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Riverine phosphorus tracing and the influence of environmental factors in the Hanzhong catchment, upper reaches of the Danjiangkou reservoir

aquatic-and-marine-chemistry
biogeochemistry
ecohydrology
environmental-contamination-and-remediation

Abstract

Background: The Hanzhong catchment is the primary agricultural area in the upper reaches of the Danjiangkou Reservoir. The challenge of quantifying natural as well as anthropogenic point and nonpoint inputs of riverine phosphorus (P) in this catchment severely hinders P management for the reservoir's upstream regions.

Methods: For the first time, a Bayesian stable isotope mixing model based on the phosphate oxygen isotope (δ 18 O-PO4) data from three hydrological periods was employed to apportion natural and anthropogenic sources and discern the influence of environmental factors.

Results: Riverine phosphate mainly derives from agricultural sources (approximately 48%). Enhanced leaching due to monsoon precipitation promotes natural inputs in most catchments. During the low flow period, the extensive application of basal fertilizer in a new agricultural production cycle resulted in a sharp rise in organic fertilizer contribution (to 40%). Increasing the slow-release fertilizer usage, avoiding fertilization during hot and rainy weather, and applying organic fertilizer in small amounts over multiple times contribute to reducing agricultural inputs. Conserving water and improving water efficiency are crucial for minimizing wastewater input. This work highlights that controlling agricultural sources, especially during the low flow period, is the primary task for P management in the Hanzhong catchment and further reveals that riverine phosphorus tracing should not omit natural inputs.

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