Eutrophication is the process by which a water body becomes enriched with nutrients, primarily nitrogen and phosphorus, leading to excessive growth of algae and aquatic plants and resulting in degraded water quality and ecological imbalance. In stormwater management, eutrophication is a major concern because runoff from developed and disturbed areas often carries elevated nutrient loads into lakes, ponds, rivers, and estuaries.
The process typically begins when nutrient inputs increase beyond natural background levels, often due to sources such as fertilizer runoff, failing septic systems, wastewater discharges, and sediment-bound nutrients transported by stormwater. These nutrients stimulate rapid growth of algae, including harmful algal blooms, and dense aquatic vegetation.
As these organisms grow and eventually die, they are decomposed by microorganisms, a process that consumes dissolved oxygen in the water. This can lead to hypoxic or anoxic conditions, where oxygen levels are too low to support aquatic life, resulting in fish kills, loss of biodiversity, and shifts in species composition. This oxygen depletion is closely associated with impacts on dissolved oxygen levels, which are critical for the survival of fish and other aquatic organisms.
Eutrophication also reduces water clarity, increases turbidity, and can produce toxins and unpleasant odors, making water bodies unsuitable for recreation, drinking water supply, and ecological functions. In severe cases, it can lead to long-term degradation known as cultural eutrophication, which is accelerated by human activities.
From a stormwater management perspective, controlling eutrophication involves reducing nutrient inputs at their source and managing runoff to limit the transport of both dissolved nutrients and those attached to sediment. Practices such as vegetated buffers, nutrient management, infiltration systems, and sediment and erosion controls are essential for mitigating the conditions that lead to eutrophication.
Overall, eutrophication represents a critical link between land use, stormwater runoff, and water quality, highlighting the importance of integrated watershed management.