Delayed flood recession in central Yangtze floodplains can cause significant food shortages for wintering geese: results of inundation experiment.

Carex meadows are critical habitat for wintering geese in the floodplains of the middle and lower reaches of Yangtze River, China. These meadows follow a growth cycle closely tied to the seasonal hydrological fluctuation: as water levels recede in the fall, exposed mudflats provide habitat for Carex spp. growth. The seasonal growth of Carex overlaps the arrival of wintering geese and provides an important food source for the migrants. Recent alterations to the Yangtze's hydrology, however, have disrupted the synchronous relationship between water levels, Carex growth and wintering geese at Dongting Lake. In October 2012, we carried out an outdoor mesocosm experiment to investigate potential impacts of delayed water recession on the germination and growth of Carex heterolepis, the dominant Carex species at Dongting Lake, to understand how changes in hydrology might impact wintering goose habitat. Results showed that the delayed flood recession exerted significant impact on the first growth cycle of Carex growth. Prolonged inundation significantly lowered the intrinsic growth rate (P = 0.03) and maximum growth rates (P = 0.02). It also took significantly longer time to reach the peak growth rate (P = 0.04 and 0.05 for number of shoot and biomass, respectively). As a result, biomass accumulation was reduced by 45, 62 and 90 % for 10-day, 20-day and 30-day inundation treatments, respectively. These results indicate a severe risk of food shortage for wintering geese when water recession delayed. This potential risk should be taken into consideration when operating any hydrological control structures that alter the flood regimes in Dongting Lake.