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From: mrh@cybvax0.UUCP (Mike Huybensz)
Newsgroups: net.sci,net.bio
Subject: Re: Acid rain damage query
Message-ID: <1036@cybvax0.UUCP>
Date: Tue, 29-Apr-86 11:59:27 EDT
Article-I.D.: cybvax0.1036
Posted: Tue Apr 29 11:59:27 1986
Date-Received: Fri, 2-May-86 23:44:27 EDT
References: <202@brl-smoke.ARPA>
Reply-To: mrh@cybvax0.UUCP (Mike Huybensz)
Distribution: net
Organization: Cybermation, Inc., Cambridge, MA
Lines: 55
Xref: watmath net.sci:775 net.bio:427

In article <202@brl-smoke.ARPA> wmartin@brl-smoke.ARPA (Will Martin ) writes:
> Publicity about acid rain indicates that some types of pollution cause
> rainfall to become acidic enough that lakes which collect such rainfall
> eventually themselves turn acidic enough to kill off the natural biota
> and become nearly sterile. How acidic is this?

Without checking textbooks, I'd say that natural pH's of the subject lakes
are around 6 to 8, and the damaging pH's range from 4 to 6.  Keep in mind
that the pH measurement is the negative log of the concentration: a pH of
5 means a hundred times more hydrogen ions than a pH of 7.

> How acidic is this? I ask this because of a
> fact mentioned in the recent PBS National Geographic special on the
> Okeefenokee swamp -- the statement was made there that this swamp water
> was "as acid as strong tea".

Tea is a good comparison: the brown color of swamp and bog waters results
from the dissolving of tannic acids from leaves (and humic acids from soils.)

> Yet, even though acidic, this area teems
> with life. Are the lakes damaged by acid rain more acidic than this
> swamp water? If not, is it just because they are in colder climates that
> the (seemingly) acid-tolerating lifeforms that flourish in the acid
> swamp cannot live in these more-northerly acidified lakes? Or could such
> acid-tolerating biota be introduced into those lakes and create a new
> ecosystem that could survive the acidification? (And that this would
> happen naturally, given long enough time, but these areas are sterile
> now just because the acid-tolerating biota haven't yet been introduced?)

Acid rain doesn't make lakes more acid than some naturally occuring lakes
and swamps: the problem is that it does so suddenly, killing off organisms
which are not adapted to changes in pH.

In general, northern lakes tend to have simpler ecosystems with less biomass
than southern.  Less biomass means less ability to buffer the environment.
Swamps are where (among other things) organic matter carried downstream
gets deposited, making them very butrient rich.

Acid-tolerant species tend to come from waters with nutrient-rich sources of
organic acids.  Acidified lakes don't have those nutrients: their acids come
from inorganic sources such as rainfall.

There tends to be very little natural exchange of species between freshwater
rivers, lakes, and streams.  Much of the natural distribution of fish, clams,
etc. is due to the history of retreat of the last glaciation.  It is very
unlikely that acid-tolerant fish would spread into acidified lakes naturally;
other organisms (such as plants) might be more likely.

We could try to construct new ecosystems in the acidified lakes by the
introduction of tolerant species.  But changing an entire regional fauna
as a patch-job for a preventable side-effect of our industry doesn't sound
like a wise idea to me.
-- 

Mike Huybensz		...decvax!genrad!mit-eddie!cybvax0!mrh