scholarly journals Deep-water inflow event increases sedimentary phosphorus release on a multi-year scale

2021 ◽  
Author(s):  
Astrid Hylén ◽  
Sebastiaan J. van de Velde ◽  
Mikhail Kononets ◽  
Mingyue Luo ◽  
Elin Almroth-Rosell ◽  
...  
Keyword(s):  
Deep Water ◽  
Oxygen Depletion ◽  
Inorganic Phosphorus ◽  
Phosphorus Release ◽  
Water Inflow ◽  
Low Oxygen ◽  
In Situ Experiment ◽  
Inflow Event ◽  
Bottom Waters ◽  
The Baltic

Abstract. Phosphorus fertilisation (eutrophication) is expanding oxygen depletion in coastal systems worldwide. Under low-oxygen bottom-water conditions, phosphorus release from the sediment is elevated which further stimulates primary production. It is commonly assumed that re-oxygenation could break this ‘vicious cycle’ by increasing sedimentary phosphorus retention. Recently, a deep-water inflow into the Baltic Sea created a natural in-situ experiment that allowed us to investigate if temporary re-oxygenation stimulates sedimentary retention of dissolved inorganic phosphorus (DIP). Surprisingly, during this three-year-long study, we observed a transient but considerable increase, rather than a decrease, in the sediment efflux of DIP and other dissolved biogenic compounds. This suggested that the oxygenated inflow elevated the organic matter degradation in the sediment. As a result, the net sedimentary DIP release per m2 was 35–70 % higher over the years following the re-oxygenation than before. In contrast to previous assumptions, our results show that inflows of oxygenated water to anoxic bottom waters can increase the sedimentary phosphorus release.

scholarly journals Deep-water inflow event increases sedimentary phosphorus release on a multi-year scale

2021 ◽  
Vol 18 (9) ◽  
pp. 2981-3004
Author(s):  
Astrid Hylén ◽  
Sebastiaan J. van de Velde ◽  
Mikhail Kononets ◽  
Mingyue Luo ◽  
Elin Almroth-Rosell ◽  
...  
Keyword(s):  
Organic Matter ◽  
Deep Water ◽  
Oxygen Depletion ◽  
Inorganic Phosphorus ◽  
Phosphorus Release ◽  
Water Inflow ◽  
Low Oxygen ◽  
In Situ Experiment ◽  
Inflow Event ◽  
The Baltic

Abstract. Phosphorus fertilisation (eutrophication) is expanding oxygen depletion in coastal systems worldwide. Under low-oxygen bottom water conditions, phosphorus release from the sediment is elevated, which further stimulates primary production. It is commonly assumed that re-oxygenation could break this “vicious cycle” by increasing the sedimentary phosphorus retention. Recently, a deep-water inflow into the Baltic Sea created a natural in situ experiment that allowed us to investigate if temporary re-oxygenation stimulates sedimentary retention of dissolved inorganic phosphorus (DIP). Surprisingly, during this 3-year study, we observed a transient but considerable increase, rather than a decrease, in the sediment efflux of DIP and other dissolved biogenic compounds. This suggested that the oxygenated inflow elevated the organic matter degradation in the sediment, likely due to an increase in organic matter supply to the deeper basins, potentially combined with a transient stimulation of the mineralisation efficiency. As a result, the net sedimentary DIP release per m2 was 56 %–112 % higher over the years following the re-oxygenation than before. In contrast to previous assumptions, our results show that inflows of oxygenated water to anoxic bottom waters can increase the sedimentary phosphorus release.

scholarly journals Deep-water inflow event increases sedimentary phosphorus release on a multi-year scale

2021 ◽  
Author(s):  
Per Hall ◽  
Astrid Hylén ◽  
Sebastiaan van de Velde ◽  
Mikhail Kononets ◽  
Mingyue Luo ◽  
...  
Keyword(s):  
Deep Water ◽  
Phosphorus Release ◽  
Water Inflow ◽  
Inflow Event

scholarly journals Causes of the extensive hypoxia in the Gulf of Riga in 2018

2021 ◽  
Author(s):  
Stella-Theresa Stoicescu ◽  
Jaan Laanemets ◽  
Taavi Liblik ◽  
Māris Skudra ◽  
Oliver Samlas ◽  
...  
Keyword(s):  
Bottom Layer ◽  
Oxygen Depletion ◽  
Phosphorus Release ◽  
Meteorological Conditions ◽  
Mitigation Measures ◽  
Sediment Surface ◽  
Water Volume ◽  
Gulf Of Riga ◽  
Baltic Proper ◽  
The Baltic

