Calculator Inputs
Example Data Table
| Scenario | TP (µg/L) | TN (mg/L) | Chl‑a (µg/L) | Secchi (m) | Temp (°C) | Residence (days) | Likely Risk |
|---|---|---|---|---|---|---|---|
| Clear, low nutrients | 8 | 0.4 | 1.8 | 4.5 | 18 | 8 | Low |
| Enriched, seasonal blooms | 35 | 1.1 | 12 | 1.7 | 24 | 35 | Moderate |
| Frequent nuisance blooms | 120 | 2.8 | 45 | 0.8 | 28 | 120 | Very High |
Values are illustrative. Local standards and sampling methods may differ.
Formula Used
Each indicator is converted to a 0–100 sub‑score, then combined using weights:
Risk Score = Σ(wᵢ × Sᵢ) / Σ(wᵢ for provided indicators)
For concentration‑type indicators, a smooth log scaling is used:
S = 100 × ln(x/low) / ln(high/low), clipped to 0–100
Where low is a low‑risk reference and high is a high‑risk reference.
If provided, these equations estimate trophic state:
- TSI(TP) = 14.42 × ln(TP) + 4.15
- TSI(Chl) = 9.81 × ln(Chl) + 30.6
- TSI(SD) = 60 − 14.41 × ln(SD)
The calculator averages the available TSI values.
Units: TP and Chl in µg/L, Secchi depth in meters.
This tool estimates risk for screening and education. For regulatory decisions, use local monitoring protocols and watershed models.
How to Use This Calculator
- Enter at least one key indicator: phosphorus, nitrogen, chlorophyll‑a, or Secchi depth.
- Add optional inputs (oxygen, turbidity, temperature, residence time) for better context.
- Select the waterbody type to apply a suitable weighting preset.
- Optionally enable custom weights if you have site‑specific priorities.
- Click Calculate Risk to view results above the form.
- Export the report using the CSV or PDF buttons.
Nutrient concentration signals
Total phosphorus and total nitrogen are primary bloom drivers in many waters. Screening studies often flag TP above 25 µg/L and TN above 1.0 mg/L as elevated for lakes and slow reservoirs. The tool converts higher nutrient levels into higher sub-scores on a log scale so increases from 10 to 100 µg/L matter more than small changes near background.
Algae and clarity response
Chlorophyll‑a summarizes algal biomass, with 2–10 µg/L commonly observed in clearer systems and >30 µg/L linked to frequent nuisance blooms. Secchi depth provides a direct clarity measure; values below 1.0 m often align with turbid, bloom‑affected conditions. Turbidity above 50 NTU can mask blooms, reduce light, and transport particulate phosphorus during storm-driven pulses in many catchments. When you enter TP, Chl‑a, or Secchi depth, the calculator also estimates TSI values and reports a mean TSI when multiple indicators are available.
Oxygen stress and internal loading
Dissolved oxygen is included because low DO can coincide with high respiration, sediment oxygen demand, and potential internal phosphorus release. As a practical threshold, DO below 5 mg/L can stress aquatic life, while sustained hypoxia near 2–3 mg/L signals severe risk in deeper zones. The tool assigns the worst sub-score at 4 mg/L and improves toward 8 mg/L.
Hydrology, temperature, and residence time
Warm water accelerates algal growth and can favor cyanobacteria; risk rises steadily from 10°C toward 30°C in the scoring curve. Residence time represents how long water remains in the system; values above 30–60 days can allow blooms to develop, while very short residence times can dilute and flush algae. Rivers and estuaries typically rely more on TN, land use pressure, and wastewater influence.
Turning scores into management actions
Use the overall score to prioritize actions, then use subscores to target sources. High land-use pressure suggests runoff controls, fertilizer timing, and riparian buffers. A phosphorus‑limited N:P ratio (>20) supports focusing on erosion, detergents, and sediment disturbance, while nitrogen limitation (<10) points toward wastewater and stormwater reductions. Track the score seasonally to verify that interventions reduce both indicators and bloom response.
FAQs
1) What does the risk score represent?
It is a 0–100 screening score built from the indicators you provide using normalized weights. Higher scores suggest stronger conditions for blooms and eutrophication symptoms, but local standards and sampling design still matter.
2) Which inputs most influence the result?
The strongest drivers are usually nutrients (TP, TN) and the algae response (chlorophyll-a, Secchi). Hydrology, temperature, land-use pressure, and wastewater influence refine the estimate when those fields are provided.
3) Can I use data from a single sampling event?
Yes, but treat it as a snapshot. Blooms can change quickly after storms and during warm periods. For planning, compare several dates or seasonal averages and look for consistent trends in nutrients and clarity.
4) How should I interpret the N:P ratio output?
The tool converts TN and TP into an approximate molar N:P ratio. Values below 10 suggest nitrogen limitation, above 20 suggest phosphorus limitation, and intermediate values indicate mixed or co-limited conditions.
5) Why are temperature and dissolved oxygen included?
Warmer water can increase algal growth rates and favor cyanobacteria, while low oxygen can signal high respiration and possible internal nutrient release from sediments. These factors help explain risk even when nutrients are moderate.
6) How do I export results for reports?
After calculating, use the Download CSV button for spreadsheets or the Download PDF button for a printable summary. Include the timestamp and waterbody type so readers understand the selected weighting preset.