Toward a typology of river functioning: a comprehensive study of the particulate organic matter composition at the multi-river scale

Dynamics of particulate organic matter composition in coastal systems: A spatio-temporal study at multi-systems scale

Seasonal and interannual variation of the stable carbon (C) and nitrogen (N) isotope composition of suspended particulate organic matter (POM) was measured in the brackish and tidal freshwater regions of the Mattaponi River, a tributary of the York River, Virginia, and a pristine end member on a continuum of anthropogenic modification within Chesapeake Bay. A principal components analysis indicated that seasonal variation was related to physical mixing and river discharge. Freshwater POM had high C : N (.12), depleted particulate organic carbon isotopic composition (d13CPOC, 226% to 230%), and depleted particulate nitrogen isotopic composition (d15NPN, 2–10%) compared to brackish water POM, which had lower C : N and enriched d13CPOC (224% to 227%) and d15NPN (7–15%). During high discharge events, the d13CPOC was enriched, the d15NPN depleted, and the C : N high relative to low discharge periods, indicating a large contribution from terrestrial-derived material. Within tidal freshwater, POM was comprised of humic-rich sediment, vascular plant matter, and phytoplankton produced in situ. Nonconservative mixing behavior was observed. Endogenously produced phytoplankton increased POC concentrations in tidal freshwater and oligohaline portions during base flows. Where estuarine and riverine POM mixed, the isotopic composition of the POM was homogenized, blurring source-specific characters observed upriver and thereby emphasizing the need to characterize the freshwater end member of estuaries carefully in order to identify POM sources. In estuaries, identifying the origin of particulate organic matter (POM) is difficult because POM is received from multiple sources, including riparian vegetation, adjacent marsh vegetation, submerged and emergent aquatic vegetation and associated epiphytes, and phytoplankton produced in situ. Early research using the stable isotope composition of estuarine POM to identify its dominant origins and fates led investigators to conclude that estuarine phytoplankton and terrestrial material were the major contributors to estuarine organic matter (OM; dissolved and particulate fractions) and that these sources

Riverine particulate organic matter (POM) samples were collected bi‐weekly to monthly from 40 sites in the Mississippi, Colorado, Rio Grande, and Columbia River Basins (USA) in 1996–97 and analysed for carbon and nitrogen stable isotopic compositions. These isotopic compositions and C : N ratios were used to identify four endmember sources of POM: plankton, fresh terrestrial plant material, aquatic plants, and soil organic material. This large‐scale study also incorporated ancillary chemical and hydrologic data to refine and extend the interpretations of POM sources beyond the source characterizations that could be done solely with isotopic and elemental ratios. The ancillary data were especially useful for differentiating between seasonal changes in POM source materials and the effects of local nutrient sources and in‐stream biogeochemical processes.Average values of δ13C and C : N for all four river systems suggested that plankton is the dominant source of POM in these rivers, with higher percentages of plankton downstream of reservoirs. Although the temporal patterns in some rivers are complex, the low δ13C and C : N values in spring and summer probably indicate plankton blooms, whereas relatively elevated values in fall and winter are consistent with greater proportions of decaying aquatic vegetation and/or terrestrial material. Seasonal shifts in the δ13C of POM when the C : N remains relatively constant probably indicate changes in the relative rates of photosynthesis and respiration. Periodic inputs of plant detritus are suggested by C : N ratios >15, principally on the Columbia and Ohio Rivers. The δ15N and δ13C also reflect the importance of internal and external sources of dissolved carbon and nitrogen, and the degree of in‐stream processing. Elevated δ15N values at some sites probably reflect inputs from sewage and/or animal waste. This information on the spatial and temporal variation in sources of POM in four major river systems should prove useful in future food web and nutrient transport studies. Published in 2001 by John Wiley & Sons, Ltd.

Particulate organic matter (POM) characteristics and variability have been widely studied along the land-ocean aquatic continuum, yet, gaps remain in quantifying its source composition, fluxes, and dynamics at the river-estuary interface. POM in rivers consists of a complex mixture of sources, derived both from locally produced (i.e. phytoplankton) and from adjacent ecosystems (e.g. terrestrial POM). Each source differ in its trophic and biogeochemical characteristics, hence impacting its integration into local food webs, its transfer to estuaries and sea, and its contribution to biogeochemical processes. In this study, we use a robust approach based on in situ POM to characterize river POM end-members, to quantify POM composition and dynamics, and to identify the related key drivers. This study was performed at the River-Estuary interface of one of the main rivers in Western Europe (the Loire River, France). For 3 years, we conducted bimonthly measurements of carbon and nitrogen isotopic (δ13C, δ15N) and elemental (C/N) ratios to quantify the contribution of two sources (phytoplankton and terrestrial POM) to the POM mixture and calculated annual fluxes of particulate organic carbon (POC) and nitrogen (PN) sources. Throughout the year, POM consisted of ~65% phytoplankton and 35% terrestrial POM. The mean annual export fluxes were 40.6 tPOC/year and 2.45 tPN/year over the studied period, with half of it originating from phytoplankton (53 and 55% for POC and PN, respectively). We observed a clear seasonal pattern in POM composition: phytoplankton predominated from March to October, in relation to high primary production, while terrestrial contributions were the highest from November to February, driven by greater autumn-winter hydrodynamics. Our study illustrate the interest of such an approach to quantify POM composition in aquatic system and estimate source fluxes, and provide fundamental results for estimating seasonal baselines in food webs, establishing biogeochemical budgets, and quantifying POM exports to estuarine and marine environments. Applying this methodology across a broad spectrum of aquatic systems should enhance our understanding of biogeochemical processes and organic matter transformation along the land-ocean continuum and illustrates the contribution of these ecosystems to global biogeochemical cycles.

