Geochemists often create graphs to compare samples from different locations or different days. Many of these graphs are specialized graphs that require data to be in a particular order or formatted in a particular way. Grapher makes it easy to create all of the graph types you desire with a few different combinations of plot types. This article will discuss a few different graph types that are useful to geochemists or can be modified for other disciplines.
The attached zip file contains an Excel file with multiple sheets and Grapher files for the plots used in this article. All the plots discussed below are created directly using the Excel file. To generate the plots, simply replace the data in the Data sheet with your own data. The Piper, Durov, and Schoeller sheets have information that is automatically generated based on the information you type into the Data sheet. After updating the Data sheet with your data, save the Excel file. Each specific geochemical plot type is automatically created from a specific sheet with your data when you open the GRF file in Grapher. Each sheet will be briefly discussed below in the plot type sections.
|Type your data directly into the Data sheet of the Excel file.|
A note regarding the layout and formulas used: The data on the Data sheet must be entered in mg/l (or ppm). If the data is input in other units, the calculations on the remaining tabs will not be successful. Most of the plots are displayed in milliequivalent percents (mEq%). The milliequivalent percents are calculated using the equation:
A Piper plot is a graphical representation of the chemistry of water samples. The Piper plot is created from two ternary diagrams, depicting the normalized mEq% of anions and cations. A diamond in the center is created by projecting the sample locations from the two triangles to the position where the sample lines cross. The milliequivalent percentages are calculated on the Piper sheet in the Excel file. In addition, the Piper sheet has the equations necessary for plotting in the diamond section. All of these calculations are automatically done in the attached Excel file and plotted using the geochem-piper.grf file located in the previously attached zip file.
|The Piper plot displays the cation and anion concentrations of many samples.|
The Durov plot is used to graphically illustrate the cation and anion concentrations. In addition, the extended Durov plot can be used to display the total dissolved solids (TDS) and pH of the sample. Durov plots are considered easier to read than Piper charts because of the straightforward layout. In addition, the Durov plot displays some possible geochemical processes by interpreting the center rectangle.
This plot is also created from two ternary diagrams, depicting the normalized mEq% of anions and cations. The central rectangle is created by dropping horizontal and vertical lines from the triangles onto the center rectangle. The milliequivalent percentages are calculated on the Durov sheet in the Excel file. In addition, the Durov sheet has the equations necessary for plotting in the center rectangle section, the TDS, and a copy of the pH. All of these calculations are automatically done in the attached Excel file and plotted using the geochem-durov.grf file located in the previously attached zip file.
|The Durov plot displays the anion and cation concentrations of many samples.|
A modified Durov plot is created by also displaying the TDS and pH of the sample. These are turned off in the attached Grapher file. To turn these on, check the box next to the Extended Durov group in the Object Manager.
|The Durov plot is displayed with the TDS and pH additions.|
A Schoeller plot can also be created. This plot also displays the relative concentrations of various anions and cations from multiple samples on a single graph. The Schoeller plot is a series of line/scatter plots where the X value is the cation or anion and the Y value is the mg/l values from the raw data.
Because of the way data is read in Grapher, the raw data must be transposed and ordered in Excel before plotting. This should be done on the Schoeller sheet in the Excel file. In addition, the order of the points should match the order you want to see on the plot. To get the data in the proper format:
- Once the raw data is input into the Data sheet, highlight all of the data on the Data sheet.
- Click the Home | Clipboard | Copy command.
- Click on the Schoeller tab.
- In cell A1, click the Home | Clipboard | Paste | Paste Special command.
- In the Paste Special dialog, select Transpose and click OK.
- Delete columns Valence and Ion FW, as these are not used for a Schoeller plot.
- Rearrange the rows so that the order of the rows is K, Mg, Ca, Na, Cl, SO4, HCO3, and NO3 (or whatever order is desired).
- Click the Home | Editing | Find & Select | Replace command (or press CTRL+H on the keyboard).
- In the Find what, type mg/l .
- Leave the Replace with empty.
- Click Replace All and then Close.
- Save the Excel file and open the geochem-Schoeller.grf file from the previously attached zip file.
The graph is automatically created using the column A for the categories on the X axis. Each plot is colored a different color. If additional samples are input, additional line/scatter plots can be added by following these steps:
- Click on the top line/scatter plot (named L) in the attached GRF file.
- In the Property Manager, click the Plot tab.
- Click the New plot option where it says Create. A new line/scatter plot is added using the same X column (row number) and the next Y column (sample).
- Repeat this process until all samples are displayed.
- Change the line properties by clicking on each new line/scatter plot and changing the line Color on the Line tab in the Property Manager.
|The Schoeller plot is displayed using multiple line/scatter plots in Grapher.|
Grapher can create many different types of graphs for the geochemist by combining multiple plot types into a single complex graph. In addition, stiff diagrams and radar plots can also be created directly in Grapher to aid in analysis of multiple components for each specific sample. Examples of both the stiff diagram and radar plot are included in the Grapher Samples directory. Line/scatter plots can be created comparing multiple cations or anions on the same graph and descriptive statistics are generated in the worksheet.
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