The Whalley, Hawkes, Paisley & Trigg (WHPT) metric is a water quality assessment methodology used under the EU Water Framework Directive to evaluate river health based on benthic macroinvertebrate communities. It improves upon the older Biological Monitoring Working Party (BMWP) system by assigning pollution tolerance scores (1-10) to specific taxa based on their abundance rather than just presence/absence.
Key Aspects of the WHPT Methodology:
Metric Components: The WHPT method primarily uses two metrics calculated from family-level identification:
WHPT-NTAXA: The number of scoring taxa present.
WHPT-ASPT: The Average Score Per Taxon (total score divided by the number of scoring taxa).
Abundance Weighting: Unlike BMWP, which is binary (present/absent), WHPT accounts for the abundance of each taxon, providing a more refined measure of general degradation and organic pollution.
Sampling: Standardized kick sampling is typically used to collect invertebrates, which are then identified and counted.
Classification: The scores (NTAXA and ASPT) are often converted into Ecological Quality Ratios (EQRs) by comparing the observed score to a predicted score based on the site's environmental characteristics.
Application: It is particularly sensitive to organic enrichment and toxic pollution, helping determine the ecological status of water bodies.
The method combines data across seasons (typically averaging seasonal means) to produce a final, robust ecological classification for a water body.
The
Whalley, Hawkes, Paisley, and Trigg (WHPT) methodology is a biological river quality assessment protocol used in the UK to evaluate "General Degradation," primarily organic pollution. It serves as the modernized successor to the Biological Monitoring Working Party (BMWP) system.
1. Sampling Methodology
The protocol relies on standardized benthic macroinvertebrate collection:
Active Kick Sampling: A 3-minute "kick" sample where the riverbed is disturbed upstream of a 1 mm mesh hand net.
Manual Search: A additional 1-minute manual search for invertebrates on submerged surfaces like stones, logs, or plant stems.
Deep Water Alternatives: For deeper rivers, sweeping long-handled nets or using air-lift samplers/dredges is permitted.
Frequency: To achieve official classification, samples are typically collected twice a year—once in Spring (March–May) and once in Autumn (September–November).
2. Metric Calculation
Unlike its predecessor, WHPT incorporates abundance-weighted scoring rather than simple presence/absence.
Scoring System: Each of the 106 taxa (mostly families) is assigned a pollution tolerance score from 1 (very tolerant) to 10 (intolerant).
Abundance Weighting: The individual taxon score varies based on how many organisms are present in the sample, providing more precise data for environmental status boundaries.
Key Indices:
WHPT-NTAXA: The total number of scoring taxa recorded in the sample.
WHPT-ASPT (Average Score Per Taxon): The total WHPT score divided by the number of scoring taxa, representing the average pollution sensitivity of the community.
3. Classification and Data Analysis
The raw scores are contextualized using the River Invertebrate Classification Tool (RICT).
Ecological Quality Ratio (EQR): RICT compares the observed (sampled) results against "expected" results for a site of that specific type in pristine condition.
Environmental Modeling: Site-specific reference values are predicted based on environmental variables like altitude, slope, discharge, and substrate type.
WFD Status: The final assessment combines the EQRs of both ASPT and NTAXA to determine the river's ecological status (e.g., High, Good, Moderate, Poor, or Bad) according to Water Framework Directive standards.