Very few studies of estuarine hypoxia have simultaneously examined the impacts of nutrients from the land, the atmosphere, and from the coastal ocean. However, all three nutrient sources can be important to estuarine oxygen dynamics, and can have important ramifications for managers, since in general inputs from the atmosphere and coastal ocean are more difficult to control at the local level....
The coastal ocean is increasingly affected by eutrophication, i.e., the supply of excess nutrients with subsequent enhancement of productivity and potentially harmful occurrences of toxic algal blooms and hypoxia or anoxia. Hypoxia occurs when dissolved oxygen concentrations drop below 2 mg/L. Because some systems are naturally prone to hypoxia, a quantification of the relative influence of...
Depending on time scales, magnitude and persistency, fluctuating oxygen (O2) levels at the boundaries of oxygen deficient areas strongly affect benthic element cycling and redox-sensitive mobilization of nutrients and trace metals. Via feedback loops, this contributes to maintain or even amplify low oxygen levels. Beside biological consumption, bottom water availability of O2 in such...
The Black Sea is an almost enclosed Sea that combines naturally-induced permanent anoxia in its deep part with anthropogenically-induced hypoxia on the bottom of its north-western shelf. Shelf hypoxic events occur during the stratification period in regions with high accumulation of organic matter and low ventilation rates. These events started in the 70-80s when eutrophication developed with...
Estuaries received eroded sediments from catchment with heavy anthropogenic nutrient and organic loadings serving as a bioreactor favoring intensive cycling of elements, such as nitrogen and organics. Increasing evidences showed the importance of active particle mediated aerobic-anaerobic metabolisms in estuary and coastal waters, however, little is known about the production of N2O, a strong...
The coastal waters around Hong Kong are affected by persistent and increasing eutrophication. This deteriorating situation may increase the frequency of HABs, expand the area of hypoxic zones and lead to other ecosystem disruptions and worse of all, offset the environmental improvements achieved through the costly Harbour Area Treatment Scheme over the last decade. Eutrophication/hypoxia in...
Excessive nutrient inputs over the last century have altered the subtle balance between oxygen supply and oxygen consumption and changed the Baltic Sea from a state with hypoxia confined to the deepest bottom waters to widespread hypoxia in most bottom waters. The Baltic Sea is naturally susceptible to hypoxia because the pronounced vertical stratification in the water column prevents the...
Aquatic environments experiencing low-oxygen conditions have been described as hypoxic, suboxic or anoxic zones, oxygen minimum zones, and, in the popular media, the misnomer “dead zones.” This review aims to elucidate important aspects underlying oxygen depletion in diverse coastal systems, and provides a synthesis of general relationships between hypoxia and its controlling factors. After...
Shelf seas and their coastal areas are highly dynamic environments subject to many natural processes and anthropogenic pressures. They exhibit large spatial and seasonal gradients in pelagic and benthic oxygen concentrations both naturally with depth, temperature, hydrography, stratification and sediment type and in response to a range of pressures including anthropogenic nutrient inputs,...
Many studies have shown that coastal hypoxia is primarily associated with autochthonous organic carbon (Auto-OC) production, stimulated by coastal eutrophication resulting from excessive terrestrial nutrient runoff. Nutrients stimulate algal blooms in coastal surface waters. Sinking and remineralization of algal biomass drive dissolved oxygen (DO) consumption below the pycnocline. Therefore,...
River systems worldwide are increasingly influenced by flood control measures and river diversion operations. Yet, surprisingly little is known about the effects of river management on coastal hydrodynamics, nutrient transport pathways, and hypoxia. Freshwater diversions on the Lower Mississippi River play a central role in the proposed 50-billion, 50-year strategy for restoring the...
The northern Gulf of Mexico receives excessive nutrient inputs from the Mississippi-Atchafalaya River Basin that promote high phytoplankton production and high respiration rates due to algal decomposition. Every summer, respiration, in combination with vertical stratification, results in hypoxia, high dissolved inorganic carbon concentrations and low pH in bottom waters. By the end of the...
Hypoxia is a potent stressor on living resources in waters adjacent to populated coastal areas due to excessive nutrient inputs, and may be further impacted by global climate change. The Chesapeake Bay, the largest estuary in the continental United States located in the Mid-Atlantic region of the east coast, undergoes hypoxic conditions annually and is also experiencing increases in sea level,...
In the last 10 years the coast of south-central Chile was strongly perturbed by two events of different origin on a scale of tens to hundreds of kilometers. The first, which occurred in January 2008, was a natural hypoxic event associated with the coastward intrusion of upwelled water low in dissolved oxygen, which produced massive mortality of benthic and planktonic organisms in Coliumo Bay....
We investigated the seasonal and annual variability of surface sulphur plumes in the Namibia Benguela upwelling system because of their significant impacts on the marine ecosystem, fishing industry, aquaculture farming and tourism due to their toxic properties. We identified the sulphur plumes in ocean colour satellite data for the 2002-2012 time period using the differences in the spectral...
Coastal upwelling supports highly productive ecosystems in eastern boundary currents that provide ecologically and economically important habitats, e.g., off the west coast of North America. However, upwelling of nutrient-rich deep waters poses ecosystem risks as well as benefits, as cold upwelled waters are increasingly enriched in CO2 and depleted in oxygen. Because the mechanisms...
Coastal and estuarine hydrography along with trace metal (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) distribution in sediments were studied in the Cochin estuary (southwest coast of India) during pre-upwelling (April 2016) and upwelling (July 2016) periods. Oxygenated, high saline and low nutrient coastal waters were found (30kms) in the estuary during the pre-upwelling period where coastal...
Dissolved oxygen concentrations in natural water bodies are governed by the balance between oxygen production, consumption, and exchange with the atmosphere. The occurrence of coastal hypoxia/anoxia can be natural, human influenced, or result from the interaction between natural and anthropogenically induced processes. Naturally occurring hypoxia/anoxia is found: in bottom waters of silled...