Potential Impact Of Changed Hydrology Regime On Food Resource And Distribution Of Wintering Geese In Dongting Lake, China

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. The main reason why the migratory geese select middle and lower Yangtze floodplains as their main wintering ground is receding water levels in the fall in this region allow for the initial growth of Carex which corresponds to the arrival of hundreds of thousands of migratory of geese.East Dongting Lake National Nature Reserve at China is listed as a Ramsar site due to its global significance in migratory water bird conservation, especially for geese. For example, more than 90%of East Asian population of the vulnerable Lesser White-fronted Goose (Anser erythropus) (LWFG), and large numbers of Bean Goose (A.fabilis) (BG) and Greater White-fronted Goose (A. albifrons) (GWFG) overwinter here every year from October to next March. However, the habitat and food quality of the wintering geese are threatened by hydrological alternation due to the operation of the Three Gorges Dam. In order to mitigate the economic impacts of the TGD, Hunan provincial government proposed hydrological control structures to manage the flows between the lake and the Yangtze River. The specific function of the proposed hydrological control structures is to retain more water in the lakes during the dry season to mitigate drought effects. It is currently unclear how damming the lakes might alter their ecology. One potential consequence is delayed water recession of Dongting Lake, with unknown consequences for wet meadows of these ecosystems and would bring new challenge to the conservation of waterbird. Understanding the diets of three geese species and investigation of the response of wet meadow plants to the hydrology change is needed to management and conservation of wintering geese. Such knowledge also could inform the operation of future infrastructure operations (including the TGD and proposed control structures) and mitigate the potential negative impacts to ecosystem such as large-scale biodiversity loss.We used stable isotopic ratios of the body tissues of three predominant goose species (i.e. LWFG, BG and GWFG) and their potential diet items (six grass species), and applied the multiple-source mixing models (i.e. SIAR) to quantify the contribution of different food items to the diet of geese. The results showed that 813C values of blood sample were significantly different from feather, and the difference was consistent for the three geese species. These results indicated clear dietary shifts from their breeding ground at high Arctic to the wintering ground at Dongting Lake. The blood δ13C values of the three geese show no significant difference (ANOVA, p=0.265) suggesting that they share the same food sources at Dongting Lake. Moreover, the SIAR mixing models indicates that no single plant has a contribution greater than 35% at 0.95 confident level (0.50 and 0.95 credibility intervals of the posterior distributions range from 0.24-0.25 and 0.32-0.34, respectively) to the diet of geese. The results indicate that the geese have no preference for a particular plant. The findings suggest that patch level features (e.g. vegetation greenness and development stage) but plant species may be the decisive factor in geese habitat selection.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.Habitat suitability and selection are key concepts in wildlife management, especially in protection of critical habitat and conservation of sensitive and endangered populations. In recent years, many approaches have been developed to link habitat suitability with animal occurrence and abundance. These approaches typically involve identifying existing habitats, defining habitat quality metrics, and estimating the association between animal occurrence/abundance and measured habitat metrics. In this study, we first tested whether we could measure habitat quality at Dongting Lake, China, one of the most important migratory waterbird wintering sites in the East Asian Flyway, for a group of Anatidae using metrics derived from the freely available multi-temporal MODIS vegetation index. The results showed that goose counts could be sufficiently modelled using mean winter season EVI (enhanced vegetation index) and habitat size computed from EVI time series and topographic wetness index (TWI). We then quantified the relationships between hydrological regimes and the habitat quality metrics. Our findings suggested that the right timing of water recession is critical for the development of Carex marshes, which are the major foraging source for the herbivorous geese. The results have direct conservation implications as water recession timing is highly manageable through water flow regulation.Hydrology is the driving force of wetland ecosystems, we analysis the relationship between hydrology, flora and geese populations at Dongting Lake, china. It was the first time that the diet selection of geese was identified by using isotope techniques method in China. Application of new techniques (e.g. isotope method) makes research methods of bird diet selection were enriched in China. We obtained quantified data about the impact of the proposed Water Control Project on food resource of wintering geese in the Dongting Lake. We proposed appropriate water recession patterns for the conservation of wintering geese in the Dongting Lake. The results can be taken into consideration when operating any hydrological control structures that alter the flood regimes in Dongting Lake in future.