## 2 Materials and Methods
### LUIPLES Method for the Assessment of Pollution-Related Pressure Levels
The weighting factor was assigned by ranking each land use over a range from 0 to 1, as low (0.0 to 0.2), middle (0.3 to 0.6), and high (0.7 to 1). The determination of the degree of contribution (specific weighting factor) of each land use to each pressure type was then fixed within these ranges based on the literature, mainly using technical reports on pressure evaluations and their impacts in lentite waterbodies [43], as well as scientific papers and monographies on the impact of the land uses causing the increases in the assessed pressures (e.g., [44; 45; 46] for eutrophication, [47] for organic enrichment, [48; 49] for acidification, and [50; 51; 52] for pollutants). To obtain the final pressure values, the percentage coverage of each relative area of the different land use groups in the catchment was multiplied by the associated weighting factor for the pressure type evaluated (autrophication, organic enrichment, acidification and specific pollutants), then, these weighted relative contributions were added to sum up the pressure level of each waterbody for the specific pressure type. Table 2 summarizes the weighting factors used for the estimation of the contribution of each land use class to the different pressure type. The weighting factors used for the calculation of the eutrophication pressure level consider the contribution of land use to nutrient runoff to the waterbody [44; 45; 46]. Irrigated agriculture is the land use type with stronger effects due to the use of fertilizers in agricultural practices [44]. Weighting for dumps is also high as they are an important source of inorganic nutrients. Less relevant, but also having an impact, rainfed agriculture and urban uses are also considered as they are potential sources of nutrients for the waterbodies [50]. Finally, meadows and pastures, which may be used for livestock feeding, are taken into account [46], but with a lower weighting because they are just indirect indicators of livestock activity. With respect to organic enrichment, dumps are considered as one of the greatest sources for this pressure, because of their high content of organic matter that potentially may end up in the waterbody. Urban uses are also an important source of organic compounds when they are located in a waterbody catchment area [47] because wastewater and other waste could reach the waterbody. Pastures could also be considered as indirect sources of contamination due to livestock drops dragged by runoff towards the waterbody. Agriculture generates a lower pressure level in comparison to its effect on eutrophication, although with a higher impact of irrigation agriculture due to the wider water pollutant dispersal capacity. \begin{table}
\begin{tabular}{c c c c c} \hline
**Land Use Group** & **Eutrophication** & **Organic Enrichment** & **Acidification** & **Specific Pollultants** \\ \hline Irrigated agriculture & 0.8 & 0.2 & 0.0 & 0.7 \\ Rainfed agriculture & 0.3 & 0.1 & 0.0 & 0.3 \\ Pastures (livestock) & 0.3 & 0.4 & 0.3 & 0.5 \\ Urban uses & 0.4 & 0.6 & 0.2 & 0.5 \\ Communication infrastructures & 0.0 & 0.0 & 0.2 & 0.7 \\ Mining & 0.0 & 0.0 & 0.9 & 0.9 \\ Dumps & 0.7 & 0.8 & 0.8 & 0.8 \\ \hline \end{tabular}
\end{table} 
Table 2: Weighting factors applied for the quantification of the pressure type level for each land use group. Regarding acidification, land use for dumps and mining are considered as more important than other land use types and could have a strong negative impact on this pressure [48; 49]. Livestock, urban uses, and communication infrastructures could also contribute to acidification pressures [49]. Finally, the strongest source of pollution by priority and non-priority specific chemical pollutants is mainly linked to mining and dumps. Communication infrastructures, mainly roads, and urban uses could also exert important pressures due to the spillage of chemical substances. Livestock could also be an important source of some types of chemical substances, due to the use of drugs and hormones in farming.