Seasonal and spatial distribution of dissolved and particulate organic carbon and bacteria in the bank of an impounding reservoir on the Enns River, Austria

1. Interstitial bacterial abundance, production and ectoenzyme activity were investigated over an annual cycle in an Austrian river when infiltration of oligotrophic river water into a river-bank was artificially enhanced. These microbial parameters were related to porewater chemistry and the concentration of particulate (POC) and dissolved organic carbon (DOC).
2. Porewater chemistry reflected the hydrodynamic mixing of infiltrating river water with riparian groundwater. Seasonal fluctuations in the microbial parameters resulted mainly from changes in temperature and organic matter supply. Seasonal change in porewater chemistry in the river-bank was detectable laterally only within the first metre of the sediment and decreased rapidly with increasing distance from the sediment–water interface.
3. The DOC concentration decreased only slightly during lateral transport through the aquifer, while total organic carbon (TOC) concentration as well as abundance and activity of interstitial bacteria were reduced by up to one order of magnitude within the top metre of the sediment. Retention of incoming particulate matter structured the lateral distribution pattern of TOC concentration. The POC and not the DOC pool was the main source of carbon for interstitial bacteria and, therefore, the quality of POC determines the distribution of microbial metabolism within the riparian zone.     

Abundance and production of bacteria, and relationship to phytoplankton production, in a large tropical lake (Lake Tanganyika)

1. Abundance and bacterial production (BP) of heterotrophic bacteria (HBact) were measured in the north and south basins of Lake Tanganyika, East Africa, during seasonal sampling series between 2002 and 2007. The major objective of the study was to assess whether BP can supplement phytoplankton particulate primary production (particulate PP) in the pelagic waters, and whether BP and particulate PP are related in this large lake. HBact were enumerated in the 0–100 m surface layer by epifluorescence microscopy and flow cytometry; BP was quantified using ³H‐thymidine incorporation, usually in three mixolimnion layers (0–40, 40–60 and 60–100 m). 2. Flow cytometry allowed three subpopulations to be distinguished: low nucleic acid content bacteria (LNA), high nucleic acid content bacteria (HNA) and Synechococcus‐like picocyanobacteria (PCya). The proportion of HNA was on average 67% of total bacterial abundance, and tended to increase with depth. HBact abundance was between 1.2 × 10⁵ and 4.8 × 10⁶ cells mL⁻¹, and was maximal in the 0–40 m layer (i.e. roughly, the euphotic layer). Using a single conversion factor of 15 fg C cell⁻¹, estimated from biovolume measurements, average HBact biomass (integrated over a 100‐m water column depth) was 1.89 ± 1.05 g C m⁻². 3. Significant differences in BP appeared between seasons, especially in the south basin. The range of BP integrated over the 0–100 m layer was 93–735 mg C m⁻² day⁻¹, and overlapped with the range of particulate PP (150–1687 mg C m⁻² day⁻¹) measured in the same period of time at the same sites. 4. Depth‐integrated BP was significantly correlated to particulate PP and chlorophyll‐a, and BP in the euphotic layer was on average 25% of PP. 5. These results suggest that HBact contribute substantially to the particulate organic carbon available to consumers in Lake Tanganyika, and that BP may be sustained by phytoplankton‐derived organic carbon in the pelagic waters.     

Ectoenzymatic activity and glucose heterotrophic metabolism in a shallow estuary (Ria de Aveiro,Portugal): influence of bed sediments and salt marshes

