The application of a laboratory apparatus for the study of nutrient fluxes between sediment and water

Sediments of the river Elbe estuary have been studied to assess their impact on the total nitrogen budget of the estuary. A new laboratory incubation apparatus was used to provide a means of regulating important parameters such as temperature and oxygen concentrations. With this apparatus sediment cores from a typical shallow water area with high organic carbon content were incubated under varying oxygen concentrations in the overlying water. Measurements of ammonium, nitrite, nitrate and nitrous oxide in the water phase were carried out and the fluxes between sediment and water phase calculated. During aerobic conditions in the water phase overall nitrate fluxes between + 4 and –3.5 mmol Nm^–2d^–1 across the sediment/water interface were observed. Under anaerobic conditions the fluxes increased up to –10 mmol Nm^–2 d^–1. Nitrous oxide was formed within the sediment under both aerobic and anaerobic conditions. Fluxes into the water phase were highest when the oxygen concentrations in the water phase were low (between 0.1 and 0.6 mg l^–1).     

Influence of bed media characteristics on ammonia and nitrate removal in shallow horizontal subsurface flow constructed wetlands

Two bed media were tested (gravel and Filtralite) in shallow horizontal subsurface flow (HSSF) constructed wetlands in order to evaluate the removal of ammonia and nitrate for different types of wastewater (acetate-based and domestic wastewater) and different COD/N ratios. The use of Filtralite allowed both higher mass removal rates (1.1 g NH₄–N m⁻² d⁻¹ and 3 g NO₃–N m⁻² d⁻¹) and removal efficiencies (>62% for ammonia, 90–100% for nitrate), in less than 2 weeks, when compared to the ones observed with gravel. The COD/N ratio seems to have no significant influence on nitrate removal and the removal of both ammonia and nitrate seems to have involved not only the conventional pathways of nitrification–denitrification. The nitrogen loading rate of both ammonia (0.8–2.4 g NH₄–N m⁻² d⁻¹) and nitrate (0.6–3.2 g NO₃–N m⁻² d⁻¹) seem to have influenced the respective removal rates.     

Fluxes of gases in an ice related ecosystem in the north-western Weddell Sea

Summary During the European Polarstern Study (EPOS leg 1 and leg 2) measurements of temperature, salinity, inorganic nutrients, chlorophyll-a, oxygen and total inorganic carbon dioxide were performed from October to January 1988–1989 in north-south sections at 47–49 °E in the NW Weddell Sea from approximately 58 °S to 63 °S (Hempel 1989; Hempel et al. 1989). In order to explain parts of the obtained data, a time-dependent ecological model was constructed by Svansson (1991). He found that a moderate mixing with a constant diffusion coefficient from sea surface downwards resulted in good agreement between computed and measured chlorophyll. In this paper we introduce the gas fluxes, mainly oxygen but also carbon dioxide, into the model work. It turns out that air-sea fluxes are necessary to explain the vertical oxygen distribution. The annual development of chlorophyll, phosphate, oxygen and total inorganic carbon dioxide are computed. Hours of day-light, losses and the eddy diffusion coefficient are allowed to vary during the year with the condition that the mean total chlorophyll at 14 selected leg 1 stations was nearly double the magnitude of that of 18 selected leg 2 stations. This yields variations consistent with the observations. Different steady-state solutions after 91 days are also tested to show effects of one selected variation at a time, for example the eddy diffusion coefficient or the loss rate. The oxygen air-sea flux, of about 90 mmol m^–2 day^–1 in the time variable model computation, is compared to estimated fluxes by a gas transfer formula. The formula used gives a flux which is about 5 times smaller than the model flux. Some of the 91 days solutions give results of fluxes which are less than 90 mmol m^–2 day^–1 but still higher than the transfer formula result. Fluxes of total inorganic carbon dioxide in the model computation are always directed from air to sea.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Chlorophyll <Emphasis Type="Italic">a</Emphasis> as a measure of seasonal coupling between phytoplankton and the monsoon periods in the Gulf of Oman

