Export of non-point source suspended sediment, nitrogen, and phosphorus from sloping highland agricultural fields in the East Asian monsoon region

Abstract

Excess sediment and nutrient export from agricultural fields with steep slopes is a major concern linked to surface water quality in Korea. In this study, the export of suspended sediment (SS), total nitrogen (TN), and total phosphorus (TP) and their event mean concentrations (EMCs) in surface runoff from a highland mixed land use (61% forested, 30% cropped, 9% other) watershed were quantified. In 2007, the Korean Ministry of Environment (MoE) declared the study area as a priority region for non-point source (NPS) pollution management and initiated various best management practices (BMPs) in the study watershed. SS, TN, and TP concentrations in Mandae Stream were monitored for 5 years (2009-2013) to evaluate the effectiveness of BMPs. Average EMCs for SS, TN, and TP were as high as 986, 3.4 and 0.8 mg/L, respectively. The agricultural export coefficients of agricultural land in the study watershed for SS, TN, and TP were 5611, 171, and 6.83 kg/ha/year, respectively. A comparison with results from other studies shows that both EMCs and agricultural export coefficients in the study watershed were much higher than most of the results reported for watersheds in other regions. The results show that sediment and nutrient export from intensive agriculture areas with steep slopes continue to be a major concern for the downstream reservoir, Lake Soyang. Remedial strategies should be directed towards controlling sources of SS, TN, and TP to improve downstream water quality in sloping highland agricultural areas in Korea.

Phosphorus Budget for a Forested-Agricultural Watershed in Korea

“…Approximately 90% of the annual rainfall occurs during the April to October cropping season [11]. The 10 year (2004The 10 year ( -2013 mean annual temperature in the Haean watershed is 10.9 • C with a mean annual precipitation of 1506 mm [4].…”

“…Approximately 90% of the annual rainfall occurs during the April to October cropping season [11]. The 10 year (2004The 10 year ( -2013 mean annual temperature in the Haean watershed is 10.9 °C with a mean annual precipitation of 1,506 mm [4]. The soils in the watershed are classified as Cambisols but most agricultural soils are Anthrosols due to the long-term use of soil amendments with sandy soil as a top dressing [13].…”

“…Eutrophication is a serious environmental challenge in Korea and P export from agricultural fields has been identified as major contributor to nonpoint source (NPS) nutrient pollution [3]. The characteristic intense rainfall during the East Asian summer monsoon dramatically influences the export of NPS derived nutrients from highland agricultural croplands in Korea [4]. Some studies have shown that P export from agricultural fields in Korea is higher than in other regions [3,4].…”

“…The characteristic intense rainfall during the East Asian summer monsoon dramatically influences the export of NPS derived nutrients from highland agricultural croplands in Korea [4]. Some studies have shown that P export from agricultural fields in Korea is higher than in other regions [3,4]. To ensure short-term productivity as well as long-term sustainability, minimizing P losses and achieving a balance between P inputs and P outputs in agricultural systems is important.…”

“…The study area is an advantageous location for studying the watershed P budget because it has only a single outlet (Mandae Stream). Previous studies on NPS of sediment and nutrient have conducted in the Haean watershed and the watershed is known as a hot spot for soil erosion and export of NPS pollution to Lake Soyang [4].…”