## 3 Materials and Methods
### Process-Based or Conceptual Models
Soil evaporation phenomena were calculated by using the Penman-Monteith equation [111]. Outflows of the groundwater table are determined by a linear empirical drainage function. Soluble organic matter (SOM), (N) mineralization and plants' water uptake are dependent on moisture and soil temperature. Other dissolved forms of (C) and (N) comprise nutrient pools in the roots. Microbial biomass of the seeded roots (mycorrhiza) regulates stoichiometry of \(\mathrm{C}/\mathrm{N}\) ration and carbon use efficiency (CUE). Any changes in the nitrifying biomass of a specific soil layer affect eminently the soil nitrification flux and therefore the nitrification rate and the soil-water-ammonium conc., since dissolved organic nitrogen (DON) and ammonium (N-NH\({}_{4}\)) are in chemical equilibrium in both the soil-water and soil-solid phases [112]. The Nitrogen Loss and Environmental Assessment Package (NLEAP) is a powerful mechanistic model that provides rapid site-specific estimates of N-NO\({}_{3}\) leaching potential below the root zone of crops and the impact of nitrate leaching into groundwater [113]. Under various combinations of soil profile characteristics, weather data, and farming practices, the aforementioned model is used to estimate the residual nitrates and potential nitrate leaching losses from cropland soils into subsurface layers [114]. It runs in three temporal modes, i.e., annual, monthly and event-by-event for certain water-nitrogen cases and potential leaching. The updated and improved NLEAP-GIS (version 4.2), coupled with geographic information system (GIS) spatial soil database as a complementary component, increases the capability of assessing (N) losses towards risky landscapes and combinations of different cropping systems and evaluates more accurately management practices over nitrogen transformation and mitigation. Testing over the north China plains, cultivated in seasonal rotation with wheat and maize crops, combined with meta-analysis by exploiting relevant literature, showed remarkable reliability [115; 116]. The updated version of the model includes infiltration and transport of nitrates and soil water; carbon and nitrogen terrestrial cycle; soil surface and soil profile propagation  
Figure 4: Operational modules of the APSIM crop growth model over individual fields of interest include soil-water interaction and nitrogen/crop/canopy dynamics. and transformations; water, nitrate/ammonium surface runoff; nitrate leaching from the root zone and ammonium uptake from the seeded plants; denitrification losses and ammonia volatilization. Each individual process is prescribed by detailed algorithms and equations [116]. Model inputs such as daily meteorological data, including maximum and minimum temperatures, daily rainfall, relative humidity and evaporation are prerequisites to running various scenarios enriched with soil profile information and fertilizing events. During the winter wheat and summer maize season, a specific (N) application rate is recommended so as to be achievable; concurrently, higher (N) use efficiency and grain yield result in lower groundwater nitrate pollution risk. Nitrate leaching indicates the presence of a nitrogen pool which might affect local aquifers, identifying regional soil profile characteristics. The model's outcome is validated by using older measured nitrate leaching reports. Results in many cases are comparable with other models' outcomes, e.g., the DNDC model [117], on a regional scale [118]. In the large-scale and spatial variation simulation of nitrate leaching in the region of experimental interest (location in China), the rate of fertilizer N application was positively correlated with rainfall density; however, it was negatively correlated with N use efficiency [119]. Climate change and the interrelation of anthropogenic pressure on waterbodies' catchments and basins are of great importance. Therefore, the evaluation and simulation of water resource management scenarios for adopted, resilient plans over coastal agricultural watersheds were conducted.