Study On Distribution And Influence Factors Of Soil Carbon And Phosphorus In Yellow River Estuary Wetland

In this paper, four field investigations and in-lab simulation experiments werecarried out respectively in October2008, May and August2009, August2010in thewetlands of Yellow River Estuary. The spatial distribution pattern and seasonal changecharacteristics of carbon and phosphorus in the soil of Yellow River estuary wetlandwere studied, and the factors of soil physical and chemical properties, vegetationdistribution and microbial activity that influenced on the distribution characteristicsand seasonal variations of carbon and phosphorus in soil were analyzed. The reservesof organic carbon and phosphorus in this field were estimated. The study revealed thespatial and temporal variation characteristics of carbon and phosphorus in the YellowRiver freshwater wetland soil, and provided the reference for further evaluate andprotect the Yellow River estuary wetland ecosystem. The results showed that:The spatial and temporal distribution pattern of soil carbon in Yellow Riverestuary wetland: carbon contents in surface soil of agriculture area were lower thanthose of natural wetlands, The horizontal and vertical variations of soil carboncontents were relatively significant, in the horizontal direction, the contents of TOC,DTC, DOC and DIC were1.12~18.24mg/g,40.24~248.24mg/kg,6.41~151.64mg/kgand33.83~200.16mg/kg respectively, DIC was the main form of dissolved carbonwhich account for about72%of DTC content, DOC content was low and accountedfor about1.23%of TOC content, TOC content in the surface soil of natural wetlandswas at Level Ⅲ or even blow.In the vertical direction, the contents of TOC, DTC,DOC and DIC gradually reduced with soil depth in all sampling profiles. The carboncontents in0-10cm were significantly higher than that below10cm. Horizontal andvertical seasonal dynamic variation amplitude of carbon content was greater, andseasonal dynamic variation in TOC content was greatest with variation coefficientbeing74.57%and87.79%.The influencing factors of carbon distribution characteristics in soil were soilproperties and vegetation: TOC contents in surface soil exhibited a negativecorrelation with pH and a positive correlation with TN and TP contents, desolvedcarbon contents exhibited a negative correlation with bulk density and a positivecorrelation with TN and TP contents; TOC content in Reed rhizosphere were higher than that in non-rhizosphere, while dissolved carbon were insignificant; TOC, DTC,DOC, DIC content in Salsa rhizosphere were much higher than that innon-rhizosphere.The spatial and temporal distribution pattern of soil phosphorus in Yellow Riverestuary wetland: phosphorus contents in surface soil of agriculture area were higherthan those of natural wetlands, horizontal and vertical variations of TP contents wererelatively insignificant, which were429.19~693.30mg/kg and408.55~663.03mg/kg,while those of Olsen-P contents were relatively significant, which were0.27~13.48mg/kg and0.08~9.57mg/kg respectively. Olsen-P content was very lowand accounted for about0.93%of TP content, Olsen-P content in the surface soil ofnatural wetlands was at Level Ⅳ or even blow.Horizontal and vertical seasonaldynamic variation amplitude of TP content was minor, with variation coefficientbeing5.80%and1.15%respectively. Seasonal dynamic variation in Olsen-P contentwas significantly greater than that of TP content, with variation coefficient being29.21%and31.09%.The influencing factors of phosphorus distribution characteristics in soil weresoil properties, vegetation and microorganism: TP contents in surface soil exhibited asignificant positive correlation with its clay and silt content, total nitrogen, organiccarbon content, and a significant negative correlation with bulk density; Olsen-Pcontent exhibits a significant positive correlation with clay and silt content. TPcontent in the two vegetation rhizosphere were slightly higher than that innon-rhizosphere. Olsen-P contents in Salsa rhizosphere were much higher than that innon-rhizosphere, while those were insignificant in Reed rhizosphere andnon-rhizosphere. Accumulation of phosphorus in Reed and Salsa exhibited aninsignificant negative relationship with phosphorus content in the rhizosphere. Themicrobial activity in Reed and Salsa rhizosphere exhibited a significant positivecorrelation with Olsen-P content.The reserves of organic carbon, total phosphorus and effective phosphorus inprofile soil of Yellow River estuary wetland: the reserves of organic carbon were2.08~12.34kg/m~3in0-60cm profile soil, the organic carbon reserves in0-10cm wasthe highest, and in October were much higher than those in May and August; the totalphosphorus reserves were0.67~1.02kg/m~3in0-60cm profile soil，its vertical andseasonal variation were not obviously; while the vertical and seasonal variation ofeffective phosphorus reserves were significantly which were0.27~10.48g/m~3in 0-60cm profile soil.To sum up, TOC content in soil of Yellow River estuary natural wetland waslower, and the spatial and temporal distribution pattern was relatively significant thatmainly affected by the vegetation rhizosphere effect, the temporal and spatial dynamicchanges of dissolved carbon contents were less than TOC that mainly affected by soilproperties, vegetation and microbial activity were not significantly. TP content in soilof Yellow River estuary natural wetland was rich, its spatial and temporal distributionpattern was relatively insignificant that mainly affected by the soil physicochemicalproperties; while Olsen-P content was lower and its spatial and temporal distributionpattern was significant that mainly affected by the vegetation and the microbialactivity. The distribution of phosphorus in Yellow River estuary wetland was copedwith the consistency of soil parent material and the diversity of vegetation.