A sampling plan and monitoring programme - how to design it
The most common mistake in monitoring is to start with the measurements rather than with the plan. Yet it is the plan that decides whether the data will be representative, comparable and useful - or whether you will be left with a set of readings from which it is hard to conclude anything. Before you head into the field, it is worth answering a few questions.
Why we measure - the aim
It all begins with the aim: assessing status, detecting changes, controlling a discharge, responding to an event, scientific research. The aim decides everything else - trend monitoring requires different points and frequency than early warning.
Where - measurement points
- Representativeness - a point should reflect what you want to assess (the current, not a stagnant pocket; a typical reach, not an exception).
- Constancy - the same, unambiguously described sites, so that results can be compared over time.
- The logic of the layout - e.g. above and below a potential source, on the inflows and the outflow of a lake.
When and how often
- Frequency is matched to the aim and the dynamics of the phenomenon: a trend - less often, but for a long time; events (blooms, floods) - more densely, in periods of risk.
- Seasonality - many indicators have an annual rhythm; the plan should cover the right times.
- A fixed time within the day where the daily rhythm matters (e.g. oxygen).
What we measure - the range of indicators
Match the indicators to the aim - from the basic field ones (oxygen, pH, conductivity, temperature) to the biological and laboratory ones (nutrients, priority substances). The logic of the elements of status assessment can be helpful.
Resources and feasibility
The best plan is one that can be delivered: a realistic number of points, equipment, people and time. It is better to have fewer sites run consistently than an ambitious plan abandoned after a season.
In practice
It is worth recording the plan and keeping it together with the data. In LimnoLog the structure of a project (stations, sessions, indicators) reflects your plan, and the sampling planner helps you keep to the schedule. On how to present the results later, we write in the article A monitoring report.
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