53608024
Nitrogen uptake by heterotrophic bacteria and phytoplankton in the nitrate-rich Thames estuary
The uptake of ammonium, nitrate, amino acids and urea was examined in the nitrate- rich Thames estuary and adjacent area in the North Sea during February 1999. The majority of uptake was by heterotrophic bacteria, as demonstrated by addition of a prokaryotic inhibitor that lowered uptake rates by 82, 66, 49 and 86% for ammonium, nitrate, amino acids and urea, respec- tively. Amino acids were preferred over ammonium and urea, which in turn were preferred over nitrate. Urea was not important as nitrogen substrate. Amino acids were the main nitrogen substrate offshore and at the mouth of the estuary, but in the inner estuary nitrogen was mainly taken up as ammonium and, even more, as nitrate. Nitrate appeared to be the main substrate in the inner estuary (60 to 90%) despite its low affinity for nitrate. The high nitrate uptake by heterotrophic bacteria is probably due to high ambient concentrations of nitrate (up to 650 µM).
82529732
Production and consumption of biological particles in temperate tidal estuaries
The question is reviewed whether a balance exists between production and consumption of biological particles in temperate tidal estuaries and what the relationships are between the magnitude of production and consumption processes and system carbon metabolism. The production terms considered are primary production by phytoplankton, microphytobenthos, macroalgae and vascular plants and the chemoautotrophic production, mainly by nitrifying bacteria. The consumption terms are generalized by considering pelagic and benthic mineralization, but major consumer compartments, heterotrophic bacteria, zooplankton, meiobenthos, and macrobenthos are considered in detail. The proposition that estuaries are heterotrophic systems, and become more so when nutrient inputs are higher, is confirmed, and a general equation relating respiration to production is proposed as log R = 0.081 + 1.02 log P (R and P in gC m(-2) yr(-1)). This equation suggests that the amount of heterotrophy is a constant fraction of production. Annual pelagic primary production values lower than 160 gC m(-2) yr(-1) in nutrient- rich or heterotrophic systems are the result of light limitation. The overall recycling efficiency is constant, between 0.7 and 0.8, and is thus independent of system characteristics. Organic loading, rather than inorganic nitrogen loading, ultimately appears to control the primary production in estuarine systems. It is difficult to predict and compare phytoplankton primary production in different estuaries because it is not always clear whether gross or net primary production has been measured. Annual production in some estuaries is probably nitrogen-limited. When phytoplankton is light-limited, annual gross primary production can reasonably be predicted from biomass, incident irradiance and light availability in the water column (photic depth). It appears that interannual variations in annual production are mainly due to (the timing of) different climatological conditions, such as the amount of rainfall and sunshine. Phytoplankton biomass is lower in macrotidal estuaries than in microtidal estuaries. Despite the fact that phytoplankton primary production is controlled by nutrients or light, phytoplankton biomass seems to be determined by the biomass of suspension feeders. Primary production by nitrifying bacteria can be important in estuaries with a heavy organic load. The main suspension feeders in macrotidal estuaries belong to the macrobenthos. The feeding relations between macrobenthos and the production and sedimentation of organic matter in the water are therefore emphasized. For macrobenthic suspension feeders, it is argued that the system-wide biomass and secondary production are limited by the planktonic primary production of the system, whereas the local biomass is highly dependent on hydrodynamic conditions. Macrobenthic deposit feeders take a share of the sedimenting organic matter that depends on the quality and quantity of the organic carbon arriving at the sediment/water interface. Surface deposit feeders directly take up a considerable fraction of the freshly deposited organic matter. Deep deposit feeding is limited by adverse chemical conditions al high organic loading; microbiota take the largest share under these conditions. At low and intermediate loading levels, deep-deposit feeding animals are responsible for a relatively large share of the macrobenthos. [KEYWORDS: Copepod eurytemora-affinis; long-island sound; particulate organic-matter; mesohaline chesapeake bay; coastal marine-sediments; eelgrass zostera-marina; st-lawrence-estuary; mytilus-edulis-l; macrobenthic community structure; bacterial sulfate reduction]
6240197
CARBON AND CARBONATE METABOLISM IN COASTAL AQUATIC ECOSYSTEMS
The coastal zone is where land, ocean, and atmosphere interact. It exhibits a wide diversity of geomorphological types and ecosystems, each one displaying great variability in terms of physical and biogeochemical forcings. Despite its relatively modest surface area, the coastal zone plays a considerable role in the biogeochemical cycles because it receives massive inputs of terrestrial organic matter and nutrients, is among the most geochemically and biologically active areas of the biosphere, and exchanges large amounts of matter and energy with the open ocean. Coastal ecosystems have therefore attracted much attention recently and are the focus of several current national and international research programs (e.g. LOICZ, ELOISE). The primary production, respiration, calcification, carbon burial and exchange with adjacent systems, including the atmosphere, are reviewed for the major coastal ecosystems (estuaries, macrophyte communities, mangroves, coral reefs, and the remaining continental shelf ). All ecosystems
8071951
Utilization of inorganic and organic nitrogen by bacteria in marine systems1
Professorships for Women Program (grant RTI-83 10369) and by NSF grants OCE 83-08753 (to P. A. Wheeler) and OCE 8 1-17834 (to R. E. Hodson).
