Spatial And Temporal Characteristics Of Greenhouse Gas Emissions From Soils In The Lakeshore Zone

With both aquatic and terrestrial characteristics,the lakeshore zone serves as a transition between aquatic and terrestrial ecosystems.The soil in the lakeshore zone accumulates a significant quantity of organic pollutants,nitrogen,and other nutrients,which alters the soil’s biochemical cycling process and may have an impact on the dynamics of greenhouse gas（N₂O,CH₄,and CO₂）emission.This study examined the physical and chemical features of soils in Lake Donghu,Lake Nanhu,Lake Tangxun,and Lake Yezhi in Wuhan City in order to comprehend the geographical and temporal characteristics of greenhouse gas emissions in the lakeshore zone and their affecting variables.Then,two distinct vegetation lakeshore zones—woody cover and herbaceous cover—were chosen as the study subjects.Soil N₂O,CH₄ and CO₂ gas emission fluxes were monitored at distances of 1,3,5,and 10 m from the lake water body by static box method,and N₂O,CH₄ and CO₂ gas concentrations were monitored at various depths by gas well method.Environmental factors were also tracked,and the physicochemical characteristics of the soil were also examined.The main variables influencing the temporal and spatial patterns of greenhouse gas emissions in the lakeshore zone were examined.The main results of this study are as follows:1.Similar distribution patterns of soil ammonium,nitrate,and dissolved organic carbon in the lakeshore zone of Lake Donghu,Lake Nanhu,Lake Tangxun,and Lake Yezhi can be observed in the soil profile,with values decreasing with depth.According to a correlation analysis,soluble organic carbon,nitrate nitrogen,and ammonium in the soil all showed strong negative relationships with depth.Due to the effect of the lake’s water column,the distribution of soil ammonium,nitrate,and dissolved organic carbon varies with distance,with a maximum soil water content occurring at 1 m from the lake.2.At distances of 1 m,3 m,5 m,and 10 m from the lake’s water column,soil emission fluxes of N₂O,CH₄,and CO₂ were all seasonally varied throughout the year,with the CO₂ fluxes’seasonal pattern being the most evident,increasing from March to a peak in July.N₂O,CH₄,and CO₂ were all sources at both sampling locations,with CH₄only occasionally sinking at closer distances to the lake’s water column from April to July.The cumulative soil N₂O emissions from the shoreline zone covered in woody vegetation at 3 m were 2.10±0.17 kg ha^-1,which was substantially higher than the cumulative soil N₂O emissions from the lakeside zone covered in herbaceous vegetation at 3 m of 1.43±0.11 kg ha^-1（p<0.05）.The cumulative soil CH₄uptake from the lakeshore zone covered in woody vegetation at 1 m was 1.26±0.11 kg ha^-1,which was substantially higher than the uptake from the zone covered in herbaceous vegetation at 1 m.The cumulative soil CH₄ uptake at 1 m and at 3 m was 0.34±0.08 kg ha^-1 and 0.80±0.06 kg ha^-1,respectively.These values were significantly lower than the cumulative soil CH₄ uptake at 3 m in the herbaceous lakeshore zone,which was 1.09±0.09 kg ha^-1.The cumulative soil CO₂emissions at 1 and 3 m in the woody lakeshore zone were 55383.27±2817.94 and48153.34±1674.05 kg ha^-1（p<0.05）.3.The primary determinants of N₂O emissions from the woody cover lakeshore zone were air temperature,soil moisture content,and soil nitrate content,whereas the primary determinants of N₂O emissions from the herbaceous cover lakeshore zone were soil temperature,soil moisture,and nitrate content.In both sample sites,soil temperature had the biggest impact on CO₂ emissions,while soil moisture content had a substantial and positive correlation with CH₄ fluxes.4.N₂O and CO₂ concentrations in the soil profile increased and subsequently fell with depth,with the maximum concentrations usually occurring between 40 cm and 60cm;CH₄ concentrations were highest in the surface layer and decreased with depth.N₂O,CH₄ and CO₂ concentrations were not significantly related to soil ammonium and nitrate nitrogen contents,and were not the main influencing factors.However,soil moisture content was a limiting factor for greenhouse gas concentrations in the woody cover lakeshore zone.The concentrations of N₂O,CH₄,and CO₂ were not the key determining factors and were not significantly correlated with the ammonium and nitrate nitrogen contents of the soil.In conclusion,the greenhouse gas emission fluxes are primarily influenced by temperature and soil moisture content,whereas the greenhouse gas emission fluxes in the lakeshore zone are characterized by spatial and temporal variability throughout the year,and their concentrations vary accordingly in different soil profiles.As a result,this study recommends that when developing a GHG emission inventory for the lakeshore zone with strong heterogeneity,the spatial and temporal variability of GHG emissions be considered,as well as the environmental factors and the physical and chemical characteristics of the soil,in order to more effectively develop corresponding emission reduction measures and policies.