Browsing by Subject "algal blooms"
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Item Global divergent trends of algal blooms detected by satellite during 1982–2018(Wiley, 2022-04) Fang, Chong; Song, Kaishan; Paerl, Hans W.; Jacinthe, Pierre-Andre; Wen, Zhidan; Liu, Ge; Tao, Hui; Xu, Xiaofeng; Kutser, Tiit; Wang, Zongming; Duan, Hongtao; Shi, Kun; Shang, Yingxin; Lyu, Lili; Li, Sijia; Yang, Qian; Lyu, Dongmei; Mao, Dehua; Zhang, Baohua; Cheng, Shuai; Lyu, Yunfeng; Earth and Environmental Sciences, School of ScienceAlgal blooms (ABs) in inland lakes have caused adverse ecological effects, and health impairment of animals and humans. We used archived Landsat images to examine ABs in lakes (>1 km2) around the globe over a 37-year time span (1982–2018). Out of the 176032 lakes with area >1 km2 detected globally, 863 were impacted by ABs, 708 had sufficiently long records to define a trend, and 66% exhibited increasing trends in frequency ratio (FRQR, ratio of the number of ABs events observed in a year in a given lake to the number of available Landsat images for that lake) or area ratio (AR, ratio of annual maximum area covered by ABs observed in a lake to the surface area of that lake), while 34% showed a decreasing trend. Across North America, an intensification of ABs severity was observed for FRQR (p < .01) and AR (p < .01) before 1999, followed by a decrease in ABs FRQR (p < .01) and AR (p < .05) after the 2000s. The strongest intensification of ABs was observed in Asia, followed by South America, Africa, and Europe. No clear trend was detected for the Oceania. Across climatic zones, the contributions of anthropogenic factors to ABs intensification (16.5% for fertilizer, 19.4% for gross domestic product, and 18.7% for population) were slightly stronger than climatic drivers (10.1% for temperature, 11.7% for wind speed, 16.8% for pressure, and for 11.6% for rainfall). Collectively, these divergent trends indicate that consideration of anthropogenic factors as well as climate change should be at the forefront of management policies aimed at reducing the severity and frequency of ABs in inland waters.Item Improving Remote Sensing Algorithms Towards Inland Water Cyanobacterial Assessment From Space(2021-09) Ogashawara, Igor; Li, Lin; Moreno-Madriñán, Max Jacobo; Druschel, Gregory K.; Hwang, Taehee; Wang, LixinWater is an essential resource for life on Earth, and monitoring its quality is an important task for mankind. However, the amount of water quality data collected by the traditional method is insufficient for the conservation and sustainable management of this important resource. This challenge will be exacerbated by increasing harmful algal blooms at the global scale. To fill this gap, Earth Observations (EO) have been proposed to help stakeholders make their decisions, but the use of EO for monitoring inland water quality is still in development. In this context, the main objective of this study was to improve the estimation of cyanobacteria via remote sensing data. To achieve this goal, the water type classification was first used to identify the dominant optically active constituents within aquatic environments. This information is crucial for understanding the optical properties of inland waters and selecting the best remote sensing algorithm for specific optical water types. The next research question was to develop a universal structure for retrieval of the inherent optical properties of several important aquatic systems around the world, which can be used as a corner stone for developing a globally applicable remote sensing algorithm. The third research topic of this dissertation is about removing the interference of chlorophyll-a with the absorption strength at 620 nm where phycocyanin exhibits its diagnostic absorption so that the estimation of phycocyanin concentration can be improved. Despite the novelty of the proposed remote sensing algorithms which are able to accommodate distinct water optical properties, there are abundant opportunities for improving the parameterization of the proposed models to retrieve inland water quality and optical properties when a global database of optical and water quality measurements is available. Considering the current advancement in spaceborne technology and the existence of a coordinate effort for global calibration and validation of remote sensing algorithms for monitoring inland waters, there is a high potential for operational assessment of harmful cyanobacterial blooms using the remote sensing algorithms proposed in this dissertation.Item Monitoring Phycocyanin with Landsat 8/Operational Land Imager Orange Contra-Band(MDPI, 2022-03-19) Ogashawara, Igor; Li, Lin; Howard, Chase; Druschel, Gregory K.; Earth and Environmental Sciences, School of ScienceThe Operational Land Imager (OLI) onboard the Landsat 8 satellite has a panchromatic band (503–676 nm) that has been used to compute a virtual spectral band known as “orange contra-band” (590–635 nm). The major application of the orange contra-band is the monitoring of cyanobacteria which is usually quantified by the measurement of the concentration of phycocyanin (PC) which has an absorption peak around 620 nm. In this study, we evaluated the use of the orange contra-band approach for estimating PC concentration from in situ proximal hyperspectral data from Eagle Creek Reservoir (ECR), in Indiana, USA. We first validated the empirical relationship for the computation of the orange contra-band by using the panchromatic, red, and green spectral bands from ECR. PC concentration retrieval using the orange contra-band were not successful when using the entire dataset (R2 < 0.1) or when using only PC concentrations higher than 50 mg/m3 (R2 < 0.24). Better results were achieved when using samples in which PC was 1.5 times higher than the chlorophyll-a concentration (R2 = 0.84). These results highlighted the need for the development of remote sensing algorithms for the accurate estimation of PC concentration from non-PC dominant waters which could be use to track and/or predict cyanobacteria blooms.