Carolina Olid - Academia.edu (original) (raw)

Papers by Carolina Olid

Natural peatlands contribute significantly to global carbon sequestration and storage of biomass,... more Natural peatlands contribute significantly to global carbon sequestration and storage of biomass, most of which derives from Sphagnum peat mosses. Atmospheric CO2 levels have increased dramatically during the 20th century, from 280 to > 400 ppm, which has affected plant carbon dynamics. Net carbon assimilation is strongly reduced by photorespiration, a process that depends on the CO2 to O2 ratio. Here we investigate the response of the photorespiration to photosynthesis ratio in Sphagnum mosses to recent CO2 increases by comparing deuterium isotopomers of historical and contemporary Sphagnum tissues collected from 36 peat cores from five continents. Rising CO2 levels generally suppressed photorespiration relative to photosynthesis but the magnitude of suppression depended on the current water table depth. By estimating the changes in water table depth, temperature, and precipitation during the 20th century, we excluded potential effects of these climate parameters on the observed...

Abstract. Tidal salt marshes are known to accumulate “blue carbon” at high rates relative to thei... more Abstract. Tidal salt marshes are known to accumulate “blue carbon” at high rates relative to their surface area, which render these systems among the Earth’s most efficient carbon (C) sinks. However, the potential for tidal salt marshes to mitigate global warming remains poorly constrained because of the lack of representative sampling of tidal marshes from around the globe, inadequate areal extent estimations, and inappropriate dating methods for accurately estimating C accumulation rates. Here we provide the first estimates of organic C storage and accumulation rates in salt marshes along the Pacific Coast of Canada, within the Clayoquot Sound UNESCO Biosphere Reserve and Pacific Rim National Park Reserve, a region currently underrepresented in global compilations. Within the context of other sites from the Pacific Coast of North America, these young Clayoquot Sound marshes have relatively low C stocks but are accumulating C at rates that are higher than the global average, with p...

Snow depth increases observed in some artic regions and its insulations effects ... more Snow depth increases observed in some artic regions and its insulations effects have led to a winter-warming of permafrost-containing peatlands. Permafrost thaw and the temperature-dependent decomposition of previously frozen carbon (C) is currently considered as one of the most important feedbacks between the artic and the global climate system. However, the magnitude of this feedback remains uncertain because winter effects are rarely integrated and predicted from mechanisms active in both surface (young) and thawing deep (old) peat layers. Laboratory incubation studies of permafrost soils, in situ carbon flux measurements in ecosystem-scale permafrost thaw experiments, or measurements made across naturally degrading permafrost gradients have been used to improve our knowledge about the net effects of winter-warming in permafrost C storage. The results from these studies, however, are biased by imprecision in long-term (decadal to millennial) effects due to the short time scale of the experiments. Gradient studies may show longer-term responses but suffer from uncertainties because measurements are usually taken during the summer, thus ignoring the long cold season. The need for robust estimates of the long-term effect of permafrost thaw on the net C balance, which integrates year-round C fluxes sets the basis of this study. Here, we quantified the effects of long-term in situ permafrost thaw in the net C balance of a permafrost-containing peatland subjected to a 10-years snow manipulation experiment. In short, we used a peat age modelling approach to quantify the effect of winter-warming on net ecosystem production as well as on the underlying changes in surface C inputs and losses along the whole peat continuum. Contrary to our hypothesis, winter-warming did not affect the net ecosystem production regardless of the increased old C losses. This minimum overall effect is due to the strong reduction on the young C losses from the upper active layer associated to the new water saturated conditions and the decline in bryophytes. Our findings highlight the need to incorporate long-term year-round responses in C fluxes when estimating the net effect of winter-warming on permafrost C storage. We also demonstrate that thaw-induced changes in moisture conditions and plant communities are key factors to predicting future climate change feedbacks between the artic soil C pool and the global climate system.

Water

Streambed morphology, streamflow dynamics, and the heterogeneity of streambed sediments criticall... more Streambed morphology, streamflow dynamics, and the heterogeneity of streambed sediments critically controls the interaction between surface water and groundwater. The present study investigated the impact of different flow regimes on hyporheic exchange in a boreal stream in northern Sweden using experimental and numerical approaches. Low-, base-, and high-flow discharges were simulated by regulating the streamflow upstream in the study area, and temperature was used as the natural tracer to monitor the impact of the different flow discharges on hyporheic exchange fluxes in stretches of stream featuring gaining and losing conditions. A numerical model was developed using geomorphological and hydrological properties of the stream and was then used to perform a detailed analysis of the subsurface water flow. Additionally, the impact of heterogeneity in sediment permeability on hyporheic exchange fluxes was investigated. Both the experimental and modelling results show that temporally i...

