Hypoxia and Anoxia Research Papers (original) (raw)

This article presents a scientific overview of the processes and the impact of environmental degradation of coastal waters due to human activities on the adjoining land. The direct effects range from eutrophication, harmful algae blooms,... more

This article presents a scientific overview of the processes and the impact of environmental degradation of coastal waters due to human activities on the adjoining land. The direct effects range from eutrophication, harmful algae blooms, to hypoxia and anoxia. The indirect effects are more subtle and can also lead to the collapse of the ecosystem; such is the case of coral reefs. Engineering solutions alone are not available to prevent this degradation that can only be reversed, or prevented, using a basin-wide ecohydrology approach.

Insects exhibit a remarkable array of adaptations that allow them to handle more or less severe hypoxia associated with numerous aquatic and terrestrial habitats. We consider these habitats and then discuss physiological, behavioral and... more

Insects exhibit a remarkable array of adaptations that allow them to handle more or less severe hypoxia associated with numerous aquatic and terrestrial habitats. We consider these habitats and then discuss physiological, behavioral and morphological mechanisms that facilitate insect life under oxygen deprivation. Actually or potentially hypoxic habitats include aquatic systems, flood-prone soils and burrows, intertidal zones, ice encasement and high altitudes. Some microhabitats, including dung, carrion, mammalian alimentary canals, grain and wood, also are subject to hypoxia. Adaptations to hypoxia include the ability to switch from aerobic to anaerobic metabolic pathways (with attendant generation of end products), the ability to drastically attenuate basal metabolic rates, altered behaviors and enlarged tracheal system volumes. Research into the biology of hypoxia seems to be progressing from early observations of the abilities of some insects to withstand exposure to hypoxia or anoxia through studies of organismal mechanisms operating in hypoxia to detailed investigations of cellular and intracellular signaling processes. Our hope is this essay will help crystallize the emergent picture of this area for those interested in contributing to future research.

Waterlogging is a serious problem, which affects crop growth and yield in low lying rainfed areas. The main cause of damage under waterlogging is oxygen deprivation, which affect nutrient and water uptake, so the plants show wilting even... more

Waterlogging is a serious problem, which affects crop growth and yield in low lying rainfed areas. The main cause of damage under waterlogging is oxygen deprivation, which affect nutrient and water uptake, so the plants show wilting even when surrounded by excess of water. Lack of oxygen shift the energy metabolism from aerobic mode to anaerobic mode. Plants adapted to waterlogged conditions, have mechanisms to cope with this stress such as aerenchyma formation, increased availability of soluble sugars, greater activity of glycolytic pathway and fermentation enzymes and involvement of antioxidant defence mechanism to cope with the post hypoxia/anoxia oxidative stress. Gaseous plant hormone ethylene plays an important role in modifying plant response to oxygen deficiency. It has been reported to induce genes of enzymes associated with aerenchyma formation, glycolysis and fermentation pathway. Besides, nonsymbiotic-haemoglobins and nitric oxide have also been suggested as an alternative to fermentation for maintaining lower redox potential (low NADH/NAD ratio), and thereby playing an important role in anaerobic stress tolerance and signaling.

The Late Pennsylvanian Midcontinent Sea (LPMS) of North America, which existed during glacioeustatic highstands of the late Paleozoic ice age, was an immense (>1 × 10 6 km 2) cratonic interior sea exhibiting large-scale estuarine... more

The Late Pennsylvanian Midcontinent Sea (LPMS) of North America, which existed during glacioeustatic highstands of the late Paleozoic ice age, was an immense (>1 × 10 6 km 2) cratonic interior sea exhibiting large-scale estuarine circulation, with a low-salinity surface plume overlying a high-salinity, anoxic, deep water mass. As in river estuaries, these conditions resulted in trapping and recycling of nutrients and organic-reactive elements (e.g., trace metals such as Mo, U, and Zn) in the subpycnoclinal water mass, leading to total organic carbon (TOC) to 40% and peak trace metal enrichment factors (EFs) of 540 (Mo), 73 (U), and 75 (Zn) in the black shale facies of the Hushpuckney Shale. Trace metal EFs increase gradually from distal (Oklahoma) to proximal (Iowa) areas of the Midcontinent Shelf before decreasing abruptly in the Illinois Basin, located to the east of the Mississippi River Arch (MRA). Owing to similar productivity (TOC) and redox (Fe T /Al) proxy values on both sides of this arch, the large differences in trace metal EFs are interpreted to reflect divergent deep-water chemistries; specifically, much larger aqueous trace metal inventories on the Midcontinent Shelf than in the Illinois Basin. This condition implies that (1) deep waters of the Midconti-nent Shelf and Illinois Basin were physically separated by the MRA, demonstrating its existence as a positive bathymetric feature during the Late Pennsylvanian, and (2) the saltwater wedge to the west of the MRA functioned as a nutrient trap in which organic-reactive trace metals were strongly concentrated through water-column recycling.

