dose requirements and coagulation efficiencies were similar (i.e., removal of DOC, precursors of THMs and HAAs were 52-56%, 69-70%, 78-79%, respectively) in unburned and pre-burned leachate samples. (c) 2020 Elsevier Ltd. All rights reserved.

Large, high-severity wildfires alter the physical and biological conditions that determine how catchments retain and release nutrients and regulate streamwater quality. The short-term water quality impacts of severe wildfire are often dramatic, but the longer-term responses may better reflect terrestrial and aquatic ecosystem recovery. We followed streamwater chemistry for 14 years after the largest fire in recorded Colorado history, the 2002 Hayman Fire, to characterize patterns in nitrogen (N) and carbon (C) export. Throughout the post-fire period, stream nitrate and total dissolved N (TDN) remained elevated in 10 burned catchments relative to pre-burn periods and 4 unburned control catchments. Both the extent of fire in a catchment and wildfire severity influenced stream N concentrations. Nitrate was more than an order of magnitude higher in streams draining catchments that burned to a high extent (> 60% of their areas) compared to unburned catchments. Unburned catchments retained more than 95% of atmospheric N inputs, but N retention in burned catchments was less than half of N inputs. Unlike N, stream C was elevated in catchments that burned to a lesser extent (30–60% of their areas burned), compared to either unburned or extensively burned catchments. Remotely sensed estimates of upland and riparian vegetation cover suggest that burned forests could require several more decades before forest cover and nutrient demand return to pre-fire levels. The persistent stream N increases we report are below drinking water thresholds, but exceed ecoregional reference concentrations for healthy stream ecosystems and indicate that extensively burned headwater catchments no longer function as strong sinks for atmospheric N. Combined with increasing trends in wildfire severity and elevated N deposition, our findings demonstrate the potential for substantial post-wildfire changes in ecosystem N retention and have implications for nutrient export to downstream waters.

Tropical- and subtropical-storm surges combined with sea level rise cause saltwater intrusions into low-lying coastal ecosystems along the southeastern coast of the United States, gradually converting freshwater forested wetland into saltmarsh. The transition zone between freshwater and saltwater ecosystems becomes a degraded forested wetland, where the combination of high levels of soil organic matter and elevated concentrations of halide ions creates a dynamic biogeochemical environment that may be a potential hotspot for halocarbon formation such as chloroform, methyl chloride, and methyl bromide. This study conducted field measurements at a transition zone in coastal South Carolina to quantify halocarbon exchange rates and laboratory soil incubations to determine the contributions of biotic versus abiotic processes. The degraded forested wetland showed significant chloroform emission rates (146 ± 129 nmol m–2 d–1). The degraded forested wetland remained a net sink for methyl chloride and a negligible ...

In recent years, the Chinese government has strengthened its efforts in surface water protection and restoration through strict policies and heavy investments. A clear understanding of the impacts of land use on water quality is necessary in order to ensure an effective and efficient implementation of the ongoing surface water restoration program in China. To this end, four small watersheds (less than 5000 ha) in southeastern China, which have clear gradients in the intensities of agriculture (17.0–45.4%), forest (35.2–73.6%) and built-up area (3.3–8.5%), were investigated regarding the impacts of land use on water quality. In addition to the general water quality indices, characteristic components derived by fluorescence excitation-emission matrices (FEEMs) coupled with parallel factor analysis (PARAFAC) were employed to explore a more accurate association between land use and water quality. The results show that agricultural intensity has significant effects by elevating the concentrations of dissolved organic carbon (DOC, an approximate six-fold increase) and total phosphorous (TP, an approximate four-fold increase) in the surface waters. A total of five PARAFAC components representing terrestrial (three components) and protein-like (two components) substances were identified. The PARAFAC results indicate that land-use patterns affected the dissolved organic matter (DOM) in the aspects of both amount and composition. The intensity (R.U.) of the terrestrial components showed a strong correlation (r2 = 0.95, p = 0.01) with agricultural land percentage. Moreover, although the proportion of built-up area varies with a relatively small range, a protein-like component could predict its impact with excellent sensitivity (r2 = 0.94, p = 0.02), whereas the general water quality indices were incapable of predicting the impact due to their multiple sources. The results of this study demonstrate that the FEEMs-PARAFAC technique provides an inexpensive and effective tool for policy makers to overcome the insensitivity of general water quality indices, particularly for the restoration of watersheds with complex land-use patterns.

