Biological uptake is the process by which living organisms absorb, assimilate, and incorporate dissolved or particulate substances, most commonly nutrients and contaminants, from stormwater into their biomass as part of normal metabolic activity.
In the context of stormwater management, biological uptake primarily refers to the removal of nutrients such as nitrogen and phosphorus by plants, algae, and microorganisms within systems like bioretention areas, wetlands, swales, and detention or retention basins. These organisms take up nutrients from the water and soil for growth, effectively reducing the concentration of these substances in runoff before it is discharged to downstream waters.
Vegetation plays a major role in biological uptake by absorbing nutrients through root systems and storing them in plant tissues. Microbial communities in soils and sediments also contribute by assimilating nutrients and organic compounds during processes such as microbial growth and metabolism. In aquatic environments, algae and phytoplankton can rapidly take up dissolved nutrients, although excessive uptake in natural receiving waters may contribute to eutrophication if not properly managed.
Biological uptake is influenced by environmental conditions including temperature, light availability, oxygen levels, soil moisture, and the presence of active microbial populations. It is often seasonal, with higher uptake rates occurring during growing periods when vegetation and microbial activity are most vigorous.
As a stormwater treatment mechanism, biological uptake is considered a key component of many green infrastructure and low impact development practices. However, it is not necessarily a permanent removal pathway unless the accumulated biomass is harvested or otherwise removed from the system. Without such removal, nutrients stored in plant material or microbial biomass may eventually be released back into the system through decay, contributing to internal cycling and potential downstream transport.