Dr Marc Schallenberg prepares to test the water of Lake
Hayes. Photo by Christina McDonald.
A tiny non-native ''water flea'' may hold the key to
restoring Lake Hayes' water to its original state.
Fresh water scientist Dr Marc Schallenberg, a research fellow
at the Otago University, has been studying Lake Hayes since
1995 and believes the key to reducing algal bloom is to
increase the number of daphnia - commonly known as the water
Dr Schallenberg has recently begun a three-year study, which
involves monthly testing of the lake and which is endorsed by
the Friends of Lake Hayes association.
Because of its sediment makeup, the top layer of water in
Lake Hayes heats up during summer, while the bottom layer
remains the same temperature as it is during winter.
The warm layer prevents oxygen filtering down to the bottom
layer and it subsequently becomes anoxic - meaning without
oxygen - causing a chemical reaction which releases
phosphorus and ammonia.
Lakes Wakatipu and Moke do not have this issue. During summer
the bottom layer got higher and higher in nutrients, then in
winter the two layers combined and ''you suddenly get a huge
pulse'' of phosphorus and nitrogen, encouraging algae to
A study by Niwa in 2010, failed to find a way to reduce algae
levels because the lake suddenly cleared up.
Dr Schallenberg hypothesised water fleas, in large
concentrations, filtered the smaller algae in the lake and
also had an indirect effect on larger algae.
''There's nothing else we can point to ... It was
unprecedented how clear it was.''
''At the time we were thinking that if it is the daphnia that
is clearing the lake, it will probably only last for a year
or two. I speculated at the time that if the daphnia were the
cause we would then have lots of little fish because they
would be feeding on the daphnia.
''This number of daphnia coming in has unbalanced the lake in
a favourable way.''
If the daphnia were proven to cut algae levels, allowing the
flea to flourish would result in a clear lake, he said.
This could be done by decreasing the number of smaller fish
by either netting them or introducing large fish to feed on
the smaller ones.
At present, Lake Hayes has little or no daphnia and ''the
algae problem'' is returning.
''I think this lake is a jewel of this area ... It's
important that we have it clean because people fly over it
and at the moment it's brown and that's not a good look.''
Dr Schallenberg is confident the study will determine how
best to deal with the algae and Niwa is also looking at other
methods to bind the phosphorus.
''We're talking about really complex food webs, where if you
change one thing the repercussions echo throughout the whole
system. ... But I think we have some pretty good leads about
how to improve the lake.''