Posts Tagged 'sediment'

Biological effects of the antihypertensive losartan under different ocean acidification scenarios

Highlights

  • Losartan was quantified in samples of marine water (up to 7.63 ng/L) and sediment (up to 3.10 ng/g).
  • Sediment spiked with an environmental concentration of losartan affected lysosomal stability.
  • Losartan effects were pH dependent and pH effects were dependent on the concentration of losartan.
  • Ocean acidification exacerbates the negative effects of losartan in waterborne exposure.

Abstract

Since the last decade, several studies have reported the presence and effects of pharmaceutical residues in the marine environment, especially those of the antihypertensive class, such as losartan. However, there is little knowledge about the physiological effects of losartan in marine invertebrates regarding its behavior under possible coastal ocean acidification scenarios. The objective of this study was to evaluate biological effects on marine organisms at different levels of the biological organization caused by the compound losartan in water and sediment under coastal ocean acidification scenarios. Water and sediment samples were collected at five sites around the Santos Submarine Sewage outfall (SSO) and two sites around the Guarujá Submarine Sewage Outfall (GSO). Losartan was found in concentrations ranging from <LOD to 7.63 ng/L in water and from <LOQ to 3.10 ng/g in sediments. Statistical analysis showed interactive effects pH and losartan on the toxicity results. The water toxicity test with Echinometra lucunter embryos/larvae showed LOECs 50–100 mg/L, with values decreasing as the pH decreased. In the sediment assays, LOEC value for sea urchin embryo-larval development was 1.0 μg/g for all tested pHs. Regarding the lysosomal membrane stability assays with adult bivalves, a LOEC of 3000 ng/L was found for Perna perna in water exposure (both at pH 8.0 and 7.6). Effects for Mytella guyanensis were observed at environmentally relevant concentrations in sediment (LOEC = 3 ng/g at pH 8.0 and 7.6). This study demonstrated that coastal ocean acidification by itself causes effects on marine invertebrates, but can also increase the negative effects of losartan in waterborne exposure. There is a need to deepen the studies on the ecotoxicity of pharmaceutical residues and acidification of the marine environment.

Continue reading ‘Biological effects of the antihypertensive losartan under different ocean acidification scenarios’

First record of straight-needle pteropod Creseis acicula Rang, 1828 bloom in the Çanakkale Strait (NE Aegean Sea, Turkey)

Pteropods are marine pelagic calcifier mollusks sensitive to chemical changes in seawater due to their highly soluble aragonite shells. Increased acidity (reduced pH) of seawater causes difficulties in precipitating their shells and/or results in their dissolution, which is related to increased atmospheric CO2 concentrations and warming of seawater. They are therefore indicators of environmental changes. In this paper, we present the first record of the straight-needle pteropod Creseis acicula Rang, 1828 bloom in the surface waters of the Ҫanakkale Strait, Turkey (NE Aegean Sea), encountered in July 2020, when the highest sea surface temperatures and pH levels since 2007 were recorded. In coastal zones, such as the Ҫanakkale Strait, anthropogenic activity contributes significantly to environmental changes. Consequently, the increase in pH at elevated temperatures indicates an auxiliary factor (i.e. anthropogenic activity) that triggered the C. acicula bloom, rather than global atmospheric CO2 levels.

Continue reading ‘First record of straight-needle pteropod Creseis acicula Rang, 1828 bloom in the Çanakkale Strait (NE Aegean Sea, Turkey)’

Stimulation of N2O emission via bacterial denitrification driven by acidification in estuarine sediments