We present data from a long time-series study to describe the factors that control phytoplankton population densities and biomass in the coastal waters of Oman. Surface temperature, salinity, nutrients, dissolved oxygen, chlorophyll a (Chl a), and phytoplankton and zooplankton abundance of sea water were measured as far as possible from February 2004 through February 2006, at two stations along the southern coast of the Gulf of Oman. The highest concentrations of Chl a (3 mg m⁻³) were recorded during the southwest monsoon (SWM) when upwelling is active along the coast of Oman. However, results from our study reveal that the timing and the amplitude of the seasonal peak of Chl a exhibited interannual variability, which might be attributed to interannual differences in the seasonal cycles of nutrients caused either by coastal upwelling or by cyclonic eddy activity. Monthly variability of SST and concentrations of dissolved nitrate, nitrite, phosphate, and silicate together explained about 90% of the seasonal changes of Chl a in the coastal ecosystem of the Gulf of Oman. Phytoplankton communities of the coastal waters of Oman were dominated by diatoms for most part of the year, but for a short period in summer, dinoflagellates were dominant.     

Benthic fluxes in San Francisco Bay

Measurements of benthic fluxes have been made on four occasions between February 1980 and February 1981 at a channel station and a shoal station in South San Francisco Bay, using in situ flux chambers. On each occasion replicate measurements of easily measured substances such as radon, oxygen, ammonia, and silica showed a variability (±1) of 30% or more over distances of a few meters to tens of meters, presumably due to spatial heterogeneity in the benthic community. Fluxes of radon were greater at the shoal station than at the channel station because of greater macrofaunal irrigation at the former, but showed little seasonal variability at either station. At both stations fluxes of oxygen, carbon dioxide, ammonia, and silica were largest following the spring bloom. Fluxes measured during different seasons ranged over factors of 2–3, 3, 4–5, and 3–10 (respectively), due to variations in phytoplankton productivity and temperature. Fluxes of oxygen and carbon dioxide were greater at the shoal station than at the channel station because the net phytoplankton productivity is greater there and the organic matter produced must be rapidly incorporated in the sediment column. Fluxes of silica were greater at the shoal station, probably because of the greater irrigation rates there. N + N (nitrate + nitrite) fluxes were variable in magnitude and in sign. Phosphate fluxes were too small to measure accurately. Alkalinity fluxes were similar at the two stations and are attributed primarily to carbonate dissolution at the shoal station and to sulfate reduction at the channel station. The estimated average fluxes into South Bay, based on results from these two stations over the course of a year, are (in mmol m^–2 d^–1): O₂ = –27 ± 6; TCO₂ = 23 ± 6; Alkalinity = 9 ± 2; N + N = –0.3 ± 0.5; NH₃ = 1.4 ± 0.2; PO₄ = 0.1 ± 0.4; Si = 5.6 ± 1.1. These fluxes are comparable in magnitude to those in other temperate estuaries with similar productivity, although the seasonal variability is smaller, probably because the annual temperature range in San Francisco Bay is smaller.Budgets constructed for South San Francisco Bay show that large fractions of the net annual productivity of carbon (about 90%) and silica (about 65%) are recycled by the benthos. Substantial rates of simultaneous nitrification and denitrification must occur in shoal areas, apparently resulting in conversion to N₂ of 55% of the particulate nitrogen reaching the sediments. In shoal areas, benthic fluxes can replace the water column standing stocks of ammonia in 2–6 days and silica in 17–34 days, indicating the importance of benthic fluxes in the maintenance of productivity.Pore water profiles of nutrients and Rn-222 show that macrofaunal irrigation is extremely important in transport of silica, ammonia, and alkalinity. Calculations of benthic fluxes from these profiles are less accurate, but yield results consistent with chamber measurements and indicate that most of the NH₃, SiO₂, and alkalinity fluxes are sustained by reactions occurring throughout the upper 20–40 cm of the sediment column. In contrast, O₂, CO₂, and N + N fluxes must be dominated by reactions occurring within the upper one cm of the sediment-water interface. While most data support the statements made above, a few flux measurements are contradictory and demonstrate the complexity of benthic exchange.     

