Amount Of Dissolved Organic Carbon Research Articles

Dissolved organic matter released from beach wrack is source-specific and molecularly highly diverse

AbstractBeach wrack is an important supplier of nutrients and organic matter to sandy beach ecosystems and underlying subterranean estuaries (STEs), producing metabolic hotspots in these otherwise organic carbon- and nutrient-poor environments. To assess the impact of beach wrack type (e.g., marine, terrestrial, plant, animal) and environmental settings (e.g., tidal inundation, precipitation, and solar irradiation) on nutrient and dissolved organic matter (DOM) release, a series of leaching experiments was conducted. Quantities of leached nutrients and dissolved organic carbon (DOC) were determined, and DOM molecular composition was investigated using Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Millimolar—to molar amounts of DOC and dissolved nitrogen were released from the beach cast per kg dry weight, with type of wrack and leaching medium (fresh- vs. saltwater) exerting the biggest influences. Exemplary for animal cast, jellyfish leached up to two 100-fold more, mostly organic, nitrogen compared to all other beach wrack types. FT-ICR-MS data of solid-phase extracted DOM indicated that beach wrack releases compounds with putative mono- and oligosaccharide-, amino acid- and vitamin-type molecular formulae, which likely serve as valuable substrate for heterotrophic microorganisms. DOM from the brown seaweed Fucus sp. was more aromatic than seawater DOM and even beach wrack of terrestrial origin, probably from structural components and secondary metabolites such as phlorotannins. We conclude that DOM and nutrient release from beach wrack strongly depends on wrack type and leaching medium, may obscure molecular provenance proxies (e.g., terrestrial indices), and adds a nutritional boost to infiltrating sea- and rainwater which likely impact microbial respiration rates in the STE.

Metagenomic analysis of the microbial communities and associated network of nitrogen metabolism genes in the Ryukyu limestone aquifer.

While microbial biogeochemical activities such as those involving denitrification and sulfate reduction have been considered to play important roles in material cycling in various aquatic ecosystems, our current understanding of the microbial community in groundwater ecosystems is remarkably insufficient. To assess the groundwater in the Ryukyu limestone aquifer of Okinawa Island, which is located in the southernmost region of Japan, we performed metagenomic analysis on the microbial communities at the three sites and screened for functional genes associated with nitrogen metabolism. 16S rRNA amplicon analysis showed that bacteria accounted for 94-98% of the microbial communities, which included archaea at all three sites. The bacterial communities associated with nitrogen metabolism shifted by month at each site, indicating that this metabolism was accomplished by the bacterial community as a whole. Interestingly, site 3 contained much higher levels of the denitrification genes such as narG and napA than the other two sites. This site was thought to have undergone denitrification that was driven by high quantities of dissolved organic carbon (DOC). In contrast, site 2 was characterized by a high nitrate-nitrogen (NO3-N) content and a low amount of DOC, and this site yielded a moderate amount of denitrification genes. Site 1 showed markedly low amounts of all nitrogen metabolism genes. Overall, nitrogen metabolism in the Ryukyu limestone aquifer was found to change based on environmental factors.

Deterioration of single-use biodegradable plastics in high-humidity air and freshwaters over one year: Significant disparities in surface physicochemical characteristics and degradation rates

More single-use plastics are accumulating in the environment, and likewise biodegradable plastics (BPs), which are being vigorously promoted, cannot escape the fate. Currently, studies on the actual degradation of BPs in open-air and freshwaters are underrepresented despite they are potentially headmost leakage and contamination sites for disposable BPs. Herein, we compared the degradation behavior of six BP materials and non-degradable polypropylene (PP) plastics over a 1-year in situ suspension in the high-humidity air, a eutrophic river, and an oligotrophic lake. Moreover, a 3-months laboratory incubation was performed to detect the release of dissolved organic carbon (DOC) from BPs. In both air and freshwaters, poly(p-dioxanone) (PPDO) degraded significantly while PP and polylactic acid (PLA) showed no signs of degradation. The average degradation rates of three poly(butylene adipate-co-terephthalate) (PBAT)-based films varied: 100% in river, 55% in lake, and 10% in air. In addition to PLA, surface chemical groups, hydrophilicity, and thermal stability of BPs changed, and microplastics were found on their surfaces. Correspondingly, BPs with faster degradation rates released relatively higher amounts of DOC. Environmental microbial and chemical characteristics may contribute to differences in BP degradation besides polymer specificity. Altogether, our results indicate the need for appropriate monitoring of BPs.