As part of a study of the effects of seasonal hypoxia on sediment properties, samples were collected during the spring and late summer of 2009 from four sites of similar sediment type and water depth (30-39 m), but different recent... more

As part of a study of the effects of seasonal hypoxia on sediment properties, samples were collected during the spring and late summer of 2009 from four sites of similar sediment type and water depth (30-39 m), but different recent history of bottom water oxygen concentration on the continental shelf of Louisiana. Sediment profile imaging (SPI), box coring, x-radiography, and computed tomography (CT) imaging were employed to characterize the biogenic structural differences in surficial sediments among a normoxic control site and three sites subjected to hypoxic events varying in frequency of occurrence. Results of the CT imagery indicated that macrobenthic biogenic structures were the most numerous at the H7 site that had experienced the least hypoxia in the past 23 years. The E4 site that had experienced hypoxia seasonally with a frequency between 50% and 75% of the time had the fewest biogenic structures in spring 2009, but exhibited recovery in terms of their abundance and diameter in summer 2009. E4 also exhibited high rates of bioturbation during the late-summer sampling as determined from excess 234Th. This suggests that the macrobenthos community at this site was in an active phase of recovery from hypoxia. At the A6 site, exposed to hypoxia with an annual frequency ≥ 75%, biogenic structures were numerous but dimensionally small, correlating with the average individual size of macrobenthos found there. The total volume maxima occupied by biogenic structures in the sediment occurred below the uppermost sediment intervals, with the exception of the spring sample from the D5 site that experienced hypoxia between 25% and 50% of the time. CT-imagery indicating effects of seasonal hypoxia on biogenic structure in the top 10 cm of sediments detected more structures than SPI, x-radiographic imagery, or macrobenthos census data. The presence of relict burrows probably inflated estimates of biogenic structures in the subcores, rendering an integrated result that included creation, destruction, and preservation of burrows and voids over time.

Eutrophication, or excessive nutrient enrichment, is a growing problem around the world. For the past years, it became a serious environmental issue in Manila Bay. This occurrence is continuously degrading its ecological integrity and... more

Eutrophication, or excessive nutrient enrichment, is a growing problem around the world. For the past years, it became a serious environmental issue in Manila Bay. This occurrence is continuously degrading its ecological integrity and causing major changes in its community structure and production. Thus, a deeper understanding of the dynamics of excessive nutrient fluxes in the bay is important in establishing management practices for the recovery of its ecosystem. In this study, more recent field surveys and time-series analyses were done (i) to document the current state of nutrient pollution in Manila Bay from January 2017- November 2018, and (ii) to determine the significant trends of eutrophication from 2012 to present.

The Cariaco Basin is the world’s largest truly marine anoxic basin. We have conducted a comprehensive multidisciplinary investigation of the water column (42–750 m) bracketing the redox boundary (a 250-m thick ‘‘chemocline’’) of the... more

The Cariaco Basin is the world’s largest truly marine anoxic basin. We have conducted a comprehensive multidisciplinary investigation of the water column (42–750 m) bracketing the redox boundary (a 250-m thick ‘‘chemocline’’) of the Cariaco Basin to evaluate linkages between lipid biomarkers, distributions of major dissolved chemical species, and the microbial community and associated redox processes. Our multidimensional data set includes: hydrography, water column chemistry, microbial distributions and rates, and lipid biomarkers. Multivariant statistical analysis of this data set partitions the investigated water column into 5 distinct zones, each characterized by different chemistries, microbiologies and biomarker compositions. The core of this chemocline is a 25-m thick suboxic zone where both dissolved oxygen and sulfide were below detection limits, bacterial and archaeal cell numbers and the rate of chemoautotrophic (dark) carbon fixation are elevated, and dissolved chemical species and bacterial and archaeal lipid biomarkers are indicative of tightly coupled cycles of carbon, nitrogen, and sulfur through chemoautotrophy.