Nitrification, denitrification, and nitrate ammonification in sediments of two coastal lagoons in Southern France

Summary Seasonal and diurnal variations in sediment-water fluxes of O₂, NO ₃ ^– , and NH ₄ ⁺ as well as rates of nitrification, denitrification, and nitrate ammonification were determined in two different coastal lagoons of southern France: The seagrass (Zostera noltii) dominated tidal Bassin d'Arcachon and the dystrophic Etang du Prévost. Overall, denitrification rates in both Bassin d'Arcachon (<0.4 mmol m^–2 d^–1) and Etang du Prévost (<1 mmol m^–2 d^–1) were low. This was mainly caused by a combination of low NO ₃ ^– concentrations in the water column and a low nitrification activity within the sediment. In both Bassin d'Arcachon and Etang du Prévost, rates of nitrate ammonification were quantitatively as important as denitrification.Denitrification played a minor role as a nitrogen sink in both systems. In the tidal influenced Bassin d'Arcachon, Z. noltii was quantitatively more important than denitrification as a nitrogen sink due to the high assimilation rates of the plants. Throughout the year, Z. noltii stabilized the mudflats of the bay by its well- developed root matrix and controlled the nitrogen cycle due to its high uptake rates. In contrast, the lack of rooted macrophytes, and dominance of floating macroalgae, made nitrogen cycling in Etang du Prévost more unstable and unpredictable. Inhibition of nitrification and denitrification during the dystrophic crisis in the summer time increased the inorganic nitrogen flux from the sediment to the water column and thus increased the degree of benthic-pelagic coupling within this bay. During winter, however, benthic microalgae colonizing the sediment surface changed the sediment in the lagoon from being a nitrogen source to the over lying water to being a sink due to their high assimilation rates. It is likely, however, that this assimilated nitrogen is liberated to the water column at the onset of summer thereby fueling the extensive growth of the floating macroalgae, Ulva sp. The combination of a high nitrogen coupling between sediment and water column, little water exchange and low denitrification rates resulted in an unstable system with fast growing algal species such as phytoplankton and floating algae.     

Nitrogen fluxes and budget seasonality in the Ria Vigo [2pt] (NW Iberian Peninsula)

Inorganic and organic nitrogen fluxes in the Ria Vigo have been quantified in order to recognise the contrasting nitrogen budget scenarios and understand the biogeochemical response to eutrophication events. According to the nitrogen biogeochemical pathways of the ria reservoir (photosynthesis, remineralization, denitrification, PON rain rate and sedimentation), three main seasonal behavioural trends are emphasised: (1) low inorganic nitrogen inputs and low organic nitrogen fluxes, (2) high inorganic nitrogen input and output, (3) high inorganic nitrogen input and high organic nitrogen output. The first scenario occurs in late spring and in summer during non-upwelling situations. The consumption of inorganic nitrogen by net photosynthesis is approximately 2 mol N s^–1 and the ria is oligotrophic (12 mgC m^–2 h^–1). The outgoing estuarine residual current transports phytoplanktonic material towards the mouth of the ria whereupon it sediments and is remineralized as it falls to the lower water layers and the incoming residual current. The regenerated nitrogen is reintroduced to the photic ria layer which leads to the greatest reduction in dissolved oxygen concentration (50% of saturation). Recycled nutrients play an important role in primary production during this oligotrophic state of the ria. Thus, approximately half of the inorganic nitrogen utilised by photosynthesis is ammonium. The majority of PON is deposited inside the ria (0.8 mmol N m^–2 d^–1) and the denitrification rate is 0.3 mmol N₂ m^–2 d^–1. The other two cases occur in winter and spring–summer with upwelling. In winter, estuarine circulation and freshwater contributions control the nitrogen cycle. The ria mainly exports nitrate (up to 14 mol N s^–1) and so there is fertilisation but no eutrophication. In spring and summer, the nitrogen cycle is controlled by upwelling circulation. The inorganic nitrogen consumption by net photosynthesis is high, 7–14 mmol N m^–2 d^–1, and the ria is a natural eutrophic system (70 mgC m^–2 h^–1). Accordingly, 90% of organic nitrogen is synthesised from nitrate and the upwelling-increased circulation exports 6.5 mol N s^–1 of organic nitrogen.     

