BEACHNET==> New publication of interest

[Sheridan K Haack <skhaack@usgs.gov>]

Environmental Factors and Flow Paths
Related to Escherichia coli Concentrations at Two Beaches on Lake St. Clair,
Michigan, 
2002–2005. U.S. Geological Survey Scientific
Investigations Report 2008–5028
By David J. Holtschlag, Dawn Shively,
Richard L. Whitman, Sheridan K. Haack, and Lisa R. Fogarty

http://pubs.usgs.gov/sir/2008/5028/

Abstract
        Regression
analyses and hydrodynamic modeling were used to identify environmental
factors and flow paths associated with Escherichia coli (E. coli) concentrations
at Memorial and Metropolitan Beaches on Lake St. Clair in Macomb County,
Mich. Lake St. Clair is part of the binational waterway between the United
States and Canada that connects Lake Huron with Lake Erie in the Great
Lakes Basin. Linear regression, regression–tree, and logistic regression
models were developed from E. coli concentration and ancillary environmental
data.
        Linear
regression models on log10 E. coli concentrations indicated that rainfall
prior to sampling, water temperature, and turbidity were positively associated
with bacteria concentrations at both beaches. Flow from Clinton River,
changes in water levels, wind conditions, and log10 E. coli concentrations
2 days before or after the target bacteria concentrations were statistically
significant at one or both beaches. In addition, various interaction terms
were significant at Memorial Beach. Linear regression models for both beaches
explained only about 30 percent of the variability in log10 E. coli concentrations.
        Regression–tree
models were developed from data from both Memorial and Metropolitan Beaches
but were found to have limited predictive capability in this study. The
results indicate that too few observations were available to develop reliable
regression–tree models.
        Linear
logistic models were developed to estimate the probability of E. coli concentrations
exceeding 300 most probable number (MPN) per 100 milliliters (mL). Rainfall
amounts before bacteria sampling were positively associated with exceedance
probabilities at both beaches. Flow of Clinton River, turbidity, and log10
E. coli concentrations measured before or after the target E. coli measurements
were related to exceedances at one or both beaches. The linear logistic
models were effective in estimating bacteria exceedances at both beaches.
A receiver operating characteristic (ROC) analysis was used to determine
cut points for maximizing the true positive rate prediction while minimizing
the false positive rate.
        A
two–dimensional hydrodynamic model was developed to simulate horizontal
current patterns on Lake St. Clair in response to wind, flow, and water–level
conditions at model boundaries. Simulated velocity fields were used to
track hypothetical massless particles backward in time from the beaches
along flow paths toward source areas. Reverse particle tracking for idealized
steady–state conditions shows changes in expected flow paths and traveltimes
with wind speeds and directions from 24 sectors. The results indicate that
three to four sets of contiguous wind sectors have similar effects on flow
paths in the vicinity of the beaches. In addition, reverse particle tracking
was used for transient conditions to identify expected flow paths for 10
E. coli sampling events in 2004. These results demonstrate the ability
to track hypothetical particles from the beaches, backward in time, to
likely source areas. This ability, coupled with a greater frequency of
bacteria sampling, may provide insight into changes in bacteria concentrations
between source and sink areas. 

***************************************************
Sheridan Kidd Haack
USGS, Lansing, Michigan 48911
Phone: 517-887-8909
Fax: 517-887-8937