Jun-Jian Wang

Improved fluorescence excitation-emission matrix regional integration to quantify spectra for fluorescent dissolved organic matter.

The purpose of this short communication is to demonstrate the importance of numerical analysis and wavelength increment selection when characterizing fluorescent dissolved organic matter (FDOM) using fluorescence excitation-emission matrix (EEM) regional integration. A variety of water samples, representing a landscape gradient and different types of FDOM, were analyzed for their percentage distribution of five operationally defined FDOM fractions (aromatic protein I, aromatic protein II, fulvic acid-like, soluble microbial byproduct-like, and humic acid-like) using three numerical methods in integrating volume under the surface of the fluorescence EEMs: Riemann summation, composite trapezoidal rule, and composite Simpsons rule. The influence of wavelength increment was also examined for the precision of the percentage distribution of each fraction. Our results show that the FDOM fraction estimated by Riemann summation with a 10- or 5-nm excitation wavelength can cause >40% or >5% errors, respectively, when compared with the best estimated values obtained by averaging results from composite trapezoidal rule and composite Simpsons rule with 1-nm excitation wavelength at the same emission increment. Also, our experiments show that fluorescence matrix regional integration could underestimate the two aromatic protein fractions but could overestimate the soluble microbial byproduct-like and humic acid-like fractions if improper increment and integral methods are used. The error can be reduced if a smaller wavelength increment is used. The smallest increment in a spectrofluorometer and composite Simpsons rule should be used for scanning fluorescence EEMs and calculating the percentage distribution of each FDOM fraction. Alternatively, 5-nm wavelength increments with composite Simpsons rule could be cost effective, and the error of each FDOM fraction commonly falls within 5% compared with those estimated by 1-nm increments.

Disinfection byproduct formation from chlorination of pure bacterial cells and pipeline biofilms

Disinfection byproduct (DBP) formation is commonly attributed to the reaction between natural organic matters and disinfectants, yet few have considered the contribution from disinfecting bacterial materials - the essential process of water disinfection. Here, we explored the DBP formation from chlorination and chloramination of Escherichia coli and found that most selected DBPs were detectable, including trihalomethanes, haloacetonitriles, chloral hydrate, chloropicrin, and 1,1,1-trichloro-2-propanone. A positive correlation (P = 0.08-0.09) between DBP formation and the log reduction of E. coli implied that breaking down of bacterial cells released precursors for DBP formation. As Pseudomonas aeruginosa is a dominant bacterial species in pipeline biofilms, the DBP formation potentials (DBPFPs) from its planktonic cells and biofilms were characterized. Planktonic cells formed 7-11 times greater trihalomethanes per carbon of those from biofilms but significantly lower (P < 0.05) chloral hydrate, highlighting the bacterial phenotypes impact on the bacteria-derived DBPFP. Pipe material appeared to affect the DBPFP of bacteria, with 4-28% lower bromine incorporation factor for biofilms on polyvinyl chloride compared to that on galvanized zinc. This study revealed both the in situ disinfection of bacterial planktonic cells in source water and ex situ reaction between biofilms and residual chlorine in pipeline networks as hitherto unknown DBP sources in drinking water.

Phenolic profile within the fine‐root branching orders of an evergreen species highlights a disconnect in root tissue quality predicted by elemental‐ and molecular‐level carbon composition

Fine roots constitute a significant source of plant productivity and litter turnover across terrestrial ecosystems, but less is known about the quantitative and qualitative profile of phenolic compounds within the fine-root architecture, which could regulate the potential contribution of plant roots to the soil organic matter pool. To understand the linkage between traditional macro-elemental and morphological traits of roots and their molecular-level carbon chemistry, we analyzed seasonal variations in monomeric yields of the free, bound, and lignin phenols in fine roots (distal five orders) and leaves of Ardisia quinquegona. Fine roots contained two-fold higher concentrations of bound phenols and three-fold higher concentrations of lignin phenols than leaves. Within fine roots, the concentrations of free and bound phenols decreased with increasing root order, and seasonal variation in the phenolic profile was more evident in lower order than in higher order roots. The morphological and macro-elemental root traits were decoupled from the quantity, composition and tissue association of phenolic compounds, revealing the potential inability of these traditional parameters to capture the molecular identity of phenolic carbon within the fine-root architecture and between fine roots and leaves. Our results highlight the molecular-level heterogeneity in phenolic carbon composition within the fine-root architecture, and imply that traits that capture the molecular identity of the root construct might better predict the decomposition dynamics within fine-root orders.

