Degradation Of DOM Research Articles

Composition of Stream Dissolved Organic Matter Across Canadian Forested Ecozones Varies in Three Dimensions Linked to Landscape and Climate

AbstractDissolved organic matter (DOM) is a key variable influencing aquatic ecosystem processes. The concentration and composition of DOM in streams depend on both the delivery of DOM from terrestrial sources and on aquatic DOM production and degradation. However, there is limited understanding of the variability of stream DOM composition at continental scales and the influence of landscape characteristics and disturbances on DOM across different regions. We assessed DOM composition in 52 streams at seven research sites across six forested ecozones in Canada in 2019–2022 using 26 indices derived from five analytical approaches: absorbance and fluorescence spectroscopy, liquid chromatography—organic carbon detection, Fourier‐transform ion cyclotron resonance mass spectrometry, and asymmetric flow field‐flow fractionation. Combined analyses showed clear clustering and redundancy across analytical techniques, and indicated that compositional variations were primarily related to three axes of DOM composition: (a) aromaticity, which was greater in low‐relief, wetland‐dominated catchments, (b) oxygenation, which was greater in colder and drier ecozones, and (c) biopolymer content, which was greater in lake‐influenced catchments. Variability in DOM composition among research sites was greater than variability of streams within a site and variability over time within a stream. Forest harvesting and wildfire disturbances had no common influence on DOM composition across research sites, emphasizing the need for regional studies. Our study provides a broad understanding of the variability of stream DOM composition and its associations with landscape and catchment characteristics at a subcontinental scale, and provides key insights for the choice and interpretation of DOM indices from various analytical approaches.

Characteristics of dissolved organic matter contribute to Geogenic ammonium enrichment in coastal versus alluvial-lacustrine aquifers

Elevated concentration levels of geogenic ammonium in groundwater arise from the mineralization of nitrogen-containing natural organic matter in various geological settings worldwide, especially in alluvial-lacustrine and coastal environments. However, the difference in enrichment mechanisms of geogenic ammonium between these two types of aquifers remains poorly understood. To address this knowledge gap, we investigated two representative aquifer systems in central Yangtze (Dongting Lake Plain, DTP) and southern China (Pearl River Delta, PRD) with contrasting geogenic ammonium contents. The use of optical and molecular characterization of DOM combined with hydrochemistry and stable carbon isotopes has revealed differences in DOM between the two types of aquifer systems and revealed contrasting controls of DOM on ammonium enrichment. The results indicated higher humification and degradation of DOM in DTP groundwater, characterized by abundant highly unsaturated compounds. The degradation of DOM and nitrogen-containing DOM was dominated by highly unsaturated compounds and CHO+N molecular formulas in highly unsaturated compounds, respectively. In contrast, the DOM in PRD groundwater was more biogenic, less degraded, and contained more aliphatic compounds in addition to highly unsaturated compounds. The degradation of DOM and nitrogen-containing DOM was dominated by aliphatic compounds and polyphenols and CHO+N molecular formulas in highly unsaturated compounds and polyphenols, respectively. As DOM degraded, the ammonium production efficiency of DOM decreased, contributing to lower ammonium concentrations in DTP groundwater. In addition, the CHO+N(SP) molecular formulas were mainly of microbial-derived and gradually accumulated with DOM degradation. In this study, we conducted the first comprehensive investigation into the patterns of groundwater ammonium enrichment based on DOM differences in various geological settings.

Differential utilisation of dissolved organic matter compound fractions by different biofilter microbial communities

Abstract Dissolved organic matter (DOM) is a complex mixture of carbon-based compounds present in natural aquatic systems, which significantly affects drinking water treatment processes. Biofiltration, utilising biologically active beds of porous medium, offers a low-energy and low-chemical solution for controlling bioavailable DOM. However, the impact of microbial community composition on DOM degradation in biofilters remains poorly understood. This study aimed to explore the abilities of microbial communities from the top, middle, and bottom (TOP, MID, and BOT) of a biofilter to process DOM. We showed varying growth rates on the DOM, with bottom community exhibiting the highest cell abundance at the end of the experiment (1.83 × 106 ± 9 × 103; 2.06 × 106 ± 1 × 104; 2.15 × 106 ± 7 × 103 cells/mL for the TOP, MID, and BOT, respectively). The three communities showed different preferences for utilising specific DOM fractions, with the bottom community targeting more complex ones. The microbial communities from the bottom of the biofilter had a higher relative abundance of the Curvibacter genus, suggesting it could play a crucial role in degrading complex DOM fractions. These findings highlight the influence of microbial community composition on DOM degradation in biofilters, providing valuable insights for optimising their performance.

