Suspended Particulate Organic Carbon Research Articles

Bacterial carbon content and the living and detrital bacterial contributions to suspended particulate organic carbon in the North Pacific Ocean

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 62:165-176 (2011) - DOI: https://doi.org/10.3354/ame01462 Bacterial carbon content and the living and detrital bacterial contributions to suspended particulate organic carbon in the North Pacific Ocean Nobuyuki Kawasaki1,2,*, Rumi Sohrin3, Hiroshi Ogawa4, Toshi Nagata4, Ronald Benner1 1University of South Carolina, Marine Science Program, Columbia, South Carolina 29208, USA 2National Institute for Environmental Studies, 16-2 Onogawa Tsukuba, Ibaraki 305-8506, Japan 3Shizuoka University, 836 Ohya Shizuoka, Shizuoka 422-8529, Japan 4Atmosphere and Ocean Research Institute, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan *Email: kawasaki.nobuyuki@nies.go.jp ABSTRACT: Carbon-normalized yields of amino acids in size-fractionated seawater samples and bacterial cultures were used in a novel application to estimate the carbon content of heterotrophic marine bacteria. The estimated carbon content (6.3 ± 1.6 fg C cell–1) of open ocean bacteria derived using this approach was lower than most values estimated in previous studies. Based on these values, living heterotrophic bacteria accounted for 6.8 ± 1.1% of suspended particulate organic carbon (POC) in surface waters at Stn ALOHA in the North Pacific gyre. Living cyanobacteria accounted for 13.3 ± 2.2% of suspended POC in surface waters. Carbon-normalized yields of muramic acid, D-alanine and D-glutamic acid, unique biomarkers of bacteria, were used to estimate that bacterial detritus accounted for 4.3 ± 2.9% of suspended POC in surface waters. The relative contribution of bacterial detritus to suspended POC increased dramatically with increasing depth, indicating that some components of bacterial detritus are resistant to decomposition in the deep ocean. The total living and detrital bacterial contribution to suspended POC in surface waters was ~25%. KEY WORDS: Bacterial carbon content · Bacterial detritus · Bacterial biomarkers · Suspended particulate organic carbon Full text in pdf format PreviousNextCite this article as: Kawasaki N, Sohrin R, Ogawa H, Nagata T, Benner R (2011) Bacterial carbon content and the living and detrital bacterial contributions to suspended particulate organic carbon in the North Pacific Ocean. Aquat Microb Ecol 62:165-176. https://doi.org/10.3354/ame01462 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 62, No. 2. Online publication date: January 19, 2011 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2011 Inter-Research.

Photooxidation of particulate organic matter, carbon/oxygen stoichiometry, and related photoreactions

We investigated photoredox transformations of oxygen, carbon, peroxides, and iron that accompany “photodissolution” of suspended marine particulate organic carbon (POC), a sunlight-induced process that transfers POC to the dissolved organic carbon (DOC) pool. During 18- to 24-hour photodissolution experiments with POC of varying composition, about 0.28 mol of O 2 was consumed per mole POC photodissolved. Mean dissolved inorganic carbon (DIC) production was 6% of initial POC in suspended river delta sediments and 1% in algal membrane detritus. The mean O 2 loss:DIC production ratio was − 1.3:1 in sediment suspensions, which slightly exceeds the typical range reported for DOC. The O 2 loss:DIC production ratio was − 7.7:1 in suspensions of algal detritus, which implies significant oxygen incorporation into (oxygenation of) organic matter. Irradiated sediment suspensions rapidly achieved low, steady-state peroxide concentrations but rose more slowly with algal detritus. Elevated iron concentrations in the 0.7–8.0 μm particle size fraction after 24 h of irradiation are consistent with photoredox cycling of metals and/or with physical disintegration of organic-mineral aggregates driven by organic matter dissolution. These oxidation and oxygenation results differ from analogous reactions previously found for marine DOC, and estimates of DIC production in particle-rich environments will require incorporation of POC-specific information.

Aquatic macrophytes drive sediment stoichiometry and the suspended particulate organic carbon composition of a tropical coastal lagoon

Aquatic macrophytes drive sediment stoichiometry and the suspended particulate organic carbon composition of a tropical coastal lagoon

Comparative evaluation of sediment trap and 234Th-derived POC fluxes from the upper oligotrophic waters of the Gulf of Mexico and the subtropical northwestern Pacific Ocean

