| Dissolved organic matter (DOM), including dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP), is often described as solutes passing filter < 0.45nm in pore size. DOM contributes significantly to carbon, nitrogen, phosphorus and nutrient eyeing, its mobilization and transport is of central importance to soil-forming processes, and transport of heavy metals.Numerous studies have examined internal cycling or fluvial export of DOM in forested landscapes. Fluvial export of DOM (major in DOC) has received considerable attention, and has been the subject of several review papers in which global compilations and cross-biome comparisons are made. Internal fluxes of DOM (measurements of DOM in rainfall, throughfall, stemflow, forest floor extract solution, runoff and soil solution) are much less frequently reported, and characterization of differences across biomes has not been attempted.Despite considerable information on various aspects of DOM cycling, very few studies address the many linkages between precipitation and its solution processes that work to regulate the concentration, composition, and fluxes of DOM within a sub-tropic forest ecosystem. Multidisciplinary studies within the Minbei Located Research Station of Water and Soil Conservation provide an opportunity to make some of this linkages. This thesis show the internal concentrations and fluxes and their dynamics (monthly and seasonal dynamics )of DOM during 2002 within the Schima superba and Ctominghamia lanceolata plantation ecosystems such as:1) In precipitation, annual mean concentrations of DOC and DON were 1.65 and 0.13 mg-L-1 respectively. DOM concentrations increased with pass through water through different ecosystem profiles (the forest canopy, forest floor, soil etc.). In Schima superba and Curminghamia lanceolata plantation ecosystem, annual mean concentrations were estimated as 11.17 and 1025 , 17.55 and19.07, 45.06 and 34.43, 26286 and 22.66,37.56 and 24.15 mg-L"1 in throughfall, stemflow, forest floor extract solution, runoffand soil solution respectively. While those for DON were 0.24 and 0.19, 0.48 and 0.66, 0.81 and 0.49,0.67and 0.47,0.62 and 0.36 mg-L-1. Annual fluxes of DOC in through, stemflow and runoff were 16.74 and 12.05 , 0.64and2.18, 4.56 and 2.96 g *m"2 *yf\ respectively. DON fluxes was lower than DOC in both ecosystems, and were estimated as 037 and 0.24 , 0.068 and0.022, 0.124and0.066g m"2 yr-1.2) In precipitation, monthly concentrations of DOC ranged from 1.5 to 1.8 mg-L"1, while those for DON ranged from 0.08 to 0.17 mg-L"1. Peak monthly fluxes of DOC and DON occurred in June, and both lowest values were observed in February. DOC and DON concentrations in throughfall peaked in February and May respectively in both forest While the lowest concentrations of DOC and DON occurred in January and October respectively. The trends of monthly mean DOC concentration dynamics showed in the following order: decreasing at the beginning and increasing later. While DON showed the reverse response. Monthly fluxes of DOM did not exhibit significant trend. Concentrations of DOC in top soil solutions acted the same dynamic trends in both forest types. Lowest concentrations of DOM were observed in April, and then increased gradually. The average concentration of DOM in top soil solution in Schima superba site was highter than that in Ciffininghamia lanceolata site.3) Seasonal mean concentrations of DOC in precipitation had no obvious difference. However DON showed the seasonal dynamics and increased in the following order spring < winter < summer < fall. Seasonal fluxes of DOM in precipitation increased in following order winter < fall < spring < summer. Seasonal fluxes of DOC concentration in throughfall in both forest types exhibited as follows: fall < summer |
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