Ecological Integrity

State and federal agencies have multiple policy mandates to maintain and restore the chemical, physical, and biological integrity of aquatic ecosystems (e.g. Clean Water Act and BLM’s Fundamentals of Rangeland Health Policy). In the United States, biological integrity was defined as “the capability of supporting and maintaining a balanced, integrated, adaptive community of organisms having a composition and diversity comparable to that of the natural habitats of the region” (Frey, 1977). This concept has been extended to include functional components of ecosystems as general ecological integrity and is frequently measured as departure from reference conditions, where reference conditions are least disturbed conditions on the landscape (Stoddard et al. 2006; Hawkins et al. 2010).

Measuring ecological integrity in practice requires the following steps:

  1. Determining the scale and appropriate sample design for assessments
    1. Generalized Random Tessellation Stratified (GRTS) designs are frequently used at regional scales to select spatially balanced random points across the landscape.
  2. Collecting data and measuring indicators
    1. Macroinvertebrate or fish communities are frequently used as indicators of biological integrity.
  3. Computing indices and setting benchmarks for those indices to determine departure from reference conditions
    1. O/E or MMI indices may be computed from macroinvertebrate and fish indicator data.

Steps for computing indices and determining benchmarks requires

  1. Identifying an appropriate set of reference sites that characterize the naturally occurring environmental and biological variability across the region of interest.
  2. Compiling and standardizing the raw data to be used in index development.
  3. Calculating candidate assessment endpoints.
  4. Selecting candidate environmental variables to account for naturally occurring biological variation among sites.
  5. Selecting the final assessment endpoints to be used.
  6. Documenting index performance in terms of precision, accuracy, responsiveness, and sensitivity.
  7. Choosing appropriate benchmarks based on index performance, stakeholder engagement, and best professional judgement.

Once conditions are determined stressors and management actions can be identified to diagnose and restore degraded systems. Additional monitoring is then done to determine if management actions had desired impacts.

Steps with images. Step 1: Sample network of reference sites. Step 2: Delineate catchments. Step 3: Compute catchment statistics for geology, climate, begetation, soils, topography, etc. Step 4: Build reference site models. Step 5: Predict reference conditions of test sites. Step 6: Compare observed values at test sites to those predicted to occur.

Literature Cited

  • Frey, D. G. 1977. Biological integrity of waters: an historical approach. Pages 127–140 in R. K. Ballentine and L. J. Guarraia, editors. The integrity of water: a symposium. United States Environmental Protection Agency, Washington, D.C., USA.
  • Stoddard, J. L., D. P. Larsen, C. P. Hawkins, R. K. Johnson, and R. H. Norris. 2006. Setting expectations for the ecological condition of streams: the concept of reference condition. Ecological Applications 16:1267–1276.
  • Hawkins, C. P., J. R. Olson, and R. A. Hill. 2010. The reference condition: Predicting benchmarks for ecological and water-quality assessments. Journal of the North American Benthological Society 29:312–343.