Organic Carbon Supply Research Articles

An integrated system of solar light, artificial light and organic carbon supply for cyclic photoautotrophic-heterotrophic cultivation of photosynthetic cells under day–night cycles

An integrated system of solar light, artificial light and organic carbon supply was developed for cyclic photoautotrophic-heterotrophic cultivation of photosynthetic cells. The energy source for the culture is automatically switched to solar light energy (when the weather is sunny), to artificial light energy (during the cloudy period of the day) or to organic carbon source (at night). Thus minimum amount of artificial light is used while ensuring continuous light supply to the culture during the photoautotrophic phase. The α-tocopherol productivity by Euglena gracilis in this system was more than 5 times higher than the value obtained in pure photoautotrophic culture under the same experimental conditions.

Food-web structure and elemental (C, N and P) fluxes in the eastern tropical North Atlantic

The flow of biogenic elements (C, N and P) in the upper tropical Atlantic (29–5°N, 17–22°W) was studied are the Latitude II cruise 1995 with the aim of examining planktonic food web controls on these fluxes. The transect crossed three distinct water masses, a productive area in the NW African upwelling between 18° and 23°N, a warm water mass between 6° and 13°N, and unproductive waters at the northern range of the transect. The contrasting phytoplankton biomass and production across the eastern tropical N Atlantic appear to be driven by major changes in the supply of nutrients across the thermocline, which averaged 0.99±0.6 mmol N m−2 d−1 and 0.13±0.07 mmol P m−2 d−1, and was particularly high at the upwelling area off NW Africa. This supply was relatively low in nitrogen relative to that in phosphorus, driving the system towards nitrogen limitation. This was further enhanced by an important sinking flux of nitrogen in dissolved organic matter, which averaged 14.8±6.8 mmol N m−2 d−1 and exceeded the average internal input of nitrate by seven fold. There was, therefore, a severe nitrogen deficit that must have been offset by lateral and/or atmospheric inputs. Evaluation of the likely size of these sources indicates that lateral inputs must be important in the southern range of the area investigated, while atmospheric inputs seem to deliver the required N to balance losses in the northern area of the eastern subtropical Atlantic. Planktonic biomass was dominated by heterotrophs, and community respiration rates and bacterial carbon requirements exceeded the net primary production in the most unproductive areas. There must be significant allocthonous inputs of organic carbon and nitrogen in this region of the ocean. The distribution of primary production was uncoupled to that of the calculated CO2 flux across the ocean surface. The productive area off the NW African upwelling acted as a source of CO2 to the atmosphere (0.5 mmol C m−2 d−1), driven by high DIC inputs from the thermocline's interior, whereas the less productive areas at the northern and southern edges of the transect acted as net sinks for atmospheric CO2 (up to 2.5 mmol C m−2 d−1). The carbon sink in these unproductive regions seems to be supported largely by a downward dissolved organic carbon flux, partially supported by DOC excretion from phytoplankton cell lysis (30–70% of the net primary production in the area), twice as high as the average upward DIC flux. Provided that heterotrophic carbon requirements exceed the measured net primary production, the net downward flux into the thermocline's interior must be driven by the supply of allocthonous organic carbon, from atmospheric deposition and/or lateral supply.

Mmobilization and bacterial utilization of dissolved organic carbon entering the riparian zone of the alpine Enns River, Austria

In order to understand the factors controlling the removal of riverine dissolved organic carbon (DOC) in the riparian zone of an alpine river, concentrations of DOC and dissolved oxygen, as well as bacterial abundance and production, were determined in interstitial waters of an experi- mental bank filtration site of the Enns River, Austria. Four porewater stations exhibiting differing sedimentologic and hydrologic characteristics were sampled over an annual cycle. We found that concentrations of DOC, oxygen, bacterial biomass and production decreased significantly within the first meter from the sediment-water interface. Differences in the grain size distribution among the sampling stations led to spatial heterogeneity in the permeability of the riparian sediments and in the hydraulic residence time of the infiltrating river water, resulting in specific patterns in DOC immobilization and microbial respiration. Porewater bacterial abundance and production and apparent microbial oxygen consumption were positively correlated with the hydraulic residence time of the infiltrating water. DOC occasionally accumulated in the shallow porewater layers during the winter. During the summer, DOC infiltrating from the river surface potentially explained only 36 ± 25% of the apparent interstitial oxygen consumption. This suggests that particulate organic car- bon (POC) contributes substantially to the microbial organic carbon supply in the hyporheic zone. We conclude that the availability of POC rather than DOC infiltration determines hyporheic micro- bial metabolism.