To better understand the inter-relationships between particulate organic carbon (POC) fluxes and phytoplankton and bacteria biomass and production, we compared POC fluxes determined in sediment traps and approaches based on size-fractionated (1–10, 10–50, 50–150 and > 150 μm) suspended particulate 234Th and POC concentrations in oligotrophic sections of the Gulf of Mexico during August 2005 and May 2006 and in the oligotrophic northwestern Pacific Ocean during 2009. In 2005, the sediment trap POC flux near the bottom of the euphotic zone (120 m) ranged from 71 to 94 mg C m − 2 day − 1 , while 234Th-derived POC fluxes using POC/ 234Th ratios in the 10–50 µm and 50–150 µm varied from 71 to 150 mg C m − 2 day − 1 . In 2006, the sediment trap POC flux at 120 m ranged from 24 to 67 mg C m − 2 day − 1 , while the 234Th-derived POC fluxes in the 10–50 µm fraction were comparable or somewhat higher, ranging from 71 to 119 mg C m − 2 day − 1 . The POC fluxes in 2006, calculated by using POC/ 234Th ratios in the 1–10 µm and the 50–150 µm fractions were much higher, ranging from 847 to 1369 mg C m − 2 day − 1 . Correlations with biological and chemical parameters support a likely mechanism of sinking aggregates of haptophytes (0.2–20 µm) of higher density held together by Th-complexing and uronic acid containing exopolymeric substances. The observations that 234Th (and POC) is mainly associated with medium-sized (10–15 µm) suspended particles rather than larger (50–150 µm) ones may be caused by the use of a one-filter method and standard filtration and processing procedures that were applied here for collecting suspended particles. This then raises the question of what constitutes representative material from the ocean that settles on the characteristic time scale of 234Th. As a comparison, size-fractionated trap-collected particles in the oligotrophic northwestern Pacific Ocean showed that the 10–50 μm fraction contained the largest proportion of POC (22–41%), followed by the 50–150 μm (22–37%), the > 150 μm (15–27%), and the 1–10 μm (17–23%) fraction. The partitioning of 234Th in trap-collected particles was slightly different from that of POC, with the 1–10 μm fraction representing the largest proportion (27–48%) of 234Th flux. Together, the < 50 μm particles contributed, on average, 52 ± 6% of POC, which suggests that the POC/ 234Th ratios traditionally derived from large (> 50 µm) pump-collected particles may not accurately reflect the majority of sinking particles. Therefore, estimated POC fluxes may be significantly biased using a conventional 234Th based approach, i.e., using POC/ 234Th ratios from a single filter obtained from large (> 50 µm) pump-collected particles.

The Boston Harbor Project, and large decreases in loadings of eutrophication-related materials to Boston Harbor

Boston Harbor, a bay–estuary in the north-east USA, has recently been the site of one of the largest wastewater infrastructure projects conducted in the USA, the Boston Harbor Project (BHP). The BHP, which was conducted from 1991 to 2000, ended over a century of direct wastewater treatment facility discharges to the harbor. The BHP caused the loadings of total nitrogen (TN), total phosphorus (TP), total suspended solids (TSS) and particulate organic carbon (POC) to the harbor, to decrease by between 80% and 90%. Approximately one-third of the decreases in TSS and POC loadings occurred between 1991 and 1992; the remaining two-thirds, between 1995 and 2000. For TN and TP, the bulk of the decreases occurred between 1997 or 1998, and 2000.

The isotopic composition of particulate organic carbon in mountain rivers of Taiwan

Small rivers draining mountain islands are important in the transfer of terrestrial particulate organic carbon (POC) to the oceans. This input has implications for the geochemical stratigraphic record. We have investigated the stable isotopic composition of POC (δ13Corg) in rivers draining the mountains of Taiwan. In 15 rivers, the suspended load has a mean δ13Corg that ranges from −28.1±0.8‰ to −22.0±0.2‰ (on average 37 samples per river) over the interval of our study. To investigate this variability we have supplemented suspended load data with measurements of POC in bedrock and river bed materials, and constraints on the composition of the terrestrial biomass. Fossil POC in bedrock has a range in δ13Corg from −25.4±1.5‰ to −19.7±2.3‰ between the major geological formations. Using coupled δ13Corg and N/C we have found evidence in the suspended load for mixing of fossil POC with non-fossil POC from the biosphere. In two rivers outside the Taiwan Central Range anthropogenic land use appears to influence δ13Corg, resulting in more variable and lower values than elsewhere. In all other catchments, we have found that 5‰ variability in δ13Corg is not controlled by the variable composition of the biomass, but instead by heterogeneous fossil POC. In order to quantify the fraction of suspended load POC derived from non-fossil sources (Fnf) as well as the isotopic composition of fossil POC (δ13Cfossil) carried by rivers, we adapt an end-member mixing model. River suspended sediments and bed sediments indicate that mixing of fossil POC results in a negative trend between N/C and δ13Corg that is distinct from the addition of non-fossil POC, collapsing multiple fossil POC end-members onto a single mixing trend. As an independent test of the model, Fnf reproduces the fraction modern (Fmod) in our samples, determined from 14C measurements, to within 0.09 at the 95% confidence level. Over the sampling period, the mean Fnf of suspended load POC was low (0.29 ± 0.02, n = 459), in agreement with observations from other mountain rivers where physical erosion rates are high and fossil POC enters river channels. The mean δ13Cfossil in suspended POC varied between −25.2±0.5‰ and −20.2±0.6‰ from catchment to catchment. This variability is primarily controlled by the distribution of the major geological formations. It also covers entirely the range of δ13Corg found in marine sediments which is commonly thought to derive from mixing between marine and terrigenous POC. If land-sourced POC is preserved in marine sediments, then changes in the bulk δ13Corg observed offshore Taiwan could instead be explained by changes in the onshore provenance of sediment. The range in δ13Corg of fossil organic matter in sedimentary rocks exposed at the surface is large and given the importance of these rocks as a source of clastic sediment to the oceans, care should be taken in accounting for fossil POC in marine deposits supplied by active mountain belts.

