Unraveling the sources and fluorescence compositions of dissolved and particulate organic matter (DOM and POM) in Lake Taihu, China

Chlorination of Biopterin in Water: Deciphering the Kinetics, Disinfection Byproducts, and Toxicity

Pterins, including biopterin prevalent during cyanobacterial blooms, are nitrogen-containing heterocyclic compounds ubiquitous in both natural and engineered environments. However, their roles and associated human risks in water treatment remain poorly understood. This study systematically investigated the kinetics, disinfection byproducts (DBPs), and toxicity of biopterin in chlorination. For deciphering the reaction kinetics, 1,3,5-trimethoxybenzene proved to be a more effective chlorine quencher than the commonly used reducing agents, as it preserved N-chlorinated intermediates without reversing them back to biopterin. The pH-dependent kinetics demonstrated that both chlorine and biopterin species had a significant influence on the reaction rates, with deprotonated biopterin exhibiting a markedly higher reactivity toward HClO/ClO-. Based on time-of-flight mass spectrometry, ten transformation products (TPs) including seven halogenated N-Cl ones, have been identified for the first time. These cyclic TPs were transformed into various aliphatic carbonaceous and nitrogenous DBPs during the subsequent chlorination process. Notably, theoretical predictions and the luminescent bacteria assay confirmed potential higher toxicities of these products than biopterin. These findings highlight the potential risks of pterins during water disinfection and provide a reference framework for accurately revealing the chlorination behavior of emerging nitrogenous chemicals.

Effects of acid mine drainage on photochemical and biological degradation of dissolved organic matter in karst river water

Dissolved organic matter (DOM) can be removed or transformed by photochemical and biological processes, producing the negative effect of transforming organic carbon into inorganic carbon, which plays a vital role in the karst carbon cycle. However, acid mine drainage (AMD) will affect this process, so the degradation of DOM in karst river water (KRW) needs to be studied in this context. In this study, to reveal the evolution processes of DOM under photochemical and biological conditions in AMD-impacted KRW, AMD and KRW were mixed in different ratios under conditions of visible light irradiation (VL), biodegradation (BD), ultraviolet irradiation (UV) and ultraviolet irradiation + biodegradation (UV+BD). The average DOC concentrations in samples after mixing AMD and KRW in different proportions decreased significantly (by 23%) in UV+BD, which was 1.2-1.4 times higher than under the other conditions and would lead to a significant release of inorganic carbon. Further analysis of the fluorescence parameters via parallel factor analysis (PARAFAC) revealed that the DOM fluorescence components in AMD comprised mainly protein-like substances derived from autochthonous components, while the DOM fluorescence components in KRW were mainly humic-like substances with both autochthonous and allochthonous sources. Therefore, AMD could promote both the photochemical and biological degradation of DOM in karst receiving streams, resulting in the conversion of DOC to inorganic carbon. The results showed that the synergistic effects of UV+BD and AMD accelerated the degradation of DOM and the release of inorganic carbon in KRW, thus affecting the stability of the karst carbon cycle.

Distribution pattern of dissolved organic matter in pore water of sediments from three typical areas of western Lake Taihu and its environmental implications

The migration, transformation, and accumulation of dissolved organic matter (DOM) in pore water of sediment cores play a pivotal role in lacustrine carbon cycling. In order to understand the dynamics of DOM in the sediments of large shallow eutrophic lakes, we examined the vertical profiles of DOM and the benthic fluxes of dissolved organic carbon (DOC) in sediment cores located in algae accumulated, dredged, and central areas of eutrophic Lake Taihu, China. Optical properties showed the significant influence of terrestrial inputs on the DOM components of pore water in the algae accumulated area but an abundant accumulation of autochthonous DOM in the central area. The benthic fluxes of DOC ranging from -458.2 to -139.4 mg·m-2·d-1 in the algae accumulated area displayed an opposite diffusion direction to the other two areas. The flux ranges of 9.5-31.2 mg·m-2·d-1 in the dredged area and 14.6-48.0 mg·m-2·d-1 in the central area were relatively smaller than those in the previously reported lake ecosystems with low trophic levels. Dredging engineering disturbed the pre-dredging distribution patterns of DOM in sediment cores. The deposition, accumulation, and transformation of massive algae scums in eutrophic lakes probably promoted the humification degree of sediments.

