PIANC Smart Rivers 2022

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Globally, heavy metal pollution in the lake ecosystem is a major concern, especially in developing countries. Water is a significant portion of the ecosystem and has ecological, social, and economic importance, providing habitat and nutritional resources for many aquatic species. These lake ecosystems have, however, been rapidly destroyed by anthropogenic activities. Industrial runoff, agriculture, transportation, atmospheric deposition, etc. contribute thousands of known and unknown hazardous contaminants to rivers, estuaries, and lakes. In recent years, there has been an increase in concern over heavy metal accumulating in China. Dolphins are well-known and highly respected residents of Chinese seas, where they play a vital part in the marine ecology. Humans have had a huge influence on dolphins and their surroundings over the years. The impact of heavy metals is particularly concerning due to the possible harmful consequences on marine life as well as the overall health and productivity of the ecosystem. Dolphins are at the top of the food chain, making them vulnerable to contaminants like heavy metals that may accumulate throughout the food chain.
Heavy metals, which may have accumulated through the food chain, are a particular concern because dolphins are long-lived and at the top of the food chain and are therefore susceptible to such pollutants. The effects of heavy metals on marine life may be acute or long-term, and may have a significant impact on the health and productivity of the entire ecosystem. 
In this study, Poyang Lake, a largest river-connected lake and China's largest freshwater lake, in the middle reaches of the Yangtze River was chosen as the research field. 
We investigated the heavy metals coming from four the sites; Kangshan, Benghu, Xingzi and Duchang to the Poyang Lake. The water of Poyang lake was tested in the year 2018 where the amounts of Arsenic, Selenium and Zinc were present at higher levels. The Poyang lake water was then tested in 2020 which showed high level of heavy metals added up in the coming years which were Mercury, Chromium, Selenium and Arsenic this was a matter of concern as heavy metals load has increased therefore in order to identify the sources that might be adding the potential load, Kangshan, Benghu, Xingzi and Duchang were selected. 
Heavy metal concentrations were experienced more in the water during the time periods that followed no rainfall and lead to a condition of draught. These time periods are considered to be more dangerous to the species living in the Poyang lake. Arsenic is observed to be high in the months of September-December due to lack of water in the lake, Zinc is experienced in high levels from January-March and Selenium from November-December. The year 2018 data showed less heavy metal concentration therefore we collected samples from the sites which were considered contributing towards deterioration of Poyang lake water as the sites had more industrial and agricultural runoffs. While comparing the data with the year 2018-2020, water quality was highly deteriorated as the levels of heavy metals had exceeded in the time period of two years which can be due to rapid development and excessive drainage in the water level. High amounts of Mercury and Chromium and Arsenic were observed in the months of April-June, Arsenic was also found in higher concentrations during the months of August-December which means that the concentration of Arsenic has considerably risen in the Poyang Lake, traces of Selenium were also detected in considerably larger amounts as compared to previous year where it was observed in negligible amounts
Water transparency decreased in the months December > April > September > March > August > October, November > June, July > May. The transparency of water was being effected by the presence of algal blooms which result due to the excessive amounts of nitrogen and phosphorous in the water. The presence of algal structures was identified by measuring chlorophyll-a which was highest in July > August > May > October > September > December > November March > June > April i.e. (0.00711 > 0.00688 > 0.00641 > 0.00617 > 0.00604 > 0.00578 > 0.00400 > 0.00348 > 0.00301 > 0.00276). 
Temperature of a waterway is significant because it affects the amount of dissolved oxygen in the water. 
As the water temperature increases, the Chemical Oxygen demand increases. Chemical Oxygen Demand is the total measurement of all chemicals (organics & inorganics) in the water; the chemical oxygen demand (COD) increases COD as shown in figure-9. This means that the periods of extreme rainfalls i.e. April- June receive a large amount of chemicals through runoffs of agriculture and industrial sites thus leading to the accumulation of heavy metals and production of algal blooms. Chemical Oxygen Demand was observed the lowest in the months of April and October followed by September and May, March and July, November and December i.e. (13.00, 16.00, 18.00, 20.00, 23.00) and was observed highest in the month of June i.e. (24.00).

The tissue distribution of heavy metals accumulated in the finless porpoise an endangered species was taken from a secondary study. When comparing the proportion/percentage of Hg present in different tissues of FP, we found that Liver has the highest amount of Mercury and Copper as compared to other major tissues of the FP.33.35 mg/kg of Hg of found in the major tissues of FP, out of which 73% was present in the liver, Zn was the dominant element in all tissues with a maximum mean concentration of 177.85 mg kg-1 dw in the liver.
 Overall, health risk assessment of trace elements in finless porpoises suggested that greater attention should be given to Hg, As, Cd, and Se.

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