Environmental DNA analysis provides remarkable insight into species presence through traces left in water. However, eDNA results require careful interpretation:
In flowing water, DNA travels downstream, so detections may reflect species present upstream rather than at the sampling point itself.
Absence from the dataset does not confirm absence from a site. Detection depends on DNA shedding rates, environmental degradation, sampling timing, and laboratory sensitivity.
Some identifications should be treated with caution. Our dataset includes sequences assigned to species unlikely to occur in UK rivers (e.g. wolf!). This arises because:
The UK Barcode of Life project is working to address these reference library gaps by generating verified DNA barcodes for all UK species.
Water samples were collected from chalk stream sites across the study area. At each site, water was filtered through 0.8μm filters to capture environmental DNA. Multiple filters were collected at some sites to assess sampling variability but have been combined here pending further analysis.
DNA was extracted from filters and amplified using four sets of metabarcoding primers targeting invertebrates and vertebrates, in particular fish and mammals.
Sequences were processed to generate Exact Sequence Variants (ESVs) - unique DNA sequences. These ESVs were assigned taxonomy using global DNA reference databases (BOLD and MIDORI). Note: This report uses species-level analysis, where ESVs have been aggregated to species-level units for diversity and composition metrics.
Biodiversity metrics were calculated including Species richness, species counts, and EPT (Ephemeroptera, Plecoptera, Trichoptera) indices. Community similarity was assessed using Jaccard indices. Indicator species analysis identified taxa characteristic of specific rivers.
2 rivers, 20 sites
3 rivers, 13 sites
6 rivers, 50 sites
The eDNA analysis detected a diverse community dominated by aquatic insects. The sunburst chart below shows the breakdown of all detected taxa down to family level.
The table below summarises biodiversity findings for each river, ranked by Species diversity.
| River | Catchment | Sites | Species | Genera | Families | EPT Families | Rank |
|---|---|---|---|---|---|---|---|
| Beane | Upper Lea (Hertfordshire) | 10 | 1,013 | 651 | 270 | 13 | #1 |
| Misbourne | Colne | 10 | 756 | 490 | 225 | 17 | #2 |
| Lea | Upper Lea (Hertfordshire) | 10 | 717 | 464 | 213 | 15 | #3 |
| Chess | Colne | 10 | 676 | 458 | 222 | 14 | #4 |
| Mimram | Upper Lea (Hertfordshire) | 10 | 640 | 431 | 195 | 14 | #5 |
| Ash | Upper Lea (Hertfordshire) | 7 | 584 | 395 | 202 | 14 | #6 |
| Rib | Upper Lea (Hertfordshire) | 10 | 528 | 369 | 180 | 15 | #7 |
| Ewelme Brook | Thames & Chilterns South | 7 | 451 | 331 | 175 | 13 | #8 |
| Hamble Brook | Thames & Chilterns South | 5 | 294 | 220 | 123 | 9 | #9 |
| Channel | Thames & Chilterns South | 1 | 259 | 178 | 91 | 6 | #10 |
| Stevenage Brook | Upper Lea (Hertfordshire) | 3 | 225 | 166 | 95 | 6 | #11 |
EPT Families: Count of mayfly (Ephemeroptera), stonefly (Plecoptera), and caddisfly (Trichoptera) families - key indicators of water quality.
The following species of conservation concern were detected:
| Species | Common Name | Sites | Rivers |
|---|---|---|---|
| Anguilla anguilla | European eel | 2 | Chess; Misbourne |
| Arvicola amphibius | Water vole | 47 | Ash; Beane; Channel; Chess; Ewelme Brook; Lea; Mimram; Misbourne; Rib; Stevenage Brook |
| Lutra lutra | Eurasian otter | 2 | Chess; Lea |
| Neomys fodiens | Water shrew | 19 | Ash; Beane; Chess; Ewelme Brook; Hamble Brook; Mimram; Misbourne; Rib |
| Triturus cristatus | Great crested newt | 1 | Beane |
The following invasive species were detected and may require management attention:
| Species | Common Name | Sites | Rivers |
|---|---|---|---|
| Crangonyx pseudogracilis | Northern river crangonyctid | 23 | Chess; Hamble Brook; Lea; Mimram; Misbourne; Rib; Unknown |
| Dikerogammarus haemobaphes | Demon shrimp | 1 | Lea |
| Pacifastacus leniusculus | Signal crayfish | 55 | Ash; Beane; Channel; Chess; Ewelme Brook; Lea; Mimram; Misbourne; Rib; Stevenage Brook; Unknown |
