What is a Water Quality Index?
A Water Quality Index (WQI) is a calculated score that expresses the overall quality of water. This value serves as a single, comprehensive indicator based on analytical values of various parameters, making it easier to interpret water data. The WQI for Choate Pond is determined by five key parameters: temperature, dissolved oxygen (DO), pH, turbidity, and salinity. The WQI scale ranges from 0 to 100, with 100 representing excellent water quality, as illustrated on the right.
How is the WQI Calculated?
We utilized the National Sanitation Foundation for Water Quality Index (NSFWQI) formula below:
Qi = Value of the ith water parameter
Wi = Weight associated with the ith water quality parameter (sum of parameter weights is equal to 1)
n = Number of water quality parameters
The formula involves summing each parameter multiplied by its assigned weight for each recorded data point. The resulting indexes for a specific time period are then averaged to obtain the weekly Water Quality Index of Choate Pond. We referenced the Purdue Simple WQI Calculator when creating our calculation.
Factors that can affect WQI
- Stormwater Runoff
- Urban development prevents the absorption of rainwater.
- Paved surfaces accumulate pollutants that are picked up by rainwater and carried to nearby stormwater drains or into water bodies (rivers, lakes, oceans, etc.).
- Loss of Wetlands and Forests
- Wetland vegetation plays a crucial role in capturing sediment, filtering out nutrients, and neutralizing harmful chemicals that enter waterways from sources such as roads, urban areas, industrial sites, and agricultural fields.
- Forested areas enhance water absorption, reduce sediment flow into freshwater streams, and provide vital shaded habitats for aquatic life and plants.