scholarly journals Nutrient budgets for large Chinese estuaries

2009 ◽  
Vol 6 (10) ◽  
pp. 2245-2263 ◽  
Author(s):  
S. M. Liu ◽  
G.-H. Hong ◽  
J. Zhang ◽  
X. W. Ye ◽  
X. L. Jiang
Keyword(s):  
Anthropogenic Activities ◽  
Inorganic Nitrogen ◽  
World Ocean ◽  
Northeast Asia ◽  
Anthropogenic Sources ◽  
Phytoplankton Production ◽  
Nutrient Budgets ◽  
China Sea ◽  
Coastal Sea ◽  
Chinese Estuaries

Abstract. Chinese rivers deliver about 5–10% of global freshwater input and 15–20% of the global continental sediment to the world ocean. We report the riverine fluxes and concentrations of major nutrients (nitrogen, phosphorus, and silicon) in the rivers of the contiguous landmass of China and Korea in the northeast Asia. The rivers are generally enriched with dissolved inorganic nitrogen (DIN) and depleted in dissolved inorganic phosphate (PO43−) with very high DIN: PO43− concentration ratios. DIN, phosphorus, and silicon levels and loads in rivers are mainly affected by agriculture activities and urbanization, anthropogenic activities and adsorption on particulates, and rock types, climate and physical denudation intensity, respectively. Nutrient transports by rivers in the summer are 3–4 times higher than those in the winter with the exception of NH4+. The flux of NH4+ is rather constant throughout the year due to the anthropogenic sources such as the sewer discharge. As nutrient composition has changed in the rivers, ecosystems in estuaries and coastal sea have also changed in recent decades. Among the changes, a shift of limiting nutrients from phosphorus to nitrogen for phytoplankton production with urbanization is noticeable and in some areas silicon becomes the limiting nutrient for diatom productivity. A simple steady-state mass-balance box model was employed to assess nutrient budgets in the estuaries. The major Chinese estuaries export <15% of nitrogen, <6% of phosphorus required for phytoplankton production and ~4% of silicon required for diatom growth in the Chinese Seas (Bohai, Yellow Sea, East China Sea, South China Sea). This suggests that land-derived nutrients are largely confined to the immediate estuaries, and ecosystem in the coastal sea beyond the estuaries is mainly supported by other nutrient sources such as regeneration, open ocean and atmospheric deposition.

scholarly journals Re-examining the Antarctic Paradox: speculation on the Southern Ocean as a nutrient-limited system

1998 ◽  
Vol 27 ◽  
pp. 661-668 ◽  
Author(s):  
Julian Priddle ◽  
David B. Nedwell ◽  
Michael J. Whitehouse ◽  
David S. Reay ◽  
Graham Savidge ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Carbon Fixation ◽  
Nitrogen Nutrition ◽  
Inorganic Nitrogen ◽  
World Ocean ◽  
Euphotic Zone ◽  
Grazing Pressure ◽  
Limiting Factors ◽  
Nutrient Concentrations ◽  
Phytoplankton Production

The Southern Ocean is the largest of the high-nutrient, low-chlorophyll (HNLC) regions of the world ocean. Phytoplankton production fails to utilise completely the pool of inorganic nutrients in the euphotic zone, giving rise to low phytoplankton bio-mass and leaving relatively high summer nutrient concentrations. This enigma is of considerable significance for our understanding of the role of the oceans in the global carbon cycle. Various limiting factors have been considered: low light, low temperature, absence of necessary trace elements, grazing pressure and other means of biomass removal. The dynamics of nitrogen uptake by phytoplankton are of particular importance. Classically, nitrate mixed into the surface layer during winter provides the nitrogen pool for growth in the spring bloom. Some organic material is exported to depth, whilst the remainder is recycled, providing ammonium and other reduced species as nitrogenous substrates for growth during the remainder of the season. The oxidation state of the inorganic nitrogen supply thus identifies new and recycled carbon fixation. Whilst this is convenient “shorthand” for the nitrogen nutrition of carbon export in much of the ocean, it is an inappropriate model for the Southern Ocean. Here, nitrate and ammonium use are simultaneous, and nitrate is never exhausted by the annual phytoplankton production. We speculate that a range of environmental factors combine to make the large pool of nitrate partially inaccessible to phytoplankton. in addition to the documented effects of low iron availability and high ammonium concentrations, the low temperatures characteristic of the Southern Ocean may decrease nitrate availability because of the increased energetic overheads in its uptake and reduction. This in turn makes ammonium an important nitrogenous substrate, and its production by zooplankton and heterotrophic microorganisms is an important component of the plankton nitrogen cycle. There is some evidence that ammonium production by large grazing animals may stimulate phytoplankton growth. Microbial removal of nitrogen from sedimenting phytoplankton cells may result in local decoupling between the carbon and nitrogen cycles, allowing some reduced nitrogen to remain in the euphotic zone whilst carbon is exported to depth.

