**1. Introduction**

Reservoirs are significant freshwater reserves that have experienced severe, negative effects that have changed their physico-chemical composition both qualitatively and quantitatively. These changes have, in turn, had an impact on the fauna and flora [1]. With the growth of industry and agriculture, there was a significant increase in the nutrient inputs into rivers and lakes, which led to the eutrophication of the water bodies [2]. Due to the readily available nutrients in lakes, algal blooms have become more frequent, intense, and widespread around the world in recent years. Information on the algal composition and dominance in a body of water can provide insight into the dynamics of toxin-producing species such as cyanobacteria. A change in the algal population can have serious environmental consequences, especially when there is an increase in harmful species. The cyanobacteria that produce cyanotoxins endanger both the aquatic ecosystem and human health. To evaluate and reduce the impact of potentially harmful species, it is crucial to monitor and model algal blooms and their composition. A significant group of organisms known as cyanobacteria are in charge of eutrophication-related environmental issues [3]. Although other factors such as water temperature, pH, light, and dissolved oxygen also have an impact on cyanobacteria reproduction, the availability of nutrients plays a major role in this process. Among the factors affecting water quality (such as pH, conductivity, nitrate nitrogen, phosphorus, etc.) dissolved oxygen (DO) levels are one of the most crucial general health indicators when evaluating aquatic ecosystems [4]. For the health of aquatic

**Citation:** Mudaliar, A.; Pandya, U. Assessment of Cyanobacterial Chlorophyll A as an Indicator of Water Quality in Two Wetlands Using Multi-Temporal Sentinel-2 Images. *Environ. Sci. Proc.* **2023**, *25*, 68. https://doi.org/10.3390/ ECWS-7-14252

Academic Editor: Athanasios Loukas

Published: 16 March 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

life, inland waters must maintain high DO levels. Aquatic organisms experience negative effects on metabolic activity, predation risk, and behavior when DO concentrations drop to low thresholds (below 5 mg/L) [5].

The Water Policy Framework can be improved by new technologies and methods that have been developed in recent decades. Blue-green algae or cyanobacteria in particular can be found using spectrometric sensors carried by satellites to monitor phytoplankton growth and composition [6]. Sentinel-2 data, which operates at spatial resolutions of 10 m, 20 m, and 60 m and collects data from 13 different wavelengths, is proving to be very helpful for monitoring blue-green algae blooms in aquatic environments. Based on measurements of their primary pigments Chl-a and phycocyanin, these measurement zones have interesting applications in the evaluation of phytoplankton and cyanobacteria [2,7–10]. Temperature is another crucial indicator of water quality that can be determined using satellite imagery in addition to dissolved oxygen measurement.

An earlier investigation revealed that human activity is to blame for the decline in Wadhwana's water quality [11]. Therefore, the purpose of this study was to estimate chlorophyll a using multi-temporal Sentinel-2 data along with dissolved oxygen and temperature to comprehend the current water quality of two wetlands in the Vadodara District.

### **2. Study Area**

Vadodara is a city in the state of Gujarat. It is 39 meters above mean sea level and can be located at 22◦1759 North Latitude and 73◦1518 East Longitude. The Wadhwana Reservoir was constructed in 1910 in what is now Vadodara, formerly known as the Baroda State. The Wadhwana Wetland (Figure 1), in the Dabhoi taluka, is one of the Ramsar sites and is well known among bird watchers in the state. On a global scale, the wetland is significant for its bird life because it provides a wintering habitat for migratory waterbirds, including more than 80 species that migrate along the Central Asian flyway. The middle of winter in 2020 saw the completion of a waterbird census, which counted about 46,000 different species. The wetland serves as an international example of how a wetland originally developed for irrigation has evolved into an important habitat for water birds and a center for ecotourism and nature education. The wetland is used as a global illustration of how a wetland that was initially developed for irrigation has transformed into an essential water bird habitat and a hub for ecotourism and nature education.

Following Wadhwana, Lake Timbi is the largest lake. It attracts many migratory birds. However, both wetlands are under threat from large amounts of irrigation water and other industrial wastewater. Consequently, the aquatic life in these wetlands is in danger.

**Figure 1.** Study area (**a**) Timbi wetland in Waghodia Taluka and (**b**) Ramsar site- Wadhwana Wetland.

### **3. Materials and Methodology**

In this investigation, measurements and water samples were collected in April 2018. Random sampling was used to gather samples from various locations in the wetlands of

Wadhwana and Timbi. Dissolved Oxygen was extracted following the standard procedure by the American Public Health Association [12].
