Sources Of Particulate Organic Matter Research Articles

Unlocking the potential of hydrogen isotopes (δ2H) in tracing riverine particulate organic matter sources and dynamics

Unlocking the potential of hydrogen isotopes (δ2H) in tracing riverine particulate organic matter sources and dynamics

Characterizing fluvial impact on the biochemical composition of particulate organic matter in the Laptev Sea and Western East Siberian Sea during the late summer of 2018

The Laptev Sea (LS) and Western East Siberian Sea (W-ESS) are paradigmatic examples of seas dominated by terrestrial organic matter, attributed to substantial Siberian River discharges and coastal erosion. The influx of terrestrial organic matter significantly alters the biochemical composition of particulate organic matter (POM) in these Arctic coastal regions, potentially reducing the nutritional quality available to higher trophic levels. This study investigated the origin and qualitative characteristics of POM in the LS and W-ESS during the late summer of 2018 by analyzing elemental ratios (C/N ratio), stable carbon isotopes (δ13C), and biochemical compositions (biomolecular and amino acid (AA) compositions). The conspicuously depleted δ13C values (mean ± standard deviation (SD) = −30.2 ± 0.5 ‰) and alongside elevated molar C/N ratios (mean ± SD = 18.1 ± 6.2) suggest that terrestrial organic matter is the predominant source of POM in the study area. Although carbohydrates (CHO) were the dominant biomolecules, their prevalence was higher in the river-influenced W-ESS region (67.7 ± 6.6 %) than in the LS region (58.6 ± 13.9 %; p < 0.05). Furthermore, the CHO composition was closely associated with freshwater content and river fraction, suggesting that the heightened contribution of CHO may stem from terrestrial organic matter delivered by river inputs. Lower concentrations of particulate hydrolyzable AA (PAA) and carbon and nitrogen normalized yields of AAs (AA-POC% and AA-PON%) along with reduced contribution of glycine suggested a substantial contribution of terrestrial POM to both LS and W-ESS POM. Overall, this study provides valuable insights into the terrestrial influence on POM composition in Arctic marine ecosystems, emphasizing the need for continued monitoring of the consequences of terrestrial carbon inputs in the changing Arctic environment.

Coupling Imports of Dissolved Inorganic Nitrogen and Particulate Organic Matter by Aquaculture Sewage to Zhangjiang Estuary, Southeastern China

Estuary ecosystems serve as crucial connectors between terrestrial and marine environments, thus playing vital roles in maintaining the ecological balance of coastal marine ecosystems. In recent years, the eutrophication in estuaries caused by aquaculture sewage has been revealed, highlighting the necessity to understand its influence on the nutrient conditions and carbon storage of estuaries. In this study, δ15N and δ18O were used to indicate the contribution of aquaculture-derived sewage to dissolved inorganic nitrogen in Zhangjiang Estuary, and δ13C and C:N ratio were used to reveal its effects on the particulate organic matter. The major results are as follows: (1) Aquaculture water contributed 62~86% and 60~100% of the total nitrate and ammonium in Zhangjiang Estuary, respectively, and the drainage periods of the cultured species has a great influence on the content and composition of dissolved inorganic nitrogen. (2) Aquaculture water was also the major source of particulate organic matter (24~33% of the total content) here, most of which may be derived from crab ponds. (3) The imports of nutrients by aquaculture water may potentially regulate particulate organic matter in Zhangjiang Estuary by promoting the growth of phytoplankton and zooplankton. Our study revealed the coupling effects of aquaculture activities on the nitrogen and carbon storage in an estuarine ecosystem. It also indicates that isotopes may be efficient in the monitoring of a coastal environment, which may further aid the management of inshore cultivation.

Remote sensing estimation of δ15NPN in the Zhanjiang Bay using Sentinel-3 OLCI data based on machine learning algorithm

Remote sensing estimation of δ15NPN in the Zhanjiang Bay using Sentinel-3 OLCI data based on machine learning algorithm

Drifting along: using diatoms to track the contribution of microbial mats to particulate organic matter transport in a glacial meltwater stream in the McMurdo Dry Valleys, Antarctica.

