DOC), Nitrogen Research Articles

A global database of dissolved organic matter (DOM) concentration measurements in coastal waters (CoastDOM v1)

Abstract. Measurements of dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) concentrations are used to characterize the dissolved organic matter (DOM) pool and are important components of biogeochemical cycling in the coastal ocean. Here, we present the first edition of a global database (CoastDOM v1; available at https://doi.org/10.1594/PANGAEA.964012, Lønborg et al., 2023) compiling previously published and unpublished measurements of DOC, DON, and DOP in coastal waters. These data are complemented by hydrographic data such as temperature and salinity and, to the extent possible, other biogeochemical variables (e.g. chlorophyll a, inorganic nutrients) and the inorganic carbon system (e.g. dissolved inorganic carbon and total alkalinity). Overall, CoastDOM v1 includes observations of concentrations from all continents. However, most data were collected in the Northern Hemisphere, with a clear gap in DOM measurements from the Southern Hemisphere. The data included were collected from 1978 to 2022 and consist of 62 338 data points for DOC, 20 356 for DON, and 13 533 for DOP. The number of measurements decreases progressively in the sequence DOC > DON > DOP, reflecting both differences in the maturity of the analytical methods and the greater focus on carbon cycling by the aquatic science community. The global database shows that the average DOC concentration in coastal waters (average ± standard deviation (SD): 182±314 µmol C L−1; median: 103 µmol C L−1) is 13-fold higher than the average coastal DON concentration (13.6±30.4 µmol N L−1; median: 8.0 µmol N L−1), which is itself 39-fold higher than the average coastal DOP concentration (0.34±1.11 µmol P L−1; median: 0.18 µmol P L−1). This dataset will be useful for identifying global spatial and temporal patterns in DOM and will help facilitate the reuse of DOC, DON, and DOP data in studies aimed at better characterizing local biogeochemical processes; closing nutrient budgets; estimating carbon, nitrogen, and phosphorous pools; and establishing a baseline for modelling future changes in coastal waters.

Growing seasonal characteristics of soil and plants control the temporal patterns of bacterial communities following afforestation

Soil microbial communities are closely associated with aboveground plant communities and soil properties. This study explored the dynamics of soil bacterial communities during the plant growing season and their interaction with soil carbon and nitrogen, physicochemical properties, plant biomass and diversity following afforestation. The study investigated afforested lands containing Robinia pseudoacacia L (RP) and Caragana korshinskii Kom (CK), as well as abandoned land (AL) and farmland (FL) in the Loess Hilly Region of northern China. After establishment on former FL for 40 years, the Richness and Shannon's index, above-ground herbaceous biomass (AGB) and below-ground biomass (BGB) in RP and CK increased by 0.5, 0.1, 1.2 and 1.7 times, respectively, compared with AL. Additionally, the soil organic carbon (SOC), total nitrogen (TN), dissolved organic carbon/nitrogen (DOC/N) and microbial biomass carbon/nitrogen (MBC/N) increased by 1.7, 1.9, 0.8 and 2.5 times, respectively, while the soil bacterial abundance and alpha diversity (Shannon index) increased by 4.7% and 2.0% compared with FL. During the growing season, the soil carbon and nitrogen content was higher in August or October than in April or June. Particularly, the AGB, DOC and MBC showed a temporal pattern of normal distribution that was 36.7%, 48.2% and 74.9% higher in August than the rest of the study period. The BGB also increased by 123.5% in October compared with June in all study areas. The soil bacterial abundance in afforested lands was also higher in October, and beta bacterial diversity (Principal coordinates analysis plots: PCoA) was greater in June and August than in April and October. The dominant bacterial taxa, Proteobacteria and Bacteroidetes, were significantly higher in afforested lands than in FL, and Proteobacteria increased from April to October, while Actinobacteria and Acidobacteria peaked in June or August. These seasonal changes in the soil bacterial community were significantly correlated with carbon and nitrogen levels of soil and plant biomass, especially with DOC and BGB. Additionally, soil variables explained 41.2% of the total variation in bacterial-dominant phyla, while plant biomass only explained 20.2% of it, which indicates that soil properties are more important controlling factors of the bacterial community than plant biomass. In conclusion, soil variables change seasonally, which drives the composition and diversity of the soil bacterial community to exhibit a temporal pattern over the growing season after return of AL to forest.

