Anthropogenic activities have been putting our aquatic life under constant stress! With the rise in greenhouse gas emissions and the corporates and governments defaulting on their emission mitigation pledges, the concentration of carbon dioxide — a gas which traps heat — has been rising in the atmosphere, contributing to the phenomenon of global warming. The warmer ocean water and increased CO2 levels have led to ocean acidification which has been weakening shelled animals and drastically affecting their population. Other activities such as dredging for oil and gas exploration, increasing sea traffic and military exercises have wreaked havoc on marine life with high-level noise pollution. Additionally, the enrichment of water bodies with various nutrients have not only been suffocating the aquatic life by a process known as Eutrophication but have also been deteriorating the quality of water.
When salts of minerals or nutrients — especially of Nitrogen and Phosphorus — enrich rivers, lakes and oceans, this stimulates an overgrowth of various algae and aquatic vegetation or phytoplankton in the water which can cause several issues for the aquatic biodiversity. This algal bloom or eutrophication has harmful ecological consequences which decrease biodiversity, skews species composition and dominance and may even have toxic effects. With algal bloom covering the surface of water bodies, the sunlight reaching the bottom-dwelling vegetation and animals gets limited or restricted. What’s more, the overgrowth may also deplete oxygen dissolved in water at some regions; the bacteria and other micro-organisms which feed on and decompose the dead masses of algae and overgrown vegetation may result in a dramatic reduction of oxygen in the water bodies, sometimes creating dead zones where no life can exist! In addition to making the water bodies deprived of oxygen and killing fish and other aquatic life, the process of eutrophication can cause toxic effects on plants and animals by “harmful algal bloom”. Further, with loss of desirable fish species and harvested shellfish, the livelihood of communities depending on fisheries and aquaculture product is severely impacted as well.
Most of these nutrients salts in the water bodies are a result of poor agricultural or farming practices and unethical waste disposal from industries. The run-offs from agricultural lands form the main source of nitrogen pollution, whereas the emission from households and industries contribute to phosphorus pollutants. Phosphorus is often the limiting nutrient in the freshwaters, while nitrogen is the key limiting nutrient in the marine water. Scientists and researchers warn that with the current rate, the eutrophication or greening may boost the emission of a greenhouse gas like methane in our atmosphere, somewhere by 30 to 90 per cent, over the next the century. As the population of the world continues to grow and is expected to increase by 50 per cent in the next seventy-eighty years, more agricultural run-off and more sewage will keep on adding to eutrophication. With incidents of extreme weather events like storms and floods increasing, the run-off from land will enrich more in-land water with nutrients. Warmer water boosts algal production, which would mean more methane emitting surface waters; this will further accelerate climate change.
A growing concern, eutrophication in water bodies has not only added to our already worsening climate change but it has also put the life of aquatic animals and plants at risk. Coastal communities, especially in the poorer and developing nations will bear the brunt the most. To reverse the greening or eutrophication, improving the nutrients management practices is the need of the hour. This will not only reduce methane production but will also increase oxygen in the affected regions.