Flow pulses mobilize particulate organic matter (POM) in streams from the surrounding landscape and streambed. This POM serves as a source of energy and nutrients, as well as a means for organismal dispersal, to downstream communities. In the barren terrestrial landscape of the McMurdo Dry Valleys (MDV) of Antarctica, benthic microbial mats occupying different in-stream habitat types are the dominant POM source in the many glacier-fed streams. Many of these streams experience daily flow peaks that mobilize POM, and diatoms recovered from underlying stream sediments suggest that mat-derived diatoms in the POM are retained there through hyporheic exchange. Yet, 'how much' and 'when' different in-stream habitat types contribute to POM diatom assemblages is unknown. To quantify the contribution of different in-stream habitat types to POM diatom assemblages, we collected time-integrated POM samples over four diel experiments, which spanned a gradient of flow conditions over three summers. Diatoms from POM samples were identified, quantified, and compared with dominant habitat types (i.e., benthic 'orange' mats, marginal 'black' mats, and bare sediments). Like bulk POM, diatom cell concentrations followed a clockwise hysteresis pattern with stream discharge over the daily flow cycles, indicating supply limitation. Diatom community analyses showed that different habitat types harbor distinct diatom communities, and mixing models revealed that a substantial proportion of POM diatoms originated from bare sediments during baseflow conditions. Meanwhile, orange and black mats contribute diatoms to POM primarily during daily flow peaks when both cell concentrations and discharge are highest, making mats the most important contributors to POM diatom assemblages at high flows. These observations may help explain the presence of mat-derived diatoms in hyporheic sediments. Our results thus indicate a varying importance of different in-stream habitats to POM generation and export on daily to seasonal timescales, with implications for biogeochemical cycling and the local diatom metacommunity.

Coupling and Decoupling Between Sedimentary Mercury and Organic Carbon Preservation in the Oxygenated Marine Environment

AbstractMercury (Hg) enrichment relative to total organic carbon (TOC) in sedimentary records has been widely used as a volcanism proxy. However, the depositional and diagenetic effects on Hg burial are not well understood, limiting the reliability of the proxy. Here, we report a systematic investigation of Hg sedimentation under well‐oxygenated bottom water. Most of the studied cores show total mercury content (THg) to TOC ratio between 50 and 300 ppb/%, including northwest Pacific ODP Site 1208, East Equatorial Pacific ODP Sites 677 and 1241, the Antarctic Zone ODP Site 1094, and East China Sea sediment core EC2005. The consistent THg/TOC ratio confirms the strong coupling between Hg and particulate organic matter (POM) despite large differences in geographic locations, sedimentation rates, TOC content, POM sources, and early diagenetic environments. Nevertheless, the THg/TOC ratio is higher in sediments under well‐oxygenated bottom water than in those under oxygen‐depleted waters, probably as a result of a higher degree of organic matter degradation in oxygenated sediments during early diagenesis. The THg in the high TOC variability section at Site 1208 is abnormally high, resulting in decoupling between Hg and POM. Mercury in this section is still leachable by oxidizing solution and has a similar trend of variability with easily reducible iron content, implying that the metal oxide‐organic matter association might act as Hg bounding phase. We suggest that the enriched Hg is probably supplied by the neighboring high TOC sediment. Therefore, while THg/TOC &gt; 300 ppb/% could be considered as distinct Hg enrichment in sedimentary records, the diagenetic mobilization effect should be first excluded as the possible cause as demonstrated by the records of site 1208. Our study therefore provides new insights into the Hg cycle in the modern ocean and the utilization of Hg enrichment as a volcanism proxy.

