Environmental Engineering Reference
In-Depth Information
Water
Floodplains, swamps
Upstream
ecosystems
DOM
Bacteria
Primary
producers
Heterotrophic
protozoa
Downstream
ecosystems
FPOM
Invertebrate
drift
Terrestrial
ecosystems
Predators
Interstitial
DOM
Algae
Filtering
collectors
Extra cellular
matrix
Scrapers
Gathering
collectors
Benthic
CPOM
Bacteria
Protozoa
Fungi
Bacteria
Shredders
Benthic
FPOM
Algae
Meiofauna
Protozoa
Gathering
collectors
Bacteria
Protozoa
Meiofauna
Unstable substrates
FIGURE 16.3
Diagram of the food web in the Ogeechee River, a southeastern blackwater river. The food web
is a mosaic of webs, each characteristic of a particular habitat type and linked by flowing water. Each habitat is
denoted by a different color: water column (green), unstable substrates (mustard yellow), and stable substrates
(blue). Brick-colored arrows denote consumption by predators, green arrows indicate movement into the water.
(From
Meyer 1990
.)
Stable substrates
and inputs of light and nutrients, which alter productivity and food web structure
in streams (e.g.,
Webster et al. 1992
). Human actions on the land influence stream ecosys-
tems via many pathways: altered hydrologic and temperature regimes, increased
sedimentation, increased nutrient and contaminant inputs, less woody debris, and
changes in organic matter inputs (
Allan 2004
). Understanding the mechanisms by which
landscape alteration impacts streams is a difficult task because a change in land use
altersmanypathwaysatthesametime(e.g., converting a forest to a housing develop-
ment reduces leaf litter inputs to streams while also increasing sedimentation, nutrient
inputs, and light).
To better understand just one of these pathways (reduced inputs of leaf litter), my collea-
gues and I used an experimental approach in a small headwater stream. We prevented leaf
litter from entering the stream by putting a net over it (Fig. 3.6), and observed marked
