亚热带典型花岗岩小流域径流化学特征与化学风化

Chemical characteristics and chemical weathering of surface runoff in typical granitic watersheds of subtropical China

为了解小流域尺度下生物地球化学过程对径流水体的影响及花岗岩化学风化对CO2的吸收,对亚热带典型花岗岩区不同利用条件下的2个相邻小流域(F-森林、FA-森林/农田)的地表径流及其常量离子和溶解Si含量进行了连续3年的定期观测和分析.结果表明,溶解Si,Na+和HCO3-构成地表径流的主要化学成分,FA流域离子总量高于F流域,反映了流域内农业活动对其化学径流的贡献.皖南典型花岗岩小流域(F、FA)径流中Sidiss/Na+和NO3-/SO24-比值均远高于同一生物气候带内富含碳酸盐岩的太湖流域径流中的相应值,揭示了区域岩性差异和人类活动导致的大气酸沉降组成差异是决定径流化学组成的主要因素.皖南花岗岩小流域(F、FA)径流化学组分约43%和38%来源于大气降水,57%和50%来源于岩石风化,FA流域内农业活动对其化学径流的贡献约为12%.皖南小流域(F、FA)花岗岩化学风化过程对CO2的消耗通量分别为(0.67—0.96)×105 mol.km-.2a-1和(0.64—1.05)×105 mol.km-.2a-1,远低于同一生物气候带内石灰岩母质流域.

In order to study the effect of biogeochemical cycling processes on surface runoff and the consumption of CO2 by chemical weathering of granite at small-watershed scale,the surface runoffs in two small watersheds（F-forest,FA-forest/farmland） with different land uses,which located in the typical granitic region of subtropical China,were monitored continuously for three years,and the major ions and dissolved Si were analyzed.The results showed that the dissolved Si,Na＋ and HCO-3 were the predominant ions in the chemical composition of surface runoffs,and the total dissolved salts of FA watershed were higher than those of F watershed,showing the contribution of agricultural activities in FA watershed to the chemical runoffs.The ratios of Sidiss/Na＋ and NO-3/SO2-4 in typical granitic watersheds（F,FA） of south Anhui Province were much higher than those in the Taihu Basin,which was rich in carbonate rocks and located in the same bioclimatic zone,indicating that the lithology and the chemical composition of acid deposition caused by human activities were the primary factors controlling the chemical runoffs.The contribution of precipitation to the chemical composition of surface runoffs in the granitic watersheds（F,FA） of south Anhui Province was 43% and 38% respectively,and the contribution of rock weathering was 57% and 50% respectively,while the contribution of the agricultural activities in the FA watershed was 12%.The consumption of CO2 by chemical weathering of granite in the small watersheds（F,FA） of south Anhui Province was（0.67—0.96）×105 mol · km-2 · a-1 and（0.64—1.05）×105 mol · km-2 · a-1 respectively,which were much lower than those of watersheds with carbonate rocks.