Riparian influences on carbon isotopic composition of tree rings in the Slave River Delta, Northwest Territories, Canada

Tree-ring cores from two white spruce (Picea glauca) trees at each of three sites within the Slave River Delta, Northwest Territories, Canada, were separated, processed for α-cellulose and analyzed for their carbon isotope composition. The three carbon isotope (δ13Ccellulose) time series, collectively covering the time period from 1689 to 2003, were statistically correlated with average Historical Monthly Climate Grid temperature and precipitation for the period 1901-2000. The results suggest that the trees from all three sites show a distinct trend towards more enriched δ13Ccellulose values with time, implying more stressful environmental conditions possibly related to the overall 20th Century drying of the Slave River Delta. Anthropogenic impacts of heavy logging and the construction of a large upstream dam may also be present in the δ13Ccellulose time series. The main focus of the study relates to the different nature of the three riparian sites. The δ13Ccellulose values of the trees from the two sites ≥ 50 m from the river at higher elevation suggest a relationship with moisture-deficit-stress (MDS) emanating from hydroclimate effects during the non-growing and growing seasons. The δ13Ccellulose values from a site adjacent to the river at lower elevation, however, suggest that these same effects can manifest as moisture-excess-stress (MES) on the trees. The relationships between these two types of moisture stress and the δ13Ccellulose values of the trees from the sites with obvious riparian differences are discussed in detail.