Composition and bioavailability of dissolved organic matter in different water masses of the East China sea

The degradation of dissolved organic matter (DOM) is affected by ocean currents, but this influence is poorly understood in the East China Sea (ECS), a dynamic shallow continental shelf characterized by several discrete water masses. This study investigates dissolved organic carbon (DOC), nitrogen (DON) and total dissolved amino acids (TDAA) in different water masses of the ECS. Bioassay experiments were also conducted to determine the labile fraction of DOM. Carbon-normalized yields of TDAA [TDAA (%DOC)] as well as the degradation index (DI) was used to investigate the diagenetic state of organic matter in different water masses. Generally, DOM concentration decreased from the Coastal Current Water (CCW), to the Shelf Mixed Water (SMW), to the Taiwan Warm Current Water (TWCW), and to the Kuroshio Current Water (KCW). DOM in CCW is relatively labile due to inputs from phytoplankton production, while that in the TWCW exhibits low bioavailability, which may be related to nutrient limitation leading to low productivity. The long residence time of the KCW resulted in a high degree of biodegradation associated with nutrient regeneration. Intrusion of nutrient-rich KCW may contribute to the high primary productivity in shelf water, while complex hydrodynamic processes and stratification may control DOM availability in SMW.

Seasonal dynamics and bioavailability of dissolved organic matter in two contrasting temperate estuaries

Production and bioavailability of dissolved organic matter (DOM) were followed during a year in the nutrient-rich estuary, Roskilde Fjord (RF), and the more oligotrophic strait, Great Belt (GB), in Denmark. Bioavailability of dissolved organic carbon (DOC), nitrogen (DON), and phosphorous (DOP) was determined during incubations over six months. Overall, RF had three to five times larger pools of total nitrogen (TN) and total phosphorous (TP) and five to eight times higher concentrations of inorganic nutrients compared to GB. However, the allocation of carbon, nitrogen, and phosphorous into different pools were remarkably similar between the two systems. DON and DOP contributed with about equal relative fractions in the two systems: 72 ± 13% of total nitrogen and 21 ± 12% of total phosphorous. The average bioavailability of DOM was 25 ± 15, 17 ± 5.5, and 49 ± 29% for carbon, nitrogen, and phosphorous, respectively. The observed release of DIN from degradation of DON amounted to between 0.1 (RF winter) and 14 times (GB summer) the loadings from land and contributed with half of the total input of bioavailable nitrogen during summer. Hence, this study shows that nitrogen in DOM is important for the nitrogen cycling, especially during summer. The sum of inorganic nutrients, particulate organic matter, and bioavailable DOM (the dynamic pools of nutrients) accounted for 42 and 92% of nitrogen, and phosphorous, respectively, and was remarkably similar between the two systems compared to the difference in nutrient richness. It is hypothesized that the pelagic metabolism of nutrients in marine systems dictates a rather uniform distribution of the different fractions of nitrogen and phosphorous containing compounds regardless of eutrophication level.

Microbial use of low molecular weight DOM in filtered and unfiltered freshwater: Role of ultra-small microorganisms and implications for water quality monitoring

Dissolved organic matter (DOM) plays a central role in regulating productivity and nutrient cycling in freshwaters. It is therefore vital that we can representatively sample and preserve DOM in freshwaters for subsequent analysis. Here we investigated the effect of filtration, temperature (5 and 25°C) and acidification (HCl) on the persistence of low molecular weight (MW) dissolved organic carbon (DOC), nitrogen (DON) and orthophosphate in oligotrophic and eutrophic freshwater environments. Our results showed the rapid loss of isotopically-labelled glucose and amino acids from both filtered (0.22 and 0.45μm) and unfiltered waters. We ascribe this substrate depletion in filtered samples to the activity of ultra-small (<0.45μm) microorganisms (bacteria and archaea) present in the water. As expected, the rate of C, N and P loss was much greater at higher temperatures and was repressed by the addition of HCl. Based on our results and an evaluation of the protocols used in recently published studies, we conclude that current techniques used to sample water for low MW DOM characterisation are frequently inadequate and lack proper validation. In contrast to the high degree of analytical precision and rigorous statistical analysis of most studies, we argue that insufficient consideration is still given to the presence of ultra-small microorganisms and potential changes that can occur in the low MW fraction of DOM prior to analysis.