Hydrological connectivity controls dissolved organic carbon exports in a peatland-dominated boreal catchment stream

Abstract. The magnitudes of dissolved organic carbon (DOC) exports from boreal peatlands to streams through lateral subsurface flow vary during the ice-free season. Peatland water table depth and the alternation of low and high flow in peat-draining streams are thought to drive this DOC export variability. However, calculation of the specific DOC exports from a peatland can be challenging considering the multiple potential DOC sources within the catchment. A calculation approach based on the hydrological connectivity between the peat and the stream could help to solve this issue, which is the approach used in the present research. This study took place from June 2018 to October 2019 in a boreal catchment in northeastern Canada, with 76.7 % of the catchment being covered by ombrotrophic peatland. The objectives were to (1) establish relationships between DOC exports from a headwater stream and the peatland hydrology; (2) quantify, at the catchment scale, the amount of DOC laterally exported to the draining stream; and (3) define the patterns of DOC mobilization during high-river-flow events. At the peatland headwater stream outlet, the DOC concentrations were monitored at a high frequency (hourly) using a fluorescent dissolved organic matter (fDOM) sensor, a proxy for DOC concentration. Hydrological variables, such as stream outlet discharge and peatland water table depth (WTD), were continuously monitored at hourly intervals for 2 years. Our results highlight the direct and delayed control of subsurface flow from peat to the stream and associated DOC exports. Rain events raised the peatland WTD, which increased hydrological connectivity between the peatland and the stream. This led to increased stream discharge (Q) and a delayed DOC concentration increase, typical of lateral subsurface flow. The magnitude of the WTD increase played a crucial role in influencing the quantity of DOC exported. Based on the observations that the peatland is the most important contributor to DOC exports at the catchment scale and that other DOC sources were negligible during high-flow periods, we propose a new approach to estimate the specific DOC exports attributable to the peatland by distinguishing between the surfaces used for calculation during high-flow and low-flow periods. In 2018–2019, 92.6 % of DOC was exported during flood events despite the fact that these flood events accounted for 59.1 % of the period. In 2019–2020, 93.8 % of DOC was exported during flood events, which represented 44.1 % of the period. Our analysis of individual flood events revealed three types of events and DOC mobilization patterns. The first type is characterized by high rainfall, leading to an important WTD increase that favours the connection between the peatland and the stream and leading to high DOC exports. The second is characterized by a large WTD increase succeeding a previous event that had depleted DOC available to be transferred to the stream, leading to low DOC exports. The third type corresponds to low rainfall events with an insufficient WTD increase to reconnect the peatland and the stream, leading to low DOC exports. Our results suggest that DOC exports are sensitive to hydroclimatic conditions; moreover, flood events, changes in rainfall regime, ice-free season duration, and porewater temperature may affect the exported DOC and, consequently, partially offset the net carbon sequestration potential of peatlands.

Do drinking water treatment residuals underperform in the presence of compost in stormwater media filters?

Drinking water treatment residuals (WTR), a waste-derived product, are often recommended to use as an amendment in stormwater biofilters to enhance their capacity to remove phosphate and microbial pollutants. However, their efficacy has been assumed to remain high in the presence of compost, one of the most common amendments used in biofilters. This study tests the validity of that assumption by comparing the removal capacities of WTR-amended biofilters with and without the presence of compost. Our results show that amending sand with WTR increased E. coli removal by at least 1-log, but the addition of compost in the sand-WTR media lowered the removal capacity by 13 %. Similarly, the addition of WTR to sand improved phosphate removal to nearly 1177 %, but the removal decreased slightly by 8 % when adding compost to the media. The results confirmed that dissolved organic carbon (DOC) leached from the compost could compete for adsorption sites for bacteria and phosphate, thereby lowering WTR's adsorption capacity based on the amount of DOC adsorbed on WTR. Collectively, these results indicate that the stormwater treatment industry should avoid mixing compost with WTR to get the maximum benefits of WTR for bacterial removal and improve the performance lifetime of WTR-amended biofilters.

Stoichiometry of carbon, nitrogen, and phosphorus released from the leaf litter of various temperate tree species.