Response mechanism of sediment organic matter of plateau lakes in cold and arid regions to climate change: a case study of Hulun Lake, China

Lake organic matter is one of the important forms of terrestrial carbon, and its sedimentary evolution is affected by many factors such as climate and sources. However, few studies have been conducted on the feedback mechanism of the sedimentary evolution of organic matter to climate change in cold and arid lakes. Historical variations and compositions of sources of the sediment organic matter (SOM) of Hulun Lake, a typical lake in the cold and arid region of China, were studied by multiple methods. The interactions and fee7dback mechanisms between the sedimentary evolution of SOM and climate change, and compositions of SOM source change, were also discussed. Overall, the characteristic indexes of the SOM, including total organic carbon (TOC), carbon stable isotope (δ¹³C), carbon to nitrogen ratio (C/N), and fluorescence intensity (FI) of the protein-like component in water extractable organic matter (WEOM), showed obvious and uniform characteristics of periodical changes. The indexes were relatively stable before 1920, and fluctuated from 1920 to 1979. Since the 1980s, values of TOC, δ¹³C, and FI of the protein-like component in WEOM has increased, while C/N decreased. The absolute dominant contribution of terrestrial source to the SOM had changed, and the relative average contribution rate of autochthonous source increased from 17.6% before 1920 to 36.9% after 2000. The increase of temperature, strong evaporation concentration effect, and change of compositions of SOM sources are the important driving factors of the sedimentary evolution of organic matter in Hulun Lake.

Differences in the composition, source, and stability of suspended particulate matter and sediment organic matter in Hulun Lake, China

The occurrence, migration, transformation, and stability of sediment (SOM) and suspended particulate (SPOM) organic matters have important effects on the environmental behaviors of carbon, nitrogen, phosphorus, and other pollutants in a water environment. The content, composition, fluorescence characteristics, source, and stability of SOM and SPOM in Hulun Lake, a typical lake in cold and arid region of China, were compared by sequential extraction, three-dimensional fluorescence spectroscopy, parallel factor technique, carbon-nitrogen ratio, and stable carbon isotope. Contents of SOM and SPOM in north and west were higher than those in east and south. The average content of SPOM (24.70 ± 4.63 g/kg) was slightly higher than that of SOM (23.04 ± 10.27 g/kg), but the difference was not significant. Humin was the dominant component in SOM and SPOM, accounting for 73.7% and 61.2%, respectively. Humus was the main fluorescence component of water-extractable organic matter in SOM and SPOM, accounting for 79.9% and 70.4%, respectively, of the total fluorescence intensity. SOM and SPOM were derived from terrestrial sources with a relative contribution rate of about 70%. SPOM was more influenced by autochthonous sources and had a significantly lower humification degree and stability than SOM. Effects of climate changes on migration, transformation, stability, and bioavailability of organic matters and endogenous pollutants closely related to organic matters in lakes of cold and arid regions should be paid attention in the future.

Comparison of organic matter (OM) pools in water, suspended particulate matter, and sediments in eutrophic Lake Taihu, China: Implication for dissolved OM tracking, assessment, and management

Suspended particulate matter (SPM) and sediments are important sources of dissolved organic matter (DOM) in lake water. However, studies on what extent and how both sources affect DOM composition are lacking, which hampers DOM management. Herein, DOM, SPM-extracted particulate organic matter (POM), and sediment-extracted organic matter (SOM) were characterized and compared in terms of absorption spectral properties and chemical composition in Lake Taihu, a large cyanobacterial bloom-affected shallow lake. A statistical method was proposed to quantify the similarity of organic matter (OM) in the different states and to evaluate the potential effects of SPM and sediments on DOM. Results showed that POM and DOM were mainly composed of small-molecular-size and low-humified organic components (i.e., 27 %-38 % tryptophan-like and ~30 % protein-like substances), and most of them were derived from autochthonous sources. While tyrosine-like (57 %) and humic-like (27 %) substances were dominant in SOM. The OM similarity between POM and DOM was approximately 1.5 times higher than that between SOM and DOM, indicating the greater effect of SPM than sediments on DOM composition. High pH and low nitrogen (e.g., nitrate and ammonia) were positively correlated to the OM similarity between POM and DOM. Further, the findings indicated that nitrogen limitation enhanced the OM exchange between POM and DOM by promoting the production of extracellular polymeric substances (EPS) in cyanobacterial aggregates. The obtained findings highlighted the importance of SPM in shaping the DOM composition relative to sediments and facilitating the DOM management in bloom-affected lakes.