Seasonal variations of dissolved organic matter and nutrients in sediment pore water in the inner part of Tokyo Bay

At four stations in Tokyo Bay, pore water profiles of dissolved organic carbon (DOC), nitrogen (DON), phosphorus (DOP), and inorganic nutrients were determined at 3-month intervals over 6 years. Concentrations of dissolved organic matter (DOM) and nutrients were significantly higher in pore waters than in the overlying waters. Pore water DOC, DON, and DOP concentrations in the upper most sediment layer (0–1 cm) ranged from 246 to 888 μM, from 14.6 to 75.9 μM, and from 0.02 to 9.83 μM, respectively. Concentrations of DOM and nutrients in pore waters occasionally showed clear seasonal trends and were highest in the summer and lowest in the winter. The seasonal trends in the pore water DOM concentrations were coupled with trends in the overlying water temperature and dissolved oxygen concentration. Benthic effluxes of DON and DOP were low compared with those of inorganic nutrients, accounting for only 1.0 and 1.5 % of the total benthic effluxes of nitrogen and phosphorus, respectively; thus benthic DOM fluxes were quantitatively insignificant to the inorganic nutrient fluxes in Tokyo Bay. The DOM fluxes represented about 7, 3, and 10 % of the riverine discharge of DOC, DON, and DOP to Tokyo Bay, respectively.

Implications of elevated CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; on pelagic carbon fluxes in an Arctic mesocosm study – an elemental mass balance approach

Abstract. Recent studies on the impacts of ocean acidification on pelagic communities have identified changes in carbon to nutrient dynamics with related shifts in elemental stoichiometry. In principle, mesocosm experiments provide the opportunity of determining temporal dynamics of all relevant carbon and nutrient pools and, thus, calculating elemental budgets. In practice, attempts to budget mesocosm enclosures are often hampered by uncertainties in some of the measured pools and fluxes, in particular due to uncertainties in constraining air–sea gas exchange, particle sinking, and wall growth. In an Arctic mesocosm study on ocean acidification applying KOSMOS (Kiel Off-Shore Mesocosms for future Ocean Simulation), all relevant element pools and fluxes of carbon, nitrogen and phosphorus were measured, using an improved experimental design intended to narrow down the mentioned uncertainties. Water-column concentrations of particulate and dissolved organic and inorganic matter were determined daily. New approaches for quantitative estimates of material sinking to the bottom of the mesocosms and gas exchange in 48 h temporal resolution as well as estimates of wall growth were developed to close the gaps in element budgets. However, losses elements from the budgets into a sum of insufficiently determined pools were detected, and are principally unavoidable in mesocosm investigation. The comparison of variability patterns of all single measured datasets revealed analytic precision to be the main issue in determination of budgets. Uncertainties in dissolved organic carbon (DOC), nitrogen (DON) and particulate organic phosphorus (POP) were much higher than the summed error in determination of the same elements in all other pools. With estimates provided for all other major elemental pools, mass balance calculations could be used to infer the temporal development of DOC, DON and POP pools. Future elevated pCO2 was found to enhance net autotrophic community carbon uptake in two of the three experimental phases but did not significantly affect particle elemental composition. Enhanced carbon consumption appears to result in accumulation of dissolved organic carbon under nutrient-recycling summer conditions. This carbon over-consumption effect becomes evident from mass balance calculations, but was too small to be resolved by direct measurements of dissolved organic matter. Faster nutrient uptake by comparatively small algae at high CO2 after nutrient addition resulted in reduced production rates under future ocean CO2 conditions at the end of the experiment. This CO2 mediated shift towards smaller phytoplankton and enhanced cycling of dissolved matter restricted the development of larger phytoplankton, thus pushing the system towards a retention type food chain with overall negative effects on export potential.

