Calcium carbonates (CaCO
) often accumulate in mangrove and seagrass sediments. As CaCO
production emits CO
, there is concern that this may partially offset the role of Blue Carbon ecosystems as CO
...sinks through the burial of organic carbon (C
). A global collection of data on inorganic carbon burial rates (C
, 12% of CaCO
mass) revealed global rates of 0.8 TgC
yr
and 15-62 TgC
yr
in mangrove and seagrass ecosystems, respectively. In seagrass, CaCO
burial may correspond to an offset of 30% of the net CO
sequestration. However, a mass balance assessment highlights that the C
burial is mainly supported by inputs from adjacent ecosystems rather than by local calcification, and that Blue Carbon ecosystems are sites of net CaCO
dissolution. Hence, CaCO
burial in Blue Carbon ecosystems contribute to seabed elevation and therefore buffers sea-level rise, without undermining their role as CO
sinks.
Our knowledge of the factors that can influence the stock of organic carbon (OC) that is stored in the soil of seagrass meadows is evolving, and several causal effects have been used to explain the ...variation of stocks observed at local to national scales. To gain a global‐scale appreciation of the drivers that cause variation in soil OC stocks, we compiled data on published species‐specific traits and OC stocks from monospecific and mixed meadows at multiple geomorphological settings. Species identity was recognized as an influential driver of soil OC stocks, despite their large intraspecific variation. The most important seagrass species traits associated with OC stocks were the number of leaves per seagrass shoot, belowground biomass, leaf lifespan, aboveground biomass, leaf lignin, leaf breaking force and leaf OC plus the coastal geomorphology of the area, particularly for lagoon environments. A revised estimate of the global average soil OC stock to 20 cm depth of 15.4 Mg C ha−1 is lower than previously reported. The largest stocks were still recorded in Mediterranean seagrass meadows. Our results specifically identify Posidonia oceanica from the Mediterranean and, more generally, large and persistent species as key in providing climate regulation services, and as priority species for conservation for this specific ecosystem service.
Key Points
To understand global drivers of seagrass carbon stocks, we compiled data on species traits and stocks at multiple geomorphological settings
Globally, we identify large and long‐lived seagrass species in lagoon environments as key in providing climate regulation services
The Mediterranean is a hotspot of seagrass carbon sequestration, given the distinct capacity of Posidonia oceanica to support large stocks
Certain coastal ecosystems such as mangrove, saltmarsh and seagrass habitats have been identified as significant natural carbon sinks, through the sequestration and storage of carbon in their biomass ...and sediments, collectively known as 'blue carbon' ecosystems. These ecosystems can often thrive in extreme environments where terrestrial systems otherwise survive at the limit of their existence, such as in arid and desert regions of the globe. To further our understanding of the capability of blue carbon ecosystems to sequester and store carbon in such extreme climates, we measured carbon sediment stocks in 25 sites along the Western Arabian Gulf coast. While seagrass meadows and saltmarsh habitats were widely distributed along the coast, mangrove stands were much reduced as a result of anthropogenic pressures, with 90% of stands having been lost over the last century. Carbon stocks in 1 m deep surface sediments were similar across all three blue carbon habitats, with comparable stocks for saltmarsh (81 ± 22 Mg Corg ha−1), seagrass (76 ± 20 Mg Corg ha−1) and mangroves (76 ± 23 Mg Corg ha−1). We recorded a 38% decrease in carbon stocks between mature established mangrove stands (91 Mg Corg ha−1) and recently planted mangroves (56 Mg Corg ha−1). Mangroves also had the lowest carbon stock per total area owing to their very limited spatial coverage along the coast. The largest stock per total area belonged to seagrass beds as a result of their large spatial coverage within the Gulf. We employed 210Pb dating to determine the sediment accretion rates in each ecosystem and found mangrove habitats to be the most efficient carbon sequesters over the past century, with the highest carbon burial rate of the three ecosystems (19 g Corg m−2 yr−1), followed by seagrass (9 g Corg m−2 yr−1) and saltmarshes (8 g Corg m−2 yr−1). In this work, we describe a comprehensive comparison of sediment stocks in different blue carbon ecosystems within a single marine environment and across a large geographical area, and discuss our results in a global context for other blue carbon ecosystems in the dry tropics.
This paper focuses on how a community of researchers under the COMET (CO-ordination and iMplementation of a pan European projecT for radioecology) project has improved the capacity of marine ...radioecology to understand at the process level the behaviour of radionuclides in the marine environment, uptake by organisms and the resulting doses after the Fukushima Dai-ichi nuclear accident occurred in 2011. We present new radioecological understanding of the processes involved, such as the interaction of waterborne radionuclides with suspended particles and sediments or the biological uptake and turnover of radionuclides, which have been better quantified and mathematically described.
