Abstract：
Canada has more lakes than any other country, making comprehensive monitoring a huge challenge. As more and more satellite data become readily available, and as faster data processing systems make massive satellite data operations possible, new opportunities exist to use remote sensing to develop comprehensive assessments of water quality at very large spatial scales. In this study, we use a published empirical algorithm to estimate Secchi depth from Landsat 8 reflectance data in order to estimate water clarity in lakes across southern Canada. Combined with ancillary information on lake morphological, hydrological, and watershed geological and landuse characteristics, we were able to assess broad spatial patterns in water clarity for the first time. Ecological zones, underlying geological substrate, and lake depth had particularly strong influences on clarity across the whole country. Lakes in western mountain ecozones had significantly clearer waters than those in the prairies and plains, while lakes in sedimentary rock formations tended to have lower clarity than lakes in intrusive rock. Deep lakes were significantly clearer than shallow lakes over most of the country. Water clarity was also significantly influenced by human impact (urbanization, agriculture, and industry) in the watershed, with most lakes in high impact areas having low clarity or very low clarity. Finally, we used in situ measured data to help interpret the underlying optical water column constituents influencing clarity across Canada, and found that chlorophyll-a, total suspended solids, and color dissolved organic matter all had strong but varying underlying effects on water clarity across different ecozones. This research provides an important step towards further research on the relationship between water column optical properties and the health and vulnerability status of lakes across the country.
摘要：
加拿大的湖泊比其他任何国家都多，使全面监测成为一个巨大的挑战。随着越来越多的卫星数据变得容易获得，随着更快的数据处理系统使大规模卫星数据操作成为可能，利用遥感在很大的空间尺度上发展水质综合评估的新机会。在这项研究中,我们使用已发布的经验算法从Landsat8反射率数据中估算Secchi深度，以估算加拿大南部湖泊的水透明度。结合湖泊形态的辅助信息，水文,以及流域地质和土地利用特征，我们首次能够评估水透明度的广泛空间模式。生态区,底层地质基底，湖泊深度对整个国家的清晰度影响特别大。西部山区生态区的湖泊的海水明显比草原和平原的湖泊清澈，而沉积岩地层中的湖泊往往比侵入岩中的湖泊具有更低的清晰度。在全国大部分地区，深湖明显比浅湖更清澈。水的透明度也受到人类影响的显著影响(城市化，农业,和工业)在分水岭，高影响地区的大多数湖泊清晰度低或清晰度非常低。最后,我们使用原位测量数据来帮助解释影响整个加拿大透明度的潜在光学水柱成分，发现叶绿素a,总悬浮固体，和颜色溶解的有机物对不同生态区的水透明度都有强烈但不同的潜在影响。这项研究为进一步研究水柱光学特性与全国湖泊健康和脆弱性状况之间的关系迈出了重要一步。
