An earthquake, low dissolved oxygen, and mass fish death in Kameng river, Arunachal - an update
Arunachal river witnesses mass fish death - An analysis
- The story: It emerged that landslides caused by an earthquake of 3.4 magnitude close to the border with China led to mass fish death in the Kameng river in Arunachal Pradesh. The region is placed into Seismic Zone V, the 'most vulnerable' to earthquakes.
- Details of the incident: The earthquake happened near the source of the river at an elevation of about 6,300 metres above Mean Sea Level (MSL).
- The resulting landslides dumped several tonnes of mud and rocks into the river, substantially reducing the flow of water. As a result, the river turned blackish due to very high turbidity resulting in low dissolved oxygen (DO) that killed the fish.
- Low dissolved oxygen concentrations can arise through natural phenomena that include seasonality, changes in river flow, and both saline and thermal stratification of the water column.
- Low dissolved oxygen levels can also indicate an excessive demand on the oxygen in the system.
- Dissolved oxygen: Dissolved oxygen refers to the level of free, non-compound oxygen present in water or other liquids. It is an important parameter in assessing water quality because of its influence on the organisms living within a body of water. In limnology (the study of lakes), dissolved oxygen is an essential factor second only to water itself. A dissolved oxygen level that is too high or too low can harm aquatic life and affect water quality. Non-compound oxygen, or free oxygen (O2), is oxygen that is not bonded to any other element.
- Dissolved oxygen is the presence of these free O2 molecules within water.
- The bonded oxygen molecule in water (H2O) is in a compound and does not count toward dissolved oxygen levels. One can imagine that free oxygen molecules dissolve in water much the way salt or sugar does when it is stirred.
- Dissolved oxygen is necessary to many forms of life including fish, invertebrates, bacteria and plants. These organisms use oxygen in respiration, similar to organisms on land. Fish and crustaceans obtain oxygen for respiration through their gills, while plant life and phytoplankton require dissolved oxygen for respiration when there is no light for photosynthesis. The amount of dissolved oxygen needed varies from creature to creature. Bottom feeders, crabs, oysters and worms need minimal amounts of oxygen (1-6 mg/L), while shallow water fish need higher levels (4-15 mg/L).
- Dissolved oxygen enters water through the air or as a plant byproduct. From the air, oxygen can slowly diffuse across the water’s surface from the surrounding atmosphere, or be mixed in quickly through aeration, whether natural or man-made. The aeration of water can be caused by wind (creating waves), rapids, waterfalls, ground water discharge or other forms of running water. Man-made causes of aeration vary from an aquarium air pump to a hand-turned waterwheel to a large dam.
- Dissolved oxygen is also produced as a waste product of photosynthesis from phytoplankton, algae, seaweed and other aquatic plants.
- Kameng River: It originates in Tawang district from the glacial lake below snow-capped Gori Chen mountain on the India-Tibet border, and is not a transboundary river. It flows through Bhalukpong circle of West Kameng District, Arunachal Pradesh and Sonitpur District of Assam, and becomes a braided river in its lower reaches and is one of the major tributaries of the Brahmaputra River. It joins Brahmaputra river at Tezpur, just east of the Kolia Bhomora Setu bridge, Assam. Tributaries are the Tippi, Tenga, Bichom and Dirang Chu. Between 13th to early 16th century, it marked the borders between the Chutiya kingdom and the Kamata kingdom. Later, after the annexation of the Chutiya kingdom by the Ahoms and the downfall of Kamata kingdom, it acted as the border between the Ahom kingdom and Baro-Bhuyan rule. (The Chutiya Kingdom (also Sadiya) was a late medieval state that developed around Sadiya in present Assam and adjoining areas in Arunachal Pradesh)
- Summary: The power of nature is often beyond human comprehension, and the best man can do it to mitigate once things turn sour.
- EXAM QUESTIONS: (1) Explain the idea of DO - dissolved oxygen - and how earthquake like incidents can be fatal for fish living in rivers. (2) Explain the range of natural disasters that can affect marine life.
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