Decadal trends in water chemistry of Alpine lakes in calcareous catchments driven by climate change

M Rogora; L Somaschini; A Marchetto; R Mosello; G A Tartari; L Paro

doi:10.1016/j.scitotenv.2019.135180

Decadal trends in water chemistry of Alpine lakes in calcareous catchments driven by climate change

Sci Total Environ. 2020 Mar 15:708:135180. doi: 10.1016/j.scitotenv.2019.135180. Epub 2019 Nov 21.

Authors

M Rogora¹, L Somaschini², A Marchetto², R Mosello², G A Tartari², L Paro³

Affiliations

¹ CNR Water Research Institute, L.go Tonolli 50, I-28922 Verbania Pallanza, Italy. Electronic address: michela.rogora@irsa.cnr.it.
² CNR Water Research Institute, L.go Tonolli 50, I-28922 Verbania Pallanza, Italy.
³ Regional Agency for Environmental Protection of the Piedmont Region (ARPA Piemonte) - Dept. Natural and Environmental Risks - Geological Monitoring and Studies, Via Pio VII, 9, I-10135 Torino, Italy.

PMID: 31812417
DOI: 10.1016/j.scitotenv.2019.135180

Abstract

High mountain lakes are considered sensitive indicators of the effects of natural and anthropogenic drivers, including atmospheric deposition and climate change. In this study, we assess long-term trends in the chemistry of a group of high altitude lakes in the Western Alps, Italy, lying in bedrock with a relevant presence of basic, soluble rocks. An in-depth investigation was performed on two key-sites (Lakes Boden Inferiore and Superiore) for which continuous chemical data are available for a period of 30 years. A group of 10 additional lakes in the same area was also considered; these lakes were sampled at the end of the ice-free period during irregular surveys in the period 1980-2017. Water samples were analysed for the main chemical variables, including pH, electrical conductivity, major ions (Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃^-, Cl^-, SO₄^2-, NO₃^-) and algal nutrients (phosphorus and nitrogen compounds, reactive silica). A steep increase in conductivity and ion concentrations was detected at the key-sites: conductivity increased from 40-45 to 60-70 µS cm^-1 over the period 1984-2017; sulphate concentrations more than doubled over the same period (from 50-60 to 120-180 µeq L^-1) and base cations increased from 400-500 to 600-750 µeq L^-1. An increase in the solute content was also detected in the survey lakes (average conductivity from 39 ± 20 to 57 ± 23 µS cm^-1). The analysis of meteorological data revealed a significant increase of air temperature (0.019 °C y^-1 over the period 1950-2017), mainly in spring and summer (0.033 °C y^-1), and a decrease of snow cover depth and duration. Meteo-climatic drivers were identified as the responsible for the chemical changes occurred in the lakes. Climate-driven effects on weathering rates were mainly indirect and occurred by affecting the flow paths of water at both surface and subsurface level. Cryosphere modification (reduced snow cover and permafrost thawing) also played a role.

Keywords: Biogeochemistry; Long-term trends; Mountain lakes; Permafrost; Weathering.