Sampling issues in river health Sampling issues in river health assessmentassessment

Dr Chris Gippel, AustraliaDr Chris Gippel, Australia

Workshop on China’s national river health assessment programWorkshop on China’s national river health assessment program

Ministry of Water ResourcesMinistry of Water Resources

2012 February 222012 February 22

Basin andcatchment

Functional processzone

Reach Site Microhabitat

100 – 1,000,000 km2 10 – 1000 km2 100 – 10,000 m 1 – 100 m 0.1 – 1.0 m

Scale

Sensitivity to changeLow High

Report aggregatedsite scores

Report individualsite scores

Border Rivers

Fish Macroinvertebrates

How many sites?• Murray-Darling Basin

– 1,061,469 km2

– 506 fish sites; 773 invertebrate sites• 1 site per 2,100 km2 for fish• 1 site per 1,370 km2 for macroinvertebrates

• Victoria– 227,416 km2

– 1,040 reaches/sites• 1 site per 219 km2

• SE Queensland– 22,420 km2

– 135 sites• 1 site per 166 km2

• Budget• Objective

– Confirm known issues (e.g. sewerage pollution)• Wherever the issues are located

– Monitor catchment health change over time• Sufficient statistical power to detect change

How many sites?

Number ofsites required

to detect change

few

many

Variation in space Variation in time

low

low

high

high

high

low

high

low

• Budget• Objective

– Seasonal variation important (depends on system)– 2 times per year

– Fit in with annual reporting schedules

– 1 or 2 times per year

– Long term change is main priority– Every 2 – 5 years

– Slowly changing parameters (e.g. vegetation, physical form)– Every 2 – 5 years

How often to sample?

Where to locate the sites?• Budget• Objective

• Random– Most expensive– Most statistically sound– Mix of fixed and non-fixed sites

• Stratified– Freedom to chose exact site within a specified zone

• Non-random– “Data hunting” – looking for evidence of known issues– Avoiding sites with poor health– Selecting only large rivers, or high profile sites– Risk of systematic bias (e.g. all sites near roads or bridges)

Sampling at the chosen site

• If chosen because of easy access, avoid unusual activity:– vehicles crossing the stream;– waste disposal;– recreational angling;– sand and gravel extraction;

– timber collection;

– washing clothing and vegetables

• Follow standard protocols

Summary

• Sampling strategy depends on:– Budget– Objectives– Expected variability of the data– Reporting scale

Need to establish these things before setting the sampling sites

• Program sampling strategy should be designed by a statistician– As a minimum, report the sampling strategy

• Follow standard protocols at the site