Bulk organic δ 13C and C/N as indicators for sediment sources in the Pearl River delta and estuary, southern China

Preservation of organic matter in estuarine and coastal areas is an important process in the global carbon cycle. This paper presents bulk δ 13C and C/N of organic matter from source to sink in the Pearl River catchment, delta and estuary, and discusses the applicability of δ 13C and C/N as indicators for sources of organic matter in deltaic and estuarine sediments. In addition to the 91 surface sediment samples, other materials collected in this study cover the main sources of organic material to estuarine sediment. These are: terrestrial organic matter (TOM), including plants and soil samples from the catchment; estuarine and marine suspended particulate organic carbon (POC) from both summer and winter. Results show that the average δ 13C of estuarine surface sediment increases from −25.0 ± 1.3‰ in the freshwater environment to −21.0 ± 0.2‰ in the marine environment, with C/N decreasing from 15.2 ± 3.3 to 6.8 ± 0.2. In the source areas, C 3 plants have lower δ 13C than C 4 plants (−29.0 ± 1.8‰ and −13.1 ± 0.5‰ respectively). δ 13C increases from −28.3 ± 0.8‰ in the forest soil to around −24.1‰ in both riverbank soil and mangrove soil due to increasing proportion of C 4 grasses. The δ 13C POC increases from −27.6 ± 0.8‰ in the freshwater areas to −22.4 ± 0.5‰ in the marine-brackish-water areas in winter, and ranges between −24.0‰ in freshwater areas and −25.4‰ in brackish-water areas in summer. Comparison of the δ 13C and C/N between the sources and sink indicates a weakening TOM and freshwater POC input in the surface sedimentary organic matter seawards, and a strengthening contribution from the marine organic matter. Thus we suggest that bulk organic δ 13C and C/N analysis can be used to indicate sources of sedimentary organic matter in estuarine environments. Organic carbon in surface sediments derived from anthropogenic sources such as human waste and organic pollutants from industrial and agricultural activities accounts for less than 10% of the total organic carbon (TOC). Although results also indicate elevated δ 13C of sedimentary organic matter due to some agricultural products such as sugarcane, C 3 plants are still the dominant vegetation type in this area, and the bulk organic δ 13C and C/N is still an effective indicator for sources of organic matter in estuarine sediments.

Aquatic macrophytes drive sediment stoichiometry and the suspended particulate organic carbon composition of a tropical coastal lagoon