Bacterioplankton abundance and activity were studied in the estuarine system of Ria de Aveiro (Portugal) to test if tidal resuspension of sediments and transport of particles from the salt marshes may act as factors of variability of bacterial communities. The total and attached cell abundance, ectoenzymatic activity and the heterotrophic metabolism of glucose, as well as seston, chlorophyll a and particulate organic carbon (POC) were monitored during four 10-h periods along the tidal cycle at four sampling sites across a transect. The variation of particulate materials (seston, POC and chlorophyll a ) along the transect was not significantly correlated with either distance to the margin or distance to the sediment surface. Nevertheless, proximity to the salt marsh or to the bottom sediment surface favoured glucose incorporation and aminopeptidase activity. A multiple stepwise linear regression analysis using temperature, salinity, seston, POC, chlorophyll a , distance to sediment surface and distance to the margin as independent variables explained 66.5% of the variability of the fraction of particle-attached bacteria and only a very small proportion (12–43%) of the observed variability of total bacterial abundance, ectoenzymatic activity and glucose utilization. The spatial patterns of variation of the concentration of particulate material (seston, POC and chlorophyll a) do not clearly indicate the occurrence of sediment resuspension and runoff from the margins. This, together with the poor contribution of these parameters to the transversal and tidal variability of bacterial activity, dismisses the importance of inputs of suspended material across the sediment/water interface and from neighbouring salt marshes in the control of bacterial density and activity.     

Distribution of bacteria and chlorophyll A at a nearshore station in Lake Ontario

Analysis of weekly water samples taken at three depths from a nearshore station in Lake Ontario indicated significant (P > 0.05) relationships between particulate organic carbon (POC), total particulate nitrogen (TPN), chlorophyll a and total bacteria. Application of a stepwise multiple regression indicated that particulate organic carbon (POC) and temperature were the only two measured parameters that had significant effect on total bacterial numbers.     

Biochemical composition of particulate organic matter and bacterial dynamics at the sediment–water interface in a Mediterranean seagrass system

The seagrass Posidonia oceanica is the most productive system of theMediterranean Sea. In order to gather information on the temporal andspatial variability of the suspended particulate matter in relation tobacterial dynamics, water samples were collected at 10 cm above thesediments over a period of 13 months in the Prelo Bay (Ligurian Sea, NWMediterranean). Measurements of seston concentration, as well as theelemental (POC and PON) and biochemical composition (lipids, proteins,carbohydrates and nucleic acids) of particulate matter were carried out toassess the origin, composition and bacterial contribution to the foodpotentially available in the seagrass system to consumers. Lipids andproteins were the main biochemical classes of organic compounds, followed bycarbohydrates. Despite the highly refractory composition of the seagrassleaves, particulate organic matter was mostly composed of labile compounds(69.9% of POC). POM temporal patterns were controlled by currentspeed at the sediment–water interface that resuspended only smallparticles largely colonised by bacteria after an intensive process offractionation and aging. In the seagrass system, the POM appears to bedominated by bacteria (density ranging from 0.7 to 2.5×10⁹ cells l^™1, representing more than48.3% of POC and 68.7% of the biopolymeric carbon, as the sumof lipid, protein and carbohydrate carbon). This feature was characteristicof the seagrass system since much lower bacterial densities were foundoutside the Posidonia meadow. Bacteria were negatively correlated with theconcentration of nitrite and nitrate suggesting a selective utilisation ofinorganic nutrients to support their growth. This revised version was published online in July 2006 with corrections to the Cover Date.     

The sub-ice fauna of the Laptev Sea and the adjacent Arctic Ocean in summer 1995

The sub-ice habitat and fauna in the Laptev Sea and the adjacent Arctic Ocean were investigated during the “Polarstern” cruise ARK XI/1 in summer 1995. At the ice-water interface a thin thermo- and halocline developed at many stations due to melting processes. In the lower centi- to decimetres of the ice, an accumulation of organic matter was found (particulate organic carbon: 1.9 mg l⁻¹, chl a: 3.3 μg l⁻¹) that may have provided a food source for the fauna. The water layer directly beneath the ice was inhabited by high numbers of various nauplii (130–23911 ind. m⁻³), and two ecological groups, the pelagic sub-ice fauna that originates from the surface water plankton, and the sympagic sub-ice fauna that migrates into this boundary layer from the ice interior. The pelagic fauna dominated the sub-ice community both in terms of species number and abundance. Both groups mainly comprised small copepods (e.g. Oithona similis, Oncaea borealis, Pseudocalanus spp., Halectinosoma spp., Tisbe spp.), but foraminifers and pteropods, for example, also occurred regularly. Diversity was generally low. Factors influencing the composition and abundance of the sub-ice fauna were most likely water depth, salinity and sea-ice sediments. Accepted: 6 July 1998     