Dissolved organic matter and inorganic nutrients released from forest leaf litter through leaching are the important energy and nutrient sources that support the production of aquatic food webs. Leaf litter-derived dissolved organic carbon (DOC) is a critical energy source for aquatic heterotrophic microbes, and inorganic nitrogen and phosphorus can enhance primary production. In this study, we experimentally measured the release efficiencies and amounts of DOC, total dissolved nitrogen (TDN), and total dissolved phosphorus (TDP) of the leaf litter from 11 temperate tree species by soaking the leaf litter in water for 28 days. We found that the maximal release efficiency (% of element released per estimated mass of the element) was the highest for P and lowest for N. These efficiencies were species-specific. Additionally, the DOC:TDP, DOC:TDN, and TDN:TDP ratios varied among the leachate of different leaf litter species. DOC:TDP increased with the C:P ratio in leaf litter biomass but is considerably lower; TDN:TDP was lower than the N:P ratio in leaf litter biomass as well; DOC:TDN ratio was higher than the C:N ratio in leaf litter biomass. These results suggest that the ratios of DOC to dissolved N and P nutrients released into water are related to, but not the same as, the stoichiometry of leaf litter biomass. Based on these findings, we concluded that changes in the vegetations with different leaf litter stoichiometry can alter the relative importance of detrital and grazing food chains in aquatic ecosystems.

Dissolved organic carbon export in a small, disturbed peat catchment: Insights from long‐term, high‐resolution, sensor‐based monitoring

AbstractUnderstanding dissolved organic carbon (DOC) export dynamics from carbon‐rich environments is critical. Peatlands act as terrestrial carbon stores, and consequently supply substantial amounts of DOC to drainage. This DOC flux is temporally heterogeneous and subject to long‐ and short‐term variability. Ultrahigh temporal resolution sampling (< hourly) is still in‐frequent in peatland catchments. We used a field‐deployable —ultraviolet–visible light spectrometer (Spectro::lyser™) and monitored DOC flux from a temperate peatland over 31 months to examine seasonal and event dynamics. DOC concentration varied from 6.8 to 63.5 mg L−1, in the higher reported range for peatlands and showed clear seasonal (high‐summer, low‐winter) variability coinciding with elevated biological productivity in the peatland. Discharge was an unreliable predictor of instantaneous DOC concentration overall, with antecedent water temperatures proving the most reliable predictor overall. Discharge drove total DOC export in the catchment, where the top 10% of flow events, accounted for 41.3% of all DOC exported—increasing to 84.6% in the top 50% of flow events. Total estimated catchment DOC flux was sensitive to measurement frequency: increasing from every 30 min to daily altered export estimates by < 1%, increasing to > 10% at 1‐week intervals. The variation in estimated flux increased approximately linearly with reduced sampling frequency, reaching > 40% at monthly intervals. High‐resolution data reveal the large amount of within‐site complexity of DOC export dynamics in a temperate peatland and provide evidence on the subsequently recommended sampling frequency for the future elucidation of detailed DOC budgets in these environments.

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.

Origin, accumulation and fate of dissolved organic matter in an extreme hypersaline shallow lake

Hypersaline endorheic aquatic systems (H-SEAS) are lakes/shallow playas in arid and semiarid regions that undergo extreme oscillations in salinity and severe drought episodes. Although their geochemical uniqueness and microbiome have been deeply studied, very little is known about the availability and quality of dissolved organic matter (DOM) in the water column.. A H-SEAS from the Monegros Desert (Zaragoza, NE Spain) was studied during a hydrological wetting-drying-rewetting cycle. DOM analysis included: (i) a dissolved organic carbon (DOC) mass balance; (ii) spectroscopy (absorbance and fluorescence) and (iii) a molecular characterization with Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The studied system stored a large amount of DOC and under the highest salinity conditions, salt-saturated waters (i.e., brines with salinity > 30%) accumulated a disproportionate quantity of DOC, indicating a significant in-situ net DOM production. Simultaneously, during the hydrological transition from wet to dry, the DOM pool showed strong alterations of it molecular composition. Spectroscopic methods indicated that aromatic and degraded DOM was rapidly replaced by fresher, relatively small, microbial-derived moieties with a large C/N ratio. FT-ICR-MS highlighted the accumulation of small, saturated and oxidized molecules (molecular O/C > 0.5), with a remarkable increase in the relative contribution of highly oxygenated (molecular O/C>0.9) compounds and a decrease of aliphatic and carboxyl-rich alicyclic moleculesThese results indicated that H-SEAS are extremely active in accumulating and processing DOM, with the notable release of organic solutes probably originated from decaying microplankton under large osmotic stress at extremely high salinities.