Using stable carbon isotopes of lignin-derived methoxy to improve historical apportionments of particulate organic matter and sediment sources incorporating multiple Suess corrections

PurposeSoil erosion models are essential to improving sediment management strategies. Sediment source fingerprinting is used to help validate erosion models. Fingerprinting sediment sources with organic isotopic tracers faces challenges from aquatic sources and co-linearity. To address these complexities, integrating another land-use-specific tracer is essential. Suess corrections incorporating multiple mean-residence-times are necessary to accurately model historical sediment apportionments. In previous studies, compound specific isotopic tracers indicated forest as the dominant source. We hypothesize that there is an overestimation of forest contribution, attributed to the misclassification of particulate organic matter as forest.MethodsIn this study, we utilize stable carbon isotope (δ13C) values of fatty acids and the average chain length in combination with the δ13C values of lignin-derived methoxy groups as an additional tracer. We apply different Suess corrections to explore the effect of the changing atmospheric δ13CO2 values on sediment apportionment. The performance of the unmixing model is evaluated with 300 mathematical mixtures. To determine shifts in sediment sources throughout the last 130 years, particulate organic matter contributions are determined and removed to apportion sediment soil sources. We investigate the potential misclassification of forest contributions by merging particulate organic matter and forest sources to simulate tracers which are unable to discriminate.ResultsThe inclusion of δ13C values of lignin methoxy groups and the alkane average chain length as additional tracers successfully removed tracer co-linearity. Additionally, we used an updated concentration dependent point in polygon test to identify sediment with increased potential for incorrect source apportionments. Changes in the dominant sediment sources over time (Forest: pre-1990, Pasture: 1910–1940, Arable: post 1940) highlight the effect of policy-induced land-use changes. Additionally, the inability to discriminate particulate organic matter and forest sources was revealed to cause a 37% overestimation of forest contributions from 1944 to 1990.ConclusionUsing δ13C values of lignin methoxy groups as an additional tracer, we identified critical points in the 130-year sediment history of Lake Baldegg. Furthermore, we highlight the importance of incorporating multiple Suess effects. Through mathematical mixtures, we assessed the confidence that should accompany apportionment estimates. While merging forest and particulate organic matter sources did not result in forest as the dominant source over the last 130 years, separating these sources resulted in more accurate apportionment. These insights offer valuable information to enhance the accuracy of sediment fingerprinting, which can then be used to assist soil erosion models employed for sediment mitigation policies.

Source apportionment of suspended particulate organic matter in a shallow eutrophic lake of Southwest China using MixSIAR model

Eutrophication has become prominent in many lakes of the world, resulting in a continuous rise of suspended particulate organic matter (POM) that can be of vital consequence for water quality and carbon cycling. While the accumulation and decomposition of POM can enhance nutrient cycling at a rate depending on the property of lake-water organic carbon, it is important to identify the source of suspended POM for evaluating eutrophication and carbon burial. Here we analyzed the distribution of stable isotopic ratios (δ13C and δ15N) and the carbon/nitrogen ratio (C/N) in suspended POM in a shallow eutrophic lake of subtropical China, for apportioning the POM sources using Bayesian mixing model. Specifically, we collected seasonal samples of lake-water POM (>0.7 μm) from 20 sites in Yilong Lake from September 2020 to June 2022, as well as six types of modern samples covering the main carbon sources in the catchment. The spatial surveys showed that in the dry year (low water level) the δ13C of POM was more enriched in the western basin than those in the central and eastern basins, while the seasonal surveys showed the most enriched δ13C of POM in September. However, this spatio-temporal heterogeneity disappeared in the wet year (high water level). It was also found that the δ13C, δ15N and C/N values of POM varied significantly with those of phytoplankton across sites and seasons. Application of the MixSIAR model further showed that phytoplankton was the predominant source of POM in Yilong Lake (79.8 ± 13.4 %), but with large annual difference, 68.9 ± 10.3 % in the dry year and 90.7 ± 3.7 % in the wet year. In comparison, the contribution of the other five endmembers was much more moderate. In particular, the proportion of allochthonous organic carbon in POM was relatively low, with terrestrial plants and soils contributing 6.1 ± 4.8 % and 4.3 ± 2.5 % of POM, respectively. Our quantitative evidence for the dominance of the autochthonous source (i.e., phytoplankton) in lake-water POM over time and space suggested a determining role of eutrophication in the composition of lake organic carbon. Therefore, the coupling of algal blooms with organic carbon cycling in inland waters can be enhanced with continuous catchment development and regional warming.

