forWater Webinar: Hannah McSorley's research findings from Greater Victoria

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Join Hannah McSorley as she shares insights from 400+ stream samples collected over 16 months across a Greater Victoria water supply area.

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This research established a stream water sampling program across a second-growth forested drinking water supply area (Vancouver Island, British Columbia, Canada) to contribute to our understanding of variability in natural organic matter (NOM), a master water quality variable important for source drinking water treatability. Over sixteen months (October 2018 to February 2020), 426 stream water samples were collected from 12 sites (ranging from 9.6 to 37 km2, elevation 215 to 870 m a.s.l) from across the Greater Victoria water supply area. Samples were analyzed for NOM quality (via UV-Vis absorbance) and quantity (as dissolved organic carbon, DOC). Results were used to evaluate spatial and temporal patterns and to identify key drivers for NOM dynamics. Important for contaminant transport, NOM quantity was correlated with several metals (e.g. total mercury, aluminum, iron), and its molecular character was correlated to carbonaceous chlorinated disinfection by-products.

Six sites in Leech River watershed (~96 km2) were equipped with vertical passive sampling racks to evaluate hydrograph rising limb NOM dynamics. Approximately 80% of the time, DOC concentration peaked with stream stage. Hydrologic connectivity to terrestrial source pools increased throughout wet seasons and antecedent wetness was important for stream NOM molecular quality, which shifted from predominantly aliphatic in the dry-season to predominantly aromatic in the wet-season. This suggests that in-stream, biological processes dominated NOM quality during the dry-season (summer), whereas wet-season (fall and winter) NOM was more linked to the landscape and driven by hydrology. Random Forest variable importance measure (RF VIM) identified warm and wet conditions as key drivers for NOM dynamics. RF VIM showed that forest age and harvest history were somewhat important predictor variables for NOM aromaticity and molecular size, but that subsurface parent material (e.g. metamorphic rather than igneous) was relatively more important as a predictor of NOM quantity and quality.


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