New Deoxygenation Threshold for N2 and N2O Production in Coastal Waters and Sediments

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 148:155-168 (1997) - doi:10.3354/meps148155 Monitoring and modeling primary production in coastal waters: studies in Massachusetts Bay 1992-1994 Kelly JR, Doering PH During 1992-1994, we made shipboard incubations suitable for determining rates of primary production in water from Boston Harbor, Massachusetts Bay, and Cape Cod Bay (Massachusetts, USA). These measurements were part of an extensive baseline monitoring program to characterize water quality prior to diversion of effluent from Boston Harbor directly into Massachusetts Bay via a submarine outfall diffuser. Production (P) was measured using whole-water samples exposed to irradiance (I) levels from ~5 to 2000 µE m-2 s-1. P-I incubations were performed on 6 surveys a year, spaced to capture principal features of the annual production cycle. The number of stations and depths examined varied between years. There were 10 stations and 2 depths sampled in 1992-1993. In 1994, we performed in-depth studies at 2 stations (Boston Harbor's edge and western Massachusetts Bay) by sampling 4 depths. Using depth-intensive 1994 data a simple empirical regression model, using information on chlorophyll biomass, incident daily light, and the depth of the photic zone, predicted integrated primary production rates derived from P-I incubations. The regression model was virtually the same as described for other coastal waters, giving confidence in general use of the model as an extrapolation tool. Using the 1994-based empirical model, we obtained favorable comparisons with production rates modeled from 1992-1993 P-I incubations. Combining the regression model with data on chlorophyll, light, and the photic zone collected on frequent hydrographic surveys (up to 16 yr-1), annual primary production was estimated for 1992-1994. Primary production in an intensively studied region of western Massachusetts Bay (21 hydrographic profile stations in an area ~100 km2) ranged from 386 to 468 g C m-2 yr-1. For a station at the edge of Boston Harbor near Deer Island extrapolations suggested production rates of 263 to 546 g C m-2 yr-1. Based on 2 stations in central Cape Cod Bay (1992-1993 only), model extrapolations suggested an annual production of 527 to 613 g C m-2 yr-1. Analyses using incubation and modeling results suggested that production variability was strongly related to fluctuations in incident irradiance, especially at daily to seasonal time scales. Chlorophyll variability secondarily influenced production, especially at seasonal to annual time scales. Finally, we provide a case where equivalent production was achieved in environments with contrasting water quality (nutrient and chlorophyll concentrations) because of variations in the depth of the photic zone (controlled by both chlorophyll and non-chlorophyll turbidity). Comparative analyses showed that our study estimates of primary production were consistent with the literature on nutrient-rich shelf environments. In conclusion, our study validated an empirical modeling approach to determining primary production in coastal marine waters. Primary production · Monitoring · Modeling · Massachusetts Bay · Boston Harbor Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 148. Publication date: February 27, 1997 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1997 Inter-Research.

Environmental controls on marine methane oxidation : from deep-sea brines to shallow coastal systems

Current estimates indicate that atmospheric nitrogen deposition is responsible for 26 to over 70% of “new” nitrogen (N) input to North Carolina estuaries and coastal waters. Concentrations of N in coastal rainfall events in a 2-yr period (August 1990 to 1992) ranged from 0.7 to 144 μM for NO 3 - and 0.5 to 164 μM for NH 4 + . The δ15N values of the NO 3 - and the NH 4 + were determined in 15 rain events. NH4 + values averaged-3.13‰ (range:-12.5 to+3.6), while NO 3 - plus dissolved organic N fractions had an average δ15N of+1.0‰ (range:-2.0 to+4.7). The uptake of this isotopically light N into particulate N, in parallel with primary productivity and biomass (as chlorophyll a) determinetions, was examined in microcosm and mesocosm bioassays. As phytoplankton productivity and biomass increased with added rainwater N, the δ15N of particulate N decreased. To investigate the effects of significant atmospheric N loading with stable isotope tracers, we measured the δ15N of the>1 μm fraction from surrounding coastal waters. Owing to the episodic nature of atmospheric deposition and the great variation in N loading with each event, a simple assessment of the atmospheric contribution was not possible. During a period in which rainfall inputs were significant and frequent (August 1992), δ15N values were several ‰ more negative than during periods of drought (Fall 1990). These experiments and observations emphasize the contribution of atmospheric nitrogen deposition to “new” production in coastal waters.