Significant contribution of different sources of particulate organic matter to the photoaging of microplastics

Particulate organic matter (POM), as an important component of organic matter, can act as a redox mediator and thus intervene in the environmental behavior of microplastics (MPs). However, quantitative information on the role of POM in the photoaging of MPs under ultraviolet (UV) light is still lacking. To raise the knowledge gap, through environmental simulation experiments and qualitative/quantitative experiments of active substances, we found that POM from peat soil has stronger oxidation capacity than POM from sediment, and the involvement of POM at high water content makes the aging of MPs more obvious. This is because the persistent radicals and electron-absorbing groups on the surface of POM indirectly generate reactive oxygen species (ROS) by promoting electron transfer, and the dissolved organic matter (DOM) released from POM under UV light (POM-DOM) is further excited to generate triplet-state photochemistry of DOM (3DOM*) to promote the aging of MPs. Theoretical calculations revealed that the benzene ring, mainly C = C, and C = O in the main chain in the plastic macromolecule structure are more susceptible to ROS attack, and the differences in the vulnerable sites contained in different plastic structures as well as the differences in the energy band gaps lead to differences in their aging processes. This study firstly elucidates the key role and intrinsic mechanism of POM in the photoaging of MPs, providing a theoretical basis for a comprehensive assessment of the effect of POM on MPs in the environment.

Distribution and sources of particulate organic matter from the anthropogenically disturbed Iyidere River to the Black Sea coast

Understanding the biogeochemical processes of particulate organic matter occurring in the river under anthropogenic disturbances and its transport to the coastal system is important for environmental resource management. In this study, we investigated the sources and distribution of particulate organic matter (POM) from the upper reaches of the Iyidere River, Türkiye, to the coastal water of the Black Sea during the fall and spring seasons using the elemental (POC and PON (%), C/N), isotopic (δ13C and δ15N), and Bayesian mixing model (MixSIAR) analysis. The POC (%), PON (%), and C/N of POM varied seasonally, indicating that the composition of POM varied with river hydrology, which varies depending on the climate of the region. Both the mixing model and the isotopic and elemental ratios of POM have revealed that the organic matter sources contributing to the riverine of POM, during the fall season, when the precipitation is severe, exhibited a uniform distribution. Heavy rain increased soil erosion along the high-slope land, and as a result, soil and bacteria were identified as the main contributor of POM along the Iyidere River. The results showed that the organic matter sources contributing to POM in the spring season showed significant spatial variation. Terrestrial vegetation, soil OM, and bacteria were the main contributors of POM depending on sites, and these contributions did not show a regular trend along the river. δ15N of POM had significant spatial variation in both seasons that was likely caused by nitrogen inputs derived from anthropogenic activities along the river. The anthropogenic activities and cascade dams causing variations in the contribution of organic matter to the POM are the likely important driving factors in this river-coastal system.

A classification-based approach to mapping particulate organic matter (POM) in inland water using OLCI images.

