Gray Andrew, Krolikowski Monika, Fretwell Peter, Convey Peter, Peck Lloyd S, Mendelova Monika, Smith Alison G, Davey Matthew P
Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom.
Field Spectroscopy Facility (Natural Environment Research Council), University of Edinburgh, Edinburgh, United Kingdom.
Front Plant Sci. 2021 Jun 16;12:671981. doi: 10.3389/fpls.2021.671981. eCollection 2021.
Snow algae are an important group of terrestrial photosynthetic organisms in Antarctica, where they mostly grow in low lying coastal snow fields. Reliable observations of Antarctic snow algae are difficult owing to the transient nature of their blooms and the logistics involved to travel and work there. Previous studies have used Sentinel 2 satellite imagery to detect and monitor snow algal blooms remotely, but were limited by the coarse spatial resolution and difficulties detecting red blooms. Here, for the first time, we use high-resolution WorldView multispectral satellite imagery to study Antarctic snow algal blooms in detail, tracking the growth of red and green blooms throughout the summer. Our remote sensing approach was developed alongside two Antarctic field seasons, where field spectroscopy was used to build a detection model capable of estimating cell density. Global Positioning System (GPS) tagging of blooms and life cycle analysis was used to validate and verify our model output. WorldView imagery was then used successfully to identify red and green snow algae on Anchorage Island (Ryder Bay, 67°S), estimating peak coverage to be 9.48 × 10 and 6.26 × 10 m, respectively. Combined, this was greater than terrestrial vegetation area coverage for the island, measured using a normalized difference vegetation index. Green snow algae had greater cell density and average layer thickness than red blooms (6.0 × 10 vs. 4.3 × 10 cells ml) and so for Anchorage Island we estimated that green algae dry biomass was over three times that of red algae (567 vs. 180 kg, respectively). Because the high spatial resolution of the WorldView imagery and its ability to detect red blooms, calculated snow algal area was 17.5 times greater than estimated with Sentinel 2 imagery. This highlights a scaling problem of using coarse resolution imagery and suggests snow algal contribution to net primary productivity on Antarctica may be far greater than previously recognized.
雪藻是南极洲重要的陆地光合生物群体，它们大多生长在低洼的沿海雪地中。由于其水华的短暂性以及在那里旅行和开展工作所需的后勤保障，对南极雪藻进行可靠观测很困难。此前的研究已利用哨兵2号卫星图像对雪藻水华进行远程检测和监测，但受到空间分辨率粗糙以及检测红色水华存在困难的限制。在此，我们首次使用高分辨率的世界观多光谱卫星图像详细研究南极雪藻水华，在整个夏季追踪红色和绿色水华的生长情况。我们的遥感方法是在两个南极实地考察季期间开发的，在此期间利用实地光谱学构建了一个能够估算细胞密度的检测模型。通过对水华进行全球定位系统（GPS）标记和生命周期分析来验证和核实我们的模型输出。然后，世界观图像成功用于识别安克雷奇岛（莱德湾，南纬67°）上的红色和绿色雪藻，估计其峰值覆盖面积分别为9.48×10和6.26×10平方米。综合来看，这一面积大于使用归一化差异植被指数测量的该岛陆地植被面积覆盖。绿色雪藻比红色水华具有更高的细胞密度和平均层厚度（分别为6.0×10和4.3×10个细胞/毫升），因此对于安克雷奇岛，我们估计绿藻的干生物量是红藻的三倍多（分别为567千克和180千克）。由于世界观图像的高空间分辨率及其检测红色水华的能力，计算得出的雪藻面积比用哨兵2号图像估计的面积大17.5倍。这凸显了使用低分辨率图像时的尺度问题，并表明雪藻对南极洲净初级生产力的贡献可能远大于此前的认识。
