Effects of natural and human-induced hypoxia on coastal benthos
TL;DR: Large areas of low oxygen persist seasonally or continuously beneath upwelling regions, associated with the upper parts of oxygen minimum zones (SE Pacific, W Africa, N Indian Ocean), and support a resident fauna that is adapted to survive and reproduce at oxygen concentrations.
Abstract: . Coastal hypoxia (defined here as Hypoxia alters both the structure and function of benthic communities, but effects may differ with regional hypoxia history. Human-caused hypoxia is generally linked to eutrophication, and occurs adjacent to watersheds with large populations or agricultural activities. Many occurrences are seasonal, within estuaries, fjords or enclosed seas of the North Atlantic and the NW Pacific Oceans. Benthic faunal responses, elicited at oxygen levels below 2 ml L−1, typically involve avoidance or mortality of large species and elevated abundances of enrichment opportunists, sometimes prior to population crashes. Areas of low oxygen persist seasonally or continuously beneath upwelling regions, associated with the upper parts of oxygen minimum zones (SE Pacific, W Africa, N Indian Ocean). These have a distribution largely distinct from eutrophic areas and support a resident fauna that is adapted to survive and reproduce at oxygen concentrations
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TL;DR: In this paper, the authors pointed out that the formation of hypoxic areas has been exacerbated by any combination of interactions that increase primary production and accumulation of organic carbon leading to increased respiratory demand for oxygen below a seasonal or permanent pycnocline, and the consequences of eutrophication-induced hypoxia can be reversed if longterm, broad-scale, and persistent efforts to reduce substantial nutrient loads are developed and implemented.
Abstract: . Water masses can become undersaturated with oxygen when natural processes alone or in combination with anthropogenic processes produce enough organic carbon that is aerobically decomposed faster than the rate of oxygen re-aeration. The dominant natural processes usually involved are photosynthetic carbon production and microbial respiration. The re-supply rate is indirectly related to its isolation from the surface layer. Hypoxic water masses ( Hypoxia development and continuation in many areas of the world's coastal ocean is accelerated by human activities, especially where nutrient loading increased in the Anthropocene. This higher loading set in motion a cascading set of events related to eutrophication. The formation of hypoxic areas has been exacerbated by any combination of interactions that increase primary production and accumulation of organic carbon leading to increased respiratory demand for oxygen below a seasonal or permanent pycnocline. Nutrient loading is likely to increase further as population growth and resource intensification rises, especially with increased dependency on crops using fertilizers, burning of fossil fuels, urbanization, and waste water generation. It is likely that the occurrence and persistence of hypoxia will be even more widespread and have more impacts than presently observed. Global climate change will further complicate the causative factors in both natural and human-caused hypoxia. The likelihood of strengthened stratification alone, from increased surface water temperature as the global climate warms, is sufficient to worsen hypoxia where it currently exists and facilitate its formation in additional waters. Increased precipitation that increases freshwater discharge and flux of nutrients will result in increased primary production in the receiving waters up to a point. The interplay of increased nutrients and stratification where they occur will aggravate and accelerate hypoxia. Changes in wind fields may expand oxygen minimum zones onto more continental shelf areas. On the other hand, not all regions will experience increased precipitation, some oceanic water temperatures may decrease as currents shift, and frequency and severity of tropical storms may increase and temporarily disrupt hypoxia more often. The consequences of global warming and climate change are effectively uncontrollable at least in the near term. On the other hand, the consequences of eutrophication-induced hypoxia can be reversed if long-term, broad-scale, and persistent efforts to reduce substantial nutrient loads are developed and implemented. In the face of globally expanding hypoxia, there is a need for water and resource managers to act now to reduce nutrient loads to maintain, at least, the current status.
936 citations
Cites background or methods from "Effects of natural and human-induce..."
...…little doubt that there have been ecosystem-level changes in coastal systems as a result of eutrophication and associated hypoxia (Baden et al., 1990a; Bakan and Buyukgungor, 2000; Rabalais and Turner, 2001; Wang 2006; Turner et al., 2008; Ekau et al., 2009; Kemp et al., 2009; Levin et al., 2009a)....
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...Hypoxic waters from OMZs and upwelling systems may also impinge on coastal areas with similar affects as humaninduced hypoxia (Levin et al., 2009a)....
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...…on the seafloor of continental slopes and shelves, and sea mounts, specialized low biodiversity communities have evolved to survive at dissolved oxygen concentrations as low as 0.1 mg L−1 or less (Graham, 1990; Childress and Seibel, 1998; Sakko, 1998; Levin, 2002; Levin et al., 2000, 2009a)....
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...Modified from Dı́az and Rosenberg (2008) and Levin et al. (2009a)....
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...These bacterial mats are indicators of suboxic condition and are commonly observed in both eutrophication driven hypoxia and where OMZs intersect the seabed (Graco et al., 2001; Levin et al., 2009a)....
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01 Oct 2012
TL;DR: The Global Energy Assessment (GEA) as mentioned in this paper brings together over 300 international researchers to provide an independent, scientifically based, integrated and policy-relevant analysis of current and emerging energy issues and options.