Understanding the relationship between fire intensity and fuel mass is essential information for scientists and forest managers seeking to manage forests using prescribed fires. Peak burning temperature, duration of heating, and area under the temperature profile are fire behavior metrics obtained from thermocouple-datalogger assemblies used to characterize prescribed burns. Despite their recurrent usage in prescribed burn studies, there is no simple protocol established to guide the orientation of thermocouple installation. Our results from dormant and growing season burns in coastal longleaf pine ( Mill.) forests in South Carolina suggest that thermocouples located horizontally at the litter-soil interface record significantly higher estimates of peak burning temperature, duration of heating, and area under the temperature profile than thermocouples extending 28 cm vertically above the litter-soil interface ( < 0.01). Surprisingly, vertical and horizontal estimates of these measures did not show strong correlation with one another ( ≤ 0.14). The horizontal duration of heating values were greater in growing season burns than in dormant season burns ( < 0.01), but the vertical values did not indicate this difference ( = 0.52). Field measures of fuel mass and depth before and after fire showed promise as significant predictive variables ( ≤ 0.05) for the fire behavior metrics. However, all correlation coefficients were less than or equal to = 0.41. Given these findings, we encourage scientists, researchers, and managers to carefully consider thermocouple orientation when investigating fire behavior metrics, as orientation may affect estimates of fire intensity and the distinction of fire treatment effects, particularly in forests with litter-dominated surface fuels.

Two intense rainfalls [Hurricane Joaquin (2015) and Hurricane Matthew (2016)], one year apart, provided a unique opportunity to examine changes in dissolved organic matter (DOM) dynamics in coastal blackwater rivers under extreme flooding conditions in the southeastern United States. Two sites along Waccamaw River (a coastal blackwater river) and the outflow of 18 sub-basins of Yadkin-Pee Dee Basin were sampled during and after the flooding events. The peaks of dissolved organic carbon (DOC) and nitrogen (DON) concentrations were observed 18 and 23 days after peak discharge in 2015 and 2016, respectively. Moreover, DOM aromaticity and abundance of humic substances significantly increased during the same period. Separation of discharge hydrograph into surface runoff and subsurface flow suggested that temporal changes were mainly due to contributions from subsurface flow flushing organic matter from wetlands and organic-rich riparian zones. The spatial analysis highlighted the key role of the forested wetlands as the only land use that significantly correlated with both DOM quantity (DOC and DON load) and DOM composition (i.e., aromaticity). The Yadkin-Pee Dee River basin alone exported more than 474 million kg DOC into the ocean during high-flow conditions from the 2016 event, indicating that such extreme short-term events mobilized enormous amounts of organic carbon and nitrogen to the ocean. Considering the predicted increase in frequency and intensity of extreme rainfall events in the eastern U.S., the results of this study can shed light on changes in DOM dynamics that may occur under such conditions in the near future.

Forested wetlands dominated by baldcypress (Taxodium distichum) and water tupelo (Nyssa aquatica) are commonly found in coastal regions of the southeastern United States. Global climate change and in particular sea level rise will alter the frequency and magnitude of wet/dry periods and salinity levels in these ecosystems. Soil microcosm experiments were set up to identify the effects of water level variations (0.4–3.0 g-water g-soil−1) and salinity changes (0, 1 and 5 ppt of NaCl) on greenhouse gas emissions (CH4, CO2, and N2O) and dissolved organic carbon (DOC) characteristics from forested wetland soils. Our results indicate that, the effect of water level was much greater than salt intrusion on C and N cycling. Wet–dry treatments significantly decreased DOC production and total CH4-C loss, aromatic and humic-like substance compounds in DOC were increased in both flooding and wet–dry treatments after 60-d incubation. The molecular weight (MW) of DOC, as indicated by E2/E3 ratio and spectral slope, after flooding treatments was higher than that in wet–dry treatments. A first order kinetic model showed there was a positive linear correlation (r2 = 0.73) between CO2 emission rate and DOC concentration which indicated that CO2 was mainly generated from DOC. An exponential kinetic model was applied to describe the correlation between CH4 emission rate and DOC concentration (r2 = 0.41). This study demonstrates that an increase in salinity, and in particular variations in wet–dry cycles, will lead to changes in the formation of climate-relevant greenhouse gases, such as CH4, CO2, and N2O.