Methane (CH4) is a key greenhouse gas. Coastal areas account for a major proportion of marine CH4 emissions. Eutrophication and associated bottom water hypoxia enhance CH4 production in coastal sediments. Here, we assess the fate of CH4 produced in sediments at a site in a seasonally anoxic eutrophic coastal marine basin (Scharendijke, Lake Grevelingen, the Netherlands) in spring (March) and late summer (September) in 2020. Removal of CH4 in the sediment through anaerobic oxidation with sulfate (SO42-) is known to be incomplete in this system, as confirmed here by only slightly higher values of δ13C-CH4 and δD-CH4 in the porewater in the shallow sulfate-methane-transition zone (~5-15 cm sediment depth) when compared to deeper sediment layers. In March 2020, when the water column was fully oxygenated, CH4 that escaped from the sediment was at least partially removed in the bottom water through aerobic oxidation. In September 2020, when the water column was anoxic below ~35 m water depth, CH4 accumulated to high concentrations (up to 73 µmol L-1) in the waters below the oxycline. The sharp counter gradient in oxygen and CH4 concentrations at ~35 m depth and increase in δ13C-CH4 and δD-CH4 above the oxycline indicate mostly aerobic water column removal of CH4. Water column profiles of particulate and dissolved Fe and Mn suggest redox cycling of both metals at the oxycline, pointing towards a potential role of metal oxides in CH4 removal. Water column profiles of NH4+ and NO3- indicate removal of both solutes near the oxycline. Analyses of 16S rRNA gene sequences retrieved from the water column reveal the presence of aerobic CH4 oxidizing bacteria (Methylomonadaceae) and anaerobic methanotrophic archaea (Methanoperedenaceae), with the latter potentially capable of NO3- and/or metal-oxide dependent CH4 oxidation, near the oxycline. Overall, our results indicate sediment and water column removal of CH4 through a combination of aerobic and anaerobic pathways, which vary seasonally. Some of the CH4 appears to escape from the surface waters to the atmosphere, however. We conclude that eutrophication may make coastal waters a more important source of CH4 to the atmosphere than commonly assumed.

Performance of Fast Repetition Rate fluorometry based estimates of primary productivity in coastal waters

Primary production in the Gulf of Mexico coastal waters using “remotely-sensed” trophic category approach

Most of the tropical coastline between 25° N and 25° S latitude is vegetated by forested wetlands called mangroves (McGill, 1958). These plant communities have received considerable botanical investigation because of their unique taxonomy and ovivipary (Tomlinson, 1986), and the diverse fauna that inhabit these coastal areas (Macnae, 1968;Chapman, 1976). However, the ecology of mangroves is poorly understood, particularly the significance of these ecosystems to the productivity and nutrient cycling of estuarine and adjacent coastal waters. It has been suggested that the high fishery yields of coastal tropical waters are due to the presence of these communities (Macnae, 1974; Turner, 1977; Jothy, 1984), yet there is no evidence of a cause and effect relationship for mangroves and fisheries (Macnae, 1974). Thus the function of these wetlands in supporting secondary productivity continues to be a complex issue. Mangroves may also influence the primary productivity of coastal waters by controlling the fate of dissolved nutrients and suspended sediments. Mangroves are considered a source of organic detritus yet a nutrient sink, contributing to the confusion of their role in coastal processes.