OBJETIVO: O objetivo desta pesquisa foi avaliar: (1) a influencia das macrofitas aquaticas Typha domingensis Pers., Eleocharis interstincta (Vahl) Roem. & Schult. (emergentes) e Potamogeton stenostachys K. Schum. (submersa), sobre a estequiometria do sedimento e (2) a contribuicao desta comunidade para a composicao do carbono orgânico de diferentes compartimentos de uma lagoa costeira tropical, Lagoa de Cabiunas (Macae, RJ); METODOS: Perfis de sedimento de 10 cm, fracionados de 2 em 2 cm foram coletados nas regioes litorânea e limnetica para analises de nutrientes (C, N e P). Na regiao litorânea, o sedimento foi coletado em tres estacoes: bancos de T. domingensis, E. interstincta e P. stenostachys. Para avaliacao da ciclagem do C na lagoa Cabiunas foi determinada a assinatura δ13C de diversos compartimentos da lagoa (zoo e fitoplancton, macrofitas aquaticas e material dissolvido e suspenso na agua) e da restinga (vegetacao terrestre); RESULTADOS: As concentracoes de C e N na regiao colonizada por E. interstincta e T. domingensis foram significativamente maiores que na regiao limnetica. Em relacao a concentracao de fosforo, o sedimento colonizado pela macrofita T. domingensis apresentou valor significativamente maior que a regiao limnetica e a regiao colonizada por P. stenostachys. Quanto as razoes molares, a regiao litorânea apresentou elevadas razoes C:P, principalmente nos bancos colonizados por E. interstincta e P. stenostachys. As razoes N:P tambem foram maiores na regiao litorânea. As analises isotopicas (δ13C) mostraram que o carbono orgânico particulado na coluna d'agua tem origem principalmente nos tecidos das macrofitas aquaticas; CONCLUSOES: As macrofitas aquaticas emersas contribuem de maneira significativa para o enriquecimento de nutrientes do sedimento da lagoa Cabiunas. O detrito das plantas acumulado no sedimento da regiao litorânea, em geral, altera sua estequiometria e qualidade para os decompositores, possuindo proporcionalmente mais C do que N e P se comparado a regiao limnetica. Sua importância, no entanto, nao se restringe ao sedimento, pois apresentou forte influencia na constituicao do carbono particulado suspenso na coluna d'agua dessa lagoa, consistindo em importante conexao entre compartimentos desse ecossistema.

A field study on the conversion ratio of phytoplankton biomass carbon to chlorophyll-a in Jiaozhou Bay, China

A one-year field study was conducted to determine the conversion ratio of phytoplankton biomass carbon (Phyto-C) to chlorophyll-a (Chl-a) in Jiaozhou Bay, China. We measured suspended particulate organic carbon (POC) and phytoplankton Chl-a samples collected in surface water monthly from March 2005 to February 2006. The temporal and spatial variations of Chl-a and POC concentrations were observed in the bay. Based on the field measurements, a linear regression model II was used to generate the conversion ratio of Phyto-C to Chl-a. In most cases, a good linear correlation was found between the observed POC and Chl-a concentrations, and the calculated conversion ratios ranged from 26 to 250 with a mean value of 56 µg µg−1. The conversion ratio in the fall was higher than that in the winter and spring months, and had the lowest values in the summer. The ratios also exhibited spatial variations, generally with low values in the near shore regions and relatively high values in offshore waters. Our study suggests that temperature was likely to be the main factor influencing the observed seasonal variations of conversion ratios while nutrient supply and light penetration played important roles in controlling the spatial variations.

14C as a tool for evaluating riverine POC sources and erosion of the Zhujiang (Pearl River) drainage basin, South China

Radiocarbon can serve as a powerful tool for identifying sources of organic carbon and evaluating the erosion intensity in river drainage basins. In this paper we present 14C-AMS measurements of particulate organic carbon (POC) collected from the three major tributaries of the Zhujiang (Pearl River) system: the Xijiang (Western River), Beijiang (Northern River) and Dongjiang (Eastern River) rivers. Furthermore, we discuss the distribution of POC 14C apparent ages and the related watersheds erosion of these rivers. Results yield Δ14C values of −425‰ to −65‰ which indicate that the 14C apparent ages of suspended POC in the entire area are in the range of 540–4445 years. The POC apparent ages from Xijiang are mostly between 2000 and 4000 years, while in Dongjiang they mostly range from 540 to 1010 years. These 14C apparent ages indicate that the watershed erosion of the Xijiang is more severe than that of the Dongjiang. This is in agreement with other data showing deeper erosion in Xijiang due to human activities.

Partitioning of endocrine disrupting compounds in inland waters and wastewaters discharged into the coastal area of Thessaloniki, Northern Greece

