Climate change enhances the mobilisation of naturally occurring metals in high altitude environments

Manmade climate change has expressed a plethora of complex effects on Earth's biogeochemical compartments. Climate change may also affect the mobilisation of natural metal sources, with potential ecological consequences beyond mountains' geographical limits; however, this question has remained largely unexplored. We investigated this by analysing a number of key climatic factors in relationship with trace metal accumulation in the sediment core of a Pyrenean lake. The sediment metal contents showed increasing accumulation trend over time, and their levels varied in step with recent climate change. The findings further revealed that a rise in the elevation of freezing level, a general increase in the frequency of drier periods, changes in the frequency of winter freezing days and a reducing snow cover since the early 1980s, together are responsible for the observed variability and augmented accumulation of trace metals. Our results provide clear evidence of increased mobilisation of natural metal sources - an overlooked effect of climate change on the environment. With further alterations in climate equilibrium predicted over the ensuing decades, it is likely that mountain catchments in metamorphic areas may become significant sources of trace metals, with potentially harmful consequences for the wider environment

Ecosystem-bedrock interaction changes nutrient compartmentalization during early oxidative weathering

Ecosystem-bedrock interactions power the biogeochemical cycles of Earth's shallow crust, supporting life, stimulating substrate transformation, and spurring evolutionary innovation. While oxidative processes have dominated half of terrestrial history, the relative contribution of the biosphere and its chemical fingerprints on Earth's developing regolith are still poorly constrained. Here, we report results from a two-year incipient weathering experiment. We found that the mass release and compartmentalization of major elements during weathering of granite, rhyolite, schist and basalt was rock-specific and regulated by ecosystem components. A tight interplay between physiological needs of different biota, mineral dissolution rates, and substrate nutrient availability resulted in intricate elemental distribution patterns. Biota accelerated CO2 mineralization over abiotic controls as ecosystem complexity increased, and significantly modified stoichiometry of mobilized elements. Microbial and fungal components inhibited element leaching (23.4% and 7%), while plants increased leaching and biomass retention by 63.4%. All biota left comparable biosignatures in the dissolved weathering products. Nevertheless, the magnitude and allocation of weathered fractions under abiotic and biotic treatments provide quantitative evidence for the role of major biosphere components in the evolution of upper continental crust, presenting critical information for large-scale biogeochemical models and for the search for stable in situ biosignatures beyond Earth.Comment: 41 pages (MS, SI and Data), 16 figures (MS and SI), 6 tables (SI and Data). Journal article manuscrip

Small lakes in big landscape : multi-scale drivers of littoral ecosystem in alpine lakes.

In low nutrient alpine lakes, the littoral zone is the most productive part of the ecosystem, and it is a biodiversity hotspot. It is not entirely clear how the scale and physical heterogeneity of surrounding catchment, its ecological composition, and larger landscape gradients work together to sustain littoral communities. A total of 113 alpine lakes from the central Pyrenees were surveyed to evaluate the functional connectivity between littoral zoobenthos and landscape physical and ecological elements at geographical, catchment and local scales, and to ascertain how they affect the formation of littoral communities. At each lake, the zoobenthic composition was assessed together with geolocation, catchment hydrodynamics, geomorphology and topography, riparian vegetation composition, the presence of trout and frogs, water pH and conductivity. Multidimensional fuzzy set models integrating benthic biota and environmental variables revealed that at geographical scale, longitude unexpectedly surpassed altitude and latitude in its effect on littoral ecosystem. This reflects a sharp transition between Atlantic and Mediterranean climates and suggests a potentially high horizontal vulnerability to climate change. Topography (controlling catchment type, snow coverage and lakes connectivity) was the most influential catchment-scale driver, followed by hydrodynamics (waterbody size, type and volume of inflow/outflow). Locally, riparian plant composition significantly related to littoral community structure, richness and diversity. These variables, directly and indirectly, create habitats for aquatic and terrestrial stages of invertebrates, and control nutrient and water cycles. Three benthic associations characterised distinct lakes. Vertebrate predation, water conductivity and pH had no major influence on littoral taxa. This work provides exhaustive information from relatively pristine sites, and unveils a strong connection between littoral ecosystem and catchment heterogeneity at scales beyond the local environment. This underpins the role of alpine lakes as sensors of local and large-scale environmental changes, which can be used in monitoring networks to evaluate further impacts