Organic Carbon Supply and Metabolism in a Shallow Groundwater Ecosystem

Organic Carbon Supply and Metabolism in a Shallow Groundwater Ecosystem

Resource competition and community structure in aquatic micro-organisms: experimental studies of algae and bacteria along a gradient of organic carbon to inorganic phosphorus supply

Two microbial communities were grown in chemostats receiving a low supply of inorganic Phosphorus (P) (10 µM) and different supplies of organic carbon (OC), ranging from 0 to 600 µM, either as glucose or a mixture of organic substrates. One community was a natural assemblage of lake plankton and the other was a model community composed of cultured organisms. As the supply ratio of OC to inorganic P increased, concentrations of dissolved OC increased, concentrations of dissolved P decreased and abundances of phototrophic algae decreased. Abundances of bacteria and phago- trophic organisms did not consistently change with the OC:P supply ratio. The model community was first established with a phototroph (Scenedesmus quadricauda) and bacteria; the steady states of this community were invasible by the mixotroph Ochromonas danica under all OC:P supply ratios used. When OC supply was high, both microbial communities persisted with higher concentrations of dissolved OC when mixed substrates, rather than glucose, were supplied. Otherwise, the effects of organic substrate composition appeared to be secondary to those of the OC:P supply ratio. These experiments confirm some elements of published theory on resource-based interactions among heterotrophic bacteria and phototrophic algae.

Holocene accumulation of organic carbon at the Laptev Sea continental margin (Arctic Ocean): sources, pathways, and sinks

Composition and accumulation rates of organic carbon in Holocene sediments provided data to calculate an organic carbon budget for the Laptev Sea continental margin. Mean Holocene accumulation rates in the inner Laptev Sea vary between 0.14 and 2.7 g C cm−2 ky−1; maximum values occur close to the Lena River delta. Seawards, the mean accumulation rates decrease from 0.43 to 0.02 g C cm−2 ky−1. The organic matter is predominantly of terrigenous origin. About 0.9 × 106 t year−1 of organic carbon are buried in the Laptev Sea, and 0.25 × 106 t year−1 on the continental slope. Between about 8.5 and 9 ka, major changes in supply of terrigenous and marine organic carbon occur, related to changes in coastal erosion, Siberian river discharge, and/or Atlantic water inflow along the Eurasian continental margin.

Subsurface denitrification in a forest riparian zone: interactions between hydrology and supplies of nitrate and organic carbon.

The influence of hydrology andpatterns of supply of electron donors and acceptors onsubsurface denitrification was studied in a forestriparian zone along the Boyne River in southernOntario that received high nitrogen inputs from a sandaquifer. Two hypotheses were tested: (1) subsurfacedenitrification is restricted to localized zones ofhigh activity; (2) denitrification zones occur atsites where groundwater flow paths transportNO3 − to supplies of available organiccarbon. A plume of nitrate-rich groundwater withconcentrations of 10–30 mg N L−1 flowed laterallyat depths of 1.5–5 m in sands beneath peat for ahorizontal distance of 100–140 m across the riparianzone to within 30–50 m of the river. In situ acetyleneinjections to piezometers revealed that significantdenitrification was restricted to a narrow zone ofsteep NO3 − and N2O decline at theplume margins. The location of these denitrificationsites in areas with steep gradients of groundwater DOCincrease supported hypothesis 2. Many of thesedenitrification “hotspots” occurred near interfacesbetween sands and either peats or buried river channeldeposits. Field experiments involving in situadditions of either glucose or NO3 − topiezometers indicated that denitrification wasC-limited in a large subsurface area of the riparianzone, and became N-limited beyond the narrow zone ofNO3 − consumption. These data suggest thatdenitrification may not effectively removeNO3 − from groundwater transported at depththrough permeable riparian sediments unlessinteraction occurs with localized supplies of organicmatter.

