Can river clean itself ? School experiment diary by Jaś Węsławski
(II Liceum Ogólnokształcące in Gdynia) How I found out what to do for the
school experiment contest The school experiments for the Biological
Olympics have two basic assumptions: - no
one gets hurt (you may not kill the animals) - the
project is doable with the skills and equipment available to
every school pupil In June 2009, leading Polish newspaper
have published interview with dr Lech Kotwicki from „Wielkie żarcie „ Nowy DF nr 159, wydanie z dnia 09/07/2009reportaż,
str. 8 „Człowiek leży
sobie spokojnie na plaży, opala się na kocyku, a pod nim zjadany
jest kotlet schabowy Z DR. LECHEM KOTWICKIM ROZMAWIA ADAM
WAJRAK-. Tam jest życie, mnóstwo życia.-...” The story was about living sand on
the marine beach. According to dr Kotwicki, sandy beach works as
a living biological filter, consuming contaminants and excess organic
matter that is left there by humans. As I use to spent my vacations
at the small forest river (Wda, known also as Black Water – Czarna
Woda) I was wondering whether or not sandy shores of my favorite
river may act as the water purification system as well. Dr Kotwicki
explained that permeable sand allows numerous minute animals to
dwell between the sand grains and feed on organic particles that
are transported with the water between sand grains. Most of those
organisms are bacteria, fungi and animals smaller than 1mm, known
as meiofauna – here belong very small worms, earthworms, spiders,
crustaceans and alike. All that life may consume as much as several
(up to 40) kg of organic wastes per m2 per year. I have emailed
dr Kotwicki (lechk@iopan.gda.pl)
and got from him a nice response with a suggestion how to organize
an experiment that will allow me to assess the river potential
in contamination combat. The methodology is presented on the web
page devoted for sandy shores project (http://www.iopan.gda.pl/rbdo/mekodb/litus/). I
was surprised that scientists are also working out very simple
experiments, that can be copied easily by anyone at secondary school
level. No fancy equipment, just a good will and basic kitchen utensils.
The experiment My question was: is the river bank
as efficient as the marine beach in organic matter consumption
? The method To test this question I have used
the litter bag method, common in forest research and other ecological
studies. Litter bag method is the exposition of pieces of weighted
organic matter (like leaves, paper, food) in number of mesh bags,
and removal of selected bags after 2, 7, 14
and 21 days to control the loss of sample weight. If you put into
the google words “litter bag method” lots of info will appear –
like http://www.jstor.org/pss/1933396,
or example of studies from 1)the shallow, sandy river bed with
washed strong water current, temperature beteen 18 and 20oC during
the experiment. 2) silent river channel with bottom covered by decaying leaves and mud.
Temperature between 19 and 21oC during the experiment. I have collected samples of sediments
from both sites, samples were dried to remove the water (few days
on the sun or several hours in kitchen oven in temperature not
exceeding 60oC), then dry sediment was weighted, and placed in
the very hot oven used by the hobby of ceramics (available for
public use in a workshop at I
was also looking for small animals crawling on the sediment surface
– there were no
insects or snails on the river sand - the current was too fast.
On the contrary there was a lot of larvae and beetles on the muddy
bottom of the channel. Considering that channel sediment is so
organic rich and filled with small fauna, I was wondering, whether
the coarse river sand with no bugs visible can compete in the race
of organic matter destruction.
Litter bags were prepared from the
pieces (10 per 10cm) of mosquito net with 1mm mesh size. Twenty
four bags were prepared, 12 for the river and 12 for the channel.
Each set of 12 bags was wrapped in mosquito net and buried under
5cm of sediment. Each bag was divided in two halfs,
first half was filled with weighted slice of fresh potato (about
10g), second half with similar, weighted slice of hard boiled
eggs white. Each sample was numbered, notes were taken into the
excel
table. Three bags were removed from each site at a time - after
2, 7, 15 and 21 days. Removed bags were gently washed and
frozen in common freezer (-18oC).
The results Final result shows clearly that potato
was consumed very fast at almost the same rate in channel and the
river. The big difference was shown in eggs white. The protein
was consumed much faster in the river than in the channel. It took
21 days to consume almost 90% of exposed egg, and even after 2
day the weight loss was clear (nearly 30%). After comparison with the marine sandy beach – it looks that my river bank is the most efficient substrate for the protein decomposition. So, I may hope that the river can take care of itself and remove most of the contaminants in the very natural way.
References: Jędrzejczak M. F., 1999, The degradation of stranded carrion
on a |
Samples were placed few centimeters
under the sand in the shallow site of the