Effect of colloidal fluorescence properties on the complexation of chloramphenicol and carbamazepine to the natural aquatic colloids

The complexation mechanism between pharmaceuticals and natural colloids is still uncertain due to the complexity, heterogeneity, and polydispersity of colloids. Therefore, this study investigated the effect of fluorescence properties on the complexation of chloramphenicol (CAP) and carbamazepine (CBZ) to the colloids from Poyang Lake Basin based on the multiple spectroscopic techniques and methods. Three-dimensional excitation-emission matrix fluorescence spectroscopy-parallel factor analysis results illustrated that two humic-like components and two protein-like components of colloids from the rivers and lakes were identified, with the much higher fluorescence intensity of the protein-like substance observed in lake samples. The protein-like substance decreased dramatically with the addition of CAP and CBZ, suggesting its higher binding capacity towards these drugs, especially for CBZ. In addition, the fluorescence quenching titration was proceeded to explore the binding mechanism between the colloids and the pharmaceuticals. Results of synchronous fluorescence spectra and two-dimensional correlation spectroscopy demonstrated that the fluorescence quenching effect occurred preferentially between the protein-like substances and the pharmaceuticals, with the stronger complexation for CBZ. Ryan-Weber model fitting results showed that the stability constant ranged from 4.02 to 5.04 with the higher binding capacity observed for the tryptophan-like substance. Combined, the fluorescence components in aquatic colloids could be significantly impacted the complexation of the pharmaceuticals. This study provides deep insights into the fate and pollution protection of pharmaceuticals.

Exploring applicability of end member mixing approach for predicting environmental reactivity of dissolved organic matter

Despite the wide applications of end member mixing analysis (EMMA) for assigning the sources of dissolved organic matter (DOM) in aquatic environment, there was no study attempting to test the applicability of EMMA for predicting environmental reactivity of DOM. This study aimed to explore the feasibility of EMMA, or the concept of ideal mixing behavior of end members, for describing several well-known DOM reactivities using two DOM end member sources (i.e., soil and algae) at varying mixing ratios. The selected DOM reactivities were trihalomethane formation potential (THMFP), mineral adsorption amount, pyrene binding, membrane resistance, and biodegradation potential. Among the tested DOM functions, all were found to follow the ideal mixing behavior, presenting the linear relationships between the source mixing ratios and the tested reactivity with the R² value of >0.80. The ideal mixing behavior of the DOM functions was more pronounced than that based on several spectroscopic indicators derived from UV absorption and fluorescence spectroscopy. This study provided insight into potential applicability and limitation of EMMA approach in monitoring and predicting environmental functions of DOM in aquatic systems where identified DOM sources are mixed and vary dynamically with the mixing ratios.

Effects of C/N ratio variation in swine biogas slurry on soil dissolved organic matter: Content and fluorescence characteristics

Nutrient-rich biogas slurry shows favorable prospects for application as an organic fertilizer in farmland. At the same time, due to differing sources and treatment methods, the C/N ratio of biogas slurry varies greatly. The effect of differences in C/N of biogas slurry on soil organic matter properties remains unclear. In this experiment, pig farm biogas slurry differing in C/N (3, 6, 8.84 and 12) was applied instead of fertilizer. Fluorescence spectroscopy combined with parallel factor analysis and principal component analysis were used to determine dissolved organic carbon (DOC) and fluorescent dissolved organic matter (FDOM) in soil dissolved organic matter (DOM). The experimental results showed that the DOC and FDOM contents of soil could be significantly increased at the initial stage of biogas slurry application. Compared with CK, on the 60th day, biogas slurry with a C/N of 12 exhibited the greatest improvement in DOC, FDOM as well as for Component 1, Component 2 and Component 3 contents in soil FDOM, 40.93%, 66.25%, 65.35%, 40.47%, and 78.42% respectively. However, compared with the 0th day, by the 60th day, biogas slurry with a C/N of 8.84 exhibited the greatest decrease in Component 4 content in soil FDOM, 74.68%. Biogas slurry with a C/N of 8.84 exerted the greatest promotion effect on corn growth, the utilization and transformation of Component 4 by plants and microorganisms in the soil. And it showed the strongest improvement in the degree of FDOM humification in the soil, the humification index increased from 4.16 ± 0.17 to 4.92 ± 0.58, compared with CK. This study provided new insights for the utilization of biogas slurry with respect to soil physical and chemical properties and maize plant growth.