The Balgzand (Dutch Wadden Sea) tidal flats as a source of soluble silicate

Summary The huge numbers of molluscs, worms and bacteria found in the sheltered tidal flats of the Dutch Wadden Sea, decompose large amounts of organic matter. In this process nutrients incorporated in the particulate organic matter are transferred to the dissolved state. The importance of this process for nutrient budgets was first demonstrated by POSTMA (1954) and later by various authors with emphasis on tidal watersheds and sheltered bays (see Neth. J. Sea Res., 8 (2/3). 1974).The nutrient budgets of the Balgzand tidal flats, as a typical example of a sheltered bay, have been studied during one tidal period by TIJSSEN and VAN BENNEKOM (1976) and recently for a longer period in a cooperative project by the Studiedienst Hoorn of Rijkswaterstaat (DE BOER, 1978) and the Netherlands Institute for Sea Research (MANUELS, 1978). A qualitative measure for the high intensity of mineralization are the high concentrations of nutrients in the water on the Balgzand, compared to those in the Marsdiep (Table I).Simple box models can be used to derive the intensity of nutrient production from the concentration differences in which also the water depth and the exchange velocity of the water with adjacent areas contribute. As a first approximation all mineralization is thought to be situated in the surface sediment (VAN BENNEKOM et al., 1974) and the characteristics parameter becomes the nutrient production per m² per day. For reactive silicate this parameter shows a pronounced seasonal cycle. In January, February and Marchin situ production is hardly detectable while in July and August 500 mg SiO₂ m^–2d^–1 is found. For comparison, weathering of soil by rain water gives 4–30 mg SiO₂.m^–2d^–1 with only slight seasonal variations. The difference is at least partially explained by assuming a different source: diatom frustules in the case of the Balgzand and silicate minerals in the case of normal weathering.The scarce data available indicate that the seasonal cycles of in situ production of phosphate, nitrate and ammonia on the Balgzand are less pronounced than for reactive silicate. The picture is further complicated because ammonia is always produced, but sometimes nitrate is consumed, apparently by denitrification.The nutrient ratios change during the year (Table II). Especially in summer the contribution of silicate is relatively large. This is in marked contrast with the nutrient ratios in the coastal sea water where during the summer the amount of silicate is relatively low. The nutrient ratios are probably an important factor in the seasonal and regional species composition of the phytoplankton.     

Denitrification in the water column of an intermittently anoxic fjord

Denitrification was studied in the water column in the Bunnefjord, inner part of the Oslofjord in southern Norway, using a ¹⁵N-technique (the isotope pairing method). The fjord is 150 m deep and during our surveys in September–December 1998 hydrogen sulphide was present in the deep water below 80 m. No significant denitrification was found in water samples from the surface layer (4 m depth), but high rates were observed within a deep density gradient between 62 and 78 m depth. Oxygen concentration within this layer was low (<21 mmol m^–3), and the concentration of NO₃ decreased from ca. 15 mmolm^–3 at 62 m depth to not detectable below 78 m. Pronounced peaks of NO₂ up to 4.4 mmol m^–3 were observed at 70–78 m depth. The maximum denitrification rate of 1.5 mmol N m^–3 d^–1 was observed at 70 m depth. Integrated for the whole layer, the denitrification rate was 13 mmol N m^–2 d^–1. A significant linear correlation was found between the denitrification rate and the ambient nitrate concentration which indicated that the rate was primarily controlled by the availability of nitrate in the O₂-poor water. Compared to rates reported for coastal water, denitrification in the water column in the Bunnefjord was high and the process appears to be a major sink of bioavailable nitrogen in the fjord.     

Oxygen consumption and ammonia accumulation in the hypolimnion of Walker Lake, Nevada

