[Groundwater depth and its relation with typical vegetation distribution in the Poyang Lake wetland, China]

Groundwater level directly affects soil water content, which in turn impacts the growth, distribution, and succession of wetland vegetation. Based on the groundwater monitoring data during 2014 to 2018, we analyzed the inter- and intra-annual variations in groundwater level of the wetland in Poyang Lake. We set up a groundwater numerical model to investigate the spatial patterns of groundwater flow field and distribution of groundwater depth. The relationship between groundwater depth and distribution of typical vegetation was explored with Gaussian regression analysis. Results showed that groundwater level of the wetland showed inter-annual variation, with the trend highly consistent to the changes in lake water level. There was a lag of one month between the inter-annual change in groundwater depth and the seasonal distribution of precipitation. The annual groundwater level showed a decreasing trend from upstream to downstream. The range of groundwater depth in upstream area of the wetland was narrower (0.1-1.1 m) than that of the downstream area (0.1-5.6 m). The groundwater flow field was directed from the hilly upstream area to the relatively flat downstream lake area, with the flow direction consistent with the change in elevation. The ground-water depth decreased with decreasing distance to the lake water body, with an average value of 2.07 m in the study are. The optimal groundwater depths for the growth of Carex, Phragmites aus-tralis, and Artemisia capillaris communities were 1.1, 3.7 and 5.7 m, respectively. The typical vegetation distribution showed different responses to groundwater depth. The ecological width of A. capillaris communities was larger than the Carex and P. australis communities. The three types of community were overlapped in ecological niche when the groundwater depth ranged 1.1-5.7 m. The vegetation distribution index of Carex decreased rapidly, that of P. australis increased firstly and then decreased, while that of A. capillaris increased continually to the maximum and began to decrease when the groundwater depth reached 5.7 m.