AUTHOR=Hajati Mithra-Christin , White Shane , Moosdorf Nils , Santos Isaac R. 

TITLE=Modeling Catchment-Scale Nitrogen Losses Across a Land-Use Gradient in the Subtropics

JOURNAL=Frontiers in Earth Science

VOLUME=Volume 8 - 2020

YEAR=2020

URL=https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2020.00347

DOI=10.3389/feart.2020.00347

ISSN=2296-6463

ABSTRACT=Changing land use in subtropical and tropical catchments to farmland can result in higher
nitrogen (N) loss to aquatic ecosystems. Here, we developed a lumped water and N balance
model to estimate regional N losses to creeks at catchment scale within understudied subtropical
catchments in Australia. The conceptual water balance model CoCa-RFSGD was extended
by the nitrogen mass balance in top and sub soil by adding nitrogen cycle transformation
estimates depending on meteorological, soil and land use properties. The model estimates the
impact of pristine and agricultural land use on catchment-wide water quality using only loworder creek samples as water quality measurements of nitrate and nitrite (NOx), with increased
model performance with increased agricultural coverage. The model revealed that an agricultural
proportion of 3% in the study site drove a 3.5-fold increase of N losses to creeks and a 6.7-fold
increase of N losses to the atmosphere compared to catchments without agriculture. Agricultural
land use lost 92 kg-N ha−1, of which 85% evaded to the atmosphere and 15% discharged via
surface waters. A change from forest to cleared land may increase the total denitrification potential
of a catchment. Overall, our lumped model provides a simple but effective tool to upscale local
aquatic water quality measurements to the catchment scale, allowing assessment of changing
land use on aquatic N loads in areas with limited data availability.