However, some of the data fails to support this: populations of freshwater macro invertebrates remain low, following a steady decline over many decades. Therefore while the overall tone of the report is one of optimism, some researchers have claimed that the data has been deliberately cherry-picked in order to present as positive a result as possible.
Of course, there are countless examples of interested parties skewing scientific data for their own ends, with government organisations and private corporations among the most common culprits. In this case, the recorded drop in nitrate levels has been promoted at the expense of the continued low population of small-scale fauna. You might well ask what use these worms, snails and insects are, but even a basic understanding of food webs shows that numerous native bird and freshwater fish species rely on these invertebrates for food. As I've mentioned so often the apparently insignificant may play a fundamental role in sustaining human agriculture (yes, some other species practice farming too!)
So what is it that is preventing the invertebrates' recovery? The answer seems to be an increase in photosynthetic cyanobacteria, or as is more commonly - and incorrectly known - blue-green algae. If it is identified at all, it's as a health food supplement called spirulina, available in smoothies and tablet form. However, most cyanobacteria species are not nearly as useful - or pleasant. To start with, their presence in water lowers the oxygen content, so thanks to fertiliser runoff - nitrogen and phosphorus in particular - they bloom exponentially wherever intensive farming occurs close to fresh water courses. Another agriculture-related issue is due to clearing the land for grazing: without trees to provide shade, rivers and streams grow warmer, encouraging algal growth. Therefore as global temperatures rise, climate change is having yet another negative effect on the environment.
Most species of cyanobacteria contain toxins that can severely affect animals much larger than fresh water snails. Dogs have been reported as dying in as little as a quarter of an hour from eating it, with New Zealand alone losing over one hundred and fifty pet canines in the past fifteen years; it's difficult to prevent consumption, since dogs seem to love the smell! Kiwis are no stranger to the phylum for other reasons, as over one hundred New Zealand rivers and lakes have been closed to swimmers since 2011 due to cyanobacterial contamination.
Exposure to contaminated water or eating fish from such an environment is enough to cause external irritation to humans and may even damage our internal organs and nervous system. Drinking water containing blue-green algae is even worse; considering their comparable size to some dogs, it is supposed that exposure could prove fatal to young children. Research conducted over the past few years also suggests that high-level contamination can lead to Lou Gehrig's disease, A.K.A. amyotrophic lateral sclerosis, the same condition that Stephen Hawking suffered from.
What research you might ask is being done to discover a solution to this unpleasant organism? Chemicals additives including copper sulphate and calcium hypochlorite have been tried, but many are highly expensive while the toxicity of others is such that fish and crustacean populations also suffer, so this is hardly a suitable answer.
A more elegant solution has been under trial for the past two years, namely the use of ultrasound to sink the blue-green algae too deep to effectively photosynthesise, thus slowly killing it. A joint programme between New Zealand and the Netherlands uses a high-tech approach to identifying and destroying ninety per cent of each bloom. Whereas previous ultrasonic methods tended to be too powerful, thereby releasing algal toxins into the water, the new technique directly targets the individual algal species. Six tests per hour are used to assess water quality and detect the species to be eradicated. Once identified, the sonic blasts are calibrated for the target species and water condition, leading to a slower death for the blue-green algae that avoids cell wall rupture and so prevents the toxins from escaping.
Back to the earlier comment as to why the report's conclusions appear to have placed a positive spin that is unwarranted, the current and previous New Zealand Governments have announced initiatives to clean up our environment and so live up to the tourist slogan of '100% Pure'. The latest scheme requires making ninety percent of the nation's fresh water environments swimmable by 2040, which seems to be something of a tall order without radical changes to agriculture and the heavily polluting dairy sector in particular. Therefore the use of finely target sonic blasting couldn't come a moment too soon.
Our greed and short-sightedness has allowed cyanobacteria to greatly increase at the expense of the freshwater ecosystem, not to mention domesticated animals. Now advanced but small-scale technology has been developed to reduce it to non-toxic levels, but is yet to be implemented beyond the trial stage. Hopefully this eradication method will become widespread in the near future, a small victory in our enormous fight to right the wrongs of over-exploitation of the environment. But as with DDT, CFCs and numerous others, it does make me wonder how many more man-made time bombs could be ticking out there...
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