Coastal watersheds link land to sea
Coastal watersheds are the nexus of land, ocean, and atmosphere. The Hakai Watersheds group uses watershed measurement, mapping, and modelling to discover how freshwater creates land-sea linkages from local to regional scales. We consider the past, the present, and the projected climate. We combine local observations with geospatial data to model river exports to the coastal ocean and to evaluate the changing state of freshwater ecosystems relevant to anadromous fish. The Quadra Island Field Station is an ideal location to access and study a wide range of coastal watersheds.
Icefield to ocean linkages in rainforest fjordlands
The marine waters around our field station are affected by local runoff from Quadra Island and also by runoff from the larger more mountainous watersheds of the adjacent mainland, including the glacierized watersheds of Bute Inlet. For example, the Homathko and Southgate watersheds at the head of the inlet discharge large quantities of suspended sediment and particulate organic matter into Bute Inlet, impacting fjord circulation, water clarity, carbon sequestration in marine sediments, and even turbidity currents along the seafloor.
Glacierized coastal watersheds across the Pacific coast are rapidly changing due to the warming climate, with a wide range of potential implications for people and ecosystems downstream. Progressive reductions in glacier volume are changing freshwater export dynamics, with a shift toward more rain-dominated streamflow regimes and forest dominated biogeochemical exports over decades. This makes it important to understand a baseline understanding of the linkages between watersheds and the ocean across the diverse watershed types of this region.
In addition to these kinds of incremental changes, Bute Inlet has recently demonstrated the potential for sudden and extreme change in glacierized watersheds, with implications reaching to the coastal ocean. In late November of 2020, a glacial lake outburst flood in the Southgate watershed sent vast quantities of water, sediment, logs and other organic matter into Bute Inlet, creating a turbid plume more than 60 km down the inlet. Along the way, the torrent of water destroyed significant areas of salmon habitat and triggered the establishment of the Bute Inlet Salmon Roundtable: a multi-stakeholder initiative to study and restore salmon in the inlet, led by Homalco First Nation and involving Hakai Institute among other partners.
Climate and forestry effects on stream ecosystems
Climate change also poses threats in the non-glacierized watersheds that dominate the land west from Bute Inlet. In fact, stream temperatures are expected to be most sensitive to increasingly frequent extreme heat in rain-fed watersheds, followed by snow-fed watersheds, and then glacierized watersheds. The thermal buffering provided by spring and summer meltwaters is expected to decrease in the decades to come, making it important to develop model projections for stream temperatures in this region. Forest cover can provide shade and a refuge from extreme heat, but the necessary level of riparian forest protection is unclear. These two knowledge gaps led to the creation of the Nanwakolas Council 50 Watersheds Project: an Indigenous-led science partnership with the Hakai Institute and other partners. The project developed tools to monitor and address threats that climate change and forest management pose to salmon habitat in the territories of Mamalilikulla, Tlowitsis, Wei Wai Kum, We Wai Kai, and K’omoks First Nations. This work involves using LIDAR to model solar radiation reaching streams, eDNA to evaluate aquatic insects as indicators of salmon habitat, and hydrological modelling to simulate stream temperatures for many decades to come.