Walker Lake (area = 140 km², Z _mean = 19.3 m) is a large, terminal lake in western Nevada. As a result of anthropogenic desiccation, the lake has decreased in volume by 75% since the 1880s. The hypolimnion of the lake, now too small to meet the oxygen demand exerted by decaying matter, rapidly goes anoxic after thermal stratification. Field and laboratory studies were conducted to examine the feasibility of using oxygenation to avoid hypolimnetic anoxia and subsequent accumulation of ammonia in the hypolimnion, and to estimate the required DO capacity of an oxygenation system for the lake. The accumulation of inorganic nitrogen in water overlaying sediment was measured in laboratory chambers under various DO levels. Rates of ammonia accumulation ranged from 16.8 to 23.5 mg-N m^–2 d^–1 in chambers with 0, 2.5 and 4.8 mg L^–1 DO, and ammonia release was not significantly different between treatments. Beggiatoa sp. on the sediment surface of the moderately aerated chambers (2.5 and 4.8 mg L^–1 DO) indicated that oxygen penetration into sediment was minimal. In contrast, ammonia accumulation was reversed in chambers with 10 mg L^–1 DO, where oxygen penetration into sediment stimulated nitrification and denitrification. Ammonia accumulation in anoxic chambers (18.1 and 20.6 mg-N m^–2 d^–1) was similar to ammonia accumulation in the hypolimnion from July through September of 1998 (16.5 mg-N m^–2 d^–1). Areal hypolimnetic oxygen demand averaged 1.2 g O₂ m^–2 d^–1 for 1994–1996 and 1998. Sediment oxygen demand (SOD) determined in experimental chambers averaged approximately 0.14 g O₂ m^–2 d^–1. Continuous water currents at the sediment-water interface of 5–6 cm s^–1 resulted in a substantial increase in SOD (0.38 g O₂ m^–2 d^–1). The recommended oxygen delivery capacity of an oxygenation system, taking into account increased SOD due to mixing in the hypolimnion after system start-up, is 215 Mg d^–1. Experimental results suggest that the system should maintain high levels of DO at the sediment-water interface (10 mg L^–1) to insure adequate oxygen penetration into the sediments, and a subsequent inhibition of ammonia accumulation in the hypolimnion of the lake.     

Examining the relationship between bacteria and heterotrophic nanoflagellates in Funka Bay (Japan) using the size-fractionation method

The chemical and biological conditions, and the bacteria-heterotrophic nanoflagellate (HNF) relationship were investigated in the vicinity of Funka Bay, southwest of Hokkaido, Japan during early spring 1999. At the time of sampling, chlorophyll a concentration, bacteria, phycoerythrin rich-cyanobacteria, and HNF abundance were in the following ranges: 0.3–3.6 g l^–1, 2.5–5.6 × 10⁵ cells ml^–1, 0.6–1.2 × 10³ cells ml^–1, and 2.2–4.2 × 10³ cells ml^–1, respectively. Dissolved inorganic nitrogen, phosphate and silicate concentrations were in the ranges: 8.7–12.2 M, 0.9–2.0 M, and 21.6–25.5 M, respectively. Primary production ranged from 6.4 to 76.3 mg C m^–3 d^–1. Using water samples from regions of different productivity levels (in and outside bay), the bacteria - HNF relationship was uncoupled experimentally by the size-fractionation technique. Higher primary production (19.9 mg C m^–3 d^–1) in the bay supported higher bacterial growth rate (0.029 h^–1). However, outside the bay both primary production (6.4 mg C m^–3 d^–1) and bacterial growth rate (0.007 h^–1) were lower. The HNF growth rates and grazing rates were similar for both but by comparing both HNF grazing capacity and bacterial production, there was net decrease in bacterial abundance outside the bay and net increase inside the bay. The microbial parameters (rates and abundance) and the amount of carbon flow estimated through the phytoplankton – dissolved organic matter (DOM) – bacteria loop were different between the coastal station and the open ocean station. However HNF grazing and growth rates was similar for both stations.     

Effects of aluminum,iron, oxygen and nitrate additions on phosphorus release from the sediment of a Danish softwater lake