Geographical location and water depth are important driving factors for the differences of suspended particulate organic matter (SPOM) in lake environment across nationwide scale: Evidences from n-alkane fingerprints

Suspended particulate organic matter (SPOM) plays a connective role in global biogeochemical carbon cycles and energy flows in aquatic ecosystems. However, little is known about the occurrence and source of SPOM in lake environment and their driving factors across nationwide scale. Here, we utilize the molecular markers of n-alkanes and their fingerprints in 46 typical lakes and reservoirs with different water depths across China from both sides of the Hu Line to study this issue. Σ₂₉n-alkanes, Σ biogenic n-alkanes and Σ anthropogenic n-alkanes ranged from 104.8 to 10332 ng·L^-1, from 88.5 to 4843 ng·L^-1, and from 16.2 to 5488 ng·L^-1, respectively. Their occurrences were only associated with water depth. Then, we compared the differences of carbon-chain distribution of both biogenic and anthropogenic n-alkanes and related proxies in different lake groups. The profiles of different biogenic and anthropogenic n-alkanes posed large differences in different lake groups. Finally, linear discriminant analysis (LDA) was applied to test the possible effects of geographical location and water depth on the holistic differences of SPOM in different lakes and reservoirs across China. The results illustrated that both geographical location and water depth were important driving factors for the holistic differences of SPOM in different lakes and reservoirs across China. Intensive anthropogenic activities narrowed the differences between shallow and deep lakes in eastern China. In conclusion, this study provided new insights into the driving factor analysis of SPOM in lakes and reservoirs on large scale.

Sources and selective preservation of organic matter in the karst watershed: evidence from sediment records in a plateau deep lake, Southwestern China

Human activities have greatly altered terrestrial carbon (C) dynamics associated with vegetation cover and land use changes, thereby influencing the C sink in downstream ecosystems. However, the transport and preservation of organic C from soils that experience serious erosion in the karst area are scarce, particularly at catchment scales. In this study, chemical characteristics of organic matter (OM) isolated from the topsoil, overlying water, and lake sediments, as well as subsequent source identification, were inferred from the molecular, spectroscopic, and carbon isotopic (δ¹³C) signatures in a typical karst catchment, Southwestern China. The results indicated that the elemental compositions of the calcareous soil and paddy soil significantly differed from the yellow soil. High similarities existed in the fluorescence spectra of humic substances (HS) extracted from the front two soil types with those of lake sediments, indicating the homogeneous nature of OM molecular structure. The C/N ratios of six dissolved OM fractions and sedimentary HS along with δ¹³C values consistently reflected the primary terrestrial source. It was estimated to account for 60% of total organic C in sedimentary OM by end-member mixing modeling in accordance with soil erosion intensity and large recharge coefficient of this catchment. The evolution of soil loss and lake productivity can be well deduced from sediment records of organic C content, C/N ratio, and the specific information of HS. This research highlighted that the composition, source, and fate of OM in the karst lake was mainly dominated by the terrestrial C flux, rather than in-lake production. Furthermore, soil type and erosion intensity have significant effects on the nature of eroded OM and ultimate preservation.

Refractory Humic-like Substances: Tracking Environmental Impacts of Anthropogenic Groundwater Recharge

To unravel the crucial components of natural organic matter that respond to the process of anthropogenic groundwater recharge (AGR) from different recharge water sources, dissolved organic matter (DOM) and base-extractable particulate organic matter (POM) in groundwater and surface water were analyzed using excitation-emission matrix spectroscopy coupled with parallel factor analysis (EEM-PARAFAC). The EEM and traditional spectral indices of samples show that the fluorescent intensity, molecular weight, and humification degree of the DOM were relatively higher than those of the POM, and the groundwater in the reclaimed water recharge area (RWRA) was more contaminated than in the south-to-north water recharge area (SNWRA). PARAFAC analysis indicates that the DOM was dominated by an allochthonous humic-like substance (C1), whereas the POM was dominated by tryptophan-like substances associated with microbial activity (C2). Partitioning of PARAFAC components between DOM and POM showed that the humic-like substances (C1 and C4) were more likely to be distributed into a dissolved phase compared to the protein-like substances (C2 and C3), which suggested the potential use of C1 and C4 as a tracking indicator. In particular, the clear gradient distributions along both the hydrogeological profile and different aquifer systems in terms of the concentration and composition of C1 also discriminated between the RWRA and SNWRA with regard to the effects of various AGRs on the groundwater. The association between C1 and water-quality indicators revealed by principal component analysis further indicated that refractory humic-like substances would track the environmental impacts of intentional AGR processes.

