Phosphorus is a fundamental nutrient for all life, often limiting growth in natural ecosystems. While essential, an overabundance of phosphorus can lead to significant environmental concerns, particularly in aquatic environments. Wetlands, as natural systems, help manage water quality by processing and filtering excess nutrients.
Phosphorus in Waterways
Phosphorus exists in aquatic environments in various forms, including dissolved inorganic phosphates and particulate forms bound to sediment or organic matter. Its primary sources are often human-influenced, such as agricultural runoff containing fertilizers and manure, municipal and industrial wastewater discharges, and urban runoff. Erosion of soil particles, to which phosphorus can bind, also contributes to its presence.
Excess phosphorus acts as a limiting nutrient, triggering rapid growth of aquatic plants and algae. This overgrowth leads to eutrophication, resulting in dense algal blooms. Upon decomposition, these blooms consume dissolved oxygen, creating hypoxic “dead zones” that harm aquatic life. They can also produce toxins, posing risks to human health and contaminating drinking water supplies.
How Wetlands Remove Phosphorus
Wetlands function as natural filters, removing phosphorus from water through physical, chemical, and biological mechanisms. These processes reduce phosphorus concentrations as water moves through the wetland environment.
Physical processes play a significant role, particularly sedimentation, where particulate phosphorus settles as water flow slows. Dense wetland vegetation helps reduce water velocity, allowing suspended particles with bound phosphorus to settle. Adsorption also occurs as dissolved phosphorus adheres to the surfaces of soil particles, clays, and organic matter within the wetland substrate. This binding is especially prominent with minerals containing iron and aluminum oxides.
Chemical processes contribute to phosphorus removal through precipitation reactions. Dissolved phosphate ions react with metal ions such as iron, aluminum, and calcium, forming insoluble compounds that settle out of the water. This converts soluble phosphorus into a solid form, effectively locking it into the sediment.
Biological processes involve plants and microorganisms. Wetland plants absorb inorganic phosphorus for their growth, incorporating it into their tissues as organic phosphorus. Microorganisms, including bacteria and fungi, also assimilate phosphorus into their biomass through immobilization. However, phosphorus stored within plant and microbial biomass is often temporary, as it can be released back into the water and soil upon decomposition.