The effects of oxygen, aluminum, iron and nitrate additions on phosphate release from the sediment were evaluated in the softwater Lake Vedsted, Denmark, by a 34-day experiment with undisturbed sediment cores. Six treatments were applied: (1) Control - O₂ (0–20% saturation), (2) O₂ (100% saturation) (3) Al³⁺ – O₂, (4) Fe³⁺ + O₂, (5) Fe³⁺ – O₂, and (6) NO₃ ^– – O₂. Al₂(SO₄)₃*18 H₂O and FeCl₃*4H₂O were added in amounts that theoretically should immobilize the exchangeable P-pool in the top 5 cm of the sediment, while sodium nitrate concentrations were increased to 5 mg N l^–1. The four treatments with metals or NO₃ ^– reduced the P efflux from the sediment significantly as compared to the suboxic control treatment. Mean accumulated P-release rates for suboxic treatments with Al³⁺, Fe³⁺, and NO₃ ^– were: –0.27 mmol m^–2 (st. dev = 0.02 mmol m^–2, N = 5), 0.58 mmol m^–2 (st. dev = 0.30 mmol m^–2, N = 5) and 1.40 mmol m^–2 (st. dev = 0.14 mmol m^–2, N = 5), respectively. The oxic treatment with Fe³⁺ had a P efflux of 0.36 mmol m^–2 (st. dev = 0.08 mmol m^–2, N = 5). The two highest P-release rates were observed in the control treatment and the treatment with O₂ (14.50 mmol m^–2 (st. dev = 3.90 mmol m^–2, N = 5) and 2.31 mmol m^–2 (st. dev = 0.80 mmol m^–2, N = 5), respectively). In order to identify changes in the P and Fe binding sites in the sediment as caused by the treatments, a sequential P extraction procedure was applied on the sediment before and after the efflux experiment. Addition of O₂, Fe³⁺ and NO₃ ^– to the sediment increased the amounts of oxidized Fe³⁺ and P_BD. Al³⁺ addition resulted in a lower fraction of P_BD but a correspondingly higher fraction of Al-bound P. Addition of Al³⁺ decreased the Fe-efflux from the suboxic sediment as well as the amount of oxidized Fe³⁺ in the sediment. This questions the use of Al compounds that contain sulfate because of the possible formation of FeS, which will restrict upward migration of Fe²⁺ and the formation of new Fe-oxides in the surface sediment. Instead, we suggest the use of AlCl₃ for lake restoration purposes.     

Chlorophyll/nutrient characteristics in the water masses to the north of South Georgia, Southern Ocean

Chlorophyll a and nutrient concentrations along with temperature and salinity values were measured at 22 CTD stations along a 735-km transect running to the northwest of the island of South Georgia, Southern Ocean. Measurements were repeated during five summer surveys (January and February 1994, January 1996, December 1996, January 1998) and one spring survey (October 1997). The transect sampled Sub-Antarctic Zone water in the north, Polar Frontal Zone water and Antarctic Zone water in the south. Chlorophyll a concentrations were lowest to the north of the transect and frequently high (up to 17 mg m⁻³) in the deep open ocean of the Antarctic Zone. Sub-surface peaks were measured in all zones and chlorophyll a was detectable to a depth of 150 m. There was a clear latitudinal temperature gradient in the near-surface waters (0–50 m), the warmest water occurring in the north (∼12 °C), and the coolest in the Antarctic Zone (∼2 °C). There was also a well-defined latitudinal gradient in summer near-surface silicate concentrations (∼2, 4, and 10 mmol m⁻³ in the Sub-Antarctic Zone, the Polar Frontal Zone and the Antarctic Zone, respectively), increasing to >20 mmol m⁻³ near South Georgia. Distinct differences in silicate concentrations were also evident in all three zones to a depth of 500 m. Near-surface nitrate and phosphate concentrations were relatively low to the north of the transect (∼14 and 1 mmol m⁻³, respectively) and higher in the Polar Frontal Zone and Antarctic Zone (∼18 and 1.4 mmol m⁻³, respectively). Ammonium and nitrite were restricted to the upper 200 m of the water column, and exhibited sub-surface concentration peaks, the lowest being in the Sub-Antarctic Zone (0.68 and 0.25 mmol m⁻³, respectively) and the highest in the Antarctic Zone (1.72 and 0.29 mmol m⁻³, respectively). Surface (∼6 m) spring nutrient measurements provided an indication of pre-bloom conditions; ammonium and nitrite concentrations were low (∼0.27 and 0.28 mmol m⁻³, respectively), while silicate, nitrate and phosphate concentrations were high and similar to previously measured winter values (e.g. ∼26, 23, 2 mmol m⁻³, respectively in the Antarctic Zone). Although the values measured were very variable, and there was some evidence of a seasonal growth progression, the chlorophyll a and nutrient distribution patterns were dominated by intercruise (interannual) factors. Approximate nutrient depletions (spring minus summer) appeared similar in the Polar Frontal Zone and Antarctic Zone for nitrate and phosphate, while silicate showed a marked latitudinal increase from north to south throughout the transect. Highest chlorophyll a concentrations coincided with the highest apparent silicate depletions over the deep ocean of the Antarctic Zone. In this area, relatively warm, easterly flowing Antarctic Circumpolar Current water meets cooler, westerly flowing water that is influenced by the Weddell-Scotia Confluence and is rich in nutrients, especially silicate. Accepted: 27 November 1999     