The O horizon, or detrital layer, of forest soils is linked to long-term forest productivity and health. Fuel reduction techniques, such as prescribed fire, can alter the thickness and composition of this essential ecosystem component. Developing an understanding of the changes in the chemical composition of forest detritus due to prescribed fire is essential for forest managers and stakeholders seeking sustainable, resilient, and productive ecosystems. In this study, we evaluated fuel quantity, fuel structure, and detrital chemical composition in longleaf pine ( Miller) forests that have been frequently burned for the last 40 yr at the Tom Yawkey Wildlife Center in Georgetown, SC. Our results suggest that frequent prescribed fire reduces forest fuel quantity ( < 0.01) and vertical structure ( = 0.01). Using pyrolysis-gas chromatography/mass spectrometry as a molecular technique to analyze detrital chemical composition, including aromatic compounds and polycyclic aromatic hydrocarbons, we found that the chemical composition of forest detritus was nearly uniform for both unburned and burned detritus. Our burning activities varied in the short term, consisting of annual dormant, annual growing, and biennial dormant season burns. Seasonal distinctions were present for fuel quantity and vertical fuel structure, but these differences were not noted for the benzene/phenol ratio. These results are significant as more managers consider burning existing longleaf stands while determining effective management practices for longleaf stands yet to be established. Managers of such stands can be confident that frequent, low-intensity, low-severity prescribed burns in longleaf pine forests do little to affect the long-term chemical composition of forest detritus.

Watershed management practices such as prescribed fire, harvesting and understory mastication can alter the chemical composition and thickness of forest detritus, thus affecting the quantity and quality of riverine dissolved organic matter (DOM). Long-term effects of watershed management on DOM composition were examined through parallel field and extraction-based laboratory studies. The laboratory study was conducted using detritus samples collected from a pair of managed and unmanaged watersheds in South Carolina, USA. Results showed that dissolved organic carbon (DOC), total dissolved nitrogen (TDN) and ammonium (NH4+-N) concentrations were higher in water extracts from the unmanaged watershed than from the managed watershed (P < 0.01). Pyrolysis gas chromatography-mass spectrometry analysis showed that water extracts from the unmanaged watershed contained more aromatic compounds than extracts from the managed watershed. For the field study, monthly water samples were collected for 1 year (2015) from the paired watersheds. DOC and TDN concentrations, as well as DOM aromaticity, were significantly higher in the unmanaged watershed than in the managed watershed for most of the year (P < 0.05) and were linked to detrital thickness, precipitation and flow patterns. The formation potential of two regulated disinfection by-products was lower in the unmanaged watershed for most of 2015 (P < 0.05). From this study, it appears that long-term watershed management practices may alter detrital mass and chemistry in ways that improve water quality. Joint Fire Science Program [14-1-06-19]; USEPAUnited States Environmental Protection Agency [R835864]; USDA Forest Service National Fire Plan (2014-18) We are grateful for financial support from the Joint Fire Science Program (Project 14-1-06-19), USEPA (R835864) and the USDA Forest Service National Fire Plan (2014-18). We also thank Mary-Frances Wolf, Ryan Marsh, Rob O'Neal, David Miller, Jennie Untener and Brian Williams for their assistance with fieldwork and sample collection. Public domain – authored by a U.S. government employee

