Department of Geography, University of Georgia, Athens, GA, USA.
Department of Geography, University of Georgia, Athens, GA, USA.
Sci Total Environ. 2021 May 20;770:145235. doi: 10.1016/j.scitotenv.2021.145235. Epub 2021 Jan 20.
Cyclones can produce a wide variety of short-term and long-term ecological impacts on coastal lagoons depending on cyclone's physical-meteorological characteristics and the lagoon's geographic, geomorphic, and bathymetric characteristics. Here, we theorized that in monsoon regulated tropical coastal lagoons, another important factor that could determine the impact of a cyclone is the landfall season or time of the year with reference to the monsoon season. We analyzed the impact of two cyclones which made landfall near Chilika, Asia's largest brackish water lagoon in different seasons, Cyclone Fani and Titli before and after the monsoon season. We compared field measured and satellite-derived water quality parameters including nutrient, salinity, water temperature, transparency, Chlorophyll-a (Chl-a), total suspended matter (TSM), and colored dissolved organic matter (CDOM) before and after the cyclones. We found that although both the cyclones were of similar intensities, after their land interaction, their impact on the lagoon's water quality was contrasting. The post-monsoon cyclone produced a substantial increase in total nitrogen (TN) and total phosphorous (TP), a large drop in salinity, CDOM, and Chl-a. In contrast, after the pre-monsoon cyclone, TN and TP did not show any such hike, no substantial change in salinity and CDOM either, and only a slight increase in Chl-a was observed. We found that the controlling factor in determining the impact of a cyclone is the rate and duration of freshwater discharge to the lagoon, which is normally a strong pulse for pre-monsoon and a continued high flow for post-monsoon cyclones. We conclude that the antecedent conditions of the lagoon and the watershed at the time of a cyclone's landfall is a key criterion in determining the impact. The combined use of satellite data and field data was proved critical to capture the overall impact of cyclones on the hydrological characteristics of the monsoon-regulated coastal lagoon.
旋风会根据旋风的物理气象特征和泻湖的地理、地貌和水深特征，对沿海泻湖产生各种各样的短期和长期生态影响。在这里，我们推断，在季风调节的热带沿海泻湖中，另一个可能决定旋风影响的重要因素是与季风季节相关的登陆季节或一年中的时间。我们分析了两个在不同季节登陆 Chilika 的旋风的影响，Chilika 是亚洲最大的咸水泻湖。这两个旋风分别是 Fani 和 Titli，在季风前后。我们比较了在旋风前后通过现场测量和卫星获得的水质参数，包括营养物、盐度、水温、透明度、叶绿素-a (Chl-a)、总悬浮物质 (TSM) 和有色溶解有机物质 (CDOM)。我们发现，尽管这两个旋风的强度相似，但在登陆后，它们对泻湖水质的影响却截然不同。后季风旋风导致总氮 (TN) 和总磷 (TP) 大量增加，盐度、CDOM 和 Chl-a 大幅下降。相比之下，在前季风旋风之后，TN 和 TP 没有出现任何这种增加，盐度和 CDOM 也没有明显变化，只有 Chl-a 略有增加。我们发现，决定旋风影响的控制因素是泻湖淡水排放的速度和持续时间，这通常是前季风的强烈脉冲，而后季风旋风则是持续的高流量。我们得出的结论是，泻湖和旋风登陆时流域的前期条件是决定影响的关键标准。事实证明，卫星数据和现场数据的结合对于捕捉旋风对季风调节沿海泻湖水文特征的综合影响至关重要。
