Natural and anthropogenic determinants of riverine phosphorus (P) pollution strongly vary with different ecological and socio-economic conditions and represent a substantial challenge to aquatic environment protection and ecological restoration in agricultural catchments.

A team of researchers from the Institute of Subtropical Agriculture (ISA) of the Chinese Academy of Sciences investigated the major natural and anthropogenic determinants of riverine P in one forest and ten agricultural catchments in subtropical China during 2011 to 2017.

Their investigation was based on the monitored riverine water flux and observed riverine P levels and loadings, and statistical data, through the partial least squares regression (PLSR) technique.

The results suggested that 39% of the collected stream water samples were determined to have total P (TP) pollution, indicating moderate riverine P pollution in the catchments. The catchment riverine P levels illustrated an increasing P trend during 2011-2016 but a decreasing P trend in 2017 through the Hodrick-Prescott (HP) filter analysis, and the decreasing trend was mainly caused by reduced catchment livestock density.

"Catchment geometry characteristics, land-use composition, landscape configuration and anthropogenic activities have the potential to predict riverine P levels," said lead researcher Dr. WANG Yi from ISA. "Through the final PLSR, the landscape configuration and livestock density were the only two variables that commonly had variable importance for the projection (VIP) value greater than 1.0, confirming their substantial effects on and importance to riverine water quality."

The researchers also found that the multiple linear regression prediction functions showed generally acceptable performances for riverine P but relatively poor performance in predicting P loadings in comparison to predicting P concentrations, probably due to the variations in the hydrological process in subtropical China.

The research was supported by the National Key Research and Development Program of China, the Key Research and Development Project in Hunan Province, Key Research Projects of the CAS and the Project of Youth Innovation Team at the Institute of Subtropical Agriculture, CAS.

The study entitled "Natural and anthropogenic determinants of riverine phosphorus concentration and loading variability in subtropical agricultural catchments" was published in Agriculture, Ecosystems & Environment.