The frequency of Atlantic hurricanes has been predicted to increase significantly by the end of this century. Watershed disturbance initiated by hurricanes can alter dissolved organic matter (DOM) quantity and quality in source water dramatically. DOM is an important disinfection by-product (DBP) precursor, and thus hurricanes can have a significant impact on water treatability and drinking water safety. The interactions between land use and land cover (LULC) of a watershed and DBP formation potential (FP) in source water under hurricane events have rarely been evaluated. Here, we quantified the FPs of two carbonaceous (trihalomethanes [THMs] and haloacetic acids [HAA]) and two nitrogenous (haloacetonitrile [HAN] and N-nitrosodimethylamine [NDMA]) DBPs at eighteen sub-watersheds with varying LULC along the Yadkin-Pee Dee River basin across North and South Carolina during and after the flooding condition caused by the 2016 Hurricane Matthew. Using chlorine as a disinfectant, THM FP was 238% (±117%) higher (p .001) under the flooding condition than baseflow condition, while HAA FP did not change significantly as a result of the flooding. DOM composition under the flooding condition changed in favor of the formation of THMs rather than HAAs by a decrease of fulvic acid-like compounds and an increase in DOM aromaticity (SUVA). The FPs of studied DBPs under the flooding condition compared with the baseflow, followed the order of HAN (356.5%) NDMA (246.4%) THM (115.2%) using chloramine as a disinfectant. Higher HAN FP and NDMA FP compared to THM FP suggested that more nitrogenous than carbonaceous DBPs precursors were released during this hurricane event. LULC analysis revealed that forested wetlands were the major contributor of THM, HAA, and HAN precursors, whereas NDMA precursor was derived from developed areas. This unique study highlights the dynamic interplay between LULC and exports of carbonaceous and nitrogenous DBPs precursors during and after hurricanes.

Elevated levels of nutrients due to wildfire ash input into stream waters will likely cause algal blooms. When source water is impeded by algae and requires immediate restoration, copper algaecides are usually applied. Previous studies indicate that Cu2+ can promote reactivity of dissolved organic matter in forming disinfection byproducts (DBPs). However, it is unclear that how DBP formation is changed after the treatment of post-fire algal bloom by copper algaecide. In this study Microcystis aeruginosa was cultured in the medium containing black and white ash water extracts (BE and WE) to study DBP concentrations before and after 4-days exposures to low and high copper sulfate (0.5 and 1.0 mg-Cu/L). Dissolved organic matter (DOM) was characterized by UV-VIS absorption and fluorescence spectroscopy and chlorination/chloramination-based DBP formation potential (FP) experiments. DOM concentrations and algal population in the treatments were lower than that in control, regardless of types of water extract. N-nitrosodimethylamine FP in the treatments were 4-6 times higher than the control (0.23-0.34 vs. 0.05-0.06 mu g/L), while haloacetonitrile FP revealed no significant difference (132-191 vs. 167-185 mu g/L). Trade-offs between reducing algal population and promoting DBP-FP were more pronounced for the solutions containing BE than WE. Low copper concentration was as effective as high concentration in inhibiting algal growth while minimizing promotion of DBP formation. The results can serve to support risk evaluations of algal population and DBP concentration when wildfire-induced algal bloom is left untreated and treated by copper algaecides. (C) 2019 Elsevier Ltd. All rights reserved.

Disinfection processes might alter the chemical structure of biological recalcitrant natural organic matter (NOM) in source water to form assimilable organic carbon (AOC), which can be readily utilized by microbes for growth. However, AOC has not been classified as disinfection byproducts (DBPs) before and little is known about the chemical and structural nature of AOC. This study, for the first time, considers the disinfection-induced AOC as DBPs from a microbiological perspective. The AOC formation by three types of disinfection processes, i.e., chlorination, UVC irradiation (254 nm) and photocatalysis represented by TiO2-UVA in drinking water containing two reference NOM materials of Suwannee River and Nordic Reservoir (SRNOM and NRNOM, respectively) were comparatively benchmarked using Pseudomonas aeruginosa as inoculum. Results showed that chlorination caused a substantial increase in AOC content, whereas TiO2-UVA led to a moderate increase in AOC content and UVC rendered the AOC content unchanged, independent of the types of NOM. Molecular weight indicated by spectral slope ratio and fluorescence fingerprint were found to not provide critical information about the AOC formation potential. FTIR and FT-ICR-MS results indicated that the AOC formation by chlorination was attributed to the oxidation and chlorine substitution on aromatic molecules to form molecules with carboxylic- and alcohol- functionalities, as well as chlorinated aromatics. These molecules could be metabolized and assimilated by Pseudomonas species by a catechol pathway. The results obtained in this study can provide valuable insight regarding the selection of proper technologies for disinfection to prevent microbial growth/regrowth in the distributing system and is intended to encourage more thinking and research on AOC as a new prospect of DBPs during disinfection of drinking water. Keywords: Drinking water, Natural organic matter, Assimilable organic carbon, Microbial regrowth, Disinfection byproducts