Barrier zones between oxic and anoxic water masses (redoxclines) host highly active prokaryotic communities with important roles in biogeochemical cycling. In Baltic Sea pelagic redoxclines, Epsilonproteobac-teria of the genus... more

Barrier zones between oxic and anoxic water masses (redoxclines) host highly active prokaryotic communities with important roles in biogeochemical cycling. In Baltic Sea pelagic redoxclines, Epsilonproteobac-teria of the genus Sulfurimonas (subgroup GD17) have been shown to dominate chemoautotrophic denitrification. However, little is known on the loss processes affecting this prokaryotic group. In the present study, the protist grazing impact on the Sulfurimonas subgroup GD17 was determined for suboxic and oxygen/hydrogen sulphide interface depths of Baltic Sea redoxclines, using predator exclusion assays and bacterial amendment with the cultured representative 'Sulfurimonas gotlandica' strain GD1. Additionally, the principal bacterivores were identified by RNA-Stable Isotope Probing (RNA-SIP). The natural Sulfurimonas subgroup GD17 population grew strongly under oxygen/hydrogen sulphide interface conditions (doubling time: 1–1.5 days), but protist grazing could consume the complete new cell production per day. In suboxic samples, little or no growth of Sulfurimonas subgroup GD17 was observed. RNA-SIP identified five active grazers, belonging to typical redoxcline ciliates (Oligohy-menophorea, Prostomatea) and globally widespread marine flagellate groups (MAST-4, Chrysophyta, Cer-cozoa). Overall, we demonstrate for the first time that protist grazing can control the growth, and potentially the vertical distribution, of a chemolithoautotrophic key-player of oxic/anoxic interfaces.

It is well known that many anoxia/hypoxia tolerant species when exposed to anoxia/hypoxia respond by increasing the activity/expression of antioxidant enzymes and/or glutathione levels—a phenomenon called " preparation for oxidative... more

It is well known that many anoxia/hypoxia tolerant species when exposed to anoxia/hypoxia respond by increasing the activity/expression of antioxidant enzymes and/or glutathione levels—a phenomenon called " preparation for oxidative stress " (POS). This phenomenon was also observed during freezing exposure, severe dehydration, aerial exposure of water-breathing animals and estivation. However, as far as we know, there is no analysis available of the prevalence of POS among animal species. A major problem is the very definition of POS, since many animal species show both increases and decreases of antioxidants during low oxygen stress and estivation. Therefore, we established three different criteria; from inclusive to restrictive and analyzed how widespread the POS phenomenon is in the animal kingdom. We analyzed all available papers in several databases about the modulation of antioxidant defenses during oxygen deprivation or estivation. Based on the magnitude of change (as % change) during the specific low oxygen stresses or estivation, we classified each species as POS-positive, POS-negative or POS-neutral, considering the three different criteria. The prevalence of POS-positive animals (102 species from 8 phyla) was stress-dependent: in estivation and dehydration it was 91–100%, while in hypoxia it was 37.5–53%, depending on the criteria. In the case of air exposure, anoxia and freezing the proportions of POS-positive species were 54–77%, 64–77% and 75–86%, respectively. Overall, the prevalence of POS was 58 to 68% when all stresses and all species were analyzed together. The results indicate the key importance of POS as a survival strategy of animals exposed to freezing, dehydration and estivation, and, to a lesser extent, to oxygen deprivation itself (i.e. hypoxia and anoxia).

