Study On Water Quality Of Surface Runoff And Underground Flow In Forest Ecosystems At Jinyun Mountain

The water quality in forest ecosystems could reflect the regional ecological forest conditions and physiological characteristics of the different plant communities. The types and amount of elements in rainfall and runoff were investigated in order to reveal the changes and balance of nutrients in forest ecosystems. This research could be important for nutrient management of forest trees and for protection of water resource. In the present experiment, the chemical components in precipitation and runoff from different forest communities in Jinyun Mountain, Chongqing, China, were analyzed. Five communities, ie coniferous-broadleaf forest, evergreen broad-leaved forest, bamboo, brush and bare land were selected to sample the rainfall and runoff from June 2003 to October 2004 for chemical analysis (pH, EC, NH⁺₄-N, NO^-₃-N, NO^-₂-N, TP, K⁺, Na⁺, Ca²⁺, Mg²⁺, SO^2-₄, DO, BOD5 and CODcr). The results are shown as follows.The concentrations of chemical elements in rainfall were variable greatly from runoff in five forest communities. Total concentrations of chemical elements in precipitation was 18.48 mg/L, and concentrations of several elements increased in the surface runoff and underground flows compared to those in rainfall. Total concentration of chmical elements in the surface ruoff were 42.66 (coniferous-broadleaf forest), 45.98 (evergreen broad-leaved forest), 48.46 (bamboo), 32.50 (brush ) and 40.70mg/L (bare land), respectively. In contrast, they were 63.53 (coniferous-broadleaf forest), 57.80 (evergreen broad-leaved forest), 69.59 (bamboo), 42.01 (brush) and 47.46mg/L (bare land) in underground flows, respectively.The chemical components of surface runoff varied greatly in different forest communities, but characterized by similar components to underground flow. The concentrations of SO^2-₄ and Ca²⁺ were higher, while NO^-₂-N and P were lower than other elements tested in both surface runoff and underground flows. The concentrations of Ca²⁺, Mg²⁺, NO^-₃-N and SO^2-₄ were higher in underground flow than those in surface runoff.The main components in precipitation were SO^2-₄ and, reached 78.47 kg SO^2-₄·hm^-2-2·a^-1, and 64.40 kg Ca²⁺·hm^-2·a^-1. But little P was input into forests from rainfall, ie. 0.27 kg P·hm^-2·a^-1 The output of chemicals in runoff changed in the sequence: Ca²⁺ (80.83 kghm^-2·a^-1')> SO^2-₄ (78.99 kg·hm^-2·a^-1 )> K⁺(16.87kg·hm^-2·a^-1)> Mg²⁺(9.05kg·hm^-2·a^-1 )> NO^-₃-N(6.54kg·hm^-2·a^-1)> Na⁺(4.53 kg·hm^-2·a^-1)> NH⁺₄-N(0.82kg·hm^-2·a^-1)> NO^-₂-N(0.04kg·hm^-2·a^-1)> P(0.03kg·hm^-2·a^-1). The net depression of Ca due to leaching was found in five forest ecosystems, while NH⁺_-N, NO^-_-N, NO^-₂-N and P accumulated, and K⁺, Na⁺, Mg²⁺, SO^2-₄ varied in accumulation due to forest ecosystem. Generally, nutrients increased in evergreen broad-leaved forest and brush, in contrast to coniferous-broadleaf forest, bamboo and bare land in which nutrients depressed.