Influence of legacy phosphorus, land use, and climate change on anthropogenic phosphorus inputs and riverine export dynamics

Abstract

A quantitative understanding of riverine phosphorus (P) export in response to changes in anthropogenic P inputs (NAPI), land use and climate is critical for developing effective watershed P control measures. This study indicated that annual riverine TP export for the six catchments of the Yongan River watershed in eastern China increased 4.1-30.3-fold over the 1980-2010 period. Increased riverine TP export resulted from a 61-85 % increase in NAPI and a 2.6-14.6-fold increase in riverine export fraction of NAPI due to 36-43, 30-125, and 65-76 % increases in developed land area (D%), drained agricultural land area (DA%), and storm events, respectively. For the 31-year cumulative record, 1.6-14 % of NAPI was exported by rivers, 40-64 % was stored in the upper 20 cm of agricultural soils, and 30-55 % was retained in other landscape positions. An empirical model that incorporates annual NAPI, precipitation, D%, and DA% accounted for 94 % of the variation in annual riverine TP fluxes across the six catchments and 31 years. The model estimated that NAPI and legacy P contributed 42-92 % and 8-58 % of annual riverine TP flux, respectively. The model forecasts an 8-18 % increase in riverine TP flux by 2030 due to a 4 % increase in precipitation with no changes in NAPI and land use compared to the 2000-2010 baseline condition. Enhanced export of NAPI and legacy P by changes in land use and climate will delay the decrease in riverine P flux in response to NAPI reductions and should be considered in developing and assessing watershed P management strategies.

Reconstructing historical changes in phosphorus inputs to rivers from point and nonpoint sources in a rapidly developing watershed in eastern China, 1980–2010

“…S2b), NPS TP inputs continuously increased by~19-fold over the past 31 years, implying the increasing contribution of legacy P sources (Basu et al, 2010;Sharpley et al, 2013Sharpley et al, , 2015. This is supported by an average 2.0-fold increase in TP concentration (n = 209) and an average 1.4-fold increase in Olsen-P concentration (n = 406) measured in the upper 20-cm layer of agricultural soils between 1984 and 2009 in the Yongan River watershed (Chen et al, 2015). As a result, the P concentration of eroded sediments increased (with no increase in TSS between 1980 and 2010, Fig.…”

“…Duplicate samples from the composite sample were analyzed within 4 h of collection. TP (dissolved + particle phosphorus), chloride (Cl − ), and total suspended solids (TSS) concentrations were determined by the spectrophotometric ammonium molybdate, silver nitrate titration, and gravimetric methods, respectively (Yu et al, 2010;Chen et al, 2015). Daily river discharge at Baizhiao station ( Fig.…”

“…The high flow regime (0-10% exceedance percentile) was determined by the river discharge duration curve method (Chen et al, 2012). Population, domestic animal, and land-use statistics for 1980 to 2010 were derived from the annual Statistic Yearbook for Xianju County and Linhai City (Chen et al, 2015).…”

“…LOADEST uses time-series river water discharge data and constituent concentration to calibrate a regression model that describes long-term temporal change of constituent load in terms of various functions of discharge and time (Runkel et al, 2004;Duan et al, 2013;Chen et al, 2015):…”

“…An increase in hydrologic connectivity via efficient drainage enhances P delivery from land to river due to decreased water residence time and filtering capacity with the watershed (Gentry et al, 2007;Jarvie et al, 2013). The developed land area decreases P retention and enhances flushing during rainfall events due to greater impervious surface area (Sobota et al, 2011;Chen et al, 2015).…”