Ocean acidification in nitrogen-enriched estuaries has raised global concerns. For decades, biotic and abiotic denitrification in estuarine sediments have been regarded as the major ways to remove reactive nitrogen, but they occur at the expense of releasing greenhouse gas nitrous oxide (N2O). However, how these pathways respond to acidification remains poorly understood. Here we performed a N2O isotopocules analysis coupled with respiration inhibition and molecular approaches to investigate the impacts of acidification on bacterial, fungal, and chemo-denitrification, as well as N2O emission, in estuarine sediments through a series of anoxic incubations. Results showed that acidification stimulated N2O release from sediments, which was mainly mediated by the activity of bacterial denitrifiers, while in neutral environments, N2O production was dominated by fungi. We also found that the contribution of chemo-denitrification to N2O production cannot be ignored, but was not significantly affected by acidification. The mechanistic investigation further demonstrated that acidification changed the keystone taxa of sedimentary denitrifiers from N2O-reducing to N2O-producing ones, and reduced microbial electron transfer efficiency during denitrification. These findings provide novel insights into how acidification stimulates N2O emission and modulates its pathways in estuarine sediments, and how it may contribute to the acceleration of global climate change in the Anthropocene.

Continue reading ‘Stimulation of N2O emission via bacterial denitrification driven by acidification in estuarine sediments’

Efeitos biológicos da orfenadrina sob diferentes cenários de acidificação oceânica (in Portuguese)

O aumento das emissões de gás carbônico atmosférico proveniente de atividades antrópicas desde a Revolução Industrial teve como consequência uma maior participação de águas superficiais no processo de sequestro de dióxido de carbono, a fim de amenizar o efeito estufa. A principal consequência do aumento de captura de gás carbônico pelos oceanos é um fenômeno denominado acidificação oceânica. Alguns poluentes presentes na água, como por exemplo fármacos e produtos de cuidados pessoais (FPCPs) podem sofrer alterações na sua mobilidade e biodisponibilidade por conta da diminuição do pH do meio. Atualmente a quantidade de dados sobre os efeitos e o risco ambiental de FPCPs em organismos marinhos ainda é escassa. Diante deste cenário o presente estudo teve como objetivo analisar a ocorrência, o comportamento e a biodisponibilidade do fármaco orfenadrina frente a diferentes cenários de acidificação oceânica. O fármaco orfenadrina, empregado como relaxante muscular e amplamente consumido foi observado em todos os pontos de amostragem das áreas de influência dos emissários submarinos de Santos e Guarujá – SP, com concentrações que variaram LOQ a 0,5 ng/g em sedimentos. Os resultados do ensaio de toxicidade com água empregando ouriços do mar (Echinometra lucunter) nos diferentes pHs 8,0; 7,6; 7,3 apresentaram valores de CEO de 0,05mg/L e o EpH50 foi estabelecido em 7,30. Quanto aos ensaios com mexilhões Perna perna foram observados efeitos em concentrações ambientalmente relevantes, com CEO de 200 ng/g. Os resultados dos ensaios feitos para a avaliação do desenvolvimento embriolarval em água indicaram que tanto o processo de acidificação quanto o aumento da concentração afetam o desenvolvimento dos embriões de ouriço do mar. Já nos ensaios com P. perna foi possível verificar ainda que a presença do fármaco de caráter básico reduziu os efeitos da acidificação oceânica. Os resultados da análise de bioacumulação detectaram a presença da orfenadrina em todos os tecidos analisados. A análise dos ensaios de citotoxicidade nesta ocasião refutou a hipótese inicial do estudo, visto que a presença do fármaco de caráter básico reduziu os efeitos da acidificação oceânica. Neste sentido, fica evidente necessidade de se aprofundar os estudos sobre toxicologia relacionada a fármacos sob cenários de acidificação em ambiente marinho.

Continue reading ‘Efeitos biológicos da orfenadrina sob diferentes cenários de acidificação oceânica (in Portuguese)’

Sculpture and new technologies in scientific educational outreach: 3D foraminiferal models as a referent of ocean acidification and climate change

