Modelling carbon isotopes in spruce trees reproduces air quality changes due to oil sands operations

• Long tree-ring C isotope series show increasing trends after onset of operations.
• Response-to-climate modelling suggests isotopic anomalies during operation period.
• Anomalies strongly correlate with the proxy for mining-operation emissions.
• Combined climate-airborne emissions models reproduce all measured δ13C trends.
• Tree-δ13C models offers an objective recognition of past changes in air quality.

Direct monitoring of air quality does not cover more than the last three decades in most industrialized countries. For that reason studies using growth-ring carbon isotopes (δ13C) of several species of trees have recently investigated isotopic responses in the contexts of stationary and diffuse pollution in humid continental conditions. Here, the growth-ring δ13C series (1880–2009) of spruce trees living in sub-humid subarctic conditions were measured to assess if they represent indicators for air quality changes near oil sands (OS) developments initiated in northeastern Alberta in 1967. The measured δ13C pre-operation rings at two forest sites were analyzed along local climatic conditions to develop response-to-climate statistical models and predict the natural isotopic behaviour for the most recent part of the ring series. The measured trends and climate-modelled (natural) δ13C values strongly depart during the operation period, depicting anomalies which can be nicely reproduced by multiple regression models combining climate and a proxy for OS airborne emissions. This research allows envisioning the use of carbon dendroisotopic indicators to compensate for the lack of long-term air quality measurement, and monitor environmental conditions in the sub-humid terrestrial ecosystem exposed to emissions from oil sands operations which are predicted to increase in the future.