The Characteristics Of Hydrochemical Processes In Subtropical Forest Ecosystems In Hefei And Laoshan Mountains, Anhui

Rainfall as the main nutrient source in forest ecosystems has been caused increasing concern, so it is particularly important for the relationship between forest and water. Rainfall partitioning and nutrient input from rainfall are most fields in the ecological researches on structure and function of forest ecosystems, which is important to understand the hydrological processes and the circles of bioelements. Rainfall passed through the multi-layered canopy caused the redistribution of rainfall, which made rainwater chemical characteristics change. In this study, the hydrological processes of Metasequoia glyptostroboides forest in urban Hefei and evergreen broad-leaved forest in Xiaokeng were investigated from 2008 to 2009. The main contents of the study are the pattern of bulk precipitation and its partitioning, the changes of rainfall chemistry and the effects of forest on stream-water quality. The objectives are to understand the following aspects:(1) the patterns of rainfall in the different regions and forest types;(2) the effects of forest types on water chemistry;(3) the chemical relationships among the throughfall, stemflow and rainfall; Results obtained from the study are as follows.1. Gross rainfallIn Hefei, the rainfall mainly concentrated from April to August, contributed for 63.7% of the total annual rainfall. The annual total rainfall was 1010.8 mm in 2009. In Metasequoia glyptostroboides forest, the proportions of throughfall, stemflow and canopy interception were, respectively, 81%, 2% and 17% of the bulk precipitation.In Xiaokeng, the rainfall also concentrated from April to August, contributed for 65.7% of the annual rainfall . The annual rainfall was 1556.4 mm in 2009. In subtropical evergreen broad-leaved forest, the proportions of throughfall, stemflow and canopy interception were 61%, 5% and 34% of the bulk precipitation, respectively.2. pH valueIn Metasequoia glyptostroboides forest in urban Hefei, the pH values were neutral for throughfall, and > 5.6 for stemflow. The order of pH values was: stemflow < throughfall < rainfall. In Metasequoia glyptostroboides forest, throughfall and bulk precipitation had the similarly significant seasonal patterns with the peak values in the summer and winter and lower in the spring and automn. The pH for the stemflow were high in spring and winter while lower in summer and automn.In subtropical evergreen broad-leaved forest of Xiaokeng, the pH values of throughfall and rainfall were neutral, while was acid for the stemflow. The order of pH value was stemflow < throughfall < rainfall, similar to that for Metasequoia glyptostroboides forest. The seasonal pattern of pH for the bulk precipitation was high in summer and autumn. For throughfall, the high pH was showed in spring and summer, while high pH was in summer for stemflow.3. EC valueThe EC values of rainfall, throughfall and stemflow in Metasequoia glyptostroboides forest in urban Hefei were greater than those in subtropical evergreen broad-leaved forest at Xiaokeng. It could be attributed to the greater dust in atmosphere in urban Hefei than in Xiaokeng. The seasonal variations were the same with lower EC in spring and summer for bulk precipitation, throughfall and stemflow in both Hefei and Xiaokeng. The EC value fluctuated with rainfall intensity in the hydrological processes. In the rainy season, the EC value was lower. The order of EC values was the same at both sites: stemflow > throughfall > rainfall.4. Nutrient dynamicsThere existed the significant differences in nutrient concentrations and their dynamic patterns for precipitation, throughfall, stemflow at both sites. In Metasequoia glyptostroboides forest in urban Hefei, the order of the nutrient concentrations was stemflow > throughfall > rainfall. In subtropical evergreen broad-leaved forest at Xiaokeng, the concentrations of P, K, Ca, Mg, TOC, NO3- were stemflow > throughfall > rainfall. However, the concentrations of NH4+ was ordered as stemflow > rainfall > throughfall; for Na concentration, throughfall > stemflow > rainfall. Many factors such as rainfall, forest characteristics, atmospheric conditions, seasonal change can impact nutrient concentrations of rainfall.5. Effects of forest on stream-water qualityDuring the two-year observation, it was found that the nutrient concentrations in stream-water had a strongly seasonal changes. The nutrient concentrations were lower in rainy season than in the dry season. The steam-water quality was improved through vagetation absorption and soil filtration of nutrients.