Comparing the performance of three methods to assess DOM dynamics within two distinct glacierized watersheds of the tropical Andes

Dissolved organic matter (DOM) is recognized as a good indicator of water quality as its concentration is influenced by land use, rainwater, windborne material and anthropogenic activities. Recent technological advances make it possible to characterize fluorescent dissolved organic matter (FDOM), the fraction of DOM that fluoresces. Among these advances, portable fluorometers and benchtop fluorescence excitation and emission spectroscopy coupled with a parallel factor analysis (EEM-PARAFAC) have shown to be reliable. Despite their rising popularity, there is still a need to evaluate the extent to which these techniques can assess DOM dynamics at the watershed scale. We compare the performance of in-situ measurements of FDOM with laboratory measurements of fluorescence spectroscopy within the context of two distinct glacierized watersheds in Peru. Glacierized watersheds represent unique testing environments with contrasting DOM conditions, flowing from pristine, vegetation-free headwaters through locations with obvious anthropogenic influences. We used an in-situ fluorometer and a portable multimeter to take 38 measurements of FDOM, pH and turbidity throughout the two catchments. Additionally, samples were analyzed in the laboratory using the EEM-PARAFAC method. Results were compared to dissolved organic carbon (DOC) measurements using standard high-temperature catalytic oxidation. Our results show that the three techniques together were able to capture the DOM dynamics for both studied watersheds. Taken individually, all three methods allowed detection of the watershed DOM main points of sources but in a more limited way. Due to the narrow bandwidth of the portable fluorometer used in the study, FDOM measurements were almost non-detectable to protein-like substances. Indeed, the more demanding EEM-PARAFAC was able to both differentiate between potential sources of DOM and provide an estimate of relative concentrations of different organic components. Finally, similar to FDOM but to a lesser extent, the DOC measurements showed some limits where protein-like substances make up most of the DOM composition.

Characteristics of Dissolved Organic Matter and Its Role in Lake Eutrophication at the Early Stage of Algal Blooms—A Case Study of Lake Taihu, China

Decaying algal blooms in eutrophic lakes can introduce organic matter into the water and change nutrient concentrations in the water column. The spatial distribution and composition characteristics, sources, and contribution to eutrophication of dissolved organic matter (DOM) in the overlying water of Lake Taihu, a typical eutrophic lake in China, were analyzed by ultraviolet–visible spectra and three-dimensional fluorescence excitation–emission matrix spectra combined with the statistical decomposition technique, parallel factor analysis. The concentration of DOM was represented by dissolved organic carbon (DOC), and DOC in overlying water of Lake Taihu was 2.86–11.83 mg/L. The colored DOM (CDOM) was characterized by an absorption coefficient at 280 nm (a280) and 350 nm (a350), which were 6.63–29.87 and 1.84–10.41 m−1, respectively. These values showed an increasing trend from southeast to northwest, and the high values were concentrated in the northwest and northern lake areas. The parallel factor analysis (PARAFAC) identified two protein-like (C1: tyrosine-like and C2: tryptophan-like) and one humic-like (C3: humic acid and fulvic acid) fluorescence components for fluorescent DOM (FDOM). The most dominant components were protein-like components (C1 + C2), whose fluorescence intensity contributed 87.55% ± 3.39% to the total fluorescence intensity (Ft) of FDOM (3.38 R.U.). The mean value of the fluorescence index (FI) and index of recent autochthonous contribution (BIX) of DOM was 1.77 and 0.92, and DOC, a280 and fluorescence intensities of FDOM components were all significantly and positively correlated with chl. a, indicating that DOM, CDOM, and FDOM were all mainly derived from algal activities and metabolites. The average humification index of the DOM was 0.66, which indicated a low humification degree. The protein-like DOM was correlated with DON and DOP, and might make great contributions to the continuous occurrence of algal blooms.