Origin, distribution and spatial characteristics of dissolved organic matter in the Heilongjiang River

The Heilongjiang River Basin is a vast area with significant DOM sources and composition differences. The mechanism of DOM degradation under spatial variation remains unclear. This research investigated the degradation characteristics of DOM in different watersheds of the Heilongjiang River. DOM levels were higher in midstream waters, while DOM degradation rates were higher in midstream and downstream waters. The parallel factor analysis (PARAFAC) results showed that the upstream amino acid fraction was significantly depleted, the midstream was dominated by the degradation of DOM of terrestrial origin, and the downstream humic acid fraction was decreased considerably. Gene sequencing results indicated that the upstream, middle, and downstream water bodies' microbial community composition and structure differed significantly. The network analysis results revealed microorganisms in upstream water bodies mainly utilized amino acid-like substances and small molecule humic acids. Microorganisms in the middle and lower reaches of the water column were characterized by the utilization of humic acid-like fractions. In this study, we further screened the key driving microorganisms (e.g., Flavobacterium and Lacibacter) responsible for the difference in the DOM utilization function of upstream-to-midstream and midstream-to-downstream microorganisms in the Heilongjiang River. These findings will help identify the cycling process of DOM under spatial variation and predict the succession pattern of microbial communities.

Study on the Photodegradation of Dissolved Organic Matter in Urban Water Bodies in Nanjing

This paper reviews the DOM pollution of water resources in China, and complements the organic matter degradation characteristics of urban water bodies in Nanjing. In this study, the photodegradation experiment and UV-visible spectroscopy measurement of three types of water are conducted, analyzed and discussed around the degradation of DOC and aromatic substances, and the DOM degradation characteristics of different cities are studied. It can be identified in this study that urban water bodies near human living areas and non-circulation have higher DOM content and are less susceptible to decomposition, which is related to human needs and transformation of the environment and human daily activities.

Molecular characterization by ultrahigh resolution mass spectrometry of dissolved black carbon-like molecules in summer along the Pearl River Estuary, China

• Dissolved black carbon molecules in the estuarine DOM are identified. • Numbers and intensity-weighted DBCs decrease gradually with the salinity gradient. • Intensity-weighted molecular weights of DBCs vary from m/z 301.8 to 320.2. • Compounds with O 2-3 and O 10-12 are preferentially eliminated along the PRE. • Condensed aromatic 3 or 4 rings substituted with OH and COOH are proposed. Significant amounts of organic carbon derived from black carbon (BC) are transported annually through the Pearl River Estuary (PRE) in Southern China, into the continental shelf of the South China Sea. However, molecular composition and distribution of dissolved black carbon (DBC) compounds along the PRE are still rarely studied. In this work, dissolved organic matter isolated and extracted by solid phase extraction from water samples collected in summer along the PRE are studied and characterized by negative electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), and with special attention paid to DBC molecules. The numbers and relative intensities of identified DBC molecules (CHO x class) decrease gradually with the salinity gradient from the upper reach to the open water. The DBC molecules accumulated with relatively high intensities in O 7 and O 9 classes in Site A and slightly shifted to O 5 , O 7-8 classes in Site E along the PRE. Possible three or four rings of aromatic ring structure of DBCs, with hydroxyl and carboxy substituent groups are proposed. The relatively smaller sizes of DBCs are likely to have originated from relatively larger oxidized condensed aromatic structures of black carbon. The trend of DBC distribution along the estuary could be explained by DOM degradation in the mixing zone.

