Australian bushfire and its impact on Water Bodies

Overview:

The Australian bushfire in late 2019 and early 2020 had created many environmental issues. The fire has released a large number of aerosol particles into the air which eventually affected the South Pacific Ocean. Researchers had done many satellite observations and surveyed the coastal deposition of these particles and their biochemical reaction to the water. Four types of aerosol particles were detected: wildfire smoke, mineral dust, background aerosols and residual smoke. In the Tasman Sea, in November 2019 it was concluded that 60% of mineral dust was made up of coarse particles. 

After the wildfire, these particles had affected a large amount of the atmosphere in eastern Australia, Southern Pacific water and even South America. 98.9% of smoke was made up of fine particles. These mineral dust and smoke particles emitted from the fire changed the composition of the surface ocean. The decomposition of these mineral particles resulted in an increase in the concentration of chlorophyll-a by 23.3% in just 8 days. These external particles were found at a depth of 64.7 m, resulting in the growth of chlorophyll-a in deep water also. It took around two months to recover the normal concentration of chlorophyll in the water. 

Detailed Analysis:

The high temperature and series of extreme droughts resulted in a massive bushfire in 2019-20. An estimated loss of 20 billion dollars was occurred due to this fire. Apart from the economic impact, the dust particles and smoke released into the atmosphere created a lot of side effects on human health. The quality and visibility of the air were also severely damaged. The fire has released a lot of nutrients like nitrogen, phosphorous and iron into the atmosphere. When these nutrients mix with ocean water, it directly affects the marine ecosystem. These nutrients damage the carbon exchange rate in deep water, which eventually create long term climate change. 

The addition of heavy metal like iron in the ocean water increases the growth of phytoplankton. It was concluded from a number of studies that the dissolved aerosols in the water had a large proportion of iron. Also, the atmospheric mineral dust had around 3% of iron by mass and a small amount of soluble iron, most probably Fe(II). The Fe deposited from direct emission from combustion sources and atmospheric pollutants played a vital role in ocean fertilisation. Ocean fertilisation is the addition of additional nutrients in the surface water which alters the phytoplankton growth rate.

 In the oligotrophic regions, there is a lack of natural nutrients. So the deposition of atmospheric nutrients is more likely to affect the water. A hypothesis is created that the bushfire might have resulted in the ocean fertilisation of the global oligotrophic ocean area. 

Results from various studies:

The results from the observations by Moderate Resolution Imaging Spectroradiometer (MODIS) showed that the bush fire of 2019-20 had a greater impact on climate than the previous fires of 2012-13 and 2014-15. The fire of 2019-20 released about 8500 Gg (Gigagrams) and 17,320 Gg carbon into the atmosphere in November 2019 and January 2020 respectively. A detailed analysis of pollution was done through satellite imaging. During November 2019 and January 2020, the coastal areas reported a large number of particles released due to bushfire. The results showed that the eastern coast and South Pacific ocean were greatly affected till mid-February 2020. Furthur surveys showed that the winds of the eastern coast carry a large proportion of pollutants. 

The uncontrolled emission by bushfire in Victoria was quickly spread to south-eastern Australia and covered the Tasman Sea and New Zealand. The satellite images showed that the pollutants reached South America in December 2019. By late January, the emission was carried up to Chile and Argentina.

The concentration of deposited particles on the surface water was the highest for the past 18 years. The fire released a huge amount of carbon dioxide. Ocean water will absorb a large volume of the release of CO2. This will increase the carbon dioxide concentration in water and will make oceans even more acidic. The species which depends on calcium (like corals and shellfish) are not used to the acidic water. Ocean Acidification will damage their growth rate and reproduction rate. A wide range of Australian seafood animals like oysters, abalone, scallops etc depends on calcium. Thus the emitted carbon dioxide from the bushfire will indirectly affect the fisheries and marine food chain. 

The coastal marine ecosystem is greatly damaged due to bushfire. The sediments and solid debris from the bushfire can travel many kilometres inside the water, damaging the deepwater species. The ash and smoke from bushfire also contain heavy metals like copper, lead, zinc etc. These metals could affect marine species by changing their physiological behaviour, eventually damaging the food chain. The dissolved ash and solid debris also affect the breeding and feeding area of many fishes. Fishes were forced to leave their breeding area due to polluted surface and deep water.

Another problem from the increased heavy metals and nutrients is algae blooms. The sudden growth in the population of surface algae will blanket the surface ocean. This will prevent the sunlight from reaching deep water and eventually damaging the photosynthetic activities of seafloor plants like seaweeds. Seagrass and corals are already facing many problems due to heat stress and climate change. The polluted water and increased nutrients will further increase their problems. The dissolved ash has risked the survival of many freshwater fishes.

The fishing industry has also faced a great economic loss. Most of the fishing activities are done in the coastal areas. The polluted coastal water has damaged these activities. In many areas, the coastal water was turned black due to a high concentration of dissolved ash. Fishes do not tend to survive longer in such polluted water. 

Apart from ocean water, the pollutants from bushfire have contaminated many freshwater sources. A large volume of drinking water from natural sources was damaged due to the pollutants. The ash, aerosols and other debris increase the turbidity of water of river or stream. This has decreased the photosynthesis activity of freshwater plants and has killed many fishes. Fishes got no place to lay eggs in such polluted water. Also according to one study, the dissolved pollutants and ash have damaged the gills of fish. The sudden increase in the death rate of freshwater fishes greatly affected the food chain. The growth of bacteria and algae was also observed in the freshwater sources due to bushfire. In late January, a red alert was given around the areas of Murray -Darling basin due to blue-green algae blooms.

After the fire, the nitrogen level was doubled, the phosphorus level was increased fourfold and mercury was increased fivefold in many lakes. Mercury now has moved up in the food chain. If not stopped or controlled, soon the mercury will start to enter the human body. After the bushfire, the Australian rivers were having more nutrients than ever. 

A series of bushfires in the last few decades has greatly damaged the marine ecosystem and freshwater bodies of Australia. We cannot stop the bushfire to occur, but we can try to minimize the damage after the fire.