The Research On LUCC And Soil Organic Carbon Pool Of Shanghai Based On RS And GIS

As an important component of terrestrial ecosystem carbon pool,soils play ansignificant role in regulating the concentration of carbon dioxide (CO₂) and mitigatingglobal warming.Land use and cover change (LUCC) caused by human activitiesbecomes one of the key factors affecting the soil organic carbon (SOC) pool.With thedevelopment of urbanization and increasing urbanized area,soils adjacent to citiesexperience rapid change.Therefore an assessment of SOC pool in urban area,theirspatial distribution and temporal variation associated with LUCC,can providescientific basis for government to make effective measures to reduce carbon emissionand increase carbon sink.In addition,it can contribute to the research of global SOCcycling research and the prediction of global change in the future.On the basis of combined methods involving geographical information system(GIS),remote sensing (RS) and soil carbon analyses,this paper discusses the land usechange of Shanghai during the years 1994-2006,and the associated with soil carbonpool dynamics.The main conclusions are as follows:During the years 1994-2006,land use change is significant in Shanghai.Amongall types of land use,farmland has the greatest change in area,which has decreased94007.72 hm² in total area,at a rate of 7833.98 hm² per year.Urban greenland showsthe largest increase in area with dynamic degree of 18.76% in 12 years.Most of thedecreased farmland (54.47%) has been converted to urban construction land(including industrial,traffic and residential use).There is notable spatial differencein comprehensive dynamic degree of land use,which shows declining trend with thedistance from central urban district.The comprehensive dynamic degree of land usechange for Pudong New District is the largest,while that of Chongming County is thesmallest.The difference of LUCC is closely related to the location,economiccondition and policies of each district.Distinct difference exists in SOC density of different land use in Shanghai.SOC density of paddy field (3.859 kg/m²) is the highest,which indicates that paddyfield has the largest carbon sequestration capacity.SOC density of tidal flat (1.379 kg/m²)is the smallest,suggesting limited carbon sequestration capacity.SOC densityof the other land use types is 3.173 kg/m² (upland),3.147 kg/m² (forestland),2.727kg/m² (abandoned land),2.647 kg/m² (urban lawn) and 2.130 kg/m² (garden land),respectively.Three types of land use change are studied to assess its impact on soil carbonpool.The conversion of paddy field to upland has resulted in obvious reduce of SOCcontent,total nitrogen content (TN) and SOC density.When farmland has beenabandoned,SOC,TN content and SOC density only increase in the topsoil of 0-5cmbut decrease in the depth of 0-35cm in total.It suggests that abandonment offarmland has poor effect in improving carbon and nitrogen sequestration capacity inthe Yangtze Delta region.SOC,TN content and SOC density of topsoil decrease whenpaddy field is converted into artificial forestland for 4-5 years.Therefore,comparedwith artificial forestland,paddy field has better soil carbon and nitrogen sequestrationcapacity.Based on measured SOC density of different land use type,combined with theresult of LUCC in Shanghai,this paper estimates SOC storage of topsoil in depthrange of 0-20 cm in the year of 1994,2000,2003 and 2006.They are 14.9047 Mt(1994),13.9912 Mt (2000),12.8356 Mt (2003) and 11.8580Mt (2006),respectively,showing declining trend with time.The mean SOC density is 35.41 t/hm² (1994),35.44 t/hm² (2000),35.06 t/hm² (2003) and35.15 t/hm² (2006),respectively.TheSOC storage of topsoil increases from central urban and suburb areas to the outskirts,which is related closely to the distribution of land use and regional difference ofdisturbance extent by human activities.Among all the administrative districts,theSOC storage of topsoil of Chongming County (3.0528 Mt,2006) is highest,while thatof the central urban district (0.0531 Mt,2006) is the lowest.All districts showdecreased SOC pool with time,with the loss of Songjiang (0.51 Mt) being the largest,and that of Qingpu (0.41 Mt) the second,and that of the central urban district (49.4 Tt)the least.As for different land use,the SOC storage of topsoil of farmland shows areduction of 3.3692 Mt in total,while those of urban greenland,artificial forestlandand garden land display an increase of 0.2691 Mt,41.9 thousand tons and 42.2thousand tons during the period of 1994 to 2006.Generally speaking,the loss of SOC storage of topsoil caused by LUCC in Shanghai amounts to 3.0699 Mt,correspondingto 7.71% of the amount of emission of carbon from fossil fuel combustion (39.81 Mt)in Shanghai in 2000.Therefore,it is concluded that LUCC caused by human activitiesbecomes thekey factor in changing SOC storage of topsoil in Shanghai.A number of measures can be taken to improve the carbon sequestration capacityof soil,including increasing the use of green manure,improving the percentage ofstraw returning,fertilizer application combined with organic manure in farmland,afforestation,urban greenland construction and better management.In addition,tidalflat has great potential for carbon sequestration by proper use.