Watershed Classification Predicts Streamflow Regime and Organic Carbon Dynamics in the Northeast Pacific Coastal Temperate Rainforest

Image credit: Ian Giesbrecht

Watersheds transfer large amounts of freshwater to the ocean, yet each watershed does this differently from the next. Geographic differences in climate and topography affect the global biogeochemical cycling of elements like carbon. However, most rivers in regions like the carbon-dense rainforest of western North America have no measurements of streamflow or carbon, making it hard to predict how river dynamics change across geographic locations. Our goal was to classify and map watershed types for an entire coastal region, with consideration of both water and carbon. Our results show the locations of watershed types with very different amounts and seasonality of runoff and of dissolved organic carbon (DOC). While we focused on DOC, these watershed types might naturally differ in other aspects of river biogeochemistry such as organic nitrogen and iron. Maps of watershed types should help society understand how land and sea are linked together over complex regions within a changing climate. However, certain watershed types have little or no long-term monitoring to guide climate adaptation. While many studies have classified watersheds from a hydrology perspective, few have considered carbon as well. Combining hydrology and biogeochemistry when mapping watershed types may be useful in other regions of the world.

Photos are from the unceded lands and waters of the Heiltsuk Nation, Da'naxda'xw-Awaetlala First Nation, Wuikinuxv Nation, and Homalco First Nation. The research spans the territories of many Indigenous peoples.