Riverine Nitrate Export Response to Hydro-Climatic Variability in a Coastal Watershed

Riverine nitrate export is expected to increase in the future as climate change. More intense precipitation may produce larger amount of runoff thus export more nutrient to coastal water leading to serious environmental problems related to eutrophication and drinking water security. Long-term historical data of hydro-climatic variables and nitrate concentration during 1961-2013 were collected in this study to examine the potential impact of climate changes on riverine nitrate export from Jiulong River Watershed, an agricultural coastal watershed in Southeast China. This study discovered the annual nitrate export increased exponentially from 169 to 26034 ton N yr^-1 over the past five decades. It was positively correlated with the significant increase in nitrate concentration, induced by intensive anthropogenic activities in a catchment. Nitrate export showed an obvious intra- and inter-annual pattern in response to these patterns in hydro-climatic variability. Maximum exports occur during wet season (i.e. May, June, and August) and wet year. More than 50% of annual nitrate exports are discharged in this season. Nutrient which had been stored in the catchment during dry period will be flushed out as precipitation and runoff increased in the wet period. We identified the potential impact of climate changes on nitrate export is by altering the timing of export. For the changes in magnitude, it is mainly driven by anthropogenic activities. Strategic management to reduce nitrate concentration must be seriously undertaken in this watershed in order to prevent over nutrient enrichment in Xiamen coastal water, especially during wet season.