A Trophic State Index is a standard used to determine the nutritional state of a water body i.e the quantity of biologically useful nutrients like phosphorus, nitrogen etc dissolved in a water body. The most commonly used trophic indices is the Carlson’s index, whereby the trophic state of a water body is described as the total weight of biomass contained in it. In this regard, a water body can be classified as Oligotrophic, Eutrophic, Mesotrophic or Hypereutrophic.
Both man-made and natural activities influence the trophic state of a water body in one way or the other. For example sewage flowing intentionally or accidentally into a water body, agricultural run-offs from crop-fields or fertilizer leaches are some of the different ways in which nutrients are added to a water body due human activities. A water body may also be naturally located in an area with high or low level of nutrients.
What Is Oligotrophic Lake/ Water Body?
An Oligotrophic lake or water body is a one with relatively low productivity, as a result of low nutrient content. These lakes have low algal production and consequently, often have very clear waters. The waters of such lakes are of high-drinking quality. This lakes or water bodies support aquatic species that require well-oxygenated, cold waters such as lake trout, char and whitefish.
Characteristics Of Oligotrophic Lakes/Ocean
- Oligotrophic lakes are usually found in northern Minnesota and have deep clear water, rocky and sandy bottoms and very little algae.
- They are usually deep in depth.
- Oligotrophic lakes have low densities of vascular aquatic plants, phytoplankton and algae.
- Oligotrophic lakes are usually found in the cold regions of the world where mixing of nutrients is rare and slow due to the low temperatures of the lake waters.
- The water is clear and oxygen is found at high levels throughout the water column.
- High species diversity with low population
- Poor nutrient content in the water especially phosphates and nitrates.
- Low levels of biological productivity
- Green algae dominate in the ecosystem.
- Algal blooms occur very rarely
- The content of chlorophyll in water is very low
- The waters of these lakes are of high drinking quality.
- This lakes support aquatic species that require well-oxygenated, cold waters such as lake trout, char and whitefish.
What Is Eutrophic Lake/Water Body?
Eutrophic lakes or water body is one with relatively high levels of biological productivity. Eutrophic lakes are very fertile from all the nutrients carried into the lake from the surrounding landscape. Due to high contents of nutrients especially nitrogen and phosphorus these water bodies support a large number of plants and algae.
Characteristics of Eutrophic Lakes/Water Bodies
- They are usually shallow in depth with murky water and soft bottoms.
- Eutrophication might occur naturally or due to human impact on the environment.
- Eutrophic lakes have high densities of vascular aquatic plants, phytoplankton and algae.
- Eutrophic lakes are very fertile from all the nutrients carried into the lake from the surrounding landscape.
- Water usually dark or blue-green to growth of algae
- Low species diversity with high population densities.
- High nutrient content in the water especially nitrates and phosphates.
- High level of (biological) or primary productivity
- Blue green algae dominate in the ecosystem
- Algal blooms occur very frequently.
- Chlorophyll content in water is very high.
- In eutrophic lakes, common fish include largemouth bass, northern pike, perch and pinfish.
Difference Between Oligotrophic And Eutrophic Lakes In Tabular Form
| BASIS OF COMPARISON | OLIGOTROPHIC LAKES | EUTROPHIC LAKES |
| Location | Oligotrophic lakes are usually found in the cold regions of the world where mixing of nutrients is rare and slow due to the low temperatures of the lake waters. | Eutrophic an be found anywhere. They are usually very fertile from all the nutrients carried into the lake from the surrounding landscape. |
| Nutrient Content | Poor nutrient content in the water especially phosphates and nitrates. | High nutrient content in the water especially nitrates and phosphates. |
| Depth | They are usually deep in depth. | They are usually shallow in depth with murky water and soft bottoms. |
| Plant Densities | Oligotrophic lakes have low densities of vascular aquatic plants, phytoplankton and algae. | Eutrophic lakes have high densities of vascular aquatic plants, phytoplankton and algae. |
| Water Color | The water is clear and oxygen is found at high levels throughout the water column. | Water usually dark or blue-green to growth of algae |
| Occurrence | Oligotrophication in many occurs naturally. | Eutrophication might occur naturally or due to human impact on the environment. |
| Algal Bloom | Algal blooms occur very rarely. | Algal blooms occur very frequently. |
| Primary Productivity | Low levels of biological productivity | High level of (biological) or primary productivity |
| Chlorophyll Content | The content of chlorophyll in water is very low | Chlorophyll content in water is very high. |
| Species Diversity | High species diversity with low population | Low species diversity with high population densities. |
| Algae | Green algae dominate in the ecosystem. | Blue green algae dominate in the ecosystem |
| Common Species | Common Species found in Oligotrophic Lakes include lake trout, char and whitefish. | Common species found in Eutrophic lakes include largemouth bass, northern pike, perch and pinfish. |