This
study demonstrates the importance of the nitrogen-leaching
lag effect, soil nitrogen release, and climate change on anthropogenic
N inputs (NANI) and riverine total nitrogen (TN) export dynamics using
a 30-yr record for the Yongan River watershed in eastern China. Cross-correlation
analysis indicated a 7-yr, 5-yr, and 4-yr lag time in riverine TN
export in response to changes in NANI, temperature, and drained agricultural
land area, respectively. Enhanced by warmer temperature and improved
agricultural drainage, the upper 20 cm of agricultural soils released
270 kg N ha–1 between 1980 and 2009. Climate change
also increased the fractional export of NANI to river. An empirical
model (R
2 = 0.96) for annual riverine
TN flux incorporating these influencing factors estimated 35%, 41%,
and 24% of riverine TN flux originated from the soil N pool, NANI,
and background N sources, respectively. The model forecasted an increase
of 45%, 25%, and 6% and a decrease of 13% in riverine TN flux from
2010 to 2030 under continued development, climate change, status-quo,
and tackling scenarios, respectively. The lag effect, soil N release,
and climate change delay riverine TN export reductions with respect
to decreases in NANI and should be considered in developing and evaluating
N management measures.
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