Potencial de Membrana Celular

The base station in RHESSys includes spatially explicit time-series climate data and dated agricultural management inputs (fertilizer, irrigation). Although climate data is necessary for model run and dated input data is optional. Base stations don’t belong to any specific hierarchical unit (basin, hillslope, zone, patch or stratum), but a base station can be attached to any hierarchical unit. In most RHESSys applications, base stations are attached to zones, and are mainly used to provide climate data (Tmin, Tmax and precipitation) for zones. Although the standard version of RHESSys has the potential to provide fertilizer data, there is no clear procedure for using the base stations to provide

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fertilizer data. Since fertilizer is a key source for phosphorus, we developed a method to use spatial-temporal fertilizer application data in RHESSys-P (also applicable for RHESSys), and phosphorus fertilizer functions were added in RHESSys-P to process agriculture land use fertilizer application.

5.2.3.1 Two-level base station construction

In order to use spatial-temporal fertilizer data, we developed a method called the “two-level base station construction”. Level one base station construction is based on climate data (real climate station data or reanalysis grid data). This level of base station construction is the same as constructing a base station in standard RHESSys. Level two base station construction is based on the level one base station map but uses an agricultural land use map to construct the level two base station map.

Level 1 base station map

To create the base station map, weather stations or climate reanalysis grid data are used to create Thiessen polygons (Figure 5.5 a). In RHESSys-P, zones are the hierarchical unit for processing climate data. Each zone uses the climate base station for the Thiessen polygon in which it is located (Figure 5.5 b). If the zone lies in multiple Thiessen polygons, majority rule is used to determine which climate base station is used.

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Figure 5.5 Level one base station map. a. Climate base stations are used to create Thiessen polygons. b. RHESSys-P zones use the climate base station based on the polygon ID, which is the same as the base station ID. In the example above, zone1 and zone2 both use the climate base station data associated with polygon 1.

Land management scheme

Before constructing the level two base station map, a land management map needs to be created. For agricultural land use, different land may have different fertilizer application dates, amounts or harvest dates. The combination of all the land management practices is called the land management scheme (Figure 5.6).

The items in the land management scheme are defined by users. Commonly used items include fertilizer application (NO3-N, NH4-N, DIP, DOP), and harvest date. Non- agricultural land uses are set to 0, which has no management practices. For agricultural

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land use in the study basin, a scheme must be created with details based on the agricultural land management practices (Figure 5.6).

Figure 5.6 Agricultural land use management schemes include different user-defined land use management practices, including fertilization amounts, types, dates and harvest dates. Scheme 0 has no management practices and is used for non-agriculture land. Any difference between two agriculture land management practices leads to a different scheme. In this example, Scheme 1 has a different DOP application amount from Scheme 2.

Figure 5.7 shows an example of the scheme map creating process and how the spatial data is linked with the schemes using polygon 1 as an example. The land use map is first reclassified to agricultural and non-agricultural land (Figure 5.7 a). The agricultural land is then further divided into different schemes based on the agricultural land management (Figure 5.7 b).

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Figure 5.7 Land management scheme creating process, using one Thiessen polygon as an example. a. Divide the study area into agricultural and non-agricultural land. b. Divide the agricultural land into different schemes based on the land management.

Level 2 base station map

Once the land management scheme map is created, concatenating the level 1 base station map with the scheme map creates level 2 base station map for each pixel (Figure 5.8). If we assume there are N schemes and the number N has n digits, the level 2 base station map is calculated with equation (18) using GIS raster calculation:

(18) where is the level 2 base station raster map, and is the level 1 base station raster map, and is the scheme raster map. A raster calculation with equation (18)

1 10n

L2=L  +scheme

L2 L1

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generates the level 2 base station map (Figure 5.9). Each pixel value in the level 2 base station map contains the appropriate climate and land management information.

Figure 5.8 Level 2 base station map pixel value is the concatenation of climate base station and management scheme.

Within the level 2 base station map, a climate station is assigned to each pixel using equation (19):

(19) where is the climate base station ID, is the function to extract integer value, is the level 2 base station map, and is the digit number of the total number of schemes. Each pixel is assigned a management scheme using equation (20):

_

_

int( 2 10 )

climate station ID=

L



_ _

climate station ID int

2

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(20) where is the land management scheme ID, is the function to calculate the remainder. Through the encoding and decoding procedures, RHESSys-P can process the spatial-temporal input data.

Figure 5.9 Level 2 base station map creating process. a. Overlap the level 1 base station map on the scheme map. b. Concatenating level 1 base station map pixel value with scheme map pixel value to create the level 2 base station map.