Les amphibiens contre les pluies acides

Dans les lacs du sud de la Nouvelle-Écosse, la disparition des grenouilles et des salamandres s’enclenche avec les pluies acides. La toxicité des pluies n’affecte pas les amphibiens adultes ; ce sont les œufs qui en sont mortellement atteints. Un contenu toxique trop élevé empêche la croissance des œufs, stoppant définitivement leur développement.

En dépit de l’acidité contenu dans les étangs, les adultes reviennent à chaque année pondre leurs œufs dans le même milieu. Ils ne tiennent pas compte du nombre d’œufs qui n’ont pas pu se développer les années précédentes. En définitive, cela veut dire qu’il n’y aura plus de grenouilles ou de salamandres dans milieux trop acides après la mort des adultes.

Il y a cependant une lueur d’espoir. Le Canada et les États-Unis se sont déjà entendus pour réduire davantage la toxicité des pluies dans le nord-est du continent.

Pickled Eggs and
Frogs' Legs

John Brownlie
Naturalist

January 1999

 

n.gif (432 bytes)o. This is not what I ordered last night at the new bistro in Moncton. Eggs and legs are two of the reasons for the disappearance of frogs and salamanders in Canada.

In western Canada, legs ARE on the menu, and over-collection of pickerel frogs, together with a disease called "red leg", has caused a dramatic decline in their population.

eggs.gif (974 bytes) ==========
Frogs Eggs
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Here in the east the problem is toxic rain, better known as acid rain. It's not toxic to adult frogs and salamanders, but it's deadly to their eggs. The result is "pickled eggs" -- eggs that never develop, never hatch.

I was shocked last week to discover that the most acidic rainfall in New Brunswick (in the whole of maritime Canada, in fact) falls in Fundy National Park!! Wow! I guess that's why the wardens have been carefully watching over our frogs and salamanders for about 15 years now. Every spring they check the breeding ponds for pickled eggs. So far--none.

The only pickled frogs eggs we've had in Fundy have been in Caribou Lake at the bog. Here, the acidity is natural -- it seeps out of the bog. Occasionally, a few wood frogs wander over from Little Caribou Lake nearby and lay their eggs in Caribou Lake by mistake. These eggs never develop -- "pickled eggs".

Even though the most toxic rain falls here in southern New Brunswick, we have the good fortune of having calcium in our rocks and soils. This calcium buffers or counteracts the acidity of the rain, keeping our ponds and lakes from becoming too acidic.

frogtailnotabsorbed4-b.jpg (15544 bytes)
(photo: Minnesota Pollution Control Agency)
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Tail not
absorbed:
(not fully developed)
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The biggest problem is in southern Nova Scotia where the granitic soils have no calcium to buffer the toxic rain. Lakes in southern Nova Scotia are the most acid-sensitive lakes in the Maritimes, and they are the focus of attention in workshops happening right now as I write this (January 1999).

Canada and the United States have been working hard for the last 20 years to reduce toxic rain by switching to other fuels and installing pollution control devices on smokestacks. We have successfully reduced our acidic emissions by more than half since 1980. This means that 90% of the lakes in the Maritimes are doing well. What about the other 10% -- those most acid-sensitive lakes in southern Nova Scotia?

Well, Canada and the U.S. have already agreed to further reduce toxic rain in the northeast. The January workshops happening now are designed to figure out how to attack the problem using the most modern science available. Hopefully, within the next 20 years, we'll be able to say that all the lakes in the Maritimes are safe from acid rain.

Now, let's get back to frogs and salamanders for a bit. They don't watch over their eggs like birds do. Once laid, the eggs are left to develop on their own while the adults return to other froggy activities. And it's a risky world out there. If there's a cold snap, some eggs will freeze at the surface of the pond. If it's a dry spring, the pond may dry up before the frogs and salamanders fully develop -- sometimes even before the eggs hatch. Or you may have a lot of red mites or caddis worms in your pond -- they love to eat amphibian eggs. Maybe you live in southern Nova Scotia and your pond or lake has become acidic from toxic rain.

Whatever the risk, the adults never know what happened last year. They continue to come back every year to the same pond or lake to mate and lay eggs, regardless of how many eggs made it last year. So, amphibian populations can fluctuate wildly from year to year. But over the long term, the population remains.

After 20 years of laying eggs in an acidic lake, however, the adult stops returning. Not because she realizes the water is too acidic, but because that is her lifespan -- about 20 years. And if no eggs have hatched in the past 20 years, the population disappears.

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Frog
with extra
leg,
due to
toxins
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frog
(photo:M.P.C.A.)

So, by the year 2020, we hope to have corrected our toxic rain problem and even those most acid-sensitive lakes in southern Nova Scotia will be safe from acid rain. Of course, by then, wood frogs, spotted salamanders and perhaps other species of amphibians will have already disappeared.

But there will still be people like me around who love frogs and salamanders; who like to hear them singing in the spring and who observe their mating rituals in breeding ponds. These people will re-introduce amphibians to ponds and lakes from which they have disappeared.

In the meantime, your job and my job is to reduce our consumption of oil, gas, and coal (cars, home-heating, electricity). Important also is to continue to appreciate frogs and salamanders where they still survive, and to introduce others to the joy of watching and listening to these creatures. For only by making nature a part of our lives will we be able to truly protect it. the end