Wildfire Altering Terrestrial Precursors of Disinfection Byproducts in Forest Detritus

Wildfire occurrence and intensity are increasing worldwide causing severe disturbances to forest watersheds used for potable water supply. The effects of wildfire on drinking water quality are not well understood, especially in terms of terrestrial dissolved organic matter (DOM) and DOM-associated formation of disinfection byproducts (DBP). As the forest floor layer is a major source of terrestrial DOM, we investigated characteristics and DBP formation of water extractable organic matter (WEOM) from the 0-5 cm depth of nonburned detritus (control) and burned detritus with black ash (moderate severity) and white ash (high severity) associated with the 2013 Rim Fire in California. Spectroscopic results suggested that the aromaticity of WEOM followed white ash > control > black ash and fluorescence region II (excitation 220-250 nm; emission 330-380 nm) of the emission-excitation-matrix was identified as a potential burn severity indicator. Compared to the control, WEOM from white and black ashes had lower reactivity in forming trihalomethanes (55%-of-control) and haloacetic acids (67%-of-control), but higher reactivity in forming the more carcinogenic haloacetonitrile after chlorination (244%-of-control) and N-nitrosodimethylamine after chloramination (229%-of-control). There was no change in reactivity for chloral hydrate formation, while WEOM from black ash showed a higher reactivity for haloketone formation (150%-of-control). Because wildfire consumed a large portion of organic matter from the detritus layer, there was lower water extractable organic carbon (27%-of-control) and organic nitrogen (19%-of-control) yields in ashes. Consequently, the wildfire caused an overall reduction in water extractable terrestrial DBP precursor yield from detritus materials.

Fine Root Mercury Heterogeneity: Metabolism of Lower-Order Roots as an Effective Route for Mercury Removal

Fine roots are critical components for plant mercury (Hg) uptake and removal, but the patterns of Hg distribution and turnover within the heterogeneous fine root components and their potential limiting factors are poorly understood. Based on root branching structure, we studied the total Hg (THg) and its cellular partitioning in fine roots in 6 Chinese subtropical trees species and the impacts of root morphological and stoichiometric traits on Hg partitioning. The THg concentration generally decreased with increasing root order, and was higher in cortex than in stele. This concentration significantly correlated with root length, diameter, specific root length, specific root area, and nitrogen concentration, whereas its cytosolic fraction (accounting for <10% of THg) correlated with root carbon and sulfur concentrations. The estimated Hg return flux from dead fine roots outweighed that from leaf litter, and ephemeral first-order roots that constituted 7.2-22.3% of total fine root biomass may have contributed most to this flux (39-71%, depending on tree species and environmental substrate). Our results highlight the high capacity of Hg stabilization and Hg return by lower-order roots and demonstrate that turnover of lower-order roots may be an effective strategy of detoxification in perennial tree species.

Water quality of small seasonal wetlands in the Piedmont ecoregion, South Carolina, USA: Effects of land use and hydrological connectivity.

Small, shallow, seasonal wetlands with short hydroperiod (2-4 months) play an important role in the entrapment of organic matter and nutrients and, due to their wide distribution, in determining the water quality of watersheds. In order to explain the temporal, spatial and compositional variation of water quality of seasonal wetlands, we collected water quality data from forty seasonal wetlands in the lower Blue Ridge and upper Piedmont ecoregions of South Carolina, USA during the wet season of February to April 2011. Results indicated that the surficial hydrological connectivity and surrounding land-use were two key factors controlling variation in dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) in these seasonal wetlands. In the sites without obvious land use changes (average developed area <0.1%), the DOC (p < 0.001, t-test) and TDN (p < 0.05, t-test) of isolated wetlands were significantly higher than that of connected wetlands. However, this phenomenon can be reversed as a result of land use changes. The connected wetlands in more urbanized areas (average developed area = 12.3%) showed higher concentrations of dissolved organic matter (DOM) (DOC: 11.76 ± 6.09 mg L(-1), TDN: 0.74 ± 0.22 mg L(-1), mean ± standard error) compared to those in isolated wetlands (DOC: 7.20 ± 0.62 mg L(-1), TDN: 0.20 ± 0.08 mg L(-1)). The optical parameters derived from UV and fluorescence also confirmed significant portions of protein-like fractions likely originating from land use changes such as wastewater treatment and livestock pastures. The average of C/N molar ratios of all the wetlands decreased from 77.82 ± 6.72 (mean ± standard error) in February to 15.14 ± 1.58 in April, indicating that the decomposition of organic matter increased with the temperature. Results of this study demonstrate that the water quality of small, seasonal wetlands has a direct and close association with the surrounding environment.

Greenhouse cultivation mitigates metal-ingestion-associated health risks from vegetables in wastewater-irrigated agroecosystems

Wastewater irrigation can elevate metal concentrations in soils and crops and increase the metal-associated health risks via vegetable ingestion in arid and semiarid northwestern China. Here, we investigated the As, Cd, Cr, Cu, Ni, Pb, and Zn concentrations in four vegetable species from Dongdagou and Xidagou farmlands in Baiyin, Gansu, China. We evaluated the effects of irrigation type (Dongdagou: industrial wastewater; Xidagou: domestic wastewater) and cultivation mode (open field and greenhouse) on the vegetable metal concentration, metal partitioning, soil-to-plant bioconcentration factor (BCF), and the health risk index. All stream waters, soils, and vegetables were found most severely polluted by As and Cd, with higher severity in the industrial-wastewater-irrigated Dongdagou than the domestic-wastewater-irrigated Xidagou. All vegetables had higher or, at least, comparable metal mass allocated in the shoot than in the root. Greenhouse cultivation could reduce metal-ingestion-associated health risks from edible vegetable biomass by decreasing the soil to plant bioaccumulation (BCF) and the metal concentration. This effect was always significant for all vegetables within Xidagou, and for carrot within Dongdagou. This mitigation effect of greenhouse cultivation could be attributed to the metal sorption by a higher level of soil organic matter and faster growth rate over metal uptake rate in greenhouses compared to open fields. Such mitigation effect was, however, insignificant for leafy vegetables within Dongdagou, when much more severely polluted water for irrigation was applied in greenhouses compared to open fields within Dongdagou. The present study highlights greenhouse cultivation as a potential mitigating approach to providing less-polluted vegetables for residents in the severely polluted area in addition to the source pollution control.

