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- Title
Long‐Term Disconnect Between Nutrient Inputs and Riverine Exports in a Semi‐Arid, Agricultural Watershed: Yakima River Basin 1945–2012.
- Authors
Grieger, S. R.; Harrison, J. A.
- Abstract
Nutrient budgets are useful tools in addressing impaired water quality from increasing anthropogenic nitrogen (N) and phosphorus (P) inputs to watersheds. Long term analyses can identify temporal ecological responses to past nutrient management strategies. Multidecadal watershed analyses of nutrient dynamics traditionally have been limited to large humid or mesic river basins focused primarily on a single nutrient (N or P). Here we present a long term, dual N and P input‐output budget for the agriculturally rich Yakima River Basin (YRB) located in the semi‐arid western U.S. We quantified N and P terrestrial inputs from 1945 to 2012 using past agricultural and water quality data to investigate interactions between water flow and N and P exports in the YRB. Between 1945 and 2012, N and P inputs to agricultural lands increased by over 18 and 10‐fold, respectively, with synthetic fertilizer accounting for the majority of input increases. While such increases in nutrient inputs were comparable to other U.S. basins, observed riverine N and P export did not significantly increase over time. Rather, we found that since the mid‐1970s both N and P loads and concentrations in the Yakima River have decreased, indicating a temporal disconnect between nutrient inputs and riverine exports in the YRB. This disconnect highlights a need to further investigate nutrient dynamics at local scales in semi‐arid watersheds. Our analysis raises questions about long‐term N and P retention in the YRB and potential impacts on future water quality across the western US. Plain Language Summary: Human needs for agriculture have increased nitrogen (N) and phosphorus (P) inputs to lands for many decades. When large amounts of these nutrients enter freshwater they negatively affect humans, animals, and ecosystems. To prevent these consequences there has been extensive work to estimate amounts of nutrients entering rivers in the U.S. over time, but comparatively little of it has focused on river basins in the American West. Therefore, we investigated how sources of N and P changed over 67 years in the Yakima River Basin, an agricultural watershed in central Washington, U.S. We examined the relationship between nutrient sources and river water quality over time. Total inputs of both nutrients to land surfaces increased over time, primarily as fertilizer. However, over the same period, the amount of N and P in the Yakima River decreased or remained unchanged. This mismatch between nutrients on land and water quality indicates a substantial amount of applied nutrients are being stored in aquifers, cycled through soils or returned to the atmosphere rather than entering the river. Overall, our study suggests past relationships between nutrient sources and water quality in the western U.S. may be different than in well‐studied basins located in other parts of the country. Key Points: Agricultural nutrient inputs to the Yakima Basin have increased since 1945, with the largest increases in surplus occurring since 1997River nitrogen and phosphorus exports have not increased in response to increasing watershed inputs; rather, in recent years they have declinedA lack of relationship between nutrient inputs and river export highlights a need for future study of nutrient storage in semi‐arid areas
- Subjects
YAKIMA River Watershed (Wash.); YAKIMA River (Wash.); NITROGEN in water; PHOSPHORUS in water; WATER quality
- Publication
Journal of Geophysical Research. Biogeosciences, 2021, Vol 126, Issue 9, p1
- ISSN
2169-8953
- Publication type
Article
- DOI
10.1029/2020JG006072