Spatio-Temporal Dynamics of Algae and Macrophyte Cover in Urban Lakes: A Remote Sensing Analysis of Bellandur and Varthur Wetlands in Bengaluru, India

Abstract

Rapid urbanization processes and indiscriminate disposal of urban wastewaters are major causes for anthropogenic lake-sediment deposition and eutrophication. However, information about the spatial and temporal variation of macrophyte and phytoplankton distribution as indicators for water contamination is limited. To gain insights into the dynamics, we analyzed lake-cover changes of Bellandur and Varthur Lake in the S-Indian megacity of Bengaluru for the post-rainy seasons of the years 2002–2019. Supervised maximum likelihood classifications were conducted on 62 freely available, true-color satellite images in order to distinguish between macrophytes, algae, and free water surface. The image-derived results were verified by supervised classification and manual mapping of two simultaneously recorded multispectral satellite images (Sentinel-2 and WorldView-2). Seasonal interrelations between macrophytes and algae distribution were similar for both lakes. The increase in macrophyte cover during post-rainy season negatively correlated with algal abundance. Macrophyte expansion progressively suppressed algae development at both lakes, reflective of increasing eutrophication caused by on-going wastewater input. Seasonal variation in precipitation, wind direction, and temperature seemed to trigger intra-annual shifts of macrophytes and algae while similar macrophyte spread intensities during the post-monsoon season indicated independence of nutrient loads in the lake water.

Water Quality and Water Hyacinth Monitoring with the Sentinel-2A/B Satellites in Lake Tana (Ethiopia)

“…Robust and consistent atmospheric correction is crucial for the retrieval of aquatic downstream science products from remotely sensed imagery [48]. Most previous studies on water hyacinth monitoring did not report on the atmospheric corrections algorithms applied, if any [34,35,49]. For example, the water hyacinth coverage in Lake Tana was processed using Sentinel-2 level 1 (TOA) products by Dersseh et al (2020) and using PlanetScope level 1 TOA products by Worqlul et al (2020) [26,37].…”

Understanding the Spatial–Temporal Patterns of Floating Islands Impacting the Major Dams of the White Nile

“…However, these studies do not examine the spatial-temporal variations of these islands. Nonetheless, other studies have enlightened the spatial-temporal dynamics of the floating islands across water bodies in Asia, e.g., [19,20]. Likewise, refs.…”

Identifying Urban Wetlands through Remote Sensing Scene Classification Using Deep Learning: A Case Study of Shenzhen, China

“…On the one hand, urban wetlands mostly exist in scattered forms [15], and the pixels containing these small wetlands in remote sensing images are easily mixed with other surrounding pixels [16]. On the other hand, urban wetlands exhibit special dynamic changes because they are affected by naturally and artificially controlled hydrological dynamics [17,18], making it difficult to fully identify the real-time coverage pixels of a wetland even when considering multitemporal remote sensing observations [19]. In fact, an urban wetland in a real environment is usually a scene composed of vegetation, water, tidal flats, and other land cover types, rather than a single, static land-cover type.…”