In the Water Framework Directive 2000/60/EC, environmental objectives for the proper quality of inland, surface, transitional, coastal, and ground waters have been set. Member states are required to identify chemical pollutants of significance in the water bodies, to establish emission control measures, and to achieve quality standards. A specific category of pollutants are the compounds that may possess endocrine-related functions known as endocrine disrupting compounds (EDCs). This means that member states have the obligation to take action in order to prevent human exposure to these compounds via aquatic environment. The objective of this research was to study the occurrence and distribution of phenolic and steroid EDCs in inland waters and wastewaters discharged in the area of Thermaikos Gulf, Thessaloniki, Northern Greece. Samples were collected from three rivers, four streams, and four municipal and industrial wastewaters from the area of Thessaloniki, Northern Greece, during the period 2005-2006. The samples were analyzed for 14 EDCs (nonylphenol, octylphenol, their mono- and di-ethoxylate oligomers, bisphenol A, estrone, 17alpha-estradiol, 17beta-estradiol, estriol, mestranol, and 17alpha-ethynylestradiol). The compounds were recovered by solid phase extraction and ultrasonic extraction from the dissolved phase and particulate phase, respectively, and determined by employing gas chromatography-mass spectrometry. Results revealed the presence of phenolic EDCs (NP, NP1EO, NP2EO, tOP, OP1EO, OP2EO, and BPA) in all water and wastewater samples. Steroid EDCs were not found at detectable concentrations. The relationships between field partition coefficients of EDCs and concentration of total suspended solids, dissolved, and particulate organic carbon were investigated. Rivers exhibited concentrations of EDCs similar to minimally impacted surface waters worldwide. The concentrations of NP and OP occasionally exceeded the environmental quality criteria proposed for inland waters. The concentrations of EDCs in streams exhibited wide variations due to low flow rate in these systems and the impact of wastewaters from various pollution sources. Wastewater from tannery activities showed extremely high concentrations of NP, whereas relatively high concentrations of EDCs were determined in effluents from the industrial wastewater treatment plant. Field partition coefficients of EDCs are negatively correlated with concentrations of total suspended solids and dissolved organic carbon and positively correlated with particulate organic carbon. The examined rivers (Aliakmon, Axios, and Loudias) exhibited concentrations of EDCs similar to minimally impacted surface waters worldwide. However, special attention should be paid to these systems since the concentrations for NP and OP occasionally were above the proposed quality standards, revealing the impact of urban, industrial, and agricultural activities. High concentrations of EDCs were determined in streams, urban, and industrial wastewater posing significant risk to the aquatic environment they discharged. The occurrence of EDCs in inland waters and wastewaters discharged to Thermaikos Gulf results in an increased risk to the marine environment. Thus, these systems should be regularly monitored, especially for NP, OP, and BPA that are considered as priority hazardous compounds in the Water Framework Directive.

Base-line variations in stable isotope values in an Arctic marine ecosystem: effects of carbon and nitrogen uptake by phytoplankton

Stable isotope values are useful for elucidating C and N cycling and pathways in marine and aquatic ecosystems. Variations in the base-line isotope values, the δ13C and δ15N values of phytoplankton, put constraints on their usefulness as tracers for trophic interactions and sources of organic matter in food web studies, however. We investigated the C and N stable isotope values of suspended particulate organic matter in relation to uptake of total dissolved inorganic carbon and nitrate, chlorophyll a concentration and the isotope composition of dissolved inorganic carbon in an Arctic marine environment (northern Barents Sea) in order to improve the understanding of factors regulating the variation in stable isotope values at the base of the marine food web. The stable isotope values of water-column suspended particulate organic carbon (δ13Corg) and nitrogen (δ15Norg) varied from −28.3‰ to −20.2‰ and 2.9‰ to 8.3‰, respectively, among stations sampled during spring and summer. δ13Corg was not linearly related to carbon uptake, but the values were on average 3‰ higher at stations in a late-bloom stage, characterised by higher carbon uptake compared to early-bloom stations. Accumulation of phytoplankton biomass had a strong impact on δ13Corg values, reflected in a positive relationship between δ13Corg and chlorophyll a concentration. δ15Norg was positively related to the percentage of nitrate taken up from initial (winter) concentrations. These results indicate a strong relationship between bloom progression and isotope composition of particulate organic C and N pools. Synoptic data on stable isotope compositions, nutrient concentrations and phytoplankton biomass therefore improve the interpretation of isotope values when these are compared across pools with different turnover times, such as phytoplankton and consumers or suspended and sedimentary organic matter.

Lateral POC transport and consumption in surface and deep waters of the Canary Current region: A box model study

We have estimated the lateral transport and consumption, from surface to 3000 m, of suspended particulate organic carbon (POC), through a box model approach, in the Canary Current region (subtropical northeast Atlantic). Our results show that lateral POC fluxes are up to 3 orders of magnitude higher than vertical fluxes. In the mesopelagic ocean, the central waters (100–700 m) presented a net carbon consumption of 8.51 × 108 mol C d−1 with the highest POC entering through the more coastal section. This lateral flux accounted for 28–59% of the total mesopelagic respiration (R), on the basis of lower and upper case scenarios of vertical POC inputs and dissolved organic carbon contribution to R. We suggest that boundary currents may support higher lateral export of coastally produced POC than previously assumed. A large fraction of this POC would, however, be remineralized in the upper 1000 m instead of being transported to the ocean interior.