83796081
Inorganic nitrogen utilization by assemblages of marine bacteria in sea-water culture
Stimulation of heterotrophic bacterial growth by inorganic nitrogen (nitrate and ammonium) was observed in natural assemblages of marine bacteria growth in continuous culture with unsupplemented sea water as primary medium. In the presence of nitrogenous supplements, bacterial numbers increased approximately 3-fold. These results indicate that re-evaluation of the role of heterotrophic bacterioplankton in the pelagic nitrogen cycle may be necessary.
20022093
The uptake of inorganic nutrients by heterotrophic bacteria
It is now well known that heterotrophic bacteria account for a large portion of total uptake of both phosphate (60% median) and ammonium (30% median) in freshwaters and marine environments. Less clear are the factors controlling relative uptake by bacteria, and the consequences of this uptake on the plankton community and biogeochemical processes, e.g., new production. Some of the variation in reported inorganic nutrient uptake by bacteria is undoubtedly due to methodological problems, but even so, uptake would be expected to vary because of variation in several parameters, perhaps the most interesting being dissolved organic matter. Uptake of ammonium by bacteria is very low whereas uptake of dissolved free amino acids (DFAA) is high in eutrophic estuaries (the Delaware Bay and Chesapeake Bay). The concentrations and turnover of DFAA are insufficient, however, in oligotrophic oceans where bacteria turn to ammonium and nitrate, although the latter only as a last resort. I argue here that high uptake of dissolved organic carbon, which has been questioned, is necessary to balance the measured uptake of dissolved inorganic nitrogen (DIN) in seawater culture experiments. What is problematic is that this DIN uptake exceeds bacterial biomass production. One possibility is that bacteria excrete dissolved organic nitrogen (DON). A recent study offers some support for this hypothesis. Lysis by viruses would also release DON.While ammonium uptake by heterotrophic bacteria has been hypothesized to affect phytoplankton community structure, other impacts on the phytoplankton and biomass production (both total and new) are less clear and need further work. Also, even though bacteria account for a very large fraction of phosphate uptake, how this helps to structure the plankton community has not been examined. What is clear is that the interactions between bacterial and phytoplankton uptake of inorganic nutrients are more complicated than simple competition.
86471943
Ammonium uptake by heterotrophic bacteria in the Delaware estuary and adjacent coastal waters
Uptake of NH4+ by heterotrophic bacteria and the relative importance of NH,+ and dissolved free amino acids (DFAA) as nitrogen sources for bacterial production were examined in the Delaware estuary and adjacent coastal waters during 1988 and 1990. Although total uptake of NH,+ and bacterial production were -4-fold higher in 1988 than in 1990, percent NH,+ uptake by bacteria in the upper and lower estuary was similar for both years. Bacterial uptake rates were highest at the mouth of the bay in summer and represented lo-25% of total uptake of NH,+. Less than 5% of NHd+ uptake was by bacteria at salinities <207& In contrast to NH4+ uptake, DFAA uptake was greatest in the upper estuary and often exceeded nitrogen requirements for bacterial growth. Bacteria accounted for 15-35% of total NH,+ uptake at coastal and offshore stations in 1990. About 50% of bacterial nitrogen demand was supported by NH4+ at the mouth of the bay and in coastal waters during summer, when DFAA concentrations were generally lowest. Although DFAA concentration and uptake did not explain all variability, they appeared to explain large-scale features in NH,+ uptake by heterotrophic bacteria. Ammonium uptake by bacteria was lowest in the estuary, where DFAA concentrations and uptake were highest; at an offshore station, where DFAA concentrations and uptake were low, relative NH,+ uptake by bacteria was highest. These and other results suggest that NH,+ uptake by bacteria is relatively high in oligotrophic water and low in eutrophic systems, which has important implications on the role of heterotrophic bacteria in the N cycling of marine environments.
84357462
Uptake of ammonium and nitrate by heterotrophic bacteria and phytoplankton in the sub-Arctic Pacific
Heterotrophic bacteria are known to account frequently for a large fraction of NH+4 uptake in many oceans, but NO-3 uptake by bacteria is not thought to be as important. As part of the SUPER program, NH+4 and NO-3 uptake by heterotrophic bacteria in the sub-Arctic Pacific was examined and compared with use of dissolved free amino acids (DFAA). Heterotrophic bacteria accounted for 31% (range of <5–40%) and 32% (5–60%) of total uptake of NH+4 and NO-3, respectively, over 4 months of study. Although the average uptake of NO-3 by bacteria was equal to that of NH+4, bacteria actually assimilated relatively more NO-3 than NH+4 in those samples when the two processes were measured simultaneously. Uptake of NH+4 or NO-3 alone was about equal to bacterial biomass production, whereas uptake of dissolved free amino acids (DFAA) was only 40% of bacterial production, suggesting that the uptake of other dissolved organic nitrogen sources is relatively small. Uptake of NH+4 by bacteria correlated significantly with bacterial production, and both NH+4 uptake and bacterial production correlated significantly with DFAA turnover. In contrast, there was no significant correlation between any microbial parameter and NO-3 uptake. Biomass production of heterotrophic bacteria appears to be supported largely by DIN uptake and, to a lesser extent, uptake of DFAA in the sub-Arctic Pacific. Uptake of NO-3 is more important in supporting bacterial growth than previously hypothesized, although it remains the least preferred N source.