Protist abundance and carbon concentration during a Phaeocystis-dominated bloom at an Antarctic coastal site

Summary Changes in the concentrations of bacteria, phytoplankton, protozoa, dissolved organic carbon (DOC), particulate organic carbon (POC), particulate carbohydrate (PCHO) and particulate organic nitrogen (PON) were followed throughout the summer at an Antarctic coastal site. The colonial prymnesiophyte Phaeocystis pouchetii was the first major phytoplankton species to bloom, reaching concentrations of 6 × 10⁷ cells · 1^–1 and remained numerically dominant for most of the summer. During the P. pouchetii bloom the concentration of most other autotrophs did not increase. Microheterotroph abundance peaked during or immediately after the Phaeocystis bloom. Their peak coincided with very high concentrations of organic carbon, particularly DOC which exceeded 100 mg · 1^–1, and low bacterial abundance. Maximum bacterial abundance was reached after the decline in microheterotroph numbers. Bacterial utilization of carbon substrates and microheterotroph grazing of bacteria and uptake of DOC may form an important link to higher trophic levels during Antarctic Phaeocystis blooms.     

Seasonal variation of nutrients,organic carbon,ATP, and microbial standing crops in a vertical profile of Pyramid Lake,Nevada

Previous studies of Pyramid Lake, Nevada, led to the hypothesis that detritus could be an important food source for zooplankton because abundance of palatable algal species did not seem to be enough to support the zooplankton community throughout the year. Furthermore, a large portion of the annual primary productivity was attributed to a nonpalatable blue-green alga, Nodularia spumigena. We felt this alga became important to the Pyramid Lake aquatic community upon death, as edible detritus and a source of new nitrogen. Changes in pelagic detritus concentrations and microbial standing crops were monitored to determine the availability of these potential foods. Epilimnetic particulate organic carbon (POC) was primarily living phytoplankton. During holomixis and following spring primary production, hypolimnetic POC was 60–97% detrital, but these profundal POC concentrations were low (ca 650 µg l^-1). Detritus-bacteria aggregates were observed only following the September cyanophyte bloom. Although pelagic detritus availability for zooplankton was low, bacterial populations were sufficient to be at least a supplemental food source. Bacteria numbers ranged from 0.50 10⁶ to 24.7 10⁶ ml^-1 and increased in response to photosynthetic peaks. Microbial diversity, contribution to POC, and particle association were notable after July. The percentage of living carbon (assessed with ATP measurements) attributable to bacteria was highest in late summer and fall hypolimnetic samples. Patterns of change in organic phosphorus and nitrogen, the presence of a nitrogen-fixing cyanophyte, the N:P ratio, and results of other research demonstrated that non-nitrogen-fixing algae of Pyramid Lake are limited by inorganic nitrogen. The importance of N. spumigena to the aquatic community appeared to be as a source of new nitrogen, rather than as a forage; its mineralization is critical for the growth of palatable diatoms and green algae following winter mixing.     

Production and retention of biogenic matter in the southeast Beaufort Sea during 2003�C2004: insights from annual vertical particle fluxes of organic carbon and biogenic silica

Regional variability in the annual fluxes of particulate organic carbon (POC) and biogenic silica (Si) at the periphery of the Mackenzie Shelf (Beaufort Sea) was investigated using eight long-term sediment traps moored at ~100-m depth. Relatively high autochthonous POC and Si fluxes were recorded in the Mackenzie Trough (4.1 and 8.9 g m⁻² year⁻¹ respectively) and off Cape Bathurst (6.6 and 79 g m⁻² year⁻¹), two areas where upwelling events are frequently observed. Diatomaceous new production was minimum on the mid-slope of the Mackenzie Shelf (2.8 g C m⁻² year⁻¹), moderate in the Mackenzie Trough (14.5 g C m⁻² year⁻¹), and highest off Cape Bathurst (128.7 g C m⁻² year⁻¹). High annual autochthonous POC flux corresponded to high diatom production. Among sites, the vertical attenuation of the POC flux increased with diatomaceous new production. Hence, the retention of autochthonous POC in the surface layer (<100 m) was highest (95%) at the highly productive site off Cape Bathurst, intermediate (72%) in the moderately productive Mackenzie Trough, and low (4%) at the unproductive mid-slope of the shelf. Our results indicate that, on Arctic shelves, upwelling and the production of diatoms increase the fraction of the POC which is retained in the surface layer and diverted to the pelagic food web. In the relatively unproductive waters of the Arctic Ocean, biological hot spots such as the one identified off Cape Bathurst where the food web promotes retention rather than vertical export could be disproportionately important as feeding grounds for higher trophic levels.     

