Spatial And Temporal Patterns And Provenance Analysis Of Organic Carbon In Water From Baijianghe Mire

The increased loss of dissolved organic carbon(DOC)and particulate organic carbon(POC)through water migration is an important way of carbon loss in mire.Understanding the variation pattern of DOC and POC concentrations in different habitats provides an important basis for assessing carbon loss at regional scale.The concentrations and fractions of organic carbon may be significantly affected by different habitats.Baijianghe mire is located in Jingyu county,Baishan city,and includes relatively complete natural area,drainage area after drainage,and restoration area after hydrological restoration experiment.The streams flow through forests and Baijianghe mire.Water samples were collected from four different biotopes in mire of Baijianghe and the streams running through it,respectively,from June to October in 2019 and2020.The study analyzed the concentrations and components of DOC and POC to reveal their spatial and seasonal variation characteristics and material sources.The study also revealed the influencing factors of DOC and POC in mire combined with the meteorological and hydrological data such as water level,precipitation,and air temperature to explore the variation mechanism of organic carbon composition in mire.The main conclusions were as follows:(1)The DOC and POC concentrations of the mire water showed significant spatiotemporal pattern.The spatial pattern of DOC concentration was drainage area>natural area>restoration area,and was natural area>drainage area>restoration area for the POC in 2019.During the study period,the organic carbon concentrations increased first and then decreased with the maximum value in August and minimum value in end of June.(2)The DOC concentration of streams showed a spatial pattern of confluence point>exit point>upstream point>spring water in 2020.The POC concentration of streams showed a spatial pattern of spring water>confluence point>upstream point>exit point in 2019.The spatial heterogeneity of streams POC concentration was small among different habitats in 2020.The POC concentration decreased first and then increased in 2019,however,in 2020,DOC and POC concentrations increased first and then decreased during the study period.The organic carbon concentrations mostly reached its maximum value in August and September,and its minimum appeared in October.(3)The organic carbon fractions and sources of mire water were different among different habitats.The absorbance ratio(E₄/E₆)at 400 nm and 600 nm of the natural area was higher than that of the drainage area,but the specific to ultraviolet absorbance(SUVA₂₅₄)of the drainage area was higher than that of the natural area.The humification degree of DOC in the drainage area was higher than those of the other areas,which indicated that the aromaticity,colored components,stability of DOC in the drainage area were greater than other areas.The average absorbance ratio(E₂/E₃)at 250 nm and 365 nm in the drainage area was lower than that in the natural area,which indicated that the greater molecular weight of DOC in the drainage area.The C/N ratio of DOC was less than 20 in June,July,and October,indicating that a mixed source of DOC from water source and terrigenous sources.The DOC mainly came from terrigenous source in August and September.The mean C/N ratio of POC in mire water was greater than 12.There was a strong correlation between suspended particulate matter(TSM)and POC concentration both in 2019 and 2020(R²=0.866,0.949,respectively),indicating the terrigenous source of POC in the mire water.(4)The components and sources of organic carbon varied from the upstream to the downstream.The SUVA₂₅₄ and Abs_400nm/DOC increased gradually from the spring water to the outflow point with the E₂/E₃ decreased gradually from the spring water to the confluence,which indicated that the aromatic fraction,colored fraction,and molecular weight of DOC increased gradually from upstream to downstream.The C/N ratio of stream DOC was greater than 20 in2019 and 2020,indicating the terrigenous source of DOC And the same to the DOC from the end of August to the middle of September in 2020.The DOC in August and September in 2020mainly came from water source.The average C/N ratio of stream POC was 15.06 and 10.43 in2019 and 2020,respectively.There was a strong correlation between TSM and POC(R²=0.813)in 2019,but relatively weak(R²=0.742)in 2020.This demonstrated that the POC in the streams water mainly came from terrigenous source in 2019 but from a mixed source of water source and terrigenous in 2020.The C/N ratio of DOC and POC increased first and then decreased in the growing season,Fi decreased first and then increased in the growing season,indicating that the terrestrial proportion of organic carbon increased first and then decreased,and the microbial proportion decreased first and then increased.(5)Organic carbon was mainly affected by water temperature and pH value in mire water.The increase of temperature and pH lead to the increase of DOC concentration in mire water.The increase of pH value and DO concentration led to the increase of C/N ratio of DOC.The increase of temperature and precipitation contributed to the decrease of POC concentration in mire water.(6)Streams organic carbon was mainly affected by temperature and pH value.The increase of temperature and pH value led to the increase of DOC concentration in streams.The increase of temperature led to the decrease of Fi.The increase of pH value led to the increase of POC concentration.