to cut right to the chase, let's ask what happens to the food web
and to the partial pressure of CO2
in the lakes with nutrient additions. If the CO2
level goes below the line, the lake is a CO2
sink; above the line, it is a CO2
source. Looking first at the reference lake, Paul Lake, it is, as
predicted, supersaturated with CO2,
and a persistent source of CO2 to
the atmosphere. The planktivore-dominated Lake where we added nitrogen
and phosphorus, became a CO2 sink
for the first year. These results are the similar to the ELA results
and gives us some confidence that we know parts of the lake system.
In Peter Lake, there are no large fish; there are small planktivores
minnows, but large zooplankton such as Daphnia are very rare. The
algae bloom like crazy, and we get a nice CO2
drawdown from the very beginning.
This other lake, which is a piscivore-dominated lake, with nitrogen
and phosphorus added, starts out somewhat as a CO2 sink, but becomes
a source very fast. In other words, in the piscivore-dominated lake
with nutrients added, we were unable to create a CO2 sink in this
those of you who aren't scientists, this looks worse than it is.
I've just showed you one year of data. Now I'm going to show you
the data for the entire five-year experiment using partial pressure
of CO2 and partial pressure of oxygen, which should mirror each
other. That is, as CO2 levels decrease, the oxygen levels should
increase since the phytoplankton use CO2 and produce oxygen in photosynthesis.
we started fertilizing the experiment, the lakes were supersaturated
in CO2, and correspondingly undersaturated in oxygen. We add nutrients
for five years and then we stop. At the end of the experiment, the
lake is supersaturated in CO2 and under-saturated in oxygen. During
the experiment, we see the control lake and the piscivore lakes
are supersaturated with CO2. Only the planktivores lake is consistently
a CO2 sink, and we see the mirror image in the increase in oxygen.
It's a very consistent set of data.