The Eutrophication Process
All lakes undergo eutrophication. It is a normal process, often
referred to as the 'aging of a lake'. Over the duration of tens
of thousand of years a crystal clear deep lake will eventually be
transformed into a murky shallow bog filled with plant matter, possessing
very low oxygen concentrations that will only support highly specialized
The catalyst for the eutrophication process is phosphorus. The annual phosphorus
input to the lake provides the necessary nutrients for aquatic
plant growth. Each year these aquatic plants reach the end of
their annual life cycle and sink to the bottom of the lake where
their decomposition depletes the water of oxygen. The phosphorus
contained within this plant matter is stored in the sediment on
the bottom of the lake.
catalyst for the eutrophication process is phosphorus. The
annual phosphorus input to the lake provides the necessary
nutrients for aquatic plant growth.
Each year these aquatic plants reach the end of their annual
life cycle and sink to the bottom of the lake where their
decomposition depletes the water of oxygen. The phosphorus
contained within this plant matter is stored in the sediment
on the bottom of the lake.
continues to be stored in the sediment year after year until the
lake enters into a 'mid life crisis' so to speak. In this stage,
the lake loses its ability to store the annual phosphorus input
due to a severe depletion in the oxygen at the bottom of the lake.
The absence of oxygen at the bottom triggers the re-suspension
of the stored phosphorus and when this available phosphorus is
combined with the annual phosphorus input to the lake, the production
of aquatic plant growth increases significantly. The lake now
enters into a transition phase - from 'mid life' to 'old age'.
The plant matter continues to accumulate on the bottom, the oxygen
depletion eventually extends throughout the entire water column
and the phosphorus is continually recycled. The lake now begins
to resemble a swamp and eventually will cease to exist and become
land. The eutrophication process occurs so slowly that we are
unable to visibly detect the changes over the course of our lifetime.
Accelerated Eutrophication Process
In contrast to the natural aging process - the accelerated eutrophication
of a lake occurs as a direct result of the input of phosphorus
from sources above and beyond the naturally occurring sources.
In essence - the lake is forced into a state of 'premature aging'
because of the excessive phosphorus inputs. We begin to be able
to visibly observe:
- A noticeable
decrease in the transparency of the water.
weed growth and algae.
- A decrease
in fish species that require high levels of oxygen (e.g. trout)
and an increase in fish species that can survive in low oxygen
Accelerated Eutrophication Process - You & Your Cottage
In most instances the primary source of phosphorus that tips the
scale in favor of accelerated eutrophication on most area lakes
are waterfront cottagers. Other artificial sources - such as agricultural
activity bordering on a lake and industrial or commercial installations
have the potential to be a major factor - but in their absence:
cottages are the number 1 source of artificial phosphorus
to cottage country lakes & consequently the primary cause
of accelerated eutrophication.
cottage is capable of inputting between approximately 535 and
3345 grams (perhaps more) of phosphorus to the lake environment
per cottage season depending on the following critical factors:
of household products that contain phosphorus
cottage (like most) has a typical septic tank and drainage
field configuration, between 70% and 90% of all phosphorus
entering your septic system eventually ends up in the lake.
This traditional method of treating waste water was primarily
designed to prevent outbreaks of water borne disease (such
as cholera and typhoid). The system is not designed to be
an effective method of removing phosphorus from waste water.
The drainage field eventually becomes saturated with phosphorus
and looses its capacity to retain the phosphorus. The phosphorus
then works its way into the lake.
of yard products that contain phosphorus and removal of native
trees & shrubs
available fertilizer used to stimulate growth of lawns, vegetable
and flower gardens contain a lot of phosphorus. After application,
the fertilizer lies on the surface until the first rainfall.
The surface run-off generated by the rainfall carries the soluble
phosphorus into the lake. The greater the surface area that
is fertilized and slope of the terrain - the more phosphorus
that is deposited into the lake. Compounding this problem is
the removal of native shoreline vegetation. Small trees and
shrubs slow down the speed of surface runoff after a rainfall
and absorb some of the phosphorus making its way to the lake.
modest changes in your habits and behaviour at the lake - you
can make a significant reduction in the amount of phosphorus your
cottage inputs into the lake. You can:
- Use phosphate-free
- Stop using
commercially available fertilizer on your lawn, flower and vegetable
gardens. Instead - try cornposting your fruit, vegetable and
yard waste. Compost is an excellent soil conditioner and releases
its phosphorus slowly - whereas the phosphorus in commercially
available fertilizer is not retained by the soil and quickly
washes into the lake after application.
- Avoid clearing
your property of trees and vegetation - especially near the
shoreline. Consider replanting species native to the shoreline.
This also helps to reduce erosion.