The impacts of reservoirs on the sources and transport of riverine organic carbon in the karst area: A multi-tracer study

Reservoirs have been constructed as clean energy sources in recent decades with various environmental impacts. Karst rivers typically exhibit high dissolved inorganic carbon (DIC) concentrations, whether and how reservoirs affect carbon cycling, especially organic carbon (OC)-related biogeochemical processes in karst rivers, are unclear. To fill this knowledge gap, multiple tracer methods (including fluorescence excitation-emission matrix (EEM), ultraviolet (UV) absorption, and stable carbon (δ13C) and radiocarbon (Δ14C) isotopes) were utilized to track composition and property changes of both particulate OC (POC) and dissolved OC (DOC) along river-transition-reservoir transects in the Southwest China karst area. The changes in chemical properties indicated that from the river to the reservoir, terrestrial POC is largely replaced by phytoplankton-derived OC, while gradual coloured dissolved organic matter (CDOM) removal and addition of phytoplankton-derived OC to the DOC pool occurred as water flowed to the reservoir. Higher primary production in the transition area than that in the reservoir area was observed, which may be caused by nutrient released from suspended particles. Within the reservoir, the production surpassed degradation in the upper 5 m, resulting in a net DIC transformation into DOC and POC and terrestrial DOM degradation. The primary production was then gradually weakened and microbial degradation became more important down the profile. It is estimated that ~3.1–6.3 mg L−1 (~15.5–31.5 mg-C m−2 (~10–21%)) DIC was integrated into the OC pool through the biological carbon pump (BCP) process in the upper 5 m in the transition and reservoir areas. Our results emphasize the reservoir impact on riverine OC transport, and due to their characteristics, karst areas exhibit a higher BCP potential which is sensitive to human activities (more nutrient are provided) than non-karst areas.

The relevance of environment vs. composition on dissolved organic matter degradation in freshwaters

AbstractDissolved organic matter (DOM) composition exerts a direct control on its degradation and subsequent persistence in aquatic ecosystems. Yet, under certain conditions, the degradation patterns of DOM cannot be solely explained by its composition, highlighting the relevance of environmental conditions for DOM degradation. Here, we experimentally assessed the relative influence of composition vs. environment on DOM degradation by performing degradation bioassays using three contrasting DOM sources inoculated with a standardized bacterial inoculum under five distinct environments. The DOM degradation kinetics modeled using reactivity continuum models showed that composition was more important than environment in determining the bulk DOM decay patterns. Changes in DOM composition resulted from the interaction between DOM source and environment. The role of environment was stronger on shaping the bacterial community composition, but the intrinsic nature of the DOM source exerted stronger control on the DOM degradation function.

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.

How trophic cascades and photic zone nutrient content interact to generate basin-scale differences in the microbial food web

Abstract In linear food chains, resource and predator control produce positive and negative correlations, respectively, between biomass at adjacent trophic levels. These simple relationships become more complex in food webs that contain alternative food chains of unequal lengths. We have used a “minimum” model for the microbial part of the pelagic food web that has three such food chains connecting free mineral nutrients to copepods: via diatoms, autotrophic flagellates, and heterotrophic bacteria. Trophic cascades from copepods strongly modulates the balance between the three pathways and, therefore, the functionality of the microbial food web in services such as food production for higher trophic levels, DOM degradation, and ocean carbon sequestration. The result is a theoretical framework able to explain, not only apparent conflicts in Arctic mesocosm experiments, but also biogeochemical features of the Mediterranean. Here, the fundamental difference between Arctic and Mediterranean microbial food webs is the way they are predator driven by seasonal migration of large copepods in the Arctic, but resource driven due to the anti-estuarine circulation in the Mediterranean. In this framework, global change effects on microbial ecosystem functions are more like to come indirectly through changes in these drivers than through direct temperature effects on the microbes.

Distribution, seasonality, and fluxes of dissolved organic matter in the Pearl River (Zhujiang) estuary, China

