The groundwater input provides the depth of the groundwater table and the nitrate concentration of the groundwater. The input is optional; without groundwater input the groundwater table is assumed to be far below the soil profile.

The groundwater table is used by the watercycle models (e.g., WatercycleDNDC) to determine saturated soil layers. Soil layers below the groundwater table exchange nitrate with the groundwater (e.g., soilchemistry models MeTrX and DNDC).

Input items and units

Each item can be given as a constant in the attributes section (used as average/default value) and/or as a time series column in the data section. Column names are case sensitive and must match the names below exactly. Columns with unknown names are ignored silently.

Name	Description	Unit	Default
watertable	depth of groundwater table below soil surface	m	99.0
no3	nitrate concentration of groundwater (as nitrogen)	mg N l-1	0.0

watertable is positive downwards, e.g., 1.0 means that the groundwater table is 1 m below the soil surface. Negative values are interpreted as water table above the soil surface (surface water). The default of 99 m means no groundwater influence.
no3 is given as nitrogen mass (mg N l-1), consistent with the wet deposition concentrations nh4 and no3 of the airchemistry input (g N m-3 = mg N l-1). Measurements given as nitrate mass have to be converted using the ratio of molar masses (14 / 62), e.g., 10 mg NO3 l-1 correspond to 2.26 mg N l-1.

Both items are averaged if the data are given at a finer resolution than the simulation time step.

The exchange of nitrate between soil layers below the groundwater table and the groundwater is controlled by the site parameter GROUNDWATER_NUTRIENT_RENEWAL. Its default value is 0, i.e., without setting this parameter the nitrate concentration of the groundwater has no effect.

Time axis

The time stamp of the first record and the record resolution are given by time in the global section, written as YYYY-MM-DD/r with r records per day:

time = "2000-01-01/1" : one record per day (daily data)
time = "2000-01-01/24": 24 records per day (hourly data)

The resolution must be given explicitly. Otherwise, missing parts of time would be taken from the simulation schedule and the records would be misinterpreted (e.g., with schedule "2003-01-01/24", daily records would be read as hourly records). Therefore, the simulation terminates with the error "groundwater input: time resolution not given" if /r is missing, and with the error "groundwater input: time not given" if time is missing completely.

If the data end before the end of the simulation, values after the last data record are synthesized from the attributes (or defaults). To repeat the given data instead, set endless in the project file:

<attributes use="0">
    <groundwater endless="yes" />
</attributes>

Example

Daily groundwater table and nitrate concentration:

%global
    time = "2006-01-01/1"
 
%groundwater
    id = 0
 
%attributes
    watertable = "2.0"
    no3 = "3.24"
 
%data
watertable  no3
1.85        3.24
1.83        3.30

The following groundwater attributes can be defined (input name [unit]):

watertable [m], depth of groundwater table below soil surface (negative: above surface)
no3 [mg N l-1], nitrate concentration of groundwater given as nitrogen mass