Note that the page comes up with graphs of default indicators Nitrogen Concentration (top) and Precipitation (bottom) over a year. The sidebar radio buttons and pop-up menus for the top and bottom graphs allow the simultaneous display of different quality indicators for the same station, or for different sub stations. (Or even different ranges of the same graph).
The date stamp on the left side of each graph shows that the graph is created on the fly from output of a simulation program running on the server. Scroll down so you can see both graphs and the relationship between Nitrogen Concentration and Precipitation.