Abstract. Dissolved organic carbon (DOC) concentration in the Pearl River estuary (PRE) of China was measured in May, August, and October 2015 and January 2016. Chromophoric and fluorescent dissolved organic matter (CDOM and FDOM) in the latter three seasons were characterized by absorption and fluorescence spectroscopy. CDOM and FDOM exhibited negligible seasonal variations, while DOC displayed a significant seasonality, with the average concentration being highest in May (156 µmol L−1), lowest in November (87 µmol L−1), and comparable between January (118 µmol L−1) and August (112 µmol L−1). Although DOC, CDOM, and FDOM in surface water were generally higher than in bottom water, the difference between the two layers was statistically insignificant. DOC showed little cross-estuary variations in all seasons, while CDOM and FDOM in January were higher on the west side of the estuary than on the east side. All three variables showed rapid drawdowns in the head region of the estuary (salinity <5); their dynamics in the main estuary were primarily controlled by conservative mixing, leading to linearly declining or relatively constant (for DOC in May and November only) contents with increasing salinity. The decrease in FDOM with salinity was 5 %–35 % faster than that of CDOM, which in turn was 2–3 times quicker than that of DOC. Salinity and CDOM absorption coefficients could serve as indicators of DOC in August and January. Freshwater endmembers in all seasons mainly contained fresh, protein-rich DOM of microbial origin, a large part of it likely being pollution-derived. Protein-like materials were preferentially consumed in the head region but the dominance of the protein signature was maintained throughout the estuary. Exports of DOC and CDOM (in terms of the absorption coefficient at 330 nm) into the South China Sea were estimated as 195×109 g and 266×109 m2 for the PRE and 362×109 g and 493×109 m2 for the entire Pearl River Delta. The PRE presents the lowest concentrations and export fluxes of DOC and CDOM among the world's major estuaries. DOM delivered from the PRE is, however, protein-rich and thus may enhance heterotrophs in the adjacent coastal waters. Overall, the PRE manifests lower abundance and smaller spatiotemporal variability of DOM than expected for a sizable estuary with a marked seasonality of river runoff due supposedly to the poorly forested watershed of the Pearl River, the rapid degradation of the pollution-derived DOM in the upper reach, and the short residence time of freshwater.

The Variability of CDOM Along the Salinity Gradients of the Seomjin River Estuary During Dry and Wet Seasons

The distribution patterns of Chromophoric Dissolved Organic Matter (CDOM) and the chemical characteristics of CDOM in the Seomjin river estuary were investigated in March, June and July 2012 in order to determine the spatial and temporal variability of CDOM along the salinity gradient considering the effects of mixing, nutrients and Chl a. The average CDOM values were 1.0 ± 0.3 m -1 , 1.3 ± 0.4 m -1 , and 1.4 ± 0.3 m -1 in March, June and July, respectively. A high concentration of CDOM (greater than 1.5 m -1 ) was found at the head of the river which decreased towards the river mouth to as low as less than 0.5 m -1 . The average concentrations of CDOM increased from the dry season (March and June) to the wet season (July), and the average slope values (S 300-500 ), which were used as indicators of CDOM characteristics and sources, were in the range of 0.013 - 0.018 ㎚ -1 . The CDOM and S 300-50 values showed that not only the concentration of CDOM but also the chemical properties of DOM clearly changed between upstream and downstream in the Seomjin river. CDOM and FDOM showed a negative correlation with salinity (R² ＞ 0.8), and CDOM was positively correlated with FDOM. Furthermore, the mixing pattern of CDOM was confirmed as conservative for all seasons. The main environmental factors influencing the concentration of CDOM was confirmed as conservative for all seasons. The main environmental factors influencing the concentration of CDOM were salinity (mixing) and water temperature, which meant the dilution of low CDOM seawater, was the controlling factor for the spatial distribution of CDOM. Increases in water temperature seemed to induce the production of CDOM during summer (June and July) through the biological degradation of DOM either by microbial activity or photo-degradation.

Production and degradation of fluorescent dissolved organic matter in surface waters of the eastern north Atlantic ocean

The distribution and fate of coloured dissolved organic matter (CDOM) in the epipelagic Eastern North Atlantic was investigated during a cruise in the summer 2009 by combining field observations and culture experiments. Dissolved organic carbon (DOC) and nitrogen (DON), the absorption spectra of CDOM and the fluorescence intensity of proteins (Ex/Em 280/320nm; F(280/320)) and marine humic-like substances (F(320/410)) were measured in the upper 200m. DOC and DON showed higher concentrations in the top 20m than below, and DOC increased southwards, while DON decreased. F(280/320) and F(320/410) showed maxima near the deep chlorophyll maximum (at about 50m), suggesting that these fluorophores were linked to phytoplankton production and the metabolism of the associated microbial community. The coloured and fluorescent fractions of DOM showed low levels south of the Azores Front, at about 35°N, likely due to the accumulated photobleaching of the waters transported eastwards by the Azores current into the study area (at 20°W). Twelve culture experiments were also conducted with surface water (5m) to assess the impact of microbial degradation processes on the bulk, coloured and fluorescent fractions of DOM. After 72h of incubation in the darkness, 14±9% (average±SD) of the initial DON was consumed at an average rate of 0.24±0.14µmol l−1 d–1 and the protein-like fluorescence decayed by 29±9% at a net rate of 0.06±0.03 QSU d–1. These rates were significantly lower south of the Azores front, suggesting that DOM in this region was of a more recalcitrant nature. Conversely, the marine humic-like fluorescence increased at a net rate of 0.013±0.003 QSU d–1. The close linear relationship of DON uptake with F(280/320) consumption (R2= 0.91, p <0.0001, n=12) and F(320/410) production (R2= 0.52, p <0.008, n=12) that we found during these incubation experiments suggest that the protein-like fluorescence can be used as a proxy for the dynamics of the labile DON pool and that marine humic-like materials can be produced as a by-product of microbial DOM degradation.

