Different forms of nitrogen in the typical intertidal zones in China

Spatial distributions of nitrogen in sediment interstitial water and overlying water together with the sediment grain size and human activities were analyzed at 14 typical tidal zones in China to study the nitrogen distribution and related impact factors. The results showed that surrounding human activities played important roles to the nitrogen distribution of the intertidal zones and the nitrogen loadings from the river input explained the higher nitrogen concentrations in sediment interstitial water in the river estuaries compared to the non-estuary zones. Besides, the nitrogen conservation differences related to different sediment grain sizes also affected the nitrogen concentrations in sediment interstitial water. For the estuary intertidal zones, population, agriculture area and sewage discharge increased the DIN concentrations in sediment interstitial water and aquaculture mainly showed effects on DON concentrations. Interstitial water nitrogen concentrations in the Daliao River estuary, Jiulong River estuary and the Pearl River estuary were mainly related to the surrounding population, in the Dagu River estuary were related to the population and agriculture area, in the Min River estuary were related to population and sewage discharge, and in the Yellow River estuary were mainly related to aquaculture. For the non-estuary intertidal zones, obvious effects of sewage discharge on DON concentrations were found, and the aquaculture area and type both related to the DIN concentration and structure. For example, Northern Suzhou shoal was mainly affected by sewage discharge and the nitrogen concentration and structure in intertidal zones of Yingluo bay, Sishili bay and Beidai River beaches were mainly affected aquaculture.