34741526
Uptake of dissolved inorganic nitrogen in turbid, tidal estuaries
Ammonium and nitrate uptake was measured in 6 European tidal estuaries (Ems, Rhine, Scheldt, Loire, Gironde and Douro) using N-15-tracer techniques. Uptake rates of ammonium and nitrate ranged from 0.005 to 1.56 mu mol N l(-1) h(-1) and 0.00025 to 0.25 mu mol N l(-1) h(-1), respectively, and differed significantly between and within estuaries. Analysis of nitrogen uptake using the relative preferential index (RPI) indicated ammonium to be the preferred substrate. The turnover times of particulate nitrogen (0.7 to 31 d) and dissolved ammonium (0.1 to 27 d) were similar to or shorter than estuarine-water residence times, whereas turnover times of dissolved nitrate (19 to 2160 d) were longer than residence times. Assimilation of nitrate in the water column of estuaries consequently does not influence its distribution, and most nitrate entering or produced in estuaries flushes through unless significant denitrification and/or burial in the sediment occur. As ammonium and particulate nitrogen are efficiently recycled, most allochthonous organic matter is extensively microbially modified before export, burial, or consumption by higher trophic levels. [KEYWORDS: nitrogen uptake; nitrogen turnover; ammonium; nitrate; estuary; heterotrophy Ecosystem model moses; north-atlantic ocean; schelde estuary; sw netherlands; river estuary; heterotrophic bacteria; westerschelde estuary; organic nitrogen; delaware estuary; nitrate uptake]
53593120
Contribution of dissolved free amino acids and ammonium to the nitrogen requirements of heterotrophic bacterioplankton
We investigated the contribution of dissolved free amino acids (DFAA) and ammonium (NH;) to the nitrogen demand (N-demand) of bacterioplankton in the subarctic Pacific and the Delaware Estuary. Bacteria were isolated from other microorganisms by gravity-filtration through 0.8 pm filters, and then bacterial abundance and nutrient concentrations were measured over time. During exper~ments lasting between 36 and 130 h, DFAA and N H 2 contributed 51 + 45 % and 64 + 54 % (n = 14) to the estimated N-demand, respectively. In 9 of the 14 experiments, DFAA and NHZ contributed over 90 % of the estimated N-demand, implying that dissolved organic nitrogen aside from DFAA (e.g. dissolved combined amino acids) was not a significant source of nitrogen. Additions of glucose (0.1 to 1.0 pM) increased the contribution of NHZ and DON other than DFAA to the bacterial N-demand. In most cases, measurements of amino acid and NH; uptake are sufficient for estimating bacterial nitrogen use.
41736780
Dissolved free amino acids, combined amino acids, and DNA as sources of carbon and nitrogen to marine bacteria
Utilization of naturally-occurring dissolved free and combined amino acids (DFAA and DCAA) and dissolved DNA (D-DNA) was studied in batch cultures of bacteria from 2 shallow marine environments, Santa Rosa Sound (SRS), Florida. USA, and Flax Pond (FP), Long Island, New York, USA. In addition to control experiments, cultures were enriched with various sources of C and N. In the SRS cultures, net C assimilation of DCAA, DFAA and D-DNA made up from 4 2 to 60 %of net bacterial C production. The average, relative incorporation of C from DCAA, DFAA and D-DNA was 0.13, 0.77 and 0.10, respectively. The corresponding values of N were 0.10, 0.81 and 0.09. Addition of NH,', DFAA, or both, increased the incorporation of DCAA, DFAA and D-DNA. Incorporation of N from DCAA, DFAA and D-DNA equaled 11 1 to 219 % of the bacterial N production. Including incorporation of NH,' and release of NO,-, calculated net bacterial N incorporation made up 4 8 and 290 %of bacterial N production. In the FP experiment, net assimilation of DCAA. DFAA and D-DNA equaled 66 to 91 % (average 77 %) of net bacterial C production. Largely all C incorporation was due to assimilation of DFAA. Enrichment of the cultures with NH4+, glucose, methylamines, and high-molecular-weight dissolved organic matter all increased bacterial production. Net N incorporation of DCAA, DFAA and D-DNA corresponded to between 100 and 180 % of net bacterial N production. In 3 cultures DFAA were the dominant (> 50 %) bacterial N source. In the other cultures, DFAA and NH,' were similar in importance as an N source, and together they accounted for 80 to 99 % of bacterial N incorporation. Including uptake of NH4' and uptake or release of NO3in the N budgets, bactenal N incorporation equaled 155 to 413 % of bactenal N production. The reason for this apparently excessive N uptake in both sets of cultures may be the release of organic nitrogen compounds.
