First Institute of Oceangraphy, Ministry of Natural Resources, Qingdao, Shandong 266061, China.
First Institute of Oceangraphy, Ministry of Natural Resources, Qingdao, Shandong 266061, China.
Mar Pollut Bull. 2019 Mar;140:330-340. doi: 10.1016/j.marpolbul.2019.01.037. Epub 2019 Feb 2.
Since 2007, green tide blooms with Ulva prolifera as the dominant species have occurred every summer in the Yellow Sea. Biomass is a critical parameter used to describe the severity of green tide blooms. In this study, we analyzed the relationships between several indices (normalized difference vegetation index (NDVI), floating algae index (FAI), ratio vegetation index (RVI), enhanced vegetation index (EVI), ocean surface algal bloom index (OSABI), Korea Ocean Satellite Center (KOSC) approach) and the biomass per unit area of Ulva prolifera by using the in situ measurements from a water tank experiment. EVI, NDVI, and FAI showed strong exponential relationships with Ulva prolifera biomass per unit area. In order to apply the relationships to satellite remote sensing data, the impacts of the atmosphere (different aerosol optical depth at 550 nm) and mixed pixels to the relationships were analyzed. The results show that atmosphere has little effect on the relationship between EVI and Ulva prolifera biomass per unit area with R = 0.94 and APD (the average percentage deviation) = 19.55% when EVI is calculated from R (Rayleigh-corrected reflectance), and R = 0.95 and APD = 17.53% when EVI is calculated from R (top-of-atmosphere reflectance). Due to the low sensitivity to the atmosphere, the EVI relationship can be directly utilized in the top-of-atmosphere (TOA) reflectance without atmospheric correction. In addition, the EVI was slightly affected by mixed pixels with the APD only increased by 10%. The EVI relationship was then applied to a long MODIS image time series to obtain the maximal total biomass of floating Ulva prolifera in the Yellow Sea from 2007 to 2016. The results showed that the maximum and minimum total biomass occurred in 2016 (1.17 million tons) and 2012 (~0.074 million tons), respectively. The main factors that caused the inter-annual biomass variability were analyzed. The total amount of nutrients from Sheyang River which was the largest river on the northern coast of Jiangsu Province, and Porphyra cultivation in the Radial Sand Ridges of Jiangsu Province had both strong correlation with Ulva prolifera total biomass.
自 2007 年以来，黄海每年夏季都会出现以石莼（Ulva prolifera）为优势种的绿潮。生物量是描述绿潮严重程度的关键参数。本研究通过水箱实验的现场测量，分析了归一化植被指数（NDVI）、浮藻类指数（FAI）、比值植被指数（RVI）、增强植被指数（EVI）、海洋藻类水华卫星监测指数（OSABI）和单位面积石莼生物量之间的关系。EVI、NDVI 和 FAI 与单位面积石莼生物量呈强烈的指数关系。为了将这些关系应用于卫星遥感数据，分析了大气（不同的 550nm 气溶胶光学深度）和混合像元对这些关系的影响。结果表明，在 EVI 是从 R（瑞利校正反射率）计算得到时，大气对 EVI 与单位面积石莼生物量之间关系的影响很小，R 值为 0.94，平均百分比偏差（APD）为 19.55%；在 EVI 是从 R（大气顶部反射率）计算得到时，R 值为 0.95，APD 为 17.53%。由于对大气的低敏感性，EVI 关系可以在无需大气校正的情况下直接应用于大气顶部（TOA）反射率。此外，EVI 受混合像元的影响较小，仅使 APD 增加了约 10%。然后将 EVI 关系应用于长时间 MODIS 图像时间序列，以获得 2007 年至 2016 年黄海漂浮石莼的最大总生物量。结果表明，最大和最小总生物量分别出现在 2016 年（约 117 万吨）和 2012 年（约 74 万吨）。分析了导致年际生物量变化的主要因素。江苏省北部海岸最大的射阳河以及江苏省辐射沙洲的紫菜养殖所带来的营养物质总量与石莼总生物量均具有很强的相关性。