Wildfire-altered soil may be an important source of polycyclic aromatic hydrocarbons (PAHs) in the environment. With projected increase of wildfire frequency and intensity due to changing global climate, understanding the quantity and speciation of PAHs, including halogenated PAHs (XPAHs), resulting from different burn intensities has important ramifications for environmental quality concerns and global soil carbon dynamics. Here, we quantified levels of 16 U.S. Environmental Protection Agency regulated PAHs, 3 chlorinated PAHs, and 6 brominated PAHs in nonburned forest soils and burned ash/soil samples covered with black ash (B-Ash; moderate burn intensity) or white ash (W-Ash; severe burn intensity) from the 2013 Rim Fire (1,041 km 2 ) in California. The - 16 PAH concentrations follow (mean ± standard deviation; μg/kg) B-Ash (893 ± 285) > W-Ash (515 ± 333) ≈ nonburned soils (247 ± 58). Moreover, the - 16 PAH profiles were altered by both moderate and severe burn conditions with the size of aromatic structures following B-Ash > W-Ash > nonburned soils. Neither chlorinated nor brominated PAH concentration was significantly elevated by moderate or severe wildfire. Overall, fire intensity is critical in regulating soil PAH concentrations and profiles. Given the high erodibility of wildfire ash, these PAHs can be easily transported to rivers and reservoirs where they could impact the aquatic food web and drinking source water.

Small ephemeral wetlands are commonly found in the Piedmont ecoregion of the southeastern USA. Ephemeral wetlands have important ecological functions but information about their water quality over its flooding periods is relatively limited. In this study, the water chemistry and physical parameters of three ephemeral wetlands and their nearby water bodies, including first order and second order streams and groundwater in the Piedmont ecoregion of South Carolina, were closely monitored during their flooding periods from January to June 2012. Nutrient and water quality analyses demonstrated the chemistries of wetlands, stream, and groundwater were different from each other in spite of their proximity. Greater concentrations of dissolved organic carbon (DOC) and dissolved organic nitrogen with a major portion in humic-acid-like and fulvic-acid-like fractions were generally found in wetland waters. In contrast, significantly lower DOC concentrations with a greater portion of inorganic nitrogen were observed in stream and groundwater. Electrical conductivity at 25 °C (EC25) and temperature measurements showed a greater fluctuation in wetlands, indicating their poor buffering capacity against environmental changes. Results of this field study suggested that these small ephemeral wetlands in the Piedmont Ecoregion have relatively unique biogeochemistry in comparing their adjacent water bodies.

The Rim Fire ignited on August 17, 2013 and became the third largest wildfire in California history. The fire consumed 104,131ha of forested watersheds that were the drinking water source for 2.6 million residents in the San Francisco Bay area. To understand temporal variations in dissolved organic matter (DOM) after the wildfire and its potential impacts on disinfection byproduct (DBP) formation in source water supply, we collected the 0-5cm ash/soil layer with surface deposits of white ash (high burn severity) and black ash (moderate burn severity) within the Rim Fire perimeter in Oct 2013 (pre-rainfall) for five sequential extractions, and in Dec 2013 (∼87mm cumulative precipitation) and Aug 2014 (∼617mm cumulative precipitation) for a single water extraction. Water-extractable DOM was characterized by absorption and fluorescence spectroscopy and DBP formation tests. Both increasing cumulative precipitation in the field or number of extractions in the lab resulted in a significant decrease in specific conductivity, dissolved organic carbon, and DBP formation potential, but an increase in DOM aromaticity (reflected by specific UV absorbance). However, the lab sequential leaching failed to capture the increase of the NOx(-)-N/NH4(+)-N ratio and the decrease in pH and dissolved organic carbon/nitrogen ratio of ash/soil extracts from Oct 2013 to Aug 2014. Increasing cumulative precipitation, inferring an increase in leaching after fire, led to an increase in DOM reactivity to form trihalomethanes, haloacetic acids, and chloral hydrate, but not for haloketones, haloacetonitrile, or N-nitrosodimethylamine, which were more related to the original burn severity. This study highlights that fire-affected DBP precursors for different DBP species have distinct temporal variation possibly due to their various sensitivity to biogeochemical alterations.