55403821
Nitrogen-specific uptake rates of marine phytoplankton isolated from natural populations of particles by flow cytometry
Phytoplankton were isolated from natural, heterogeneous populations of part~cles in Boothbay Harbor, M a ~ n e , USA using flow cytornetry with cell sorting to measure true rates of nitrogenspecific uptake of 15N without the bias due to detritus, bactena or other heterotrophs that affects tradltional filtration techniques. After incubation under light or dark conditions with I5NH4+ or "NO3-, particles were either directly filtered or were sorted to isolate phytoplankton and then filtered for isotopic analysis. Nitrogen-specific (pN, t i m e ' ) and absolute uptake rates (mass volume-' time-l) of ammonium were greater for small (3-10 pm) phytoplankton than for larger (10-53 pm) phytoplankton, whereas the opposite was observed for uptake of nitrate. Accounting for pronounced diel variations in uptake from both nitrogen sources, algal growth rates were calculated to be 0.38 d' on ammonium and 0.05 d ' on nitrate. The absolute rate of NH,+ uptake by all particles as assayed by filtration was approximately balanced by the summed rates of the 2 sorted fractions and the small (<3 ).]m) particles that were removed prior to sorting: phytoplankton represented only 50% of the total rate. In contrast, phytoplankton uptake of nitrate represented only about one-third of the total uptake, and the remaining fractions contributed only 10% leaving about 60% unaccounted for. Future applicat~ons of flow cytornetry with stable isotopes could be used to investigate diel variations in p~ and pc (carbon-specific uptake rates) and provide an estimate of phytoplankton growth rates.
34137224
Carbon dioxide emission from european estuaries
The partial pressure of carbon dioxide (pCO2) in surface waters and related atmospheric exchanges were measured in nine European estuaries. Averaged fluxes over the entire estuaries are usually in the range of 0.1 to 0.5 mole of CO2 per square meter per day. For wide estuaries, net daily fluxes to the atmosphere amount to several hundred tons of carbon (up to 790 tons of carbon per day in the Scheldt estuary). European estuaries emit between 30 and 60 million tons of carbon per year to the atmosphere, representing 5 to 10% of present anthropogenic CO2 emissions for Western Europe.
96236887
Rapid analysis of organic carbon and nitrogen in particulate materials
Abstract A method for rapid determination of organic carbon and nitrogen in natural particulate materials is described. The procedure allows the determination of 60 samples per day by a single analyst. It involves the determination of carbon and nitrogen using an automatic CN-analyzer following the partitioning of inorganic and organic carbon phase by acidification with 25% HCl in situ within silver sample cups. The technique eliminates reweighing procedures, losses of organic and inorganic compounds (except carbonates and sulphides) and is free from matrix interferences. Extensive testing and application showed long-term precisions for organic carbon and nitrogen of about 3%. The accuracy is excellent, irrespective of the calcium carbonate content of the sample.
55583137
Organic matter mineralization in intertidal sediments along an estuarine gradient
A seasonal study of organic matter mineralization rates was made at 8 intertidal stations in the Westerschelde Estuary (The Netherlands). Organic matter mineralization rates, based on the gaseous emission of carbon dioxide and methane, showed significant dynamic temporal and spatial variability at various scales. Annual rates of organic matter mineralization varied from 8 to about 339 mol C m(-2) yr(-1). The temperature dependence of organic matter degradation was described using an Arrhenius-type equation. Activation energies ranged from 54 to 125 kJ mol(-1) and correlated negatively with depth-integrated rates of mineralization. Spatial differences in mineralization were mainly due to differences in the lability of the organic matter, since the quantity of organic matter was similar between stations on an areal or volume basis. Average first- order decomposition rate constants ranged from 0.2 to 7 yr(-1) and decreased towards the seaward end of the estuary due to ageing of riverine-derived material, Intertidal sediments were estimated to account for about 25% of the total carbon retention in the Westerschelde estuary. [KEYWORDS: organic matter; mineralization; intertidal sediments; estuary; methane; carbon budget; activation energy Coastal marine basin; long-island sound; oak river estuary; sulfate reduction; oxygen-consumption; carbonate dissolution; nutrient regeneration; salinity gradient; north-carolina; fresh-water]
85066506
Nitrogenous nutrition of the plankton in the Chesapeake Bay. 1. Nutrient availability and phytoplankton preferences
Eight stations in the main body of Chesapeake Bay and one on the continental shelf were sampled seven times over a period of 13 months to investigate the nitrogenous nutrition of the phytoplankton. The rates at which the phytoplankton were utilizing NO,, NO,, NHr+, and urea N were determined. The data demonstrate that for a large portion of the year there is inadequate N nutrient available to permit a single doubling of the particulate N. Over temperatures from 4” -28°C and salinities from 2-32&, there was a universally high phytoplankton preference for NH4+ and urea N over NO,and NO,. A relative preference index indicated that NHa’ concentrations in excess of O-5-1.0 pg-atom N liter-l almost totally suppressed NO, utilization. Urea N was used after NH,+ in order of prcfcrence, and when the sum of available NH4+ and urea N was insufficient to meet the phytoplankton N nutrient demand, NO; was used. When the sum of all available N nutrients was less than that required