A Phosphorus Dynamic model for lowland Polder systems (PDP)

•A new Phosphorus (P) Dynamic model for lowland Polder systems (PDP) was developed.•Five water levels were proposed to describe the manual operations of water exchange.•P dynamics in water area were described due to long retention time of runoff water.•Cross-validation showed the acceptable performance of PDP (an r2 value of 0.594).•Estimating P export from polders using PDP could help managers identify the P source.

Estimating phosphorus export from the lowland polder areas is a critical step for controlling phosphorus loading of a watershed. However, most existing models assumed lowland polder area to be a freely draining catchment, and did not adequately represent its phosphorus dynamics. To better estimate the phosphorus sink and source of the polder systems, a process-based Phosphorus Dynamic model for lowland Polder systems (PDP) consisting of six modules was developed to simulate the daily phosphorus exchanges between lowland polder systems and their surrounding rivers. The unique pattern of water and phosphorus dynamics in polder systems (i.e., manual operation of water exchange between the polder and its surrounding rivers and the phosphorus dynamics in the water area) was accounted for in PDP. Based on a dataset collected from Polder Jian located in Lake Taihu Basin, China during 2014, seven sensitive parameters in PDP were identified based on sensitivity analysis, and were optimized using Genetic Algorithm. A k-fold cross-validation method was used to assess model goodness-of-fit, and resulted in an acceptable model with an r2 (coefficient of determination) value of 0.594. The case study in Polder Jian showed the reliability of PDP to estimate the phosphorus source and sink from polder systems. Such estimation is helpful for water managers to identify the phosphorus source, and thus take corresponding measures to control the aquatic eutrophication.