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TitleImpacts within saltmarshes sub-index
CustodianWater and Marine Resources Division, Department of Primary Industries, Parks, Water and Environment
CreatorSteve Carter, Environmental Dynamics
DescriptionAn index which rates the relative condition of saltmarshes according to impacts (i.e. land disturbance, stock grazing and drainage disturbance) within the saltmarsh.
Input data
Lineage
A condition score reflecting the impacts within saltmarshes was established using an expert rule system (see ‘Assigning values to ecosystem spatial units’ below). Information on expert rules systems can be found in Appendix 3 of the CFEV Project Technical Report. The inputs to the expert rule system were variables describing land disturbance (calculated using an expert rules system), drainage disturbance and grazing within saltmarshes, weighted by experts in order of their influence, respectively. The impacts within saltmarshes sub-index was one of two inputs into the overall saltmarsh N-score expert rule system; the other being impacts adjacent to saltmarshes.
The impacts not calculated using an expert rules system were assessed by inspecting aerial photographs and were scored between 0 (disturbed) and 1 (pristine) according to the details in Table 1.
Table 1. Summary of variables assessed using aerial photographs for impacts within saltmarshes condition variable. Scores indicate condition, (0 - degraded, 1 - pristine).
Variable | Score | Other comments |
Grazing | Present (0) or absent (1) | Apparent grazing inferred from context i.e. local knowledge, evidence of horses, cattle tracks, or if adjacent to farm and no evidence of fences. |
Drainage disturbance | 1 – absent, 0.5 – little, 0.25 – moderate, 0 – extensive | Presence/extent of drainage channels, realignment of natural drainage |
The method for assigning an impacts within saltmarshes sub-index score to the saltmarsh spatial units is provided below.
Date createdNovember 2004
Scale and coverage1:25 000; Statewide
Column headingSM_IMWIN
Type of dataContinuous but has been converted to categorical format (see Table 3).
Number of classes3
Assigning values to ecosystem spatial units
An impacts within saltmarshes sub-index score (0 = poor condition – 1 = good condition) was assigned to saltmarsh spatial units as SM_IMWIN using the expert rule system shown as a definition table in Table 2 (e.g. if the saltmarsh has a HIGH score for land disturbance within the saltmarsh, LOW score for grazing within and HIGH score for drainage disturbance within the saltmarsh, then assign a score of 0.6). 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 2. Expert rules system definition table for the impacts within saltmarshes sub-index for saltmarshes.
Land disturbance within (SM_LDWIN) | Grazing within (SM_GRWIN) | Drainage disturbance within (SM_DRWIN) | Impacts within saltmarshes score (SM_IMWIN) |
H | H | H | 1 |
H | H | L | 0.5 |
H | L | H | 0.6 |
H | L | L | 0.4 |
L | H | H | 0.2 |
L | H | L | 0.1 |
L | L | H | 0.15 |
L | L | L | 0 |
The saltmarsh spatial data layer has the continuous impacts within saltmarshes sub-index data categorised according to Table 3. The categorical data was used for reporting and mapping purposes.
Table 3. Impacts within saltmarshes sub-index categories for saltmarshes.
Category | Min to max values |
1 | 0 to <0.2 |
2 | 0.2 to <0.8 |
3 | 0.8 to 1 |
CFEV assessment framework hierarchy