Transcript No Slide Title

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
– 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
–
–
–
–
–
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
10000
1200
event
event
monthly
1000
flow
800
flow
100
600
400
monthly
10
200
1
1May03
0
9Aug03
17Nov03
25Feb04
Date
4Jun04
12Sep04
21Dec04
Flow (cumecs)
E. coli (MPN/100 ml)
1000
Concentrations
Kolmogorov-Smirnov p=0.000
105
E. coli (MPN/100 ml)
104
103
102
101
100
baseflow
rising
falling
• concentrations high
during events –
particularly on rising
limbs of hydrographs
E. coli vs flow
E. coli (MPN/100 ml)
10000
1000
100
baseflow
rising
falling
10
1
1
10
100
Flow (m3/s)
1000
10000
E. coli vs turbidity
E. coli (MPN/100 ml)
10000
1000
100
baseflow
rising
falling
10
1
1
10
100
Lab turbidity (NTU)
1000
18-22 Sep 03
5000
1000
E. coli
E. coli
Flow
Field turbidity (NTU)
900
800
3000
600
Flow
500
2000
400
300
1000
200
Turbidity
0
18Sep03 12:00
100
0
19Sep03 12:00
20Sep03 12:00
Date
21Sep03 12:00
22Sep03 12:00
3
700
Flow (m /s) and turbidity (NTU)
E. coli (MPN/100 ml)
4000
18-21 June 2004
9000
1200
E. coli
8000
Flow
Field turbidity (NTU)
E. coli
6000
800
5000
600
4000
Flow
3
E. coli (MPN/100 ml)
7000
3000
400
2000
Turbidity
200
1000
0
18Jun04
19Jun04
20Jun04
Flow (m /s) and turbidity (NTU)
1000
21Jun04
22Jun04
Date
23Jun04
24Jun04
25Jun04
0
26Jun04
Loads
• LOADEST
– USGS model
– log-linear regression
– lnQ, lnQ2, seasonality, decimal time (centred to
eliminate collinearity)
LOADEST
10000000000
1000000000
• E = 0.55
• r2 = 0.69
• mean Ld = 1.4
x 107 #/day
• max Ld = 9 x
108 #/day
Inst loadobs
Load (#/day)
100000000
10000000
1000000
100000
10000
10Dec02
Daily loadpred
20Mar03
28Jun03
06Oct03
14Jan04
Date
23Apr04
01Aug04
09Nov04
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