Abstract: The Global Energy Assessment (GEA) brings together over 300 international researchers to provide an independent, scientifically based, integrated and policy-relevant analysis of current and emerging energy issues and options. It has been peer-reviewed anonymously by an additional 200 international experts. The GEA assesses the major global challenges for sustainable development and their linkages to energy; the technologies and resources available for providing energy services; future energy systems that address the major challenges; and the policies and other measures that are needed to realize transformational change toward sustainable energy futures. The GEA goes beyond existing studies on energy issues by presenting a comprehensive and integrated analysis of energy chalenges, opportunities and strategies, for developing, industrialized and emerging economies. This volume is a invaluable resource for energy specialists and technologists in all sectors (academia, industry and government) as well as policymakers, development economists and practitioners in international organizations and national governments.
812 citations
TL;DR: Major observed trends include a shift in the acid-base chemistry of seawater, reduced subsurface oxygen both in near-shore coastal water and in the open ocean, rising coastal nitrogen levels, and widespread increase in mercury and persistent organic pollutants.
Abstract: Climate change, rising atmospheric carbon dioxide, excess nutrient inputs, and pollution in its many forms are fundamentally altering the chemistry of the ocean, often on a global scale and, in some cases, at rates greatly exceeding those in the historical and recent geological record. Major observed trends include a shift in the acid-base chemistry of seawater, reduced subsurface oxygen both in near-shore coastal water and in the open ocean, rising coastal nitrogen levels, and widespread increase in mercury and persistent organic pollutants. Most of these perturbations, tied either directly or indirectly to human fossil fuel combustion, fertilizer use, and industrial activity, are projected to grow in coming decades, resulting in increasing negative impacts on ocean biota and marine resources.
714 citations
TL;DR: In this article, the authors provide a concise review of the consequences of coastal hypoxia for sediment biogeochemistry, showing that changes in bottom-water oxygen levels have consequences for early diagenetic pathways (more anaerobic at expense of aerobic pathways), the efficiency of reoxidation of reduced metabolites and the nature, direction and magnitude of sediment-water exchange fluxes.
Abstract: The intensity, duration and frequency of coastal hypoxia (oxygen concentration <63µM) are increasing due to human alteration of coastal ecosystems and changes in oceanographic conditions due to global warming. Here we provide a concise review of the consequences of coastal hy- poxia for sediment biogeochemistry. Changes in bottom- water oxygen levels have consequences for early diagenetic pathways (more anaerobic at expense of aerobic pathways), the efficiency of re-oxidation of reduced metabolites and the nature, direction and magnitude of sediment-water exchange fluxes. Hypoxia may also lead to more organic matter accu- mulation and burial and the organic matter eventually buried is also of higher quality, i.e. less degraded. Bottom-water oxygen levels also affect the organisms involved in organic matter processing with the contribution of metazoans de- creasing as oxygen levels drop. Hypoxia has a significant effect on benthic animals with the consequences that ecosys- tem functions related to macrofauna such as bio-irrigation and bioturbation are significantly affected by hypoxia as well. Since many microbes and microbial-mediated biogeo- chemical processes depend on animal-induced transport pro- cesses (e.g. re-oxidation of particulate reduced sulphur and denitrification), there are indirect hypoxia effects on biogeo- chemistry via the benthos. Severe long-lasting hypoxia and anoxia may result in the accumulation of reduced compounds in sediments and elimination of macrobenthic communities with the consequences that biogeochemical properties dur- ing trajectories of decreasing and increasing oxygen may be different (hysteresis) with consequences for coastal ecosys- tem dynamics.
573 citations
Cites background from "Effects of natural and human-induce..."
...There is an extensive literature on the dynamical response of fauna to hypoxia (Diaz and Rosenberg, 1995, 2008; Levin et al., 2009a), which is beyond the scope of this paper focusing on the consequences for biogeochemistry....
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...Another important factor governing the sensitivity of organisms to hypoxia is the duration of hypoxic conditions, as short-lived events can be survived or avoided by migration (Levin et al., 2009a)....
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...While standard defi-5 nitions of hypoxia are often given, threshold effects vary among taxa, life stages, and settings, and sublethal effects often occur at much higher oxygen levels (e.g., 100µM) (Vaquer-Sunyer and Duarte, 2008; Levin et al., 2009a, b)....
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...…hypoxia will result in migration (away) of large, mobile invertebrates, mortality of selected taxa, emergence and a shallowing of infaunal ac-10 tivities within the sediment column of all but the most hypoxia-tolerant taxa (Pihl et al., 1992; Rabalais et al., 2001a, b; see also Levin et al., 2009)....
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...Naqvi et al. (2009)5 discuss the production and emission of climate active gases from hypoxic areas and Levin et al. (2009) have reviewed the effect of natural and human-induced hypoxia on benthic communities....
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01 Apr 2010
TL;DR: In this paper, the authors estimate dissolved oxygen differences across the global tropical and subtropical oceans within the oxygen minimum zone (200-700-dbar depth) between 1960-1974 (an early period with reliable data) and 1990-2008 (a recent period capturing ocean response to planetary warming).