Mean Sea Level as a Reference for Geodetic Leveling

1974 ◽  
Vol 28 (5) ◽  
pp. 524-530 ◽  
Author(s):  
G. W. Lennon
Keyword(s):  
Sea Level ◽  
World Ocean ◽  
Equipotential Surface ◽  
Scientific Discipline ◽  
Mean Sea Level ◽  
Sea Levels ◽  
Coastal Sea ◽  
Long Time ◽  
Marine System

The use of mean sea level as a surface of reference that might provide an independent control for geodetic leveling has been a long term goal arising from the classical analogy between the geoid as an equipotential surface and the surface assumed by a hypothetical undisturbed world ocean. The problems associated with this aim are now known to be vast, and are associated with the dynamics of the marine system, notably its response to meteorological forces, to variations in density and to the effects of basic circulation patterns. In consequence the mean sea level surface varies rapidly in both time and space. This identifies in fact a distinctive scientific discipline, coastal geodesy, in which contributions are required by both geodesists and oceanographers. It has come to be recognized that the coastal zone is a hazardous environment for all observational techniques concerned. On the one hand, the difficulties of measurement of coastal sea levels have only recently been understood; on the other hand, precise leveling procedures are now known to be influenced by the attraction of marine tides and by crustal deformation of tidal loading. Much of the data available for study are therefore inadequate and, moreover, it should be noted that long-time series are required. It is now possible to lay plans for both geodetic and oceanographic procedures to remedy these deficiencies in the long-term interests of the study.

Nutrient status and winter hardiness of red spruce foliage

1989 ◽  
Vol 19 (6) ◽  
pp. 754-758 ◽  
Author(s):  
Richard M. Klein ◽  
Timothy D. Perkins ◽  
Helen L. Myers
Keyword(s):  
Inorganic Nitrogen ◽  
Sufficient Conditions ◽  
Nutrient Status ◽  
Cloud Water ◽  
Winter Hardiness ◽  
Red Spruce ◽  
Anthropogenic Sources ◽  
Freezing Injury ◽  
Ion Leakage ◽  
Anthropogenic Nitrogen

Increased ecosystem loading with inorganic nitrogen compounds derived from anthropogenic sources has been proposed to prolong vegetative growth of spruce, rendering them more susceptible to winter injury. Severely nutrient-deficient 4-year-old red spruce (Picearubens Sarg.) seedlings and adequately fertilized seedlings were provided with synthetic cloud water lacking or containing nitrate, ammonium, or both, for a full growing season, and then exposed to normal winter chilling. Needles from these seedlings were stressed at −25 or −30 °C, and freezing injury was measured as ion leakage. Cloud water condensates had no effect on hardiness of needles of either nutrient status. Initially nutrient-sufficient seedlings transferred to nutrient-deficient conditions also exhibited no change in hardiness. Severely nutrient-deficient seedlings had needles that were significantly more sensitive to winter injury than seedlings under nutrient-sufficient conditions. Improving the nutrient status of initially nitrogen-deficient seedlings reduced their sensitivity to freezing injury. Based upon experimental results and consideration of the amounts of inorganic nitrogen reaching upper-elevation conifer forests, there is no evidence to support the hypothesis that anthropogenic nitrogen supplies significantly reduce winter hardiness of spruce foliage. It is improbable that winter injury due to elevated anthropogenic nitrogen is a causal factor in contemporary forest decline.

scholarly journals Suspended Particular Matter drives the spatial segregation of nitrogen turnover along the hyper-turbid Ems estuary

2021 ◽  
Author(s):  
Gesa Schulz ◽  
Tina Sanders ◽  
Justus E. E. van Beusekom ◽  
Yoana G. Voynova ◽  
Andreas Schöl ◽  
...  
Keyword(s):  
Stable Isotopes ◽  
Nitrous Oxide ◽  
Water Column ◽  
Anthropogenic Activities ◽  
Inorganic Nitrogen ◽  
Nitrate Removal ◽  
Tidal River ◽  
Nutrient Loads ◽  
Ems Estuary ◽  
Nitrogen Turnover