Uncoupling of Bacterial and Terrigenous Dissolved Organic Matter Dynamics in Decomposition Experiments

The biodegradability of terrigenous dissolved organic matter (tDOM) exported to the sea has a major impact on the global carbon cycle, but our understanding of tDOM bioavailability is fragmentary. In this study, the effects of preparative tDOM isolation on microbial decomposition were investigated in incubation experiments consisting of mesocosms containing mesohaline water from the Baltic Sea. Dissolved organic carbon (DOC) consumption, molecular DOM composition, bacterial activities, and shifts in bacterial community structure were compared between mesocosms supplemented with riverine tDOM, either as filtered, particle-free river water or as a concentrate obtained by lyophilization/tangential ultrafiltration, and those containing only Baltic Sea water or river water. As shown using ultra-high-resolution mass spectrometry (15 Tesla Fourier-transform ion cyclotron resonance mass spectrometry, FT-ICR-MS) covering approximately 4600 different DOM compounds, the three DOM preparation protocols resulted in distinct patterns of molecular DOM composition. However, despite DOC losses of 4–16% and considerable bacterial production, there was no significant change in DOM composition during the 28-day experiment. Moreover, tDOM addition affected neither DOC degradation nor bacterial dynamics significantly, regardless of the tDOM preparation. This result suggested that the introduced tDOM was largely not bioavailable, at least on the temporal scale of our experiment, and that the observed bacterial activity and DOC decomposition mainly reflected the degradation of unknown, labile, colloidal and low-molecular weight DOM, both of which escape the analytical window of FT-ICR-MS. In contrast to the different tDOM preparations, the initial bacterial inoculum and batch culture conditions determined bacterial community succession and superseded the effects of tDOM addition. The uncoupling of tDOM and bacterial dynamics suggests that mesohaline bacterial communities cannot efficiently utilize tDOM and that in subarctic estuaries other factors are responsible for the removal of imported tDOM.

Integrated Principal Component Analysis of Microcystis aeruginosa Dissolved Organic Matter and Assessment of UV‐C Pre‐Treatment on Cyanobacteria‐Containing Water

The intrinsic characteristic of chromophoric dissolved organic matter (CDOM) and bioactivity materials derived from toxic Microcystis aeruginosa was investigated. Fluorescence excitation emission matrix combined with parallel factor analysis (EEM‐PARAFAC) determined six CDOM components, and principal component analysis (PCA) identified two integrated principle factors. PCA factor 1 mainly represented the intracellular and extracellular microbial active components, and factor 2 represented the extracellular residuals and degraded products. These two PCA factors accounted for 53 and 31% of the variance in nine parameters distributions, and were used to assess the variation pattern of DOM. The variation tendencies of PCA factors in experiments using single UV‐C (254 nm), UV‐C/H2O2, , , and UV‐C/humic acid were estimated. Photolysis and photo‐oxidation were dominating processes in single UV‐C irradiation, and H2O2 improved photo‐oxidation, resulting in high efficient removal of intracellular DOM and extracellular DOM. The presences of , and humic acid had negative effects on the degradation of extracellular DOM, but little influence on intracellular DOM. Results revealed that UV‐C/H2O2 can be considered as an option for the pretreatment of cyanobacteria‐contained water, and EEM‐PARAFAC‐PCA can be applied to simplify multiple parameters in water treatment process, which would be benefit to water quality monitoring and management.

