Spatiotemporal Characterization of Chromophoric Dissolved Organic Matter (CDOM) and CDOM-DOC Relationships for Highly Polluted Rivers

Salt pollution reduces turbidity, dissolved organic matter, and cyanobacteria in experimental vernal pool communities

Anthropogenic activities such as the over-application of road deicers are causing an increase in the concentration of salts in historically fresh waters. Experimental and field investigations demonstrate that freshwater salinization disrupts ecosystem functions and services, causing the death of freshwater organisms and changes to nutrient conditions. Wetland habitats are one system negatively affected by salt pollution, including ephemeral wetlands (vernal pools) that fill with salt-polluted water after snowmelt. In urbanized areas, the degradation of these ecosystems could result in irreversible ecological damage including reduced water quality and a reduction in biodiversity. To investigate the effects of freshwater salinization on vernal pool communities, we exposed soils from vernal pools to water containing no salt (control), or four concentrations of three salts standardized by chloride concentration (50 mg Cl- L-1, 100 mg Cl- L-1, 200 mg Cl- L-1, and 400 mg Cl- L-1; magnesium chloride, calcium chloride, and sodium chloride). The results of this experiment suggest that emerging zooplankton communities in vernal pools are sensitive to low concentrations of salt pollution, and that alternative salts such as magnesium chloride and calcium chloride are more toxic than sodium chloride. We did not find positive or negative changes in the abundance of eukaryotic phytoplankton but did find negative effects of salt on cyanobacteria abundance, possibly due to corresponding reductions in turbidity which might be needed as a fixation site for cyanobacteria to form heterocysts. Finally, we found that salt pollution likely caused flocculation of Dissolved Organic Matter (DOM), resulting in reduced concentrations of DOM which could alter the buffering capacity of freshwater systems, light attenuation, and the populations of planktonic heterotrophs.

Residues, potential source and ecological risk assessment of polycyclic aromatic hydrocarbons (PAHs) in surface water of the East Liao River, Jilin Province, China

The environmental risks posed by polycyclic aromatic hydrocarbons (PAHs) and the diversity of their anthropogenic origins make them a global issue. Therefore, it is of utmost significance for protecting the aquatic environment and the growth of neighboring populations to identify their possible origins and ecological risk. Here, we detail the contamination profiles of 15 PAHs found in the East Liao River's surface waters in Jilin Province and use the receptor model Absolute Principal Component Analysis - Multiple Linear Regression (APCS-MLR) and diagnostic ratios method to identify the primary potential sources of pollution. Based on the natural hazard risk formation theory (NHRFT), an ecological risk assessment (ERA) model for PAHs in the East Liao River was developed. The method assesses the ecological risk status of PAHs by integrating the risk quotient (RQ) approach and the DPSIRM (driving force, pressure, state, impact, response, management) conceptual framework. Total concentrations in the surface water body were between 396.42 and 624.06 ng/L, with an average of 436.99 ng/L. The source research revealed that coal, biomass, and traffic emission sources are the most likely PAH contributors to the East Liao River. The ERA found that the majority of the sites' locations of the study were at low risk for PAHs in surface water bodies (30.7 % and 32.2 %, respectively), while only a tiny percentage of sites were at high or very high risk (1.8 % and 13.6 %). The study results provide theoretical support for the East Liao River's ecological, environmental protection, and policy formulation.