The Foraminifera Project is a collaboration between researchers of the Faculty of Fine Arts and the Faculty of Geological Sciences at the Complutense University (UCM, Madrid, Spain). The work, based on scientific dissemination through art, is framed in the theme “Climate change and Ocean Acidification” as part of the course “Art, Science and Nature” of the Master’s Degree in Research in Art and Creation (Faculty of Fine Arts, UCM). The team used recent sediment samples from Indian Ocean and Red Sea that contained healthy and unhealthy foraminifera specimens to create 3D specimen models. These models were made using traditional sculpture techniques, photogrammetry, and 3D printing to show different states of foraminifera dissolution and corrosion from ocean acidification. The end result of this project resulted in nine interactive pieces which were part of the exhibition “Drift & Migrate” open to the public during the month of November 2019 in the exhibition hall of the Faculty of Fine Arts (UCM). The 3D models of foraminifera were displayed with educational graphics and blind-accesible explanatory signage (Braille) to share the scientific facts of foraminifera and their role in the ocean ecosystem. The main objective of the collaboration is to raise awareness of anthropogenic effects on foraminifera and the marine ecosystems in general and to expand research opportunities between the arts and sciences at the university.

Continue reading ‘Sculpture and new technologies in scientific educational outreach: 3D foraminiferal models as a referent of ocean acidification and climate change’

Ocean acidification may mitigate negative effects of warming on carbon burial potential in subtidal unvegetated estuarine sediments

Estuarine sediments make an important contribution to the global carbon cycle, but we do not know how this will change under a future climate, which is expected to have lower pH oceans and frequent high-temperature days. Six combinations of warming and partial pressures of CO2 (pCO2) were chosen to investigate the combined and individual effects of short-term pressures on the diel metabolic response of shallow unvegetated sediments ex-situ. Whereas warming significantly increased respiration, making sediments more heterotrophic, high-pCO2 increased net primary productivity, resulting in less heterotrophic sediments. As a result, warming decreased the carbon burial potential of estuarine sediments and high-pCO2 had the opposite effect. High-pCO2 mitigates the negative effects of warming on benthic metabolism under the combined scenario, with carbon burial similar to that expected under high-pCO2 conditions alone. Climate scenarios also changed the diurnal pCO2 variation, with ranges increasing by 33% with warming, and almost doubling under high-pCO2 conditions. An additive response in pCO2 variability was observed under the combined scenario, increasing to 2.3× the current diel-pCO2 range, highlighting the reduced buffering capacity of the water associated with a high CO2 climate. Future carbon burial and export under increased frequencies of unseasonably warm days projected for mid and end of century (30% and 50% of days-per-year, respectively) were estimated with and without ocean acidification. By 2100, warming alone could decrease annual estuarine sediment burial potential by 25%. However, ocean acidification could mitigate the negative effects of more frequent high-temperature days and increase carbon burial potential over current conditions by ~18%.

Continue reading ‘Ocean acidification may mitigate negative effects of warming on carbon burial potential in subtidal unvegetated estuarine sediments’

Multiple ecological parameters affect living benthic foraminifera in the river-influenced west-central Bay of Bengal

The huge riverine influx and associated processes decrease the ambient salinity, stratify the water column, modulate the oxygen-deficient zone, and are also responsible for the recent acidification in the Bay of Bengal. Here, we have studied the effect of these riverine influx-dominated ecological parameters on living benthic foraminifera in the west-central Bay of Bengal. We report that the pH below 7.6 in front of the Krishna river, reduces the diversity and the richness of living benthic foraminifera on the adjacent shelf and the slope. A similar decreased diversity and richness is also observed in front of the Godavari River. We delineate three prominent assemblages, representing different depth zones with associated distinct physico-chemical conditions. The shallow water assemblage (∼27–100 m) is represented by Nonionella labradoricaHanzawaia nipponicaBrizalina dilatataAmmonia tepida, and Nonionella limbato-striata. These species are adapted to relatively warmer temperatures and more oxygenated waters. The deepwater assemblage (∼1,940–2,494 m) includes Bulimina cf. delreyensis, Bulimina marginataHormosinella guttiferaCassidulina laevigata, and Gyroidinoides subzelandica and can tolerate a relatively colder temperature. The intermediate-depth assemblage (∼145–1,500 m) dominated by Eubuliminella exilis, Bolivinellina earlandiFursenkoina spinosaBolivinellina lucidopunctataGlobobulimina globosa, Fursenkoina spinosa, Eubuliminella cassandrae, Uvigerina peregrina, Rotaliatinopsis semiinvoluta, and Cassidulina laevigata, represents oxygen-deficient and organic carbon-rich environment. Besides the pH, temperature, dissolved oxygen and organic matter, we also report a strong influence of bathymetry, coarse fraction (CF) and the type of organic matter on a few living benthic foraminifera. The ecological preferences of 40 such dominant living benthic foraminifera, each representing a specific environment, have also been reported for site-specific proxy. We conclude that although the huge riverine influx affects living benthic foraminifera on the shelf, the dissolved oxygen and organic carbon mostly control benthic foraminiferal distribution in the deeper west-central Bay of Bengal.