Contrasting effects of substrate and grazer manipulations on picoplankton in oceanic and coastal waters off Brazil

In two contrasting regions off the coast of Brazil, picoplankton (<1 μm) responses to removal of larger grazers and to the additions of glucose and amino acids were determined. Effects of glucose and amino acid additions (1 μM) on particulate nitrogen and chlorophyll a concentrations, and on rates of NH4+ uptake and regeneration, were observed after 5 h pre-incubation. In the oceanic waters, removal of the >1 μm fraction had no significant effect on the chlorophyll a of the picoplankton after 5 h. However, the addition of glucose stimulated both uptake and regeneration by a mean of 27%, and the addition of arginine led to significant decreases in the rates of NH4+ uptake and regeneration. In contrast, in the coastal waters, significant increases in chlorophyll and particulate nitrogen concentrations were found after 5 h incubation in both the amended samples and in the controls, and mean rates of NH4+ uptake and regeneration were affected to a lesser degree by the additions of either glucose or amino acids than in the oceanic waters. The oceanic responses were suggestive of carbon limitation of heterotrophic bacteria. In the coastal region, on the other hand, the supply of organic carbon and nitrogen was likely to have been sufficient to meet the nutritional requirements of the heterotrophic bacteria and cyanobacteria. Grazing by larger organisms on the picoplankton appeared to play a more significant role in the nitrogen cycle in the coastal waters than in the oceanic waters.

Internal heterotrophy following the switch from macrophytes to algae in Lake Apopka, Florida

Measurements of photosynthesis and community respiration in Lake Apopka, Florida, U.S.A. indicate that this lake may be heterotrophic, and that the source of extra organic carbon is internal rather than external to the lake. This large and shallow lake (area 124 km2, mean depth 1.7 m) was dominated by macrophytes until hurricane-associated winds disrupted the plants in 1947, and the lake switched to a turbid, algal state. A layer of flocculent, organic sediments covers the lakebed to an average depth of 45 cm and winds regularly resuspend the upper portion into the water column. We used the diel oxygen curve method to estimate production and respiration and also reanalyzed the results of five past studies of production in the lake. The production measurements did not support the hypothesis that the flocculent layer represented excess algal production since 1947. Community respiration exceeded gross production on 60 out of 76 days sampled with statistically significant negative net production found in two of the three studies using the light and dark bottle oxygen method. External supplies of organic carbon are relatively small and are balanced by losses through the outlet. If the lake is heterotrophic, the excess respiration is most likely supported by the remains of macrophytes deposited in the sediments prior to the switch to an algal state. Similar sediment oxidation probably occurs in other shallow lakes that switch from the macrophyte to the algal state.

Planktonic production and respiration in oligotrophic Shield lakes

A precise oxygen method was used to measure primary production, community respiration and to determine the importance of exogenous organic carbon as an energy source to planktonic communities in the epilimnion of 12 oligotrophic to mesotrophic Shield lakes. Median photosynthetic parameters observed with the oxygen method were up to twice as high as those measured with 14C in other oligotrophic Shield lakes. Gross photosynthesis was almost always larger than community respiration, with a median P:R ratio of 1.7. We observed strong relationships between respiration and gross photosynthesis, but could not detect any significant trend between respiration or the P:R ratio and the concentration of dissolved organic carbon (DOC). DOC appeared to depress both photosynthesis and respiration. These results argue against the importance of exogenous organic carbon supply as a significant energy source to freshwater planktonic communities. Previously low P:R ratios reported for oligotrophic fresh waters may be due to the uncertain meaning of 14C production data.