A series of C15–C20 mid-chain methoxylated fatty acids (FAs) has been tentatively identified in suspended particulate matter samples from within the chemocline of the Cariaco Basin. The concentrations appeared to be highest (50 ng/l)... more

A series of C15–C20 mid-chain methoxylated fatty acids (FAs) has been tentatively identified in suspended
particulate matter samples from within the chemocline of the Cariaco Basin. The concentrations appeared
to be highest (50 ng/l) within the core of the chemocline (245–256 m), where they constituted 25% of the
total FAs, 9-methoxy-C16:0 and 10-methoxy-C16:0 being 73% of the total methoxy acids. Mid-chain methoxy
acids in the chemocline had d13Cvalues of ca.34‰. In stable isotope probing experiments using 13Clabeled
bicarbonate and various sulfur species (S2O2
3 , SO2
3 and particulate S0), up to 80% of 9-/10-methoxy-C16:0
were 13C labeled when thiosulfate was provided. Therefore, we propose that mid-chain methoxy FAs are
key membrane lipids in sulfur-metabolizing chemoautotrophs within the core of the chemocline. Sulfuroxidizing
bacteria belong to both the e- and b-proteobacteria; half of the bacteria within the chemocline
are either e-proteobacteria (40%) or b-proteobacteria (11%), providing a possible clue to the phylogeny
of chemoautotrophs and a link to the production of chemoautotrophic biomarkers.Wethus demonstrate an
association between the presence and activity of sulfur-utilizing chemoautotrophs and occurrence of midchain
methoxylated FAs within the chemocline of the Cariaco Basin.

Prolyl 4-hydroxylases (P4H; EC 1.14.11.2) have been studied extensively in various organisms and recently in relation to oxygen deficiency while little is known about their role in response to similar stresses in plants. To this... more

Prolyl 4-hydroxylases (P4H; EC 1.14.11.2) have been studied extensively in various organisms and recently in relation to oxygen deficiency while little is known about their role in response to similar stresses in plants. To this direction, we investigated the expression patterns of Arabidopsis P4Hs under hypoxia, anoxia and mechanical wounding. The 13 Arabidopsis P4Hs are low-abundance transcripts with differential patterns of expression in response to two hypoxic, 1.5% and 5% O2, anoxic conditions and mechanical wounding. The majority of AtP4Hs showed higher levels of expression in roots compared with shoots under hypoxia and anoxia. Hypoxia of 1.5% O2 induced the expression of six AtP4Hs, while hypoxia of 5% O2 and anoxia induced the expression of three and two AtP4Hs, respectively. Moreover, we identified in silico, 308 Arabidopsis genes among the differentially expressed genes under hypoxia that contain proline hydroxylation motifs. It is likely that the AtP4Hs hydroxylate proline residue(s) of the 308 polypeptides suggest involvement in their post-translational modification process. This modification might serve as an alternative level of regulation for the function of these polypeptides in the context of hypoxic response. Furthermore, six AtP4Hs were upregulated in response to mechanical wounding, suggesting involvement in this stress response.

A large area of axis sediment (>500 m2) may be annually removed from the head of Monterey Submarine Canyon with the first onshore storm of the fall/winter storm season. In this scenario, flushing events are followed by accumulation of... more

A large area of axis sediment (>500 m2) may be annually removed from the head of Monterey Submarine Canyon with the first onshore storm of the fall/winter storm season. In this scenario, flushing events are followed by accumulation of sediment and organic debris—especially macro-algae—in the shallow axis. Net accumulation of this fill material increases during the calmer spring and summer until the next fall-flushing. The benthic community at a canyon axis station was characterized by highly fluctuating populations of opportunistic polychaete worms and gammarid amphipods, primarily Capitella spp., Armandia brevis, and Orchomene pacifica. The canyon axis community was very different from communities living at two other stations where sudden flushing does not occur—an adjacent sloping-wall station and a sandflat station. Sloping-wall and sandflat stations harbored more and longer-lived species, larger individuals, and a less-variable population structure during a year of sampling. The Loma Prieta earthquake in the fall of 1989 triggered small sediment slumps on the canyon walls, but it did not trigger axis-flushing. The usual seasonal flushing of the axis occurred 2 weeks after the earthquake with the arrival of the first storm. Benthic communities were reduced in abundance inside earthquake-induced slumps; however, the slumped areas were rapidly colonized by Prionospio pygmaea, a polychaete opportunist common to the sandflat. Surprisingly, the physical and biological impacts of the earthquake were much less severe than the seasonal axis-flushing associated with storms. Observations of sediment-flushing combined with measurements of benthic community changes in Monterey Canyon head represent a step towards an ecological model of mass wasting with implications for the continental shelf and slope and possibly the deep sea. © 1997 Elsevier Science Ltd

