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  • Ammonium; Benguela Upwelling System; BUSUC 1; Continuous Segmented Flow Analyzer, SEAL Analytical, QuAAtro39; CTD, Sea-Bird SBE 911plus; CTD/Rosette; CTD-RO; DATE/TIME; DEPTH, water; Event label; Field observation; LATITUDE; LONGITUDE; M157; M157_10-7; M157_11-4; M157_12-2; M157_14-2; M157_16-25; M157_16-3; M157_16-6; M157_17-16; M157_17-2; M157_24-1; M157_25-1; M157_2-8; M157_28-1; M157_2-9; M157_36-2; M157_41-14; M157_42-2; M157_43-2; M157_43-6; M157_9-2; Meteor (1986); Microstructure profiler, Sea & Sun Technology, MSS90L; Namibia; Nitrate; Nitrite; nutrients; Oxygen; oxygen minimum zone; PCTD-RO; Phosphate; PumpCTD/Rosette; Salinity; Sample code/label; Silicate; Station label; Temperature, water; Water mass; water mass fraction  (1)
  • Bering Sea  (1)
  • Germany  (1)
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  • 1
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    Fate of nitrate during groundwater recharge in a fractured karst aquifer in Southwest Germany (2021)
    Visser, Anna-Neva ; Lehmann, Moritz F. ; Rügner, Hermann ; [et al.]
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-08-08
    Description: Over the past decades, fractured and karst groundwater systems have been studied intensively due to their high vulnerability to nitrate (NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉) contamination, yet nitrogen (N) turnover processes within the recharge area are still poorly understood. This study investigated the role of the karstified recharge area in NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 transfer and turnover by combining isotopic analysis of NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 and nitrite (NO〈sub〉2〈/sub〉〈sup〉−〈/sup〉) with time series data of hydraulic heads and specific electrical conductivity from groundwater monitoring wells and a karstic spring in Germany. A large spatial variability of groundwater NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 concentrations (0.1–0.8 mM) was observed, which cannot be explained solely by agricultural land use. Natural-abundance N and O isotope measurements of NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 (δ〈sup〉15〈/sup〉N and δ〈sup〉18〈/sup〉O) confirm that NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 derives mainly from manure or fertilizer applications. Fractional N elimination by denitrification is indicated by relatively high δ〈sup〉15〈/sup〉N- and δ〈sup〉18〈/sup〉O-NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉 values, elevated NO〈sub〉2〈/sub〉〈sup〉−〈/sup〉 concentrations (0.05–0.14 mM), and δ〈sup〉15〈/sup〉N-NO〈sub〉2〈/sub〉〈sup〉−〈/sup〉 values that were systematically lower than the corresponding values of δ〈sup〉15〈/sup〉N-NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉. Hydraulic and chemical response patterns of groundwater wells suggest that rain events result in the displacement of water from transient storage compartments such as the epikarst or the fissure network of the phreatic zone. Although O〈sub〉2〈/sub〉 levels of the investigated groundwaters were close to saturation, local denitrification might be promoted in microoxic or anoxic niches formed in the ferrous iron-bearing carbonate rock formations. The results revealed that (temporarily) saturated fissure networks in the phreatic zone and the epikarst may play an important role in N turnover during the recharge of fractured aquifers.