L´ASIMMETRIA DEGLI ANFIBI, UN METODO UTILE PER VALUTARE LA QUALITÀ AMBIENTALE

This study aimed to determine the morphological stress experienced by Rana perezi, an anuran endemic to the Iberian Peninsula, in an agricultural landscape with different levels of management impact, by using the fluctuating asymmetry (FA) of its skeleton. Tibio-fibula, a highly functional trait, had the lowest FA level, whereas radio-ulna was the most asymmetric. This indicates that traits under directional selection are more prone to reflect stress than the functionally important ones. Metatarsus and radio-ulna were less able to cope with the stress in rice fields than in reservoirs. In ontogeny FA level decreased towards the adult stage suggesting that the mechanism of developmental stability buffered against the stress. In conclusion metatarsal and radio-ulna asymmetry of R. perezi juveniles can be used to assess environmental disturbances in agricultural landscapes.Cette étude a visé de déterminer le stress morphologique éprouvé par Rana perezi, un anoure endémique de la Péninsule Ibérique, dans le paysage agricole, en utilisant l'asymétrie fluctuante (AF) de son squelette. Le tibio-péroné, un trait très fonctionnel, montrait le plus faible degré d'asymétrie, alors que le radio-cubitus a était le plus asymétrique. Il révèle que les traits sous sélection directionnelle sont plus prédisposés au stress que les traits fonctionnels importants. En outre, le métatarse et le radio-cubitus font moins face aux stress dans les rizières que dans les réservoirs. Dans l'ontogenèse, le niveau d’AF a diminué en s'approchant du stade, suggérant que le mécanisme de la stabilité développementale protège contre le stress. En conclusion, l´AF du métatarse et du radio-cubitus des juvéniles de R. perezi pourrait être utilisée pour l'évaluation des perturbations environnementales dans des paysages agricoles.Questo studio mira a determinare lo stress morfologico vissuto da Rana perezi, un anura endemico della Penisola Iberica, nel paesaggio agricolo, utilizzando l'asimmetria fluttuante (AF) del suo scheletro. Il tibio-perone, un tratto altamente funzionale, ha mostrato il più basso grado di AF, mentre la radio-ulna è risultata la più asimmetrica. Si rileva che tratti sotto selezione direzionale sono più inclini a riflettere stress che tratti funzionalmente importanti. Inoltre, metatarso e radio-ulna sono meno capaci di far fronte allo stress in campi di riso che in riserve d'acqua. In ontogenesi, il livello di AF diminuisce verso la fase adulta suggerendo che il raggiungimento di stabilità nello sviluppo dell'organismo rappresenta una protezione dallo stress. In conclusione l´asimmetria del metatarso e radio-ulna di forme giovani di R. perezi può essere utilizzato per valutare disturbi ambientali in paesaggi agricol

Enhanced deposition of trace elements driven by climate change in a mountain catchment

