Water quality describes the chemical, physical, and biological characteristics of water, assessed against standards for its intended use. It encompasses a complex interplay of properties that determine its suitability for various purposes. Clean water is a foundational element for life across the planet, influencing the health and function of countless natural systems.
Supporting Aquatic Life and Biodiversity
Water quality directly affects organisms living within aquatic environments. Parameters such as dissolved oxygen, pH, and temperature are important for the survival and reproduction of fish, amphibians, invertebrates, aquatic plants, and microorganisms. For instance, warmer water holds less dissolved oxygen, which can stress aquatic life and lead to large-scale fish mortality. Many aquatic species have specific temperature ranges, and deviations can reduce their populations.
The pH level, indicating acidity or alkalinity, plays a significant role. Aquatic organisms are sensitive to pH levels, with extreme values outside a typical range of 4.5 to 10.0 being harmful. Low pH can reduce fish egg hatching rates and challenge fish and macroinvertebrates. Pollutants like heavy metals and chemicals can accumulate in aquatic organisms through a process called bioaccumulation. These toxins become more concentrated higher up the food chain, a phenomenon known as biomagnification, leading to health issues, reproductive problems, or death in top predators. Such disruptions impact aquatic food webs and reduce overall biodiversity.
Connecting Terrestrial and Aquatic Ecosystems
Water quality in aquatic environments directly influences the health of surrounding terrestrial ecosystems. Land-based animals depend on clean water for drinking. Riparian zones, which are vegetated areas along rivers and streams, act as natural filters. They remove excess nutrients, sediments, and contaminants from runoff before these reach water bodies.
Wetlands also serve as filters, slowing water flow and allowing sediments and pollutants to settle. Wetland plants absorb nutrients like nitrogen and phosphorus, and microorganisms break down other contaminants, purifying the water. This natural filtration can remove a significant percentage of pollutants, including up to 90% of sediment runoff and nitrogen. Water quality also impacts soil health and vegetation near water bodies. Healthy soils retain more water and nutrients, reducing the amount of sediment and nutrients carried into waterways. Eroded soil particles can carry nutrients and contaminants into water bodies, reducing water clarity and affecting aquatic habitats.
Facilitating Natural Cycles and Processes
Water quality is intertwined with ecological functions and cycles. The global water cycle, involving evaporation, condensation, and precipitation, relies on water purity. Contaminants can enter the water cycle through pathways like chemicals evaporating into the air and returning as acid rain, or pollutants infiltrating soil to contaminate groundwater. Human activities introducing pollutants can alter the water cycle, affecting the availability of clean water.
Water quality is important for nutrient cycling, particularly the nitrogen and phosphorus cycles. Excess nutrients from agricultural runoff and sewage can enter water bodies, leading to excessive algal growth. This overgrowth depletes dissolved oxygen, creating conditions harmful to aquatic life and disrupting nutrient cycles. Wetlands contribute to natural purification processes, filtering pollutants and maintaining water quality, which supports these cycles.