Continue reading ‘Multiple ecological parameters affect living benthic foraminifera in the river-influenced west-central Bay of Bengal’

Biogeochemical feedbacks to ocean acidification in a cohesive photosynthetic sediment

Ecosystem feedbacks in response to ocean acidification can amplify or diminish the diel pH oscillations that characterize productive coastal waters. We report that benthic microalgae generate such oscillations in the porewater of cohesive sediment and ask how carbonation (acidification) of the overlying seawater alters these in the absence and presence of biogenic calcite. To do so, we placed a 1-mm layer of ground oyster shells (Treatment) or sand (Control) onto intact sediment cores free of large dwelling fauna, and then gradually increased the pCO2 in the seawater above half of the Treatment and Control cores from 472 to 1216 μatm (pH 8.0 to 7.6, CO2:HCO3 from 4.8 to 9.6 x 10-4). Vertical porewater [O2] and [H+] microprofiles measured 16 d later showed that this carbonation had decreased O2 penetration in all cores, indicating a metabolic response. In carbonated seawater: (1) sediment biogeochemical processes added and removed more H+ to and from the porewater in darkness and light, respectively, than in ambient seawater increasing the amplitude of the dark–light porewater [H+] oscillations, and (2) the dissolution of calcite decreased the porewater [H+] below that in overlying seawater, reversing the dark sediment–seawater H+ flux and decreasing the amplitude of diel [H+] oscillations. This dissolution did not, however, counter the negative effect of carbonation on sediment O2 penetration. We hypothesise that the latter effect and the observed enhanced acidification of the sediment porewater were caused by an ecosystem feedback: a CO2-induced increase in the microbial reoxidation of reduced solutes with O2.

Continue reading ‘Biogeochemical feedbacks to ocean acidification in a cohesive photosynthetic sediment’

Impacts of multiple stressors on a benthic foraminiferal community: a long-term experiment assessing response to ocean acidification, hypoxia and warming

Ocean chemistry is changing as a result of human activities. Atmospheric carbon dioxide (CO2) concentrations are increasing, causing an increase in oceanic pCO2 that drives a decrease in oceanic pH, a process called ocean acidification (OA). Higher CO2 concentrations are also linked to rising global temperatures that can result in more stratified surface waters, reducing the exchange between surface and deep waters; this stronger stratification, along with nutrient pollution, contributes to an expansion of oxygen-depleted zones (so called hypoxia or deoxygenation). Determining the response of marine organisms to environmental changes is important for assessments of future ecosystem functioning. While many studies have assessed the impact of individual or paired stressors, fewer studies have assessed the combined impact of pCO2, O2, and temperature. A long-term experiment (∼10 months) with different treatments of these three stressors was conducted to determine their sole or combined impact on the abundance and survival of a benthic foraminiferal community collected from a continental-shelf site. Foraminifera are well suited to such study because of their small size, relatively rapid growth, varied mineralogies and physiologies. Inoculation materials were collected from a ∼77-m deep site south of Woods Hole, MA. Very fine sediments (<53 μm) were used as inoculum, to allow the entire community to respond. Thirty-eight morphologically identified taxa grew during the experiment. Multivariate statistical analysis indicates that hypoxia was the major driving factor distinguishing the yields, while warming was secondary. Species responses were not consistent, with different species being most abundant in different treatments. Some taxa grew in all of the triple-stressor samples. Results from the experiment suggest that foraminiferal species’ responses will vary considerably, with some being negatively impacted by predicted environmental changes, while other taxa will tolerate, and perhaps even benefit, from deoxygenation, warming and OA.