Particulate organic matter (POM) plays a major role in freshwater ecosystems by serving as a bridge for the conversion of various nutrients. The composition and sources of POM in inland lakes are complex, making it difficult to estimate its concentration accurately via remote sensing. Therefore, a classification-based method based on the sources and composition of POM is proposed for estimating POM concentrations in inland lakes. In this study, 379 samples were collected from ten lakes in the Yangtze River Delta (YRD) at different times. A water-type classification method based on OLCI [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] was developed for POM estimation based on biological and optical characteristics. Water type 1 is relatively clear, and POM may originate from aquatic vegetation or sediment. Water type 2 was dominated by inorganic suspended matter, and POM mainly originated from the attachment and entrainment of inorganic minerals. Water type 3 is an algae-dominated water body, and POM is mainly derived from fresh algal particles and the microbial degradation of phytoplankton. Therefore, specific POM estimation algorithms were developed for each water type. OLCI [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] were used for water type 1; [Formula: see text], [Formula: see text], and [Formula: see text] were adopted for water type 2; and [Formula: see text], [Formula: see text], and [Formula: see text] were selected for water type 3. Using an independent dataset to evaluate the estimation accuracy of the developed algorithm, the results show that the estimation performance of this algorithm is significantly improved compared to the two other algorithms used; the mean absolute percentage errors (MAPE) decreased from 72.56% and 52.21% to 32.61%, and the root mean square errors (RMSE) decreased from 3.05mg/L and 2.24mg/L to 1.75mg/L. A random error analysis of the atmospheric correction demonstrated that this algorithm is robust and can still perform well within a random error of 30%. Finally, this method was successfully applied to map the POM concentrations in the YRD using OLCI images acquired on November 12, 2020.

Sources and fates of particulate organic matter in inland waters with complex land use patterns

Elucidating the sources of particulate organic matter (POM) is the foundation for understanding their fates and the seasonal variation of their movement from the land-to-ocean aquatic continuum (LOAC). The POM from different sources has different reactivity, which determines their fates. However, the key link between the sources and fates of POM, especially in the complex land use watersheds in bays is still unclear. Stable isotopes and contents of organic carbon and nitrogen were applied to reveal them in a complex land use watershed with different gross domestic production (GDP) in a typical Bay, China. Our results showed that the POMs preserved in suspended particulate organic matter (SPM) were weakly controlled by assimilation and decomposition in the main channels. Source apportionments of SPM in the rural area were controlled by soil (46 % ~ 80 %), especially inert soils eroded from land to water due to precipitation. The contribution of phytoplankton resulted from slower water velocity and longer residence time in the rural area. The soil (47 % ~ 78 %) and manure and sewage (10 % ~ 34 %) were the two major contributors to SOMs in the developed and developing urban areas. The manure and sewage were important sources of active POM in the urbanization of different LUI, which showed discrepancies in the three urban areas (10 % ~ 34 %). Due to soil erosion and the most intensive industry supported by GDP, the soil (45 % ~ 47 %) and industrial wastewater (24 % ~ 43 %) were the two major contributors to SOMs in the industrial urban area. This study demonstrated the close relationship between the sources and fates of POM with complex land use patterns, which could reduce uncertainties in future estimates of the LOAC fluxes and secure ecological and environmental barriers in a bay area.

Interactions between particulate organic matter and dissolved organic matter in a weak dynamic bay revealed by stable isotopes and optical properties

Few studies have incorporated the tools of stable isotopes and optical properties to study the biogeochemical process of organic matter (OM), including particulate organic matter (POM) and dissolved organic matter (DOM), which prevents our comprehension of the interactions between POM and DOM in the marine environment. In this study, the origin, distribution, and fate of POM and DOM in Tieshangang Bay, a weak dynamic bay were investigated by measuring δ13C and δ15N of POM, dissolved organic carbon (DOC), and absorption and fluorescence of DOM (CDOM and FDOM). In the upper bay, POM source was mainly originated from terrestrial discharge, whereas the high fluorescence index (FI) indicated that external aquatic organism activity dominated DOM sources. In contrast, in the outer bay, the slightly increased δ13C and enriched δ15N of POM and enhanced fluorescence intensities of protein-like DOM components indicated the considerable contributions of the in situ biological activities to OM. A net addition of DOC and optical components of DOM occurred in both the upper and outer bays. The decomposition of terrestrial POM was responsible for the addition of DOM due to the weak dynamics in the upper bay, whereas the enhanced primary production and the strong decomposition of freshly produced POM jointly contributed to the addition of DOM in the outer bay. Our study suggests that hydrodynamics regulate the biogeochemistry and interactions of POM and DOM in the weak dynamic bay.

