Zaharescu, Dragos G., Burghelea, Carmen I. and Hooda, Peter S. (2010) Enhanced deposition of trace elements driven by climate change in a mountain catchment. In: Global Change and the World's Mountains Conference; 26-30 Sep 2010, Perth, U. K..

Abstract

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.

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