Watershed ecology is as much a philosophy as a scientific investigation. It is a purposeful search for communal awareness, that interconnectedness that ties together everything on and within this water planet. It integrates geology, hydrology, chemistry, biology, sociology, economics, history and art into a composite science that can transcend many artificial boundaries of academics.

It is a complexity of perspectives that witnesses life as individuals and communities, cycles and flows, biofilms and biosphere. Watershed ecology is a management-based scientific pursuit that seeks not to manage streams and rivers, but the behavior of ourselves and our societies interacting with and depending on these watershed ecosystems.

Our approach to watershed ecology is one of systems. Through a description of watershed structure, functions and dynamics, we can mentally dissect, compartmentalize and disassemble a watershed, and then put it back together again. This mental process, guided by watershed maps and flow charts, allows us to realize the complexity of watersheds and begin to appreciate that the whole is greater than the sum of its parts.

Our sweep takes us through a watershed continuum from headwaters to reefs, ridge crests to main channels, surface waters to aquifers as we both describe and explore upstream/downstream connections, lateral connections, vertical connections and web-of-life connections within watershed systems. Many of the world's major rivers have been severely abused by our industries, cities and agriculture. Sediment, heavy metals, pesticides, hazardous materials, sewage and engineering projects have impacted our flowing water systems for decades. Many of these impacts are being exported to other countries as the technology and economic influence spread from developed nations to other parts of the world.

In order to begin to understand the nature of local, regional and global scale effects of these multiple impacts, an understanding of the nature and function of not just rivers, but entire watersheds, is required.

Watersheds are discrete units of land area defined by ridges and divides that shed water into a common drainage or outlet to a lake or sea. They are denudation systems defined by patterns of regional geology and climate that sculpt and define landscapes. Watersheds are predominately unidirectional collection, storage, processing and transport systems for water, energy, sediment, nutrients and life connecting the land and the sea. Watersheds are transitional, multi-layered complexes of ecosystems and ecotones that transect many different environments from headwaters to river mouths, uplands to mid channels and surface waters to aquifers. Watersheds are the natural habitat of most people of the world and therefore the ecosystem complex most impacted by human exploitation, ignorance and carelessness. At any one point in time, the streams and rivers of the world contain only about 0.0001% of the ecosphere's water. However, all of the active waters of the Earth have cycled though these global flowing water systems many times throughout the eons. We are just beginning to recognize and appreciate the importance of watersheds on such a scale.

Forests feed streams. Streams feed rivers. Rivers feed the sea. Headwaters are composed of many small, branching streams that form the headwaters, representing most of the total stream length within a watershed. Leaves, fruit, branches and whole trees of stream side forests fall into these headwater streams. Fungi and bacteria grow on the surface of this detritus and begin to break down the complex cellulose molecules of dead plant material. A group of aquatic invertebrates collectively called "shredders" tear apart decaying plant material as they ingest the rich biofilm of fungi, bacteria and associated protozoans and microinvertebrates growing on the surface of detritus materials.

As shredders gnaw through wood and leaf, they create fine particulate organic matter that is filtered from the flowing water by collectors. This group of organisms, invertebrates that spin fine capture nets or are equipped with long bristles, can collect these small suspended particles coated with biofilm communities. Collectors build up nutrients in their own biomass or fecal pellets. These nutrients thus become available as food for predators.

Energy laden nutrients, originally derived from riparian forests, are eaten and released and eaten again as they spiral downstream. These nutrients flow from headwaters to mid-reach streams where other aquatic communities await. Nutrients flowing from mid-reach to lower river reaches are harvested by a different community of collectors. Excess nutrients finally flow out of river mouths to enrich estuaries. Estuaries in turn release their nutrients into the world's coastal waters.

Watersheds are far more complex than just streams and rivers. They are composed of swamps, marshes, blackwater streams and other special habitats. Watersheds include not just surface waters, but aquifers, groundwaters and the hyporheic zone. The high energy hyporheic zone forms a wet sleeve of solid material and water that surrounds the free flowing waters of streams, rivers and wetlands and is one of the most challenging frontiers of watershed ecology. Rapid assessment, routine monitoring and detailed study of rivers and entire watersheds are critical to further our understanding of not just general watershed ecology, but local streams systems in particular.

We are often not able to afford time and money to conduct such detailed investigations as may be required. Rapid Bioassessment protocols have been developed as alternatives to costly field monitoring activities. RBAs can be used to quickly characterize the existence and intensity of local land use practices, identify sources and causes of impacts and describe ecosystems conditions. RBA methods are becoming available to watershed residents concerned for the health of their local watersheds. Through these methods, citizens are able to take charge of assessing the condition of neighborhood ecosystems and alert government agencies when threatening conditions are identified. In the hands of communities, such tools promote the advancement of a system of environmental democracy where citizens are assessing environmental conditions and compelling government agencies to take appropriate actions under the watchful eyes of watershed resident advocacy networks.