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As hobbyists, many of us pride ourselves on making the
conditions for our finned friends as accurate as possible. We
recognize the fact that these creatures (particularly wild specimens) are used to a particular type of waters and water
quality. So we mix our concoctions to correct our hardness and pH
values, we set our heaters to where they need to be, we perform our
water changes, we diligently watch our water quality values, we feed
what foods we believe to be the “best”. Regardless, there seems
to be confusion generated on the hobbyist is trying to accomplish
when they wish to create an appropriate biotope. The question being,
how close can you really get to natural water values in the confines
of aquaria? Is it really possible to recreate the native waters? How
alike are the Lakes in reality? Are they alike enough to mix
species?
To get a better idea, it helps to know what you are, in
actuality, shooting for and what can, and cannot, be accomplished.
It may come as a surprise as to how different the Lakes really are,
as well as where the similarities lie.
In hopes to clear up some confusion, we will explore the
three main Rift Lakes known to most cichlid keepers, Malawi,
Tanganyika, and Victoria from a physical and chemical point of view.
Lake
Malawi
It seems that more has been written and is known about Lake
Malawi by the average African cichlid keeper than any other Lake.
This is hardly surprising, as it is home to an estimated 600 species
of fish, more than any other lake in the world. Of the 200+ recorded
species, roughly 80% of these are endemic.
Lake Malawi is the southern most and the third largest of the
east African Rift valley Lakes, with a length north to south of
around 595.5 km, and width varying from 16-80.5 km. In addition to
being one of the largest Rift Lakes, it is also one of the oldest
freshwater lakes in the world having existed in one form or another
for nearly a million years, a major contributing factor in its
biodiversity.
This being said, the chemistry of Malawi is rather simplistic
(in comparison to Lakes such as Tanganyika, anyway). Lake Malawi,
like Victoria, receives most of its water from either direct run off
or from one of its many low salinity tributaries, and the chemistry
is rather “reasonable”. What this means for you is, if you were
to begin with neutral water or moderate GH and KH, is ideally less
“tinkering” with water parameters as would be required for
Tanganyikan water. With Malawi being such a large body of water, it
should not come as a surprise that the pH values are rarely agreed
upon, with values ranging from 7.7-8.8, depending upon where you
look it up. Frankly, it makes me want to fly out to Africa armed
with a pH tester, but luckily for me, Francesco has already done so!
To see what he found, click here.
With Malawi water, you are basically dealing with water that
is high in sodium (~21.0mg/L), calcium (~ 16.4-19.4 mg/L), magnesium
(~4.7-8.8 mg/L), chloride (~4.0mg/L), and sulfate (~5.5 mg/L), while
being surprisingly low in carbonates and bicarbonates (~2.4-2.6 meq/L).
To see a full table of these values and some of the ones I will
mention for Victoria and Tanganyika, as well as a nice article on
Rift Lake water chemistry, see Michael Oliver’s
What
is the Chemical Composition of Lake Malawi Water?
Lake
Victoria
Most who know of Lake Victoria are at least a little familiar
with the crisis it is experiencing.
Described as “smelly, murky, and chocked with algae” (People and the
Planet), Victoria’s problems are blamed on a
combination of a rapidly growing population, clearing of shoreline
vegetation, fish-export industry, dumping by industries, and the
disappearance of several native fish species. The last of which can
be largely contributed to the introduction of the Nile perch, which
has resulted in a loss of nearly half the cichlid species population. The Nile perch was
introduced, along with the Nile Tilapia, when over fishing became a
problem. The Nile perch can grow
to 1.8 meters, 90.7 kg., and feeds primarily on smaller fish. When
you are that large, just about anything is “smaller”.
Add this to the fact that, in a study conducted in 1995, it
was found that Tanzania was responsible for roughly 2 million liters
of untreated sewage and industrial waste being introduced to the
lake on a daily basis, and it is very easy to see why Victoria is
suffering.
Lake Victoria is the largest of all African Lakes, is second
in width only to Lake Superior (~241.4 km), and the third largest
lake in the world in terms of surface area (~69,929.68 sq km). Like
Malawi, it receives a huge volume of its water from its many
inflowing rivers, though it receives more from rainfall than all
combined. It is also considered the primary source of the Nile River.
Of the three, Victoria possesses the lowest amount of
multivalent metallic cation concentrations, meaning lower general
hardness, as well as lower levels of dissolved carbonates and
bicarbonates, which, of course, translates to lower carbonate
hardness. This being said, values for Lake Victoria are very similar
to Malawi, moderately hard, with a pH range of, again, 7.7-8.8,
while generally on the lower end.
To
compare, the chemical analysis would be as follows: Sodium (~10-13
mg/L), calcium (~5-15 mg/L), magnesium (~1.5-8mg/L), chloride
(~4-7mg/L) and sulfate (~2.3mg/L). As I mentioned before, it
contains a rather low concentration of carbonate and bicarbonate (~.
