Find further information on the Conservation of Freshwater Ecosystem Values (CFEV) Program and its data at www.dpipwe.tas.gov.au/cfev.
TitleWetland water quality sub-index
CustodianWater and Marine Resources Division, Department of Primary Industries, Parks, Water and Environment
CreatorSteve Carter, Environmental Dynamics
DescriptionAn index which predicts the status of water quality for wetlands based on potential nutrient inputs associated with land use impacts and catchment disturbance.
Input data
Lineage
Water quality scores were generated using an expert rule system with input variables of catchment disturbance and land use (nutrients) (see ‘Assigning values to ecosystem spatial units’ below). These variables were chosen due to their strong links with water quality. Experts rated land use (nutrients) as having a greater influence on water quality than catchment disturbance. Information on expert rules systems can be found in Appendix 3 of the CFEV Project Technical Report.
The method for assigning a water quality sub-index score to the wetlands spatial units, using definition tables developed for the expert rules systems, is provided below.
Date createdNovember 2004
Scale and coverage1:25 000; Statewide
Column headingWL_WATER
Type of dataContinuous but has been converted to categorical format (see Table 2).
Number of classes5
Assigning values to ecosystem spatial units
A water quality sub-index score (0 = poor condition – 1 = good condition) was assigned to wetland spatial units as WL_WATER using the expert rule system shown as a definition table in Table 1 (e.g. if the wetland has a HIGH score for land use (nutrients) and a LOW score for catchment disturbance, then assign a score of 0.3). Using fuzzy logic enables input data and output results to be continuous rather than categorical as implied here (i.e. inputs and output data can range on a continuous scale between 0 and 1, and the process of executing the expert rule system will determine its membership as being HIGH or LOW) (refer to Appendix 3 of the CFEV Project Technical Report for more information on expert rules systems).
Table 1. Expert rule system definition table for the water quality sub-index for wetlands.
Land use (nutrients) (WL_NUTRI) | Catchment disturbance (WL_CATDI) | Water quality score (WL_WATER) |
H | H | 1 |
H | L | 0.3 |
L | H | 0.1 |
L | L | 0 |
The wetlands spatial data layer had the continuous water quality sub-index data categorised according to Table 2. The categorical data was used for reporting and mapping purposes.
Table 2. Water quality sub-index categories for wetlands.
Category | Min to max values |
1 | 0 to <0.2 |
2 | 0.2 to <0.4 |
3 | 0.4 to <0.8 |
4 | 0.8 to <1 |
5 | 1 |
CFEV assessment framework hierarchy