Abstract. Estuaries are nutrient filters and change riverine nutrient loads before they reach coastal oceans. They have been extensively changed by anthropogenic activities like draining, deepening, and dredging to meet economic and social demand, causing significant regime changes like tidal amplifications and in some cases to hyper-turbid conditions. Furthermore, increased nutrient loads, especially nitrogen, mainly by agriculture cause coastal eutrophication. Estuaries can either act as a sink or as a source of nitrate, depending on environmental and geomorphological conditions. These factors vary along an estuary, and change nitrogen turnover in the system. Here, we investigate the factors controlling nitrogen turnover in the hyper-turbid Ems estuary (Northern Germany) that has been strongly impacted by human activities. During two research cruises in August 2014 and June 2020, we measured water column properties, dissolved inorganic nitrogen, dual stable isotopes of nitrate and dissolved nitrous oxide concentration along the estuary. Overall, the Ems estuary acts as a nitrate sink in both years. However, three distinct biogeochemical zones exist along the estuary. A strong fractionation (~ 26 ‰) of nitrate stable isotopes points towards nitrate removal via water column denitrification in the hyper-turbid Tidal River, driven by anoxic conditions in deeper water layers. In the Middle Reaches of the estuary nitrification gains in importance turning this section into a net nitrate source. The Outer Reaches are dominated by mixing with nitrate uptake in 2020. We find that the overarching control on biogeochemical nitrogen cycling, zonation and nitrous oxide production in the Ems estuary is exerted by suspended particulate matter concentrations and the linked oxygen deficits.

scholarly journals Sediment Metal Contamination, Bioavailability, and Oxidative Stress Response in Mangrove Avicennia marina in Central Red Sea

2021 ◽  
Vol 9 ◽  
Author(s):  
Abdullahi Bala Alhassan ◽  
Mohammed Othman Aljahdali
Keyword(s):  
Antioxidant Enzyme ◽  
Red Sea ◽  
Anthropogenic Activities ◽  
Sediment Quality ◽  
Principal Component ◽  
Avicennia Marina ◽  
Anthropogenic Sources ◽  
Antioxidant Enzyme Activities ◽  
Metal Concentrations ◽  
Mangrove Ecosystems

Anthropogenic activities have been on the increase in the urban environment and have led to contamination of the environment with toxic metals. However, mangrove plants’ response to heavy metal stress due to anthropogenic activities explains the metal bioavailability and its potential ecotoxicological effect. We carried out a multi-approach study to investigate i) if the concentrations of metals (Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Cd, Pb, Sr, and V) in mangroves at the central Red Sea are due to the anthropogenic influence and are above the sediment quality guidelines and ii) if an increase in metal concentration influences height and antioxidant enzyme (catalase, CAT; glutathione S-transferase, GST; and superoxide dismutase, SOD) activities in Avicennia marina. There were significant variations (p &lt; 0.05) in metal concentrations and antioxidants across the six mangrove ecosystems with higher concentrations at Al Lith (LT) and south Jeddah (SJ). Even though the concentrations of metals in mangrove leaves are slightly higher in LT than SJ, principal component analysis showed that higher concentrations of Cr, Co, Zn, Cd, and Pb in mangrove leaves from SJ influence higher antioxidant enzyme activities and the lowest average mangrove height (2.01 m). This suggests that higher metal concentrations be factors for the biggest stress in these mangrove ecosystems. However, among the 13 metals, Cr (82.07 mg/kg), Cu (41.29 mg/kg), and As (10.30 mg/kg) in sediments have values within the ERL range of probable effect, while Ni (53.09 mg/kg) was above the ERM threshold. Hence, there is need to focus on monitoring these metals in mangrove sediments and their anthropogenic sources.

Substantial accumulation of mercury in the deepest parts of the ocean and implications for the environmental mercury cycle

2021 ◽  
Vol 118 (51) ◽  
pp. e2102629118
Author(s):  
Maodian Liu ◽  
Wenjie Xiao ◽  
Qianru Zhang ◽  
Shengliu Yuan ◽  
Peter A. Raymond ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Food Webs ◽  
Deep Sea ◽  
Anthropogenic Activities ◽  
Sediment Cores ◽  
Anthropogenic Sources ◽  
Biogeochemical Cycle ◽  
Vertical Profiles ◽  
Surface Ocean ◽  
Increasing Trends

