森林转换对地表径流可溶性有机碳输出浓度和通量的影响

米槠次生林转换成米槠人工幼林和米槠人工促进天然更新幼林(以下简称"人促幼林")后,以这三种森林类型为研究对象,连续监测每次降雨后地表径流量及径流水中可溶性有机碳(DOC)的含量及通量,比较不同森林类型观测结果的差异,并分析降雨对实验结果的影响。结果表明:米槠人工幼林单次产流量是米槠次生林的1.5—19.0倍,观测期间总径流量为5.9倍;米槠人促幼林单次径流量和总径流量均与米槠次生林无显著差异(P0.05)。观测期间米槠次生林、人工幼林、人促幼林径流水DOC浓度值范围为5.9—18.4 mg/L,4.3—13.5 mg/L和3.2—9.9 mg/L,米槠次生林径流水浓度均值(12.6 mg/L)分别是米槠人促幼林(7.6 mg/L)和米槠人工幼林(5.3 mg/L)的1.6和2.4倍。回归分析表明,径流水中DOC浓度与降雨前土壤含水率呈显著相关;降雨前土壤含水率20.8%是一个临界值,含水率低于20.8%时,径流水DOC浓度与降雨前含水率呈显著正相关(P0.05);高于20.8%时,径流水DOC浓度与降雨前土壤含水率呈显著负相关(P0.05)。米槠人工幼林地表径流DOC输出通量是米槠次生林的0.7—5.4倍,观测期间总输出通量为2.1倍;米槠人促林DOC单次通量和观测期间总通量均与米槠次生林差异不显著(P0.05)。三种森林类型DOC输出通量均与降雨量呈显著相关(P0.05)。可见,米槠次生林转变成米槠人工幼林后DOC输出浓度降低,但径流量显著增加,导致DOC输出通量增加;而转变成米槠人促幼林后DOC输出浓度也降低,但径流量并未增加,因而并未增加DOC输出通量。

Effects of forest conversion on concentrations and fluxes of dissolved organic carbon in runoff

In order to elucidate the relationships between runoff parameters and variation in rainfall, we compared the volume, dissolved organic carbon (DOC) concentration, and DOC flux of runoff from Castanopsis carlesii (C.carlesii) secondary forest (SF) and from SF plots converted to young plantation (BC) or assisted naturally regenerated young forest (NR) after individual rainfall events. Our results indicated that the volume of the BC runoff was 1.5 to 19.0 times that that of the SF runoff, depending on the specific rainfall event. The total accumulated volume of the BC runoff during the research period was 5.9 times that of the SF runoff. However, neither the per-event nor the accumulated volume of the NR runoff differed significantly from those of the SF runoff. Meanwhile, the DOC concentration of the NR, BC, and SF runoff ranged from 5.9 to 18.4 mg/L, 4.3 to 13.5 mg/L, and 3.2 to 9.9 mg/L, respectively, and the mean DOC concentration of the SF runoff (12.6 mg/L) was 1.6 times that of the NR runoff (7.6 mg/L) and 2.4 times that of the BC runoff (5.3 mg/L). Regression analysis indicated that the DOC concentration of runoff water was significantly related to pre-rain soil water content, and DOC concentration was observed to increase with soil water content when the pre-rain soil water content was lower than 20.8%, and to decrease with soil water content when the pre-rain soil water content was higher than 20.8%. In addition, the DOC flux of the BC runoff was 0.7 to 5.4 times that of the SF runoff, and the total accumulated DOC flux from the BC runoff was 2.1 times that of the SF runoff. However, differences between the DOC flux of the NR and SF runoff were insignificant (P > 0.05), and for all three forests, the DOC flux was significantly (P < 0.05) related to rainfall. Therefore, the conversion of SF to BC reduced the DOC concentration of the runoff, but increased overall DOC flux owing to dramatic increases in runoff volume, whereas the conversion of SF to NR had no significant effects on DOC flux owing to the runoff''s relatively low DOC concentration and volume.