Paired Synoptic and Long-Term Monitoring Datasets Reveal Decadal Shifts in Suspended Sediment Supply and Particulate Organic Matter Sources in a River-Estuarine System

The San Francisco Estuary, in central California, has several long-running monitoring programs that have been used to reveal human-induced changes throughout the estuary in the last century. Here, we pair synoptic records of particulate organic matter (POM) composition from 1990–1996 and 2007–2016 with more robust long-term monitoring program records of total suspended sediment (TSS) concentrations generally starting in the mid-1970s to better understand how POM and TSS sources and transport have shifted. Specifically, POM C:N ratios and stable isotope values were used as indicators of POM source and to separate the bulk POC pool into detrital and phytoplankton components. We found that TSS and POC sources have shifted significantly across the estuary in time and space from declines in terrestrial inputs. Landward freshwater and brackish water sites, in the Delta and near Suisun Bay, witnessed long-term declines in TSS (32 to 52%), while seaward sites, near San Pablo Bay, recorded recent increases in TSS (16 to 121%) that began to trend downwards at the end of the record considered. Bulk POM C:N ratios shifted coeval with the TSS concentration changes at nearly all sites, with mean declines of 12 to 27% between 1990–1996 and 2007–2016. The widespread declines in bulk POM C:N ratios and inferred changes in POC concentrations from TSS trends, along with the substantial declines in upstream TSS supply through time (56%), suggest measurable reductions in terrestrial inputs to the system. Changes in terrestrial TSS and POM inputs have implications for biotic (e.g., food web dynamics) and abiotic organic matter cycling (e.g., burial, export) along the estuarine continuum. This work demonstrates how human-generated environmental changes can propagate spatially and temporally through a large river-estuary system. More broadly, we show how underutilized monitoring program datasets can be paired with existing (and often imperfect) synoptic records to generate new system insight in lieu of new data collection.

Assessment of sources variability of riverine particulate organic matter with land use and rainfall changes using a three-indicator (δ13C, δ15N, and C/N) Bayesian mixing model

In intensive agricultural watersheds, riverine particulate organic matter (POM) may be transported from many sources such as rice paddies, crop uplands, forests, and livestock farming areas during rainy seasons. However, the impacts of land-use and rainfall changes on the POM sources are not well understood. In this study, changes in the sources of riverine POM were investigated in an agricultural area of Korea between 2014 and 2020/21. During this period, land-use and rainfall patterns changed dramatically. The δ13C, δ15N, and C/N of the POM sources as well as those of riverine POM were analyzed, and a stable isotope analysis in R (SIAR) model was utilized for source apportionment. There were differences in δ13C, δ15N, and C/N among the sources. For example, manure had higher δ13C (−22.6 ± 3.3‰) and δ15N (+10.6 ± 5.9‰) than soils (from −28.0 ± 0.8‰ to −25.1 ± 1.2‰ for δ13C and +3.6 ± 1.7‰ to +9.8 ± 1.4‰ for δ15N). For soils, the δ13C and δ15N were higher for upland soils, while C/N was greater for forest soils than for others. For riverine POM, the δ15N marginally changed; however, the δ13C and C/N increased from −26.1 ± 0.9‰ to −20.8 ± 5.3‰ and from +7.7 ± 1.7 to +18.8 ± 8.3 between 2014 and 2020/21, respectively. The SIAR model showed that the contributions of paddy (from 41.0% to 14.9%) and upland fields (from 48.1% to 23.7%) to riverine POM decreased between the periods due to decreased paddy area and the implementation of best management practice on upland fields, respectively. However, the contribution of forests (from 3.5% to 28.0%) and manure (from 7.4% to 33.5%) increased probably due to improper management of forest clear-cutting sites and livestock manure storage sites. The contributions of agricultural soils to riverine POM decreased in drier years. Our study suggests that land management rather than land-use area is critical in riverine POM management, particularly in wetter years.

