Abstract:Phosphorus (P) is an essential and limiting nutrient in wetland ecosystems and it plays a vital role in eutrophication. Remote sensing (RS) offers an up-to-date and relatively accurate means to measure the soil P content. Recently, some studies have shown that it was feasible to estimate the total P (TP) content of terrestrial ecosystem soil based on hyper-spectral RS data. However, little information is available on TP content estimation by RS technology on wetland soil. The aim of this study was to estimate the TP content of wetland soil using hyper-spectral RS data. Min river estuarine wetland, located in the subtropical zone, is one of the most typical and important estuarine wetlands in southeast China. Soil samples, from Shanyutan tidal marsh in the Min River Estuary, were collected in sixteen profiles at five depths (0-10 cm, 10-20 cm, 20-30 cm, 30-40 cm, and 40-50 cm) along an elevation gradient, in May of 2013. Estimation and validation models were constructed by spectrum parameters, including original spectral reflectance (R), simple ratio soil index (RSI), normalized difference soil index (NDSI), and organic matter diagnosis index (OII) calculated by optimal bands. The results indicated that the spectral reflectance of the soil increased with depth at 350-580 nm, while an opposite trend was observed at 580-2500 nm. Soil TP content showed a negative correlation with R at 350-600 nm, whereas a positive correlation was observed at 600-2500 nm. The highest correlation coefficient value was -0.816 and occurred at 406 nm. The correlation coefficient between soil TP content and OII exhibited a bimodal distribution, with peaks at 446 nm (r = -0.843) and 634 nm (r = 0.798). NDSI and RSI were each calculated by bands in three zones, (420-440 nm and 440-590 nm, 460-470 nm and 590-1000 nm, and 550-590 nm and 550-590 nm, respectively), which had higher correlation coefficients with TP content than those in other zones. The determination coefficient (r2) and root means square error (RMSE) of estimation models ranged from 0.657-0.805 and 0.052-0.067, respectively, and those of the validation models ranged from 0.606-0.893 and 0.037-0.044, respectively. These results indicate that TP content of the Min River estuarine soil could be estimated by most of the selected parameters. The evaluation parameters of the estimation models supported that estimating the TP content of high and middle tidal flats soil individually could improve the estimation accuracy of some parameters such as RSI(R430, R830), RSI(R460, R810), and NDSI(R430, R830). Additionally, the estimation accuracy of soil TP content also depended on the P fractions. Iron bound phosphorus (Fe-P), occluded phosphorus (O-P), and organic phosphorus (Org P) had higher correlation coefficients with R than did aluminum bound phosphorus (Al-P) and calcium bound phosphorus (Ca-P). The corresponding changes in the contents of TP within organic matter and a redox environment in wetland soil could be used as important mechanisms for estimating soil TP content. In conclusion, it was feasible to estimate TP content of subtropical estuarine wetland soils based on hyper-spectral RS data.