Seasonal variations in CDOM characteristics and effects of environmental factors in coastal rivers, Northeast China

Colored dissolved organic matter (CDOM) is highly spatiotemporally varied due to the effects of complex environmental factors within a catchment or system. The seasonal nutritional status and potential risks of heavy metals in the coastal rivers of the Liaohe River basin were evaluated based on 40 water samples in January, April, May, and September. Meanwhile, the effects of environmental factors on CDOM, especially human activities, were quantitatively analyzed. The trophic state index (TSI) and the potential ecological risk index (RI) of heavy metals in the Liaohe River basin exhibited significant differences. The rivers were mesotrophic in January, lightly eutrophic in May, and highly eutrophic in April and September. An extremely high RI was shown in April and May, while a high RI was exhibited in September. CDOM exhibited great seasonal characteristics and showed significant seasonal correlations with environmental factors. Based on multiple general linear model analysis, total phosphorus (TP) was the most influential factor and significantly explained 62.1% of a_CDOM(440) (p < 0.01) among the water parameters, followed by total alkalinity (38.3%). The percentages of built-up area exerted significantly positive effects on a_CDOM(440) (R² = 0.44), while distance from oil extraction sites significantly negatively affected a_CDOM(440) (r = - 0.328, p < 0.05). Polluting enterprises showed non-significant correlation with CDOM (r = 0.314, p = 0.178).

The evolution of different dissolved organic matter components and release characteristics of heavy metals in leaching process from sewage sludge under simulated rain

Pollution of municipal sewage sludge with heavy metals (HMs) inevitably causes secondary contamination, threatening ecosystems and human health. Dissolved organic matters (DOM) would serve as HMs carriers or ligands, directly influencing the transport and distribution. So it is of essential importance to simultaneously evaluate the release characteristics of HMs and DOM from MSS. In this paper, we investigated leaching characteristics of HMs (Cd, Cr, Cu, Zn, Ni, and Mn) and DOM from raw sewage sludge (RSS) and lime-conditioned sewage sludge (LCSS) under simulated rain with different acidities (pH 6.5 and 2.9) via column leaching experiments. The results showed the release of HMs could be divided into two distinct stages, a rapid decreasing changes in the early stage and a slow and steady change in the later stages with a slight increase in the middle of time. At the early stage, DOM was dominated by protein-like components (tryptophan-like, tyrosine-like). As time passed, protein-like components decreased while humic-like components (fulvic acid and humic acid) increased gradually. Protein-like components showed significant positive correlations with HMs, while humic acid-like components showed strong negative correlations with them. Moreover, the leaching efficiencies of Cd, Zn and Mn at pH 2.9 was about 1.5 times higher than that at 6.5, and the fluorescence intensity of humic-like components at pH 2.9 was higher than that at pH 6.5, suggesting that acid rain accelerated the release of HMs and the humification of DOM. Compared with the RSS, the DOM of LCSS showed noticeable differences, especially an obvious increase of the fulvic acid component. And the leaching efficiencies of Cd, Cr, Cu, Ni, and Mn in LCSS were much lower than that in RSS, indicating lime treatment retarded the release of HMs. Thus, our findings will be a guide to the treatment of HMs contaminants in MSS.

Spectral characteristics of dissolved organic carbon (DOC) derived from biomass pyrolysis: Biochar-derived DOC versus smoke-derived DOC, and their differences from natural DOC

Biochar-derived dissolved organic carbon (BDOC) and smoke-derived dissolved organic carbon (SDOC) are two different biomass-pyrogenic DOCs. They inevitably enter soil and water, then potentially pose different impacts on the chemistry of these media. This study systemically investigated the emissions and spectral characteristics of BDOC and SDOC as well as their differences from natural DOC. The results showed that the emission of SDOC was 1-3 orders of magnitude greater than that of BDOC after biomass pyrolysis. UV-vis spectra indicated that BDOC had higher aromaticity and molecular weight as well as lower polarity than SDOC. The two-dimensional correlation infrared spectrum (2D-PCIS) matrix indicated that BDOC contained more chemical groups with stronger temperature-dependence than SDOC. Fluorescence EEM-PARAFAC analysis showed that BDOC was dominated by macromolecular humic-like substances, while SDOC was primarily composed of small molecules of aromatic protein/polyphenols-like compounds. The fluorescence indicators including humification index (HIX) (0.08-0.76) and biological index (BIX) (1.18-1.72) of SDOC were significantly different from those of BDOC (HIX: 1.64-12.68, and BIX: 0.17-1.62). The higher BIX and more small molecules of aromatic protein/polyphenols-like compounds indicated SDOC had potentially higher bioavailability and turnover rate in the environment than BDOC. Furthermore, the UV-vis spectral indicator (S_275-295) and fluorescence spectral indicators (HIX, and BIX) of BDOC were equivalent to those of natural DOC, whereas these indicators of SDOC were significantly different from those of natural DOC. This study demonstrated that BDOC and SDOC had significantly different components and properties and they might present different environmental behaviors and effects.