Photochemical and microbial transformation of particulate organic matter depending on its source and size

Particulate organic matter (POM) in water systems can be converted into dissolved organic matter (DOM) through various pathways depending on its properties and transformation. Thus, information on the behavior of POM is crucial for fully understanding water systems and the carbon cycle. In this study, the effects of particle size and the source of POM, as well as photochemical and microbial changes in DOM characteristics subsequently released from POM were evaluated using various spectral indices, excitation-emission matrix combined with parallel factor analysis components, and principal component analysis. The amount of dissolved organic carbon (DOC) released from POM during suspension was significantly associated with the carbon content of POM (p < 0.05). The amount of DOC (mg-C/g-SS) decreased in mineral-bound POM as a result of microbial degradation but increased in biogenic POM as a result of microbial dissolution, owing to the structural differences in organic matter from different sources. Mineral-bound POM showed more DOC production by photochemical desorption than microbial degradation, whereas biogenic POM displayed the opposite trend. The DOM derived from fine POM had more humified terrestrial humic-like substances than those derived from coarse POM. Principal components 1 and 2 were associated with DOC production and degree of humification, respectively. The increase in the degree of aromaticity and humification of organic matter was higher in mineral-bound POM by photochemical desorption of highly humified organic matter and in the biogenic POM by microbial dissolution. In conclusion, this study was able to provide basic information on the transformation of POM, thus, it is expected to broaden the knowledge of the biogeochemical cycle of organic matter.

Seasonally and Spatially Variable Organic Matter Contributions From Watershed, Marine Macrophyte, and Pelagic Sources to the Northeast Pacific Coastal Ocean Margin

Globally, coastal waters are considered biogeochemical hotspots because they receive, transform, and integrate materials and waters from both land and the open ocean. Extending from northern California to southeast Alaska, the Northeast Pacific Coastal Temperate Rainforest (NPCTR) region is no exception to this, and hosts a diversity of watershed types (old-growth rainforest, bog forest, glaciers), and tidal (sheltered, exposed) and pelagic marine (deep fjord, shallow estuary, well-mixed channel) environments. With large freshwater fluxes to the coastal ocean, cross-ecosystem connectivity in the NPCTR is expected to be high, but seasonally variable, with pulses in runoff from rainfall, snowmelt and glacial melt, and primary production associated with changes in ocean upwelling and incident light. However, the relative contribution of each ecosystem to surface ocean organic matter pools over time and space remains poorly constrained, despite their importance for the structure and function of coastal marine ecosystems. Here, we use a four-year dataset of particulate organic matter (POM) chemical composition (δ13C, δ15N, C:N ratio) to quantify the relative contributions of watershed materials via riverine inputs, marine phytoplankton, and macrophytes (macroalgae and seagrass) to surface waters (0-10 m) at 11 stations representing fjord, shallow non-fjord estuary, sheltered channel and well-mixed coastal environments at the heart of the NPCTR in British Columbia, Canada. Watershed, marine phytoplankton, and macrophyte contributions to surficial POM ranged between 5-78%, 22-88%, and 0.1-18%, respectively, and varied by season and station. Watershed inputs were the primary source of POM across all stations in winter and were important throughout the year within the fjord. Marine phytoplankton were the principal source of POM in spring and at all stations outside of the fjord through summer and autumn, while macrophyte contributions were greatest in summer. These results demonstrated high, but seasonally and spatially variable, connectivity between ecosystems that are often considered in isolation of one another and highlight the need to consider coastal waters as integrated land-ocean meta-ecosystems. Future work should investigate how heterogeneity in POM sources determines its fate in coastal ecosystems,and the relative importance of different basal organic matter sources for the marine food web.

