Biological Monitoring Working Party
In the context of macroinvertebrates and freshwater biomonitoring,
BMWP stands for Biological Monitoring Working Party.
It is a widely used, rapid scoring system designed to assess the biological water quality of rivers and streams by analyzing the benthic macroinvertebrate families present in a sample.
Key Aspects of the BMWP Score
Pollution Sensitivity: The system assigns a score between 1 and 10 to each family of aquatic invertebrates based on their tolerance to organic pollution.
High Score = Clean Water: Organisms that are very sensitive to pollution (e.g., Mayfly nymphs) receive high scores (up to 10).
Low Score = Polluted Water: Organisms that are tolerant to high pollution levels (e.g., worms, midge larvae) receive low scores.
Total Score: The final BMWP score is the sum of the individual tolerance scores of all families found in the sample. A higher total score indicates better water quality.
Related Metrics
ASPT (Average Score Per Taxon): To account for differences in sample size or total number of taxa found, the total BMWP score is often divided by the number of scoring families to produce the Average Score Per Taxon.
RIVPACS: The BMWP is often used alongside the River Invertebrate Prediction and Classification System (RIVPACS) to compare the observed score against an "expected" score for a clean site.
The BMWP system was originally developed in the UK in the late 1970s and has since been adapted globally to monitor the impact of organic pollution on aquatic ecosystems.
It is a standardized scoring system used to assess the biological water quality of rivers based on the presence of various macroinvertebrate families.
Key Features of the BMWP System
Sensitivity Scoring: Different families of macroinvertebrates are assigned a score from 1 to 10 based on their tolerance to organic pollution.
High Scores (8–10): Sensitive organisms that require clean, oxygen-rich water (e.g., mayfly or stonefly nymphs).
Low Scores (1–3): Pollution-tolerant organisms that can survive in poor conditions (e.g., worms or midge larvae).
Calculation: The total BMWP score for a site is the sum of the individual scores for all families found in a sample.
Interpretation: A higher total score generally indicates better water quality and a healthier environment.
Score >100: Very good (unpolluted).
Score 11–40: Poor (polluted).
Score 0–10: Very poor (heavily polluted).
Related Metrics
ASPT (Average Score Per Taxon): Calculated by dividing the total BMWP score by the number of scoring families. It is often considered more reliable because it is less affected by the size of the sample.
WHPT (Walley Hawkes Paisley Trigg): A more recent update to the BMWP system used in the UK that accounts for the abundance of each family, rather than just their presence.
The Biological Monitoring Working Party (BMWP) survey system assesses water quality by identifying macroinvertebrates to the
family level and assigning scores (1–10) based on their sensitivity to organic pollution. The system commonly uses over 80 different families.
Here are the key macroinvertebrate families included in BMWP surveys, grouped by their sensitivity (10 = most sensitive, 1 = most tolerant):
Highly Sensitive Families (Score: 10 - "Clean Water")
This category includes many families of Mayflies (Ephemeroptera), Stoneflies (Plecoptera), Caddisflies (Trichoptera), and certain Bugs (Hemiptera).
Sensitive to Moderate (Score: 8-9)
This group includes Crayfish/Crustacea and various families of Dragonflies and Damselflies (Odonata).
Moderate Sensitivity (Score: 5-7)
Families in this range include certain Mayflies (with Baetidae scoring 4), Stoneflies, Caddisflies, Snails/Mussels, Shrimps, many families of Beetles (Coleoptera), some Flies/Midges (Diptera), and Flatworms.
Tolerant to Organic Pollution (Score: 1-4)
This category contains Leeches/Worms, Snails, Crustacea such as Asellidae (Hog louse), Midges like Chironomidae (scoring 2), and Oligochaeta (all aquatic worms scoring 1).
Key Points on Application:
Highly sensitive groups typically include stoneflies and mayflies, while worms and Chironomidae (midges) are generally very tolerant.
The BMWP system focuses on the presence or absence of these families, not the total number of individuals.
A standard sampling method involves a 3-minute kick/sweep sample followed by a 1-minute visual inspection.
In the UK, the original BMWP system has largely been replaced by the WHPT system, which utilizes similar families but with improved sensitivity measures.