to satiate the phytoplankton demand, NIL’, urea N, NO,-, and NO,were all utilized at rates proportional to their availability. For the midbay region in October 1973, NO, was the dominant N nutrient present both in the water and in the diet of the phytoplankton. The Chesapeake Bay and its tributaries receive nitrogen in discharges of treated sewage from metropolitan areas of the District of Columbia and Baltimore at rates excceding 10 and 7 tonnes d-l. Carpenter et al. (1969) observed high levels of NOS(30100 pg-atoms N liter-l) in the open waters of the north half of the bay during winter and spring, levels undoubtedly sufficient to meet the nutritional needs of the indigenous phytoplankton. The persistence of such levels for several weeks in spring suggests that the rates of supply and loss were approximately balanced during this period. In summer and early autumn the NOs-concentration fell to <l lug-atom N liter-l; often it was analytically undetectable. A pronounced north-south gradient led Carpenter et al. (1969) to conclude that the Susquehanna River, which enters the bay l This research was supported by National Science Foundation grants GA 33445 and DES 7502846 and by U.S. Energy Research and Dcvelopment Administration contract E ( ll-l)-3279, document No. COO-3279-21. Chesapeake Bay Institutc Contribution 240. above the major metropolitan arcas, was the major source of NOsfor the open waters of the Chesapeake Bay, but since the distribution of NI14+ showed little spatial or temporal variability they postulated that the primary origin of NIL+ in the open water of the bay was linked to local biological activity. Studies with unialgal laboratory cultures and artificially enriched coastal seawater have shown that marinc phytoplankton prefcr NH4+ .to NOs( cf. Grant et al. 1967; Eppley et al. 1969; Eppley and Rogers 1970; McCarthy and Epplcy 1972). The preferential assimilation of NH‘*+ in the presence of NO:%has been observed or inferred from data for the Peru Current ( MacIsaac and Dugdale 1969)) the subtropical Pacific Ocean (Goering et al. 1970), the Saronikos Gulf ( MacIsaac and Dugdale 1972), and the California Current (McCarthy 1972a). The importance of urea as a source of N for natural populations of phytoplankton (e.g. Carpenter et al. 1972; Eppley et al. 1973; Webb and Haas in press) enlarges LIMNOLOGY AND OCEANOGRAPHY 996 NOVEMBER 1977, V. 22( 6) N nutrition of phytoplankton conceptualIy the importance of “regenerated nitrogen” advanced by Dugdalc and Goering (1967). Whereas NH4+ at elevated concentrations will be used in preference to urea, urea N and NOsare utilized simultaneously over a wide range of concentrations ( McCarthy and Eppley 1972). At low ambient concentrations of all forms of nitrogenous nutrient, compensation for any difference between the concentration required for optimal growth and the concentration of the most highly preferred form, i.e. NH4+, might presumably be by use of an alternate form. For NOs-, this requires an energy expenditure for both induction of the enzyme system and reducing potential (Eppley et al. 1969). In eucaryotic algae, either an ATP : urea amidolyase enzyme system or a urease system is considered essential for the assimilation of urea N (Leftley and Syrett 1973). Some marine phytoplankters do not use urea (Guillard 1963; Thomas 1968; McCarthy 1972h) and there is no evidence that either of the identified enzyme systems is other than constitutive. Low ambient lcvcls of nitrogenous nutrients in most offshore marine waters and low densities of algal biomass preclude careful scrutiny of the nutritional preferences of unperturbed phytoplankton asscmblages. The relatively high standing crop of phytoplankton and the great temporal and spatial variability of nitrogenous nutrient concentrations in the Chesapeake Bay allow us to observe in situ the rate of utilization of a single N nutrient when others are present over a wide range of concentrations. In particular, we can examine the significance of the rapidly recycled NIL+ and urea during periods of both high and low NOsconcentration. We acknowledge M. E. Loftus for technical assistance and R. W. Eppley and K. L. Webb for helpful comments on an earlier draft of this manuscript.
129519430
Temporal and spatial variability in phytoplankton ammonium and nitrate uptake in the Delaware Estuary
Abstract Phytoplankton NH 4 + and NO 3 − uptake was examined along the longitudinal salinity gradient of the Delaware Estuary over several seasonal cycles using 15 N-tracer techniques. Saturated nitrogen uptake rates increased directly with water temperature and reached a maximum of 380 nmol Nl −1 h −1 during summer. This temperature dependence was related primarily to changes in the rate of maximum chlorophyll specific uptake, which varied exponentially between 2 and 70 nmol N [μg Chl h] −1 over a temperature range of 2–28°C. Despite these high uptake rates, balanced growth (C:N⋍7:1) could be maintained over the diel light cycle only by highly efficient nitrogen uptake at low light intensities and dark uptake below the photic zone and at night (dark uptake=25% maximum uptake). Ammonium fulfilled 82% of the annual phytoplankton nitrogen demand in the estuary despite dominance of NO 3 − in the ambient dissolved inorganic nitrogen pool. The predominance of NH 4 + uptake occurred because of the general suppression of NO 3 − assimilation at NH 4 + concentrations in excess of 2 μ m . This suppression, however, was not as universal as has been reported for other systems, and it is suggested that the extremely high NO 3 − concentrations found in the estuary contribute to this pattern. Nitrate was a significant source of nitrogen only during periods of high phytoplankton production in summer, and when NH 4 + concentrations were low towards the end of the spring bloom.
