Posts Tagged 'sediment'

Potential influence of ocean acidification on deep-sea Fe–Mn nodules and pelagic clays: an improved assessment by using artificial seawater

In order to assess the potential risk of metal release from deep-sea sediments in response to pH decrease in seawater, the mobility of elements from ferromanganese (Fe–Mn) nodules and pelagic clays was examined. Two geochemical reference samples (JMn-1 and JMS-2) were reacted with the pH-controlled artificial seawater (ASW) using a CO2-induced pH regulation system. Our experiments demonstrated that deep-sea sediments have weak buffer capacities by acid–base dissociation of surface hydroxyl groups on metal oxides/oxyhydroxides and silicate minerals. Element concentrations in the ASW were mainly controlled by elemental speciation in the solid phase and sorption–desorption reaction between the charged solid surface and ion species in the ASW. These results indicated that the release of heavy metals such as Mn, Cu, Zn and Cd should be taken into consideration when assessing the influence of ocean acidification on deep-sea environment.

Continue reading ‘Potential influence of ocean acidification on deep-sea Fe–Mn nodules and pelagic clays: an improved assessment by using artificial seawater’

Insight into deep-sea life – Cibicidoides pachyderma substrate and pH-dependent behaviour following disturbance

Highlights

• First observations of Cibicidoides pachyderma var. C. mundulus under in situ pressure and temperature.
• Option for an epi- or endobenthic habitat is pH-dependent.
• Under normal pH exhibits strong rheotaxis.
• Growth in Cibicidoides pachyderma var. C. mundulus requires a protective sedimentary cyst.

Abstract

Most palaeo-deep-water reconstructions are based on geochemical information stored in the calcareous shells of Cibicidoides species but hardly anything is known about their life cycle, population dynamics or ecology. The number of specimens of a single Cibicidoides species can locally be very limited and species may be lacking completely during certain intervals in the geological past. As a consequence, geochemical analyses are often carried out on lumped Cibicidoides spp. assuming that they share the same epizoic to epifaunal habitat and precipitated their shell in comparable offsets to surrounding bottom water mass properties. However, there is a growing body of evidence that particularly Cibicidoides pachyderma and its morphotypes C. mundulus and C. kullenbergi, may not be reliable bottom water recorders.

We have recently developed aquaria that allowed, for the first time, observations of Cibicidoides pachyderma var. C. mundulus under in situ pressure and temperature. Experiments were carried out with and without artificial sediments to simulate soft sediments and rocks, respectively. Seawater was set to pH 8 and pH 7.4 to simulate more or less particulate carbon export or more or less ventilation of bottom water. Our experiments demonstrate that C. mundulus may opt for an epifaunal or an infaunal habitat depending on elapsed time following physical disturbance, pH, current activity, the availability of sediments and growth. The specimen’s initial response following transfer from atmospheric pressure into the high-pressure aquaria was to immerse into the sediment or to cover more or less parts of the test with aggregated sediments or algae. However, within 24 h a strong rheotaxis became apparent and most specimens moved to sites of increased current activity under normal pH conditions (pH 8). Only few specimens remained in algae cysts or in the sediment in the pH-8 experiment. On the contrary, all specimens under pH 7.4 agglutinated a firm sediment cyst around their test and remained infaunal throughout the experimental period of three months.

Independent of pH, growth was only observed in specimens that lived within an agglutinated cyst or infaunal. A solid thick cyst covered the specimens of the pH 7.4 experiment throughout the experiment and possibly restricted water exchange between the in-cyst water and the surrounding artificial bottom water mass. We suggest that a more fragile and possibly more porous sedimentary envelope may, at least temporally, have covered the infaunal specimens under pH 8 but no evidence for this was found upon termination of the experiment.

Continue reading ‘Insight into deep-sea life – Cibicidoides pachyderma substrate and pH-dependent behaviour following disturbance’

The bloom-forming macroalgae, Ulva, outcompetes the seagrass, Zostera marina, under high CO2 conditions

This study reports on experiments performed with a Northwest Atlantic species of the macroalgae, Ulva, and the seagrass, Zostera marina, grown under ambient and elevated levels of pCO2, and subjected to competition with each other. When grown individually, elevated pCO2 significantly increased growth rates and productivity of Ulva and Zostera, respectively, beyond control treatments (by threefold and 27%, respectively). For both primary producers, significant declines in tissue δ13C signatures suggested that increased growth and productivity were associated with a shift from use of HCO3 toward CO2 use. When grown under higher pCO2, Zostera experienced significant increases in leaf and rhizome carbon content as well as significant increases in leaf carbon-to-nitrogen ratios, while sediments within which high CO2 Zostera were grown had a significantly higher organic carbon content. When grown in the presence of Ulva; however, above- and below-ground productivity and tissue nitrogen content of Zostera were significantly lower, revealing an antagonistic interaction between elevated CO2 and the presence of Ulva. The presence of Zostera had no significant effect on the growth of Ulva. Collectively, this study demonstrates that while Ulva and Zostera can each individually benefit from elevated pCO2 levels, the ability of Ulva to grow more rapidly and inhibit seagrass productivity under elevated pCO2, coupled with accumulation of organic C in sediments, may offset the potential benefits for Zostera within high CO2 environments.

Continue reading ‘The bloom-forming macroalgae, Ulva, outcompetes the seagrass, Zostera marina, under high CO2 conditions’

Does nutrient availability regulate seagrass response to elevated CO2?