25-1.5 meq/L). Victoria
does have comparatively high readings for dissolved silica, 3-20 mg/L in comparison to Malawi’s 1-1.4
mg/L and Tanganyika’s
.3-6.6 mg/L. It also is high in nitrate and phosphorus, while both
components are undetected or dubious in either of the other Lakes.
I’m guessing the sewage doesn’t help
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Lake
Tanganyika
Lake Tanganyika is interesting in the fact that though it is
one of the most ancient of the lakes, in comparison to Malawi and
even Victoria, it has a relatively low count of native fish. As of
ten years ago, 200+ species were native to the lake; while around
180 of this count is endemic. Tanganyika is also known for its
indigenous organisms, such as neothauma snails.
This is contributed to an extended period of isolation. A
large portion of Tanganyika is surrounded by mountainous regions and
poorly developed coastal plains. The steep walls of the Great Rift
Valley, reaching 2,000 m, form the west coast shoreline. All this
kept Tanganyika rather secluded for quite some time.
Also, unlike Malawi and Victoria, Tanganyika has only one
outlet river, the Lukuga, and has a substantially lower number of
inlets, thus receives less water in that way. It is also the second
largest of the African lakes with a surface area of ~32, 000 sq km,
the second deepest (~1,471 km at maximum depth), and has an
incredible North to South extension (~670 km).
Tanganyika is also around non-basaltic volcanoes, and picks
up some of its chemistry from lava drainage. This is a factor in
making Tanganyika quite a bit higher in pH and hardness, and more
complex. Tanganyikan pH ranges from 8.7-9.0, and has a much higher
amount of metallic cations that contribute to general hardness. Also
higher are the reading for carbonates and bicarbonates. There are an
absolutely incredible amount of dissolved solids in Tanganyika that
are not found in the other two lakes and thus, has a
very high electrical conductivity.
Again, to compare: Sodium (~57-64), calcium (~9.2-17.6),
magnesium (~39-43), chloride (~29-37), sulfate (~7-15), with a
carbonate, bicarbonate count of ~6.0-6.8. As you can see, the values
are comparatively quite high, with the exception of calcium.
Now that you know a little about the lakes, the question is
now, “What do I do with it?” My first suggestion is to take into
account their history…you simply cannot recreate in aquaria what
time and the intricacies of nature have provided. For example,
consider the high silica readings for Victoria. Silica is basically
an inert substance, but this is not the case within the lakes.
Diatoms take up silica in the construction of their shells, and
release it back into the water, as they dissolve in the water column, and some of the diatoms get buried and preserved within the
substrate. Simply adding sand is not going to contribute in the same
way, and unless you are a “diatom farmer” with some magical way
to control them, you are pretty much out of luck. Similarly, you
would have the same problems with Tanganyika. If you were determined
to add all the chemicals found in the lake, not only would
you spend a small fortune, you would most likely have to dedicate
your life to the process.
This being said, it is possible to create a similar
suitable environment. George has an excellent article on recreating
Malawi chemistry here.
A suitable Tanganyikan environment can be made in relatively the
same way by making minor alterations and
“upping the dosage”, and Victoria, by dropping the
dosages a bit. One
thing to keep in mind when altering water conditions is that all
metallic cations are not created equal. Only multivalents contribute
to general hardness. This added to the fact that carbonate substance, like calcium
carbonate, a.k.a. limestone, are more alkaline, but with a very low solubility
(meaning no matter how alkaline, it is not capable of contributing much to your
water),
while bicarbonates (like baking soda) are less alkaline, but freely
soluble. Choose your chemicals wisely!
I hope this clears up some confusion on the generalities of
the three lakes. My personal conclusion is not to expect perfection,
while at the same time, realizing that a suitable environment is not
very difficult to create. In addition to this, I feel that, taking
the chemical differences into account, yet another reason species
from different lakes should not be mixed becomes apparent,
particularly Tanganyikans with Malawis or Victorians.
References
Lake
Nyasa. Encyclopedia Britannica. 1999-2001.
http://www.britannica.com/eb/article?eu=57978&tocid=0
Lake Victoria: A Sick Giant. People and the Planet. 1995. http://www.oneworld.org/patp/pap_victoria.html
Oliver,
Michael. What is the Chemical Composition of Lake Malawi Water?
1997-2001.
www.malawiccichlids.com/mw01011.htm
Lake Nyasa (Lake Malawi). World Lakes Database. ILEC Foundation. http://www.ilec.or.jp/database/afr/afr-13.html
Lake Tanganyika. World Lakes Database. ILEC Foundation. http://www.ilec.or.jp/database/afr/afr-06.html
Lake Victoria. World Lakes Database. ILEC Foundation. http://www.ilec.or.jp/database/afr/afr-05.html
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