Factors controlling the C:N:P stoichiometry of dissolved organic matter in the N-limited, cyanobacteria-dominated East/Japan Sea

The vertical and horizontal distributions of dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP), together with dissolved inorganic nitrogen (DIN), phosphorus (DIP), silicate (DSi), and photosynthetic pigments, were measured in the euphotic layer (0–100m) along the south–north transect of the East/Japan Sea (EJS) in May 2007. In the mixed layer, the DIN concentrations were lower than 3μM, and the DIN:DIP ratios were lower than 10. Under this DIN-limited condition, cyanobacteria (20–65%) and diatoms (20–50%) dominated the phytoplankton community. The concentrations of DOC (60–83μM) and DOP (0.1–0.4μM) in the EJS fell into a range similar to those found in the major oceans, whereas the concentration of DON (2–7μM) was lower than that in the Pacific Ocean (7–13μM). The correlation analyses showed that the distributions of DOC, DON, and DOP in the study region were affected mainly by the physical characteristics of water masses. The lower DON concentrations, higher DOC:DON ratios, and lower DON:DOP ratios in the EJS, relative to the major oceans, together with a strong negative correlation between the concentrations DON and zeaxanthin, suggest that DON is preferentially taken up by cyanobacteria in this environment. Thus, our results show that the C:N:P stoichiometry of dissolved organic matter (DOM) in the EJS is controlled mainly by the physical and biological characteristics of water masses.

Seasonal dynamics of dissolved organic matter on a coastal salinity gradient in the northern Baltic Sea

During the phytoplankton growth season, the vertical distributions of dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP) were followed biweekly along with key physical, chemical and biological variables on a shore-to-open-sea salinity gradient in the Gulf of Finland. Moreover, bioavailable shares of DOC and DON were evaluated with natural bacterial surface and deepwater samples. Dissolved organic matter (DOM) accumulated in the surface layer throughout the productive season, and the accumulated DOM was N-rich (molar C:N ratio of 10) compared to the bulk DOM pool (C:N 20–29). Redundancy analysis showed a negative correlation between phytoplankton and DOM concentrations, suggesting that most DOM release occurred during declining phases of spring and late summer algal blooms. During the spring bloom, bioavailable shares of DOM were small, whereas during and after the late summer bloom of filamentous cyanobacteria, 3–9% and 10–20% of the respective total DOC and DON pools were degraded by bacteria within 2 weeks. Vertical mixing over the thermocline was estimated by constructing a steady state budget for water and salt mass flows between key GoF basin compartments (inflows equal outflows). The flow estimates suggested that the net changes in surface DOC and DON pools underestimated the respective total accumulations by ca 40% and 20%, respectively, over the 4-mo thermal stratification period. Thus, integral export of surface DOC and DON after autumn overturn amounted to ca 710mmolCm−2 and 40mmolNm−2, corresponding respectively to ca 12–25% and 11% of reported annual particulate organic carbon and nitrogen sedimentation in our study area.

New insights into C, N and P stoichiometry in the Mediterranean Sea: The Adriatic Sea case

Vertical distributions of dissolved organic carbon (DOC), nitrogen (DON) and phosphorous (DOP) were studied in the Southern Adriatic basin in two contrasting periods: autumn (high stratification) and winter (high extent of mixing). These data provide the first observations of dissolved organic matter (DOM) stoichiometry in a key area of the Mediterranean Sea.DOC and DON values are similar to those reported for other areas of the Mediterranean Sea as well as for tropical and temperate regions of the oceans. Surface DOP values are about one order of magnitude lower than those reported for the oceanic waters, confirming the low availability of P in the Mediterranean Sea. Consequently, surface DOM (C:N:P=1189–1411:86–88:1) has higher proportions of C and N with respect to P than in the oceans. DOM stoichiometry in the deep waters of the Southern Adriatic ranged between 993:85:1 and 1693:108:1, indicating a depletion of DOC (or an elevation of DON and DOP) with respect to the old western Mediterranean deep waters. This finding can be explained by the young age of the water masses in the Southern Adriatic, which can mask the effect of mineralization. Our data clearly show that physical processes (water mass circulation, deep water formation and extent of stratification) affect both distribution and stoichiometry of DOM. Finally, we discuss the role of the Adriatic Sea in maintaining the high N:P ratio observed in the Eastern Mediterranean Sea.

