Effects Of The Benthic Macroinvertebrates On The Distribution Characteristics Of Soil Biogenic Elements In Estuarine Wetlands

It is important to explore the effects of bioturbation in the nutrient cycling of estuarine wetland ecosystem.In this paper,two dominant species?Perinereisaibuhitensis and Helice tridens tientsinensis?in the Dagu estuary of Jiaozhou Bay were selected as objective in order to explore the effects of bioturbation on distribution pattern of soil carbon,nitrogen and phosphorus as well as the fluorescence characteristics of DOM.The effects of bioturbation were analyzed by measuring soil DOC,TOC,NH₃-N,NO₃^--N,and total phosphorus.In addition,the ultraviolet parameters and three-dimensional fluorescence spectra of DOM were also exaimed.The main conclusions are as follows:?1?The differences of bioturbation depended on their activity intensity and range.The cave of the clamworm is a passageway with a diameter of about 0.5 cm.There is a 2-cm-high protruding mound at the hole.The burrows of crab are mostly 2-3 cm in diameter with the shape Y or J.Feeding,movement and other activities of clamworm are the main bioturbation behavior in the passageway,which can increase the permeability of the soil,while burrowing of the crab,which can divert the bottom soil to the surface layer,is the main behavior.Both benthic macroinvertebrates are active in the middle and upper layers of soil in the early stage.Both species were active throughout the entire soil layer with exuberant vitality in the middle and late stages.?2?The bioturbation promoted the release of DOC and TOC from the soil into the water.The content of DOC showed a decreasing trend.At the end of the experiment,there was significantly different between the experimental group and the control group?p<0.05?,while no significant difference between the two experimental groups?p>0.05?.The DOC values of experimental group were significantly lower than that of the control group.?3?The bioturbation promoted the release of NH₃-N,NO₃^--N,TP from the soil to the water.Benthic macroinvertebrate bioturbation intensity depended on the active area.The releases of soil NH₃-N,NO₃^--N and TP ranked as follows:crab>clamworm>control.The clamworm group had a significant bioturbation on NH₃-N in the second layer soil?p<0.05?.The crab had a significant effect on the NO₃^--N content of each layer of soil?p<0.05?,especially the fifth layer?2.45 mg/kg?.The clamworm had a significant effect on the TP in the surface,third and fourth layers?p<0.05?,and the crab only had no significant impact on the bottom soil?20-25 cm??p>0.05?,both species ad no significant effect on TP in the bottom soil.?4?The bioturbation of benthic macroinvertebrates changed characteristics of soil DOM.The values of SUVA254 and SUVA280 showed a decreasing trend with the progress of the experiment.The changes of SUVA254 and SUVA280 values the experimental group were less significant than that of the control group.The changes of A250/A365 values were opposite to that of SUVA254 and SUVA280.The A250/A365 value of the experimental group increased faster than that of the control group.The bioturbation of benthic macroinvertebrates reduced the degree of soil humus and aromatization.?5?The bioturbation of benthic macroinvertebrates increased the protein-like substances and decreased the humus-like substances in the soil.It meant that bioturbation reduced the gap of protein-like substances and humus-like substances among soil layers.Disturbing behaviors such as burrowing and crawling have changed the texture conditions of the soil,enhanced the permeability of the soil,promoted the migration of substances in the vertical direction,and reduced the difference in the content of protein-like substances and humus-like substances among the soil layers.