Bacterial abundance and production in river sediments as related to the biochemical composition of particulate organic matter (POM)

The major proportion of heterotrophic activity in running waters islocalized on the solid surfaces of sediments in the benthic and hyporheic zoneand is dominated by microorganisms. However, this assertion is based on thestudies of small streams, and little is known about the microbial metabolism oforganic matter in river ecosystems. We therefore explored the relationshipsbetween bacterial abundance and production and the gradients of organic matterquality and quantity in sediments of a sixth-order lowland river (Spree,Germany). We found vertical gradients of detrital variables (particulateorganicmatter (POM), particulate organic carbon (POC), nitrogen (PN), and protein) andof bacterial variables (abundance, production, turnover time, and proportion ofbacterial carbon in total POC) in two different sediment types. These gradientswere steeper in stratified sediments than in the shifting sediments. Detritalvariables correlated strongly with bacterial abundance and production. The bestcorrelation was found for detrital variables indicating substrate quantity andquality (r_S = 0.90 for PN with abundance). Although bacterialbiomasscomprised only 0.7% of the POC (1.9% of PN, 3.4% of the protein) in sediments,the turnover of sedimentary organic carbon was fast (median = 62d), especially in the shifting sediments. Our findings demonstratethat sediment dynamics significantly foster organic carbon metabolism in riversystems. Thus, these sediments, which are typical for lowland rivers, stronglyinfluence the metabolism of the whole ecosystem.     

Long-term trends of epilimnetic and hypolimnetic bacteria and organic carbon in a deep holo-oligomictic lake

We analysed the long-term dynamics (1980–2007) of hypolimnetic and epilimnetic bacterial abundances and organic carbon concentrations, both dissolved (DOC) and particulate (POC), in the deep holo-oligomictic Lake Maggiore, included in the Southern Alpine Lakes Long-Term Ecological Research (LTER) site. During the 28 years of investigation, bacterial abundance and POC concentrations did not decrease with declining phosphorus concentrations, while DOC concentrations showed a pronounced decrease in the epi- and hypolimnion. We used the annual mean total lake heat content and total annual precipitation as climate-related variables, and in-lake total phosphorus as a proxy for trophic state. The model (forward stepwise regression, FSR) showed that reduced anthropogenic pressure was more significant than climate change in driving the trend in DOC concentrations. Bacterial dynamics in the hypolimnion mirrored the fluctuations observed in the epilimnion, but average cell abundance was three times lower. The FSR model indicates that bacterial number variability was dependent on POC in the epilimnion and DOC in the hypolimnion. In the hypolimnion, cell biovolumes for rod and coccal morphotypes were significantly larger than in the epilimnion.     

Distribution and characterization of dissolved and particulate organic matter in Antarctic pack ice

Distribution and composition of organic matter were investigated in Antarctic pack ice in early spring and summer. Accumulation of organic compounds was observed with dissolved organic carbon (DOC) and particulate organic carbon (POC) reaching 717 and 470 μM C, respectively and transparent exopolymeric particles (TEP) up to 3,071 μg Xanthan gum equivalent l⁻¹. POC and TEP seemed to be influenced mainly by algae. Particulate saccharides accounted for 0.2–24.1% (mean, 7.8%) of POC. Dissolved total saccharides represented 0.4–29.6% (mean, 9.7%) of DOC, while dissolved free amino acids (DFAA) accounted for only 1% of DOC. Concentrations of TEP were positively correlated with those of saccharides. Monosaccharides (d-MCHO) dominated during winter–early spring, whereas dissolved polysaccharides did in spring–summer. DFAA were strongly correlated with d-MCHO, suggesting a similar pathway of production. The accumulation of monomers in winter is thought to result from limitation of bacterial activities rather than from the nature of the substrates.     