Abstract. The Gulf of Riga is a relatively shallow bay connected to the deeper central Baltic Sea (Baltic Proper) via straits with sills. The decrease in the near-bottom oxygen levels from spring to autumn is a common feature in the gulf, but in 2018, hypoxia was exceptional. We analyzed temperature, salinity, oxygen, and nutrient data collected in 2018 and historical data available from environmental databases. Forcing data from the study year were compared with their long-term means and variability. The year 2018 was exceptional due to occasionally dominating north-easterly winds supporting the inflow of saltier waters from the Baltic Proper and meteorological conditions causing fast development of thermal stratification in spring. Existing stratification hindered vertical transport between the near-bottom layer (NBL) and the water layers above it. The estimated oxygen consumption rate at the sediment surface in spring-summer 2018 was about 1.7 mmol O2 m−2 h−1 that exceeded the oxygen input to the NBL due to advection and mixing. We suggest that the observed pronounced oxygen depletion was magnified by the prolonged stratified season and haline stratification in the deep layer that maintained a decreased water volume between the seabed and the pycnocline. The observed increase in phosphate concentrations in the NBL in summer 2018 suggests a significant sediment phosphorus release in hypoxic conditions counteracting the mitigation measures to combat eutrophication. We conclude, if similar meteorological conditions as in 2018 could occur more frequently in the future, such extensive hypoxia would be more common in the Gulf of Riga and other coastal basins with similar morphology and human-induced elevated input of nutrients.

scholarly journals A model study of warming-induced phosphorus-oxygen feedbacks in open-ocean oxygen minimum zones on millennial timescales

2016 ◽  
Author(s):  
Daniela Niemeyer ◽  
Tronje P. Kemena ◽  
Katrin J. Meissner ◽  
Andreas Oschlies
Keyword(s):  
Climate Model ◽  
Phosphorus Release ◽  
Water Volume ◽  
Low Oxygen ◽  
Oxygen Minimum Zones ◽  
Model Study ◽  
Additional Release ◽  
Bottom Waters ◽  
A Minor ◽  
Oxygen Minimum

Abstract. Observations indicate an expansion of oxygen minimum zones (OMZs) over the past 50 years, likely related to ongoing deoxygenation caused by reduced solubility, changes in stratification and circulation, and a potential acceleration of organic matter turnover in a warming climate. Higher temperatures also lead to enhanced weathering on land, which, in turn, increase the phosphorus and alkalinity flux into the ocean. The overall area of ocean sediments that are in direct contact with low oxygen bottom waters also increases with expanding OMZs. This leads to an additional release of phosphorus from ocean sediments and therefore raises the ocean's phosphorus inventory even further. Higher availability in phosphorus enhances biological production, remineralisation and oxygen consumption, and might therefore lead to further expansions of OMZs, representing a positive feedback. A negative feedback arises from the enhanced productivity-induced drawdown of carbon and also increased uptake of CO2 due to increased alkalinity, which, in turn, got there through weathering. This feedback leads to a decrease in atmospheric CO2 and weathering rates. Here we quantify these two competing feedbacks on millennial timescales for a high CO2 emission scenario. Using the UVic Earth System Climate Model of intermediate complexity, our model results suggest that the positive benthic phosphorus release feedback has only a minor impact on the size of OMZs in the next 1000 years, although previous studies assume that the phosphorus release feedback was the main factor for anoxic conditions during Cretaceous period. The increase in the marine phosphorus inventory under assumed business-as-usual global warming conditions originates, on millennial timescales, almost exclusively from the input via terrestrial weathering and causes a 4 to 5-fold expansion of the suboxic water volume in the model.

scholarly journals Long-term spatiotemporal variations in and expansion of low-oxygen conditions in the Pearl River estuary: a study synthesizing observations during 1976–2017