The Latest Miocene–Early Pliocene biogenic bloom: a revised Indian Ocean perspective

Numerous investigations of Neogene sediment sequences from the Indian and Pacific Oceans have led to a paleoceanographic hypothesis that recently has been coined the “biogenic bloom”. This hypothesis suggests that primary productivity increased substantially at Indo-Pacific upwelling zones during the Latest Miocene–Early Pliocene. Although it is clear that recognition of a widespread biogenic bloom provides a fundamental framework for understanding Late Neogene global change, it also is apparent that investigations of this phenomena require syntheses of a variety of information from time-correlated sediment sequences that span large oceanic regions. Late Neogene polarity chron boundaries and nannofossil events are placed on a common and current time scale for 12 Ocean Drilling Program (ODP) sediment sequences in order to construct a coherent description of the biogenic bloom in the Indian Ocean. Carbonate mass accumulation rates (MARs) were significantly higher than present-day in the north and west Indian Ocean between 9.0 and 3.5 Ma. Sediment deposited during this time interval also is dominated by planktic faunal assemblages that are indicative of high-productivity, and redox conditions that are explained by an increase in the supply of organic carbon. Further, sediment of this age contains benthic faunal assemblages and chemical characteristics that are consistent with low dissolved O 2 in intermediate waters. These observations collectively suggest that, between 9.0 and 3.5 Ma, productivity in the north and west Indian Ocean was significantly higher than present-day, and the intermediate water oxygen minimum zone (OMZ) was more extensive than present-day. This paleoceanographic condition was most intense between 6.0 and 5.0 Ma in the Indian Ocean. Comparison of the Indian Ocean sites with two locations in the Pacific Ocean suggests that the biogenic bloom was time-coincident in the Indian and Pacific Oceans. The biogenic bloom, therefore, implies an important change in global nutrient cycling occurred during the Latest Miocene–Early Pliocene, although a satisfactory explanation for the change remains elusive.

Annual sediment primary production and respiration in a large coral reef lagoon (SW New Caledonia)

Sediment photosynthetic production and community respiration were investigated for 1 yr in the south-west lagoon of New Caledonia (surface area: 2000 km 2 ; mean depth: 21 m). Metabolic fluxes were measured at the water-sediment interface using benthic enclosures, at 60 sampling stations randomly distributed in space and time. Mean gross primary production (P g ) was 12.06 mol C m -2 yr -1 . Mean respiration (R) was 13.68 mol C m -2 yr -1 . P g /R was thus 0.88, indicating that the whole lagoon was net heterotrophic. There were, however, large differences along a land-ocean gradient. Muddy bottoms (35 % of the lagoon surface), located along the shore and in the deeper part of the lagoon, were significantly heterotrophic (Pg/R = 0.39), whereas the ratio for sandy bottoms (65 % of the area) towards the reef were close to 1 or slightly positive, indicating potentially autotrophic benthic communities. Both P g and R followed a similar seasonal variation with higher values during the warm season (November to February), when maximum irradiance and the particulate organic carbon supply occurred. These results suggest that autotrophy, generally observed in coral reef flats, may also occur in lagoon sediments, indicating both a major importance of regeneration processes and a relative equilibrium of energy exchanges with adjacent ecosystems. Terrestrial influence results in a decrease of autochthonous production and a correlative increase of carbon sedimentation leading to benthic heterotrophy.

Biomarkers as organic-carbon-source and environmental indicators in the Late Quaternary Arctic Ocean: problems and perspectives

In order to examine the variation in marine and terrigenous sources of the organic matter during the last 15,000 Cal. yr BP, hydrogen index values, C/N ratios, and specific biomolecules (short- and long-chain n -alkanes, short-chain fatty acids, sterols, alkenones , and pigments) were determined in three sediment cores from the Laptev Sea continental margin . The results show that the interpretation of the biomarker data is much more complicated and less definitive in comparison to similar data sets from low-latitude open-ocean environments. This is mainly caused by the complexity of the Arctic Ocean system, which is characterized by a high seasonality of sea-ice cover and primary productivity, sea-ice sediment transport and a high fluvial supply of freshwater (aquatic) organic matter. A combination of organic geochemical, organic petrographic and micropaleontological data may yield to a more precise identification of organic-carbon sources for these complex systems. On the Laptev Sea shelf (cores KD9502-14 and PS2725-5), terrigenous organic-carbon input controlled by river discharge seems to be predominant during the last about 10,000 Cal. yr BP. Maximum supply of terrigenous organic carbon was reached in the Early Holocene (i.e., about 9000–10,000 Cal. yr BP). Further offshore at the upper continental slope (core PS2458-4), a major change in organic-composition occurred near 10,000 Cal. yr BP. During this period hydrogen indices as well as the amounts of short-chain n -alkanes, short-chain fatty acids, dinosterol and brassicasterol significantly increased, indicating increased relative proportions of marine organic matter preserved in the later time interval.