Hydrolytic ectoenzyme activity associated with suspended and sinking organic particles within the anoxic Cariaco Basin

Ectohydrolase activities of suspended microbiota were compared to those associated with sinking particles (sed-POM) retrieved from sediment traps deployed in the permanently anoxic Cariaco Basin. In shore-based assays, activities of aminopeptidase, β-glucosidase, chitinase and alkaline phosphatase were measured in samples obtained from oxic and anoxic depths using MUF- and MCA-labeled fluorogenic substrate analogs. Hydrolysis potentials for these enzymes in the seston varied widely over the nine cruises sampled (8 Nov 1996–3 May 2000) and among depths (15–1265 m); from <10 to over 1600 nM d −1 hydrolysate released, generally co-varying with one another and with suspended particulate organic carbon (POC) and particulate nitrogen (PN). Hydrolytic potentials, prokaryotic abundances and POC/PN concentrations in sinking debris were 400–1.3×10 7 times higher than in comparable volumes of seawater. However when normalized to PN, hydrolytic potentials in sediment trap samples were not demonstrably higher than in Niskin bottle samples. We estimate that PN pools in sediment trap samples were turned over 2–1400 times (medians=7–26 x) slower by hydrolysis than were suspended PN pools. Median prokaryotic growth rates (divisions d −1) in sinking debris were also ∼150 times slower than for bacterioplankton. Hydrolytic potentials in surface oxic waters were generally faster than in underlying anoxic waters on a volumetric basis (nM hydrolysate d −1), but were not significantly ( p>0.05) different when normalized to PN or prokaryote abundances. Alkaline phosphatase was consistently the most active ectohydrolase in both sample types, suggesting that Cariaco Basin assemblages were adapted to decomposing phosphate esters in organic polymers. However, phosphorus limitation was not evident from nutrient inventories in the water column. Results support the hypothesis that efficiencies of polymer hydrolysis in anoxic waters are not inherently lower than in oxic waters.

Molecular and isotopic constraints on the sources of suspended particulate organic carbon on the northwestern Atlantic margin

The abundance, carbon isotopic composition (Δ 14C and δ 13C), and lipid biomarker (alkenones and saturated fatty acids) distributions of suspended particulate organic matter were investigated at three stations centered on the 2000, 3000, and 3500 m isobaths over the New England slope in order to assess particulate carbon sources and dynamics in this highly productive and energetic region. Transmissometry profiles reveal that particle abundances exhibit considerable fine structure, with several distinct layers of elevated suspended particulate matter concentration at intermediate water depths in addition to the presence of a thick bottom nepheloid layer at each station. Excluding surface water samples, the Δ 14C values of particulate organic carbon (POC) indicated the presence of a pre-aged component in the suspended POC pool (Δ 14C<+38‰). The Δ 14C values at the 3000 m station exhibited greater variability and generally were lower than those at the other two stations where the values decreased in a more systematic matter with increasing sampling depth. These lower Δ 14C values were consistent with higher relative abundances of terrigenous long-chain fatty acids at this station than at the other two stations. Two scenarios were considered regarding the potential provenances of laterally transported POC: cross-shelf transport of shelf sediment (Δ 14C=−140‰) and along-slope transport of the slope sediment proximal to the sampling locations (Δ 14C=−260‰). Depending on the scenario, isotopic mass balance calculations indicate allochthonous POC contributions ranging between 15% and 54% in the meso- and bathy-pelagic zone, with the highest proportions at the 3000 m station. Alkenone-derived temperatures recorded on suspended particles from surface waters closely matched in-situ temperatures at each station. However, alkenone-derived temperatures recorded on particles from the subsurface layer down to 250 m were lower than those of overlying surface waters, especially at the 3000 m station, implying supply of phytoplankton organic matter originally produced in cooler surface waters. AVHRR images and temperature profiles indicate that the stations were under the influence of a warm-core ring during the sampling period. The low alkenone-derived temperatures in the subsurface layer coupled with the lower Δ 14C values for the corresponding POC suggests supply of OC on resuspended sediments underlying cooler surface waters distal to the study area, possibly further north or west. Taken together, variations in Δ 14C values, terrigenous fatty acid abundances, and alkenone-derived temperatures among the stations suggest that input of laterally advected OC is a prominent feature of POC dynamics on the NW Atlantic margin, and is spatially heterogeneous on a scale smaller than the distance between the stations (<150 km).