84795340
Nutrient uptake in a highly turbid estuary (the Humber, United Kingdom) and adjacent coastal waters
Surveys were conducted in April and June 1995 to quantify the uptake of dissolved nutrients in a highly turbid estuary (the Humber, United Kingdom) and to determine the factors controlling nutrient uptake rates. A combination of isotope labelling methods were used in conjunction with on-deck incubation techniques to estimate the uptake of dissolved nutrients (PO43−, NH4+, NO3−, and urea) in surface samples collected from coastal waters. Similarly, isotope labelling and laboratory incubgation techniques were employed to estimate dissolved nitrogen uptake (NH4+, NO3−, and urea) in surface samples collected from the estuary mouth. Nutrient uptake rates were at the low end of ranges for coastal and estuarine environments reported in the literature. Concentrations of chlorophyll and the availability of photosynthetically active radiation were identified as potentially important factors controlling the uptake rates of nutrients. Uptake rates of dissolved nitrogen in the Humber mouth appeared to be related to the location of smapling sites. Depletion rates of dissolved nutrients in situ were estimated on the basis of integrated water column nutrient uptake rates and indicated assimilation of up to 16% of nutrients in the entire water column. Estimated depletion rates did not indicate preferential loss of any of the nutrient species investigated.
129529338
Carbon and nitrogen primary productivity in three North Carolina estuaries.
Abstract Uptake of inorganic carbon and ammonium by the plankton community of three North Carolina estuaries was measured using 14 C and 15 N isotope methods. At 0% light, C appeared to be lost via respiration, and at increasing light levels uptake of inorganic carbon increased linearly, saturated (mean I k = 358±30 μEin m −2 s −1 ), and frequently showed inhibition at the highest light intensities. At 0% light NH 4 + uptake was significantly greater than zero and was frequently equivalent to uptake in the light (light independent); at increasing light levels NH 4 + uptake saturated (mean I k = 172±44 μEin m −2 s −1 ) and frequently indicated strong inhibition. Light-saturated uptake rates of inorganic carbon and NH 4 + were a function of chlorophyll a ( r 2 = 0·7−0·9); average assimilation numbers were 625 nmol CO 2 (μg chl. a ) −1 h −1 and 12·9 nmol NH 4 + (μg chl. a ) −1 h −1 and were positively correlated with temperature ( r 2 = 0·3−0·7). The ratio of dark to light-saturated NH 4 + uptake tended to be near 1·0 for large algal populations at low NH 4 + concentrations, indicating near light independence of uptake; whereas the ratio was lower for the opposite conditions. These data are interpreted as indicative of nitrogen stress, and it is suggested that uptake of NH 4 + deep in the euphotic zone and at night are mechanisms for balancing the C:N of cellular pools. A 24-h study using summed short-term incubations confirmed this; the cumulative C:N of CO 2 and NH 4 + uptake during the daylight period was 10–20, whereas over the 24-h period the ratio was 6 due to dark NH 4 + uptake. Annual carbon and nitrogen primary productivity were respectively estimated as 24 and 4·0 mol m −2 year −1 for the South River estuary, 42 and 7·3 mol m −2 year −1 for the Neuse River estuary, and 9·6 and 1·6 mol m −2 year −1 for the Newport River estuary.
83762387
Nitrogen assimilation by phytoplankton and other microorganisms in the surface waters of the central North Pacific Ocean
Assimilation rates of 15N-labelled ammonium, urea, and nitrate by plankton in the upper euphotic zone were measured in 2 summer, 2 winter, and 1 spring cruise in the central North Pacific Ocean. Average rates of ammonium plus urea assimilation could not be determined precisely, but were estimated to be 7 to 25 μg-at. N m-3 day-1. Indirect evidence suggested that non-photosynthetic microorganisms contributed to these rates. Nitrate assimilation was negligible in the upper waters considered in this report (above the chlorophyll maximum and the nutricline). Potential, nitrate-saturated rates were in the range 1 to 8 μg-at. N m-3 day-1. Seasonal comparison showed lowest rates of both carbon and nitrogen assimilation rates per chlorophyll a in winter.
82801475
Use of “Specific” Inhibitors in Biogeochemistry and Microbial Ecology
The above statement, although meant to be tongue in cheek, contains an essential truism: all work with inhibitors is inherently suspect. This fact has been known by biochemists for some time. However, use of chemical inhibitors of enzymic systems and membranes continues to be a common approach taken toward unraveling the biochemistry and biophysics of plants, animals, and microorganisms. Various types of “broad-spectrum” biochemical inhibitors (e.g., poisons, respiratory inhibitors, and uncouplers) have been employed by ecologists for many years in order to demonstrate the active participation of microbes in chemical reactions occurring in natural samples (e.g., soils, sediments, and water). In recent years, considerable advances have been made in our understanding of the biochemistry of microorganisms of biogeochemical interest. Concurrent with these advances have been the discoveries of novel types of compounds that will block the metabolism of one particular group of microbes, but have little disruptive effect on other physiological types. Thus, the term “specific inhibitor” has been applied to these types of compounds when they are used to probe the functions of mixed populations of microorganisms. These substances provide powerful experimental tools for investigating the activity and function of certain types of microorganisms in natural samples.