Carbon metabolism and bioavailability of dissolved organic carbon (DOC) fluxes in seagrass communities are altered under the presence of the tropical invasive alga Halimeda incrassata

Seagrass beds act as blue carbon sinks globally as they enhance the trapping of recalcitrant (i.e., low biodegradability) organic carbon in their sediments. Recent studies also show that the recalcitrant fraction of the dissolved organic carbon (DOC) pool in seawater has an important role as long-term carbon sequestration in oceans. Although seagrasses are known for the large amount of DOC they export, little attention has been given to its biodegradability, which ultimately determinates its fate in the coastal carbon cycle. In turn, invasive algae are a major global concern in seagrass ecosystems since they can deeply modify their structure and functions, which may affect carbon metabolism and DOC release. This work assesses how the presence of Halimeda incrassata, an invasive tropical calcareous macroalga, modifies carbon metabolism and DOC fluxes in invaded areas dominated by the seagrass Cymodocea nodosa. Our results show that stands with the presence of this seagrass (i.e., both monospecific and mixed meadow) had the highest production values, acting as high DOC producers in both winter (mainly of labile DOC; DOCL) and summer (mainly as recalcitrant DOC; DOCR). In contrast, monospecific H. incrassata beds exhibited low production values, and the presence of this macroalga (either as monospecific beds or mixed with C. nodosa) triggered the shift from a net DOC-producing-system in summer (mainly DOCL) to a net DOC-consuming-system in winter. This work thus suggests that C. nodosa meadows have the potential to export a significant fraction of both labile and recalcitrant DOC, and that the spread of this invasive alga might decrease the C export capacity of seagrass meadows. Such shift would imply the reduction of a quick and efficient transfer of carbon and energy to higher trophic levels, and might reduce the blue carbon potential of seagrasses as dissolved form in the water column.

Spatiotemporal carbon, nitrogen and phosphorus stoichiometry in planktonic food web in a northern coastal area

The concentrations of ambient nutrients and dissolved organic carbon (DOC) in northern coastal ecosystems often show large variations, due to the spatiotemporal differences in terrestial inputs. How these variations affect the stoichiometry of coastal planktonic organisms is, however, poorly known. Here we assessed the spatiotemporal variability of C, nitrogen (N), and phosphorous (P) concentrations of the seawater on the elemental stoichiometry of seston and dominant mesozooplankton taxa in a coastal area of the northern Baltic Sea. The freshwater inflow peaked in spring following the snowmelt and brought a significant amount of DOC, but not N and P to the coastal system. DOC was the main environmental descriptor for seston C:N stoichiometry. The C:N ratio of seston from 0.7 to 50 μm and mesozooplankton followed the temporal pattern of water C:N ratio, while the temporal trend of bacteria C:N showed an opposite pattern. Our results also indicated that the C:N ratio of seawater controlled both seston and mesozooplankton C:N ratios. Our findings imply that inflows of terrestrial DOC alter the stoichiometry and reduce the nutritional quality of planktonic food webs in northern coastal ecosystems.

Leaching and bioavailability of dissolved organic matter from petrol-based and biodegradable plastics

Petrol-based plastic debris reaching the ocean releases dissolved organic carbon (DOC) and it can also leach fluorescent dissolved organic matter (FDOM). DOC is available to microbial uptake but the FDOM bioavailability has been scarcely studied. Although the most common plastic found in the ocean is petrol-based, the use of biodegradable plastic has increased substantially over the last years. Here we analysed the DOC and FDOM released by three petrol-based (LDPE, PS and EPS) and one biodegradable plastic (PLA) in seawater and examined their bioavailability. We found that the three petro-based plastics released FDOM in the protein-like region while the biodegradable PLA did not. FDOM released by EPS was available to microbial uptake while in the LDPE and PS treatments an increase of FDOM was observed, likely because the FDOM production by bacteria was higher than the consumption in those treatments. Biodegradable PLA leached similar amounts of DOC with comparable microbial bioavailability than petrol-based plastics indicating that, in seawater, it was not degraded faster than petro-based plastics. Especial care should be taken with biodegradable plastic since not all the types degrade in the ocean.

