20 km from the hill-plain junction to the estuary,the lower reach of Xiaolinghe River has developed a series of depositional environments,including pebbely alluvial fan,channel lag,channel bars,floodplain and depressions,salt marshes and open tidal flats,etc.

Based on the study of the difference between aqua regia solution and HF-HClO_4-HNO_3-HCl solution and the distribution of elements in flood plain sediments A, B and active stream sediments, the authors hold that flood plain sediments A can be used as the effective sampling media in the ultra-low density deep penetration geochemical survey in the forest-swamp area of central Heilongjiang Province.