Adaptive management on the wintering habitat of common teals (Anas crecca) in Hwajiang estuarine wetland

• Main Authors: Gwo-Wen Hwang, 黃國文
• Other Authors: 李鴻源
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/51191028862737275232

博士 === 國立臺灣大學 === 土木工程學研究所 === 100 === This study aimed at constructing an adaptive management model for wintering habitat of Common Teal (Anas crecca) in Hwajiang Wetland. A habitat suitability index (HSI) was developed to quantify the physical environments of the Teals’ preferred habitat. The Hwajiang wetland is an important wintering site for migratory Common Teal, whose population has dramatically declined in recent years, due most likely to the persistent degradation of habitats in this wetland. Due to river morphology, the changes of sediment deposition and vegetation expansion, have reduced the available habitat for the wintering Teal. Therefore, the rehabilitation of the Teals’ habitat is urgently needed for a sustainable management in this wetland. Point-count surveys of the Common Teal were conducted at a tidal pool, an inner channel and a tidal creek in Hwajiang Wetland and Teals’ positions were recorded from October 2008 to March 2009. Twenty-two sets of data and 3615 counted individuals were collected. Three habitat variables, including slope, elevation and the distance to the nearest vegetation, were displayed on 5 m × 5 m grid cells and analyzed with GIS software. Suitability index (SI) values of habitat variables were determined using the envelop curve of maximum abundance of common teals versus the habitat variables. The results showed that Common Teal preferred habitats with gentle slopes, median elevations and areas close to vegetation. The abundance of the Common Teal was highest in the grid cells with slopes ranging from 0.7 to 1.4%, bed elevation varying from 0.3 to 0.7 m above the mean sea level, and distance to the nearest vegetation shorter than 4 m. The HSI model was constructed by calculating the minimum value of the three SIs, and the suitability map of wintering common teals was generated to represent an integrated map of habitat quality in the area. A simple regression analysis indicated that the HSI model is a reliable indicator as the maximum numbers of the Common Teal in each grid cell increased significantly with the HSI values. Four types of habitat conditions, poor, fair, good and excellent, were determined based on the HSI values. The proportions of excellent habitat were 41.9%, 17.4% and 26.4% in the tidal pool, the inner channel and the tidal creek, respectively. A principle of rehabilitation was derived from the HSI model, with slopes smaller than 1.5%, elevations between 0.0m and 0.5m, and distance of less 25 m to the nearest vegetation. The rehabilitation area should be larger than 100 m in width and 250 m in length and adjacent to the existing Teal habitat. Three rehabilitation scenarios were simulated and characterized based on field survey and the HSI model. In addition, a horizontal two dimension numerical model, CCHE2D, was employed to simulate bank-full flow characteristics such as water surface elevation, flow velocity, shear stress and so on. The bathymetry and vegetation cover were assumed the same while the location was different. The shear stress evaluation indicated that the rehabilitation of the most upstream location is the best scenario because it has the lowest sediment deposition rate and represents a minimum maintenance effort needed in the future. This study provided a foundation for determining potential habitats and information on how to mitigate a degraded wetland for the Common Teal. It encompassed the aspects of monitoring, evaluation, and decision making that would benefit future management plans directed toward the Common Teal and other waterfowl species in Taiwan. It also provided an adaptive management model for application to similar projects of wetland rehabilitation and sustainable management.