**Appendix A**

• *PATRICAL*

PATRICAL in the hydrological component includes, in addition to the variables mentioned above, GW extractions (agricultural and urban) and the evolution of the average piezometry of the aquifers. Considering the previous human activities that affect the hydrological cycle, the model compares circulating flows and piezometric levels. In this way, it obtains the modifications that take place in the GW bodies and how they affect the surface flows (Figure 2a).

The temporal variability of water resources and the historical evolution of water use and pollution sources are determining factors for the physical-chemical situation of water bodies. PATRICAL is operated in the following steps (Figure 2a):

(1) Share of liquid water and snow on the land;


The modelled basin is divided into three zones: (1) the surface soil zone; (2) the unsaturated medium, between the aquifer and the root zone, it varies according to the piezometric level in the aquifer; and (3) the aquifer (Figure 2a).

• *RREA*

The total loads of nitrogen from point sources (kg/month) were calculated according to the concentration and volume of the discharge associated with a SW rivers. When the SW-river did not have a census of discharges, it was calculated with the number of population equivalent and the treatment of wastewater purification associated with the treatment plant of the area. The procedure to obtain the number of population equivalent is similar to that already used in other RB, it was calculated based on the annual volume of discharge and the supply of drinking water per population of each municipality [75]. Reused water was considered since it decreases the amount of load brought to the water bodies.

The program performs a mass and flow balance for each river-type water body on a monthly scale. The mass balance is defined by the following variables: amount of mass that enters (*Me,i*) to the water body *i*, pollutant mass (*Mgen,i*) that is generated in the basin of the mass *i*, and the mass of pollutant that leaves the water body *j* and discharges to the mass *i* (*Ms,j(j*→*i)*). The mass balance is defined by the following equation (Paredes-Arquiola 2015):

$$M\_{\mathfrak{e},i} = M\_{\mathfrak{gen},i} + \sum\_{j=1}^{n} \left( M\_{\mathfrak{s},j} j \to i \right) \tag{A1}$$

The flow extracted is taken into account in the two balances to extract the mass of pollutant that carries the flow extracted.

$$M\_{\mathfrak{s},i} = M\_{\mathfrak{e},i} \times e^{-KL} \tag{A2}$$