2021 ◽  
Vol 18 (18) ◽  
pp. 5247-5264
Author(s):  
Jiatang Hu ◽  
Zhongren Zhang ◽  
Bin Wang ◽  
Jia Huang
Keyword(s):  
Phytoplankton Biomass ◽  
River Estuary ◽  
Pearl River Estuary ◽  
Oxygen Depletion ◽  
Pearl River ◽  
Low Oxygen ◽  
Oxygen Conditions ◽  
Bottom Waters ◽  
The Pearl River

Abstract. The Pearl River estuary (PRE) frequently experiences low-oxygen conditions in summer, with large-extent low-oxygen events and a long-term deoxygenation trend being reported recently. In this study, we provide a synthesis of the spatiotemporal patterns and incidence of different low-oxygen levels in the PRE based on the in situ observations collected from 1976 to 2017 and aim to elucidate the underlying mechanisms of low-oxygen conditions and their changes over the past 4 decades. The long-term observations show that the dissolved oxygen (DO) content in the PRE has had significant temporal variability and spatial heterogeneity. Low-oxygen conditions (DO < 4 mg L−1) have occurred mostly in the bottom waters of 5–30 m during summer and early autumn, with locations and severity varying substantially between years. Coastal waters from the southwest of Lantau Island to the northeast of the Wanshan Archipelago were identified as a hotspot area prone to subsurface low-oxygen conditions due to the combined effects of comparatively deep topography, a certain residence time and stability of the water column, and enhanced oxygen depletion related to high phytoplankton biomass. In addition, the low-oxygen waters, either directly imported from the upstream reaches or generated locally and further transported with the estuarine circulation, also had considerable impacts on the oxygen levels in the estuary. As for early autumn, marked low-oxygen conditions were present in both the surface and the bottom waters. A large area affected by low oxygen (∼ 4450 km2) was found in September 2006, where the low-oxygen conditions were comparable to the most severe ones observed in summer. The area was formed by the inflows of low-oxygen waters from the upstream reaches and enhanced oxygen depletion driven by an intricate coupling of physical and biogeochemical processes. Our analysis also reveals there has been an apparent expansion of the summertime low-oxygen conditions at the bottom of the PRE since the years around 2000, coincident with major environment changes in the Pearl River region. Overall, the PRE seems to be undergoing a transition from a system characterized by episodic, small-scale hypoxic events (DO < 2 mg L−1) to a system with seasonal, estuary-wide hypoxic conditions in summer. Although exacerbated eutrophication associated with anthropogenic nutrient inputs has generally been considered the primary cause for the deterioration of low-oxygen conditions in the PRE, the sharp decline in sediment load may play an important role as well via increasing water transparency and thereby supporting higher and broader phytoplankton biomass in the estuary.

scholarly journals Interactive impacts of meteorological and hydrological conditions on the physical and biogeochemical structure of a coastal system

2020 ◽  
Vol 17 (20) ◽  
pp. 5097-5127 ◽  
Author(s):  
Onur Kerimoglu ◽  
Yoana G. Voynova ◽  
Fatemeh Chegini ◽  
Holger Brix ◽  
Ulrich Callies ◽  
...  
Keyword(s):  
Central Region ◽  
German Bight ◽  
Outer Region ◽  
Coupled Model ◽  
Oxygen Depletion ◽  
Flood Event ◽  
Nutrient Concentrations ◽  
Biogeochemical Model ◽  
Low Oxygen ◽  
Coastal System

Abstract. The German Bight was exposed to record high riverine discharges in June 2013, as a result of flooding of the Elbe and Weser rivers. Several anomalous observations suggested that the hydrodynamical and biogeochemical states of the system were impacted by this event. In this study, we developed a biogeochemical model and coupled it with a previously introduced high-resolution hydrodynamical model of the southern North Sea in order to better characterize these impacts and gain insight into the underlying processes. Performance of the model was assessed using an extensive set of in situ measurements for the period 2011–2014. We first improved the realism of the hydrodynamic model with regard to the representation of cross-shore gradients, mainly through inclusion of flow-dependent horizontal mixing. Among other characteristic features of the system, the coupled model system can reproduce the low salinities, high nutrient concentrations and low oxygen concentrations in the bottom layers observed within the German Bight following the flood event. Through a scenario analysis, we examined the sensitivity of the patterns observed during July 2013 to the hydrological and meteorological forcing in isolation. Within the region of freshwater influence (ROFI) of the Elbe–Weser rivers, the flood event clearly dominated the changes in salinity and nutrient concentrations, as expected. However, our findings point to the relevance of the peculiarities in the meteorological conditions in 2013 as well: a combination of low wind speeds, warm air temperatures and cold bottom-water temperatures resulted in a strong thermal stratification in the outer regions and limited vertical nutrient transport to the surface layers. Within the central region, the thermal and haline dynamics interactively resulted in an intense density stratification. This intense stratification, in turn, led to enhanced primary production within the central region enriched by nutrients due to the flood but led to reduction within the nutrient-limited outer region, and it caused a widespread oxygen depletion in bottom waters. Our results further point to the enhancement of the current velocities at the surface as a result of haline stratification and to intensification of the thermohaline estuarine-like circulation in the Wadden Sea, both driven by the flood event.

