Geoscience Reference
In-Depth Information
scales (Wickham et al.
2004
; Homer et al.
2004
). Impervious surface areas
(the built environment, like buildings, roads, parking lots) increase the amount of
pollutants within and the temperature of runoff reaching streams. Forested riparian
buffers, on the other hand, preserve or increase stream quality by contributing leaf
litter, regulating temperature and sunlight, deterring erosion and retaining nutrients
(e.g. Jordan et al.
1997
; Lowrance et al.
1997
; Groffman et al.
2004
). Despite a great
deal of effort, much of the progress that has been made in restoring the health of the
nation's waterways has been offset by continued urban, suburban, and exurban
development (CBPO
1998
; Wickham et al.
2005
). The expansion of impervious
surface areas associated with this urban growth disrupts aquatic biology and
degrades water quality by inhibiting infiltration, increasing peak flows, reducing
base flows, reducing lag time between storm events and peak discharge (i.e.,
increased flashiness), facilitating the overland transport of pollutants, and increas-
ing sediment loads associated with stream channel incision and erosion (see updated
review by Schueler et al.
2009
).
Other impacts result from the associated loss of resource lands (forests,
wetlands and riparian buffer areas), which serve ecological functions such as
filtering water flows and buffering chemical pollutants (e.g. Goetz et al.
2004
).
Many of these pollutants arise from impervious surface areas, particularly the
roads and parking lots built to accommodate increased vehicle use. The adverse
effects of these changes can be mitigated by increased vegetation cover, land-
scape configuration, and low-impact development techniques, which together
reduce the volume and velocity of overland flows, uptake excess nutrients and
pollutants, maintain stream bank integrity, provide shade that reduces stream
warming, and generally reduce the negative ecological and economic impacts
of urbanization.
As a result of the processes described above, landscape configuration modifies the
relationship between land use and in-stream biological metrics, such as the widely
used index of biological integrity (IBI). Those elements that may have an effect on
stream quality at the catchment scale, such as water chemistry (Sponseller et al.
2001
)
and non-point source pollution (Paul et al.
2002
), may not retain their predictive
power at more local (e.g. riparian or near-stream) scales, and vice versa (Jones et al.
2001
). With particular reference to the relationship between stream macroinver-
tebrates and watershed scale land cover, distance to the stream channel appears to
be a key variable that can influence the relative importance of specific land cover
variables (Walsh et al.
2005
;Kingetal.
2005
; Goetz and Fiske
2008
). Recent work
also emphasizes the spatial arrangement of landscape patches (Strayer
2006
), gradi-
ent/slope complexity (Snyder et al.
2003
), and dominant substrate (Lammert and
Allan
1999
). Assessing the influence of riparian zone land cover over large areas has
also increased in recent years as a result of more widely available high resolution
sources of land cover data with relevance to riparian buffer mapping and monitoring
(see review by Goetz
2006
). It is thus now more feasible to use comparable metrics of
riparian buffer properties, combined with those of stream hydrology, lithology, and
other landscape metrics to more fully assess the influence of human land use on
stream ecosystems at a variety of spatial scales (Allan
2004
; Brabec et al.
2002
;
Grimm et al.
2008
; Nilsson et al.
2003
; Parsons et al.
2002
).
