Distribution characteristics and environmental significance of nitrogen and phosphorus in the Huainan coal mining subsidence area

With extensive coal mining, the water coverage of coal mining subsidence areas tends to expand rapidly. Seven typical subsidence water areas in Huainan mining area were selected. Then their water quality indicators were measured, which included total nitrogen (TN), total phosphorus (TP), ammonia nitrogen (NH4+-N), nitrate nitrogen (NO3--N), etc., and the water quality was assessed. The results show that: ① the mean contents of TN, NH4+-N, NO3--N and TP are 304, 061, 061 and 016 mg/L, respectively. The nitrogen and phosphorus load was serious in the studied area. ② The distributions of TN in Huainan coal mining subsidence area are: Xinzhuangzi (558 mg/L)＞Panyi (407 mg/L)＞Guqiao (277 mg/L)＞Pansan (179 mg/L)＞Zhuji and Panbei (147 mg/L)＞Paner (117 mg/L). The distributions of TP are: Pansan (029 mg/L)＞Xinzhuangzi and Zhuji (020 mg/L)＞Guqiao (017 mg/L)＞Panbei (014 mg/L)＞Panyi (011 mg/L)＞Paner (005 mg/L). The distribution of TN and subsidence time show good positive correlation, while there is no obvious regularity in the distribution of TP. ③ Data analysis indicates that TN and NH4+-N have good positive correlation. Temperature, dissolved oxygen, pH have some correlation with nitrogen and phosphorus, respectively. The evaluation results of the comprehensive water quality identification method show that the concentration of nitrogen and phosphorus is basically at level Ⅲ or below in the water quality standards, and the most important pollution factor is TN, followed by NH4+-N.