Massively parallel tag sequencing was applied to describe the bacterial diversity in the redox transition and anoxic zones of the Cariaco Basin. In total, 14 samples from the Cariaco Basin were collected over a period of eight years from... more

Massively parallel tag sequencing was applied to describe the bacterial diversity in the redox transition and anoxic zones of the Cariaco Basin. In total, 14 samples from the Cariaco Basin were collected over a period of eight years from two stations. A total of 244 357 unique bacterial V6 amplicons were sequenced. The total number of operational taxonomic units (OTUs) found in this study was 4692, with a range of 511–1491 OTUs per sample. Approximately 95% of the OTUs found in the redox transition zone and anoxic layers of Cariaco are represented by less than 50 amplicons suggesting that only about 5% of the bacterial OTUs are responsible for the bulk of the microbial processes in the basin redox transition and anoxic zones. The same dominant OTUs were observed across all eight years of sampling although periodic fluctuations in their proportion were apparent. No distinctive differences were observed between the bacterial communities from the redox transition and anoxic layers of the Cariaco Basin water column. The largest proportion of amplicons belongs to Gammaproteobacteria represented mostly by sulfide oxidizers, followed by Marine Group A (originally described as SAR406; Gordon and Giovannoni 1996), a group of uncultured bacteria hypothesized to be involved in metal reduction, and sulfate-reducing Deltaproteobacteria. Gammaproteobacteria, Deltaproteobacteria and Marine Group A make up 67–90% of all V6 amplicons sequenced in this study. This strongly suggests that the basin's microbial communities are actively involved in the sulfur-related metabolism and coupling of the sulfur and carbon cycles. According to detrended canonical correspondence analysis, ecological factors such as chemoautotrophy, nitrate and oxidized and reduced sulfur compounds influence the structuring and distribution of the Cariaco microbial communities.

Determining the biomass of microbial plankton is central to the study of fluxes of energy and materials in aquatic ecosystems. This is typically accomplished by applying proper volume-to-carbon conversion factors to group-specific... more

Determining the biomass of microbial plankton is central to the study of fluxes of energy and materials in aquatic ecosystems. This is typically accomplished by applying proper volume-to-carbon conversion factors to group-specific abundances and biovolumes. A critical step in this approach is the accurate estimation of biovolume from two-dimensional (2D) data such as those available through conventional microscopy techniques or flow-through imaging systems. This paper describes a simple yet accurate method for the assessment of the biovo-lume of planktonic microorganisms, which works with any image analysis system allowing for the measurement of linear distances and the estimation of the cross sectional area of an object from a 2D digital image. The proposed method is based on Archimedes' principle about the relationship between the volume of a sphere and that of a cylinder in which the sphere is inscribed, plus a coefficient of 'unellipticity' introduced here. Validation and careful evaluation of the method are provided using a variety of approaches. The new method proved to be highly precise with all convex shapes characterised by approximate rotational symmetry , and combining it with an existing method specific for highly concave or branched shapes allows covering the great majority of cases with good reliability. Thanks to its accuracy, consistency , and low resources demand, the new method can conveniently be used in substitution of any extant method designed for convex shapes, and can readily be coupled with automated cell imaging technologies, including state-of-the-art flow-through imaging devices.

We assessed the effects of hypoxia on macro-benthic communities in the York and Rappahannock Rivers, Chesapeake Bay, in box-core samples before and after hypoxic episodes in 2003 and 2004. Hypoxia occurred in both years and was associated... more

We assessed the effects of hypoxia on macro-benthic communities in the York and Rappahannock Rivers, Chesapeake Bay, in box-core samples before and after hypoxic episodes in 2003 and 2004. Hypoxia occurred in both years and was associated with a decrease in biomass and a shift in community structure toward opportunistic species in both rivers. Long-term data indicate that the frequency of hypoxia in the York has increased over the last 22 years. In previous work from ∼20 years ago, the macro-benthic community structure did not change in response to hypoxia in the York; however, in the present study hypoxia was associated with a reduction in community biomass and a change in community structure. We conclude that currently hypoxia is a more important environmental problem in the York than in previous years. Hypoxia likely negatively affects the estuarine food web, as lower macrobenthic biomass could decrease food availability to epibenthic predators.