Short-Term Photochemical and Biological Unreactivity of Macrophyte-Derived Dissolved Organic Matter in a Subtropical Shallow Lake

Macrophytes have been associated with low bacterial metabolism in the littoral zones of lake Mangueira, but an explanation for this pattern is largely unknown. In this study, macrophyte-derived DOM was incubated in situ for the measurement of the effect of grazers, bacteria, and light on its degradation in three experiments. The water was separated in bulk, bacterial, and control (+ HgCl2) fractions and exposed to or hidden from sunlight for 120 h. Unchange in bacterial variables in the bulk fraction suggested a combined control of radiation and grazing on bacteria. Light treatment increased bacterial density but not biomass and biovolume, while bacterial density decreased in the dark. Significant fading of water color in the bacterial fraction only occurred after light exposure, indicating a complementary pathway of light and bacteria. DOC and the Abs250 : 365 ratio did not change with incubation, indicating no net change of DOC pool and reactivity. Due to continuous carbon loading from macrophytes and low UV irradiance, the very low rates of DOM degradation provide the mechanistic explanation for the observed impacts of macrophytes in lake’s carbon metabolism in littoral zones.

太湖水体溶解性氨基酸的空间分布特征

Amino acids( AAs) are important bio-available components of organic matter( OM) and are the major forms of organic nitrogen( ON) in aquatic ecosystem. They also represent significant fractions of OM in recent coastal marine sediments,water column particles and dissolved organic matters. They are typically labile composed relative to bulk OM and ON,and account for a considerable portion of the particulate OC and ON recycled in both water column and sediments,and therefore are an important nutrient form. Owing to the different AAs monomers have different biogeochemical stability,AAs are often used as an indicator of organic matter sources and as an index of OM degradation potential. Changes in amino acid composition exhibit consistent trends and demonstrate the degradation of cellular organic matter as it sinks through water column and is incorporated into sediments. Due to the labile character of AAs,the percentage of OC and N represented by amino acid( AA-C / OC% and AA-N / ON%) and the percentage of total amino acids have proven to be useful degradation indicators. They are sensitive at different stages of OM alteration and appear uncompromised by source variation. Dissolved amino acids( DAAs) characteristics were investigated in water of Lake Taihu,a large,shallow and eutrophic freshwater lake in China. The northern lake is characterized by phytoplankton dominance,high water turbidity,and severe Microcystis spp. algal blooms. In contrast,eastern lake is characterized by submersed vegetation,clear water,and diverse communities of fishes and invertebrates. The main upstream land use types of south Taihu were classified by the mountain forests and farmland. DAAs concentrations in Taihu ranged from 0. 27 to 3. 95 μmol / L,with a mean value of 1.38 μmol / L. The large regional differences in concentrations and yields of DAAs suggested that DOM produced in situ is an important source of bio-reactive of organic matter in waters of Taihu. The spatial distributions of DAAs concentrations in Taihu were less variable than those previously reported from other aquatic environments. DAAs concentrations of north Taihu were significantly higher than south lake and east lake,with mean values of( 2. 59±0. 71) μmol / L in north Taihu,( 0. 48±0. 14) μmol / L in south Taihu,and( 0. 48 ± 0. 16) μmol / L in east Taihu,respectively( P 0. 001). Based on the relationship between amino acid yields and percent labile DOC,( 17. 65 ±17. 84) % of fresh DOC in north lake is labile,which is higher than in south lake or east lake. The results showed internal sources mainly from the decomposing of phytoplankton should be the main source of DAAs in Taihu,and DAAs was important fraction of DOM. DAAs compositions were dominated by Phenylalanine( PHE) and lysine( LYS) in north lake,while only LYS in south and east lake.Compositions and concentrations of DAAs can be possible used as an indicator,which could provide useful information about the nutritional status and bio-available DOM in Lake Taihu. But because of high spatial heterogeneity in Taihu,we need to establish DAAs-liable DOC linear model for Lake Taihu,by the means of the algal-dominated and macrophytedominated DOM degradation experiments.

