2.1.4 Nitrogen transport and human water use
For nitrogen processes, the schemes of human activities (including
nitrogen discharge and water regulation) and the riverine DIN transport
were incorporated into CAS-LSM via the coupling of the RTM. For nitrogen
discharge, the nitrogen fertilizer data were updated using the scheme of
Lu and Tian (2017), and the point source pollution was updated using the
data merged by Morée et al. (2013). For water regulation, the surface
water included the scheme of Hanasaki, Kanae and Oki (2006), and the
groundwater scheme follows that of Zou et al. (2015) and Zeng et al.
(2016). For the surface water and groundwater, the data were determined
from several source data sets, including the Food and Agricultural
Organization (FAO) water-use data set
(http://www.fao.org/nr/water/aquastat/data/query/index.html),
the Global Map of Irrigation Areas, version 5.0 (Siebert et al. 2013),
the historical monthly soil moisture levels and saturated soil moisture
levels simulated by CLM4.5 offline for the years 1965–2000 (Zeng et al.
2017), and the FAO water information system for 2010
(http://www.fao.org/nr/water/aquastat/main/index.stm).
During DIN transport, a proportion of the DIN will be affected by the
surface and groundwater regulation based on the mean DIN concentration,
and the rate of withdrawal for surface and groundwater (Liu et al.
2019). For the nitrogen river transport, based on the water transport
framework in CAS-LSM, the DIN inputs, including soil DIN runoff and
leaching, nitrogen deposition, and point source nitrogen discharge, were
used as tracers in the nitrogen transport module, along with a DIN
retention module during the transport (Nevison et al. 2016). As nitrogen
transport is associated with water temperature, this variable was also
considered in CAS-LSM following the scheme of van Vliet et al. (2012).
Anthropogenic heat discharge from thermoelectric power plants was also
considered in CAS-LSM (Liu et al. 2019), where the input data for the
emitted heat are from Raptis and Pfister (2016).