Temporal dynamics of seston: A recurring nighttime peak and seasonal shifts in composition in a stream ecosystem

We measured the baseflow concentration and composition of seston and suspended particulate organic carbon (POC) over a 1-yr period in White Clay Creek, a third-order stream in the southeastern Pennsylvania Piedmont, to assess temporal variability in seston concentration and quality at seasonal and diel timescales. Each month, we sampled stream water under baseflow conditions every 1.5 h over a 24-h period and measured seston and POC concentrations, carbon composition, pigment content, and 13C isotopic ratios. Seston and POC concentrations exhibited a strong diel pattern; nighttime concentrations exceeded daytime concentrations by 80% and 43%, respectively. Suspended chlorophyll a concentrations did not exhibit a diel pattern. We attribute the diel pattern of seston concentration to bioturbation by the nocturnal stream community, including crayfish, amphibians, eels, and macroinvertebrates. Seasonally, carbon content of seston increased from 9% throughout most of the year to 15% during November, December, and March, while seston d13C was depleted in the late fall and enriched in early spring months relative to the rest of the year. Chlorophyll a and pheophytin a concentrations in seston peaked during the early spring. Seasonal patterns in seston and POC composition reflect cycles of autumnal leaf litter inputs and vernal algal production. Bioturbation and shifts in organic carbon inputs mediate changes in POC quality and fluxes, which affect the bioavailability of POC and ultimately influence rates of heterotrophic respiration. Particulate organic carbon (POC) provides energy for microorganisms and macroinvertebrates in headwater streams and, when transported in the suspended load (seston), supports heterotrophic metabolism in downstream reaches and rivers (Wipfli and Gregovich 2002; Mayorga et al. 2005). POC transport represents a longitudinal linkage between upstream autochthonous and allochthonous production and downstream ecosystems, where the magnitude of connection is controlled by the quality, quantity, and timing of POC delivery (Mayorga et al. 2005).

Seamounts and organic matter—Is there an effect? The case of Sedlo and Seine seamounts, Part 2. Composition of suspended particulate organic matter

Abstract The suspended particulate organic matter (sPOM) around two isolated NE Atlantic seamounts, Seine (33°46′N 14°21′W; summit at ∼170 m) and Sedlo (40°19′N 26°40′W; summit at ∼780 m), was studied over a period of 2 years during four 2–4-week oceanographic surveys. Elemental (C and N), chlorophyll a and lipid biomarker concentrations and N stable isotopic values were variable close to the surface (40–90 m), although some chlorophyll a enrichment above the summits was discerned sporadically. Results from near-surface waters showed a generally “fresh”, mainly phytoplankton signature in sPOM with some seasonality, which was more pronounced around Sedlo. sPOM concentrations and composition changed with depth, apparently controlled by seasonality and proximity to the seamounts. A few metres above the Seine summit, the suspended particulate organic carbon (sPOC) concentrations and labile polyunsaturated fatty acids (% of lipids) were higher than elsewhere at similar depths (∼200 m) in summer 2004. In the same season at Sedlo, polyunsaturated fatty acids were also relatively more abundant (up to 43% of total lipids) around the topographic feature throughout the water column, indicating supply of more labile sPOM, perhaps by advection, downwelling or passive sinking of locally produced phytoplankton and/or in situ production. The high-quality sPOM that seems to be present around the seamounts could provide an important food source to the biological community.

Effect of temperature and phytoplankton concentration of Partitioned Aquaculture System water on freshwater mussel filtration

AbstractThe freshwater mussel Elliptio complanata wasprovided green algal-dominated water from a Parti-tioned Aquaculture System (PAS) over a range ofwater temperatures (6.1^32.41C) and suspendedparticulate organic carbon (POC) concentrations(o1^32.2mgCL 1 ) to determine ¢ltration rates asmgPOCkg 1 wet tissue weighth . The lowest ¢l-tration rates were observed at lowest temperaturesand POC concentrations while thehighest rates wereat intermediate temperatures and the highest POClevels. The predicted ¢ltration rate (PFR) in responseto water temperature and POC concentrations wasas follows: lnPFR51.4352 10.1192 POC 10.1399T 0.0001 T 3 . Within the experimental conditions,PFRs at any POC concentration increased withincreased water temperature to a peak at 221Candthen decreased. The maximum PFR occurredat 22 1Cand32mgCL 1 and the minimum PFRat 7 1Cand1mgCL 1 . A model to describe themussel ¢ltration rate responses to PAS waterconditions involves both water temperature and POCconcentration.Keywords: ¢ltration rate, freshwater mussel, PAS,culturesystemIntroductionA Partitioned Aquaculture System (PAS) separates aculture pond into four distinct components (paddle-wheels, algal basin, ¢lter-feeder area and culturespeciesarea)linkedbyahomogeneouswatervelocity¢eld (Brune, Schwartz, Eversole, Collier & Schwedler2004). Paddlewheels provide watercurrent, nutrientmixing,uniformsunlightexposuretophytoplanktonandcontinuous£owoverthealgalbasin,¢lterfeederand cultured species areas. Phytoplankton inthe al-galbasin(95%ofthePASarea)useinorganic¢shme-tabolic wastes (nutrients) to sustain high primaryproductivity levels. Feeding rates and ¢sh carryingcapacityof thePASisaboutthreeto ¢vetimesthatofconventional cat¢sh culture ponds because of sus-tained high phytoplanktonproductivity (Brune etal.2004).Filter-feedingorganisms,byharvestingphyto-plankton, reduce cell age and stabilize a standingcrop of faster-growing phytoplankton cells at re-duced respiration rates and increased oxygen pro-ductionper watervolume(Bruneetal.2004).Someofthetermsusedinliteraturetoexpress¢ltra-tion activity of suspension feeders include clearancerate, pumping rate, ¢ltration rate, ingestion rate, up-take rate, and retention rate (see, e.g. Foster-Smith1975; Walz 1978, Winter 1978; Riisgrd 2001a). Theterm ¢ltration rate inthis studyand inthis paper re-fers strictly to the amount of suspended phytoplank-ton(seston)removedfromthewatercolumnperunittimeandincludesboththose¢lteredparticlesconso-lidated in pseudofaeces and those consumed, and isidentical to the terms uptake rate and retention rateof Foster-Smith (1975) andWalz (1978).The role of a¢lterfeederinstabilizingalgalstandingcropbiomassin PAS water is more appropriately estimated usingthis de¢nition of ¢ltration rate than measures esti-matingtheamountofwater¢lteredoringestionrate.

