Hydro-chemical and nutrient importing characteristics of precipitation in secondary Betula platyphylla forests in northern Great Xing'an Mountains, northeastern China

We observed and sampled the precipitation, throughfall, stem flow and litter water in secondary Betula platyphylla forests in northern Great Xing'an Mountains and measured their hydro-chemical properties, in order to study the nutrient importing characteristics of precipitation. The results showed that: the precipitation in Mohe area was neutral with pH value of 7.0 and TDS of 19mg/L. The pH and TDS showed a tendency of increasing first and then declining, with the minimum values of pH and TDS both in the stem flow, 5.3 and 15mg/L, respectively, while the maximum value of pH was in the rainfall and that of TDS in litter water. The highest concentrations of F- and SO2-4 were found in the stem flow, and those of other anions in the litter water. Among the anions, the concentration of NO-3 had the greatest variation, with the maximum 101.4 times as high as the minimum. As for the metallic elements, the highest concentrations of Na+, Zn2+ and Mn occurred in the stem flow, and those of the others in the litter water, while the lowest concentrations of them were almost all in rainfall (except for Ca2+ and Cu2+). The overall nutrient input of precipitation was 95.414kg/ha. After the rain falls through forest canopy, the concentrations of F-, Cl-, NO-3, Ca2+, Fe and Cu2+ decreased to different degrees whereas the others increased, and the total nutrient content of throughfall was reduced to 93.557kg/ha. After passing through the litter layer, except for Na+, the contents of other elements increased to varying degrees, and the total amount of nutrient input was increased by 72.149kg/ha. Compared with the rainfall input, litter water input was increased by 70.296kg/ha, in which Cl-, Na+ and Cu2+ contents were lower than those in the rainfall, while other elements had increased to different degrees. Eventually the total amount of nutrient input that the rainfall brought to the soil after passing through the secondary forests was 165.711kg/ha, the amount of anions input was 37.823kg/ha, and the metallic element input was 127.888kg/ha.