Leaching of organic matters and formation of disinfection by-product as a result of presence of microplastics in natural freshwaters

Microplastics (MPs) are ubiquitous in the environment that may cause negative impacts on the aquatic organisms and human health. They exist in water and wastewater, which are from several sources, such as inappropriate disposal and littering. Therefore, it is important to evaluate the characteristics of MPs in different water types and oxidation processes and study dissolved organic carbon (DOC) leaching and chloroform formation. A commonly existing plastic matter, polyethylene (PE) was placed in different waters and gone through the Fenton-like reaction and the chlorination. The result showed that the PE leached nearly a similar amount of DOC (<1 mg L−1), which was regardless of the water types and under low-dosed irradiation/dark environment. The leached DOC caused the chloroform formation after the chlorination in the waters. During the Fenton-like reaction with the PE, a higher amount of leached DOC (∼3 mg L−1) was detected compared with that in the chlorination (∼0.8 mg L−1). The degree of DOC leaching from the PE caused by the oxidation processes was reflected by the degree of surface structural damage on the PE. However, the chlorination resulted in a higher chloroform formation from the PE (∼20 μg L−1) as the Fenton-like reaction degraded the chloroform. The higher the sodium hypochlorite concentration, the higher the chloroform concentration. When the chloroform existed in the water with the PE, adsorption of chloroform onto the PE was initially observed; however the rate of volatilization would be higher than the rate of adsorption eventually. This study offers useful information for the risk assessment of MPs in our fresh water and drinking water and possible mitigation strategies.

Sizable pool of labile organic carbon in peat and mineral soils of permafrost peatlands, western Siberia

In contrast to good knowledge of dissolved organic matter (DOM) adsorption on mineral soils in temperate climate, the behavior of DOM in frozen mineral horizons located under peat soils of permafrost-affected regions remains poorly characterized. Yet, these regions contain sizeable and potentially highly labile pools of organic (peat) carbon (C) that may migrate downwards across mineral layers in case of massive thaw in frozen peatlands induced by on-going climate warming. To quantify these pools and the lability of DOM in permafrost peat soils, we performed experiments focusing on dissolved organic carbon (DOC) desorption from, and adsorption onto, mineral horizons (iron-poor and iron-rich sands as well as silt loam) from the largest frozen peatland in the world, the Western Siberia Lowland (WSL). Desorbed DOC ranged between 0.1 and 0.6 mg C gsoil−1 depending on type of mineral substrate. The adsorption of peat leachate DOM ranged between 0.1 and 0.5 mg C gsoil−1 being highest in Al-Fe-rich mineral horizons.Field measurements of C pools in peat and underlying mineral horizons over 1 m depth in the discontinuous permafrost zone yielded 47 and 15 kg C m−2, respectively. The organic carbon (OC) adsorption capacity of the 1 m – thick mineral layers represented <2% of total amount of OC containing in the 1 m – thick peat layer. However, this adsorption capacity is comparable to the amount of DOC that can be leached from overlaying peat horizons (18%). On average, out of 1.38 ± 0.13 kg C m−2 capable of being initially released from the upper 0–100 cm of peat, 0.25 ± 0.19 kg C m−2 can be adsorbed by the underlying 100–200 cm of Fe- and Al-rich sands and clays. The remaining 1.13 kg C m−2 can be exported to lakes and rivers. Therefore, DOC released during peat thaw in upper soil horizons in permafrost regions can be sizably attenuated via adsorption on mineral layers. This should be taken into account when modeling the feedback of permafrost thaw on C export and CO2 emissions.

Low hydrological connectivity after summer drought inhibits DOC export in a forested headwater catchment