The ISME Journal

The decomposition of large stocks of soil organic carbon in thawing permafrost might depend on mo... more The decomposition of large stocks of soil organic carbon in thawing permafrost might depend on more than climate change-induced temperature increases: indirect effects of thawing via altered bacterial community structure (BCS) or rooting patterns are largely unexplored. We used a 10-year in situ permafrost thaw experiment and aerobic incubations to investigate alterations in BCS and potential respiration at different depths, and the extent to which they are related with each other and with root density. Active layer and permafrost BCS strongly differed, and the BCS in formerly frozen soils (below the natural thawfront) converged under induced deep thaw to strongly resemble the active layer BCS, possibly as a result of colonization by overlying microorganisms. Overall, respiration rates decreased with depth and soils showed lower potential respiration when subjected to deeper thaw, which we attributed to gradual labile carbon pool depletion. Despite deeper rooting under induced deep thaw, root density measurements did not improve soil chemistry-based models of potential respiration. However, BCS explained an additional unique portion of variation in respiration, particularly when accounting for differences in organic matter content. Our results suggest that by measuring bacterial community composition, we can improve both our understanding and the modeling of the permafrost carbon feedback.

ABSTRACT The past decade has seen a rapid increase in interest in the biogeochemical record prese... more ABSTRACT The past decade has seen a rapid increase in interest in the biogeochemical record preserved in peat, particularly as it relates to carbon dynamics and environmental changes. However, we still lack a complete understanding of the basic biogeochemical processes and their effect on trace element distributions. Are peat archives an absolute or relative record? What temporal resolution is realistic to interpret by using peat cores? By analyzing atmospherically deposited 210Pb, 137Cs, 241Am and 7Be as well as the trace metals Pb and Hg, in triplicate peat cores from an ombrotrophic Swedish bog we addressed two fundamental issues; the question of representativity of single cores and the incorporation of atmospheric signals in the peat. Both of these issues are of great importance and need to be considered when using peat cores as natural archives. By specifically including the short-lived tracer 7Be (T½ 53.4 days) we tested the hypothesis that downwashing of atmospherically-supplied elements may occur in well aerated peat. Our 210Pb activities all showed a non-monotonic decrease with depth suggesting some downward transport of 210Pb by percolating rainwater. Further to this, the activities of 7Be were detected to 20, 18 and 8 cm depth and there was a lack of any clear peaks in 241Am activities, which together indicate a smearing of the radionuclides to or at the water table. We conclude that this is compelling evidence for a rapid downwash of atmospherically supplied elements in peat, which extends down to the height of water table. By comparing our records to biomonitoring- and direct deposition data we were able to quantify the implications of this downwash on estimates of peat mass accumulation rates and metal (Pb and Hg) deposition. It is clear that under specific conditions the usage of a conventional CRS-dating model can lead to severe overestimations of peat mass accumulation as well as inaccurate estimations of past deposition. However, by applying a new correction model which includes a downward transport term, thereby adjusting the conventional CRS model, we suggest that this downward mobility can be successfully incorporated into age-depth models, allowing more accurate estimations of past deposition and peat accumulation.

Peat cores collected in NW Spain were used to reconstruct recent Pb deposition. ► Applicability o... more Peat cores collected in NW Spain were used to reconstruct recent Pb deposition. ► Applicability of 210 Pb-dating models (CRS) in bogs is discussed based on PCA results. ► Results showed that~20% of the 210 Pb flux was related to anthropogenic metal pollution. ► Geochemical analysis of bogs is useful to interpret the historical peat record.

