Bugs’n’mud E. coli , turbidity and flow relationships for the Motueka River

1. Bugs’n’mudE. coli, turbidity and flow relationships for the Motueka River Lucy McKergow and Rob Davies-Colley

2. Outline • background • research questions • methods • results • conclusions

3. Background • E. coli bacteria • indicator for freshwater recreation • source= faecal contamination from warm-blooded animals • transport = surface runoff, subsurface flows, direct deposition, re-entrainment of bed sediment • MfE & MoH (2003) guidelines • <260 cfu/100ml acceptable • in small streams turbidity can be used as a surrogate for E. coli

4. Research questions • can turbidity be used as a surrogate for E. coli in large rivers? • how many E. coli are exported to Tasman Bay?

5. At Woodmans Bend 2047 km2 catchment native + exotic forest 60%, pasture 20% mean flow 82 m3/s median flow 47 m3/s Motueka River

6. Dataset • flood event samples • June 03-June 04 • sample interval 10 to 30 minutes –auto sampler • continuous turbidity - OBS • lab turbidity – NTU • E. coli – Colilert, most probable number/100 mL • monthly sampling • May 03 – Dec 05

7. Monitoring period event flow monthly

8. Concentrations Kolmogorov-Smirnov p=0.000 • concentrations high during events – particularly on rising limbs of hydrographs

9. E. coli vs flow

10. E. coli vs turbidity

11. 18-22 Sep 03 E. coli Flow Turbidity

12. 18-21 June 2004 E. coli Flow Turbidity

13. Loads • LOADEST • USGS model • log-linear regression • lnQ, lnQ2, seasonality, decimal time (centred to eliminate collinearity)

14. E = 0.55 r2 = 0.69 mean Ld = 1.4 x 107 #/day max Ld = 9 x 108 #/day LOADEST Inst loadobs Daily loadpred

15. Conclusions • bugs and mud are from different sources • turbidity may not be a consistently useful surrogate for E. coli in large rivers • alternative is to use flow