Ohio State University

Sampling Watershed Quality


Measuring Watershed Quality

Traditionally stream and river quality assessments have been conducted based solely on chemical analysis to analyze the impact of land use change on water quality. While variables such as pH, dissolved oxygen, hardness and concentrations of metals, soluble chemicals, nutrients, and organics were typically measured, other extremely valuable information regarding biological species diversity and overall habitat quality was lacking.

More recently, scientists have recognized the need to incorporate this biological data in order to create a comprehensive investigation of watershed quality and response to change. This biological line of investigation is important because chemical assessments could not assess the effect of a particular pollutant after settling in the system, and could only accurately measure its short-term effects.

Biological methods take into account a variety of ecological indicators like topography, soil structure, water table levels, and surrounding vegetation and present a more conclusive picture of a watershed. These ecological variables are useful in measuring long-term effects and the ability of the water system to respond to major stress events. The Ohio EPA has highlighted the following as primary components of biological integrity:

  • Chemical Variables
    (pH, dissolved oxygen, phosphorous, etc.)
  • Energy Source
    (sunlight, seasons, available nutrients)
  • Biotic Interactions
    (reproduction, disease, parasitism, predation)
  • Habitat Structure
    (vegetation, cover, sinuosity)
  • River/Stream Flow Regime
    (precipitation, velocity, runoff)

Using ecological parameters is extremely valuable in assessing non-point pollution. With no known discharge sites and unknown times of origin, non-point pollution becomes very difficult to assess. Therefore, it is in the best interest of the planner, developer, and landowner to recognize the need for incorporating biological data into watershed assessments.

Biotic Integrity, according to Ohio EPA and watersystem scientists, is defined as the following:
An aquatic ecosystem's ability to support and maintain a community of organisms with diversity, species composition, and functionality comparable to natural habitats within a similar region. This community should also be well-balanced, integrated throughout, and adaptable to changes over time.

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