Identification of pollutant delivery processes during different storm events and hydrological years in a semi-arid mountainous reservoir basin

Abstract

A comprehensive understanding of pollutant delivery processes during storm events is essential for developing strategies to minimize adverse impacts on receiving water bodies. In this paper, hysteresis analysis and principal component analysis were coupled with identified nutrient dynamics to determine different pollutant export forms and transport pathways and analyze the impact of precipitation characteristics and hydrological conditions on pollutant transport processes through continuous sampling between different storm events (4 events) and hydrological years (2018-wet, 2019-dry) in a semi-arid mountainous reservoir watershed. Results showed pollutant dominant forms and primary transport pathways were inconsistent between different storm events and hydrological years. Nitrogen (N) was mainly exported in the form of nitrate-N(NO3-N). Particle phosphorous (PP) was the dominant P form in wet years, but total dissolved P (TDP) in dry year. Ammonia-N (NH4-N), total P (TP), total dissolved P(TDP) and PP had prominent flushing responses to storm events and were delivered mainly from overland sources by surface runoff; while the concentrations of total N(TN) and nitrate-N(NO3-N) were mainly diluted during storm events. Rainfall intensity and amount had significant control over P dynamics and extreme events played a key role in TP exports, accounting for >90 % of the total TP load exports. However, the cumulative rainfall and runoff regime during rainy season exerted significant control over N exports than individual rainfall features. In the dry year, NO3-N and TN were delivered primarily through soil water flow paths during storm events; nevertheless, wet year registered complex control on TN exports via soil water release, followed by surface runoff transport. Relative to dry year, wet year registered higher N concentration and more N load exports. These findings could provide scientific basis for determining effective pollution mitigation strategies in Miyun Reservoir basin and provide important references for other semi-arid mountain watersheds.