Integrated survey of elemental stoichiometry (C, N, P) from the western to eastern Mediterranean Sea

Abstract. This paper provides an extensive vertical and longitudinal description of the biogeochemistry along an East-West transect of 3000 km across the Mediterranean Sea during summer 2008 (BOUM cruise). During this period of strong stratification, the distribution of nutrients, particulate and dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP) were examined to produce a detailed spatial and vertically extended description of the elemental stoichiometry of the Mediterranean Sea. Surface waters were depleted in nutrients and the thickness of this depleted layer increased towards the East from about 10 m in the Gulf of Lion to more than 100 m in the Levantine basin, with the phosphacline deepening to a greater extent than that for corresponding nitracline and thermocline depths. We used the minimum oxygen concentration through the water column in combination with 2 fixed concentrations of dissolved oxygen to distinguish an intermediate layer (Mineralization Layer; ML) from surface (Biogenic Layer; BL), and deep layers (DL). Whilst each layer was represented by different water masses, this approach allowed us to propose a schematic box-plot representation of the biogeochemical functioning of the two Mediterranean basins. Despite the increasing oligotrophic nature and the degree of P-depletion along the West to East gradient strong similarities were encountered between eastern and western ecosystems. Within the BL, the C:N:P ratios in all pools largely exceeded the Redfield ratios, but surprisingly, the nitrate vs. phosphate ratios in the ML and DL tended towards the canonical Redfield values in both basins. A change in particulate matter composition has been identified by a C increase relative to N and P along the whole water column in the western basin and between BL and ML in the eastern one. Our data showed a noticeable stability of the DOC:DON ratio (12–13) throughout the Mediterranean Sea. This is in good agreement with a P-limitation of microbial activities but in contradiction of the accepted concept that N is recycled faster than C. The western and eastern basins had similar or close biological functioning. Differences come from variability in the allochtonous nutrient sources in terms of quantity and quality, and to the specific hydrodynamic features of the Mediterranean basins.

Seasonal dynamics and conservative mixing of dissolved organic matter in the temperate eutrophic estuary Horsens Fjord

This study presents the results of a year-long study investigating the characteristics of dissolved organic matter (DOM) in the Danish estuary, Horsens Fjord. The estuary is shallow with a mean depth of 2.9 m and receives high loadings of inorganic nutrients from its catchment. The behaviour of different DOM parameters i.e. dissolved organic carbon (DOC), nitrogen (DON), and phosphorous (DOP), light absorption and eight fluorescence components, were analysed relative to conservative mixing. Many of the parameters did not behave conservatively. For DON, DOP and absorption, more than 65% of the freshwater concentration was removed initially at salinities below 12. At higher salinities two general patterns were identified. Concentrations of DON, DOP and four humic fluorescent fractions were not, or only weakly, related to salinity, showing that other processes than mixing were involved. Other parameters such as DOC and two terrestrial humic components behaved conservatively. The same was true for DON during winter. These results are consistent with the finding that autochthonous DOM was the dominant source of DOM in this estuary. The molar C:N and C:P ratios for DOM (DOC:DON and DOC:DOP) in freshwater were 11 and 758, respectively. The DOC:DON ratio increased in the estuary during the productive season to average values between 13 and 17, due to accumulation of DOC and removal of DON. The DOC:DOP ratio decreased within the estuary showing that in general DOM was enriched with phosphorous, however, during the spring, when phosphorous was limiting, the DOC:DOP ratio increased due to low DOP concentrations. We hypothesise that in estuaries with high loadings of inorganic nutrients relative to DOM, production and degradation of DOM within the estuary will dominate over allochthonous inputs and control both concentration and characteristics of DOM. A conceptual model for this hypothesis is presented.

