What are the vital signs for your watershed and what might they tell us about the health condition of your watershed?
Watershed Health describes how well ecological systems are functioning. The biggest challenge is defining what "well-functioning" means for each watershed.
A physician will decide if a human patient appears to be "healthy" based on measurements of vital signs like body temperature, blood pressure, heart rate, while also considering the patients age and what is known about their health history.
An ecologist will decide if a watershed appears to be "healthy" based on measurements like presence of quality habitat, stream flow patterns and lake characteristics, presence of known contaminants and ecological risk factors, health and diversity of plant and animal communities while also considering the climate, geology, location and land use history of the watershed.
Measuring Watershed "Vital Signs"
One major difference is that there is not a set of vital signs and target values for ecologists to use to guide their diagnosis. Is this watershed running a fever or not? Does this watershed have high blood pressure or not?
In most cases, instead of having a threshold value (98.6 body temperature), watershed health is measured by comparing the current condition with an estimate of how natural systems in that location would function if it was in optimal health. Of course, many places are not currently in optimal health and there may be no existing reference condition to explore and understand for comparison.
Overcoming the obstacles
In order to move forward with sharing important information about the health of Minnesota's watersheds, the Watershed Health Assessment Framework uses health rankings to illustrate the range of results for a variety of measurements for watersheds across Minnesota. Eighteen Health Index values are used to compare results across Minnesota's 81 Major Watersheds. Each index is scored on a scale of 0 to 100.
Some of the index measurements look at the current condition of the landscape. In some cases, the condition that would score a "0" or "100" is known and may exist somewhere in Minnesota. Sometimes the condition that would score a "0" or "100" is unknown and other scientific information must be used to decide how to rank the index results.
Some of the index measurements look at the context in which the other information needs to be evaluated. Like using a patient's age and genetic pre-disposition to disease to inform human health decisions, a context index shows information about background risk factors such as erodible soils, steep slopes and climate conditions. For these index values, the "0" may indicate the most vulnerable watershed found in Minnesota. The context score may not be something that can be changed, but rather should inform choices about actions that are taken to minimize risk.