Bugs

1
BugsnmudE. 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
• lt260 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

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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

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Monitoring period
event
flow
monthly
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Concentrations
Kolmogorov-Smirnov p0.000

• concentrations high during events particularly
  on rising limbs of hydrographs

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E. coli vs flow
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E. coli vs turbidity
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18-22 Sep 03
E. coli
Flow
Turbidity
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18-21 June 2004
E. coli
Flow
Turbidity
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Loads

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

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LOADEST
Inst loadobs

• E 0.55
• r2 0.69
• mean Ld 1.4 x 107 /day
• max Ld 9 x 108 /day

Daily loadpred
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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