Seasonal abundance and feeding patterns of copepods Temora longicornis, Centropages hamatus and Acartia spp. in the White Sea (66��N)

We have studied the seasonal dynamics of abundance and feeding characteristics of three species of calanoid copepods (Acartia spp., Centropages hamatus and Temora longicornis) in the White Sea from the surface water layer (0–10 m), in order to assess their role in the pelagic food web and to determine the major factors governing their population dynamics during the productive season. These species dominated in the upper water layer (0–10 m) from June through September, producing up to 3 generations per year. Data on the food spectra revealed all species to be omnivorous; but some inter- and intraspecific differences were observed. Generally, copepods consumed diatoms, dinoflagellates and microzooplankton. The omnivory index ‘UC’ (i.e., fatty acid unsaturation coefficient) varied from 0.2 to 0.6, which implied ingestion of phytoplankton. The different degree of selectivity on the same food items by the studied species was observed, and therefore, successful surviving strategy with minimal overlapping could be assumed. In total, the populations of the three studied copepod species grazed up to 2.15 g C m⁻² day⁻¹ and released up to 0.68 g C m⁻² day⁻¹ in faecal pellets. They consumed up to 50% of particulate organic carbon, or up to 85% of phytoplankton standing stock (in terms of Chl. a), and thus played a significant role in the transformation of particulate organic matter. Seasonal changes in abundance of the studied species depended mostly on water temperature in the early summer, but were also affected by food availability (Chl. a concentration) during the productive season.     

Estimates of particulate organic carbon flowing from the pelagic environment to the benthos through sponge assemblages

Despite the importance of trophic interactions between organisms, and the relationship between primary production and benthic diversity, there have been few studies that have quantified the carbon flow from pelagic to benthic environments as a result of the assemblage level activity of suspension-feeding organisms. In this study, we examine the feeding activity of seven common sponge species from the Taputeranga marine reserve on the south coast of Wellington in New Zealand. We analysed the diet composition, feeding efficiency, pumping rates, and the number of food particles (specifically picoplanktonic prokaryotic cells) retained by sponges. We used this information, combined with abundance estimates of the sponges and estimations of the total amount of food available to sponges in a known volume of water (89,821 m(3)), to estimate: (1) particulate organic carbon (POC) fluxes through sponges as a result of their suspension-feeding activities on picoplankton; and (2) the proportion of the available POC from picoplankton that sponges consume. The most POC acquired by the sponges was from non-photosynthetic bacterial cells (ranging from 0.09 to 4.69 g C d(-1) with varying sponge percentage cover from 0.5 to 5%), followed by Prochlorococcus (0.07 to 3.47 g C d(-1)) and then Synechococcus (0.05 to 2.34 g C d(-1)) cells. Depending on sponge abundance, the amount of POC that sponges consumed as a proportion of the total POC available was 0.2-12.1% for Bac, 0.4-21.3% for Prochlo, and 0.3-15.8% for Synecho. The flux of POC for the whole sponge assemblage, based on the consumption of prokaryotic picoplankton, ranged from 0.07-3.50 g C m(2) d(-1). This study is the first to estimate the contribution of a sponge assemblage (rather than focusing on individual sponge species) to POC flow from three groups of picoplankton in a temperate rocky reef through the feeding activity of sponges and demonstrates the importance of sponges to energy flow in rocky reef environments.     