Effects on aquatic ecosystems

Effects on aquatic ecosystems

Treatment of simulated aquaculture water using biofilters subjected to aeration/non-aeration cycles

The overall objective of this research activity is the development of a fixed-film biological nutrient removal (BNR) biofilter system for the reuse and discharge of a selected aquaculture water. The three stage biofilter system used in the study provided alternating aeration/non-aeration cycles for phosphorus removal in two of the three biofilters. The removal of TOC and ammonia improved as the cycle duration (CD) increased as a result of the reduction in the frequency of the transition periods between the cycles. The system achieved limited net phosphorus removal due to the limited sludge wasting and lack of external organic carbon supplies during phosphorus uptake. However, the phosphorus activity in the system was significant and was modified by the CD. The denitrification activity was coupled with phosphorus uptake and both activities appeared to have been supplied by an internal organic carbon source. The major challenges of achieving phosphorus removal in the system include: (1) overcoming the deterioration in the performance of the system during the transition period following the start of each new cycle; and (2) wasting the excess biomass following the aeration cycle. Without active sludge wasting, the system behaves as a phosphorus reservoir with a limited storage capacity. On the other hand, frequent sludge wasting may disrupt the performance of the system.

Detrital aggregates on the sea floor: chemical composition and aerobic decomposition rates at a time-series station in the abyssal NE Pacific

Seasonal pulses of particulate matter sink to the sea floor and form visible detrital aggregates between July and December at an abyssal station (Sta. M, 4100 m depth) in the NE Pacific. We hypothesized that these detrital aggregates would create localized regions of intense biological activity on the sea floor. Detrital aggregates were collected and incubated on the sea floor using the submersible Alvin in August and three weeks later in September 1994. As a control, samples of the sediments were collected and incubated in situ in April 1995, when no aggregates were present. Detrital aggregates representing a range of sizes, colors and textures were sampled individually with Alvin using tube corers; others were incubated on the sea floor in tube core respirometers. In addition, a number of aggregate locations were documented photographically then sampled 23 and 221–223 d later, after the aggregates were no longer visible. A total of 55 tube cores with aggregates were collected in August 1994, and another 88 were collected in September 1994. Concentrations of total and organic carbon, total nitrogen, chlorophyll a and phaeopigments in the aggregates were similar to those in the sinking particulate matter collected concurrently in sediment traps at 50 m above bottom, but higher than those in the surface sediments. Oxygen consumption of diffuse floc was similar to that of the background sediment, whereas discrete aggregates and radiolarian-patch samples had rates significantly higher than background sediment. Detrital aggregates had no measurable influence on the chemical composition of the underlying sediment on time scales from 23 to 223 d or on sediment oxygen consumption after 222 d. Distinct detrital aggregates monitored visually with a time-lapse camera covered up to 4.9% of the sea floor and contributed substantially to the supply of organic carbon to the sediment community in fall 1994 while producing a minimal impact on sediment community oxygen consumption (SCOC). The annual oxygen consumption associated with detrital aggregates represented a minor contribution (0.34%) to the annual SCOC estimated at Sta. M in 1994–1995.

Late Quaternary paleoenvironment of the Ross Sea continental shelf, Antarctica

Based on sedimenlological and micropaleontological work on three sediment cores collected at about 167° Ε in the western Ross Sea, Antarctica, and accelerator mass spectrometer l4C ages of organic carbon, we have reconstructed environmental changes in the area during the late Quaternary. Since 38 ka BP at latest, this area was a marine environment with low productivity. A grounded ice sheet advanced and loaded the sediments before about 30-25 ka BP. After 25 ka BP, the southernmost site (76°46'S) was covered by floating ice (shelf ice), preventing deposition of coarse terrigenous materials and maintaining a supply of diatom tests and organic carbon until 20 ka BP. The northernmost site (74°33'S) was in a marine environment with a moderate productivity influenced by shelf ice/ice sheet after about 20 ka BP. Since about 10 ka BP, a sedimentary environment similar to the present-day one has prevailed over this area.