Continue reading ‘Impacts of multiple stressors on a benthic foraminiferal community: a long-term experiment assessing response to ocean acidification, hypoxia and warming’

Ocean acidification induces changes in virus–host relationships in Mediterranean benthic ecosystems

Acidified marine systems represent “natural laboratories”, which provide opportunities to investigate the impacts of ocean acidification on different living components, including microbes. Here, we compared the benthic microbial response in four naturally acidified sites within the Southern Tyrrhenian Sea characterized by different acidification sources (i.e., CO2 emissions at Ischia, mixed gases at Panarea and Basiluzzo and acidified freshwater from karst rocks at Presidiana) and pH values. We investigated prokaryotic abundance, activity and biodiversity, viral abundance and prokaryotic infections, along with the biochemical composition of the sediment organic matter. We found that, despite differences in local environmental dynamics, viral life strategies change in acidified conditions from mainly lytic to temperate lifestyles (e.g., chronic infection), also resulting in a lowered impact on prokaryotic communities, which shift towards (chemo)autotrophic assemblages, with lower organic matter consumption. Taken together, these results suggest that ocean acidification exerts a deep control on microbial benthic assemblages, with important feedbacks on ecosystem functioning.

Continue reading ‘Ocean acidification induces changes in virus–host relationships in Mediterranean benthic ecosystems’

Experimental assessment of the impacts of ocean acidification and urchin grazing on benthic kelp forest assemblages

Ocean acidification (OA) is likely to differentially affect the biology and physiology of calcifying and non-calcifying taxa, thereby potentially altering key ecological interactions (e.g., facilitation, competition, predation) in ways that are difficult to predict from single-species experiments. We used a two-factor experimental design to investigate how multispecies benthic assemblages in southern California kelp forests respond to OA and grazing by the purple sea urchinStrongylocentrotus purpuratus. Settlement tiles accrued natural mixed assemblages of algae and invertebrates in a kelp forest off San Diego, CA for one year before being exposed to OA and grazing in a laboratory experiment for two months. Space occupying organisms were identified and pooled into six functional groups: calcified invertebrates, non-calcified invertebrates, calcified algae, fleshy algae, sediment, and bare space for subsequent analyses of community structure. Interestingly, communities that developed on separate tile racks were unique, despite being deployed close in space, and further changes in community structure in response to OA and grazing depended on this initial community state. On Rack 1, we found significant effects of both pCO2 and grazing with elevated pCO2 increasing cover of fleshy algae, but sea urchin grazers decreasing cover of fleshy algae. On Rack 2, we found a ~ 35% higher percent cover of sediment on tiles reared in ambient pCO2 but observed ~27% higher cover of bare space in the high pCO2 conditions. On Rack 3, we found an average of 45% lower percent cover of calcified sessile invertebrates at ambient pCO2 than in high pCO2 treatments on Rack 3. Net community calcification was 137% lower in elevated pCO2 treatments. Kelp sporophyte densities on tiles without urchins were 74% higher than on tiles with urchins and kelp densities were highest in the elevated pCO2 treatment. Urchin growth and grazing rates were 49% and 126% higher under ambient than high pCO2 conditions. This study highlights consistent negative impacts of OA on community processes such as calcification and grazing rates, even though impacts on community structure were highly context-dependent.

Continue reading ‘Experimental assessment of the impacts of ocean acidification and urchin grazing on benthic kelp forest assemblages’

Warming and ocean acidification may decrease estuarine dissolved organic carbon export to the ocean (update)

