Watershed ecology is essential knowledge for watershed managers because it teaches us that watersheds have structural and functional characteristics that can influence how human and natural communities coexist within them. The gross structure of a watershed -- its headwaters area, side slopes, valley floor, and water body, as well as its soils, minerals, native plants and animals -- are, in one sense, raw material for all the human activities that may potentially occur there. The watershed's natural processes -- rainfall runoff, groundwater recharge, sediment transport, plant succession, and many others -- provide beneficial services when functioning properly, but may cause disasters when misunderstood and disrupted. It is crucial for people to understand watersheds and how they work before they make decisions or take actions that may affect important watershed structural or functional characteristics.
Watershed: An area of land that drains water, sediment and dissolved materials to a common receiving body or outlet. The term is not restricted to surface water runoff and includes interactions with subsurface water. Watersheds vary from the largest river basins to just acres or less in size.
Watershed Ecology: The study of watersheds as ecosystems, primarily the analysis of interacting biotic and abiotic components within a watershed's boundaries.
Ecosystem: A functioning natural unit with interacting biotic and abiotic components in a system whose boundaries are determined by the cycles and flux of energy, materials and organisms. It is valid to describe different ecosystems with different, overlapping sets of boundaries in the same geographic area (e.g. forest ecosystems, watershed ecosystems and wetland ecosystems). A watershed is just one of many types of ecosystems.