Particulate phosphorus in runoff in a Mediterranean agroforestry catchment driven by land use and rainfall characteristics

Abstract

AbstractThis study examined phosphorus (P) delivery and transport in flood events in an agroforestry catchment, with cropland and forestland as the main land uses. Sediments were collected in artificial‐lawn mats (MATs) distributed in five locations across the catchment (MAT1 to MAT5) along 20 seasonal campaigns during 5 years, in which rainfall with different characteristics was recorded. The properties analyzed in the surface soils under different land uses, and in the MATs used for collecting sediments included particle size and other properties such as soil organic matter (SOM), low frequency magnetic susceptibility (χLF) and P and Ti concentrations. The rainfall characteristics of the events recorded in each campaign were analyzed and the campaigns were grouped using cluster analysis taken into account the characteristics of the sediments collected. There was a P enrichment in the sediments compared to the sediment sources. The greatest P concentration was associated to sediment rich in clay and SOM. However, the sediment showed lower χLF, which could be due to higher erosion rates from the most degraded soils. The highest P losses were recorded at the catchment outlet, where the surface occupied by croplands was higher, with P values around 1.3 × times higher than at the headwaters. The differences between monitoring campaigns were attributed to differences in precipitation patterns that influence the hydrological response. The higher P concentration in the sediment during the campaigns that accumulated higher amount of rainfall in shorter periods of time confirmed the direct influence of rainfall intensity on the P mobilization.