Delaware's Watersheds

Interpreting Site Monitoring Data

Dissolved Oxygen and Water Temperature Graphs
Dissolved oxygen is a function of temperature, the colder the water temperature the more oxygen the water can hold. When both dissolved oxygen and water temperature are on the same graph you can see this inverse relationship. Only the values for the months of May, June, July, August, and September are on the graph. This is because Delaware's Department of Natural Resources and Environmental Control standards for dissolved oxygen are only for the warmest months.


pH and Alkalinity Graphs
pH and alkalinity are on the same graph as alkalinity influences pH by acting as a buffer which causes less fluctuation in pH values the higher the alkalinity value. The state standards for both are listed below.


Nitrate-Nitrogen Graphs
The target level for total nitrogen (all forms of nitrogen combined) in Delaware freshwater is 1.0 to 3.0 mg/L. Delaware Nature Society volunteers measure nitrate-nitrogen, which is only one component of total nitrogen. This means unless the nitrate-nitrogen values are above 3mg/L the graphs are unable to show whether or not the total nitrogen target level is being reached. If the nitrate-nitrogen values are at or above 3mg/L, then the total nitrogen concentration is above the targeted range.


Conductivity Graphs
Conductivity is an indicator of the amount of inorganic dissolved solids in a liquid. Conductivity values are generally consistent for a particular stream, reflecting the geographic characteristics of the watershed. Gross increases in conductivity may indicate additional inputs into the stream system, such as seawater in tidal portions of the stream or salts from the roads after a snow event.


Orthophosphate Graphs
Both phosphate and nitrate are needed for growth, a high level of one without a high level of the other will not produce the algae blooms that are the cause for concern. One must look at both values to get an accurate view of nutrient level in the water.Testing for phosphate was added to the Technical Monitoring program in March of 2002. The target range for phosphate in Delaware freshwater is 0.3 to 0.6 mg/L.