Spatial distribution, risk assessment, and source identification of heavy metals in water from the Xiangxi River, Three Gorges Reservoir Region, China

Heavy metals (HMs) contamination in rivers has attracted wide concern due to its persistence and potential risks to the natural environment and human health. In this study, eight HMs (As, Hg, Cu, Pb, Ca, Zn, Mn, and Ni) were measured by inductively coupled plasma mass spectrometry in 24 water samples to investigate HMs contamination levels in the Xiangxi River of the Yangtze River basin. A geographic information systems kriging interpolation method was used to reveal the spatial distribution of HMs contamination. The results indicate that most HMs occurred at acceptable levels below the Surface Water Quality Standard (GB 3838-2002), with the highest concentration (23.23 mg kg^-1) of Mn being observed at sampling site X20. The values of the potential ecological risk index (RI) suggest that high potential ecological risks were present at sampling sites X1, X3, X4, X14, X16, X17, and X24, which reached moderate risk level. The highest value of RI (279.56) was observed at site X17. HM spatial distributions show that upstream pollution is more severe than downstream. The hazard index was below 1 for all HMs except for Mn, indicating that HMs in Xiangxi River pose a low risk to human health. HM source identification was accomplished using principal component analysis and Pearson's correlation. Cu, Cd, Ni, and Hg originate primarily from agriculture, while Pb, Zn, and As originate primarily from transportation and mining. This research provides a reference on the risks posed by HMs in Xiangxi River and will support efforts to protect and improve water quality in Xiangxi River.

Spatiotemporal Dynamics of Dissolved Organic Carbon and Freshwater Browning in the Zoige Alpine Wetland, Northeastern Qinghai-Tibetan Plateau

The concentrations of dissolved organic carbon (DOC) and its light-absorbing fraction (chromophoric dissolved organic matter; CDOM) in surface waters, particularly those draining organic-rich peatlands, have dramatically increased over the past decade due to climate change and human disturbance. To explore the spatiotemporal dynamics of DOC and CDOM in surface waters of the northeastern Qinghai-Tibetan Plateau, we collected water samples from two rivers in the Zoige alpine wetland and from two rivers in its adjacent alpine-gorge region, during wet and dry seasons. DOC concentration ranged from 4.82 mg·L−1 to 47.83 mg·L−1, with a mean value of 15.04 mg·L−1, 2.84 times higher than the global average. The Zoige rivers had higher DOC concentration and highly terrigenous CDOM. Significantly higher DOC concentration was observed for the Zoige rivers in the wet season compared to the dry season. In contrast, the alpine-gorge rivers had higher DOC levels in the dry season. No significant correlations were observed between DOC and CDOM at all rivers due to the influence of autochthonous sources on the alpine-gorge rivers and intensive photochemical degradation of terrigenous DOM in the Zoige rivers. Significant relationships between CDOM and specific ultraviolet absorbance at 254 nm (SUVA254) and between CDOM/DOC and SUVA254 were observed, indicating that the aromaticity of DOM in the rivers was mainly determined by CDOM. Moreover, the DOC/CDOM properties of the Hei River indicate critical human-induced water quality degradation. High DOC level and high browning degree were found in rivers in the Zoige alpine wetland, indicating that large amounts of terrigenous DOC were released to the aquatic systems of the region.

