Coastal tidal wetland change in the northeastern United States

Coastal tidal wetlands are highly altered ecosystems at substantial risk due to widespread and frequent land-use change, coupled with sea-level rise, leading to disrupted hydrologic and ecologic functions and ultimately, significant reduction in climate resiliency. Knowing where and when the changes have occurred, and the nature of those changes and their associated risks, is paramount to coastal communities and natural resource management. Large-scale mapping of the costal tidal wetland changes is extremely difficult due to their inherent dynamic nature.
To bridge this gap, we developed an automated algorithm for DEtection and Characterization of cOastal tiDal wEtlands change (DECODE) using dense Landsat time series. We used DECODE to track the status of coastal tidal wetlands in the northeastern United States from 1986 to 2020. The overall accuracy of land cover classification and change detection is approximate 95.8% and 99.8%, respectively. The vegetated wetlands and open water were mapped with 94.6% and 99.0% user’s accuracy, and 98.1% and 93.5% producer’s accuracy, respectively. The cover change and condition change were mapped with 68.0% and 80.0% user’s accuracy, and 80.5% and 97.1% producer’s accuracy, respectively. We discovered that approximately 3283 km2 (12%) of coastal tidal wetlands in the northeastern United States occurred at least one time of change but condition changes were responsible for majority (84.3%). Vegetated coastal tidal wetland decreased consistently (approximately 2.6 km2 per year) in the past 35 years, largely due to its conversion to open water.

滨海潮间湿地（Coastal tidal wetlands）是受高度干扰的生态系统，面临显著风险：广泛且频繁的土地利用变化叠加海平面上升，导致其水文与生态功能遭到破坏，最终引发气候韧性大幅降低。明确变化发生的时空位置、变化本质及其关联风险，对沿海社区与自然资源管理而言至关重要。但滨海潮间湿地固有的动态特性，使其大规模变化制图工作极具挑战性。
为填补这一研究空白，我们基于密集型Landsat时间序列数据，开发了一款用于滨海潮间湿地变化检测与特征表征（DEtection and Characterization of cOastal tiDal wEtlands change，缩写DECODE）的自动化算法。我们利用该算法追踪了1986年至2020年间美国东北部滨海潮间湿地的动态状态。土地覆盖分类与变化检测的总体精度分别约为95.8%与99.8%。其中，植被湿地与开阔水体的用户精度分别为94.6%与99.0%，生产者精度分别为98.1%与93.5%；地表覆盖变化与湿地状态变化的用户精度分别为68.0%与80.0%，生产者精度分别为80.5%与97.1%。研究发现，美国东北部约3283平方千米（占总量12%）的滨海潮间湿地至少发生过一次变化，其中状态变化占总变化的84.3%，为主要变化类型。过去35年间，植被型滨海潮间湿地持续萎缩，年均减少约2.6平方千米，其主要原因为转化为开阔水体。