Environmental Engineering Reference
In-Depth Information
wastewater treatment plants and agricultural fields). Scientists and engineers studying lake
eutrophication tended to view streams as sources of water and nutrients, as “pipes” on the
landscape delivering materials to lakes. Using the mass balance approach that had proven
so powerful in understanding forested ecosystems (e.g.,
Likens and Bormann 1995
), stream
ecologists showed that stream ecosystems could not be treated as pipes; biogeochemical
processes in streams (
Figure 16.1
) transform the nutrients and organic matter entering
them, thereby altering the quantity, form, and timing of exports to downstream ecosystems
(e.g.,
Fisher and Likens 1973; Meyer and Likens 1979; Triska et al. 1984
).
Despite a general recognition that streams are ecosystems, input
output budgets for
watersheds are often interpreted as indicating only the impact of terrestrial ecological
processes on nutrient exports. Changes in nutrient export have been evaluated with
respect to changes in the terrestrial ecosystem, ignoring the nutrient transformations that
occur in the stream (e.g.,
Vitousek and Reiners 1975; Aber et al. 1998
). Yet stream
researchers have demonstrated significant removal and transformation of nutrients in
streams (e.g.,
Meyer and Likens 1979; Peterson et al. 2001
); failing to recognize those
stream processes makes it impossible to accurately identify the mechanisms causing
observed patterns in nutrient export.
SURFACE EXCHANGES
Bank and
floodplain
erosion
Gas
exchanges
Litterfall
and blow-in
Insect
emergence
Floodplain
deposition
Egg laying
Rainfall
Surface runoff
Solutes
TRANSPORT
Adsorption
Microbial uptake
Precipitation
Complexation
Desorption
Leaching
Mineralization
Dissolution
WATER
COLUMN
Suspended particles
and microbial organisms
TRANSPORT
Exudation
Sloughing
A
dsorption
Precipitation
Sedimentation
Resuspens
ion
Desorption
Dissolution
Abiotic
Particles
Plant
uptake
Plants
Herbivory
STREAM-
BED
Microbial
uptake
Sedimentation
Adsorption
Leaching
Resuspen
sion
Desorption
Mineralization
Filter
Feeding
Excretion
Egestion
Drift
Detritus and
Microbial
Organisms
Consumers
Consumption
INTERSTITIAL
WATER
TRANSPORT
Solutes
SUBSURFACE EXCHANGES
FIGURE 16.1
Conceptual diagram illustrating hydrological and biogeochemical processes that transport and
cycle nutrients and organic matter in stream ecosystems. (From
Stream Solute Workshop 1990
.)
