Copper Complexing Capacity of Throughfall and its Environmental Effect

Abstract

Copper complexing capacity (CuCC) and conditional stability constants (K′) of the complexes were analyzed for throughfall collected in Japanese cypress (Chamaecyparis obtusa), Japanese cedar (Cryptomeria japonica), Japanese red pine (Pinus densiflora), and bamboo-leafed oak (Quercus myrsinaefolia) groves (soil: light-colored Andosol) located in a suburban area of Japan (Tsukuba, Ibaraki). The method was based on the titration of throughfall samples with standard Cu2+ solution using a Cu2+-selective electrode, followed by data analysis using the van den Berg-Ruzic plot (1:1-type complexes were assumed). CuCCs (μM) obtained were in the order: C. obtusa (7.1± 5.1) ≤ C. japonica (9.6± 5.6) < P. densiflora (15.9± 16.4) < Q. myrsinaefolia (29.3± 23.9). In addition, ratios of CuCC/DOC (μmol mg−1 C) were in the order: C. obtusa (0.42± 0.26) ≅ C. japonica (0.42± 0.22) ≅ P. densiflora (0.55± 0.38) ≪ Q. myrsinaefolia (2.0± 1.3), and the ratios in the throughfall of Q. myrsinaefolia were about 4 times higher than those in the throughfall of other tree species. On the other hand, log K′ was almost the same for all tree species (about 5.5). CuCC and also CuCC/DOC increased in spring and autumn, and decreased in summer and winter, indicating that organic matter with metal complexing capacity, released from trees, changed seasonally not only in quantity but also in quality. Since throughfall accelerated the leaching of metals from grove soil and artificial material (e.g. alloy) placed in the groves, it may be involved in the behavior of metals in the plant-soil ecosystem.