1. Lucy McKergow and Rob Davies-Colley
Bugs’n’mud E. 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 MfE & MoH (2003) guidelines
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. Motueka River At Woodmans Bend 2047 km2 catchment
native + exotic forest 60%, pasture 20%
mean flow 82 m3/s
median flow 47 m3/s

6. Dataset flood event samples monthly sampling 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. LOADEST Inst loadobs E = 0.55 r2 = 0.69 mean Ld = 1.4 x 107 #/day
max Ld = 9 x 108 #/day
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