Characteristics of Phosphorus Loss from the Weathered Granite Slopes of Southeast China

Abstract

The excessive discharge of phosphorus (P) is one of the critical reasons for eutrophication that greatly influences water quality and aquatic ecosystems [1,2]. The major cause of increasing P concentrations in ground and surface waters is P loss resulting from the unreasonable application of phosphate fertilizer and the serious erosion of water and soil [3,4]. Due to the contradiction between population growth and food demand, many sloping lands have been reclaimed as cultivated lands for planting crops and vegetables [5]. The interference of artificial farming has aggravated soil erosion and loss of nutrients such as nitrogen (N) and P on the slopes, which has reduced the efficiency of Pol. AbstractThe method of artificial rainfall simulation was applied to study the effects of different slope gradients (8°, 15°) and rainfall intensities (1.0, 1.5, 2.0, 2.5 mm/min) on the pathways of phosphorus (P) loss from the weathered granite slopes of southeast China. The results showed that the runoff yield increased with runoff time while the sediment yield first increased and then decreased. The subsurface flow showed a changing trend of single-peak curve with maximums appearing under the rainfall intensity of 1.5 mm/min. The P loss amount increased with increasing rainfall intensity and slope gradient and was mainly carried away by eroded sediment that accounted for 54.23-95.62%. The mass concentrations of TP, DP and PP in runoff decreased with runoff time. The P lost via runoff from the sloping land was mainly in the form of DP, most of which reached more than 50%. Surface flow was the dominant pathway of P loss via runoff and it presented a positive power correlation with rainfall intensity (R 2 >0.982). It was necessary to attach great importance to P loss via subsurface flow, though the total loss amount was small compared to that via surface flow and sediment.