The high effectiveness of TiO2-UVA system in bacterial disinfection has gained attention to use this technology in water treatment on different source waters, including desalinated sea water and grey water. However, source waters containing a significant level of bromide could have different chemical pathways during TiO2-UVA disinfection process because reactive bromine species could be formed. To illustrate the water safety from the Br-TiO2-UVA system, this study investigated bacterial inactivation efficiency and disinfection byproduct (DBP) formation under different pH, TiO2 dosages and bromide concentrations in a laboratory setting. At a high bromide concentration (65 mg/L, equivalent to the concentration of natural sea water), the bacterial inactivation rate increased 2 times at pH 5 and more than 5 times at pH 8. However, a significant increase of brominated DBPs, which were considered more carcinogenic and toxic than chlorinated DBPs, was observed. The bacterial inactivation pattern was shifted from the “shoulder-log” to the “log-tail” under different bromide concentrations, suggesting the existence of bromide altered the bacterial inactivation mechanisms. We also observed that the inactivation kinetics of Br-TiO2-UVA system was greatly influenced by water pH. Our laboratory experiments demonstrated that bromide could improve the performance of photocatalytic inactivation, but it also could reduce the water safety by generating a higher level of brominated-DBPs in treated water. Water engineers should pay attention to the brominated DBP formation when applying TiO2-UVA photocatalysis on source waters with a significant level of bromide.

Severe wildfires combust most above ground vegetation and detritus layers, altering the content and chemical composition of soil organic matter (SOM). To evaluate the lasting effects of wildfire on SOM and the recovery of burned soils, we sampled surface (Oa horizon) and mineral soils (0−5 and 5−15 cm depths) in unburned areas and areas burned at moderate and high severity 14 years after the 2002 Hayman Fire, in Colorado, USA. We characterized SOM using Pyrolysis Gas Chromatography Mass Spectrometry (Py-GC–MS) and identified 106 pyrolysates within eight chemical classes [aromatic hydrocarbon (ArH), carbohydrate (Carb), lignin compound (LgC), nitrogen containing compound (Ntg), polyaromatic hydrocarbon (PAH), phenol compound (PhC), saturated hydrocarbon (SaH), and unsaturated hydrocarbon (UnSaH)]. Burned soils had greater total quantified peak areas (TQPA) for the pyrogenic C indicator (PyC) benzene, compared to unburned soils; however, other common PyC markers were not abundant in burned relative to unburned soils. Factor analysis on the individual pyrolysates suggests that factors 1 and 2 correlated with pyrolysate aromaticity and hydrophobicity, respectively. Sample factor scores potentially suggest that SOM aromaticity increases with fire severity, though difference between moderate and high severity was slight. Factor analysis also indicates that the ratio of [ArH + Ntg] / [PhC + LgC] may serve as index of PyC content in SOM. This study shows that wildfire effects on SOM character may persist for more than a decade of ecosystem recovery and that Py-GC–MS coupled with factor analysis has utility for evaluating how disturbance alters SOM and PyC in complex environments.

Wildfire could alter both the quantity and composition of terrestrial organic matter exported into source water, and water treatability of fire-impacted dissolved organic matter (DOM) could be different from its unburned counterpart. Currently, there is no standard protocol to treat wildfire-impacted source water. To identify the best treatment practices in handling post-fire runoffs, we conducted a systematic controlled study using leachates of unburned white fir (Abies concolor) and Ponderosa pine (Pinus ponderosa) and black and white ashes (collected immediately and one year after the 2013 Rim Fire, California) to evaluate coagulation and oxidation strategies for controlling disinfection byproducts (DBPs) formation. Results showed that the efficiency (%) of alum coagulation in removing dissolved organic carbon and nitrogen followed the order of litter > ash immediately after the fire > ash one year after the fire. Alum coagulation was less effectiveness in removing DOM and DBP precursors in ash leachates, compared to litter leachates. This may be attributed to the loss of side chains and the decrease of DOM molecular weight during the wildfire, thus inducing lower removal efficiency of the DOM and DBP precursors during the alum coagulation. Considering use of brominated flame retardants by firefighters, the addition of bromide (Br−) (100 μg/L) greatly increased the formation of haloacetonitriles by chlorine, and this increase was relatively lower in ash leachates. The influence of reaction time and pH on DOM reactivity was similar among the leachates of litter and ash samples. Our results show that alum coagulation followed by chloramination at alkaline pH is an effective strategy for reducing post-fire DBP formation in drinking water.