    Description: Projekt DEAL
    Keywords: ddc:551.49 ; Nitrate ; Karst ; Groundwater recharge ; Stable isotopes ; Germany
    Language: English
    Type: doc-type:article
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    CITATION GEO-LEO
  • 2
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    Inorganic nutrient measurements in the Benguela Upwelling System during METEOR cruise M157 (2023)
    PANGAEA
    Details
    Publication Date: 2024-06-05
    Description: Upwelling systems are significant sources of atmospheric nitrous oxide (N₂O). The Benguela Upwelling System is one of the most productive regions worldwide and a temporally variable source of N₂O. Strong O₂ depletions above the shelf are favoring periodically OMZ formations. We aimed to assess underlying N₂O production and consumption processes on different temporal and spatial scales during austral winter in the Benguela Upwelling System, when O₂-deficiency in the water column is relatively low. The fieldwork took place during the cruise M157 (August 4ᵗʰ – September 16ᵗʰ 2019) onboard the R/V METEOR. This expedition included four close-coastal regions around Walvis Bay at 23°S, which presented the lowest O₂ concentrations near the seafloor and thus may provide hotspots of N₂O production. Seawater was collected in 10 L free-flow bottles by using a rosette system equipped with conductivity-temperature-depth (CTD) sensors (SBE 911plus, Seabird-electronics, USA). Concentrations of inorganic nutrients (PO₄³⁻, NH₄⁺, NO₃⁻, NO₂⁻, and SiO₂) were measured colorimetrically according to Grasshoff et al. (1999) by means of a continuous segmented flow analyzer (SEAL Analytical, QuAAtro39). To determine the water mass fractions along the sampling transects, vertical profiles were collected using a free-falling microstructure profiler (MSS90L, Sea & Sun Technology). Temperature, dissolved oxygen, and salinity were measured with a CTD system consisting of a SeaBird 911+ probe, mounted on a sampling rosette.
    Keywords: Ammonium; Benguela Upwelling System; BUSUC 1; Continuous Segmented Flow Analyzer, SEAL Analytical, QuAAtro39; CTD, Sea-Bird SBE 911plus; CTD/Rosette; CTD-RO; DATE/TIME; DEPTH, water; Event label; Field observation; LATITUDE; LONGITUDE; M157; M157_10-7; M157_11-4; M157_12-2; M157_14-2; M157_16-25; M157_16-3; M157_16-6; M157_17-16; M157_17-2; M157_24-1; M157_25-1; M157_2-8; M157_28-1; M157_2-9; M157_36-2; M157_41-14; M157_42-2; M157_43-2; M157_43-6; M157_9-2; Meteor (1986); Microstructure profiler, Sea & Sun Technology, MSS90L; Namibia; Nitrate; Nitrite; nutrients; Oxygen; oxygen minimum zone; PCTD-RO; Phosphate; PumpCTD/Rosette; Salinity; Sample code/label; Silicate; Station label; Temperature, water; Water mass; water mass fraction
    Type: Dataset
    Format: text/tab-separated-values, 1660 data points
    Location Call Number Limitation Availability
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    DATA PANGAEA
  • 3
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    Origin of the deep Bering Sea nitrate deficit : constraints from the nitrogen and oxygen isotopic composition of water column nitrate and benthic nitrate fluxes (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 19 (2005): GB4005, doi:10.1029/2005GB002508.
    Description: On the basis of the normalization to phosphate, a significant amount of nitrate is missing from the deep Bering Sea (BS). Benthic denitrification has been suggested previously to be the dominant cause for the BS nitrate deficit. We measured water column nitrate 15N/14N and 18O/16O as integrative tracers of microbial denitrification, together with pore water-derived benthic nitrate fluxes in the deep BS basin, in order to gain new constraints on the mechanism of fixed nitrogen loss in the BS. The lack of any nitrate isotope enrichment into the deep part of the BS supports the benthic denitrification hypothesis. On the basis of the nitrate deficit in the water column with respect to the adjacent North Pacific and a radiocarbon-derived ventilation age of ∼50 years, we calculate an average deep BS (〉2000 m water depth) sedimentary denitrification rate of ∼230 μmol N m−2 d−1 (or 1.27 Tg N yr−1), more than 3 times higher than high-end estimates of the average global sedimentary denitrification rate for the same depth interval. Pore water-derived estimates of benthic denitrification were variable, and uncertainties in estimates were large. A very high denitrification rate measured from the base of the steep northern slope of the basin suggests that the elevated average sedimentary denitrification rate of the deep Bering calculated from the nitrate deficit is driven by organic matter supply to the base of the continental slope, owing to a combination of high primary productivity in the surface waters along the shelf break and efficient down-slope sediment focusing along the steep continental slopes that characterize the BS.
    Description: This study was supported by NSF grants OCE-0136449 and OCE-9981479 to D. M. S., OCE-0118126 and OCE-0324987 to D. C. M., and DFG grant LE 1326/1-1 to M. F. L. The BS cruise was funded by grant OPP-9912122.
    Keywords: Bering Sea ; Denitrification ; Nitrate isotopes
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
    Format: text/plain
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    PAPER (OA)
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