Microbiological nitrogen transformation in carbonate sediments of a coral-reef lagoon and associated seagrass beds (original) (raw)

Carbon and nitrogen dynamics in shallow photic systems: Interactions between macroalgae, microalgae, and bacteria

Limnology and Oceanography, 2011

We tracked carbon (C) and nitrogen (N) uptake into sediments in the presence and absence of benthic macroalgae using dual stable isotope tracers in combination with compound-specific isotope analyses of hydrolyzable amino acids and phospholipid-linked fatty acids to quantify the uptake and retention of C and N within bulk sediments, benthic microalgae (BMA), and heterotrophic bacteria. Stable isotope tracers (as 15 NH z 4 and H 13 CO { 3) were added to mesocosms either via the surface water or pore water for the first 14 d of the 42-d experiment. Macroalgae and sediments exposed to ambient light and dark cycles rapidly took up label from both sources and retained label for at least 4 weeks after isotope additions ended. BMA dominated sediment uptake of 13 C and 15 N, initially accounting for 100% of total uptake. Over time, heterotrophic bacterial uptake became relatively more important, increasing from 0% on day 1 to 20-50% on day 42, indicating a close coupling between BMA and bacterial production. In treatments with macroalgae, sediment 13 C and 15 N uptake was , 40% lower than treatments without macroalgae, likely because of shading of the sediment surface by macroalgae, which decreased BMA production, which in turn decreased bacterial production. Overall, sediments served as a sink for C and N through uptake and retention by the microbial community, but retention was lower in the presence of macroalgae.

Nitrogen incorporation and retention by bacteria, algae, and fauna in a subtropical, intertidal sediment: An in situ^ 1^ 5N-labeling study

Limnology and …, 2007

We performed a 15 N-labeling study to investigate nitrogen incorporation and retention by the benthic microbial community (bacteria and benthic microalgae) and fauna in the intertidal sediment of the subtropical Australian Brunswick Estuary. The main experiment involved an in situ 15 N pulse-chase experiment. After injection of 15 NH z 4 into the sediment, 15 N was traced into bulk sediment, total hydrolyzable amino acids (THAAs, representing bulk proteinaceous biomass), the bacterial biomarker D-alanine, and fauna over a 30d period. Additional experiments included short-term (24 h) incubations of sediment cores injected with different 15 N-labeled substrates (NH z 4 , NO { 3 , urea, and an amino acid mixture) and sediment core incubations for analysis of benthic fluxes of O 2 , dissolved inorganic carbon, NH z 4 , NO { x , dissolved organic nitrogen, and N 2 . 15 N was rapidly incorporated and strongly retained in microbial biomass (THAAs) during the 30-d period in situ, indicating efficient recycling of 15 N by the benthic microbial community. Analysis of 15 N in D-alanine revealed a major bacterial contribution (50-100%) to total microbial 15 N incorporation and retention. 15 N was also incorporated into fauna via grazing on 15 N-labeled microbial biomass, but this was a negligible fraction (,1%) of total 15 N in the sediment. Altogether, results show that efficient recycling of nitrogen by the benthic microbial community can be an important mechanism for nitrogen retention in the sediment and an important pathway supporting benthic microbial production.

Fine‐scale mapping of land‐derived nitrogen in coral reefs by δ15N in macroalgae

Limnology and Oceanography, 2002

We measured the C/N ratio and Δ15N values of two brown macroalgae δl Padina spp. and Dictyota sp., which are distributed over all the subtropical fringing reefs of the Ryukyu Islands, Japan— to evaluate the feasibility of these algae as indicators of the terrestrial nitrogen load to the reef. The correlations between the distance from the shoreline and algal C/N ratio and surrounding NO concentrations were not clear, although their average values among the reefs seemed to indicate differences in nitrogen loadings from the land. The Δ15N values of these algae, on the other hand, linearly or curvilinearly decreased from 18‰ to 12‰ with increasing distance from the shoreline, indicating the difference in nitrogen sources available to macroalgae. The slope of the decline among eight study areas had different characters, which seemed to depend on the residence time of reef seawater and the fluxes of terrestrial nitrogen. Using Δ15N values of brown algae as an indicator, we confirmed that...

Fine-scale mapping of land-derived nitrogen in coral reefs by d15N in macroalgae

Limnology and Oceanography, 2002

We measured the C/N ratio and ␦ 15 N values of two brown macroalgae-Padina spp. and Dictyota sp., which are distributed over all the subtropical fringing reefs of the Ryukyu Islands, Japan-to evaluate the feasibility of these algae as indicators of the terrestrial nitrogen load to the reef. The correlations between the distance from the shoreline and algal C/N ratio and surrounding NO concentrations were not clear, although their average values among the Ϫ 3 reefs seemed to indicate differences in nitrogen loadings from the land. The ␦ 15 N values of these algae, on the other hand, linearly or curvilinearly decreased from ϩ8‰ to ϩ2‰ with increasing distance from the shoreline, indicating the difference in nitrogen sources available to macroalgae. The slope of the decline among eight study areas had different characters, which seemed to depend on the residence time of reef seawater and the fluxes of terrestrial nitrogen. Using ␦ 15 N values of brown algae as an indicator, we confirmed that primary producers, such as macroalgae on the reefs, assimilated land-derived nitrogen and successfully evaluated time-integrated effects of terrestrial nitrogen on coral reef algae, which had been missed by conventional monitoring of the water column nutrients.