Intensive Livestock Production Causing Antibiotic Pollution in the Yinma River of Northeast China

Antibiotics are increasingly used in livestock production in rural China, raising concerns over pollution and health risk in countryside waterways. The Yinma River Basin in China’s far northeast is an agriculture-dominated area mixed with a densely populated province capitol city, providing a suitable area for investigating the influence of a typical land use mix in Northeast China on riverine antibiotic levels and transport. In this study, we sampled water along the Yinma River from upstream to downstream in a wet and a dry season and analyzed the samples for two popularly used antibiotics, ciprofloxacin (CIP) and norfloxacin (NOR). The goal of the study was to determine the spatiotemporal distribution of the antibiotics in Yinma’s two tributaries, Yitong and Yinma, which drain intensive livestock production land, and to elucidate which environmental and social factors influence the distribution of antibiotics in the cold and low mountainous areas. Water sample collection and instream measurements on dissolved oxygen and other ambient conditions were conducted at 17 locations along the Yinma and Yitong tributaries in August 2015 (wet season) and November 2015 (dry season). In addition to determining CIP and NOR levels, water samples were also analyzed for dissolved organic carbon (DOC), ammonia (NH3), and free chlorine. We found a significantly higher level of NOR when compared to CIP, indicating greater use of the first in livestock production. The level of both antibiotics was higher in the wet season (NOR: 61.063 ± 13.856 ng L−1; CIP: 3.453 ± 0.979 ng L−1) than in the dry season (57.435 ± 14.841 ng L−1; 3.091 ± 0.824 ng L−1), suggesting higher runoff of the antibiotics from the drainage area during the raining season. The level of antibiotics was higher in rural areas, especially forested and wetland areas where livestock typically graze, as well as in the lower river basin. However, the health risk of antibiotics is determined by the physical condition and lifestyle of the residents in the river basin, hence showing a higher vulnerability of the urban area than the rural area.

CDOM Absorption Properties of Natural Water Bodies along Extreme Environmental Gradients

We present absorption properties of colored dissolved organic matter (CDOM) sampled in six different water bodies along extreme altitudinal, latitudinal, and trophic state gradients. Three sites are in Norway: the mesotrophic Lysefjord (LF), Samnangerfjord (SF), and Røst Coastal Water (RCW); two sites are in China: the oligotrophic Lake Namtso (LN) and the eutrophic Bohai Sea (BS); and one site is in Uganda: the eutrophic Lake Victoria (LV). The site locations ranged from equatorial to subarctic regions, and they included water types from oligotrophic to eutrophic and altitudes from 0 m to 4700 m. The mean CDOM absorption coefficients at 440 nm [ a CDOM ( 440 ) ] and 320 nm [ a CDOM ( 320 ) ] varied in the ranges 0.063–0.35 m − 1 and 0.34–2.28 m − 1 , respectively, with highest values in LV, Uganda and the lowest in the high-altitude LN, Tibet. The mean spectral slopes S 280 − 500 and S 350 − 500 were found to vary in the ranges of 0.017–0.032 nm − 1 and 0.013–0.015 nm − 1 , respectively. The highest mean value for S 280 − 500 as well as the lowest mean value for S 350 − 500 were found in LN. Scatter plots of S 280 − 500 versus a CDOM ( 440 ) and a CDOM ( 320 ) values ranges revealed a close connection between RCW, LF, and SF on one side, and BS and LV on the other side. CDOM seems to originate from terrestrial sources in LF, SF, BS, and LV, while RCW is characterized by autochthonous-oceanic CDOM, and LN by autochthonous CDOM. Photobleaching of CDOM is prominent in LN, demonstrated by absorption towards lower wavelengths in the UV spectrum. We conclude that high altitudes, implying high levels of UV radiation and oligotrophic water conditions are most important for making a significant change in CDOM absorption properties.