Science of The Total Environment, 2014

Accurate dating of peat accumulation is essential for quantitatively reconstructing past changes ... more Accurate dating of peat accumulation is essential for quantitatively reconstructing past changes in atmospheric metal deposition and carbon burial. By analyzing fallout radionuclides (210)Pb, (137)Cs, (241)Am, and (7)Be, and total Pb and Hg in 5 cores from two Swedish peatlands we addressed the consequence of estimating accumulation rates due to downwashing of atmospherically supplied elements within peat. The detection of (7)Be down to 18-20 cm for some cores, and the broad vertical distribution of (241)Am without a well-defined peak, suggest some downward transport by percolating rainwater and smearing of atmospherically deposited elements in the uppermost peat layers. Application of the CRS age-depth model leads to unrealistic peat mass accumulation rates (400-600 g m(-2) yr(-1)), and inaccurate estimates of past Pb and Hg deposition rates and trends, based on comparisons to deposition monitoring data (forest moss biomonitoring and wet deposition). After applying a newly proposed IP-CRS model that assumes a potential downward transport of (210)Pb through the uppermost peat layers, recent peat accumulation rates (200-300 g m(-2) yr(-1)) comparable to published values were obtained. Furthermore, the rates and temporal trends in Pb and Hg accumulation correspond more closely to monitoring data, although some off-set is still evident. We suggest that downwashing can be successfully traced using (7)Be, and if this information is incorporated into age-depth models, better calibration of peat records with monitoring data and better quantitative estimates of peat accumulation and past deposition are possible, although more work is needed to characterize how downwashing may vary between seasons or years.

Quaternary Geochronology, 2014

ABSTRACT 210Pb dating is a key technique to study sedimentary records of environmental change in ... more ABSTRACT 210Pb dating is a key technique to study sedimentary records of environmental change in the Anthropocene over a time scale of 100-150 years. Uncertainty estimation of 210Pb ages and accumulation rates, when provided by the authors, are usually based on quadratic propagation of uncertainties. In this work, we describe the use of Monte Carlo simulation to estimate 210Pb dating uncertainties in sediment and peat cores. The methodology allows, by using nowadays common computers, the assessment of 210Pb dating uncertainties in a simple manner, using readily-accessible computers and widely-used proprietary spreadsheet software, and avoiding the derivation of rather complex formulae. Results were calculated and compared with quadratic propagation uncertainties in a marine, lacustrine and peat bog core. The analysis of the uncertainty budgets indicated that, overall, the total and unsupported (or base) 210Pb concentrations are the largest contributors to uncertainty, as well as the layer depths when sediment accumulation rates were calculated. Beyond 210Pb dating, the Monte Carlo scheme described here could be used in any field of the analytical sciences, including other radiochronological applications.

Science of The Total Environment, 2013

The natural radionuclide (210)Pb is commonly used to establish accurate and precise chronologies ... more The natural radionuclide (210)Pb is commonly used to establish accurate and precise chronologies for the recent (past 100-150 years) layers of peat deposits. The most widely used (210)Pb-dating model, Constant Rate of Supply (CRS), was applied using data from three peat cores from Chao de Lamoso, an ombrotrophic mire in Galicia (NW Spain). On the basis of the CRS-chronologies, maximum Pb concentrations and enrichment factors (EFs) occurred in the 1960s and late 1970s, consistent with the historical use of Pb. However, maximum Pb fluxes were dated in the 1940s and the late 1960s, 10 to 20 years earlier. Principal component analysis (PCA) showed that, although the (210)Pb distribution was mainly (74%) controlled by radioactive decay, about 20% of the (210)Pb flux variability was associated with atmospheric metal pollution, suggesting an extra (210)Pb supply source and thus invalidating the main assumption of the CRS model. When the CRS-ages were recalculated after correcting for the extra input from the (210)Pb inventory of the uppermost peat layers of each core, Pb flux variations were consistent with the historical atmospheric Pb deposition. Our results not only show the robustness of the CRS model to establish accurate chronologies of recent peat deposits but also provide evidence that there are confounding factors that might influence the calculation of reliable peat accumulation rates (and thus also element accumulation rates/fluxes). This study emphasizes the need to verify the hypotheses of (210)Pb-dating models and the usefulness of a full geochemical interpretation of peat bog records.

Environmental Science & Technology, 2008

210 Pb-dated ombrotrophic peat cores have been widely used to reconstruct the atmospheric fluxes ... more 210 Pb-dated ombrotrophic peat cores have been widely used to reconstruct the atmospheric fluxes of heavy metals for the past century. Many of these studies rarely include the overlying vegetation compartment (i.e., the aerial part of vegetation and decayed plant remains) in the analysis although it represents the first layer capturing atmospheric deposition. The aim of this study was to evaluate the radionuclide and Pb content of this biologically active layer in bogs and to assess its implications on the total inventories and the 210 Pb-derived chronology. We analyzed two short ombrotrophic peat cores from the same bog (Chao de Lamoso, Galicia, Spain) for 210 Pb, artificial radionuclides (137 Cs and 241 Am), and Pb. The total Pb inventory was underestimated by about 12% when the plant material was not included in the record. The atmospheric origin of 210 Pb and the uptake of 137 Cs by roots led to significant activities of these radionuclides in the upper layers. Therefore, removing them from the peat record would imply even larger underestimations of the total inventories, ranging from 25% to 36% for 137 Cs and from 39% to 49% for 210 Pb. In contrast to the chronologies inferred from the constant rate of supply (CRS) model when only peat layers are considered, the 210 Pb chronology agreed well with artificial radionuclide dating when surface vegetation was included. These results suggest that an accurate peat chronology requires an initial evaluation of the relevance of plant inventories and emphasizes the need of considering the biologically active layer when atmospheric fluxes of heavy metals and other pollutants are reconstructed.