98534812
Effectiveness of various treatments in retarding microbial activity in sediment trap material and their effects on the collection of swimmers
Laboratory and field experiments were conducted to determine the effectiveness of various poison, preservative, and antibiotic treatments currently in common use in sediment trap work. Our results agree with previous reports that most biological activity in sediment traps can be inhibited by appropriate concentrations of formaldehyde, chloroform, or mercuric chloride. Sodium azide appears to be less effective at inhibiting biological activity, while antibiotics and salt alone are probably too ineffective for long-term deployments. On the basis of laboratory experiments, effective concentrations when sustained throughout the deployment are 50% saturated chloroform, 37 mM formaldehyde, or 180 PM HgCl,. Our results also indicate, however, that the weight of swimmers (zooplankton which swim into the trap and die there from contact with the poison) collected in sediment traps is higher when more effective treatments are used. The presence of large numbers of swimmers can greatly affect the flux and composition of particulate organic matter collected in sediment traps and may decrease the effectiveness of the various treatments in inhibiting microbial activity in the traps.
85654653
Amino acid utilization by marine phytoplankton: A novel mechanism
An enzyme on the cell surface of some marine phytoplankton, particularly the genus Pleurochrysis (ffyrnenomonas), oxidizes many L-amino acids to produce H,O,, NH,, and an ol-keto acid extracellularly. The NH,+ is subsequently taken up and used for growth. The enzyme synthesized by Pleurochrysis carterue (clone CoccoII) has a half-saturation constant of 0.25 PM assayed with L-W aminobutyric acid as a model substrate. The enzyme activity is absent in NH,+-grown (logarithmic phase) cells, is present in NO,--grown (logarithmic phase) cells, and is enhanced 3.S-fold in -N-limited cells. Some Heurochrysis species show different patterns of regulation, The existence of .this novel, high-affinity mechanism for amino acid utilization-one that would not be detected by typical field methods-suggests that amino acids may be a more important source of N for phytoplankton than is currently believed.
35825121
Relations between bacterial nitrogen metabolism and growth efficiency in an estuarine and an open-water ecosystem
Bacterial uptake or release of dissolved nitrogen compounds (amino nitrogen, urea, ammonium and nitrate) were examined in 0.8 pm filtered water from an estuary (Santa Rosa Sound [SRS], northwestern Florida) and an open-water location in the Gulf of Mexico (GM). The bacterial nutrient dynamics were related to oxygen consumption and activity of enzymes involved in nitrogen assimilation (glutamate dehydrogenase [GDH], glutamine synthetase [GS] and aminopeptidase activity [leu-MCA]). Dissolved free amino acids (DFAA) were the dominant N source to the bacteria, followed by dissolved combined amino acids (DCAA), ammonium and nitrate. Nitrogen budgets of the bacteria (assimilation of N compounds relative to accumulated N biomass) demonstrated that, except for the initial 24 h period in the GM cultures, the assimilated N compounds sustained all of the bacterial N demand. Urea was released in both sets of cultures, but in the SRS cultures the produced urea was reassimilated. Major differences in the bacterial N metabolism between the open-water GM and the estuarine SRS stations were observed. Relative to the GM station, bacteria in the SRS cultures had (1) a 2.4 to 18x higher cell-specific DFAA assimilation, (2) a 2 . 5 ~ higher cell-specific leu-MCA activity, (3) a 3 to 10x higher GDH:GS activity ratio and (4) a 1.9 to 4 . 1 ~ lower cell-specific respiration. The larger nutrient availability at the estuarine station probably caused these differences in uptake and metabolism of nitrogen as well as the lower respiratory rate, relative to the open-water station. Therefore, we hypothesize that availability of nitrogen, rather than carbon, controlled the bacterial activity in the cultures. Our results suggest that bacteria in eutrophic conditions can be more important mediators of nitrogen than those in oligotrophic conditions, in which bacteria temporarily may immobilize labile nitrogen.