Optical Properties of Dissolved Organic Matter and Controlling Factors in Dianchi Lake Waters

Characterization of dissolved organic matter (DOM) is useful in understanding environment quality and carbon cycling in the lake system. In this study, the fluorescence of DOM, major ions, and nutrients in water were investigated to understand the sources and the transformation of DOM in Dianchi Lake, the sixth largest freshwater lake in China. The dissolved organic carbon content in water above the deposition layer was higher than 5 mg C∙L−1 but lower than that in pore water. Two primary components of humic (C1) and protein-like components (C2) were identified using parallel factor (PARAFAC) modeling on sample fluorescence spectra. Organic components were related to mineral structures, and encapsulation of bacterial or algal cells into particulates could be disintegrated to release DOM. The aromaticity and the hydrophobicity of optical properties were regulated by percentages of chromophores (CDOM) of DOM in surface water, whereas by percentages of fluorophores (FDOM) in DOM in pore water, the underlying water layer was defined as a belt of transition. The molecular weight enhanced with percentages of C1 in CDOM increased in water above the sediment layer and the pore water at the northern lake site, but molecular weight attenuated with percentages decreased in pore water at the southern lake site. DOM not only originated from particulate decomposition but also derived from internal transformation among different, dissolved organic molecules. Small molecules were aggregated into larger ones, and, conversely, large molecules decomposed into small sizes. Another speculation is that dissolved molecules adsorbed or were encapsulated into particulates or were degraded and released into dissolved phases. The precise factors regulated composition, structure, and spectral properties of dissolved organic matter in the Dianchi Lake. This study highlights that sources of DOM and transformation mechanisms in the lake water could be correlated with nutrients and primary geochemical factors for mobility and distribution in different water compartments.

Contaminants of emerging concern in a freeze-thaw river during the spring flood

Pharmaceuticals, personal care products, and environment estrogens, as contaminants of emerging concern (CECs), have been widely detected in aquatic environments around the world. However, surveys of seasonal freeze-thaw rivers with special hydrological features are limited. To address this, in this study the occurrence, distribution, ecological risk, and mass flux of 22 CECs in the Jilin Songhua River in northeast China, a famously seasonal freeze-thaw river at mid- and high-latitude regions, were investigated during its spring flood period. The results indicate that estriol had a maximum concentration of 27.4 ng·L^-1 in the mainstream river water. Doxycycline had a maximum concentration of 204.4 ng·L^-1 in the tributary river water and 103.0 ng·L^-1 in the riverine wastewater treatment plant (WWTP) effluents. The mean concentrations of the targeted CECs in the spring flood were 1.4 times higher than those found in our previous investigation during the summer flood. A risk assessment showed that estrone posed a high risk in the mainstream, doxycycline posed a high risk in the tributaries, and ofloxacin posed a high risk in the riverine WWTP effluents. In addition, erythromycin and lincomycin posed a medium to high risk in the river water and WWTP effluents. The major contribution of the CECs in the mainstream came from its tributaries, which contributed a total of >50% in the spring flood period. The results suggest that some appropriate measures should be taken to reduce the contribution of the CECs from the tributaries to the seasonal freeze-thaw river in its spring flood period.

Terrestrial humic-like fluorescence peak of chromophoric dissolved organic matter as a new potential indicator tracing the antibiotics in typical polluted watershed