Treatment of simulated aquaculture water using biofilters subjected to aeration/non-aeration cycles

The overall objective of this research activity is the development of a fixed-film biological nutrient removal (BNR) biofilter system for the reuse and discharge of a selected aquaculture water. The three stage biofilter system used in the study provided alternating aeration/non-aeration cycles for phosphorus removal in two of the three biofilters. The removal of TOC and ammonia improved as the cycle duration (CD) increased as a result of the reduction in the frequency of the transition periods between the cycles. The system achieved limited net phosphorus removal due to the limited sludge wasting and lack of external organic carbon supplies during phosphorus uptake. However, the phosphorus activity in the system was significant and was modified by the CD. The denitrification activity was coupled with phosphorus uptake and both activities appeared to have been supplied by an internal organic carbon source.The major challenges of achieving phosphorus removal in the system include: (1) overcoming the deterioration in the performance of the system during the transition period following the start of each new cycle; and (2) wasting the excess biomass following the aeration cycle. Without active sludge wasting, the system behaves as a phosphorus reservoir with a limited storage capacity. On the other hand, frequent sludge wasting may disrupt the performance of the system.

Community structure and spatial heterogeneity of the deep-sea macrofauna at three contrasting stations in the tropical northeast Atlantic

A study of macrofauna community structure and spatial patterns was undertaken at three deep-sea stations during three EUMELI cruises in the tropical northeast Atlantic Ocean. The benthic response to contrasting regimes of organic carbon supply at the eutrophic (E), mesotrophic (M) and oligotrophic (O) stations (1700 m, 3 100 m and 4700 m depth, respectively) was evaluated through qualitative and quantitative analysis of the composition and structure of benthic macrofauna (> 250 μm) and discussed with regard to the biological and physical conditions. The mean densities of the total macrofauna, dominated by the Polychaeta, Tanaïdacea, Isopoda and Bivalvia, decreased with increasing depth from 5403 ind. m −2 at station E to 231.5 ind. m −2 at station O. From the 16 taxonomic groups represented at the E and M sites, only eight could be sampled at the O site. The density gradient can be related to the decreasing surface production, food supply and hydrographic conditions between the three stations. The comparison of the high densities encountered at station E with other studies underlines the particular feature of this station subjected to intense upwelling activity resulting in high organic carbon input. The patchy distribution of the macrofauna at stations E and M suggests that both physical and biologically-mediated disturbances create environmental heterogeneity favouring the aggregation of organisms. This process occurs at different observation scales. At a large scale, bottom current and upwelling activity induce high densities and faunal aggregations, displaying a degree of density-dependence. At the local scale, the complexity of the food web induces biologically-mediated disturbances, and the activity of major deposit-feeding taxa, like polychaetes, create sediment microhabitats favouring patchy distribution. Faunal patch sizes are variable among the taxa considered. Most are distributed in patches less than 1 m z. Our work contributes to the understanding of how the deep benthic communities are structured, particularly under the influence of environmental conditions in tropical latitudes.

High potential activity of extracellular alkaline phosphatase in deep waters of the central Pacific

We found high potential activities of alkaline phosphatase associated with particles (0.2 μm or greater size fraction) in deep waters (1000–4000 m) of the central Pacific Ocean. The potential enzyme activity at depth (0.03 – 0.3 nM h −1) was up to 50% of that at the surface (0–125 m). In contrast, activities of α- and β- d-glucosidase in the deep layer were low (generally less than 1 % of those in the upper layer), yielding up to two orders of magnitude difference in the ratio of alkaline phosphatase and α- and β- d-glucosidase activities with depth. It is unlikely that the phosphatase is actively produced by microorganisms inhabiting the deep-sea environment, where labile organic carbon supply is limited and phosphate concentration is high (2.4 – 3.0 AM). Instead, deep-water phosphatase is probably supplied by rapidly sinking particles and their subsequent fragmentation and dissolution. Different distributions of phosphatase and glucosidase indicate that sinking particles of phytoplankton origin are an important source of alkaline phosphatase enzymes in the deep sea.