Abstract. Understanding the controls on event-driven dissolved organic carbon (DOC) export is crucial as DOC is an important link between the terrestrial and the aquatic carbon cycles. We hypothesized that topography is a key driver of DOC export in headwater catchments because it influences hydrological connectivity, which can inhibit or facilitate DOC mobilization. To test this hypothesis, we studied the mechanisms controlling DOC mobilization and export in the Große Ohe catchment, a forested headwater in a mid-elevation mountainous region in southeastern Germany. Discharge and stream DOC concentrations were measured at an interval of 15 min using in situ UV-Vis (ultraviolet–visible) spectrometry from June 2018 until October 2020 at two topographically contrasting subcatchments of the same stream. At the upper location (888 m above sea level, a.s.l.), the stream drains steep hillslopes, whereas, at the lower location (771 m a.s.l.), it drains a larger area, including a flat and wide riparian zone. We focus on four events with contrasting antecedent wetness conditions and event size. During the events, in-stream DOC concentrations increased up to 19 mg L−1 in comparison to 2–3 mg L−1 during baseflow. The concentration–discharge relationships exhibited pronounced but almost exclusively counterclockwise hysteresis loops which were generally wider in the lower catchment than in the upper catchment due to a delayed DOC mobilization in the flat riparian zone. The riparian zone released considerable amounts of DOC, which led to a DOC load up to 7.4 kg h−1. The DOC load increased with the total catchment wetness. We found a disproportionally high contribution to the total DOC export of the upper catchment during events following a long dry period. We attribute this to the low hydrological connectivity in the lower catchment during drought, which inhibited DOC mobilization, especially at the beginning of the events. Our data show that not only event size but also antecedent wetness conditions strongly influence the hydrological connectivity during events, leading to a varying contribution to DOC export of subcatchments, depending on topography. As the frequency of prolonged drought periods is predicted to increase, the relative contribution of different subcatchments to DOC export may change in the future when hydrological connectivity will be reduced more often.

Management impacts on the dissolved organic carbon release from deadwood, ground vegetation and the forest floor in a temperate Oak woodland

The forest floor is often considered the most important source of dissolved organic carbon (DOC) in forest soils, yet little is known about the relative contribution from different forest floor layers, understorey vegetation and deadwood. Here, we determine the carbon stocks and potential DOC production from forest materials: deadwood, ground vegetation, leaf litter, the fermentation layer and top mineral soil (Ah horizon), and further assess the impact of management. Our research is based on long-term monitoring plots in a temperate deciduous woodland, with one set of plots actively managed by thinning, understorey scrub and deadwood removal, and another set that were not managed in 23 years. We examined long-term data and a spatial survey of forest materials to estimate the relative carbon stocks and concentrations and fluxes of DOC released from these different pools. Long-term soil water monitoring revealed a large difference in median DOC concentrations between the unmanaged (43.8 mg L−1) and managed (18.4 mg L−1) sets of plots at 10 cm depth over six years, with the median DOC concentration over twice as high in the unmanaged plots. In our spatial survey, a significantly larger cumulative flux of DOC was released from the unmanaged than the managed site, with 295.5 and 230.3 g m−2, respectively. Whilst deadwood and leaf litter released the greatest amount of DOC per unit mass, when volume of the material was considered, leaf litter contributed most to DOC flux, with deadwood contributing least. Likewise, there were significant differences in the carbon stocks held by different forest materials that were dependent on site. Vegetation and the fermentation layer held more carbon in the managed site than unmanaged, whilst the opposite occurred in deadwood and the Ah horizon. These findings indicate that management affects the allocation of carbon stored and DOC released between different forest materials.

Climate change and drinking water from Scottish peatlands: Where increasing DOC is an issue?

Increasing levels of dissolved organic carbon (DOC) have been detected in the last decades in water bodies of the Northern hemisphere, and climate change might fuel this rise. For drinking water reservoirs located in peatland catchments, already subjected to elevated amounts of DOC that needs to be removed, this might pose a further problem. Scotland is predicted to face warmer temperatures and a change in rainfall patterns, which will result in more frequent and severe summer droughts and in heavier winter precipitation. These conditions are not ideal for peatlands, which may undergo a drastic reduction in area. Using two bioclimatic envelope models (Blanket bog Tree model and Lindsay Modified model) that project blanket bog distribution in Scotland in the 2050s, we extracted the area of blanket bog that is at risk of loss. Assuming that part of the carbon stored in this area is likely to be lost, we calculated how much of it could be added to DOC in catchments that contain public drinking water reservoirs each year. This analysis is a first estimate of the risk for the provision of drinking water from peatlands in Scotland due to climate change. The aim is to identify the catchments that may face the highest consequences of future climates in terms of the concentration of DOC ([DOC]), where more sophisticated water treatments might be needed. Our results show a great variability among the catchments, with only a few being unaffected by this problem, whereas others could experience substantial seasonal increase in [DOC]. This highlights the necessity to frequently monitor DOC levels in the reservoirs located in catchments where the major problems could arise, and to take the necessary measures to reduce it. Given that peatland condition and vegetation cover play a fundamental role in influencing DOC losses, this study also offers an indication of where peatland restoration might be useful to counteract the projected DOC increase and bring the highest benefits in terms of safe drinking water provision.