Natural surface waters are threatened globally by antibiotics pollution. In this study, we analyzed antibiotics and CDOM (Chromophoric dissolved organic matter) fluorescence in different water bodies using HPLC method and Excitation Emission Matrix- Parallel factor analysis, respectively. A combination of field studies in the Yinma River Watershed were conducted in rivers, reservoirs and urban rivers, and 65 CDOM and antibiotic samples were taken in April, May, July, and August 2016. EEM-PARAFAC analysis identified two components; a humic-like (C1) component and a tryptophan-like (C2) component. The redundancy analysis (RDA) demonstrated that CDOM could explain 38.2% (two axes) of the five antibiotics in reservoirs (N = 31), and 26.0% (two axes) of those in rivers and urban water (N = 30). Furthermore, the Pearson correlation coefficient between Sulfamethoxazole and C1 in reservoir water was 0.91 (t-test, 2-tailed, p < 0.01), and that between Sulfamethoxazole and C2 was 0.68 (t-test, 2-tailed, p < 0.01). This indicated that the humic-like component of CDOM PARAFAC fluorescence could detect Sulfamethoxazole contamination levels in the homogenized reservoir waters. Our results identified Sulfamethoxazole and Quinolones (Norfloxacin, 16.5 ng L^-1; Enrofloxacin, 0.3 ng L^-1; Ciprofloxacin, 30.9 ng L^-1) at mean concentrations of 369.5 ng L^-1 and 15.9 ng L^-1, respectively, which were the higher levels in natural surface waters. The FTIR spectroscopy of the mixture of humic acid and sulfamethoxazole showed that the absorbance at 3415 cm^-1 linked to OH stretching of OH groups and at 1386 cm^-1 because of OH bending and vibration of COOH groups became weaker, indicating that COOH groups of humic acid can adsorb and react with -NH₂ of sulfamethoxazole. The CDOM PARAFAC components can be adapted for online or in situ fluorescence measurements as an early warning of Sulfamethoxazole distribution and contamination in similar aquatic environments.

Evaluation of CDOM sources and their links with antibiotics in the rivers dividing China and North Korea using fluorescence spectroscopy

Rivers act as carriers where active cycling of chromophoric dissolved organic matter (CDOM) affected by anthropogenic activities and land cover variation may occur. Little is known about the optical properties of CDOM in relation to antibiotics; these properties could provide valuable insights into CDOM transformation processes and biogeochemical reactivity. The spatial distribution of CDOM absorption, fluorescence intensities of CDOM components, and correlations between fluorescence indices (FI₃₇₀, humification index (HIX)) and biological index (BIX)) with water quality and antibiotics were investigated in three rivers, namely, two rivers (Yalu River and Tumen River) dividing China and North Korea, and the Songhua River. Four humic-like components (C1 and C3-5), and one tryptophan-like component (C2), were identified via fluorescence excitation-emission matrices-parallel factor analysis (EEM-PARAFAC). The correlation between F_max for five EEM-PARAFAC extracted CDOM components, C1-C5, FI₃₇₀, HIX, BIX, and water quality parameters, and four antibiotics (i.e., Norfloxacin, Enrofloxacin, Sulfamethoxazole and Metronidazole), were determined through a redundancy analysis (RDA), with species-environment correlations of 0.887 and 0.833, respectively. The results showed that spatial variation in land cover, pollution sources, and terrestrial contribution in water quality affected F_max for the fluorescent components C1-C5 and the fluorescence indices, indicating a high diverse chemical composition and transformation history. The F_max for terrestrial humic-like components, C4 and C5, showed spatial variation depending on land cover and anthropogenic impacts. Further correlation and regression analyses indicated that CDOM soil fulvic-like component C5 correlated with Sulfamethoxazole and Metronidazole (t test, p < 0.01). Our results indicate that the spatial distributions of F_max for CDOM fluorescent terrestrial components, evaluated by EEM-PARAFAC, have potential implications for the monitoring of Sulfamethoxazole and Metronidazole in surface waters. Further, these findings can be used to understand the biogeochemical cycling of CDOM and its effects on antibiotics pollution in the environment.