We demonstrate that biokinetic models can better represent radionuclide transfer to biota in non-equilibrium situations, bringing more realism to predictions, especially when combining physical, chemical and biological interactions that occur in such an open and dynamic environment as the ocean. As a result, we are readier now than we were before the FDNPP accident in terms of having models that can be applied to dynamic situations.
The paper concludes with our vision for marine radioecology as a fundamental research discipline and we present a strategy for our discipline at the European and international levels. The lessons learned are presented along with their possible applicability to assess/reduce the environmental consequences of future accidents to the marine environment and guidance for future research, as well as to assure the sustainability of marine radioecology. This guidance necessarily reflects on why and where further research funding is needed, signalling the way for future investigations.
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•Marine radioecology studies at the FDNPP coast: process-based modelling and field investigations•Dynamic modelling of transfer between seawater, sediments and the biological compartments•New data on submarine groundwater discharges and ocean circulation of radionuclides•We formulate a strategy for marine radioecology based on processes-based research.•We highlight the need for more ecology knowledge in marine radioecology.
One of the world's largest smelters has been operating in South Australia since 1889, affecting environment and human health. Here we quantified the magnitude of Pb, Zn and Cd emissions from the ...smelter sequestered in the soil of an adjacent 110 km2Posidonia australis seagrass meadows. Seagrass core records show that the smelter contaminated the entire area with decreasing sequestration with increasing distance from contamination points. The soil accumulated ~1300 t of Pb, ~3450 t of Zn, and ~ 90 t of Cd since 1889, and sequestered the equivalent of ~20 % of Pb, and ~50 % of Zn and Cd cumulative smelter emissions since 1999, showing that seagrass can be significant, long-term sinks of metal pollution in highly contaminated environments. Conservation efforts should prioritize these seagrass meadows to avoid the potential release of pollutants from their soils following habitat loss, which could turn seagrasses from a sink to a source of pollution.
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•Seagrass soil can act as metals sink in highly contaminated environment.•Metals emitted by the smelter were found in the soil of the entire seagrass area.•Two hot-spots of contamination were identified within the seagrass soils.•Seagrass soils store up to the equivalent of 50 % of Pb, Zn and Cd emissions by the smelter.•Seagrass conservation should be prioritized to protect metal sinks from erosion.
The upper Spencer Gulf in South Australia hosts the world's largest single stream Pb-Zn smelter, which has caused environmental and health issues related to elevated metal concentrations in the ...surrounding environment. The area also has extensive seagrass meadows, occupying >4000 km2. We reconstructed the fluxes of heavy metals over the last ~3000 years through a multi-parameter study of the soil archives formed by the seagrass Posidonia australis. Pb, Zn and Cd concentrations increased up to 9-fold following the onset of smelter operations in the 1880s, and the stable Pb isotopic signatures confirmed the smelter has been the main source of lead pollution in the seagrass soils until present. Preliminary estimates suggest that over the past 15 years seagrass meadows within 70 km2 of the smelter accumulated ~7–15% of the smelter emissions in their soils. Here we demonstrate that seagrass meadows act as pollution filters and sinks while their soils provide a record of environmental conditions, allowing baseline conditions to be identified and revealing the time-course of environmental change.
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•Seagrass soils provide a reliable archive of metal contamination over centennial time scales.•Pb, Zn and Cd concentrations in soil increased up to 9-fold after the onset of the Port Pirie smelter.•Pb isotopes show that the Port Pirie smelter is the main source of Pb contamination.•Seagrass meadows act as significant filters and sinks of metals in Port Pirie.•Seagrass soils are a possible source of remobilized pollution following disturbance.
A multi-proxy characterization of the uppermost sedimentary infill of an Iberian alpine lake (Cimera, 2140 m a.s.l.) was performed to establish the climatic and environmental conditions for the ...Iberian Central Range (ICR) over the last two millennia. This multi-proxy characterization was used to reconstruct the intense runoff events, lake productivity and soil erosion in the lake catchment and interpret these factors in terms of temperature and precipitation variability. The Roman Period (RP; 200 BCE – 500 CE) beginning was characterized by an alternation between cold and warm periods as indicated by short-lived oscillations of intense runoff conditions and soil erosion, although warm conditions dominated the end of the period and the Early Middle Age (EMA; 500–900 CE) onset in the ICR. A noticeable decrease in intense runoff events and a progressive decrease in soil erosion during the late EMA indicated a shift to colder temperatures. In terms of precipitation, both the RP and EMA climate periods displayed a transition from dry to wet conditions that led to a decrease in lake productivity. The Medieval Climate Anomaly (MCA; 900–1300 CE) was characterized by warm and dry conditions with frequent intense runoff episodes and increases in lake productivity and soil erosion, whereas the Little Ice Age (LIA; 1300–1850 CE) showed the opposite characteristics. The Industrial Era (1850–2012 CE) presented an increase in lake productivity that likely demonstrates the influence of global warming.