The significance of side‐arm connectivity for carbon dynamics of the River Danube, Austria

Summary1. Side‐arms connected to the main stem of the river are key areas for biogeochemical cycling in fluvial landscapes, exhibiting high rates of carbon processing.2. This work focused on quantifying autochthonous and allochthonous carbon pools and, thereby, on comparing transport and transformation processes in a restored side‐arm system of the River Danube (Regelsbrunn). We established a carbon budget and quantified carbon processing from March to September 2003. In addition, data from previous studies during 1997 to 1999 were assessed.3. Gross primary production (GPP) and community respiration were estimated by diel oxygen time curves and an oxygen mass balance. Plankton primary production was determined to estimate its contribution to GPP under different hydrological conditions.4. Based on the degree of connectivity, three hydrological phases were differentiated. Most of the organic matter, dominated by allochthonous carbon, was transported in the main channel and through the side‐arm during floods, while at intermediate and low flows (and thus connectivity), transformation processes became more important and autochthonous carbon dominated the carbon pool. The side‐arm system functioned as a sink for particulate matter [total suspended solids and particulate organic carbon (POC)] and a source of dissolved organic carbon (DOC) and chlorophyll‐a.5. Autochthonous primary production of 4.2 t C day−1 in the side‐arm was equivalent to about 20% of the allochthonous inputs of 20 t C day−1 (POC and DOC) entering the area at mean flow (1% of the discharge of the main channel). Pelagic photosynthesis was generally high at mean flow (1.3–3.8 g C m−2 day−1), and contributed up to 90% of system productivity. During long stagnant periods at low discharge, the side‐arm was controlled by biological processes and a shift from planktonic to benthic activity occurred (benthic primary production of 0.4–14 g C m−2 day−1).6. The transformation of the organic matter that passes through the side‐arm under different hydrological conditions, points to the importance of these subsystems in contributing autochthonous carbon to the food web of the main channel.

동중국해 북부해역에서 여름동안 영양염, 엽록소, 부유물질의 분포 특성 및 연간 변화

In order to find out the annual variations in the marine ecosystem of the East China Sea, temperature, salinity, nutrients, chlorophyll-a, suspended solids, and suspended particulate organic carbon were extensively investigated in the northern East China Sea during the Summer of 2003 and 2006. During the Summer of 2003, the northern East China Sea was not significantly affected by the input of fresh waters from the Changjiang River. During the Summer of 2006, however, fresh waters of the Changjiang River intruded into the western part of the study area where temperature, nitrate, and phosphate in the surface waters were higher than in the other areas, and salinity, silicate, and suspended solids in the surface waters were lower. As a result of the increase in nitrate and phosphate concentrations, concentrations of chlorophyll-a and suspended particulate organic carbon increased in the western part compared with the other areas. However, the depth-integrated chlorophyll-a concentrations measured during the Summer of 2003 were rather similar to those during the Summer of 2006, and not considerably different from those measured in the East China sea during the Summer of 1994 and 1998. Therefore, the depth-integrated chlorophyll-a concentrations have not significantly changed in the East China Sea over the last 12 years. The lower concentrations of silicate and suspended solids in the western part may be related to construction of the Three-Gorges Dam since the concentrations of silicate and suspended solids in fresh waters of the Changjiang River have significantly decreased after construction of the Three-Gorges Dam in June 2003.