Lee Kuan-Ying, Shih Shang-Shu, Huang Zhong-Ze
Department of Civil Engineering, National Taiwan University, Taiwan.
Department of Civil Engineering, National Taiwan University, Taiwan; Hydrotech Research Institute, National Taiwan University, Taiwan.
J Environ Manage. 2022 Jul 15;314:115058. doi: 10.1016/j.jenvman.2022.115058. Epub 2022 Apr 19.
A healthy mangrove ecosystem includes diverse landscape structures, such as tidal flats, tidal channels, and areas with circulating waters, in addition to mangrove stands. The complex structure of mangrove forests affects the hydrodynamics and sediment transport behaviour of tidal channels. Understanding the influence of the mangrove invasion of tidal flats on the pattern and stability of tidal channels is essential. In this study, two types of remote sensing images, Google Earth images and aerial photographs, were collected to analyze the relationship between mangrove colonization and changes in tidal channel patterns. After applying binary image processing, these two kinds of images show similar abilities to discriminate the locations, extents, and boundaries of mangroves and tidal channels. We found that the mangrove area was inversely proportional to the tidal channel sinuosity and width. The tidal channels exhibited a meandering pattern with a wider width before the mangroves invaded the tidal flats. After the expansion of the mangroves, the tidal channels gradually transformed into a straight shape with a narrower width. After the mangroves developed into forests, the tidal channels maintained a straight and stable pattern. Since mangroves promote siltation and increase the elevation of the surrounding mudflats, the habitat suitability for mangroves in the neighbouring tidal flat areas may vary. These processes may help expand mangrove habitats, thereby compressing the area of flats and changing the shape of tidal channels. Due to tidal current effects, the unit stream power of a straight tidal channel is approximately twice that of a meandering channel, indicating that straight tidal channels have a stronger anti-siltation capability. Our research also found that the tidal channels may return to a meandering pattern when mangroves are degraded or die and their area decreases. This study provides key evidence that mangroves affect tidal channel types and hydrodynamic characteristics, thus providing a useful reference for restoring and managing estuarine mangrove ecosystems.
一个健康的红树林生态系统除了红树林群落外，还包括多种景观结构，如潮滩、潮汐通道和有循环水流的区域。红树林森林的复杂结构会影响潮汐通道的水动力和泥沙输运行为。了解红树林对潮滩的入侵对潮汐通道形态和稳定性的影响至关重要。在本研究中，收集了谷歌地球图像和航空照片这两种遥感图像，以分析红树林定殖与潮汐通道形态变化之间的关系。经过二值图像处理后，这两种图像在区分红树林和潮汐通道的位置、范围和边界方面表现出相似的能力。我们发现红树林面积与潮汐通道的弯曲度和宽度成反比。在红树林入侵潮滩之前，潮汐通道呈现出弯曲形态且宽度较宽。红树林扩张后，潮汐通道逐渐转变为宽度较窄的直线形状。当红树林发展成森林后，潮汐通道保持直线且稳定的形态。由于红树林促进淤积并提高周边泥滩的海拔，相邻潮滩区域对红树林的栖息地适宜性可能会有所不同。这些过程可能有助于扩大红树林栖息地，从而压缩潮滩面积并改变潮汐通道的形状。由于潮流作用，直线型潮汐通道的单位水流功率约为弯曲型通道的两倍，这表明直线型潮汐通道具有更强的抗淤积能力。我们的研究还发现，当红树林退化或死亡且面积减少时，潮汐通道可能会恢复为弯曲形态。本研究提供了关键证据，证明红树林会影响潮汐通道类型和水动力特征，从而为河口红树林生态系统的恢复和管理提供了有用的参考。
