Inorganically mediated work 

 refers to the forces attendant to 

 basic physical/chemical background 

 conditions, such as climate, which 

 affect all aspects of watershed 

 metabolism. Forces such as sun- 

 light, winds, tidal fluctuations, 

 heat flux, rainfall, atmospheric 

 chemical fallout, and osmotic gradi- 

 ents form the basic energy sources, 

 or forcing functions, that drive the 

 metabolism of the watershed. These 

 naturally occurring energy sources 

 "work" for the watershed in the 

 sense that they both force and allow 

 changes to occur in the composition 

 of the biota, soils, and water. 



Biologically mediated work 

 refers to the processes involved in 

 the transformation and storage of 

 energy and matter into plant and 

 animal biomass, and its subsequent 

 degradation. In the context of 



watershed metabolism, organisms form 

 sites at which complex energy and 

 material processing occurs, such as 

 the uptake of nutrients from the 

 soil and water, the evolution of 

 oxygen or carbon dioxide, or the 

 transformation of fish biomass into 

 bird feathers. 



Within the boundaries of a 

 watershed, these two forms of work 

 are integrated at every ecological 

 level of organization. At the spe- 

 cies level, individual populations 

 are continually fine-tuned to their 

 environment through adaptations in 

 behavior, physiology, and anatomy. 

 Simultaneously, species also develop 

 interdependencies that promote 

 mutual survival and exploitation of 

 physical/chemical energies. This 



process results in the formation of 

 characteristic environments referred 

 to as habitats, or communities. 



At higher ecological levels 

 ("higher" meaning greater spatial 

 and temporal coverage), this inte- 



gration becomes increasingly com- 

 plex. The linkage may be direct as 

 in very specific reproductive needs; 

 or indirect as in trophic web rela- 

 tionships between producers and con- 

 sumers in widely separated habitats. 

 When these factors are superimposed 

 onto natural fluctuations in cli- 

 mate, invasions of species into new 

 environments, and continual habitat 

 alteration, it becomes necessary to 

 focus on integration at the ecosys- 

 tem level. 



For our purposes the term "eco- 

 system" refers to any series of 

 interrelated habitats. An "estu- 



arine ecosystem", for instance, 

 encompasses numerous habitats such 

 as mud flats, grass beds, oyster 

 reefs, sand bottoms, muck bottoms, 

 open waters, salt marshes, and man- 

 groves. These habitats are inter- 

 connected by wind and tidal mixing, 

 freshwater flushing, and by a broad- 

 ly tolerant and wide ranging variety 

 of resident and seasonal species, 

 each with their own adaptive strat- 

 egy for survival. In an upland 

 ecosystem setting, the movements of 

 birds, mammals, and insects (beyond 

 the boundaries of vegetation types), 

 as well as massive resource move- 

 ments such as seed dispersion and 

 runoff, results in the overlapping 

 of terrestrial habitats. 



Although one could legitimately 

 look at many levels of ecological 

 organization for important patterns 

 of integration between organisms and 

 their environment, the watershed is 

 a particularly fundamental unit. 

 The hydrologic integrity of a water- 

 shed provides a fairly stable tem- 

 plate around which interconnected 

 habitats can become organized into 

 an ecosystem. Background geology, 

 soils, and latitude of the watershed 

 strongly influence the plants and 

 animals that inhabit the drainage 

 basin. These "habitats" in turn 