Foliar litter is an important terrestrial source of dissolved organic matter (DOM) and disinfection byproducts (DBPs) in the source water supply. Climate changes could alter precipitation patterns and hydroperiods in woody wetlands, resulting in a hydrologic shift along the low elevation gradient and change the productions of DOC and DBP precursors and their exports to source water. Here, we conducted an 80-week field decomposition study using fresh-fallen leaves along an elevation gradient, representing well-drained, relatively moist, and inundated environments, in Congaree National Park, South Carolina. The dissolved organic carbon (DOC) yield and formation potential (FP) of trihalomethanes (THMs; a dominant category of studied DBPs) were 48.9–79.7 mg-DOC/g-litter and 2.23–6.57 mg/g-litter in the freshly fallen leaf litter, respectively. The level of leachable DOM and its DBP FP decreased with time, and during the first 16 weeks of decomposition, the decomposing litter served as an important source of leachable DOM and DBP precursors. Week 28 was a turning point for DOM optical properties, with fewer tyrosine/tryptophan/soluble microbial byproduct-like compounds and more aromatic, humified, and fulvic/humic acid-like compounds. Litterfall primarily occurred from September to January, while less precipitation occurred from October to January, indicating that large amounts of DOC and DBP precursors could be leached from litterfall in February. In the first 16 weeks of field exposure study, we observed higher residual mass and lower water-extractable DOC and DTN in more inundated environments, demonstrating that the shifts of DOM composition and DBP precursors if climate reduces rainfall in the southeastern US.

Recent studies suggest increased fire frequency may impair soil chemistry, but few studies have examined long-term effects of repeated, frequent prescribed fires on forest soil properties in the southeastern Coastal Plain, USA. In this study, forest soil chemistry at the 0&ndash, 10 and 10&ndash, 20 cm mineral soil depths of sandy surface horizons (Entisols and Spodosols) were compared among units burned 0, 4, 6, and 8 times between 2004 and 2015 and 0 and 20 times between 1978 and 2015 in a longleaf (Pinus palustris Mill.)&ndash, loblolly (Pinus taeda L.) pine savanna at the Tom Yawkey Wildlife Center (Georgetown, SC, USA). At the 0&ndash, 10 cm soil depth, soil pH (p = 0.00), sulfur (p = 0.01), calcium (p = 0.01), iron (p &lt, 0.01), manganese (p &lt, 0.01), and aluminum (p = 0.02) treatment means differed (2004&ndash, 2015). Calcium and manganese displayed positive, significant relationships and sulfur displayed a negative, significant relationship with increasing fire frequency (p &lt, 0.05). However, correlation of these relationships was low (r2 &le, 0.23). Using linear contrasts to compare the mean of all fire treatments (20 fires from 1978 to 2015) to the mean of the unburned compartment, sulfur (p = 0.01) and iron (p &lt, 0.01) were less in soils from the burned compartments. At the 10&ndash, 20 cm soil depth, soil pH (p = 0.01), manganese (p = 0.04), phosphorus (p = 0.01), potassium (p = 0.02), and iron (p &lt, 0.01) treatment means differed (2004&ndash, 2015). Potassium displayed a negative, significant relationship and soil pH displayed a positive, significant relationship with increasing fire frequency (p &lt, 0.05). Correlation of these relationships was low (r2 &le, 0.16), however. Using linear contrasts to compare the mean of all fire treatments (20 fires from 1978 to 2015) to the unburned compartment, potassium (p = 0.00) and iron (p &lt, 0.01) were less in soils from burned compartments. These results are inconsistent with studies suggesting that forest soil chemistry is substantially altered by increased fire frequency and support other studies from this region that have documented minimal or temporary soil chemical changes associated with frequent prescribed fires.