Wetlands, including marshes, swamps, and bogs, are areas of land saturated with water, either permanently or seasonally. These unique ecosystems serve as an important link between terrestrial and aquatic environments. Their removal impacts the health and function of rivers and streams, altering natural processes and diminishing ecological integrity.
The Interconnected Role of Wetlands
Wetlands act as natural filters, removing pollutants and excess nutrients like nitrogen and phosphorus from water before it enters rivers and streams. This filtration occurs through physical, chemical, and biological processes, including sedimentation, plant uptake, and microbial activity. Wetlands also function as natural sponges, absorbing and slowly releasing large volumes of water from rainfall, snowmelt, and floodwaters. This capacity helps mitigate floods by reducing peak flows and ensures a consistent base flow in rivers and streams during dry periods.
The dense vegetation and varied topography within wetlands slow water flow, allowing suspended sediments to settle out. This prevents sediment accumulation downstream in rivers and streams. Wetlands provide important breeding grounds, nurseries, and feeding areas for diverse aquatic and semi-aquatic species. These habitats support complex food webs, benefiting fish, amphibians, invertebrates, and many bird and mammal species that rely on river and stream ecosystems.
Impacts on Water Quality
The removal of wetlands degrades the quality of water in connected rivers and streams. The loss of wetlands’ natural filtration capabilities leads to higher concentrations of nutrients, like nitrogen and phosphorus, entering waterways. This increased nutrient load can cause eutrophication, leading to excessive algal blooms that deplete dissolved oxygen when they decompose. Pesticides, heavy metals, and other pollutants are no longer effectively removed, contaminating downstream waters.
The removal of wetland vegetation and exposure of shallow waters to direct sunlight result in elevated water temperatures in rivers and streams. Higher water temperatures reduce the water’s capacity to hold dissolved oxygen, which is important for aquatic life. Increased organic matter from pollution, combined with warmer temperatures, exacerbates dissolved oxygen depletion, stressing fish and other aquatic organisms. Erosion from wetland loss introduces more suspended solids into the water, leading to increased turbidity. This increased turbidity reduces light penetration, affecting aquatic plants and visibility for visual predators.
Impacts on Water Flow and Sediment Dynamics
The removal of wetlands alters the physical movement of water and sediment in river and stream systems. Losing the water storage capacity of wetlands leads to more rapid runoff after rainfall, resulting in higher peak flows and a higher risk of flooding downstream. Areas with substantial wetland loss have seen peak flooding increase by as much as 80%. Conversely, the absence of wetlands means less water is slowly released during dry periods, leading to reduced base flows in rivers and streams. This can cause water levels to drop, sometimes leading to intermittent flow or complete drying up of sections of the waterway.
The loss of wetland vegetation, which stabilizes soil and traps sediments, leads to accelerated erosion of stream banks and beds. This increased erosion contributes more suspended sediment to the water. The elevated sediment load alters the composition of the riverbed, filling in natural pools and changing the shape and structure of the river or stream channel. This modification of sediment transport affects aquatic habitats and impacts the stability of the river system.
Impacts on Aquatic Ecosystems
The biological consequences of wetland removal for organisms within rivers and streams are extensive, beginning with direct habitat loss and degradation. Wetlands provide important breeding, feeding, and refuge areas for diverse aquatic species, including fish, amphibians, and invertebrates. Their removal eliminates these spaces, disrupting life cycles and forcing species to relocate or face decline. This loss of specialized habitat weakens ecosystem resilience and stability.
The cumulative effects of poor water quality, altered flow regimes, and habitat destruction result in a reduction in species variety and abundance. This decline in biodiversity impacts entire aquatic communities. The disruption extends to food webs, as the loss of wetland-dependent species, like insects or small fish that serve as prey, affects predator-prey relationships throughout river and stream ecosystems. This can cascade through the system, impacting the health and functionality of the aquatic environment. Stressed aquatic populations, already struggling with degraded conditions, become more vulnerable to diseases, exacerbating population declines.