Relative to their surface area, estuaries make a disproportionately large contribution of dissolved organic carbon (DOC) to the global carbon cycle, but it is unknown how this will change under a future climate. As such, the response of DOC fluxes from microbially dominated unvegetated sediments to individual and combined future climate stressors of temperature change (from Δ−3 to Δ+5 C compared to ambient mean temperatures) and ocean acidification (OA, ∼ 2× current CO2 partial pressure, pCO2) was investigated ex situ. Warming alone increased sediment heterotrophy, resulting in a proportional increase in sediment DOC uptake; sediments became net sinks of DOC (3.5 to 8.8 mmol C m−2 d−1) at warmer temperatures (Δ+3 and Δ+5 C, respectively). This temperature response changed under OA conditions, with sediments becoming more autotrophic and a greater sink of DOC (up to 4× greater than under current pCO2 conditions). This response was attributed to the stimulation of heterotrophic bacteria with the autochthonous production of labile organic matter by microphytobenthos. Extrapolating these results to the global area of unvegetated subtidal estuarine sediments, we find that the future climate of warming (Δ+3 C) and OA may decrease estuarine export of DOC by ∼ 80 % (∼ 150 Tg C yr−1) and have a disproportionately large impact on the global DOC budget.

Continue reading ‘Warming and ocean acidification may decrease estuarine dissolved organic carbon export to the ocean (update)’

The effects of decomposing invasive jellyfish on biogeochemical fluxes and microbial dynamics in an ultra-oligotrophic sea

Over the past several decades, jellyfish blooms have intensified spatially and temporally, affecting functions and services of ecosystems worldwide. At the demise of a bloom, an enormous amount of jellyfish biomass sinks to the seabed and decomposes. This process entails reciprocal microbial and biogeochemical changes, typically enriching the water column and seabed with large amounts of organic and inorganic nutrients. Jellyfish decomposition was hypothesized to be particularly important in nutrient-impoverished ecosystems, such as the Eastern Mediterranean Sea – one of the most oligotrophic marine regions in the world. Since the 1970s, this region has been experiencing the proliferation of a notorious invasive scyphozoan jellyfish, Rhopilema nomadica. In this study, we estimated the short-term decomposition effects of R. nomadica on nutrient dynamics at the sediment-water interface. Our results show that the degradation of R. nomadica has led to increased oxygen demand and acidification of overlying water as well as high rates of dissolved organic nitrogen and phosphate production. These conditions favored heterotrophic microbial activity and bacterial biomass accumulation, and triggered a shift towards heterotrophic biodegrading bacterial communities, whereas autotrophic picophytoplankton abundance was moderately affected or reduced. This shift may further decrease primary production in the water column of the Eastern Mediterranean Sea. Deoxygenation, acidification, nutrient enrichment, and microbial community shifts at the sediment-water interface may have a detrimental impact on macrobenthic communities. Based on these findings, we suggest that jelly-falls and their decay may facilitate an additional decline in ecosystem functions and services.

Continue reading ‘The effects of decomposing invasive jellyfish on biogeochemical fluxes and microbial dynamics in an ultra-oligotrophic sea’

Ocean warming and acidification uncouple calcification from calcifier biomass which accelerates coral reef decline

Global climate change will drive declines in coral reefs over coming decades. Yet, the relative role of temperature versus acidification, and the ability of resultant ecosystems to retain core services such as coastal protection, are less clear. Here, we investigate changes to the net chemical balances of calcium carbonate within complex experimental coral reefs over 18 months under conditions projected for 2100 if CO2 emissions continue unmitigated. We reveal a decoupling of calcifier biomass and calcification under the synergistic impact of warming and acidification, that combined with increased night-time dissolution, leads to an accelerated loss of carbonate frameworks. Climate change induced degradation will limit the ability of coral reefs to keep-up with sea level rise, possibly for thousands of years. We conclude that instead of simply transitioning to alternate states that are capable of buffering coastlines, reefs are at risk of drowning leading to critical losses in ecosystem functions.

