Question

Consider a pond where two species of phytoplankton (algae), A and B, live. Both species need phosphorus to grow, and there is not enough phosphorus in the pond for both species to grow indefinitely. Over time, species A dominated the pond, and species B declined to extinction (see graph). How would a biologist explain why this happened? (Note: neither species consumes the other species.)

Answer 1

Eutrophication or Hypertrophication, is the enrichment of a water body with nutrients, usually with an excess amount of nutrients. This process induces growth of plants and algae and due to the biomass load may result in oxygen depletion of the water body. One example is the "bloom" or great increase of phytoplankton in a water body as a response to increased levels of nutrients. Eutrophication is almost always induced by the discharge of phosphate-containing detergents, fertilizers, or sewage, into an aquatic system.

Eutrophication arises from the oversupply of nutrients, which leads to overgrowth of plants and algae. After such organisms die, the bacterial degradation of their biomass consumes the oxygen in the water, thereby creating the state of hypoxia.

The availability of phosphorus generally promotes excessive plant growth and decay, favouring simple algae and plankton over other more complicated plants, and causes a severe reduction in water quality. Phosphorus is a necessary nutrient for plants to live, and is the limiting factor for plant growth in many freshwater ecosystems. Phosphate adheres tightly to soil, so it is mainly transported by erosion. Once translocated to lakes, the extraction of phosphate into water is slow, hence the difficulty of reversing the effects of eutrophication.

Sources of excess phosphates are phosphates in detergent,industrial/domestic run-offs,and fertilisers.