Future increases in oceanic carbon dioxide concentrations (CO2(aq)) may provide a benefit to submerged plants by alleviating photosynthetic carbon limitation. However, other environmental factors (for example, nutrient availability) may alter how seagrasses respond to CO2(aq) by regulating the supply of additional resources required to support growth. Thus, questions remain in regard to how other factors influence CO2(aq) effects on submerged vegetation. This study factorially manipulated CO2(aq) and nutrient availability, in situ, within a subtropical seagrass bed for 350 days, and examined treatment effects on leaf productivity, shoot density, above- and belowground biomass, nutrient content, carbohydrate storage, and sediment organic carbon (Corg). Clear, open-top chambers were used to replicate CO2(aq) forecasts for the year 2100, whereas nutrient availability was manipulated via sediment amendments of nitrogen (N) and phosphorus (P) fertilizer. We provide modest evidence of a CO2 effect, which increased seagrass aboveground biomass. CO2(aq) enrichment had no effect on nutrient content, carbohydrate storage, or sediment Corg content. Nutrient addition increased leaf productivity and leaf N content, however did not alter above- or belowground biomass, shoot density, carbohydrate storage, or Corg content. Treatment interactions were not significant, and thus NP availability did not influence seagrass responses to elevated CO2(aq). This study demonstrates that long-term carbon enrichment may alter the structure of shallow seagrass meadows, even in relatively nutrient-poor, oligotrophic systems.

Continue reading ‘Does nutrient availability regulate seagrass response to elevated CO2?’

Variability in sediment-water carbonate chemistry and bivalve abundance after bivalve settlement in Long Island Sound, Milford, Connecticut

Highlights

  • Total bivalve community composition influenced by grain size, pH, alkalinity, and date
  • Short term drivers of bivalve community settlement influenced by carbonate chemistry parameters
  • Different bivalve species respond to different carbonate chemistry cues for settlement.

Abstract

Cues that drive bivalve settlement and abundance in sediments are not well understood, but recent reports suggest that sediment carbonate chemistry may influence bivalve abundance. In 2013, we conducted field experiments to assess the relationship between porewater sediment carbonate chemistry (pH, alkalinity (At), dissolved inorganic carbon (DIC)), grain size, and bivalve abundance throughout the July–September settlement period at two sites in Long Island Sound (LIS), CT. Two dominate bivalves species were present during the study period Mya arenaria and Nucula spp. Akaike’s linear information criterion models, indicated 29% of the total community abundance was predicted by grain size, salinity, and pH. When using 2 weeks of data during the period of peak bivalve settlement, pH and phosphate concentrations accounted 44% of total bivalve community composition and 71% of Nucula spp. abundance with pH, phosphate, and silica. These results suggest that sediment carbonate chemistry may influence bivalve abundance in LIS.

Continue reading ‘Variability in sediment-water carbonate chemistry and bivalve abundance after bivalve settlement in Long Island Sound, Milford, Connecticut’

Short term CO2 enrichment increases carbon sequestration of air-exposed intertidal communities of a coastal lagoon

In situ production responses of air-exposed intertidal communities under CO2 enrichment are reported here for the first time. We assessed the short-term effects of CO2 on the light responses of the net community production (NCP) and community respiration (CR) of intertidal Z. noltei and unvegetated sediment communities of Ria Formosa lagoon, when exposed to air. NCP and CR were measured in situ in summer and winter, under present and CO2 enriched conditions using benthic chambers. Within chamber CO2 evolution measurements were carried out by a series of short-term incubations (30 min) using an infra-red gas analyser. Liner regression models fitted to the NCP-irradiance responses were used to estimate the seasonal budgets of air-exposed, intertidal production as determined by the daily and seasonal variation of incident photosynthetic active radiation. High CO2 resulted in higher CO2 sequestration by both communities in both summer and winter seasons. Lower respiration rates of both communities under high CO2 further contributed to a potential negative climate feedback, except in winter when the CR of sediment community was higher. The light compensation points (LCP) (light intensity where production equals respiration) of Z. noltei and sediment communities also decreased under CO2 enriched conditions in both seasons. The seasonal community production of Z. noltei was 115.54 ± 7.58 g C m−2 season−1 in summer and 29.45 ± 4.04 g C m−2 season−1 in winter and of unvegetated sediment was 91.28 ± 6.32 g C m−2 season−1 in summer and 25.83 ± 4.01 g C m−2 season−1 in winter under CO2 enriched conditions. Future CO2 conditions may increase air-exposed seagrass production by about 1.5-fold and unvegetated sediments by about 1.2-fold.

Continue reading ‘Short term CO2 enrichment increases carbon sequestration of air-exposed intertidal communities of a coastal lagoon’

Effects of CO2 enrichment on metal bioavailability and bioaccumulation using Mytilus galloprovincialis

Highlights

• This study addresses the effects of acidification in marine ecosystems using mussels.
• CO2 enrichment in the marine ecosystem increased significantly the concentrations of some metals
• There was relationship between accumulation of metals in tissues of Mytilus galloprovincialis and the decrease of pH values
• The increase in the bioaccumulation of Fe, Ni and Zn in the body of mussels is related to acidification

Abstract

The main aim of this study was to evaluate the bioavailability of metals related to CO2 enrichment on the mussels Mytilus galloprovincialis by metal’s bioaccumulation analysis. Two sediment samples were selected and subjected to different pH levels. Concentrations of metals were measured in the overlying seawater and in the whole body of mussels exposed on the 7th, 14th and 21st days. Results showed that the CO2 enrichment in aquatic ecosystems cause significant (p < 0.05) changes on the concentrations of Cu, Zn, Ni, Mn and As between the control pH and pH 7.0 after 7 days of exposure; and in the concentration of Fe at pH 6.0 using the RSP sediment. The multivariate analysis results showed that the increase in the bioaccumulation of some metals in mussels was linked to the acidification. It was concluded that many factors may interfere in the results when the acidification and bioavailability of metals are inquired.

Continue reading ‘Effects of CO2 enrichment on metal bioavailability and bioaccumulation using Mytilus galloprovincialis’


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