Influence of a Decaying Cyclonic Eddy on Biogenic Silica and Particulate Organic Carbon in the Tropical South China Sea Based on 234Th-238U Disequilibrium

Eddies play a critical role in regulating the biological pump by pumping new nutrients to the euphotic zone. However, the effects of cyclonic eddies on particle export are not well understood. Here, biogenic silica (BSi) and particulate organic carbon (POC) exports were examined inside and outside a decaying cyclonic eddy using ²³⁴Th-²³⁸U disequilibria in the tropical South China Sea. For the eddy and outside stations, the average concentrations of BSi in the euphotic zone were 0.17±0.09 μmol L^-1 (mean±sd, n = 20) and 0.21±0.06 μmol L^-1 (n = 34). The POC concentrations were 1.42±0.56 μmol L^-1 (n = 34) and 1.30±0.46 μmol L^-1 (n = 51). Both BSi and POC abundances did not show change at the 95% confidence level. Based on the ²³⁴Th-²³⁸U model, BSi export fluxes in the eddy averaged 0.18±0.15 mmol Si m^-2 d^-1, which was comparable with the 0.40±0.20 mmol Si m^-2 d^-1 outside the eddy. Similarly, the average POC export fluxes were 1.5±1.4 mmol C m^-2 d^-1 and 1.9±1.3 mmol C m^-2 d^-1 for the eddy and outside stations. From these results we concluded that cyclonic eddies in their decaying phase have little effect on the abundance and export of biogenic particles.     

Winter fluxes of methane from Minnesota peatlands

Winter fluxes of methane were investigated in northern Minnesota during 1988–89 and 1989–90. Two bogs and a fen emitted methane throughout the snow-covered season (November through March). Fluxes decreased to a low level of 3–16 mg CH₄ m^–2 d^–1 in late March, reflecting decreasing peat temperatures and (in 1989–90) increasing depth of frost in the peat. Winter fluxes calculated by integration for an open poor fen, an open bog, a forested bog hollow, and a hummock site in the forested bog averaged 49, 12, 13, and 5 mg m^–2 d^–1, respectively, in 1989–1990 (the year most measurements were made). These comprised 11%, 4%, 15%, and 21% of total annual flux.     

Biotreatment of ammonia- and butanal-containing waste gases

The biological removal of ammonia and butanal in contaminated air was investigated by using, respectively, a laboratory-scale filter and a scrubber-filter combination. It was shown that ammonia can be removed with an elimination efficiency of 83% at a volumetric load of 100 m³·m^–2·h^–1 with 4–16 ppm of ammonia. During the experiment percolates were analysed for nitrate, nitrite, ammonium and pH. It was found that the nitrification in the biofilter could deteriorate due to an inhibition of Nitrobacter species, when the free ammonia concentration was rising in the percolate. It should be easy to control such inhibition through periodic analysis of the liquid phase by using a filter-scrubber combination. Such a combination was studied for butanol removal. Butanal was removed with an elimination efficiency of 80% by a scrubber-filter combination at a volumetric load of 100 m³·m^–2·h^–1 and a high butanal input concentration. Mixing the filter material with CaCO₃ and pH control of the liquid in the scrubber resulted in an increase of the elimination efficiency. These results, combined with previous results on the biofiltration of butanal and butyric acid, allow us to discuss the influence of odour compounds on the removal efficiency of such systems and methods for control. The results were used to construct a full-size system, which is described.     

Fluff deposition on intertidal sediments: effects on benthic biota, ammonium fluxes and nitrification rates

The effects of fluff deposit on benthic biota,NH₄ ⁺ fluxes and nitrification was studied in thelaboratory using waterlogged and reflooded intertidal sediments fromMarennes-Oléron Bay, France. The fluff deposit was enriched inNH₄ ⁺ compared to underlying sediments, and promotedchanges of the sediment pH, E_h, C:N ratio, C:chla ratio and the NH₄ ⁺ efflux tooverlying water. Statistical analysis showed that pore waterNH₄ ⁺ concentrations were strongly influenced byinteractions between fluff, drying, depth and bioturbation. The fluff depositresulted in anoxia in the top sediments and moved the nitrification zone tosurface layers in fluff. However, the NH₄ ⁺ enrichment influff did not significantly change actual nitrification rates (range 0–1mmol m^–2 d^–1) or potentialnitrification rates (range 3–11 mmolNO₃ ^– m^–2d^–1).     

