Download Mark Breunig GEOG 681 Assignment: Articulate a model topic or

Mark Breunig
GEOG 681
Assignment: Articulate a model topic or phenomenon
Model Topic: The utility of spatially explicit variables in watershed scale phosphorus water quality
modeling
The overall purpose of this model topic is to increase the effectiveness of watershed-scale phosphorus
water quality modeling. Most watershed-scale phosphorus water quality models perform poorly when
compared to observed data sets, because the scientific community does not properly understand the
complex interactions that occur at this scale. The goal of this model is to develop “spatially explicit”
variables that more accurately represent what controls the long term average phosphorus concentration
in a stream.
I will be using a data set obtained from the USGS that consists of 2001 median total phosphorus values
at 241 stream monitoring sites in Wisconsin. The agents are surface overland flow paths from origin
pixels to a receiving water body. Landscape characteristics are collected/calculated along these flow
paths. The goal is to develop one or more spatially explicit landscape characteristics that explain more
variation in the observed data set than the non-spatially explicit variables used in the USGS paper.
Potential Downfalls: There are several downfalls involved with watershed scale phosphorus water
quality modeling noted in the literature. The datasets currently available at the watershed scale (30 m
DEM, NALCD 30m, STATSGO/SSURGO) are generalizations of the landscape and have inaccuracies.
Because of this, micro-topography cannot be represented at the watershed scale. Micro-topography
can have significant impacts of the characteristics of flow paths. Observed water quality data sets also
have issues – they may not always be representative of long-term average annual conditions.