The spatio-temporal integration of the Cimera record with other Iberian reconstructions has been used to identify the main climate drivers over this region. During the RP and EMA, N–S and E–W humidity gradients were dominant, whereas during the MCA and LIA, these gradients were not evident. These differences could be ascribed to interactions between the North Atlantic Oscillation (NAO) and East Atlantic (EA) phases. During the RP, the general warm conditions and the E–W humidity gradient indicate a dominant interplay between a negative NAO phase and a positive EA phase (NAO−–EA+), whereas the opposite conditions during the EMA indicate a NAO+–EA− interaction. The dominant warm and arid conditions during the MCA and the cold and wet conditions during the LIA indicate the interplay of the NAO+–EA+ and NAO−–EA−, respectively. Furthermore, the higher solar irradiance during the RP and MCA may support the predominance of the EA+ phase, whereas the opposite scenario during the EMA and LIA may support the predominance of the EA− phase, which would favour the occurrence of frequent and persistent blocking events in the Atlantic region during these periods.
•We perform a high-resolution multiproxy study from Iberian alpine lake sediments.•Climatic conditions for Iberian Central Range over the last two millennia.•Climate gradients distinguished the Iberian Roman Period and the Early Middle Ages.•Spatial homogeneous climate conditions depicted MCA and LIA in the Iberian region.•The NAO and EA interactions drive climate patterns over Iberian Peninsula.
Measurement of radionuclides in marine samples, specifically radioactive pairs disequilibrium, has gained interest lately due to their ability to trace cutting edge biogeochemical processes. In this ...context, we developed a fast, direct method for determining (210)Pb and (210)Po water through the use of ultra low-level liquid scintillation counting and alpha-particle spectrometry respectively and through Eichrom Sr resins for the Po-Pb separation. For (210)Pb analysis, the method uses stable lead as a yield tracer measured by a robust ICP-MS technique, and (210)Po is determined through self-deposition using the conventional (209)Po yield tracer. The improvements of the method over other techniques are: a) the analysis can be completed within 6 days, simplifying other methods, b) very low limits of detection have been achieved -0.12 and 0.005mBqL(-1) for (210)Pb and (210)Po, respectively - and c) most of the method could be carried out in on-board analysis. We applied the method to different aqueous samples and specifically to marine samples. We determined (210)Pb and (210)Po in the dissolved fraction of Mediterranean Sea water and an estuary at the South-West of Spain. We found that it can be successfully employed to marine samples but we recommend to i) use a minimum of 20L water to measure the (210)Pb in the dissolved phase by LSC and lower volumes to measure total concentrations; ii) wait for (210)Pb and (210)Bi in secular equilibrium and measure the total spectrum to minimise the limit of detection and improve accuracy.
Artificial radionuclides enter the Mediterranean Sea mainly through atmospheric deposition following nuclear weapons tests and the Chernobyl accident, but also through the river discharge of nuclear ...facility effluents. Previous studies of artificial radionuclides impact of the Mediterranean Sea have focussed on shallow, coastal sediments. However, deep sea sediments have the potential to store and accumulate pollutants, including artificial radionuclides. Deep sea marine sediment cores were collected from Mediterranean Sea abyssal plains (depth >
2000 m) and analysed for
239,240Pu and
137Cs to elucidate the concentrations, inventories and sources of these radionuclides in the deepest areas of the Mediterranean. The activity — depth profiles of
210Pb, together with
14C dating, indicate that sediment mixing redistributes the artificial radionuclides within the first 2.5 cm of the sedimentary column. The excess
210Pb inventory was used to normalize
239,240Pu and
137Cs inventories for variable sediment fluxes. The
239,240Pu/
210Pb
xs
ratio was uniform across the entire sea, with a mean value of 1.24
×
10
−
3
, indicating homogeneous fallout of
239,240Pu. The
137Cs/
210Pb
xs
ratio showed differences between the eastern (0.049) and western basins (0.030), clearly significant impact of deep sea sediments from the Chernobyl accident. The inventory ratios of
239,240Pu/
137Cs were 0.041 and 0.025 in the western and eastern basins respectively, greater than the fallout ratio, 0.021, showing more efficient scavenging of
239,240Pu in the water column and major sedimentation of
137Cs in the eastern basin. Although areas with water depths of >
2000 m constitute around 40% of the entire Mediterranean basin, the sediments in these regions only contained 2.7% of the
239,240Pu and 0.95% of the
137Cs deposited across the Sea in 2000. These data show that the accumulation of artificial radionuclides in deep Mediterranean environments is much lower than predicted by other studies from the analysis of continental shelf sediments.
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