Relative importance of biotic and abiotic factors affecting bacterial abundance in Lake Biwa: an empirical analysis

To determine the relative importance of factors affecting bacterial abundance in Lake Biwa, correlation and multiple regression analyses were performed with relevant biotic and abiotic variables. Data used in the analyses were collected weekly from April 1997 to June 1998 at a pelagic site in the north basin. The bacterial abundance ranged from 1 to 7 × 10⁶ cells ml⁻¹, and its spatio-temporal pattern was virtually identical to that in previous studies conducted 12–15 years ago. In the surface layer (0–12.5 m), bacterial abundance was significantly correlated with water temperature and with protozoan and metazoan grazers, but not with chlorophyll a and nutrient concentrations. The results suggest that loss factors rather than growth factors are more important in determining bacterial abundance in this lake. However, grazing effects on bacterial abundance differed among zooplankton. Bacterial abundance correlated negatively with phagotrophic nanoflagellates (PNF) and Daphnia, but positively with Eodiaptomus. Thus, PNF and Daphnia act to reduce the bacterial abundance, while Eodiaptomus acts to stimulate. In contrast, these biotic factors did not explain changes in bacterial abundance in the middle (12.5–25 m) and deep (>25 m) layers. Instead, the bacterial abundance in the deep layer was highly correlated with vertical mixing regimes, suggesting that bacterial abundance was directly or indirectly affected by abiotic factors. These results indicate that bacterial abundance in Lake Biwa was regulated by different factors at different depths. Received: February 8, 2000 / Accepted: August 29, 2000     

Enzymatic Activities and Prokaryotic Abundance in Relation to Organic Matter along a West–East Mediterranean Transect (TRANSMED Cruise)

The distribution of extracellular enzymatic activities (EEA) [leucine aminopeptidase (LAP), ?-glucosidase (GLU), alkaline phosphatase (AP)], as well as that of prokaryotic abundance (PA) and biomass (PB), dissolved organic carbon (DOC), particulate organic carbon and particulate total nitrogen (POC, PTN), was determined in the epi-, meso-, and bathypelagic waters of the Mediterranean Sea along a West-East transect and at one Atlantic station located outside the Strait of Gibraltar. This study represents a synoptical evaluation of the microbial metabolism during early summer. Decreasing trends with depth were observed for most of the parameters (PA, PB, AP, DOC, POC, PTN). Significant differences between the western and eastern basins of the Mediterranean Sea were found, displaying higher rates of LAP and GLU and lower C/N ratios more in the eastern than in the western areas. Conversely, in the epipelagic layer, PA and PB were found to be higher in the western than in the eastern basins. PB was significantly related to DOC concentration (all data, n = 145, r = 0.53, P < 0.01), while significant correlations of EEA with POC and PTN were found in the epipelagic layer, indicating an active response of microbial metabolism to organic substrates. Specific enzyme activities normalized to cell abundance pointed out high values of LAP and GLU in the bathypelagic layer, especially in the eastern basin, while cell-specific AP was high in the epi- and bathypelagic zone of the eastern basin indicating a rapid regeneration of inorganic P for both prokaryotes and phytoplankton needs. Low activity and abundance characterized the Atlantic station, while opposite trends of these parameters were observed along the Mediterranean transect, showing the uncoupling between abundance and activity data. In the east Mediterranean Sea, decomposition processes increased probably in response to mesoscale structures which lead to organic matter downwelling.     

Organic carbon dynamics in two regulated rivers in northwestern Montana,USA

We studied the transport of particulate organic carbon (POC) and dissolved organic carbon (DOC) in two regulated rivers during minimum and increasing discharges. Mean annual concentrations of total POC, measured monthly during conditions of minimum discharge from the dams, were twice as high at a station below a dam with a selective withdrawal system on the Kootenai River (KR, 0.15 mg 1^–1), as at station below a dam with hypolimnetic water releases on the Flathead River (FR, 0.07 mg 1^–1). Annual mean concentrations of DOC were similar below both dams (1.62 mg 1^–1 FR; 1.71 KR). The percentage of POC in four size fractions differed in regulated and unregulated reaches of each river system; the smallest size fraction (0.45–10 smm) constituted a larger percentage of the total POC at the stations below the dams (50–93%), because POC in large size classes had settled out in the reservoir. The three largest size fractions (10–1000 µm) comprised a larger percentage of the total POC when samples were taken during conditions of full discharge from the dam. We measured large increases in all size classes of POC in samples collected during increasing discharges in a regulated reach, reflecting the component of sloughed periphyton and resuspended organic matter that were added during periods of hydropower generation at the dam. Seston (355 µm to 1 cm) collected in nets increased dramatically during increasing flows; concentrations of particulate organic matter (POM) in samples collected two and three hours after water levels began to rise were 572 and 1440 times higher than those collected during minimum discharge at the dam.     