Characterizing the interactions between sediment dissolved organic matter and zinc using multispectroscopic techniques

Sediment dissolved organic matter (DOM) was collected in November 2018 from Lake Dongping, China. The lake was divided into the entrance of the Dawen River, the open region of the lake, the tourism district and the macrophyte-dominated region based on principal component analysis (PCA) of 9 DOM-related parameters. Multispectroscopic tools were used to investigate the binding of zinc (Zn) with four kinds of DOM collected from the entrance of the Dawen River (EDOM), the open area of the lake (ODOM), the macrophyte-dominated area (mainly dominated by Potamogeton crispus L.) (PDOM) and the tourism district (TDOM). Three fluorescent components, the humic-like (components 1 and 3) and protein-like (component 2) components, were found by excitation-emission matrix spectra with parallel factor analysis. The EDOM, ODOM and TDOM were controlled by protein-like components, and the PDOM was controlled by humic-like components. Different components respond differently to Zn addition. The binding order of the tyrosine-like fraction > the tryptophan fraction > the humic-like fraction was identified by Synchronous fluorescence (SF) spectra and two-dimensional correlation spectroscopy (2D-COS). The fluorescence intensity of the protein-like component was suppressed, and the humic-like component was enhanced with the addition of Zn. The effective quenching constants (log K) of the protein-like component in PDOM were clearly higher than those in the EDOM, ODOM and TDOM, indicating higher metal binding potential in PDOM than in other kinds of DOM in Lake Dongping. The %F_max (the amounts of each component measured as % of the total fluorescence maxima for the three components) of the humic-like components exhibited a gradual increase in all kinds of DOM with the addition of Zn, suggesting that the addition of Zn increased the humification of DOM.

Characteristics and influencing factors of hydrochemistry and dissolved organic matter in typical karst water system

The unique hydrogeological conditions of karst area make the groundwater react rapidly to rainfall events, which makes the groundwater more susceptible to anthropogenic pollutions. The current study based on a combined excitation-emission matrix fluorescence spectroscopy and parallel factor analysis (EEM-PARAFAC) and geochemical-statistical investigation of water samples from the karst water system in Xintian County, Hunan Province, China, gives crucial information about the principal factors influencing karst water hydrochemistry and dissolved organic matter (DOM). The analyzed data revealed that both surface water and descending spring samples were within the Ca-Mg-HCO₃ water type and dominated by humic-like fluorophore, and well water samples were within both the Ca-Mg-HCO₃ and Na-HCO₃ water types and controlled by protein-like fluorophore. The chemical compositions of surface water and descending springs were mainly influenced by the weathering of silicate, carbonate, and evaporate rocks and precipitation. In addition to be affected by the weathering of silicate, carbonate, and evaporate rocks and precipitation, the well water was also impacted by ion exchange and other activities like anthropogenic. The DOM in the karst water system was affected by allochthonous and autochthonous inputs as well as the chemical compositions of the water.

Effects of fish culture on particulate organic matter in a reservoir-type river as revealed by absorption spectroscopy and fluorescence EEM-PARAFAC

Dam construction and fish culture can change the biogeochemical processes in river, yet their impact on the spectral properties of particulate organic matter (POM) remains to be studied. This was investigated in a reservoir-type river (Minjiang river, SE China) using absorption spectroscopy and fluorescence excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC). Five fluorescent components were identified from POM with PARAFAC. Four components C1-C4 were affected by the seasonal variations of rainfall and runoff, indicating the influences of hydrological condition and terrestrial inputs. The Chlorophyll a concentration (Chl a) correlated significantly with the humic-like C3 (p < 0.05) and the protein-like C4 (p < 0.01), indicating phytoplankton was an important source of C3 and C4. The Chl a and fluorescence intensities of C3-C4 were higher in the fish culture zones than in other areas, and the absorption coefficient a₃₀₀ and C1-C4 were lower downstream the dam. These results indicated that fish farming in the reservoir probably promoted the production of POM. The a₃₀₀ and C1 per unit mass of suspended particulate matter (a₃₀₀/TSM and C1/TSM) correlated significantly with the median particle size (p < 0.01), which might be related to the contribution of micro-phytoplankton. The absorption spectra of POM showed a shoulder peak at ∼280 nm, and its intensity correlated significantly and positively with Chl a (p < 0.01). These results indicated that the peak was probably derived from phytoplankton production. Our results have implications for better understanding the influences of human activities on the dynamics of river POM.