Spatial-temporal and multi-media variations of polycyclic aromatic hydrocarbons in a highly urbanized river from South China

Comprehensive studies on polycyclic aromatic hydrocarbons (PAHs) within an urban river are urgently needed to carry out strategies to limit their contamination and dispersal. Here, we analyzed 16 PAH occurrences in water, suspended particulate matter (SPM), and sediment monthly for a year in the Maozhou River mainstream (Shenzhen, South China). Monthly rainfall positively correlated with both total PAH concentrations in filtered water (water PAHs) and SPM. Sediment PAH concentration increased from the river source to estuary. Compared to the earlier record, the sediment PAHs decreased at almost all sites due to the high-molecular-weight PAH (≥4 rings; especially the 4-ring PAH) degradation, except the estuary site that accumulated more low-molecular-weight PAHs (<4 rings). Results suggest that the water and SPM PAHs had similar and recent sources (e.g., rainfall and storm runoff) and actively exchanged with each other. The sediment PAHs had relatively different and complicated sources (fossil fuel combustion: 44.0%; oil pollution: 28.4%; biomass burning: 27.6%), and showed a long-term accumulation effect and increasingly weaker source-sink relation with both water and SPM PAHs from river source to estuary. This study highlights a disconnection in the source and migration mechanism between the water body (including water and SPM) and sediment PAHs.

Electrical energy production from forest detritus in a forested wetland using microbial fuel cells

Microbial fuel cell (MFC) technology has shown great potential for harvesting energy from waste organic materials. Here, we explored the potential of MFC‐based electricity generation from forest detritus, a large untapped biomass pool. Electricity generation from in situ MFCs and relevant environmental parameters (i.e., carbon sources and concentrations, temperature, water depth) in a seasonally flooded freshwater cypress‐tupelo wetland were monitored intensively for two flooding periods. Current outputs ranged from 0 to 1.27 mA (mean of 0.40 mA for flooding period) and were highly sensitive to environmental changes, showing seasonal and diel dependences. Excluding the influence of heavy storms, drought, or wetland icing, current output was highly temperature‐dependent dielly. Seasonally, current output gradually increased in the first 3–4 months (limited by temperature) and decreased slightly during the last 1–2 months (probably limited by carbon and nutrients) of both flooding periods. Litter extract of baldcypress (Taxodium distictum) with lower C/N ratio and aromatic content showed greater stable current outputs (0.57 mA) based on 50 mg l−1 biological oxygen demand compared to extracts of water tupelo (Nyssa aquatica) and longleaf pine (Pinus palustris), suggesting that the current output of in situ MFCs could depend on the vegetation within a wetland. Our study highlights the potential application of MFC in generating green and sustainable electricity from forest biomass for powering remote sensors in wetland ecosystems.

Controlled Burning of Forest Detritus Altering Spectroscopic Characteristics and Chlorine Reactivity of Dissolved Organic Matter: Effects of Temperature and Oxygen Availability

Forest fires occur with increasing frequency and severity in the western United States, potentially altering the chemistry and quantity of dissolved organic matter (DOM) and disinfection byproduct (DBP) precursors exported from forested watersheds. However, little is known concerning effects of the fire triangle (heat, oxygen, and fuel) on DOM alteration. Using detritus from Pinus ponderosa and Abies concolor (dominant species in forests in the western United States), we prepared DOM from unburned and burned detritus under hypoxic (pyrolysis) and oxic conditions (thermal oxidation) at 250 and 400 °C. DOM characteristics and chlorine reactivity were evaluated by absorption and fluorescence spectroscopy and chlorination-based DBP formation potential tests. Spectroscopic results suggest that burned-detritus extracts had lower molecular weight (reflected by increased E2:E3 and fluorescence index) and divergent aromaticity (reflected by SUVA254) depending on oxygen availability. Temperature and oxygen availability interacted to alter the chlorine reactivity of fire-affected DOM. Increasing temperature from 50 to 400 °C resulted in decreased reactivities for trihalomethane and chloral hydrate formation and divergent reactivities for haloacetonitrile formation (unchanged for pyrolysis and increased for oxidation) and haloketone formation (increased for pyrolysis and decreased for oxidation). We demonstrate that DBP precursors in fire-affected forest detritus are highly dependent on temperature and oxygen availability.