Coastal eutrophication potential (Aqueduct 3.0)
This layer measures the potential for river-borne nutrients to trigger harmful algal blooms in coastal waters.
Source: WRI Aqueduct 3.0 Year: 2019 Category: Physical risks · Enabling services · Water condition Coverage: Global Format: Boundary polygons (river catchments) Used in risk analysis: No (contextual layer; not used in materiality scoring)
What it shows
This layer measures the potential for river-borne nutrients to trigger harmful algal blooms in coastal waters. It captures where human activities load enough nitrogen and phosphorus, relative to silica, into rivers that excess nutrients can degrade downstream coastal environments. Such nutrient enrichment can lead to eutrophication and oxygen-depleted waters, harming marine life — a key signal of water-quality pressure on coasts.
How it is built
The source is the WRI Aqueduct water-risk framework. The coastal eutrophication potential indicator assesses the balance of nitrogen, phosphorus and silica carried by a river's loadings. When nitrogen and phosphorus are discharged in excess of silica relative to the needs of diatoms (a major beneficial algae group), undesirable algal species tend to develop. The indicator therefore combines point-source and diffuse pollution inputs across river catchments to estimate the potential for harmful blooms in the coastal waters downstream.
How to read it
Higher values indicate a greater excess of nitrogen and phosphorus relative to silica, creating more favourable conditions for harmful algal growth and eutrophication in the coastal waters downstream. Lower values indicate a more balanced nutrient regime and lower eutrophication potential.
Class thresholds
The underlying quantity is the coastal eutrophication potential (CEP) score — a dimensionless index computed from a river catchment's nitrogen, phosphorus and silica loadings (the excess of N and P over silica relative to the needs of diatoms). In Darwin's data the raw score (cep_raw) runs from negative values up to roughly 80.4, with higher values meaning more excess nutrients and a greater bloom potential. The continuous score is binned into five ordered categories (cep_cat), with the score break-points shown in brackets:
| Class | CEP score (cep_raw) |
|---|---|
| Low | < −5 |
| Low – Medium | −5 to 0 |
| Medium – High | 0 to 1 |
| High | 1 to 5 |
| Extremely High | > 5 |
(A separate "No Data" value of −1 marks catchments without a score.) The categorical proximity rule in the configuration triggers on the Enabling services / Water condition dimension when cep_cat reaches High or above (category ≥ 3). In practice this is a contextual layer and is not used in materiality scoring.
How these thresholds were set. The five-class split and the underlying CEP score both follow the WRI Aqueduct methodology (coastal eutrophication potential indicator). The score break-points (−5 / 0 / 1 / 5) are taken directly from Aqueduct's published classification; their exact derivation is set in the WRI Aqueduct methodology and is not re-documented in Darwin's configuration.
Reference: WRI Aqueduct — wri.org/aqueduct.
Source
WRI Aqueduct (4.0) — coastal eutrophication potential indicator.
Comparison with the WWF Risk Filter Suite
This layer maps to WWF Biodiversity Risk Filter indicator S2_2 Water Quality and Water Risk Filter indicator B4_1 Coastal Eutrophication. It is the direct coastal-eutrophication counterpart within those frameworks.
Legend
Symbolised field: Coastal eutrophication potential
| Value (Coastal eutrophication potential) | Label | Colour |
|---|---|---|
| -1 | No Data | #d3d3d3 |
| 0 | Low (<-5) | #74afd1 |
| 1 | Low - Medium (-5 to 0) | #aac7d8 |
| 2 | Medium - High (0 to 1) | #dededd |
| 3 | High (1 to 5) | #f8ab95 |
| 4 | Extremely High (>5) | #f27454 |
Generated from darwin/layers/layer-coastal-eutrophication-potential-aqueduct-3-0.toml and risk_indicator_pairs.toml (develop).