86364064
Dependent coupling of inorganic and organic nitrogen uptake and regeneration in the plume of the Chesapeake Bay estuary and its regulation by large heterotrophs
Nitrogen uptake and regeneration in the plume of the Chesapeake Bay estuary was studied during a series of four cruises (1985-1986). During each season we followed the short-term patterns in inorganic (NH,‘, NO3 -, NO,-), and organic (urea and dissolved free amino acids-DFAA) nitrogen uptake and regeneration as plume water aged and became incorporated into ambient coastal water over l-3 d. There was little influence of seasonally changing temperature on inorganic nitrogen uptake rates: the highest specific and absolute hourly rates of uptake occurred in April, when the availability of total N was al a seasonal high; rates were somewhat lower in early and late summer and were lowest in February. NH,+ regeneration rates, on the other hand, were highly correlated with temperature, with the highest rates occurring in late summer. Rates of DFAA uptake were highest in June. Urea contributed up to 70-80% of the total N utilized during winter and summer; in spring most nitrogen uptake was in the forms of NO, and NH,‘. The seasonal differences in the patterns of release of dissolved organic N, and the role of zooplankton in mediating this flux, paralleled the patterns previously reported for the release of dissolved organic C in the Chesapeake Bay plume. That is, in winter most organic N release was not grazer mediated, but instead was more likely due to nutrient-deficient phytoplankton. In contrast, in late summer, there seemed to be more dissolved organic N release by grazers, either directly or from “sloppy feeding.” At all seasons, in the transition from the bay environment ‘to coastal waters, autotrophic populations appeared to become nutrient deficient, and a system dominated by heterotrophic processes rapidly became established.
53057885
Size-fractionated uptake of ammonium, nitrate and urea and phytoplankton growth in the North Sea during Spring 1994
The growth of 2 different algal size classes was studied in March/April 1994 during the establishment of the spring bloom along a transect from the Dogger Bank to the Shetland Islands in the North Sea. Size-differential growth rates were estimated on the basis of independent measurements of carbon and nitrogen uptake. At the shallower stations near the Dogger Bank (DB) area, chlorophyll a (chl a) levels were up to 5.8 mu g l(-1). In the bloom 89 % of the chi a was in the >5 mu m fraction. In the central North Sea (cNS) and near the Shetland Islands (SI) total chi a was 0.52 and 0.38 mu g l(-1), respectively; 60 % was in the >5 mu m fraction. Depth-integrated primary production at the DB, cNS and SI was 46, 145 and 149 mg C m(-2) d(-1), respectively, for the 5 mu m size fraction. Since the calculated specific growth rates, based on either nitrogen uptake or inorganic carbon uptake, were in good agreement with each other for both size fractions, it was concluded that smaller algae apparently grow faster than larger ones in this typically light-controlled environment. The >5 mu m fraction, however, dominated the bloom at the Dogger Bank. Our findings consolidate the concept of size differential control of phytoplankton communities under typical spring bloom conditions which originally was demonstrated in a coastal area (Riegman et al. 1993; Neth J Sea Res 31:255-265). [KEYWORDS: phytoplankton growth; size fractionation; nitrogen uptake; carbon uptake; North Sea Marine diatoms; cell-size; nitrogen assimilation; carbon fixation; populations; plankton; station; system; waters; light]
4234076
High rates of nitrification and nitrate turnover in undisturbed coniferous forests
THE importance of nitrate (NO–3) in the internal nitrogen cycle of undisturbed coniferous ecosystems has not been widely recognized1,2. Nitrate concentrations in soils from these forests tend to be low, and assays measuring net nitrification usually show exceedingly slow rates3,4. It may be, however, that microbial assimilation of NO–3 is substantial in these soils, and that net nitrification rates greatly underestimate gross rates5. Here we use a 15N isotope-dilution technique in intact soil cores to measure gross rates of nitrification and microbial assimilation of NO–3 in eleven undisturbed forest ecosystems of New Mexico and Oregon. We found that gross nitrification rates were surprisingly high in all of the forests examined. Net nitrification rates poorly predicted gross rates because the soil microbial communities had the capacity to assimilate almost all of the NO–3 produced. To our knowledge, this is the first report of gross nitrification and NO–3 assimilation rates in intact soil samples from a large number of contrasting forest ecosystems. Our results contradict previous assumptions that nitrification rates are low in mature coniferous forests and suggest that current models greatly underestimate the role of the microbial community in preventing NO–3 loss.
129089623
Biomass and nitrogen uptake by heterotrophic bacteria during the spring phytoplankton bloom in the North Atlantic Ocean
N biomass and N uptake by heterotrophic bacteria and phytoplankton were examined during the North Atlantic spring bloom (May 1989). Phytoplankton N had reached its zenith by the time the authors arrived at the station and increased only slightly during the first week of the study, while particulate nitrogen (PN) nearly doubled (increase of 450 mg N m−2), apparently due to the growth of heterotrophic organisms other than bacteria. During the second week, bacterial N doubled, increasing by 280 mg N m−2. These increases in biomass N and total PN were large compared to NO3− uptake and to N export from the upper 100 m. To examine the role of bacteria in greater detail, we estimated total N uptake and the uptake of free amino acids (DFAA), NH4+, and NO3−. The ratio of total N uptake by bacteria to total N uptake by phytoplankton varied greatly and was often high (0.2–0.9). When uptake was corrected for phytoplankton activity, heterotrophic bacteria accounted for 22–39% and 4–14% of NH4+ and NO3− uptake. DFAA, NH4+ and NO3− supplied 12–34%, 19–29% and 2–8% respectively, of the nitrogen needed for bacterial production. Preference indices further indicated that NO3− was the N source least preferred by heterotrophic bacteria. Nitrogen uptake fuelled a buildup of bacterial biomass and other suspended material that needs to be considered in reconciling new production and N export from the upper layers of the ocean during the spring bloom.