Hot Spots of Nitrification in the Elbe Estuary and Their Impact on Nitrate Regeneration

Sanders, Tina; Schöl, Andreas; Dähnke, Kirstin

doi:10.1007/s12237-017-0264-8

Cited by 41 publications

(46 citation statements)

References 37 publications

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“…According to the two end‐member mixing model, the occurrence of significant NH 4 + removal accompanying with NO 2 – addition has been observed in the upper JRE (Yan et al, ). The same phenomenon has been oft‐observed in many worldwide estuaries, such as the Pearl River (Dai et al, ), the Danshuei River estuary (Wen et al, ), and the Elbe estuary (Sanders et al, ). Like some major estuaries, including the Loire estuary (Middelburg & Nieuwenhuize, ) and the Elbe estuary (Dähnke et al, ), however, NO 3 – plots conservatively versus salinity in the JRE (Yan et al, ).…”

Section: Introductionsupporting

confidence: 69%

Biogeochemical Dynamics in a Eutrophic Tidal Estuary Revealed by Isotopic Compositions of Multiple Nitrogen Species

et al. 2019

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Estuaries sit at the land‐ocean boundary and act as natural reactors for nitrogen (N) transformations among numerous forms. Superimposing onto physical mixing, biological processes lead to nonconservative N behavior in estuaries. Under the coinfluences of biological alteration and multiple end‐members, however, some N species can exhibit apparent conservation. To explore N dynamics and potential mechanisms that modulate the mixing behaviors, we measured concentrations and natural isotopic compositions of multiple N species (nitrate: NO3−, nitrite: NO2−, ammonium: NH4+, and particulate nitrogen) in a typical eutrophic estuary in southern China. Additionally, N uptake and oxidation rates were measured by using isotope labelling techniques to evaluate processes potentially offsetting the conservative mixing of specific N pools. We found that NO3− followed conservative two end‐member mixing with dual isotopes varying in a narrow range (<1–2‰) due to low microbial preferences. Moreover, δ15N‐NO2− revealed a nonconservative pattern with an involvement of multiple end‐members. The dominant N transformation processes shifted downstream. In the upper estuary, ammonia oxidation (~20 μmol L−1 day−1) dominated NH4+ removal and was accompanied by NO2− accumulation. In the middle‐lower estuary, NH4+ uptake became dominant, with phytoplankton showing strong preference for it over NO3− and NO2−. Based on measured NH4+ uptake rates (9.1–12.5 μmol L−1 day−1 in the light and 0.9 μmol L−1 day−1 in the dark), short water residence time (<1 day) was required to maintain the conservative mixing. Coupling N isotopes in multiple nitrogen species with measurements of N uptake and nitrification, we successfully uncovered N dynamics and distinguished biological processes from physical mixing.

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Section: Introductionsupporting

confidence: 69%

Biogeochemical Dynamics in a Eutrophic Tidal Estuary Revealed by Isotopic Compositions of Multiple Nitrogen Species

et al. 2019

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“…Intriguingly, recent rate measurements revealed that both nitrification and denitrification can occur at high rates in the port region: Deek et al (2013) found highest denitrification rates in the sediments at stream km ∼630, and Sanders et al (2017) found highest nitrification rates in the water column in the same section of the estuary. This implies that both processes can potentially contribute to N 2 O production in the region of the Hamburg port where the O 2 minimum is most pronounced.…”

