Ecosystem Viltality Water Quality (WQL)
August 10, 2021 at 8:00 PMWater quality measures the state of water quality in the basin relevant for maintaining healthy aquatic ecosystems, rather than for human consumption.
Suspended solids in surface water, total nitrogen,total phosphorous and dissolved oxygen are all critical parameters that provide a measure the impact of water quality r on biodiversity and ecosystem health in a basin (UNEP 2008a). These should be measured as a deviation from an established environmental baseline, which may be derived from the basin’s historic natural conditions or the physiological tolerances of native aquatic species of concern.
Other indicators of major concern for water quality can include temperature, salinity, pH, electrical conductivity, total dissolved solids, heavy metals and coliforms, pharmaceuticals and other contaminants. The choice of what to measure can be based on local requirements and capabilities, following recommendations by the United Nations (UNEP 2008a). However, they should be selected judiciously, as and when, data and analytical capacity are available. Variables that are known to have the greatest potential impact on freshwater ecosystem health should be selected.
| Attributes | |
|---|---|
| Scale of calculation: | Sub-basin/monitoring station, aggregate to basin |
| Range of Output: | 100-95 indicates excellent water quality; 80-94 indicates good water quality; 79-65 indicates fair; 64-45; <45 indicates poor water quality |
| Reference: | Canadian Water Quality Index (CCME 2001) |
| Type/Class of Input required: | Total Suspended Solids (TSS), Total Nitrogen (TN), Total Phosphorus (TP), Dissolved Oxygen (DO) time series and concentrations of other pollutants of interest. |
| Suggested source of ‘minimum’ data to enable calculation: | Data requires local input from observation or models for minimum 4 pollutants with at least 4 data points each. |
Data Preparation:
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Time series data for WQ parameters:
Values calculated for the three “essential parameters” (Total Suspended Solids, Total Phosphorous, Total Nitrogen and Dissolved Oxygen) and additional local parameters of concern.
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Threshold for each WQ parameters:
Each parameter considered requires a threshold or range that the measured value should fall above, below or within. While the user may assign a threshold according to local conditions (e.g. effects on sensitive species or ecosystem processes) UNEP (2007; 2008b) recommendations may be adopted:
Parameter Recommended Range Suspended solids (measured as turbidity) <5 NTU Total Nitrogen < 2 mg/L – 6 mg/L Total Phosphorus < 10 μg/L – 40 μg/L Dissolved Oxygen > 6 mg/L (warm water), 9.5 mg/L (cold) The ranges reported here reflect differences across ecosystem types, with the intent that users apply a threshold within this range. Values less than these selected thresholds are then considered to satisfy the objective. Alternatively, the data-derived ecosystem-based thresholds for TN and TP for an Australian case study in the table below can be used as defaults in the same way (Hart et al. 1999). Ranges of TN and TP for natural and degraded temperate and tropical streams can be found at Allan and Castillo (2007). However, we refer users to Hart et al. (1999), CCME (2002), UNEP (2007, 2008b), and Allan and Castillo (2007) to help determine thresholds in the absence of local (often national) thresholds for maintaining healthy aquatic ecosystems. Thresholds should be chosen to reflect local conditions and not because they will provide a favorable indicator value.
Ecosystem type TN (mg/L) TP (µg/L) Lowland River 1.60 37 Upland River 0.34 35 Freshwater Lakes and Reservoirs 0.44 50 Estuaries 0.08 45 Coastal and Marine 0.35 55 Wetlands No data No data
Calculation in FHI Toolbox: CCME 2001