Identify three factors that characterize aquatic systems.

Three factors that characterize aquatic systems are:

1. Salinity: Salinity refers to the saltiness or dissolved salt content of a body of water. This is a critical factor because it influences the types of organisms that can live in the water. Freshwater systems have low salinity, marine ecosystems have high salinity (think oceans), and there are also brackish environments which have an intermediate level of salinity. The different salinity levels are a result of the water source and the rate of evaporation among other factors.

2. Depth: The depth of the aquatic system affects the amount of sunlight that can penetrate the water, which in turn influences the types of plants and animals that can survive there. In deeper waters, less light penetrates, thus restricting photosynthesis primarily to the surface layers known as the photic zone. Below this, in the aphotic zone, plants cannot survive, which in turn affects the types of animals living there.

3. Flow: The movement of water can vary greatly between different aquatic systems and is a significant ecological factor. In still waters, such as ponds and lakes, the water movement is minimal, resulting in stratification of nutrients and temperature. In contrast, rivers and streams have flowing water which affects sediment distribution, nutrient cycling, and the types of organisms that can live there. Flow can influence the oxygenation of the water, the transport of organisms and materials, and the physical shape of the aquatic habitat.