MONITORING FREQUENCIES AND OPTIMIZATIONS

3.5. Monitoring frequencies and optimizations Peter Kelderman UNESCO-IHE Institute for Water Education Online Module Water Quality Assessment

3 The type/objectives of monitoring Variations in parameter values Statistical significance and accuracy required. So within one water quality monitoring programme, there can be quite different frequencies used. Frequency of monitoring based on:

4 So frequency can be, for example: Annually for overall trend analysis in ambient monitoring Monthly/weekly for e.g. seasonal trends and more detailed ambient monitoring Permanently, in case of early warning monitoring Also the applied frequencies will always be a compromise between the “needs” and the “available resources” (e.g. budget). Frequency dependent on objectives

5 In evaluating the necessary monitoring frequency, statistical tests play an important role  See Course 4 Standard deviation and Confidence Intervals Allowable error Correlation analysis.. Why high frequencies? Well, for example to prove that a lake’s P content this year is significanty lower than that of last year. Statistics

6 Reliability of monitoring will increase with the √ (number of observations) So by increasing the monitoring frequency by a factor 12 (e.g. going from 1/year to 1/month frequency), the reliability will increase with a factor: √12 = 3.5 Question then: is this increased reliability worthwhile, taking into account the (large) increase in necessary resources ? Leading principle for frequency of monitoring

7 Taking into account the variations in time for water quality parameters, frequencies are in general: for Rivers> Lakes> Groundwater Rivers: often bi-monthly or monthly.. Lakes: monthly; quarterly.. Groundwater: 1 – few times per year (see later) Monitoring frequencies (I)

8 Also often different frequencies for different “groups” of parameters (e.g. “nutrients” vs “heavy metals”): Different temporal variations Importance Analysis cost Or different frequency for different stations in the network, based on “relevance” (e.g. in nature reserve > shipping canal). However, don’t make differences too large. It is wise, e.g. for statistical correlations, to have comparable time series for the (most relevant) parameters. Monitoring frequencies (II)

9 “Background” “Trend stations” Example: GEMS programme

10 Routine (monthly) vs. synchronized monitoring of a river discharge

11 Higher frequency needed for smaller river basins Variations “smoothened out” for larger basins Effect of river basin area

12 Physico-chemical as well biological monitoring The 28 EU countries still have very different socio- economic development Optimum monitoring frequencies are calculated statistically (procedure in Course 4); however lower frequencies may temporarily be accepted. Monitoring frequencies between 1/month for “priority substances” (e.g. heavy metals and pesticides) and 4-12/year for the other physico-chemical parameters. Much less frequent for biological/ecological variables EU Water Framework Directive

13 Minimum monitoring frequencies in EU-WFD

14 OPTIMIZATION PROGRAMMES

15 Optimization programmes to make more efficient use of the scarse resources, still having reliable data: Reducing the number of stations Reducing the monitoring frequency Reducing the number of parameters; e.g. by leaving out parameters that are “absent”. Again Statistics play a large role (see Course 4) Optimization can also be by: avoiding duplication; having more flexible monitoring; modernizing the monitoring programmes... Objectives

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17 Example- the Netherlands: Monitoring the “governmental” waters, by the central government (large rivers and lakes, coastal sea...) Over the years large increase in number of parameters  unacceptably high increase in cost How to get reliable results for same budget?  optimization programmes  –reducing (somewhat) the monitoring frequency –Especially: reducing the number of stations. Frequency of monitoring based on:

18 Strong increase in number of parameters

19 Monitoring locations in the Netherlands National Water Quality Monitoring network

20 : indicates the statistical optimization programmes Total number of measurements

21 Statistical study showed that for frequencies: < ≈8/year: too low reliability > ≈15: not much extra gain in reliability “Error” Samples per year Optimization Dutch coastal zone

22 Results of optimization, comparing 1975 and 1996: 80% less stations because of strong mutual correlations From bi-monthly to monthly intervals Extra: pesticides; more emphasis on biota and sediments. See: MTM-II, p. 287.

23 Former network: Mainly based on history, unsystematic No clear objectives set; no evaluation, no QA/QC Redesigned network: 200 “primary stations” (trend analysis; basic parameters) “Secondary network”: impacts; flexible list of parameters Special monitoring (biota, sediments)+ mobile network (see pdf, for self study) Optimization Mexico network

24 Some examples from Conferences “Monitoring Tailor-made” (see additional reading)* MTM-II, p.317: Lake and river monitoring in Sweden, with frequencies between 1 per 5 year, to 24/year. MTM-II, p. 331: Monitoring R. Seine (France), showing e.g. the reducing “errors” by increasing monitoring frequencies. MTM-II, p. 339: Monitoring the Russian water courses, with about 2,000 stations; these are subdivided into four categories, according to, a.o. “economic significance” and “water quality.” MTM-III, p. 429: Monitoring in the R.Danube delta: monitoring frequency monthly to 3 times per year, dependent on “parameter group” and monitoring objectives. * for self-study