The effect of ultraviolet radiation (UVR) and photosynthetically-active radiation (PAR) on the conversion of dissolved dimethylsulfoniopropionate (DMSPd) to dimethylsulfide (DMS) was studied in coastal, shelf and open ocean waters. Unfiltered and 0.8 μm filtered seawater samples were incubated in the dark or exposed to solar radiation for ~6 h followed by post-exposure, dark incubations with tracer additions of 35S-DMSPd. End-products resulting from 35S-DMSPd metabolism were quantified, including 35S-DMS, total volatile 35S and particle-assimilated 35S. Exposure of productive coastal and shelf waters of the Gulf of Mexico to UVR+PAR inhibited the initial rates of 35S-DMSPd consumption and the rates of 35S assimilation into cellular macromolecules by 12 to 87% and 13 to 81% respectively, compared to dark controls. After 24 h of post-exposure, dark incubation, however, the assimilation of 35S in the UVR+PAR treatments was the same as observed in dark controls. In contrast, the 35S-DMS yield from DMSPd consumption was always higher in UVR+PAR treatments than in dark controls after 24 h post-exposure, dark incubation. Exposure of mesotrophic Mediterranean Sea or oligotrophic Sargasso Sea water samples to UVR+PAR resulted in variable effects on DMS yields, with two out of four experiments showing lower, and two out of four showing higher DMS yields from 35S-DMSP compared with dark controls. In the Gulf of Mexico and Sargasso Sea, the higher 35S-DMS yields caused by UVR+PAR exposure were offset by strong inhibitory effects of UVR+PAR on 35S-DMSPd consumption rates, leading to lower 35S-DMS production overall. When DMS production from DMSPd was compared to DMS production from total DMSP, we found that only 20 to 75% of the produced DMS came from DMSPd, in one case with the lowest contributions from DMSPd in UVR+PAR treatments. Our results suggest that UVR exposure is likely an important factor promoting higher DMS yields from DMSPd in productive coastal waters, and that a substantial fraction of DMS production comes from non-DMSPd-derived sources.

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 423:1-14 (2011) - DOI: https://doi.org/10.3354/meps09010 FEATURE ARTICLE Photochemical transformation of terrestrial dissolved organic matter supports hetero- and autotrophic production in coastal waters Anssi V. Vähätalo1,2,*, Hanna Aarnos1,3, Laura Hoikkala1,4, Risto Lignell1,4 1Tvärminne Zoological Station, University of Helsinki, Hanko, Finland 2Present address: ARONIA Coastal Zone Research Team, Åbo Akademi University & Novia University of Applied Sciences, Ekenäs, Finland 3Present address: Department of Environmental Sciences, University of Helsinki, Helsinki, Finland 4Present address: Marine Center, Finnish Environmental Institute, Helsinki, Finland *Email: anssi.vahatalo@helsinki.fi ABSTRACT: We assessed the responses of a nitrogen (N)-limited <10 µm plankton community from the Baltic Sea to the 12 d photochemical transformation of dissolved organic matter (DOM). The photochemical transformation of DOM increased the biomass and the production of heterotrophic bacteria, flagellates, and ciliates in the following 10 d bioassay. The succession of heterotrophic plankton indicated a 3-level trophic transfer of photoproduced bioavailable DOM through bacteria and flagellates to ciliates. The photochemical transformation of DOM also stimulated the biomass and the production of phytoplankton through the photoproduction of bioavailable N initially incorporated into bacterial biomass. The grazing of bacterioplankton supplied N to phytoplankton directly, presumably due to mixotrophy, and indirectly by releasing dissolved N. The carbon stable isotope signature of plankton biomass was similar to that of allochthonous carbon, indicating that the photochemical transformations concerned primarily terrestrial DOM and therefore represented a microbial link between terrestrial DOM and planktonic production. The bacterial production stimulated by the photochemically produced labile DOM was related to the number of photons absorbed during the photochemical transformation of DOM for the determination of apparent quantum yield. According to the apparent quantum yield, the calculated summertime photoproduction of labile substrates contributes 2 to 5% to total bacterial production in the northern Baltic Sea. According to this study, the photochemical transformation of terrestrial DOM influences not only the initial production of bacterioplankton but can also stimulate higher trophic levels and autotrophic plankton in coastal waters. KEY WORDS: Dissolved organic nitrogen · Apparent quantum yield · Trophic transfer · Photochemistry · Bacterioplankton · Phytoplankton Full text in pdf format Information about this Feature Article NextCite this article as: Vähätalo AV, Aarnos H, Hoikkala L, Lignell R (2011) Photochemical transformation of terrestrial dissolved organic matter supports hetero- and autotrophic production in coastal waters. Mar Ecol Prog Ser 423:1-14. https://doi.org/10.3354/meps09010 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 423. Online publication date: February 10, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

Total Suspended Matter (TSM) are fine materials which suspended and floated in water column. Water column could be turbid due to TSM that reduces the depth of light penetration and causes low productivity in coastal waters. The objective of this study was to estimate TSM concentration using Landsat 8 OLI data in Lombok coastal waters Indonesia by using empirical and analytic approach between three visible bands of Landsat 8 OLI subsurface reflectance (OLI 2, OLI 3 and OLI 4) and field data. The accuracy of model was tested using error estimation and statistical analysis. Colour of waters, transparency and reflectance values showed, the clear water has high transparency and low reflectance while the turbid waters have low transparency and high reflectance. The estimation of TSM concentrations in Lombok coastal waters are 0.39 to 20.7 mg/l. TSM concentrations becoming high when it is on coast and low when it is far from the coast. The statistical analysis showed that TSM model from Landsat 8 OLI data could describe TSM from field measurement with correlation 91.8% and RMSE value 0.52. The t-test and f-test showed that the TSM derived from Landsat 8 OLI and TSM measured in field were not significantly different.

