Beyond the shoreline: A watershed-ecosystem approach

Summary

We know virtually nothing quantitatively about the actual flow path of water through natural ecosystems, or about how the chemistry of this water is altered along the path. Yet such knowledge may be critical for attempts to understand or predict the metabolic, biogeochemical or developmental patterns for lakes and streams. Such studies would seem to be of high priority for an understanding of the land-water linkage. It is proposed that not only are there differences in the chemistry of drainage water dependant on hydrologic routing, but that these differences are large. Flow paths may be highly variable on all scales, even to determining the variable characteristics of neighboring lakes.

Long-term data are necessary to delimit meaningful extremes and averages for natural ecosystems. Short-term records (1 to 3 years) may be misleading relative to (1) ecosystem characterization, (2) trends in environmental data, and (3) management recommendations. Data from the Hubbard Brook Ecosystem Study are used to illustrate these points.

It is proposed that in forested terrain, overland flow is negligible, erosion is minimal, and fluvial particulate matter originates primarily from erosion of stream channels and adjacent flood plains. Of importance limnologically is that the composition (e. g. content of carbon, phosphorus and nitrogen, size distribution of particles, proportion of inorganic to organic) of materials entering aquatic ecosystems varies depending upon sources as well as the pattern and rate of erosion. Land use changes (stream channelization, road building, urbanization, etc.) not only affect the magnitude of erosion, but also the hydrologic routing and associated processing of the eroded materials. Disturbance beyond the shoreline may overwhelm natural linkages between terrestrial and aquatic ecosystems and may dictate the biogeochemical and metabolic activity within lakes or streams.