The effects of harmful algal species and food concentration on zooplankton grazer production of dissolved organic matter and inorganic nutrients

Harmful algal blooms (HABs), including toxic species, have been increasing in frequency, range, and duration over the past several decades. The effect of a harmful or toxic algal diet on zooplankton nutrient regeneration, however, has not been previously examined. In this study, we determined the effects of non-bloom and bloom concentrations of non-toxic and toxic cultures of HAB species Prorocentrum minimum and Karlodinium veneficum on grazing and production of dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP), and inorganic nutrients, ammonium (NH 4 +) and phosphate (PO 4 3−), by the copepod Acartia tonsa and the heterotrophic dinoflagellate Oxyrrhis marina. Ingestion rates of grazers were significantly higher while feeding on bloom algal concentrations compared to non-bloom algal concentrations, but were always below 1% body C d −1 for A. tonsa (ingestion rate range of 0.5–31 ng C individual −1 d −1) and below 2% body C d −1 for O. marina (range of 0.1–8.8 pg C individual −1 d −1). However, rates of inorganic nutrient and dissolved organic matter (DOM) release, when detected, were always >100% of carbon (C), nitrogen (N), and phosphorus (P) ingested. Additionally, the quantity and forms (organic vs. inorganic) of nutrients released by zooplankton were significantly different between non-toxic and toxic algal treatments, and typically higher grazer DOM release occurred while feeding on toxic algal cultures. DOM was the only detected form of nutrient released from O. marina, and DON and DOP were significant portions of total dissolved N and P released for A. tonsa feeding on toxic K. veneficum (69–84% and 73%, respectively). Low grazing rates on all algal diets used in our study, regardless of cell concentration or toxicity, likely resulted in starvation and subsequent catabolism of grazer body tissue. The potential for additional factors affecting variable grazer nutrient release between toxic and non-toxic algal treatments, including algal nutrient quality and direct toxic effects, are discussed. Our results suggest these grazers may not be capable of controlling bloom formation of these HAB species, and that nutrient cycling dynamics in the coastal ocean may change with increases in the presence of harmful and toxic algal blooms.

Stoichiometry of dissolved organic matter and the kinetics of its microbial degradation in a coastal upwelling system

The degradation of dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP) collected in the coastal upwelling system of the Ria de Vigo (NW Iberian Peninsula) was assessed following the time-course of DOC, DON and DOP concentrations in laboratory incubations. Initial concentrations varied from 73 to 94 µM for DOC, 4.5 to 7.2 µM for DON and 0.12 to 0.32 µM for DOP. The bioavailable fraction (BDOM) represented 17 ± 6% (average ± SE) of DOC, 38 ± 6% of DON and 65 ± 9% of DOP. BDOM was significantly correlated with temperature (R 2 > 0.3, p 0.5, p < 0.05), indicating that the differences in DOM bioavailability were associated with the seasonal variations in plankton biomass and activity. The C:N:P stoichiometry of BDOM, 111 (±38):18 (±6):1, was not significantly different from the Redfield ratio (106:16:1), pointing to a phytoplankton origin of BDOM. Accordingly, exponential rate constants of BDOM suggest that this pool is very labile. Despite the reduced flushing times of the Ria de Vigo, from 3 to 8 d, as much as 70 ± 13% of BDOC (average ± SD), 81 ± 8% of BDON and 88 ± 5% of BDOP are mineralized within the embayment. The remaining C-rich BDOM is exported to the adjacent oligotrophic waters, sug- gesting that the offshore transport of labile DOM must be accounted for when considering the carbon balance of ocean surface waters adjacent to productive coastal areas.

Bioavailability and bacterial degradation rates of dissolved organic matter in a temperate coastal area during an annual cycle

