Home >> Science & Nature >> Nature

What Causes Brown Algae in a Lake?

Thousands of different species of algae inhabit both fresh and marine waters.

The group of algae is diverse, ranging from blue-green organisms with only one cell to yellow multicellular forms that grow to over 60 meters in length. Freshwater algae can float in the water or be attached to plants or rocks. The majority of freshwater algae do not cause any problems, but some species are toxic to humans and other animals.

Different Types of Algae
- Algae are an important source of food and some types of algae can absorb nutrients and heavy metals making them vital for a healthy ecosystem. The most common freshwater algae are green algae and diatoms. The blue-green algae are considered to be more closely related to bacteria and it is now referred to as cyanobacteria. Green algae are the most common type of algae found in a lake, and sometimes they grow in "cotton candy" clouds in the water.
Brown or Golden Algae
- Diatoms is a major type of algae and a common type of phytoplankton. They are commonly referred to as brown or golden algae. Brown algae produce atmospheric oxygen and the freshwater algae do not produce any toxin. Marine diatoms can produce a toxin called domoic acid, which can accumulate in shellfish. The toxic can poison humans and it acts as a neurotoxin causing permanent short-term memory loss. Diatoms occur in environments that contain water and they can be found in oceans, seas, lakes and soil. Diatoms are unicellular organisms that have a yellow-brown chloroplast that enables them to photosynthesize. Many species of diatom stay connected and they can form long chains.
High Growth Rate
- Usually brown algae follow a cycle where they bloom during spring and early summer. Brown algae in freshwater quickly reproduce when the conditions in the upper layers of the water are favorable. At the start of spring, nutrients and light conditions improve and this can lead to high growth rate. When the conditions change brown algae quickly decrease in number. A weakening in the available nutrients leads to an increase in sinking rate. The algae may stick together or the production of heavy resting spores increase the number of sinking diatoms. However, sometimes an autumn bloom may occur if the light level is sufficient and there is enough nutrients in the water.
Water Temperature and Nutrients
- Brown algae grow in cool water that contains silica and other nutrients that have accumulated during winter. The algae use silica to build its cell walls. The algae grow rapidly and give the water a brown hue, but when the water warms up the green or yellow-brown algae takes over. These types of algae grow quicker in warm water. As the water gets even warmer, cyanobacteria may take over.

Nature