Anthropogenic activities have led to widespread contamination with mercury (Hg), a potent neurotoxin that bioaccumulates through food webs. Recent models estimated that, presently, 200 to 600 t of Hg is sequestered annually in deep-sea sediments, approximately doubling since industrialization. However, most studies did not extend to the hadal zone (6,000- to 11,000-m depth), the deepest ocean realm. Here, we report on measurements of Hg and related parameters in sediment cores from four trench regions (1,560 to 10,840 m), showing that the world’s deepest ocean realm is accumulating Hg at remarkably high rates (depth-integrated minimum–maximum: 24 to 220 μg ⋅ m−2 ⋅ y−1) greater than the global deep-sea average by a factor of up to 400, with most Hg in these trenches being derived from the surface ocean. Furthermore, vertical profiles of Hg concentrations in trench cores show notable increasing trends from pre-1900 [average 51 ± 14 (1σ) ng ⋅ g−1] to post-1950 (81 ± 32 ng ⋅ g−1). This increase cannot be explained by changes in the delivery rate of organic carbon alone but also need increasing Hg delivery from anthropogenic sources. This evidence, along with recent findings on the high abundance of methylmercury in hadal biota [R. Sun et al., Nat. Commun. 11, 3389 (2020); J. D. Blum et al., Proc. Natl. Acad. Sci. U. S. A. 117, 29292–29298 (2020)], leads us to propose that hadal trenches are a large marine sink for Hg and may play an important role in the regulation of the global biogeochemical cycle of Hg.

Enhanced atmospheric solubilization of iron due to anthropogenic activities

2021 ◽  
Author(s):  
Elisa Bergas-Massó ◽  
María Gonçalves Ageitos ◽  
Stelios Myriokefalitakis ◽  
Twan van Noije ◽  
Ron Miller ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Industrial Revolution ◽  
Anthropogenic Activities ◽  
Coupled Model ◽  
Anthropogenic Sources ◽  
Anthropogenic Activity ◽  
Sea Ice Concentration ◽  
Future Projections ◽  
The North ◽  
Primary Emissions

&lt;p&gt;Atmospheric deposition of soluble iron (Fe) to the ocean has an impact on oceanic primary productivity, thus on carbon dioxide uptake. Understanding how anthropogenic activity influences the atmospheric Fe cycle is key to project ocean biogeochemical cycles and has been barely explored.&lt;/p&gt;&lt;p&gt;In this study, we assess past, present, and future soluble Fe deposition to the ocean, accounting for natural and anthropogenic sources, using an advanced atmospheric Fe cycle module implemented into the EC-Earth3 Earth System Model. This version of the model considers primary emissions of insoluble and soluble Fe forms associated with dust minerals, and anthropogenic and biomass burning combustion aerosols. Fe solubilization processes in the atmosphere include 1)&amp;#160; proton-promoted, 2)&amp;#160; oxalate-promoted (with oxalate calculated on-line), and 3) photo-reductive Fe dissolution. We run time-slice simulations using the atmosphere-chemistry model configuration constrained by past, present, and future ocean states. The necessary sea surface temperature and sea ice concentration climatologies are obtained from EC-Earth3 CMIP6 coupled model experiments. Future projections rely on three CMIP6 scenarios representing different socio-economic pathways and end-of-the-century forcing levels: SSP1-2.6, SSP2-4.5, and SSP3-7.0.&amp;#160;&lt;/p&gt;&lt;p&gt;Our setup allows us to estimate the soluble Fe deposition into the ocean while quantifying the contribution from dust, biomass burning, and anthropogenic combustion sources separately under a range of scenarios. Our preliminary results suggest nearly a 50% increase in soluble Fe deposition for the present time since the industrial revolution, attributed to increased atmospheric acidity and oxalate concentrations that result in a more efficient atmospheric processing. Future projections of soluble Fe show a high correlation between anthropogenic activity and solubility of deposited Fe, scenarios with higher anthropogenic emissions consistently yield a higher fraction of soluble over total deposited Fe. Our results also suggest diverging trends for the different ocean basins. Disentangling the factors that drive those differences in regions where Fe is known to be the limiting nutrient, such as the North Pacific or the Southern Ocean, is fundamental to improve our understanding of the atmospheric Fe cycle and its consequences for&amp;#160; the ocean biogeochemistry.&amp;#160;&amp;#160;&lt;/p&gt;

The United States and China in Northeast Asia

2017 ◽  
Author(s):  
Robert S. Ross
Keyword(s):  
United States ◽  
East China Sea ◽  
Northeast Asia ◽  
The United States ◽  
Third Party ◽  
East China ◽  
The East China Sea ◽  
Major Objective ◽  
Coercive Diplomacy ◽  
China Sea

This chapter examines alliance dynamics in U.S.–China relations in Northeast Asia. It analyzes how each nation has used third-party coercive diplomacy to compel the other to restrain its allies' challenges to great power security. A major objective of U.S. policy toward North Korea and the corresponding tension of the Korean Peninsula has been to compel China to exercise greater control over North Korea's nuclear weapons program. A major objective of Chinese policy toward Japan and the corresponding tension in the East China Sea has been to compel the United States to restrain Japanese challenges to Chinese sovereignty claims in disputed waters in the East China Sea. For a brief period, third-party coercion contributed to greater U.S.–China cooperation as each country adjusted its policies toward its respective ally, easing regional tension and U.S.–China conflict.

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