Benthic algae control sediment-water column fluxes of organic and inorganic nitrogen compounds in a temperate lagoon

Limnology and Oceanography, 2003

Coastal lagoons are a common land-margin feature worldwide and function as an important filter for nutrients entering from the watershed. The shallow nature of lagoons leads to dominance by benthic autotrophs, which can regulate benthic-pelagic coupling. Here we demonstrate that both microalgae and macroalgae are important in controlling dissolved inorganic as well as organic nitrogen (DIN and DON) fluxes between the sediments and the water column. Fluxes of nitrogen (NH , NO , DON, urea, and dissolved free and combined amino acids [DFAA,

Fate of macroalgae in benthic systems: carbon and nitrogen cycling within the microbial community

Marine Ecology Progress …, 2010

High nutrient loading to coastal bays is often accompanied by the presence of bloomforming macroalgae, which take up and sequester large amounts of C and N while growing. This pool is temporary, however, as nuisance macroalgae exhibit a bloom and die-off cycle, influencing the biogeochemical functioning of these systems in unknown ways. The objective of this study was to trace the C and N from senescing macroalgae into relevant sediment pools. A macroalgal die-off event was simulated by the addition of freeze-dried macroalgae (Gracilaria spp.), pre-labeled with stable isotopes (13 C and 15 N), to sediment mesocosms. The isotopes were traced into bulk sediments and partitioned into benthic microalgal (BMA) and bacterial biomass using microbial biomarkers to quantify the uptake and retention of macroalgal C and N. Bulk sediments took up label immediately following the die-off, and macroalgal C and N were retained in the sediments for at least 2 wk. Approximately 6 to 50% and 2 to 9% of macroalgal N and C, respectively, were incorporated into the sediments. Label from the macroalgae appeared in both bacterial and BMA biomarkers, suggesting that efficient shuttling of macroalgal C and N between these communities may serve as a mechanism for retention of macroalgal nutrients within the sediments.

Benthic metabolism and nitrogen dynamics in a sub-tropical coastal lagoon: Microphytobenthos stimulate nitrification and nitrate reduction through photosynthetic oxygen evolution

Estuarine, Coastal and Shelf Science, 2012

Keywords: benthic fluxes denitrification dissimilatory nitrate reduction to ammonium (DNRA) microphytobenthos southern Moreton Bay a b s t r a c t Benthic oxygen and nutrient fluxes, and rates of nitrate reduction, were determined seasonally under light and dark conditions at four sites within a sub-tropical coastal lagoon (Coombabah Lake, Australia). Sediments at all sites were strongly heterotrophic acting as strong oxygen sinks and sources of dissolved inorganic nitrogen (DIN) in all seasons during both light and dark incubations. Sediment oxygen demand (SOD) and DIN effluxes were greatest during summer, but showed only a relatively small degree of seasonal variation. In contrast, there was a strong spatial trend in SOD and DIN effluxes, which were consistently greater at the sites with fine grained compared to the coarser sediments. Microphytobenthos (MPB) directly influenced SOD and DIN effluxes, with lower SOD and DIN effluxes measured during all light incubations. Strong correlations were found between sediment chlorophylla content and lightedark shifts in oxygen and ammonium fluxes (DO 2 and DNH 4 þ ), and between DO 2 and DNH 4 þ . Rates of total nitrate reduction were relatively low ranging from 3 to 26 mmol N m À2 h À1 and exhibited only minor seasonal variations. Dissimilatory nitrate reduction to ammonium (DNRA) was the dominant pathway for nitrate reduction, accounting for on average, 65 and 68% of total nitrate reduction during light and dark incubations, respectively. Nitrification was the dominant source of nitrate fuelling nitrate reduction processes, accounting for approximately 90% of total nitrate supply. In contrast to typical MPB colonised sediments, rates of nitrification and, as a consequence, nitrate reduction rates were consistently stimulated in the light, indicating that MPB primarily influenced these processes through photosynthetic oxygen evolution rather than through competition for inorganic N-species.