Macroalgal release of dissolved organic carbon in coral reef and its interaction with the bacteria associated with the coral Porites lutea.

Macroalgae supersede corals in the reefs worldwide, converting the coral-dominant systems into algal-dominant ones. Dissolved organic carbon (DOC) released by macroalgae play a prominent role in degrading the coral reefs by stimulating the bacterial growth and metabolism. However, the long-term remineralization of macroalgal DOC and their contribution to the carbon pool are least studied. In this study, we quantified the DOC released by five species of macroalgae that affected live corals through their physical contact and their subsequent remineralization for 100 days by coral mucus bacteria. Also, we analyzed the changes in bacterial community structure after 30 days of exposure to the macroalgal DOC. All the macroalgae released a significant amount of DOC ranging from 2.2 ± 0.17 to 8.1 ± 0.36 μmol C g-1 h-1 (mean ± SD). After 100 days, between 9.2 and 30.9% of the macroalgal DOC remained recalcitrant to bacterial remineralization. There was no apparent change in the dominant bacterial groups exposed to the DOC released by the green macroalgae Caulerpa racemosa and Halimeda sp. In comparison, the Proteobacteria group decreased with a prominent increase in the Firmicutes, Planctomycetes, and Bacteroidetes group in the samples exposed to DOC released by the brown macroalgae Turbinaria ornata, Sargassum tenerrimum, and Padina gymnospora. These inclusive data suggest that the DOC released by different species of macroalgae differed on their lability to microbial mineralization and highlight the comparable patterns in microbial responses to macroalgal exudates across different species.

Drivers of Organic Molecular Signatures in the Amazon River

AbstractAs climate‐driven El Niño Southern Oscillation (ENSO) events are projected to increase in frequency and severity, much attention has focused on impacts regarding ecosystem productivity and carbon balance in Amazonian rainforests, with comparatively little attention given to carbon dynamics in fluvial ecosystems. In this study, we compared the wet 2012 La Niña period to the following normal hydrologic period in the Amazon River. Elevated water flux during the La Niña period was accompanied by dilution of inorganic ion concentrations. Furthermore, the La Niña period exported 2.77 Tg C yr−1 more dissolved organic carbon (DOC) than the normal period, an increase greater than the annual amount of DOC exported by the Mississippi River. Using ultra‐high‐resolution mass spectrometry, we detected both intra‐ and interannual differences in dissolved organic matter (DOM) composition, revealing that DOM exported during the dry season and the normal period was more aliphatic, whereas compounds in the wet season and following the La Niña event were more aromatic, with ramifications for its environmental role. Furthermore, as this study has the highest temporal resolution DOM compositional data for the Amazon River to‐date we showed that compounds were highly correlated to a 6‐month lag in Pacific temperature and pressure anomalies, suggesting that ENSO events could impact DOM composition exported to the Atlantic Ocean. Therefore, as ENSO events increase in frequency and severity into the future it seems likely that there will be downstream consequences for the fate of Amazon Basin‐derived DOM concurrent with lag periods as described here.

Dissolved organic carbon production and transport within a constructed fen watershed in the Athabasca Oil Sands Region, Alberta, Canada

Vast areas of wetlands in the Athabasca Oil Sands Region, Alberta, Canada have been disturbed for mining and other resource extraction activities. In recent years, these disturbed areas have become a focus for reclamation activities. To improve our understanding of the biogeochemical cycling of constructed ecosystems, it is important that we study the production of, as well as the inputs and outputs of dissolved organic carbon (DOC) in the system. The aim of our study was to investigate the hydrological DOC fluxes into a constructed fen in 2015 and 2016 (2- and 3-years post-construction respectively), relative to internal DOC production, and to assess the potential importance of each source for DOC export using DOC concentration and quality parameters. Our results show that while runoff added a small amount of DOC in both years, DOC concentration within the fen is driven largely by increased vegetation production, with DOC increasing in the years since construction. The measured quality indices (SUVA254, E2/E3, FI, HIX, and β/a) all showed that DOC present in the system is likely more recently produced and plant sourced. There was also little evidence that precipitation and runoff inputs from hillslopes impacted the quality of DOC present in the fen, while DOC export from the fen was minimal. As this constructed wetland continues to mature, it is important that monitoring of DOC continues in order to understand the trajectory of biogeochemical dynamics of the system following vegetation establishment, as well as changes under potential future climatic variations.