Water
Quality: Management, Sanitation and Investigation
Limnological
Fundamentals
Algae
Algae are photosynthetic
plants that contain chlorophyll and have a simple reproductive structure
but do not have tissues that differentiate into true roots, stems, or leaves.
They do, however, grow in many forms. Some species are microscopic single
cells; others grow as mass aggregates of cells (colonies) or in strands
(filaments). Some even resemble plants growing on the lake bottom.
The algae are an
important living component of lakes. They:
-
convert inorganic material
to organic matter through photosyn thesis;
-
oxygenate the water,
also through photosynthesis;
-
serve as the essential
base of the food chain; and
-
affect the amount of
light that penetrates into the water column. Like most plants, algae require
light, a supply of inorganic nutrients, and specific temperature ranges
to grow and reproduce. Of these factors, it is usually the supply of nutrients
that will dictate the amount of algal growth in a lake. In most lakes,
increasing the supply of nutrients (especially phosphorus) in the water
will usually result in a larger algal population.
Factors
that Affect Algal Growth
There are a number
of environmental factors that influence algal growth. The major factors
include:
-
the amount of light
that penetrates the water (determined by the intensity of sunlight, the
amount of suspended material, and water color);
-
the availability of
nutrients for algal uptake (determined both by source and removal mechanisms);
-
water temperature (regulated
by climate, altitude, et cetera);
-
the physical removal
of algae by sinking or flushing through an outflow;
-
grazing on the algal
population by microscopic animals, fish, and other organisms;
-
parasitism by bacteria,
fungi, and other microorganisms; and
-
competition pressure
from other aquatic plants for nutrients and sunlight.
It is a combination
of these and other environmental factors that determines the type and quantity
of algae found in a lake. It is important to note, however, that these
factors are always in a state of flux. This is because a multitude of events,
including the change of seasons, develop ment in the watershed, and rainstorms
constantly create "new environments" in a lake.
These environmental
changes may or may not present optimal habitats for growth or even survival
for any particular species of algae. Consequently, there is usually a succession
of different species in a lake over the course of a year and from year
to year.
The Overgrowth
of Algae
Excessive growth
of one or more species of algae is termed a bloom. Algal blooms,
usually occurring in response to an increased supply of nutrients, are
often a disturbing symptom of cultural eutrophication.
Blooms of algae can
give the water an unpleasant taste or odor, reduce clarity, and color the
lake a vivid green, brown, yellow, or even red, depending on the species.
Filamentous and colonial algae are especially troublesome because they
can mass together to form scums or mats on the lake surface. These mats
can drift and clog water intakes, foul beaches, and ruin many recreational
opportunities.
Monitoring programs
designed to monitor the algal condition of a lake usually require the volunteers
to measure:
-
the water clarity;
-
the density of the algal
population; and
-
the concentration of
the critical algal nutrient, phosphorus.
