to be used. These components will however need to be selected from the Tier 1 and/or Tier 2 protocol to ensure method consistency across the different tiers of the monitoring programmes, thereby ensuring usability of the data in the national programme, even though the focus of the Tier 3 assessment may be over a short temporal scale. In the instance where no historic data are available, the Tier 3 study may act/contribute to a future baseline study.