Abstract
Turbidity and water colour are two easily measurable properties used to monitor pollution. Here, we highlight the utility of a low-cost device—3D printed, hand-held Mini Secchi disk (3DMSD) with Forel-Ule (FU) colour scale sticker on its outer casing—in combination with a mobile phone application (‘TurbAqua’) that was provided to laymen for assessing the water quality of a shallow lake region after demolition of four high-rise buildings on the shores of the lake. The demolition of the buildings in January 2020 on the banks of a tropical estuary—Vembanad Lake (a Ramsar site) in southern India—for violation of Indian Coastal Regulation Zone norms created public uproar, owing to the consequences of subsequent air and water pollution. Measurements of Secchi depth and water colour using the 3DMSD along with measurements of other important water quality variables such as temperature, salinity, pH, and dissolved oxygen (DO) using portable instruments were taken for a duration of five weeks after the demolition to assess the changes in water quality. Paired t-test analyses of variations in water quality variables between the second week of demolition and consecutive weeks up to the fifth week showed that there were significant increases in pH, dissolved oxygen, and Secchi depth over time, i.e., the impact of demolition waste on the Vembanad Lake water quality was found to be relatively short-lived, with water clarity, colour, and DO returning to levels typical of that period of year within 4–5 weeks. With increasing duration after demolition, there was a general decrease in the FU colour index to 17 at most stations, but it did not drop to 15 or below, i.e., towards green or blue colour indicating clearer waters, during the sampling period. There was no significant change in salinity from the second week to the fifth week after demolition, suggesting little influence of other factors (e.g., precipitation or changes in tidal currents) on the inferred impact of demolition waste. Comparison with pre-demolition conditions in the previous year (2019) showed that the relative changes in DO, Secchi depth, and pH were very high in 2020, clearly depicting the impact of demolition waste on the water quality of the lake. Match-ups of the turbidity of the water column immediately before and after the demolition using Sentinel 2 data were in good agreement with the in situ data collected. Our study highlights the power of citizen science tools in monitoring lakes and managing water resources and articulates how these activities provide support to Sustainable Development Goal (SDG) targets on Health (Goal 3), Water quality (Goal 6), and Life under the water (Goal 14).
Highlights
Deterioration of water quality in rivers, lakes, and estuaries due to natural disasters such as landslides, floods, and pollution of various types and degrees, is a topic of interest to the public [1]
As we try to assess the impact of human activities on water quality and plan remedial and mitigation measures in the context of Sustainable Development Goals pertaining to water, it is essential to have simple, cost-effective methods for monitoring water quality, which can be achieved by the non-specialist
The Secchi depth increased progressively with time and reached more than 1 m in stations 2, 4, 5, and 7 within the duration of five weeks after demolition. It is evident from the paired t-test analysis (Table 1) that there is significant increase in the Secchi depth during the fourth (M = 0.69 ± 0.13, p < 0.05) and fifth (M = 0.97 ± 0.47, p < 0.05) weeks, compared with the second week post-demolition (M = 0.59 ± 0.16, p < 0.05)
Summary
Deterioration of water quality in rivers, lakes, and estuaries due to natural disasters such as landslides, floods, and pollution of various types and degrees, is a topic of interest to the public [1]. As the demolition and the subsequent pollution of the lake were of public concern, the clarity and colour of water in the Vembanad Lake in the vicinity of the demolished buildings was monitored using the 3DMSD [10] with help from local people volunteering in the programme, for four weeks after the court-mandated demolitions. We hypothesized that many basic water-quality indicators of Vembanad Lake would be immediately affected by the demolition process and that the circulation dynamics of the estuary would help in restoring normalcy with time This hypothesis was tested by assessing the percentage relative change in water quality between the weekly data sets collected for four weeks after demolition and comparing the post-demolition results with the situation at the same time the previous year. The results were compared with the turbidity values obtained from satellite remote sensing for affirmation
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