Characteristics Of Foresty Non-point Source Pollution In Red Soil Hilly Region Of Southern China

Red soil hilly region of southern China is the high-density population distribution area and the core of rapid economic development, and it is also the area with higher cultivation index and more serious soil erosion, the study of forestry non-point source pollution in the red soil hilly region will be of importance to water environmental protection and economic sustainable development. In this study, we used the runoff plots method to research non-point source pollution situation of two typical vegetation types maple and camphor mixed forest(X1),citrus plantation(X2) formed in the Nuerzhai Watershed reforestation project of Cili County, Hunan Province, and the control were natural succession(X3) and slope land(X4). We set 5 monitoring sections in watershed (river source water—RSW, the cave water outlet—CWO, the secondary outlet—WO1, two under the outlet—WO2, the total outlet—TWO) to study the chemical characteriristic of river water, and evaluate comprehensively the water quality. In addition, the feature and characteriristic of atmospheric precipitation was also studied, the results were as follows:The quantity and frequency of rainfall of watershed in 2009 was 1061.1mm and 89 times,respectively,and the main rainfall intensity was Iave<5mm/h and 130<10mm/h whose rainfall times accounted for 92.13% and 85.39% of the annual rainfall; the precipitation types primarily were heavy rain and rainstorm which accounted for 33.54% and 22.69% of total annual rainfall, respectively; a big difference exsited in the water quality of precipitation, for example, the change of pH presented in a "∧"type; ammonia nitrogen, total nitrogen, total phosphorus and nitrate nitrogen contents differed significantly and the greatest difference was 26.5 times.The runoff of different vegetation types mainly distributed in April to July, the variation trend of annual average runoff was X4>X2>X1>X3; the relationship of runoff coefficient of different forest vegetation types was X4>X2>X1>X3 which indicated that natural succession and XI controlled runoff loss better, but the control of plantations was less effective. The pH change of surface runoff water presented in "∧" type; the change trend of total nitrogen, ammonia nitrogen, nitrate nitrogen was X1>X3>X2>X4, the trend of total phosphorus was X1>X2>X3>X4, the relationship of silt content was X4>X2>X3>X1, these results showed that vegetation cover could keep water and soil and the the capacity of mixed plantation to keep soil and water was greater than plantation. pH value of surface runoff water was influenced greater by the quality of rainfall, and the correlation between the total nitrogen content of surface runoff water which covered by vegetation and rainfall was significant statistically.Rainfall was significantly related to total nitrogen content and the average rainfall intensity of surface runoff water and the correlation of the content of nutrient elements such as total nitrogen or phosphorus in the runoff covered with good vegetation type and the average rainfall intensity was significant. Forestry activities will increase the soil and nutrient loss, particularly the loss of sediment concentration, indicating that forestry non-point source pollution existed.In the 5 monitoring sections of river water, the standard deviation of total nitrogen and phosphorus were larger and the change trend of total nitrogen was RSW>TWO>CWO>W02>WO1, which showed that the water was influenced by the forestry non-point source pollution; while the total phosphorus polluted water sources less. The correlation between total nitrogen, total phosphorus, nitrate nitrogen and permanganate index were significant (P<0.01), which showed that changes of total nitrogen in river water influenced by the content of nitrate nitrogen. The comprehensive evaluation of water quality in each monitoring section was carried out by comprehensive index method, the fuzzy method and the gray relational analysis; total nitrogen, total phosphorus, permanganate index, ammonia nitrogen were as the evaluation index and the results showed that the quality of cave water and two outlet water belonged to the clean level, the quality of total outlet and two outlets belonged to under clean level, and the quality of source water belonged to mild pollution levels.