Abstract: Climate models with biogeochemical components predict declines in oceanic dissolved oxygen with global warming. In coastal regimes oxygen deficits represent acute ecosystem perturbations. Here, we estimate dissolved oxygen differences across the global tropical and subtropical oceans within the oxygen minimum zone (200–700-dbar depth) between 1960–1974 (an early period with reliable data) and 1990–2008 (a recent period capturing ocean response to planetary warming). In most regions of the tropical Pacific, Atlantic, and Indian Oceans the oxygen content in the 200–700-dbar layer has declined. Furthermore, at 200 dbar, the area with O2 <70 μmol kg−1, where some large mobile macro-organisms are unable to abide, has increased by 4.5 million km2. The tropical low oxygen zones have expanded horizontally and vertically. Subsurface oxygen has decreased adjacent to most continental shelves. However, oxygen has increased in some regions in the subtropical gyres at the depths analyzed. According to literature discussed below, fishing pressure is strong in the open ocean, which may make it difficult to isolate the impact of declining oxygen on fisheries. At shallower depths we predict habitat compression will occur for hypoxia-intolerant taxa, with eventual loss of biodiversity. Should past trends in observed oxygen differences continue into the future, shifts in animal distributions and changes in ecosystem structure could accelerate.
515 citations
References
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01 Jan 2008
TL;DR: The formation of dead zones has been exacerbated by the increase in primary production and consequent worldwide coastal eutrophication fueled by riverine runoff of fertilizers and the burning of fossil fuels as discussed by the authors.
Abstract: Dead zones in the coastal oceans have spread exponentially since the 1960s and have serious consequences for ecosystem functioning. The formation of dead zones has been exacerbated by the increase in primary production and consequent worldwide coastal eutrophication fueled by riverine runoff of fertilizers and the burning of fossil fuels. Enhanced primary production results in an accumulation of particulate organic matter, which encourages microbial activity and the consumption of dissolved oxygen in bottom waters. Dead zones have now been reported from more than 400 systems, affecting a total area of more than 245,000 square kilometers, and are probably a key stressor on marine ecosystems.
4,686 citations
TL;DR: Dead zones in the coastal oceans have spread exponentially since the 1960s and have serious consequences for ecosystem functioning, exacerbated by the increase in primary production and consequent worldwide coastal eutrophication fueled by riverine runoff of fertilizers and the burning of fossil fuels.
Abstract: Dead zones in the coastal oceans have spread exponentially since the 1960s and have serious consequences for ecosystem functioning. The formation of dead zones has been exacerbated by the increase in primary production and consequent worldwide coastal eutrophication fueled by riverine runoff of fertilizers and the burning of fossil fuels. Enhanced primary production results in an accumulation of particulate organic matter, which encourages microbial activity and the consumption of dissolved oxygen in bottom waters. Dead zones have now been reported from more than 400 systems, affecting a total area of more than 245,000 square kilometers, and are probably a key stressor on marine ecosystems.
4,667 citations
"Effects of natural and human-induce..." refers background in this paper
...The dramatic increase in incidence of hypoxia from cultural eutrophication in recent decades must be linked to human activities in hypoxia-conducive environments (Diaz and Rosenberg, 2008)....
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...Cultural eutrophication (sensu Nixon, 1995; Diaz and Rosenberg, 1995, 2001, 2008) typically occurs where human population or agricultural production is high (Rabalais, 2004)....
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...Detailed lists of estuaries and bays subject to humaninduced hypoxia and faunal responses are summarized in Diaz and Rosenberg (1995, 2001, 2008) and Gray et al. (2002)....
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...The majority of hypoxic estuaries are reported from the North Atlantic Ocean and adjacent seas (Diaz and Rosenberg, 2008)....
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...The east and west North Atlantic, along with the NW Pacific, support a majority of eutrophication-driven hypoxia records, which mainly occur in bays, estuaries, fjords and enclosed seas (Diaz and Rosenberg, 2008)....
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TL;DR: There is a need in the marine research and management communities for a clear operational definition of the term, eutrophication, and the following are proposed: this definition is consistent with historical usage and emphasizes that eUTrophication is a process, not a trophic state.
Abstract: There is a need in the marine research and management communities for a clear operational definition of the term, eutrophication. I propose the following: This definition is consistent with historical usage and emphasizes that eutrophication is a process, not a trophic state. A simple trophic classification for marine systems is also proposed: Various factors may increase the supply of organic matter to coastal systems, but the most common is clearly nutrient enrichment. The major causes of nutrient enrichment in coastal areas are associated directly or indirecdy with meeting the requirements and desires of human nutrition and diet. The deposition of reactive nitrogen emitted to the atmosphere as a consequence of fossil fuel combustion is also an important anthropogenic factor. The intensity of nitrogen emission from fertilizer, livestock waste, and fossil fuel combustion varies widely among the countries of the world. It is strongest in Europe, the northeastern United States, India/Pakistan, Jap...
2,539 citations
"Effects of natural and human-induce..." refers background in this paper
...Cultural eutrophication (sensu Nixon, 1995; Diaz and Rosenberg, 1995, 2001, 2008) typically occurs where human population or agricultural production is high (Rabalais, 2004)....
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