Study design for water quality monitoring programs
Study design is a pivotal component in the monitoring process that converts the monitoring program objectives into data collection methods. Follow our guidance on study design strategies and considerations.
Also, check with relevant local authorities in your jurisdiction who might have established study design procedures for water quality monitoring programs.
A study design should provide answers to questions about what, when and where data are collected, taking into account budgetary constraints, available resources (e.g. equipment, people, timing), implementation considerations and contextual knowledge.
Once the objectives for the study or monitoring program have been defined and (if relevant) a conceptual model has been developed, the next stage involves translating the objectives into a study design that will deliver the specific data required.
A well-planned study design is helpful to end-users because it allows them to organise the analyses for the collected data. We have provided you with a useful checklist in Box 1.
Box 1 Checklist for designing a monitoring study
- Has the study type been made explicit and agreed?
- Is the spatial and temporal context clear?
- Have spatial boundaries of the study been defined?
- Has the scale of the study been agreed?
- Has the duration of the study been defined?
- Have potential sources of variability been identified?
- Have measurement variables been chosen?
- Are they relevant?
- Do they have explanatory power?
- Can they be used to detect changes and trends?
- Can they be measured at the desired level of precision in a reliable, reproducible and cost-effective way?
- Are the variables appropriate for the spatial and temporal scales of the study?
- Have decisions been made about the smallest meaningful differences or changes that need to be detected?
- Have the locations of monitoring sites been chosen?
- Can sites be accurately identified?
- Are there sufficient sites to quantify the spatial variability?
- Are the sites accessible throughout the year and safe?
- Has the monitoring frequency been decided?
- On what basis is the frequency of sampling proposed?
- Is replication adequate to detect meaningful changes?
- Has the cost-effectiveness of the study design been examined?
- Have the data requirements for analysis been discussed and agreed?
The study design underpins the collection of monitoring data and interacts strongly with several key steps in the Water Quality Management Framework.
Step 1 — Examine current understanding
Step 1 of the framework examines the current understanding of the system. While some of that may come from the synthesis of existing monitoring data and knowledge, additional monitoring may be required to provide a snapshot of the condition and those factors that may influence condition.
Step 3 — Define relevant indicators
Existing system knowledge is represented by conceptual models and forms the basis of indicator selection in Step 3 of the framework. This involves selecting indicators to be monitored, as well as when, where and how they will be sampled. Monitoring may be useful in testing and validating those indicators, and refining the sampling methodologies used (e.g. when a required level of sensitivity is found to be impractical).
Step 4 — Determine water/sediment quality guideline values
Step 4 of the framework involves determining water/sediment quality guideline values for each of the relevant physical, chemical and biological indicators. Monitoring data underpin the derivation of a number of those guideline values (including variables modifying toxicity of a toxicant), whether they be based on locally relevant (e.g. site-specific, catchment) data or more regional default guideline values (DGVs).
Step 6 — Assess if draft water/sediment quality objectives are met
Once those guideline values are determined, monitoring data for each relevant indicator are used to assess condition and changes against those water/sediment quality objectives in Step 6 of the framework. In some cases, monitoring programs for the proposed indicators may not already be in place and need to be designed.
Adapting the study design
Acknowledging and responding to feedback loops is central to the water quality monitoring process.
While continuity in design is important, particularly for establishing any changes over time, the study design often needs to adapt as data is collected and analysed against the broader objectives of the monitoring program.
If there are deficiencies in the monitoring program’s ability to make inferences or identify gaps, then adjustments to the design should be considered.
External changes (e.g. changes in budget, new technological solutions or logistical constraints) may drive the need for alterations to the design.
Other changes may be anticipated. For instance, a deliberate strategy to sample more intensively in the early years of a pilot study to characterise variation, then subsequently altering the design to reduce sampling intensity when an informed decision can be made about the required sampling intensity.
Whatever the rationale for adapting the design, it needs to be thought through carefully and with the ramifications of any changes assessed in the context of the water body and its surrounding water quality objectives.