Origin and composition of particulate organic matter in a macrotidal turbid estuary: The Gironde Estuary, France

Bottom trawling represents nowadays one of the most severe anthropogenic disturbances at sea, and determines large impacts on benthic communities and processes. Bottom trawling determines also local sediment resuspension and the effects of the injection of large amounts of surface sediments into the water column have been repeatedly investigated. Few studies have assessed the consequences of sediment resuspension caused by bottom trawling on the quantity, biochemical composition and bioavailability of suspended organic particles and how these eventually rival those exerted by natural storms. To provide insights on this poorly addressed issue, we investigated concentrations and biochemical composition of total and enzymatically digestible pools of particulate organic matter (POM) in the Thermaikos Gulf (Mediterranean Sea) under calm sea conditions, during intensive trawling activities, and after a severe storm. We show here that sediment resuspension caused by trawling can cause large effects on POM quantity, biochemical composition and bioavailability. Both during trawling and after the storm, the relative importance of the carbohydrate pools increased (in the upper water column) and the total lipid concentrations decreased (in the intermediate and bottom layers) when compared to values measured during calm conditions. These results would suggest that bottom trawling could inject in the upper water column POM pools more refractory in nature (<em>e.g</em>., carbohydrates) than those present in calm or after-storm conditions. By contrast, we show also that the bioavailable fraction of biopolymeric C increased significantly during trawling in the upper water column of the shallowest stations and in the bottom water column layer of the deepest ones. These results provide evidence that bottom trawling can influence the overall trophic status of coastal waters, exerting effects similar or stronger than those caused by natural storms, though of variable amplitude depending on the water depth. Since bottom trawling is carried out worldwide and natural storms at sea can be frequent and intense, we claim for the need of assessing new adapting management strategies of bottom trawling in order to mitigate the synergistic impacts of anthropogenic and natural sediment resuspension on coastal biogeochemical cycles.

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.

The biochemical composition and spatial distribution of particulate organic matter (POM) were studied in the Ross Sea (Antarctica) in summer 1989 to assess the quantitative role of organic carbon fractions in the cycling of organic matter in the water column. Large differences in chemical composition were observed between surface and deep layers. The results indicated that, despite large geographical differences, POM was quite homogeneous, of phytoplankton origin and mostly detrital. Different ratios were used to investigate the changes in biochemical composition of particulate organic matter in relation to the ice-melting: C∶N (organic carbon∶organic nitrogen ratio) and C-POM∶POC (sum of carbohydrate, protein and lipid carbon∶total organic carbon ratio) were used to analyse the percentage of refractory organic material. PPRT∶PCHO (protein∶carbohydrate ratio) were used to establish POM “age” and RNA∶DNA ratios as a relative measure of particulate activity; POC∶Chl a and N-PPRT∶Chl a ratios were used to estimate the autotrophic contribution to the suspended particulate organic matter. Despite its low caloric value (5.3 Kcal g POM−1), an high caloric content in the photic layer (1.6 Kcal m−3 of POM and 2.5 Kcal m−3 of POC) was found thus indicating that a large amount of food was available to higher trophic levels.

Dual stable isotope tracing the source and composition of POM during algae blooms in a large and shallow eutrophic lake: All contributions from algae?

