Review on the study of "water stage-duration-frequency" thresholds for forming wetlands

Wetland hydrology is the driving force of wetland formation, "water stage-duration-frequency" (S, D, F) are the characteristic indexes of wetland hydrology. Aimed to promote the development of the theories and methods for determining (S, D, F) thresholds, the agreed conclusions derived from (S, D, F) threshold studies were summarized, which include: The principle of determining S threshold is "saturate to the earth's surface"; the principle of determining D threshold is "the lag time from the onset of saturation to the formation of anaerobic condition"; and F threshold should be≥50%. Through the analysis of these agreed conclusions, the results suggested: ① There are scientific problems in using the principle of determining D threshold; ② The present theories and methods for determining (S, D, F) threshold were built for the wetlands of "normal condition", and can not be used to determine the (S, D, F) threshold of "abnormal condition". In order to get (S, D, F) thresholds scientifically, new scientific theories and methods for determining (S, D, F) threshold should be built, which should include: The (S, D, F) threshold theories and methods for wetlands of both "normal condition" and "abnormal condition", and the theories and methods of scientific testing for (S, D, F) thresholds.