Nitrogen cycling in a deep ocean margin sediment (Sagami Bay, Japan)

Limnology and Oceanography, 2009

On the basis of in situ NO { 3 microprofiles and chamber incubations complemented by laboratory-based assessments of anammox and denitrification we evaluate the nitrogen turnover of an ocean margin sediment at 1450-m water depth. In situ NO { 3 profiles horizontally separated by 12 mm reflected highly variable NO { 3 penetration depths, NO { 3 consumption rates, and nitrification. On average the turnover time of the pore-water NO { 3 pool was ,0.2 d. Net release of NH z 4 during mineralization (0.95 mmol m 22 d 21 ) sustained a net efflux of ammonia (53%), nitrification (24%), and anammox activity (23%). The sediment had a relatively high in situ net influx of NO { 3 (1.44 mmol m 22 d 21 ) that balanced the N 2 production as assessed by onboard tracer experiments. N 2 production was attributed to prokaryotic denitrification (59%), anammox (37%), and foraminifera-based denitrification (4%). Anammox thereby represented an important nutrient sink, but the N 2 production was dominated by denitrification. Despite the fact that NO { 3 stored inside foraminifera represented ,80% of the total benthic NO { 3 pool, the slow intracellular NO { 3 turnover that, on average, sustained foraminifera metabolism for 12-52 d, contributed only to a minor extent to the overall N 2 production. The microbial activity in the surface sediment is a net nutrient sink of ,1.1 mmol N m 22 d 21 , which aligns with many studies performed in coastal and shelf environments. Continental margin areas can act as significant N sinks and play an important role in regional N budgets.

Effects of CO2 enrichment on benthic primary production and inorganic nitrogen fluxes in two coastal sediments

Scientific Reports, 2018

Ocean acidification may alter the cycling of nitrogen in coastal sediment and so the sediment-seawater nitrogen flux, an important driver of pelagic productivity. To investigate how this perturbation affects the fluxes of NO X − (nitrite/nitrate), NH 4 + and O 2 , we incubated estuarine sand and subtidal silt in recirculating seawater with a CO 2-adjusted pH of 8.1 and 7.9. During a 41-day incubation, the seawater kept at pH 8.1 lost 97% of its NO X − content but the seawater kept at pH 7.9 lost only 18%. Excess CO 2 increased benthic photosynthesis. In the silt, this was accompanied by a reversal of the initial NO X − efflux into influx. The estuarine sand sustained its initial NO X − influx but, by the end of the incubation, released more NH 4 + at pH 7.9 than at pH 8.1. We hypothesise that these effects share a common cause; excess CO 2 increased the growth of benthic microalgae and so nutrient competition with ammonia oxidising bacteria (AOB). In the silt, diatoms likely outcompeted AOB for NH 4 + and photosynthesis increased the dark/light fluctuations in the pore water oxygenation inhibiting nitrification and coupled nitrification/denitrification. If this is correct, then excess CO 2 may lead to retention of inorganic nitrogen adding to the pressures of increasing coastal eutrophication. Ocean acidification, a consequence of the absorption of atmospheric carbon dioxide, is expected to accelerate over the upcoming century, altering marine biota and associated ecosystem processes 1-3. Our ability to predict the functioning of the future high-CO 2 ocean, however, is still in its infancy 1,4,5. For the coastal ocean, such prediction is complicated by natural and anthropogenic phenomena rendering the seawater carbonate chemistry variable at timescales from seconds to years (reviewed by Waldbusser & Salisbury 6 , Mostofa et al. 3). Current research thus distinguishes between carbonate weather-the short-term variability in the seawater pH-pCO 2 system-and carbonate climate, the longer-term shift in the baseline pH-pCO 2 system 6. The latter may alter environmental conditions for microorganisms in coastal sediment that drive the remineralisation of organic matter and associated biogeochemical cycles 7. Given that benthic remineralisation provides 30-80% of the inorganic nutrients required by pelagic primary production 8-10 , ocean acidification-driven alterations of benthic nutrient cycles could have implications for coastal ecosystem functioning. The nitrogen cycle may be altered more than any other nutrient cycle in response to CO 2 enrichment (reviewed by Hutchins et al. 5). For example, studies have revealed evidence for CO 2-induced changes in the sediment-seawater inorganic nitrogen flux 11,12 , increased nitrogen fixation due to enhanced growth of diazotrophic cyanobacteria 13-15 , and inhibition of nitrification 7. Other studies, however, found no effects of CO 2 enrichment on benthic nitrification 16 and denitrification 17. Unravelling the mechanisms behind CO 2-induced changes in benthic nitrogen cycling is challenging because the microbial activity that drives nitrogen transformations is modulated by macrobenthic infauna reworking particles and ventilating burrows 11,18-26. In coastal waters where sunlight penetrates to the seabed, another complication exists: excess CO 2 may increase the photosynthesis of benthic microalgae 27,28 altering the activity of nitrogen transforming microbes and associated sediment-seawater inorganic nitrogen flux. Two mechanisms have been proposed; (1) benthic microalgae may outcompete ammonia-oxidizing microorganisms in the uptake of ammonia 29,30 , and (2) enhanced benthic O 2 evolution may inhibit dissimilatory nitrate reduction 29-33. Although