Ammonium nitrogen concentration in the Weihe River, central China during 2005–2015

Ammonium nitrogen is a widely used indicator to assess water quality of lakes, rivers and other water bodies. Based on an observation network of five sampling sections on the trunk stream and four on the tributaries along the Weihe River (the largest tributary of the Yellow River), the interannual and seasonal variations in ammonium nitrogen concentration of river water during 2005–2015 are analyzed. The annual mean concentrations generally increase downstream, and the concentration after 2011 is much lower than that before 2011. Seasonality of ammonium nitrogen concentration is observed along the Weihe River, especially on the trunk stream. The interannual and seasonal patterns of ammonium nitrogen concentration are jointly influenced by the anthropogenic and natural factors. The decreasing concentration is related to the strict policy on water pollution control in the recent years, and the seasonal variation in concentration is influenced by the high flow in summer months and low flow in winter months.