C Shivakumar/ Shiba Prasad Sahu
Chennai:
The
emerald green water of the Muttukadu lake that beckons many from
Chennai hides a dangerous truth: there is an algal bloom in the
backwater that gives it the colour, which, if left unchecked, has the
potential to seriously affect the marine ecology and the local
neighbourhood.
In a revelation that should sound alarm bells for authorities and
activists alike, a recently-published study has warned about a “harmful
algal bloom of the colonial form of microcystis aeruginosa,” considered
to be the one of the most cosmopolitan among the planktonic
cyanobacteria.
The bloom – a population explosion in other words – of this alga is
capable of producing a liver-damaging toxin which in high
concentrations could be fatal to humans, fish, birds and pets, warned
the study in the Indian Journal of Geo-Marine Sciences earlier this
year. It gives the opaque green colour, makes it slick and slimy, and
gives it that stench that visitors often complain about.
The reason: rapid urbanisation of the neighbourhood that has
brought industries, institutions and high-rises close to the estuary,
which bring with it sewage and effluents that has led to a spike in
inorganic nutrients nitrate and phosphate, that in turn make the warm
tropical water the perfect cocktail for the algae to bloom and colonise –
which in marine science parlance means the single cells can join
together in groups as colonies that tend to float near the surface.
The findings have understandably raised concerns among experts
about the threat it poses to aquatic organisms. “It is difficult to
control the alga due to letting out untreated sewage into the
backwater,” said a scientist from the Central Institute of Brackishwater
Aquaculture.
While fishermen have been complaining that the water has turned
toxic for nearly four years, the study by department of Marine Science
department in Bharatidasan University that was published in the journal
documents the first occurrence of a harmful algal bloom in the backwater
in June 2012. However, till now, the officials from the departments of
Tourism - that runs the boathouse - and the Public Works Department –
the guardians of the estuary – are largely unaware of the fact.
“When we saw the water turning out green, we believed it is due to
some chemical. We were not aware about the alga formation,” said an
official from the Tourism Department. According to him, the blame lies
on industries as well as residential buildings which discharge untreated
sewage into the water. Experts also cite excessive usage of fertilisers
for the spike in inorganic nutrients.
Highlighting the dangers posed by the presence of these nutrients
in water, yet another study, this time by the department of Zoology, Sir
Theagaraya College, Chennai, published in the International Journal of
Environmental Biology last year, states that nitrate, while being an
important nutrient, is toxic when in high concentration and can disturb
the aquatic environment.
While the acceptable limit is 0.5 mg/l, this study revealed that
the nitrate value was 8.07 mg/l in Muttukadu estuary and 5.11 mg/l in
the coastal water.
“The excess concentrations of nitrate and
nitrite will lead to excessive aquatic plant production, which may
negatively impact estuary water environments leading to deplete
dissolved oxygen and production of toxic algae. As a result of oxygen
depletion, sickness and death of marine organisms will take place,” the
study warns.
Importantly, both studies have found the presence of ammonia: the
first one blames it on the presence of sewage, and the latest study
cites the algal bloom as a possible reason. Also, the hydrogen ion (pH)
concentration – which controls the relative proportion of different
chemicals – is at a high level (7.85 ppm in the first study and 8.7 ppm
in the second). It would be fatal for fish if it goes above 10 ppm.
There were several reports of dead fish in the past, which the latest
study attributes to the algal bloom.
"The pollution abatement facilities like the sewage and domestic
waste treatment at Muttukadu area are inefficient, resulting in
indiscriminate discharge of waste into the backwaters. Present
investigation highlights the need of regular monitoring of harmful algal
blooms and the physico-chemical characteristics of the Muttukadu
backwaters in order to conserve the fish stocks and safeguards the human
beings," concludes the study on algal bloom.
Even as experts studies warn the impending danger awaiting the
estuary, officials admitted that they had no clear data on the level of
pollution.
An official said untreated sewage gets dumped in
the water body during midnight, and added that the culprits included
even some educational institutions into the neighbourhood.
“There has been no survey conducted by the pollution control board.
Even Directorate of Town and Country Planning turns a blind eye to the
mushrooming of illegal constructions. Many of them will not have Coastal
Regulation Zone clearance,” said an official from the Public Works
Department, the custodians of the backwater.
“We clean it up during three months of monsoon so that the mouth of
the lake opens and joins with the sea. Then the the colour of backwater
changes to the bright blue colour of the sea. But it lasts only for 15
days," he added.
According to him, the department lacks funds to clean up the lake,
and suggested that the Tourism Department and even the Salt Corporation,
which are earning revenue from the lake, should pitch in to help clean
up the water body.
“If the water body is to be brought to its original glory, then all
government institutions should work together, along with the support of
the local public," he added.
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