Continue reading ‘Ocean warming and acidification uncouple calcification from calcifier biomass which accelerates coral reef decline’

Ocean acidification and short‐term organic matter enrichment alter coral reef sediment metabolism through different pathways

Ocean acidification (OA) and organic matter (OM) enrichment (due to coastal eutrophication) could act in concert to shift coral reef carbonate sediments from a present state of net calcification to a future state of net dissolution, but no studies have examined the combined effect of these stressors on sediment metabolism and dissolution. This study used 22‐hour incubations in flume aquaria with captive sediment communities to measure the combined effect of elevated pCO2 (representing Ocean Acidification) and particulate organic carbon (representing coastal eutrophication) on coral reef sediment gross primary productivity (GPP), respiration (R), and net calcification (Gnet). Relative to control sediment communities, both OA (pCO2 ~ 1000 μatm) and OM enrichment (~ + 40 μmol C L‐1) significantly decreased rates of sediment Gnet by 1.16 and 0.18 mmol CaCO3 m‐2 h‐1, respectively, but the mechanism behind this decrease differed. The OA‐mediated transition to net dissolution was physiochemical, as rates of GPP and R remained unaffected and dissolution was solely enhanced by a decline in the aragonite saturation state (Ωarg) of the overlying water column and the physical factors governing the porewater exchange rate with this overlying water column. In contrast, the OM‐mediated decline in Gnet was due to a decline in the overlying seawater Ωarg due to the increased respiratory addition of CO2. The decrease in Gnet in response to a combination of both stressors was additive (‐ 0.09 mmol CaCO3 m‐2 h‐1 relative to OA alone) but this decrease did not significantly differ from the individual effect of either stressor. In this study OA was the primary driver of future carbonate sediment dissolution, but longer‐term experiments with chronic organic matter enrichment are required.

Continue reading ‘Ocean acidification and short‐term organic matter enrichment alter coral reef sediment metabolism through different pathways’

Effects of warming and CO2 enrichment on O2 consumption, porewater oxygenation and pH of subtidal silt sediment

We investigated the effects of seawater warming and CO2 enrichment on the microbial community metabolism (using O2 consumption as a proxy) in subtidal silt sediment. Intact sediment cores, without large dwelling infauna, were incubated for 24 days at 12 (in situ) and 18 °C to confirm the expected temperature response. We then enriched the seawater overlying a subset of cold and warm-incubated cores with CO2 (+ ΔpCO2: 253–396 µatm) for 16 days and measured the metabolic response. Warming increased the depth-integrated volume-specific O2 consumption (Rvol), the maximum in the volume-specific O2 consumption at the bottom of the oxic zone (Rvol,bmax) and the volume-specific net O2 production (Pn,vol), and decreased the O2 penetration depth (O2-pd) and the depth of Rvol,bmax (depthbmax). Benthic photosynthesis oscillated the pH in the upper 2 mm of the sediment. CO2 enrichment of the warm seawater did not alter this oscillation but shifted the pH profile towards acidity; the effect was greatest at the surface and decreased to a depth of 12 mm. Confoundment rendered the CO2 treatment of the cold seawater inconclusive. In warm seawater, we found no statistically clear effect of CO2 enrichment on RvolRvol,bmaxPn,vol, O2-pd, or depthbmax and therefore suspect that this perturbation did not alter the microbial community metabolism. This confirms the conclusion from experiments with other, contrasting types of sediment.

Continue reading ‘Effects of warming and CO2 enrichment on O2 consumption, porewater oxygenation and pH of subtidal silt sediment’

Microcalcareous seaweeds as sentinels of trophic changes and CO2 trapping in transitional water systems

Highlights

  • The presence of microcalcareous macroalgae was studied in the Italian lagoons.
  • Macroalgal growth was mainly affected by changes in the pH of the water column.
  • Small algae are a Litmus Test Paper Strip for environmental quality assessment.
  • Carbonated are accumulated in surface sediments by small calcareous macroalgae.
  • The CO2 abatement occurred in environments of good-high ecological conditions.

Abstract

Microcalcareous epiphytic seaweeds (MES) are macroalgae more sensitive than aquatic angiosperms to environmental degradation and, with their presence/absence, these species act like sentinels providing useful information on the ecological status of environments. In this study, we analyzed the environmental parameters in water column and surface sediments in relation to macrophyte variables from 257 sites, distributed in the main Italian transitional water systems (TWS). The results showed that MES are strongly correlated to pH changes, the main parameter that regulates their presence/absence. The optimal growth range is between pH 7.80 and 8.35; out of these values their growth is reduced or hampered. In oxidized sediments the carbonate crusts, composed by Mg-Calcite (an unstable compound that in the sediments quickly turns into calcite), can permanently trap up to 2.47 tonnes ha−1 yr−1 of CO2, increasing sediment thickness of approx. 0.06–0.21 mm yr−1.

