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Landscape Characterization / Impervious Surfaces / What are the effects? / Habitat degradation and destruction
What are the effects?
Habitat Degradation, Loss, and Fragmentation
Aquatic and terrestrial habitats are increasingly degraded
and lost as greater percentages of watershed areas are made impervious.
The following sections focus upon these impacts which include habitat
degradation, habitat loss, and habitat fragmentation.
Habitat degradation is the diminishment of habitat quality
and its ability to support biological communities. It stems from the
adverse effects of urban development, such as increases in impervious
surfaces within watersheds. Its adverse effects can be immediate or
cumulative.
Habitat loss is the outright destruction of habitat, such
as filling a wetland or channelizing a section of stream. Its impacts
upon biological communities are immediate and catastrophic.
Habitat fragmentation is the piecemeal disassembly of terrestrial
habitats into discontinuous, oftentimes isolated, patches as a consequence
of development. Its adverse effects are cumulative and not immediately
noticeable. Habitat fragmentation stems from habitat loss.
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Effects on aquatic organisms and streams
Aquatic and bay habitats are adversely impacted by the nonpoint pollutants
and the higher volumes of runoff issuing from urbanized lands. Observable
declines in the biological integrity of streams and the quality of
stream habitats occur when watershed imperviousness reaches 10% to
15%.
Source: NEMO after Schueler, 1994
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Observable indicators of stream health degradation
include:
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population shifts to aquatic organisms tolerant
of poor water quality and poor habitat,
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less riparian vegetation,
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reduced macroinvertebrate, fish, and amphibian
diversity,
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lower plant and amphibian density,
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increased sediment and stormwater runoff,
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fewer snags in channels to dissipate energy,
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channel instability.
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The biological degradation of streams is manifested more
quickly than physical degradation. There is a time lag, often of several
years, between both increased runoff and the sedimentation that results
from urban development and subsequent stream channel readjustment. Channel
readjustments may include bank or bed erosion and channel scour or deposition,
depending upon climate and other factors. In contrast, aquatic organisms
respond quickly to poor water quality, more frequent peak flows, higher
flow velocities and loss of resting areas, habitat loss, higher sediment
loads, and the reduced availability of food, all of which are associated
with the urbanization of streams.
Stream bank erosion due to rapid stormwater runoff.
Source: Jonson, Baltimore County DEPRM.
In some areas, natural stream channels have been replaced
by artificial channels. Artificial channels are hostile
to aquatic life and are not aesthetically pleasing.
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| Source: CGIS after Goudie, 1990 |
Effects on terrestrial organisms and habitats
Urban and suburban development, particularly spatially
dispersed forms such as large-lot single family housing, result
not only in greater amounts of impervious surfaces throughout watersheds,
but destroy and fragment terrestrial habitats. Urban growth may
reduce habitat to residual patches that are too small to meet the
ecological requirements of animals, birds, and plants, especially
those which require large tracts of uninterrupted habitat or which
are sensitive to human intrusion. Organisms in these patches become
increasingly isolated by adjacent environments which are inhospitable
and difficult or dangerous to cross.
Habitat Before and After Development
One consequence of habitat fragmentation is an increase
in the amount of edge (boundaries between different habitats), such
as that between a forest and a road or a lawn and a wetland. Some
species, such as white-tailed deer and turkeys, benefit from edges.
However, increases in edges are generally detrimental to overall
biodiversity.
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Edge Effects include:
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Increased plant desiccation and wind-throw
hazard,
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More frequent and more severe wildfires,
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Increased poaching and hunting,
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Higher predation rates,
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Heavier browsing and more disturbances
that favor opportunistic species,
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Increased cowbird parasitism of song
bird nests.
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Looking for the tools to protect your local watershed
and ideas on how to manage urban development? For factsheets and
literature on watershed protection and imperviousness, discussion
of land-use planning and management techniques, and model ordinances
check out:
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© CGIS at Towson University |
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