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ON NORTHERN POND
Forget Fertilizerfor
Northern Ponds
by Dr. Dave
Willis
O
ne of the most striking differ- probably be used from the pond water
ences between pond manage- faster than plants can replace it.
ment in northern and southern states
A great variety of organisms use disinvolves fertilization. In many south- solved oxygen from water. Fish need
ern waters, especially those areas of oxygen, as do snails and zooplankton.
the country with relatively infertile Did you know that algae and aquatic
soils, fertilization is a wonderful tech- plants also use oxygen? They produce
nique for pond management. However, oxygen during times of sunlight, but
I have never fertilized a pond in my they also use oxygen during both the
nearly 30 years of fisheries work in day and night. The process is the opponorthern states. Why the big difference site of photosynthesis, called, "respiration." Finally, there is an entire combetween geographic locations?
Most of our northern pond manage- munity of bacteria that are actually livment strategies MUST start with win- ing on dead organic matter. Whenever
terkill concerns. How deep is the a fish, a plant, a single cell of algae, or
pond? How long do we have ice cover an individual zooplankter dies, they
during winter? Is a winter aeration sys- will begin to decompose. Bacteria are
nature's decomposers in our pond system necessary and possible?
Winterkill is a function of the length tems, and a necessary part of the comof time of ice cover, the amount of munity. However, most species of bactransparency of ice and snow, and the teria require oxygen to survive and
amount of organic material decompos- perform their function. So, the more
ing under ice. With longer winters, the organic matter in a pond, the greater
risk of winterkill increases. In winters the bacterial community under the ice,
when ice is not especially transparent and the greater their demand for disor there is a lot of snow cover, a win- solved oxygen in that pond.
So, this long tale brings us back to
terkill is more likely. Finally, an inferthe
lack of need to fertilize northern
tile pond (nutrient poor) is less likely
to winterkill in any year compared to a ponds. The risk of fertilization is that if
fertile (nutrient rich) pond. More nutri- you succeed in producing a productive
ents mean more organic material to warm weather plankton bloom, the
consequences will be a net increase in
decompose, using valuable oxygen.
Length of ice cover wasn't too bad the amount of dead organic matter in
when I worked in Kansas. However, the pond during the winter. If you ferduring a harsh winter in eastern South tilized a continual algae bloom during
Dakota, ice cover can last from the summer, these algae eventually
will die and sink to the pond bottom.
November through March.
Clear ice transmits a lot of sunlight. The more dead algae, the greater the
Under clear ice, algae suspended in the risk for a winterkill.
Similarly, I have rarely used a feedwater column and surviving aquatic
plants will still undertake photosynthe- ing program for fishes in northern
sis and release oxygen into the water. ponds. Once again, we don't want to
However, thicker ice or snow on the artificially increase the nutrient level
ice will block more of the sun's rays. in a pond, and increase the amount of
As a result, dissolved oxygen will living organisms. Just the decomposi-
January/February 2004
tion of excess food could be enough to
push you over the hump of the dissolved oxygen support limits in your
pond. So, a feeding program simply
becomes another risk that increases
your chance of winterkill.
Soil fertility is the key to deciding
when to consider a fertilization program. Ponds in the plains states of the
central United States typically do not
need to be fertilized. Such ponds, built
on fertile prairie soils, can commonly
support 40-60 pounds per acre of
largemouth bass (or even more), and
100-200 pound per acre of bluegills.
However, when you live in an area of
high annual precipitation and leached
soils, a similar pond may only support
10-20 pounds per acre of largemouth
bass and 50-75 pounds per acre of
bluegills. In such infertile ponds, a fertilization program can increase the
pounds per acre of your bass and
bluegill to those of more fertile geographic locations.
Now, fertilizing a northern pond in
an area of infertile soils, or designing a
proper fish-feeding program may still
be possible and could actually be your
best management strategy. However,
such strategies will REQUIRE much
more attention to the details of pond
management. Do not undertake such
strategies unless you either 1) fully
understand and monitor the dissolved
oxygen characteristics in your pond, or
2) are working with an experienced
pond management consultant.
Dr. David W. Willis is a professor in the
Department of Wildlife and Fisheries
Sciences, South Dakota State Universityin
Brookings. He frequents the Pond Boss
forum at www.pondboss.com and can be
reached there.
POND BOSS 35