BACTERIAL CONCENTRATIONS IN BULL CREEK AUSTIN, TEXAS Patrick Sejkora

Overview  Overview  Spatial Variations  Seasonal Variations  Further Work

Bull Creek  Spring fed  Drains into Town Lake  32 mi 2 watershed  Bordered by parks Source: LCRA 2007

Bacteria in Bull Creek  Evaluate presence of harmful waterborne pathogens  Bacterial water quality is assessed by indicator bacteria  Can indicate fecal contamination  Standards for recreation are set by TCEQ Contact recreation (# per 100 ml) Noncontact recreation (# per 100 ml) E. coli (freshwater) geometric mean single sample max Fecal coliform (all waters) geometric mean2002,000 Single sample max Source: TCEQ 2007

Statistical Tests  Select focus sites  Test spatial homogeneity of indicator bacteria concentrations  Examine seasonal homogeneity of bacteria concentrations  Test for correlation between bacteria concentration and flow/precipitation

Sources of Information  Biological Information Provided by City of Austin  Flow data accessed via HydroExcel  Precipitation data from LCRA’s Hydromet

Spatial E. Coli concentrations  Examine homogeneity of E. coli concentrations between sites  t-test

Spatial E. Coli concentrations  Identify E. coli sources  Descriptive Statistics  t-test  Homogeneous between St. Edwards Park and Loop 360 (p=0.11)  Bull Creek District Park nonhomogeneous with Loop 360 and St. Edwards Park (p=3.0x10 -6 ; p= 1.1x10 -6 )  t-test suggests dogs at Bull Creek District Park could be a possible source of E. coli n: 25 Mean: 44 Median: 27 Standard Dev: 49 95% Confidence: 20 n: 57 Mean: 363 Median: 218 Standard Dev: % confidence: 121 n: 45 Mean: 69 Median: 34 Standard dev: 44 95% Confidence: 21

Weekend Hypothesis  If dogs are source, E. coli concentrations should be statistically higher on weekends  Observations  Mean E. coli concentration higher on weekends  Nonhomogeneous  Dogs appear to be cause of elevated E. coli at District Park p = 0.015

Seasonal Variations at Sites  Summer is April- October, winter is November-March  Observations  Average E. coli is higher in summer than in winter  Hypothesis  Could swallows be contributing to greater E. coli concentrations in Summer?

Winter n: 13 Summer n: 11 p = 0.04 Winter n: 34 Summer n: 23 p = 0.20 Winter n: 24 Summer n: 13 p = Seasonal E. Coli Concentrations t-test  Observations  Seasonal E. coli concentrations are:  Statistically homogeneous at Bull Creek District Park  Not homogeneous at Loop 360 or St. Edwards Park

Seasonal E. Coli Concentrations t-test  Are seasonal E. coli concentrations homogeneous between two sites?  Concentrations homogenous between seasons  Swallows cannot be conclusively linked to increased E. coli concentrations between St. Edwards and Loop 360 Winter St. Edward mean: 24.3 Loop 360 mean: 49.0 p = 0.07 Summer St. Edward mean: 62.6 Loop 360 mean: p = 0.15

E. coli concentrations and Flow  Performed on Bull Creek District Park  Homogenous yearly data  Bacteria source affected by stormwater runoff  Conclusions  No real trend

E. Coli concentrations vs. Precipitation  Precipitation may be better metric  Causes bacteria from dog doo to wash into river  Observations  Better, but still not great  Remove dry events  Much better!

Further Work  Nonparametric methods of comparing E. coli concentrations over space and time  Investigate correlation between concentrations of different indicator organisms (Fecal Coliform, Fecal Streptococci)

Questions? “People can come up with statistics to prove anything. Forty percent of all people know that!” -Homer Simpson