Stream ecology in relation to land use

The primary aquatic interface with the terrestrial environment occurs insmall watersheds and valley streams. The input of organic and inorganic materialsto streams arises on the landscape. As a result, the events in the terrestrialenvironment largely determine what materials streams receive. These lossesfrom the landscape are a relatively insignificant quantity of material so far asthe terrestrial environment is concerned. However, these organic and inorganicmaterials represent both a tremendous resource to the aquatic environment and apotential for destruction of its living resources.
For example, after a watershed is clearcut, nutrient losses (specificallynitrogen and phosphorus) from forest ecosystems are relatively low where vegetativegrowth recovers rapidly. While the values may be low in relation to the total forestnutrient capital, concentrations of nitrate and phosphate in streams draining clear-cuts may increase 20 to 100 fold for a period of 1 to 3 years after clearcutting. Themicrobial and algal communities of these streams live in an environment in whichnutrient levels are extremely low, quite possibly limiting. The effect on theseorganisms of a sudden and sustained 20 to 100 fold increase in nitrogen and phosphorusis poorly understood, but of great significance in the breakdown of organic debrisand growth of algae.
Likewise, increases in stream temperature have been shown to be significantfollowing logging in both coniferous and deciduous forests. Coupled with nutrientincreases, the impact on algal growth and the rates of decomposition of organicdebris is quite significant.
Many excellent studies have been conducted on small streams for water export,water quality, suspended sediments, and nutrient runoff. Some of these studieswere discussed by Dr. Reichle. All provide a very valuable beginning for the streambiologists. However, the approach to looking at the effects of logging, irrigationdiversion, or fertilization on streams has yet to consider the stream as a living system.
That streams have not been looked at as living systems by land-use managersis not too surprising. To look at a stream's processing structure and capabilitiesis an enormous undertaking. The formulation of suitable management practicesfor streams has been greatly hampered by the lack of fundamental data on thefunctioning of stream systems. Since it is non-polluted streams that man wishes tomaintain or restore, the data required necessarily involve the complex communitiestypical of healthy streams. Through the Analysis of Ecosystem program streamecologists have begun to provide the conceptualization and basic data essential
for the intelligent preservation, manipulation, and rehabilitation of our continentalstreams. The general strategy of the Analyses of Ecosystems stream groups has beento describe the structure and function of a "representative" stream for a geographicalarea. Emphasis has been placed on process and transfer rates.
The experimental approach has been directed at achieving predictive capabilityrelated to land manipulations that change these processing and transfer rates (e.g.,clearcutting, irrigation diversion, nutrient inputs). The attempt is being made toset the permissable ranges of alterations of various biological parts or' streams thatresult from a given manipulation of the light, temperature, current, and nutrientregimes or from particulate and dissolved organic inputs.