Biomass of pelagic fungi in Baltic rivers

Concentrations of pelagic fungal biomass, determined as the content of ergosterol in particulate matter, were measured in 49 Baltic rivers during summer 1999. The ergosterol concentration varied 12-fold, from 12.6 to 152.5 ng l⁻¹ (average of 56.4 ng l⁻¹) and correlated positively with concentrations of dissolved organic matter and inorganic nutrients as well as with spectral DOM properties indicative of terrestrial sources. The fungal biomass was 12- to 100-fold lower than the biomass of pelagic bacteria, suggesting that fungi in the water column of the rivers probably were of minor importance in the riverine ecosystems at the sampling time. Handling editor: J. Padisak     

The composition of particulate organic matter and biomass in the Peruvian upwelling region during ICANE 1977 (Nov. 14 - Dec. 2)

This paper presents the results of plankton studies in the Peruvianupwelling region off Chimbote from November - December, 1977,during the Investigación Cooperativa de la Anchovetay su Ecosistema (ICANE). Primary productivity, respiratory ETSactivity, composition of particulate organic matter, and microplanktoncell numbers were determined. Phytoplankton growth, and bacterialand ciliate carbon-uptake rates were computed from cell counts. Inshore waters were dominated by diatoms and were more productivethan offshore waters which were dominated by dinoflagellatesand ciliates. Particulate primary production averaged 5.26 ±5.24 g C m^–2d^–1, and the POC standing stock was7.75 ± 2.74 g C m^–2 for the euphotic layer of 7shelf stations. On the shelf, microplankton respiration rateswere higher in plankton populations dominated by dinoflagellatesand ciliates (47% of particulate primary production per 24 h)than those in diatom dominated populations (11%, respectively).The diatom populations, which were dominated by Chaetocerosspecies, varied in their ecophysiological properties (assimilationnumbers, proportion of water soluble carbohydrate, and protein/nitrogenratios). The relationships between these variations and growthconditions were investigated. A 40 h time-series station revealedpatchiness which was superimposed on physiological changes ofthe plankters. Bacterial numbers of 2 x 10⁶ cells/ml were foundin the euphotic layer corresponding to approximately 17 µgC/l bacterial biomass (or 6% of the POC standing stock). Ciliatebiomass (Lohmanniella oviformis was the dominating species)ranging from 2 to 9% of the POC standing stock were found evenin diatom dominated populations. From a rough carbon balancefor the euphotic layer it was deduced that in diatom dominatedpopulations, 36–77% of particulate primary productionwas potentially available to adult anchoveta grazing.     

Biogeochemical properties of a tropical swamp forest ecosystem in southern Thailand

The distributions of organic matter in the tropical swamps in southern Thailand are reported. The concentrations of particulate and dissolved organic carbon (POC and DOC) in the Bang Nara River, which drains swamp forests and nearby paddy fields, were 2.9 ± 2.0 and 6.2 ± 1.3 mg C l⁻¹, respectively. Although the variation was large, DOC concentration in the Bang Nara River seemed to be higher than POC in November 1992 (DOC/POC ratio, 2.8 ± 2.2). River waters from the upland areas were characterized by low POC and DOC concentrations as compared with Bang Nara River water. The δ¹³C values of POC and river sediments were useful to distinguish between organic matter originating in upland and swamp areas. It is suggested that the distributions of organic matter and its isotopic composition reflect the difference in drainage characteristics between lowland swamp and upland areas. Isotopic analyses of plant leaves and soils revealed that the swamp forest ecosystems were characterized by low δ¹³C and low δ¹⁵N values, which suggested low efficiency of water use by plants and large contributions of atmospheric deposition of nitrogen, respectively. Although CO₂ recycling in the forest might be an important factor determining the δ¹³C values of understory plants, the main process in carbon metabolism of tropical swamp forests would be CO₂ exchange between the atmosphere and forest canopy. Received: May 1, 2001 / Accepted: September 28, 2001