Science of The Total Environment, 2010

In order to estimate atmospheric metal deposition in Southern Europe since the beginning of the I... more In order to estimate atmospheric metal deposition in Southern Europe since the beginning of the Industrial Period (~1850 AD), concentration profiles of Pb, Zn and Cu were determined in four (210)Pb-dated peat cores from ombrotrophic bogs in Serra do Xistral (Galicia, NW Iberian Peninsula). Maximum metal concentrations varied by a factor of 1.8 for Pb and Zn (70 to 128μgg(-1) and 128 to 231μgg(-1), respectively) and 3.5 for Cu (11 to 37μgg(-1)). The cumulative metal inventories of each core varied by a factor of 3 for all analysed metals (132 to 329μgcm(-2) for Pb, 198 to 625μgcm(-2) for Zn and 22 to 69μgcm(-2) for Cu), suggesting differences in net accumulation rates among peatlands. Although results suggest that mean deposition rates vary within the studied area, the enhanced (210)Pb accumulation and the interpretation of the inventory ratios ((210)Pb/Pb, Zn/Pb and Cu/Pb) in two bogs indicated that either a record perturbation or post-depositional redistribution effects must be considered. After correction, Pb, Zn and Cu profiles showed increasing concentrations and atmospheric fluxes since the mid-XX(th) century to maximum values in the second half of the XX(th) century. For Pb, maximum fluxes were observed in 1955-1962 and ranged from 16 to 22mgm(-2)yr(-1) (mean of 18±1mgm(-2)yr(-1)), two orders of magnitude higher than in the pre-industrial period. Peaks in Pb fluxes in Serra do Xistral before the period of maximum consumption of leaded petrol in Europe (1970s-1980s) suggest the dominance of local pollutant sources in the area (i.e. coal mining and burning). More recent peaks were observed for Zn and Cu, with fluxes ranging from 32 to 52mgm(-2)yr(-1) in 1989-1996, and from 4 to 9mgm(-2)yr(-1) in 1994-2001, respectively. Our results underline the importance of multi-core studies to assess both the integrity and reliability of peat records, and the degree of homogeneity in bog accumulation. We show the usefulness of using the excess (210)Pb inventory to distinguish between differential metal deposition, accumulation or anomalous peat records.

Environmental Science and Technology, Dec 1, 2010

Osmium is among the least abundant elements in the Earth&amp;amp;amp;amp;amp;amp;amp;amp;... more Osmium is among the least abundant elements in the Earth&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s continental crust. Recent anthropogenic Os contamination of the environment from mining and smelting activities, automotive catalytic converter use, and hospital discharges has been documented. Here we present evidence for anthropogenic overprinting of the natural Os cycle using a ca. 7000-year record of atmospheric Os deposition and isotopic composition from an ombrotrophic peat bog in NW Spain. Preanthropogenic Os accumulation in this area is 0.10 +/- 0.04 ng m(-2) y(-1). The oldest strata showing human influence correspond to early metal mining and processing on the Iberian Peninsula (ca. 4700-2500 cal. BP). Elevated Os accumulation rates are found thereafter with a local maximum of 1.1 ng m(-2) y(-1) during the Roman occupation of the Iberian Peninsula (ca. 1930 cal. BP) and a further increase starting in 1750 AD with Os accumulation reaching 30 ng m(-2) y(-1) in the most recent samples. Osmium isotopic composition ((187)Os/(188)Os) indicates that recent elevated Os accumulation results from increased input of unradiogenic Os from industrial and automotive sources as well as from enhanced deposition of radiogenic Os through increased fossil fuel combustion and soil erosion. We posit that the rapid increase in catalyst-equipped vehicles, increased fossil fuel combustion, and changes in land-use make the changes observed in NW Spain globally relevant.