Influence of rainfall intensity and slope on suspended solids and phosphorus losses in runoff

Abstract

Suspended solids (SS) and phosphorus (P) losses in rainfall generated runoff can lead to the deterioration of surface water quality. Simulated rainfall experiments were conducted to investigate the effects of rainfall intensity (30, 50, 65, and 100 mm h) and land slope (0°, 5°, and 10°) on SS and P losses in runoff from experimental rigs containing bare land soil and soil planted with grass (tall fescue). In addition, total phosphorus (TP), particulate phosphorus (PP), and dissolved phosphorus (DP) losses in runoff were also measured. Results showed that tall fescue could reduce loads of SS by 86-99.5%, PP by 92-98.5%, and TP by 55-89.8% in runoff compared with losses from bare soil; this is due to a combination reduced raindrop kinetic energy at the soil surface, reduced soil erodibility in the presence of plant roots and shoots, and an increase in roughness and consequently reduced overland flow velocity resulting in the trapping of particles. Linear relationships between losses of SS and TP and between TP and PP in runoff were significant (R > 0.93) in both bare soil and grass. In addition, SS and TP losses increased greatly significantly with rainfall intensity and slope. The influence of rainfall intensity on SS and P losses was greater than the influence of slope. Simple linear regressions were constructed between losses of SS and P, the rainfall intensity (30 to 100 mm h), and land slope (0° to 10°). The multiple regression equations of SS and P losses in runoff established in this study can provide a simple predicting approach for estimating the non-point source pollution load of SS and P arising from rainfall.

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

“…TP loss load in sediment showed a liner correlation with sediment yield (R 2 >0.998) and was significantly correlated with rainfall intensity and surface flow volume. TP, DP and PP loss loads in surface flow were all positively correlated with surface flow volume (R 2 > 0.869) as well as sediment yield (R 2 >0.832), though this was partly due to the fact that runoff volume was used to calculate the P loss load [2]. The accumulative TP loss load in both runoff and sediment showed a positive power relationship with rainfall intensity (R 2 >0.982).…”

“…Overall, the sediment yield transported by the surface flow decreased with the prolongation of rainfall. But short increments of high sediment content existed in the early stage under rainfall intensities larger than 1.0 mm/min, which could be called the first flush effect [2], leading to the peaking values of sediment yield. The short increasing trends and fluctuations might be caused by the rainfall splashes, which could break the soil aggregates [38].…”

“…Drewry et al [43] also found that rainfall intensity had a significant impact on P loss through rainstorm monitoring and load estimation in the Tuross River Basin of Australia, and the nutrient loss under small rainfall intensity was mainly in dissolved form. However, many other previous studies found that the major part of TP loss via surface flow was accounted for by PP [2,[44][45][46], which could be adsorbed in soil particles and mobilized by rainfall runoff. This was consistent with laboratory experiments of P loss with surface runoff reported by Wang et al [47], with most of P transformed through sediment loss.…”

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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].

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“…Therefore, an experimental study with two slope gradients and four rainfall intensities was conducted to investigate the characteristics of P loss processes. The objectives of the present work are (1) to investigate the effects of rainfall intensity and slope gradient on soil erosion and P loss processes, (2) to study the main loss forms of P and their contributions, and (3) to reveal the main loss pathways of P under different experimental conditions.…”