Sufficient evidence has been gathered from observational records to indicate that climate change has an amplified effect on physical, chemical and biological processes in sensitive regions such as mountain landscapes (IPCC 2007). However, its potential impact on trace elements dynamics in such exposed environments has received little attention. Here, we examined whether change in sedimentary record of a number of trace elements (As, Cu, Mn, and Pb) from Bubal reservoir, a 1085m altitude waterbody from central Pyrenees, can be attributed to recent alterations in the local climate. For this purpose a sediment core was collected from the lake bed in August 2005, covering the depositionary period 1972-2004. The core was subsampled at 1.5cm intervals, corresponding to the annual sedimentation rate in the catchment (Lavilla et al. 2006). The <0.25mm fraction of each subsample was oven dried and digested for trace element contents following USEPA (1999). Arsenic, Cu, Mn and Pb were determined by ICPMS according to standard protocols. Titanium was characterised by ICP-OES. Organic matter was estimated as % loss on ignition at 550ºC. Climate data was provided by the Spanish Institute of Meteorology, Madrid. Sediment trace elements showed strong association with major elements Ti and Mn, and organic matter contents (stepwise multiple linear regression with forward selection procedure, adjusted R2= 0.41, P<0.001). This relationship, together with the generally low values of organic matter (mean %LOI= 3.4%) indicates the source of trace elements largely being the weathered material from the catchment. The metal concentrations also decreased with depth (ANOVA F ≥7.89, P<0.01), further suggesting an increased mobilisation from the catchment. This was supported by similar metal concentration peaks seen in the core metal profiles. To test whether climate factors are responsible for the observed depositionary trend, the metal concentrations were statistically checked against a number of climate factors. The results revealed a positive association between metals pool and 0ºC isotherm, and a negative relationship with the frequencies of rain and snow days (Fig. 1). It is known that changes in certain climate parameters can affect the weathering of mountain bedrock, its snow-cover surface and waterbody’s geochemistry (White and Blum 1995). In this scenario the cumulative effects of snow line elevation and increasingly dry slopes appear to have exposed more surfaces to weathering, increasing the amounts of trace and major elements released from the poorly covered mountain slopes and their subsequent accumulation in lakes. In Bubal lake catchment, the drainage of sulphide deposits from the metamorphic geology is the major potential metal source. These deposits are known for their high presence of trace elements (Subías et al. 1993). The metal containing sulphides can oxidise relatively rapidly under neutral pH conditions of high altitudes and naturally release As and other elements at enhanced rates, especially following the dry periods (Trois 1999). Our findings have implications for the understanding of the influence of climate change on mountain geochemical processes and the potential adverse consequences on ecosystems and the wider environment. Further experimental/modelling work is however needed to clearly pinpoint the causative relationships between increased trace elements dissolution rates and climate change

Predatory aquatic beetles, suitable trace elements bioindicators

Predatory aquatic beetles are common colonizers of natural and managed aquatic environments. While as important components of the aquatic food webs they are prone to accumulate trace elements, they have been largely neglected from metal uptake studies. We aim to test the suitability of three dytiscid species, i.e.Hydroglyphus pusillus, Laccophilus minutus and Rhantus suturalis, as trace elements (Al, As, Cd, Co, Cu, Fe, Mn, Mo, Ni, Pb, Se and Zn) bioindicators. The work was carried out in a case area representing rice paddies and control sites (reservoirs) from an arid region known for its land degradation (Monegros, NE Spain). Categorical principal component analysis (CATPCA) was tested as a nonlinear approach to identify significant relationships between metals, species and habitat conditions so as to examine the ability of these species to reflect differences in metal uptake. Except Se and As, the average concentrations of all other elements in the beetles were higher in the rice fields than in the control habitats. The CATPCA determined that H. pusillus had high capacity to accumulate Fe, Ni and Mn regardless of the habitat type, and hence may not be capable of distinguishing habitat conditions with regards to these metals. On the other hand, L. minutus was found less sensitive for Se in non-managed habitats (i.e. reservoirs), while R. suturalis was good in accumulating Al, Mo and Pb in rice fields. The latter seems to be a promising bioindicator of metal enrichment in rice fields. We conclude that predatory aquatic beetles are good candidates for trace elements bioindication in impacted and non-impacted environments and can be used in environmental monitoring studies. CATPCA proved to be a reliable approach to unveil trends in metal accumulation in aquatic invertebrates according to their habitat status

Trace metals and their source in the catchment of the high altitude Lake Respomuso, Central Pyrenees

Lake Respomuso is a dammed lake of glacial origin at 2200 m altitude in the Central Pyrenees. This study investigated the source of a number of trace elements (As, Cd, Co, Cu, Mn, Ni, Pb and Zn) in its catchment and their possible link to the local geology. Altogether 24 sediment and 29 water samples were collected from all major streams feeding the lake. The sediments were analysed for trace elements, major mineral components, minerals and organic matter whilst water samples were analysed for dissolved metal concentrations. The trace element levels in the catchment sediment and water were relatively high compared to other similar altitude sites, with concentrations in the headwaters being generally higher than in the lower basin because of the source being concentrated in these areas. The principal component analysis revealed that the source of sediment-bound trace elements in the Lake Respomuso catchment is geogenic, and originated possibly in the sulphide minerals from slate formations. Except at one site, none of the water samples exceeded the WHO drinking water guideline for arsenic. Arsenic in water was significantly correlated with its concentration in the sediments, possibly due to the oxidation of arsenic bearing minerals. The dissolved concentrations of all other trace elements were generally lower than the WHO drinking water guide values and they were not related to their sediment concentrations. The As, Cd, Ni contents in sediment from several catchment streams exceeded their sediment quality thresholds. This geogenic source may pose risk to the stability of fragile local biodiversity and to the wider environment in the valley bellow particularly if the metals are mobilised, possibly due to environmental change