Effects of suspended mussel culture on benthic-pelagic coupling in a coastal upwelling system (Ría de Vigo, NW Iberian Peninsula)

The influence of suspended mussel culture on the benthic-pelagic coupling was evaluated in the Ría de Vigo, in the coastal upwelling system of the NW Iberian Peninsula, during the month of July 2004. Measurements of water column properties were carried out at three stations in the Ría de Vigo: under a mussel raft (1), and at two reference sites in the main channel (2) and in the inner part (3) of the Ría. Dissolved nutrients, dissolved oxygen and inorganic carbon benthic fluxes were measured by means of a benthic chamber at stations 1 and 3. Sediment traps were deployed at 6 locations to estimate vertical fluxes. The water column structure at the three study stations was very similar, characterized by upwelling conditions during the second week of July and a posterior stratification showing a strong thermocline, with a depth fluctuation mainly modulated by the shelf wind regime. Vertical POC fluxes underneath the mussel raft (3 g C m⁻² d^− 1) were 3 times higher than those obtained between rafts and 10 times higher than in the main channel reference site. Dissolved oxygen, ammonium, silicate and phosphate benthic fluxes were significantly higher under the raft than at the inner Ría reference site. A 1D carbon budget showed the importance of benthic metabolism under the raft (2.3 ± 0.8 g C m^− 2 d^− 1), being higher than the organic carbon produced at the photic layer (0.7 ± 0.3 g C m^− 2 d^− 1), as a result of higher organic loading compared to the inner Ría reference site. The results show for the first time the important role that suspended mussel cultures play in the benthic-pelagic coupling in this coastal upwelling ecosystem.     

Removal of nitrate, nitrite, ammonium and phosphate ions from water by the aerial microalga Trentepohlia aurea

The aerial microalga Trentepohlia aurea has beeninvestigated in relation to removal characteristics of nitrate, nitrite,ammonium and phosphate ions. When the alga was cultured in medium with veryhighconcentrations of ammonium, nitrate and phosphate ions, it showed relativelyhigh growth and removal rates. It also grew quite well with high nitriteconcentration (< 141 mg NO₂-N L^–1).The removal rate was 0.28 mg NO₂-N L^–1day^–1 in the 40-day culture, when it was cultured in modifiedBold's basal medium with added 51 mg NO₂-NL^–1. In addition, we examined simultaneous removal of nutrientions. The biomass was 1.5 times higher in medium which N- and P-sourcesufficient than in ordinary medium. Higher removal ratios of nitrite andnitratefrom medium were shown in a 30-day culture, reaching 37% and 32%, respectively.It is concluded that T. aurea has the potential for use inthe purification of wastewater.     

Fluxes of methane and carbon dioxide from a small productive lake to the atmosphere

The fluxes of CH₄ and CO₂ to the atmosphere, and the relative contributions of ebullition and molecular diffusion, were determined for a small hypertrophic freshwater lake (Priest Pot, UK) over the period May to October 1997. The average total flux of CH₄ and CO₂ (estimated from 7 sites on the lake) was approximately 52 mmol m^–2 d^–1 and was apportioned 12 and 40 mmol m^–2 d^–1 toCH₄ and CO₂ respectively. Diffusion across the air-water interface accounted for the loss of 0.4and 40 mmol m^–2 d^–1 of CH₄ and CO₂ respectively whilst the corresponding figures for ebullition losses were 12.0 (CH₄) and 0.23 (CO₂) mmol m^–2 d^–1. Most CH₄ (96%) was lost by ebullition, and most CO₂ (99%) by diffusive processes. The ebullition of gas, measured at weekly intervals along a transect of the lake, showed high spatial and temporal variation. The CH₄ content of the trapped gas varied between 44 and 88% (by volume) and was highest at the deepest points. Pulses of gas ebullition were detected during periods of rapidly falling barometric pressure. Therelevance of the measurements to global estimates ofcarbon emission from freshwaters are discussed.