Influence of restoration methods on the longevity of changes in the thermal and oxygen dynamics of a degraded lake

2015 ◽  
Vol 44 (1) ◽  
Author(s):  
Jolanta Grochowska ◽  
Renata Brzozowska ◽  
Michał Łopata ◽  
Julita Dunalska
Keyword(s):  
Oxygen Depletion ◽  
Artificial Circulation ◽  
Anaerobic Conditions ◽  
Lake Volume ◽  
Depletion Rate ◽  
Bottom Waters ◽  
Phosphorus Inactivation ◽  
The City ◽  
Oxygen Dynamics ◽  
Content Of Oxygen

AbstractThe study was conducted on Lake Długie, located in the city of Olsztyn, which for 20 years received raw domestic sewage (400 m3 per day). After preliminary conservation operations, the lake was restored by artificial circulation and phosphorus inactivation methods. During artificial circulation, water temperature in the whole lake volume was equalized. The disconnection of the compressor stimulated the return to typical thermal parameters in the lake. Phosphorus inactivation did not affect the thermal regime in the lake. Artificial circulation caused an increase in the oxygen content in the whole lake, lowered the oxygen-depletion rate during stagnation, and shortened the duration of anaerobic conditions in the near-bottom waters. Phosphorus inactivation did not directly affect the content of oxygen. However, after the coagulant was added to the lake, the oxygenation of the water was further improved owing to the depressed photosynthesis caused by drastically reduced availability of phosphate for primary producers.

Nemo-Nordic 2.0: Updated Baltic Sea model based on NEMO 4.0

2021 ◽  
Author(s):  
Tuomas Kärnä ◽  
Ida Ringgaard ◽  
Vasily Korabel ◽  
Adam Nord ◽  
Patrik Ljungemyr ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Horizontal Resolution ◽  
Sea Surface ◽  
Small Scale ◽  
The Baltic Sea ◽  
Inflow Event ◽  
Arkona Basin ◽  
The Baltic ◽  
Marine Environment Monitoring ◽  
Monitoring Service

&lt;p&gt;We present Nemo-Nordic 2.0, the latest version of the operational marine forecasting model for the Baltic Sea used and developed in the Baltic Monitoring Forecasting Centre (BAL MFC) under the Copernicus Marine Environment Monitoring Service (CMEMS). The most notable differences between Nemo-Nordic 2.0 and its predecessor Nemo-Nordic 1.0 are the switch from NEMO 3.6 to NEMO 4.0 and an increase in horizontal resolution from 2 to 1 nautical mile. In addition, the model's bathymetry and bottom friction formulation have been updated. The model configuration was specially tuned to represent Major Baltic Inflow events. Focusing on a 2-year validation period from October 1, 2014, covering one Major Baltic Inflow event, Nemo-Nordic 2.0 simulates Sea Surface Height (SSH) well: centralized Root-Mean-Square Deviation (CRMSD) is within 10 cm for most stations outside the Inner Danish Waters. CRMSD is higher at some stations where small-scale topographical features cannot be correctly resolved. SSH variability tends to be overestimated in the Baltic Sea and underestimated in the Inner Danish Waters. Nemo-Nordic 2.0 represents Sea Surface Temperature (SST) and Salinity (SSS) well, although there is a negative bias around -0.5&amp;#176;C in SST. The 2014 Major Baltic Inflow event is well reproduced. The simulated salt pulse agrees well with observations in the Arkona basin and progresses into the Gotland basin in 3 to 4 months.&lt;/p&gt;

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