The chemical composition of Black Sea suspended particulate organic matter: pyrolysis-GC/MS as a complementary tool to traditional oceanographic analyses

We sampled freshwater suspended particulate organic matter (POM) to determine its carbon and nitrogen stable isotope composition and collected co‐located water chemistry data in California's Sacramento—San Joaquin Delta from sites on the Mokelumne and Cosumnes rivers. A 10‐km2 area was sampled across 12 sites and divided among three habitat types (i.e. riverine, slackwater/slough, and off‐channel), 34 times between November 2016 and July 2017. Here, we describe the variability in water quality and POM variables, and assess factors associated with that variability using dimensional reduction and linear modelling within the context of our habitat types. The stable isotope composition of freshwater POM and water chemistry variables differed significantly across small areas (<10 km) and short time frames (weekly). Hydrological connectivity amongst sites was found to be an important factor in the isotopic and elemental composition of POM. During periods of low hydrological connectivity, in situ dynamics were strongly associated with differentiation of POM in different habitats. Discharge (16–433 m3/s) and water temperature (8–30°C) were the variables most associated with variations in the composition of POM. Slackwater sites showed the greatest variability in POM composition, which may be symptomatic of longer water residence times, increased cycling rates of nutrients and organic matter, or a combination of the two. Variability in POM stable isotope composition demonstrates that caution should be exercised when interpreting analyses that assume a static POM stable isotope composition based on two‐end member mixing. Unconstrained variability in space or time could confound interpretations of models and data. Moving forward, conceptual and numerical models for river ecosystems that emphasise temporally heterogeneous lateral exchange amongst habitat patches should be prioritised when considering restoration efforts and monitoring outcomes.

The stable carbon isotope composition (δ 13 C) of particulate organic matter (POM) has been used to infer sources of organic matter and major biogeochemical processes in lakes. However, very few studies have compared the δ 13 C POM among lakes of different limnological properties. Here, we report such an analysis to understand the patterns and controls of stable isotopes of POM from 96 lakes in Florida, USA. Results indicated that δ 13 C POM increased significantly with the increases in lake area, pH and trophic state, but decreased with the increase in CO 2 concentration and water color content. δ 13 C POM in a small set of these lakes showed a positive relationship with δ 13 C of dissolved inorganic carbon (DIC). There was a widespread 13 C depletion of POM in the study lakes, especially in lakes with high water color, suggesting allochthonous subsidy of phytoplankton production. Multiple regression models pointed to the importance of trophic state, color and pH. This study demonstrated that the δ 13 C POM is indicative of carbon source, trophic state and ecosystem metabolism in lakes.

The retention efficiency of a specific reach is one key factor controlling the dynamics of particulate organic matter (POM) in running waters. Floodplains enhance the retention of riverine POM, thereby altering its structure and diagenetic state, and constitute a substantial autochthonous source. Hydrological connectivity between the river and its floodplains determines the impact of floodplains for the POM dynamics of the entire river. The elemental and isotopic (δ 13 C, δ 15 N) composition and microbial utilisation of POM was investigated in relation to hydrological connectivity in the Danube River and two floodplain segments, one of which was isolated, the other dynamically connected. The latter had been subjected to river restoration measures. An increased integration in the riverine network was the effect of the restoration. Within both floodplains, isolated, disconnected and connected conditions were distinguished depending on the location of inflow areas and the riverine water level. Hydrological connectivity, expressed as water age, significantly influenced the quantity and composition of POM in the dynamic floodplain. Carbon isotopic composition of POM clearly separated riverine and connected conditions from those disconnected and isolated, the latter representing autochthonous material mainly derived from plankton. At disconnection, the maximum contribution of phytoplankton to POC was determined (54.5 % ± 28.8 SE), which also supported the highest bacterial productivity (4.61μg Cl -1 h -1 ± 0.55 SE). Connected conditions were characterised by relatively enriched, allochthonous POM (δ 13 C: -23.27‰ ± 0.98 SE). In the isolated floodplain, high standing stocks of aquatic macrophytes developed which act as 'sinks' of carbon for the river. Restoration efforts like the Danube restoration project, which increase hydrological connectivity, enhance the importance of autochthonous POM and its further transformation by re-establishing dynamically connected floodplains in regulated, temperate large rivers.

Different sources of particulate organic matter (POM) as well as its composition affect the biological food web and hence the self-purification potential and water quality of rivers. We studied the effect of a large shallow lake on the POM pool of the water passing through it. Over four years, we analysed monthly the amount and composition of POM and a set of environmental variables in the inflows and in the outflow of Lake Võrtsjärv (Estonia). In the inflows, the live pool of POM consisted of phytoplankton – small crypto-, dino-, and chlorophytes. The concentration of chlorophyll a (Chl a), as a proxy of phytoplankton biomass, was positively correlated with temperature and total phosphorus and negatively with dissolved silica, total nitrogen, and discharge. In the outflow, the share of the live component of POM was much larger than in the inflows but was also dominated by phytoplankton represented by grazing resistant filamentous cyanobacteria. Chl a was positively correlated with total phosphorus, temperature, pH, and precipitation, and negatively with dissolved silica, total nitrogen, and discharge in the outflow. The different amounts, composition, and seasonal dynamics of POM in the inflows and in the outflow have potentially substantial impacts on the food web with a predominating classical pathway in the inflows versus a detrital pathway in the outflow.

Dynamics of particulate organic matter composition in coastal systems: Forcing of spatio-temporal variability at multi-systems scale