Multi-level Evaluation Of Mangrove Ecosystem Based On Remote Sensing Technology

Mangrove ecosystem provides a number of ecological,economic,and social benefits to humans.In the Jiulong River Estuary(JRE)of Fujian Province,China,many mangroves have been lost largely due to human activities and artificial planting has been implemented.However,the status of mangrove forests are still largely unknown at this location.Field-based assessments can be labour intensive and associated with high costs;remote sensing provides the means to accurately assess mangrove distribution,aboveground biomass and ecosystem service values in a cost effective manner.Studies that use remote sensing technology to explore mangroves are rarely reported in this area.In this study,multi-level mangrove assessments based on remote sensing in JRE were discussed.The study identified changes to mangrove distribution and aboveground biomass(AGB)in the three periods(1995-2004,2004-2014,and 1995-2014)using multi-temporal satellite images,thoroughly assessed the potential ability of high-resolution remote sensing image(PLEIADES)texture metrics at different window sizes for quantifying aboveground carbon of mangrove forests and proposed a pixel-based method for estimating the spatial variability of mangrove ecosystem services(coastal protection,carbon sequestration,nutrient retention and heavy metal retention)using a combination of high-resolution satellite data(PLEIADES)with market price and replacement cost approaches in the JRE.The purposes of this study were to determine the status of mangroves and to gain some deep insight into the cause of mangrove changes based on remote sensing.The results are expected to provide suggestion for mangrove management provide.The main conclusions are as follows:(1)Mangrove area and AGB increased from 1995 to 2014.The increased rate was 5.5%and 7.2%for mangrove area and AGB,respectively.Mangrove expansion was the main cause for AGB and area increase.In addition,AGB increase owing to growth of mangroves without extending the area also has great potential in AGB increase.Similar to AGB,aboveground carbon increased from 57 t C/ha in 1995 to 79 t C/ha in 2014,which demonstrated that mangroves in this region can mitigate climate warming.However,remarkable continuous decrease of mangrove forest in the JRE was caused by growing human activities.Moreover,tidal range change during 2004-2014 resulted in more adverse impact on mangroves.(2)The texture-based model had a much better potential for aboveground carbon(AGC)estimation with a higher R2 value of 0.934,and a lower RMSE of 3.76 t C/ha.With increasing of window size for the texture calculations,the R2 values increased and the RMSEs decreased.Model 4-7 with an R2 value of 0.878 was finally chosen for relatively accurate quantification of AGC.The AGC values at a selected site derived from the model ranged from 1 to 153 t C/ha.(3)There was a considerable variability in the ecosystem service values caused by the distance of mangroves to the coast and the different growth phases of mangrove forests.The total estimated value of the four selected ecosystem services was US$ 287,993/a for 174.58 ha(approximately US$ 1,650/ha/a).Coastal protection was estimated to provide the highest value(US$ 239,683/a),amounting to 83.23%of the total value of the ecosystem services,followed by nutrient retention(US$ 25,283/a),contributing 8.78%of the total value of the ecosystem services.Heavy metals retention(US$ 10,289/a)and carbon sequestration(US$ 12,738 in 2015/a)had relatively low values in comparison to those of coastal protection and nutrient retention.