Modeling Terrestrial N Processes in a Small Mountain Catchment through INCA-N:A Case Study in Taiwan

• Main Authors: Meng-Chang Lu, 呂孟璋
• Other Authors: Jr-Chuan Huang
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/9r3c5w

碩士 === 國立臺灣大學 === 地理環境資源學研究所 === 105 === Riverine dissolved inorganic nitrogen (DIN) is an important indicator of trophic status of aquatic ecosystems. High riverine DIN export in Taiwan, ~3,800 kg-N km-2 yr-1, which is several folders higher than the global average, urges the need of thorough understanding of N cycling processes. This study applied INCA-N (Integrated Nitrogen Catchment Model) to simulate riverine DIN export and infer terrestrial N processes using weekly rainwater and streamwater samples collected at the Fushan Experimental Forest (FEF) of northern Taiwan. Results showed that the modeled discharge and nitrate export are in good agreement with observations (EC = 0.80), suggesting the validity of our application. This modeling work revealed that the three main N removal processes, in the order of descending importance, were plant uptake, riverine N transport and denitrification at FEF. The high plant uptake rate, 4,920 kg-N km-2 yr-1, should have led to accumulation of large biomass, but biomass at FEF was relatively small compared to other tropical forests, likely due to periodic typhoon disruptions. The low DIN concentration but yielding high export highlights the hydrological control on DIN export, particularly during typhoons. The denitrification rate, 750 kg-N km-2 yr-1, at FEF was also low compared to other tropical forest ecosystems, which likely resulted from quick water drainage through the coarse-loamy top soils. The high DIN export to atmospheric deposition ratio, 0.45, suggests that FEF may be in advanced stages of N excess. This simulation provides useful insights for establishing monitoring programs and improves our understanding N cycling in subtropical watersheds.