Effects of marine produced organic matter on the potential estuarine capacity of NOx− removal

Ocean remote sensing is the only technique capable of quantitatively detecting long-term and global variability of marine primary production. However, because the spectral curves of light derived from satellite sensors have a limited capability to identify the physiological state of phytoplankton, the direct estimation of photoadaptive variables, such as daily maximum carbon fixation in a water column $({P_{{{\rm opt}}}^{{\rm b}}})$ , from the spectra of satellite sensors is difficult. This difficulty results in most of the errors in ocean color-based primary productivity models. In this paper, algorithms were developed to estimate $P_{{{\rm opt}}}^{{\rm b}}$ using statistical models known as support vector machines (SVM). The algorithms were run using three different inputs: sea surface temperature (SST); both SST and sea surface chlorophyll a concentration; and SST, sea surface chlorophyll a concentration and photosynthetically active radiation (PAR) together. The results indicate that the algorithm using the three inputs (SST, sea surface chlorophyll a concentration, and PAR) had the best performance. The algorithms based on the SVM had better results than the general statistical regression method. Using the new $P_{{{\rm opt}}}^{{\rm b}}$ algorithm, the performances of the previous primary production models, including the vertically generalized production model and the statistical model developed in our earlier research, were improved. In contrast to the previous algorithm, the global primary productivity estimated using the new $P_{{{\rm opt}}}^{{\rm b}}$ algorithm showed regional changes, with higher primary productivity in most open ocean areas and lower primary productivity in coastal waters.

Environmental conditions, physiology and community composition of phytoplankton and the carbon and nitrogen isotope signature (δ13CPOC and δ15NPN) of particulate organic matter (POM) often covary across marine environments. However, little was known on the link of δ13CPOC and δ15NPN and the community and biochemical composition of phytoplankton. In this study, particulate organic carbon (POC) and nitrogen (PN), δ13CPOC, δ15NPN, phytoplankton community composition and biomass were determined during summer, along with environmental variables, in the shelf of the northern South China Sea influenced by the Pearl River plume, upwelling and anticyclonic eddy. Our results show that variability in δ13CPOC and δ15NPN along an environmental gradient is coupled with shifts in phytoplankton community composition and carbon to chlorophyll a (C:Chl a) ratio of phytoplankton. Low δ13CPOC values (−28.4 to −27.0‰) at nearshore stations (salinity &lt;21) were primarily due to terrestrial POM input. High δ13CPOC (&gt;−21.0‰) and δ15NPN (&gt;5.6‰) values are most likely attributed to high abundance of diatoms induced by riverine nutrients in the plume‐impacted waters with intermediate salinity (21&lt; salinity &lt;33). Low δ13CPOC (&lt;−22.0‰) and δ15NPN (−1.1–3.7‰) values are associated with high abundance of slow‐growing cyanobacteria in the oligotrophic area (salinity &gt;33), where the lowest δ15NPN is most likely attributed to high abundance of N2‐fixing Trichodesmium spp., due to the influence of the anticyclonic eddy. Therefore, hydrodynamics modulates the biochemical composition and community composition of phytoplankton, leading to changes in δ13CPOC and δ15NPN. Our findings advance our understanding of the coupling of physical and biogeochemical processes in marginal seas.

