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

Outline background research questions methods results conclusions

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

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

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

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

Monitoring period event flow monthly

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

E. coli vs flow

E. coli vs turbidity

18-22 Sep 03 E. coli Flow Turbidity

18-21 June 2004 E. coli Flow Turbidity

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

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

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