## 2 Methodology
### Decision Support to Complete the Optimization Procedure  
The output from the statistical analysis provides a series of suggestions in line with the optimization objectives to optimize the WQMPs. Indeed, several authors have underlined the importance of bringing expert opinion into this step [13; 29; 30]. We thus propose that the WQMP managers be supported in this final step through questions which are integrated into the IDSS and which are based on expert knowledge [16]. The aim is to ensure consistency in the final decision-making and documentation of these decisions. For each of the sampling sites suggested for scrutiny (removal, retention or stations considered as neutral) by the application of the statistical methods, the IDSS provides an additional series of questions to support the final decision to keep or remove a station. The same applies to suggestions on sampling frequency, adding or reducing water quality parameters, etc. A selection of questions from the decision-support trees for the final optimization of a river WQMP is listed below. If the question cannot be answered immediately, the system transforms it to an actionable task (Note that this is a non-exhaustive list and the IF-THEN rules are not all shown). A selection of questions for lakes:  
* If more than one station is visited in a lake, THEN verify the justification of the selection of each site in order to understand the rationale for each site (e.g., deepest sector of a lake; close to a major inflow; in a section of a lake with recurrent cyanobacteria blooms) [31]. * For each station, verify the employed sampling strategy. These decisions can greatly affect the results: e.g., decisions taken on the profile (probe data every 0,5 m, 1 m, etc. ), decisions taken on sampling depth for laboratory parameters (chlorophyll a, total phosphorous, nitrogen compounds, cyanobacteria etc), decisions taken for the type of sampling method: e.g., horizontal bottle at a given depth, tube samplers for an integrative sample of the first n meters, etc. * Validate whether the sampling strategy responds to the objectives and whether adding new parameters is in line with the existing sampling strategy and objectives. Figure 8: Extraction of the decision-support questions on available data series to validate (and understand) integrity, comparability, and outliers. * Verify whether a river WQMP is in place in order to observe changes in the watershed which may translate to the lake. A selection of questions for rivers:
* Based on the results of the analysis provided for each station which suggest either the retention, removal or no specific action for a station, verify the following: IF a sampling site is suggested for removal, THEN verify the type of sampling site and the sampling site justification. * IF the sampling site is an integrative station, THEN keep the sampling station \(\bigcirc\) An integrative station is a station which is downstream from a subwatershed and represents the globality of the subwatershed. * IF the sampling site is a section of a river, THEN verify whether a particular goal is pursued and justified for the station \(\bigcirc\) A station of a section represents the water quality between two sampling sites and should be selected according to specific goals and pollution sources, and must be justified). * IF the sampling site justification is a witness station, THEN verify if the sampling site still qualifies \(\bigcirc\) A witness station is supposed to represent the natural water quality of a subwatershed, or, if it is not possible to have a witness station for every subwatershed, there should be a witness station for every sector representing the geology of the sectors of the WQMP. Therefore, it is necessary to verify whether sufficient witness stations are available to be representative of every type of natural background in the territory subject to the WQMP. * e.g., a waterfall
- or degraded
- e.g., a sewer overflow).