Sources and Persistence of E. coli in Inland Texas Streams

Transcription

1 Sources and Persistence of E. coli in Inland Texas Streams MICHAEL BARRETT, Ph.D. UNIVERSITY OF TEXAS AT AUSTIN CENTER FOR RESEARCH IN WATER RESOURCES

2 Acknowledgements Support for this study provided by TxDOT under Project , Project Director: Stirling Robertson Dr. Mary Jo Kirisits Patrick Sejkora

3 Study Objectives Study bird colony on a highway bridge spanning stream as point source of E. coli Bird feces a significant FIB load for inland stream? Dry weather water quality Wet weather water quality Evaluate downstream persistence Evaluate role of sediment as a reservoir of bacteria Assess how sediment affects die-off

4 Site Description Bull Creek in Austin, TX Spring fed creek 32 mi2, mostly undeveloped watershed Loop 360 Bridge over Bull Creek Northernmost and first crossing Bridge inhabited by cliff swallows (Petrochelidon pyrrhonota)

5 Cliff Swallows Migrate to Texas in April-July Build mud nests on hard vertical surfaces with a 90 overhang Inhabited by breeding pairs and nestlings Piles of swallow feces directly below nests

6 Cliff Swallows Number of Birds 2009: 438 existing, sound nests on bridge (139 nests over water; 299 over land) 2010: 358 existing, sound nests on bridge (99 over water; 259 over land) Nests over water a potential source of feces directly deposited in creek Feces from nests over land could accumulate and be flushed into stream by runoff

7 Nesting Habits Timeline Egg-laying recorded as early as April 1 in Texas day incubation of egg Brooding of nestling by parents 10 days after hatching Nestlings fledge 20 days after hatching Total time at nest is days (early April to mid-may) Feces deposition likely After nesting, bird population is more scattered Direct deposition less likely

8 Sampling Sampled well-mixed areas 200 feet upstream and downstream of bridge Dry Weather Wet Weather Produced runoff > 1 cm of rainfall

9 Combined 2009 and 2010 Dry Weather a E. coli (MPN/100 ml) Upstream Downstream Geometric Mean Contact Recreation Limit Single Sample Contact Recreation Limit Foraging Nesting Foraging Mar 1 Apr 1 May 1 Jun 1

10 2009 and 2010 Combined Dry Weather ab Upstream Downstream Geometric Mean Contact Recreation Limit Single Sample Contact Recreation Limit 1000 Foraging Nesting Foraging FC (CFU/100 ml) Mar 1 Apr 1 May 1 Jun 1

11 Dry Weather Summary Statistics Swallows Absent Swallows Present Upstream Downstream Upstream Downstream Geometric Mean E. coli Concentration (MPN/100 ml) 18 (5) 35 (5) 43 (23) 106 (23) Geometric Mean Fecal Coliform (CFU/100 ml) 12 (5) 13 (5) 27 (22) 68 (22) Geometric Mean Enterococci concentration (MPN/100 ml) 22 (5) 17 (5) 5 (22) 9 (22)

12 Dry Weather Conclusions Concentrations of EC and statistically higher downstream (birds present or absent) Colonies of cliff swallows on bridges significant sources of E. coli for limited time (20-day period between hatching and fledging of nestlings) Concentrations of FC and statistically higher downstream only when birds present Majority of samples when swallows present did not exceed single sample criteria Geometric mean of FC and EC did not exceed standards

13 Wet Weather E. coli Upstream Geometric Mean Contact Recreation Limit Present Downstream Single Sample Contact Recreation Limit Present E. coli (MPN/100 ml) /1/09 6/1/09 9/1/09 12/1/09 3/1/10

14 Wet Weather Fecal Coliform Data b Upstream Downstream Geometric Mean Contact Recreation Limit Single Sample Contact Recreation Limit Present Present FC (CFU/100 ml) /1/09 6/1/09 9/1/09 12/1/09 3/1/10

15 Wet Weather Summary Statistics Swallows Absent Swallows Present Upstream Downstream Upstream Downstream Geometric Mean E. coli Concentration (MPN/100 ml) 849 (7) 1003 (7) 78 (4) 688 (4) Geometric Mean Fecal Coliform (CFU/100 ml) 561 (7) 538 (7) 68 (4) 342 (4) Geometric Mean Enterococci concentration (MPN/100 ml) 310 (7) 716 (7) 33 (4) 76 (4)

16 Wet Weather Conclusions Geometric means of all indicators exceed standards during wet weather both upstream and downstream Nonpoint sources dominant in wet weather Concentrations of FC and EC downstream not significantly higher when swallows absent Concentrations of FC and EC downstream likely significantly higher when swallows present (sample size limited) Likely due to washoff, rather than direct deposition

17 Downstream Sampling 380 ft 1100 ft 320 ft 270 ft 2080 ft E. coli (MPN/100 ml)

18 Site Description Gilleland Creek Rural watershed Effluent-dominated stream 7 Wastewater facilities Continuous E. coli point sources Existing E. coli TMDL for Gilleland Creek

19 Sampling and Analysis Protocol Collected water and sediments from creek Water and sediment placed in bottles (reactors) Reactors run for 48+ hr Dark, 30ºC Samples taken from reactors periodically E. coli Dissolved Oxygen (DO) ph Some reactors vigorously aerated

20 Summary Statistics E. coli (CFU/100 ml) TSS (mg/l) Min Max Geometric Mean Min Max Mean Water Water w/ sediment Concentration of E. coli 3x higher in reactors with sediment Exceed contact recreation criteria

21 Bacteria Survival E. coli Concentration (CFU/100 ml) DO = mg/l 70% Reduction 95% Reduction DO (mg/l) Water Water w/ sediment Time (hours) 0

22 Conclusions Dry weather concentrations of EC and FC statistically higher downstream (birds present or absent) Majority of samples when swallows present did not exceed single sample criteria Geometric mean of FC and EC did not exceed standards Wet weather geometric means of all indicators exceed standards both upstream and downstream Stream sediments a reservoir for E. coli Resuspension increases concentration and reduces die-off

23 Questions?