Effects of pH Adjustment on the Release of Carbon Source of Particulate Organic Matter (POM) in Domestic Sewage

The use of anaerobic hydrolytic fermentation to develop more available carbon sources from domestic sewage influent particulate organic matter (POM) has received increasing attention. However, the slow hydrolysis rate of POM limits the application of this technology. This study aimed to improve the carbon source release efficiency of POM by pH adjustment and to reveal the hydrolysis mechanism. Results showed that adjusting the initial pH of POM to 3, 9, and 11 enhanced carbon source release in the anaerobic hydrolysis fermentation process of POM. The pretreatment under pH value of 11 contributed to the highest yield and productivity of carbon source, reaching the soluble chemical oxygen demand (SCOD) of 2782 mg/L at the 4th day. The pH 3 pretreatment was more beneficial for phosphorus resource recovery, which contributed to the highest release concentration of PO43−-P, reaching 48.2 mg/L at the 3rd day, accounting for 90% of TP. Microbial community structure analysis indicated that pH 11 preconditioning promoted the enrichment of proteolytic bacteria (Proteocatella and Proteiniclasticum) and polysaccharide hydrolytic bacteria (Trichococcus and Acinetobacter) and inhibited the growth of acetate-consuming methanogenic archaea, which contributed to the highest carbon release of POM in domestic sewage.

Spatial Variation in Elemental and Isotopic Compositions of Carbon and Nitrogen in a Coastal Lagoon Reveals Natural and Anthropogenic Influences

Increased delivery of particulate organic matter (POM) to coastal lagoons has caused disturbance in nutrient cycling, water quality and aquatic biodiversity. Therefore, the major concern in coastal management is assessment of sources and pathways of POM in order to maintain ecosystem health. Elemental and isotopic of POM compositions are being increasingly used as useful markers for sources of POM in coastal ecosystems to obtain understanding of the nutrient sources and anthropogenic influences. In this study, variation in elemental and stable isotope compositions of carbon (C) and nitrogen (N) were measured in Cau Hai lagoon, Central Vietnam to characterize the possible sources of C and N. Variations in values of C/N ratios (8.17 ± 0.14) and 13C (-22.00‰ ± 0.13) indicated that POM was mainly of autochthonous origin due to high microalgae productivity. The values of 15N (3.83‰ ± 0.08) were likely inferred from potential input of POM from aquaculture practices. These results suggest that main sources of POM in the lagoon were derived from autochthonous microalgae and slightly anthropogenic impacts through aquaculture activities. Control POM load should be taken into account in maintaining water quality and biodiversity in the lagoon to inhibit microalgae biomass and shading due to nutrient enrichment.

Effect of Ecosystem Degradation on the Source of Particulate Organic Matter in a Karst Lake: A Case Study of the Caohai Lake, China

The cycle of biogenic elements in lakes is intimately linked with particulate organic matter (POM), which plays a critical role in ecosystem restoration and the control of eutrophication. However, little is known regarding the functionality of ecosystem degradation on the source of POM in the water of a karst lake. To fill this knowledge gap, herein we compared the temporal and spatial distribution characteristics of POM prior to and after ecosystem degradation in the karst lake Caohai Lake, located in the southwest of China, and analyzed the source of POM using a combination of carbon and nitrogen stable isotopes (δ13C–δ15N). Our results showed that the dissolved oxygen (DO) concentration and pH values decreased, and the concentrations of POM in water increased by 11% and 31% in the wet and dry seasons, respectively. The decrease in the δ13C value of POM was accompanied by the increase in the δ15N value of POM in the water of Caohai lake. Prior to the ecosystem’s degradation, sediment resuspension (28%) and submerged macrophytes (33%) were the dominant sources of POM in lake water. In contrast, sediment resuspension (51%) was the major source of POM after the ecosystem’s degradation. Environmental factors, including DO, turbidity, water depth, and water temperature, that are related to photosynthesis and sediment resuspension are the main factors controlling the spatiotemporal distribution of POM. The resuspension of sediment reduced the transparency of the water, limiting effective photosynthesis, impeding the survival of submerged macrophytes, and, consequently, deteriorating the ecosystem. We propose that the control of sediment resuspension is important for improving the water transparency that creates an appropriate habitat for the restoration of the submerged macrophyte community.