Continue reading ‘Microcalcareous seaweeds as sentinels of trophic changes and CO2 trapping in transitional water systems’

Rapid shifts in circulation and biogeochemistry of the Southern Ocean during deglacial carbon cycle events

The Southern Ocean plays a crucial role in regulating atmospheric CO2 on centennial to millennial time scales. However, observations of sufficient resolution to explore this have been lacking. Here, we report high-resolution, multiproxy records based on precisely dated deep-sea corals from the Southern Ocean. Paired deep (∆14C and δ11B) and surface (δ15N) proxy data point to enhanced upwelling coupled with reduced efficiency of the biological pump at 14.6 and 11.7 thousand years (ka) ago, which would have facilitated rapid carbon release to the atmosphere. Transient periods of unusually well-ventilated waters in the deep Southern Ocean occurred at 16.3 and 12.8 ka ago. Contemporaneous atmospheric carbon records indicate that these Southern Ocean ventilation events are also important in releasing respired carbon from the deep ocean to the atmosphere. Our results thus highlight two distinct modes of Southern Ocean circulation and biogeochemistry associated with centennial-scale atmospheric CO2 jumps during the last deglaciation.

Continue reading ‘Rapid shifts in circulation and biogeochemistry of the Southern Ocean during deglacial carbon cycle events’

Benthic respiration in hypoxic waters enhances bottom water acidification in the northern Gulf of Mexico

It is known that surface water eutrophication enhances bottom water ocean acidification via respiration in coastal oceans. However, the role of benthic processes in influencing bottom water acidification has not been sufficiently explored. We examined this issue by analyzing a 10‐year summer carbonate chemistry dataset in bottom water together with recent benthic flux measurements and literature benthic flux data in the northern Gulf of Mexico. The difference between the observed and estimated pH (Ω) values calculated from anthropogenic CO2 increase and water column aerobic respiration were defined as ΔpH (ΔΩ). We found that ΔpH and ΔΩ values in hypoxic condition were −0.03 ± 0.04 (mean ± standard deviation) and −0.15 ± 0.39, respectively. Both ΔpH and ΔΩ values in hypoxic conditions were significantly lower than zero (p < 0.05). The net results of anaerobic respiration, oxidation of reduced chemcials, burial of iron sulfide minerals, and possible CaCO3 dissolution may have led to an alkalinity to DIC production ratio of less than 1 in porewater. This caused the ratio of alkalinity to dissolved inorganic carbon fluxes from sediment to bottom water to be less than 1, which led to additional bottom water acidification. Our analysis and model simulations demonstrate that severe hypoxic and anoxic conditions, which correspond to less water movement, favor the accumulation of benthic respiration products, leading to additional pH and Ω reductions. The findings on sediment processes contributing to acidification in bottom waters provide new insights into the sensitivity of coastal ocean acidification to low‐oxygen conditions under current and future climates and anthropogenic nutrient loading scenarios.

Continue reading ‘Benthic respiration in hypoxic waters enhances bottom water acidification in the northern Gulf of Mexico’

Coral reef sediment dissolution in a changing ocean: insights from a temporal field study

Calcium carbonate sediments form an essential part of coral reefs yet have often been overlooked when studying the effects of future ocean acidification (OA). This original field-based research aims to assess the temporal variability of organic and inorganic sediment metabolism under ambient and elevated pCO2. OA caused a shift from net precipitation to net dissolution, but the sensitivity to OA varied seasonally, depending on interactions with temperature and benthic productivity. A slack-water approach of net ecosystem calcification revealed that sediments can play an important role in carbonate budgets, particularly at night, and become increasingly important as the oceans continue acidifying.

Continue reading ‘Coral reef sediment dissolution in a changing ocean: insights from a temporal field study’

  • Reset

Subscribe

OA-ICC Highlights


%d bloggers like this: