Geoscience Reference
In-Depth Information
The basis of our comparison relies on date-matching the stream IBI and land
cover data and that all of our samples were part of one homogenous physiographic
province. The reality is that a mismatch in time is possible between our land cover
data and stream biotic samples, thus these typs of analysis (given adequate data)
should be stratified by state or, even better, well defined physiographic region.
Likewise, sample timing and seasonality can also decouple the connection between
invertebrate health/activity and land cover metrics.
The predictions of nEPT for an entirely different watershed, the upper Delaware
(Fig.
4.6
), appear consistent with our results for the New England watersheds,
despite differences in topography and, to a lesser extent, in geological substrate.
This watershed is experiencing rapid changes in land use via expanding residential
development and associated exurbanization, which implications for stream biota.
The streams of this watershed are just beginning to be systematically monitored
for aquatic biota, including nEPT, by the National Park Service. Predicted maps of
this sort, based on land cover variables, provide a baseline against which in situ
stream measurements can be compared and assessed as the program develops.
It is known from previous work (e.g. Bolstad and Swank
1997
;Boothand
Jackson
1997
), that management practices, storm water routing, point source
pollution (sewage treatment plants, poultry plants, etc.), and other factors, can
influence the relationships between land cover and stream biota. Moreover,
impacts on stream health and water quality are not threshold responses, but
more closely approximate a gradient in which even rural areas with reduced
tree cover may display impairments comparable to more urbanized reaches
(Booth et al.
2002
;Moglenetal.
2004
; Goetz and Fiske
2008
). Nonetheless,
the results presented here indicate that land cover metrics explain the majority or
variation in stream biotic metrics in southern New England watersheds, and as
such can be used as helpful indicators of stream impairment that can, in turn, be
used to focus monitoring, restoration and protection management objectives.
Moreover, these results support increasing evidence that reducing impervious
cover in new residential and commercial development, or reducing the impacts
of impervious areas through mitigation measures such as riparian buffers and
overall tree cover within a watershed, is beneficial to stream water quality and
associated biotic health.
References
Allan JD (2004) Landscapes and riverscapes: the influence of land use on stream ecosystems.
Annu Rev Ecol Evol Syst 35:257-284
Baker ME, Weller DE, Jordan TE (2006) Comparison of automated watershed delineations:
effects on landcover areas, percentages, and relationships to nutrient discharge. Photogramm
Eng Remote Sens 72(2):159-168
Bolstad PV, Swank WT (1997) Cumulative impacts of land use on water quality in a southern
Appalachian watershed. J Am Water Resour Assoc 33:519-533
