三江平原湿地多级沟渠系统底泥可溶性有机碳的分布特征

Distribution characteristics of dissolved organic carbon in the sediment of multistage canal and ditch systems in wetlands of the Sanjiang Plain

沿着土壤和土地利用类似的三江平原多级沟渠系统采集不同沟渠单元底泥，这些不同沟渠系统单元由湿地和农田边界排水沟渠到相当大的主干渠变化着，测定底泥中可溶有机碳（DOC）含量，研究多级沟渠系统底泥中DOC的分布特征。结果发现，随沟渠等级增加，DOC在底泥中所占的比重逐渐增加（40～60cm层增加近5倍），DOC富集层逐渐有规律的向底泥底层转移（40～60cm）。研究表明，排水沟渠既是湿地或农田DOC的最初汇聚地，又是河道DOC的输出源；沟渠重复性的排水将湿地或农田DOC通过零星径流带入沟渠系统中，连续的沟渠径流携带着大量DOC与不同等级沟渠系统相互作用使得沟渠系统底泥中DOC呈现出一定的水平、垂直分布特征；排水沟渠排水历时、DOC流量、滞留时间、径流发生频率等都会影响多级沟渠系统底泥中DOC的分布特征；另外，沟渠系统内生长的植被也通过径流阻塞和有机质过程影响底泥中DOC的分布特征。

Land cultivation, drainage and irrigation not only arise movement and deposit of soil dissolved organic carbon （DOC） within the canals and ditches, but also lead to the difference of sediment DOC. Previous studies were mainly performed at plot-to-field scale, but little is known about the effect of intensive agricultural catchments on the distribution of sediment DOC beyond field edges. This study was conducted to examine the distribution characteristics of sediment DOC in multi-stage canal and ditch systems in the Sanjiang Plain. Sediment samples were collected from multi-stage canal and ditch systems, which have similar soils and land use patterns, and analyzed for DOC content. Those different units of canals and ditches varied from field-edge waterways to sizeable drainages. The proportion of sediment DOC increased gradually and the sediment DOC was transferred to the deeper sediment layers （40 -60cm） with increased drainage area, such as from field canal, to lateral, to branch, to trunk, and to general main canal. Overall, the mean DOC content in sediment was the highest in general main canal （488. 747mg/kg） and the lowest in the field canal （269. 672mg/kg）. The sediment DOC in 40-60cm layers was mainly accumulated in general main canal （1270. 947mg/kg）. The regions with the highest values for 20 -40cm, 10 -20cm and 0 -10cm sediment layers were mainly in the trunk eanal （326. 147mg/kg）, field or lateral canal（ 360. 547mg/kg and 360. 547mg/kg）, and branch or trunk canal （425. 747mg/kg and 450. 947mg/kg）, respeetively. Those eanals and ditehes eolleeted and stored the DOC mass flows from wetland and farm, and then transferred them into rivers and lakes. Temporally repetitive drainage of canals and ditches transported DOC flows into canal and ditch systems by sporadic flows. The Land erosion controlled flows of DOC mass during storm events. Continuous flows of DOC interacted with multistage canal and ditch systems. The spatial distribution of sediment DOC appears, in certain extent, as horizontal distribution with hypsometric characteristics. Close relationships existed among DOC concentration, flux, period, frequency and duration and the distribution characteristics of DOC in sediment of multi-stage canal and ditch systems. In addition, the vegetative characteristics of the canals and ditches exerted an important influence on DOC distribution in the sediment of the multi-stage eanal and diteh systems that had a response to proeesses of organie matter in the sediments sueh as decomposition, humification, and stabilization of organic matter.