Water quality describes the chemical, physical, and biological characteristics of a water sample, indicating its health for various uses, including drinking, recreation, and supporting ecosystems. Maintaining good water quality is important for the survival of aquatic organisms and the overall well-being of human communities. Water bodies provide essential services, from supplying drinking water to supporting diverse aquatic life. Sediment is a significant factor that can substantially alter these characteristics and impact water quality.
Understanding Sediment and Its Origins
Sediment consists of tiny particles of rock, soil, and organic matter that are transported by water and settle at the bottom of aquatic environments. Particles range from fine clays to larger sand, gravel, and pebbles. Sediment exists in two forms: suspended solids, which are fine particles afloat in the water column, and bedload, larger particles that roll, slide, or hop along the streambed. Suspended solids are typically smaller than 2 microns, while bedload includes coarser materials.
Sediment naturally enters waterways through weathering, erosion, and decomposition. Natural erosion, from riverbed scouring, bank erosion, and geological processes, accounts for some sediment in water bodies. However, human activities accelerate its input. Human-induced sources include soil disturbance from agriculture, construction, deforestation, and urban runoff. These activities increase erosion rates, leading to greater sediment runoff into waterways.
Physical Changes to Water Quality
Sediment alters the physical characteristics of water, leading to increased turbidity. Turbidity is the cloudiness of water caused by suspended particles. Elevated turbidity reduces sunlight penetration, inhibiting photosynthesis in aquatic plants and algae, which are fundamental to the food web.
Suspended sediment can also increase water temperature by absorbing more solar radiation. Warmer water holds less dissolved oxygen, stressing aquatic organisms that require specific oxygen levels. As suspended particles settle, they accumulate on the streambed or lake bottom, known as sedimentation. This settling sediment can smother benthic habitats, covering spawning grounds for fish and burying aquatic invertebrates, disrupting their life cycles and food access.
Chemical and Biological Consequences
Beyond physical alterations, sediment introduces chemical and biological changes to water quality. Sediment particles carry pollutants into aquatic environments. These pollutants, including adsorbed pesticides, heavy metals, and industrial chemicals, bind to fine sediment particles and are released into the water column, posing risks to aquatic life.
Sediment also carries excess nutrients, such as nitrogen and phosphorus, from land into water bodies. This influx of nutrients leads to eutrophication, an excessive enrichment of water fueling rapid algal growth, known as algal blooms. When these blooms decompose, they consume large amounts of dissolved oxygen, creating hypoxic (low oxygen) or anoxic (no oxygen) conditions detrimental to aquatic life.
Direct biological impacts are substantial. Suspended sediment can cause abrasion to the gills of fish, reducing respiratory efficiency and increasing disease susceptibility. Increased turbidity also disrupts feeding behaviors by limiting their visibility to locate food. Habitat degradation due to settled sediment can reduce biodiversity, as sensitive species struggle to survive in altered environments.
Impacts on Human Use and Infrastructure
Sediment pollution directly affects human activities and infrastructure. For drinking water treatment facilities, high sediment levels increase turbidity, necessitating greater filtration and often increased chemical use. This leads to higher operational costs for water purification and can result in undesirable odors or tastes.
Recreational activities are also impacted by sediment-laden waters. Swimming, fishing, and boating become less appealing due to reduced visibility and muddy conditions. Fish populations, affected by habitat degradation and stress from sediment, decline, diminishing fishing opportunities. Industries reliant on clean water, such as those using water for cooling or manufacturing, face increased costs due to pre-treatment or equipment maintenance.
Infrastructure is vulnerable to sediment accumulation. Reservoirs experience reduced storage capacity as sediment fills them, limiting water availability. Navigation channels and harbors require frequent, costly dredging to ensure safe passage. Irrigation systems can become clogged with sediment, reducing efficiency and impacting agricultural productivity.