Bromoform production from seawater treated with bromoperoxidase

Bromoform (CHBr3; 11–486 fmol L−1 h−1), dibromomethane (CH2Br2; 0–9.4 fmol L−1 h−1), and low amounts of chloride‐substituted chlorobromomethanes were produced from southern California coastal surface seawater upon the addition of algal bromoperoxidase (BrPO) and hydrogen peroxide. Production was greater from water collected near shore than 16 km offshore, presumably reflecting the difference in the reactive dissolved organic matter (DOMreact) concentrations. In the spring, there was an increase in phytoplankton abundance, and CHBr3 production from BrPO incubations was greater, presumably due to increased DOMreact. In the winter, CH2Br2 production was enhanced, although still lower than CHBr3, suggesting a qualitative change in DOM composition due to terrestrial runoff. During the month of the highest precipitation, CHBr3 and CH2Br2 production was enhanced in samples obtained from the mouth of an urban river, suggesting a higher concentration of DOMreact of terrestrial origins. DOM was fractionated by ultrafiltration and subject to the BrPO incubation. The higher molecular weight fractions contained a higher concentration of DOM that was susceptible to BrPO bromination, yielding polybromomethanes. Polybromomethane and iodomethane production associated with phytoplankton blooms results from the reaction between the surrounding DOM, and hypobromous acid (HOBr) and hypoiodous acid released from extracellular (apoplastic) BrPO. The reaction of HOBr and DOM (biological bleaching) could represent a significant DOM degradation pathway. Cell‐free BrPO, derived from dead cells, could remain catalytically active in seawater and produce low amounts of polyhalomethanes prior to biological degradation.

Organic matter characteristics in a Mediterranean stream through amino acid composition: changes driven by intermittency

Amino acid composition (quality) and abundance (quantity) of organic matter (OM) in an intermittent Mediterranean stream were followed during transitions from wet to dry and dry to wet conditions. Amino acids were analyzed in benthic material (epilithic biofilms, sand sediments, leaf material) as well as in the flowing water (dissolved organic matter, DOM). A principal component analysis and the estimation of the amino acid degradation index (DI) elucidated differences in amino acid composition and quality among the wet–drought–wet cycle. Amino acid content and composition were dependent on the source of OM as well as on its diagenetic state. The highest-quality OM (high DI and high N content) occurred on epilithic biofilms and the most degraded and lowest-quality OM occurred in sandy sediments. Differences between the pre- and post-drought periods were evident in DOM quality; autochthonous-derived material was predominant during the pre-drought (wet period preceding drying), while allochthonous inputs dominated during the post-drought period (wet period following drying). In contrast, benthic OM compartments were more stable, but benthic OM quality decreased continuously throughout the drought period. This study revealed that wet–drought–wet cycles resulted in subtle changes in benthic OM quality, and degradation of DOM was related to flow intermittency.

Particulate-dissolved transformations as a sink for semi-labile dissolved organic matter: Chemical characterization of high molecular weight dissolved and surface-active organic matter in seawater and in diatom cultures

Chemical characterizations of high molecular weight dissolved organic matter (HMW DOM) have shown that a compositionally well-defined family of acylated polysaccharides (APS) contributes a large fraction of DOM in the surface ocean. One process that might affect APS cycling is physical removal by aggregation. To investigate the importance of this mechanism, we compared the chemical composition and transparent exopolymer particle (TEP) abundances of seawater HMW DOM with surface-active organic matter (SAOM) that accumulates as standing sea surface foam during intense wind events. We further simulated the aggregation of SAOM using bubble-adsorption of HMW DOM isolated from laboratory cultures of the diatom Chaetoceros neogracile. 1H-NMR spectroscopy and molecular-level analysis of natural and laboratory-produced HMW DOM and SAOM show important contributions from polysaccharides, acetate, and aliphatic organic matter and similar yields and distributions of neutral sugars after hydrolysis. Microbial degradation of Chaetoceros neogracile DOM removes proteins and mannose-rich polysaccharides to produce HMW DOM with spectral and molecular-level characteristics that resemble seawater APS. These results imply that APS and hydrolysable sugars are resistant to microbial degradation over the time frame of our degradation experiment (40 days). As revealed by 1H-NMR spectroscopy and by the neutral monosaccharide data, there are important similarities in the composition of APS in HMW DOM and natural and laboratory-produced SAOM foamy material, rich in TEP. Although these samples are operationally classified in two distinct pools (dissolved vs. particulate) in seawater, they exhibit similar chemical and spectral characteristics. Finally, TEP concentration measurements in SAOM samples indicate that freshly-produced diatom DOM yields SAOM with TEP concentration similar to seawater and natural SAOM, but seven times higher than SAOM produced after bubble-adsorption of degraded HMW DOM.