Characterizing fluvial heavy metal pollutions under different rainfall conditions: Implication for aquatic environment protection

Globally, fluvial heavy metal (HM) pollution has recently become an increasingly severe problem. However, few studies have investigated the variational characteristics of fluvial HMs after rain over long periods (≥1 year). The Dakan River in Xili Reservoir watershed (China) was selected as a case study to investigate pollution levels, influencing factors, and sources of HMs under different rainfall conditions during 2015 and 2016. Fluvial HMs showed evident spatiotemporal variations attributable to the coupled effects of pollution generation and rainfall diffusion. Fluvial HM concentrations were significantly associated with rainfall characteristics (e.g., rainfall intensity, rainfall amount, and antecedent dry period) and river flow, which influenced the generation and the transmission of fluvial HMs in various ways. Moreover, this interrelationship depended considerably on the HM type and particle size distribution. Mn, Pb, Cr, and Ni were major contributors to high values of the comprehensive pollution index; therefore, they should be afforded special attention. Additionally, quantitative source apportionment of fluvial HMs was conducted by combining principal component analysis with multiple linear regression and chemical mass balance models to obtain comprehensive source profiles. Finally, an environment-friendly control strategy coupling "source elimination" and "transport barriers" was proposed for aquatic environment protection.

The relationship of chromophoric dissolved organic matter parallel factor analysis fluorescence and polycyclic aromatic hydrocarbons in natural surface waters

Polycyclic aromatic hydrocarbons (PAHs), a large group of persistent organic pollutants (POPs), have caused wide environmental pollution and ecological effects. Chromophoric dissolved organic matter (CDOM), which consists of complex compounds, was seen as a proxy of water quality. An attempt was made to understand the relationships of CDOM absorption parameters and parallel factor analysis (PARAFAC) components with PAHs under seasonal variation in the riverine, reservoir, and urban waters of the Yinma River watershed in 2016. These different types of water bodies provided wide CDOM and PAHs concentration ranges with CDOM absorption coefficients at a wavelength of 350 nm (a _CDOM(350)) of 1.17-20.74 m^-1 and total PAHs of 0-1829 ng/L. CDOM excitation-emission matrix (EEM) presented two fluorescent components, e.g., terrestrial humic-like (C1) and tryptophan-like (C2) were identified using PARAFAC. Tryptophan-like associated protein-like fluorescence often dominates the EEM signatures of sewage samples. Our finding is that seasonal CDOM EEM-PARAFAC and PAHs concentration showed consistent tendency indicated that PAHs were un-ignorable pollutants. However, the disparities in seasonal CDOM-PAH relationships relate to the similar sources of CDOM and PAHs, and the proportion of PAHs in CDOM. Overlooked and poorly appreciated, quantifying the relationship between CDOM and PAHs has important implications, because these results simplify ecological and health-based risk assessment of pollutants compared to the traditional chemical measurements.

Dynamics and ecological risk assessment of chromophoric dissolved organic matter in the Yinma River Watershed: Rivers, reservoirs, and urban waters

The extensive use of a geographic information system (GIS) and remote sensing in ecological risk assessment from a spatiotemporal perspective complements ecological environment management. Chromophoric dissolved organic matter (CDOM), which is a complex mixture of organic matter that can be estimated via remote sensing, carries and produces carcinogenic disinfection by-products and organic pollutants in various aquatic environments. This paper reports the first ecological risk assessment, which was conducted in 2016, of CDOM in the Yinma River watershed including riverine waters, reservoir waters, and urban waters. Referring to the risk formation theory of natural disaster, the entropy evaluation method and DPSIR (driving force-pressure-state-impact-response) framework were coupled to establish a hazard and vulnerability index with multisource data, i.e., meteorological, remote sensing, experimental, and socioeconomic data, of this watershed. This ecological vulnerability assessment indicator system contains 23 indicators with respect to ecological sensitivity, ecological pressure, and self-resilience. The characteristics of CDOM absorption parameters from different waters showed higher aromatic content and molecular weights in May because of increased terrestrial inputs. The assessment results indicated that the overall ecosystem risk in the study area was focused in the extremely, heavily, and moderately vulnerable regions. The ecological risk assessment results objectively reflect the regional ecological environment and demonstrate the potential of ecological risk assessment of pollutants over traditional chemical measurements.