Ecosystem Composition Controls the Fate of Rare Earth Elements during Incipient Soil Genesis

The rare earth elements (REE) are increasingly important in a variety of science and economic fields, including (bio) geosciences, paleoecology, astrobiology, and mining. However, REE distribution in early rock-microbe-plant systems has remained elusive. We tested the hypothesis that REE masspartitioning during incipient weathering of basalt, rhyolite, granite and schist depends on the activity of microbes, vascular plants (Buffalo grass), and arbuscular mycorrhiza. Pore-water element abundances revealed a rapid transition from abiotic to biotic signatures of weathering, the latter associated with smaller aqueous loss and larger plant uptake. Abiotic dissolution was 39% of total denudation in plantmicrobes- mycorrhiza treatment. Microbes incremented denudation, particularly in rhyolite, and this resulted in decreased bioavailable solid pools in this rock. Total mobilization (aqueous + uptake) was ten times greater in planted compared to abiotic treatments, REE masses in plant generally exceeding those in water. Larger plants increased bioavailable solid pools, consistent with enhanced soil genesis. Mycorrhiza generally had a positive effect on total mobilization. The main mechanism behind incipient REE weathering was carbonation enhanced by biotic respiration, the denudation patterns being largely dictated by mineralogy. A consistent biotic signature was observed in La: phosphate and mobilization: solid pool ratios, and in the pattern of denudation and uptake.National Science Foundation (NSF) [EAR-1023215]; NSF [EAR-0724958, EAR-1331408, EAR-1263251, EAR-1004353]; Biosphere 2 REU program; United States-Mexico Commission for Educational and Cultural Exchange (COMEXUS): the Fulbright-Garcia Robles Scholarship program; Thomas R. Brown Foundation endowment; U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-76SF00515]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Ecosystem-bedrock interaction changes nutrient compartmentalization during early oxidative weathering

Ecosystem-bedrock interactions power the biogeochemical cycles of Earth's shallow crust, supporting life, stimulating substrate transformation, and spurring evolutionary innovation. While oxidative processes have dominated half of terrestrial history, the relative contribution of the biosphere and its chemical fingerprints on Earth's developing regolith are still poorly constrained. Here, we report results from a two-year incipient weathering experiment. We found that the mass release and compartmentalization of major elements during weathering of granite, rhyolite, schist and basalt was rock-specific and regulated by ecosystem components. A tight interplay between physiological needs of different biota, mineral dissolution rates, and substrate nutrient availability resulted in intricate elemental distribution patterns. Biota accelerated CO2 mineralization over abiotic controls as ecosystem complexity increased, and significantly modified the stoichiometry of mobilized elements. Microbial and fungal components inhibited element leaching (23.4% and 7%), while plants increased leaching and biomass retention by 63.4%. All biota left comparable biosignatures in the dissolved weathering products. Nevertheless, the magnitude and allocation of weathered fractions under abiotic and biotic treatments provide quantitative evidence for the role of major biosphere components in the evolution of upper continental crust, presenting critical information for large-scale biogeochemical models and for the search for stable in situ biosignatures beyond Earth.National Science Foundation (NSF)National Science Foundation (NSF) [EAR-1023215]; NSFNational Science Foundation (NSF) [EAR-0724958, EAR-1331408, EAR-1411609]; Biosphere 2 REU program [NSF EAR-1263251, NSF EAR-1004353]; United States-Mexico Commission for Educational and Cultural Exchange (COMEXUS): the FulbrightGarcia Robles Scholarship program; Thomas R. Brown Foundation endowment; NASA Astrobiology Institute "CAN7: Alternative Earths. Explaining Persistent Inhabitation on a Dynamic Early Earth"; U.S. Department of Energy, Office of Science, Office of Basic Energy SciencesUnited States Department of Energy (DOE) [DE-AC02-76SF00515]Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]