The bioavailability and bacterial degradation rates of dissolved organic matter (DOM) were determined over a seasonal cycle in Loch Creran (Scotland) by measuring the decrease in dissolved organic carbon (DOC), nitrogen (DON) and phosphorous (DOP) concentrations during long-term laboratory incubations (150 days) at a constant temperature of 14 °C. The experiments showed that bioavailable DOC (BDOC) accounted for 29 ± 11% of DOC (average ± SD), bioavailable DON (BDON) for 52 ± 11% of DON and bioavailable DOP (BDOP) for 88 ± 8% of DOP. The seasonal variations in DOM concentrations were mainly due to the bioavailable fraction. BDOP was degraded at a rate of 12 ± 4% d – 1 (average ± SD) while the degradation rates of BDOC and BDON were 7 ± 2% d – 1 and 9 ± 2% d – 1 respectively, indicating a preferential mineralization of DOP relative to DON and of DON relative to DOC. Positive correlations between concentration and degradation rate of DOM suggested that the higher the concentration the faster DOM would be degraded. On average, 77 ± 9% of BDOP, 62 ± 14% of BDON and 49 ± 19% of BDOC were mineralized during the residence time of water in Loch Creran, showing that this coastal area exported C-rich DOM to the adjacent Firth of Lorne. Four additional degradation experiments testing the effect of varying temperature on bioavailability and degradation rates of DOM were also conducted throughout the seasonal cycle (summer, autumn, winter and spring). Apart from the standard incubations at 14 °C, additional studies at 8 °C and 18 °C were also conducted. Bioavailability did not change with temperature, but degradation rates were stimulated by increased temperature, with a Q 10 of 2.6 ± 1.1 for DOC and 2.5 ± 0.7 for DON (average ± SD).

Dissolved organic matter release in a Posidonia oceanica meadow

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 374:75-84 (2009) - DOI: https://doi.org/10.3354/meps07715 Dissolved organic matter release in a Posidonia oceanica meadow Cristina Barrón1,2,*, Carlos M. Duarte1 1IMEDEA (CSIC-UIB), C/ Miquel Marqués 21, 07190 Esporles (Islas Baleares), Spain 2Present address: Vrije Universiteit Brussel, Analytical and Environmental Chemistry, Pleinlaan 2, 1050 Brussels, Belgium *Email: cbarron@vub.ac.be ABSTRACT: We examined annual nutrient changes (nitrate, phosphate and ammonium) and the net dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP) release using in situ benthic incubations in a Posidonia oceanica meadow and in unvegetated sediments of Magalluf Bay (Mallorca Island, Spain) at monthly intervals. We also examined the role of the P. oceanica meadow in the C:N:P ratio transformations by comparing the ratios between the inorganic and dissolved organic fluxes in the seagrass ecosystem and those in the plant material. Our results indicate that P. oceanica communities enhance DOC fluxes relative to adjacent unvegetated sediments. The net DOC release from the P. oceanica meadow represents 71% of the net community production. The C:N:P ratio in the flux of dissolved organic material (DOM) from the P. oceanica community (1450:69:1) exceeded the C:N:P ratio in the DOM flux of unvegetated sediment communities. The high flux of DOC release from this seagrass community might be enriched in carbon compounds, as these plants produce non-structural carbohydrates in excess. KEY WORDS: Benthic fluxes · Seagrasses · Dissolved organic carbon · Posidonia oceanica · Dissolved organic matter · Carbohydrates Full text in pdf format PreviousNextCite this article as: Barrón C, Duarte CM (2009) Dissolved organic matter release in a Posidonia oceanica meadow. Mar Ecol Prog Ser 374:75-84. https://doi.org/10.3354/meps07715 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 374. Online publication date: January 13, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Organic Matter and Nutrient Cycling in a Coastal Plain Estuary: Carbon, Nitrogen, and Phosphorus Distributions, Budgets, and Fluxes

Abstract Nutrient temporal and spatial distributions were evaluated, in addition to budgets and fluxes derived from the Land-Ocean Interaction in the Coastal Zone (LOICZ) biogeochemical model, to determine dissolved organic matter and inorganic nutrient distribution, flux, and fate in the Mullica River–Great Bay Estuary. Seasonal cycles were observed for dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) with increasing concentrations from spring to fall and maximum concentrations in summer/early fall. Annually, the estuarine system was a net source of DOC (+5 mol m−2 y−1), DON (+0.08 mol m−2 y−1), and dissolved inorganic phosphorus (DIP, +0.010 mol m−2 y−1), a net sink of dissolved inorganic nitrogen (DIN, −0.28 mol m−2 y−1), and in approximate balance of DOP (0.001 mol m−2 y−1). Overall, the upper estuary and mid-estuary served as net sinks for most nutrients, whereas the lower estuary served as a net source. Annual mean nutrient export from the lower estuary to the nearshore coastal r...