Section: Discussion N 2 O Source Regions In the Estuarymentioning

confidence: 97%

High Resolution Measurements of Nitrous Oxide (N2O) in the Elbe Estuary

et al. 2017

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Nitrous oxide (N 2 O) is one of the most important greenhouse gases and a major sink for stratospheric ozone. Estuaries are sites of intense biological production and N 2 O emissions. We aimed to identify hot spots of N 2 O production and potential pathways contributing to N 2 O concentrations in the surface water of the tidal Elbe estuary. During two research cruises in April and June 2015, surface water N 2 O concentrations were measured along the salinity gradient of the Elbe estuary by using a laser-based on-line analyzer coupled to an equilibrator. Based on these high-resolution N 2 O profiles, N 2 O saturations, and fluxes across the surface water/atmosphere interface were calculated. Additional measurements of DIN concentrations, oxygen concentration, and salinity were performed. Highest N 2 O concentrations were determined in the Hamburg port region reaching maximum values of 32.3 nM in April 2015 and 52.2 nM in June 2015. These results identify the Hamburg port region as a significant hot spot of N 2 O production, where linear correlations of AOU-N 2 O xs indicate nitrification as an important contributor to N 2 O production in the freshwater part. However, in the region with lowest oxygen saturation, sediment denitrification obviously affected water column N 2 O saturation. The average N 2 O saturation over the entire estuary was 201% (SD: ±94%), with an average estuarine N 2 O flux density of 48 µmol m −2 d −1 and an overall emission of 0.18 Gg N 2 O y −1 . In comparison to previous studies, our data indicate that N 2 O production pathways over the whole estuarine freshwater part have changed from predominant denitrification in the 1980s toward significant production from nitrification in the present estuary. Despite a significant reduction in N 2 O saturation compared to the 1980s, N 2 O concentrations nowadays remain on a high level, comparable to the mid-90s, although a steady decrease of DIN inputs occurred over the last decades. Hence, the Elbe estuary still remains an important source of N 2 O to the atmosphere.

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“…This pattern of seaward-decreasing NO 3 − was similar to that of NO 3 − distributions seen in other coastal areas. For example, in the Pearl River Estuary (China) [5,28], San Francisco Bay (US) [29], and Elbe Estuary (Germany) [30], higher NO 3 − concentrations occur in the upper bay stretches with a maximum value of >100 µmol•L −1 , and NO 3 − mainly originates from local river inputs. The significantly high concentrations of NO 2 − , NO 3 − , and NH 4 + only occurred at station Z1, which may have been influenced by the local contaminant discharge.…”

Section: Limiting Nutrients In Zhanjiang Baymentioning

confidence: 99%

Assessing Seasonal Nitrate Contamination by Nitrate Dual Isotopes in a Monsoon-Controlled Bay with Intensive Human Activities in South China

Cao

Lao

et al. 2020

IJERPH

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Nitrate (NO3−) dual isotope analysis was performed in Zhanjiang Bay, which is a closed bay with intensive human activities in South China, to investigate seasonal changes in the main NO3− sources and their biogeochemical processes in the monsoon-controlled climate. The relatively low N/P ratios in Zhanjiang Bay suggests that nitrogen (N) is a limiting nutrient, which indicates that the increase of N is favorable for phytoplankton proliferation. However, a sufficient amount of ammonium was found in our study area owing to intensive human activities, which can support biological processes. Thus, less NO3− biological processes were found, indicating that NO3− isotopic characteristics may reveal details of the mixing from various sources. The Bayesian mixing model showed that NO3− in the upper bay originated from manure (43%), soil N (30%), N fertilizer (17%), and N precipitation (10%) during winter, which reflects the local human activities; while NO3- sources during summer were mainly N fertilizer (36%), soil N (32%), and manure (31%), indicating the source as the runoff from the upper river basin. Our results suggest that nitrate dual-isotope was very useful for tracing the main NO3− sources in the condition of the sufficient ammonium, and runoff exerted an important impact on the shift in NO3− sources between both the local source and the source from the upper river basin during the two seasons in this monsoon-controlled bay.

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Hot Spots of Nitrification in the Elbe Estuary and Their Impact on Nitrate Regeneration

Cited by 41 publications

References 37 publications

Biogeochemical Dynamics in a Eutrophic Tidal Estuary Revealed by Isotopic Compositions of Multiple Nitrogen Species

Biogeochemical Dynamics in a Eutrophic Tidal Estuary Revealed by Isotopic Compositions of Multiple Nitrogen Species

High Resolution Measurements of Nitrous Oxide (N2O) in the Elbe Estuary

Assessing Seasonal Nitrate Contamination by Nitrate Dual Isotopes in a Monsoon-Controlled Bay with Intensive Human Activities in South China

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