Determining Water Age of Rivers and Plant-Accessible Water in California's Headwaters During Hydrologic Extremes
Abstract
The Sierra Nevada provides a large portion of freshwater resources to California. Uncertainty in storage and timing of release from mountain headwaters to major rivers leads to challenges in water management. We investigated the age of major river runoff and the age of water accessed by forest vegetation using hydrologic tracers. In a mid-elevation headwater catchment in the central Sierra Nevada, we found that vegetation is first to interact with precipitation, accessing very young water, compared to runoff. Furthermore, following both severe and seasonally typical drought conditions, vegetation accessed water that did not reach streams or rivers. To understand flow paths of Sierra Nevada rivers, we estimated the portion of runoff composed of recent water year's snowpack and we estimated the contribution of older, stored water sources. To do so, we measured sulfur-35 (half life = 87 days) and tritium (half life 12.32 years) in 17 major Sierra Nevada rivers and the McCloud river (originating from Mt. Shasta). We sampled these two cosmogenic tracers during spring runoff in the wettest year on record, 2017, and again following the summer dry season, typical of this Mediterranean climate. We observed that all rivers had similar mean residence times between 8 and 14 years with little seasonal variation. Meanwhile, the portion of river runoff made up of the most recent winter's snowpack varied considerably from river to river and season to season, with some catchments releasing large amounts of young water in spring and other river catchments showing a lag in snow melt contributions. The amount of yearly snowpack has previously been the focus of determining river runoff. However, these results highlight the contribution of water stored for several years in the headwaters and whether precipitation is accessed by, or bypasses, forest vegetation.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H43K2182T
- Keywords:
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- 1807 Climate impacts;
- HYDROLOGY;
- 1830 Groundwater/surface water interaction;
- HYDROLOGY;
- 1834 Human impacts;
- HYDROLOGY;
- 1879 Watershed;
- HYDROLOGY