River flow controls ecological processes and invertebrate assemblages in subsurface flowpaths of an ephemeral river reach

We present the first measurements of solutes, invertebrates, and microbial activity in the semi-perched hyporheic, parafluvial, and riparian flowpaths of an ephemeral river channel. Dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) concentrations decreased as water from an adjacent river mainstem moved through the flowpaths. DOC, DON, and DOP processing rates decreased with increasing mainstem flow and increased with parafluvial zone length. These patterns suggest that the surface water zones of perched river systems are organic nutrient sources to subsurface flowpaths and that parafluvial zones of these systems are strong sinks for organic matter. No longitudinal changes were detected in NO3–concentrations, and relationships between NO3–processing and hydrological variables were not significant. NO3–concentrations were uniformly high, and microbial activity and DOC and dissolved reactive phosphorus (DRP) concentrations were low, suggesting that biological NO3–removal was carbon- or phosphorus-limited. Invertebrate assemblages also varied between subsurface zones: density and taxon richness in the hyporheic and parafluvial zones were higher than in the riparian zone, and evenness was higher in the riparian zone than in the hyporheic or parafluvial zones. Distinct invertebrate assemblages in riparian zones may reflect greater hydrologic stability compared with hyporheic and parafluvial zones.

BACTERIAL AND PHYTOPLANKTON PRODUCTION IN TWO COASTAL SYSTEMS INFLUENCED BY DISTINCT EUTROPHICATION PROCESSES

Evaluating the relationships between bacterial (BP) and phytoplankton production (PP) is a fi rst step to understand carbon fl uxes through pelagic food webs. In the present study, BP and PP were compared at two tropical coastal systems infl uenced by distinct eutrophication processes in order to assess the main regulating factors of particulate organic carbon (POC) production rates. The waters of Cabo Frio region (23 o 00’S; 42 o 00’W) present high nitrate (N-NO 3 ) levels and low temperatures resulting from the upwelling of deep water masses – thus, a natural eutrophication process – while the waters in Guanabara Bay (22 o 54’S; 43 o 09’W) present high temperatures and levels of dissolved organic carbon (DOC), nitrogen (DON) and nutrients (other than nitrate), resulting from anthropogenic eutrophication, mainly because of sewage wastes. Dissolved organic matter (DOM) elemental composition indicates lower autochthonous contribution in Cabo Frio (C:N ~ 42), probably due to lower phytoplankton production. The elevated temperatures in Guanabara Bay yielded higher PP rates, increasing the phytoplankton contribution to the DOM pool which improved BP. No coupling between BP and PP was observed, and POC production was mainly due to phytoplankton in both systems.

Dissolved organic matter and bacterial production and respiration in the sea‐surface microlayer of the open Atlantic and the western Mediterranean Sea

The sea‐surface microlayer (SML) is the boundary layer between the ocean and the atmosphere. We measured bacterial production and respiration along with dissolved organic carbon (DOC), nitrogen (DON), and phosphorus, inorganic nutrients, and dissolved amino acids in the SML and the underlying water (ULW) of the subtropical Atlantic gyre (SATL) and the western Mediterranean Sea (WMED). Dissolved amino acid concentrations in the SML were one order of magnitude higher than in the ULW. DON, ammonium, and nitrate were also significantly enriched in the SML as compared with the ULW. Bacterial leucine incorporation ranged between 3 and 50 pmol L‐1 h‐1 in the SATL and 5 and 488 pmol L‐1 h‐1 in the WMED and was generally not significantly different between the SML and the ULW. In contrast, bacterial respiration was significantly higher in the SML than in the ULW, varying between 3.6 and 9.5 µmol L‐1 d‐1 O2 at both sites. The resulting bacterial growth efficiencies ranged between 0.1% and 14% using different leucine incorporation to carbon conversion factors. Given the high dissolved free amino acid (DFAA) yield of DOC (~12%) and of DON (~30%) in the SML, bacterial growth efficiencies in the SML were low. This indicates that the DFAA in the SML are not readily available for bacteria. The underlying mechanisms of this immobilization of DFAA in the SML and their production remain enigmatic.