Prokaryotic community assembly patterns and nitrogen metabolic potential in oxygen minimum zone of Yangtze Estuary water column

The consequences of detrimental alterations caused to the natural nitrogen (N) cycle are manifold. To tackle problems, such as eutrophication of coastal marine and lacustrine environments, or increasing emissions of greenhouse gas nitrous oxide (N2O), requires a clear understanding of the microbial N cycle. A promising tool to study N transformations is the measurement of the stable isotope composition of N compounds. The overall goal of this project was to improve the understanding of N transformation pathways and associated isotope effects, using the meromictic northern and the monomictic southern basins of Lake Lugano as natural model systems. Toward this goal, we collected samples from the water column of both basins for dissolved inorganic nitrogen (DIN) analyses (including N2:Ar, N2O), molecular microbiological phylogenetic analyses, 15N-labeling experiments (water column and sediments), and stable N and O isotope (and N2O isotopomer) measurements. First, we identified the main processes responsible for fixed N elimination in the Lake Lugano north basin. The stable redox transition zone (RTZ) in the mid-water column provides environmental conditions that are favorable for both, anaerobic ammonium oxidation (anammox), as well as sulfur-driven denitrification. Previous marine studies suggested that sulfide (H2S) inhibits the anammox reaction. In contrast to this we demonstrated that anammox bacteria coexist with sulfide-dependent denitrifiers in the water column of the Lake Lugano north basin. The maximum potential rates of both processed were comparatively low, but consistent with nutrient fluxes calculated from concentration gradients. Furthermore, we showed that organotrophic denitrification is a negligible nitrate-reducing pathway in the Lake Lugano north basin. Based on these findings, we next interpreted the N and O isotope signatures in the Lake Lugano north basin. Anammox and sulfide-dependent denitrification left clear N (in NO3- and NH4+) and O (in NO3-) isotope patterns in the water column. However, the associated isotope effects were low compared to previous reports on isotope fractionation by organotrophic denitrification and aerobic ammonium oxidation. We attribute this apparent under-expression to two possible explanations: 1) The biogeochemical conditions (i.e., substrate limitation, low cell specific N transformation rates) that are particularly conducive in the Lake Lugano RTZ to an N isotope effect under-expression at the cellular-level, or 2) a low process-specific isotope fractionation at the enzyme-level. Moreover, an 18O to 15N enrichment ratio of ~0.89 associated with NO3- reduction suggested that the periplasmic dissimilatory nitrate reductase Nap was more important than the membrane-bound dissimilatory Nar. While in the meromictic north basin, most fixed N elimination took place within the water column RTZ, seasonal mixing and re-oxygenation of the water column in the south basin suggests N2 production within the sediments. We showed that denitrification was the major benthic NO3- reduction pathway in the southern basin. Benthic anammox and dissimilatory nitrate reduction to ammonium (DNRA) rates remained close to the detection limit. A comparison between benthic N2 production rates and water column N2 fluxes revealed that during anoxic bottom water conditions, ~40% of total N2 production was associated with benthic and ~60% with pelagic processes. This quantitative partitioning was confirmed by N isotope analysis of water column NO3-. The N isotope enrichment factor associated with total NO3- reduction was ~14‰. This translates into a sedimentary N2 contribution of 36-51%, if canonical assumptions for N isotope fractionation associated with water column (15ewater = 20-25‰) and sedimentary (15esed = 1.5-3‰) denitrification are made. Finally, we compared the N2O production and consumption pathways in the northern and southern basin and found contrasting N2O dynamics. Maximum N2O concentrations in the south basin (>900 nmol L-1) greatly exceeded maximum concentrations in the north basin ( 32‰ in the south basin indicated nitrification via hydroxylamine (NH2OH) oxidation as the prime N2O source, whereas in the north basin N2O production was attributed to nitrifier denitrification. In the north basin, N2O was completely reduced within the RTZ. This chemolithotrophic N2O reduction occurred with an 18O to 15N enrichment ratio of ~2.5, which is consistent with previous reports for organotrophic N2O reduction. In conclusion, our study highlights the importance of chemolithotrophic processes in aquatic ecosystems. Moreover, the expression of N isotope fractionation can be variable in nature and depends on various factors such as the pathways of NO3- dissimilation (organotrophic vs. chemolithotrophic), the main catalyzing enzymes, the pathways of NH4+ oxidation (nitrification vs. anammox), and the controlling environmental conditions (e.g., substrate limitation, cell specific N transformation rates). Hence, this study suggests to refrain from universal, canonical assumptions of N isotope fractionation in N budget calculations. Additional stable isotope measurements such as O isotopes in NO3-, or the 15N site preference in N2O are powerful tools to identify and quantify microbial N transformation pathways occurring simultaneously or in close vicinity. For a successful interpretation of such data, however, a mechanistic understanding of the processes leading to certain characteristic isotopic signatures in the environment is needed.