A salinity gradient refers to the variation in salt concentration in a body of water, often observed in oceans, estuaries, and lakes. This gradient can occur vertically, where saltier water is found at greater depths, or horizontally, where different areas have varying salinity levels. Factors such as evaporation, freshwater inflow, and ocean currents contribute to these differences. Salinity gradients are important for aquatic ecosystems, influencing the distribution of marine life. For example, organisms like brine shrimp thrive in high salinity, while others, such as salmon, prefer lower salinity levels. Understanding these gradients helps in managing and conserving aquatic environments.