4.3 The Application of Catchment Scale Analysis
4.3.2 Calculating the Magnitude of Impacts of Land-cover Change on
4.3.2 Calculating the Magnitude of Impacts of Land-cover Change on Ecosystem Services
functional effectiveness. The functionality score for nitrate removal from catchment impacts for Wetland FID 0 is therefore 3.47. The functional effectiveness score ranges from 0 (minimum effectiveness) to 4 (maximum effectiveness).
Following the same methodology, the functionality scores for the other two ecosystem services evaluated, phosphate trapping and toxicant removal, were found to be 3.50 and 3.50 from catchment impacts for Wetland FID 0.
4.3.2.2 Onsite Impacts
The impacts of land use activities within wetlands were translated to magnitude of impact scores with respect to increased water use, reduced surface roughness, flow impediment, and the effect of drains or gullies. Thereafter the same method that was applied for catchment impacts to determine their effect on the provision of ecosystem services was applied to impacts that resulted from activities within wetlands. The x-value indicating the magnitude of impact for each onsite impact was substituted in the relevant equation for onsite impacts from Tables 8, 9, 10 and 11 and the functional effectiveness score for each ecosystem service was calculated.
For example, in keeping with Wetland FID 0, reduced surface roughness was the only significant impact of the four possible impacts that was identified, and the magnitude of impact of surface roughness for Wetland FID 0 was calculated to be 0.60 (Table 17). By referring to Table 9, it was determined that the equation y=-0.08x + 2.50 is used for onsite impact scores ranging between 0 and 10 for valley-bottom wetlands with regard to sediment trapping. As a result, Wetland FID 0 scored a functionality score of 2.45 for sediment trapping.
Similarly, in order to determine the functionality score for nitrate removal for Wetland FID 0 due to reduced surface roughness, the equation y=-0.18x + 3.50 from Table 9 was applied to the magnitude of impact score of 0.60 for reduced surface roughness. Wetland FID 0 was therefore found to have a functionality score of 3.39 for nitrate removal based on a reduction in surface roughness.
Often, wetlands have more than one onsite impact, in which case functionality scores for all onsite impacts need to be resolved. As Ellery et al. (in review) point out, this is because
“some activities will reduce the duration and extent of inundation (direct water losses, reduced surface roughness and the presence of drains or gullies), while others might prolong it (presence of impeding features increases water retention above the impeding feature and reduces water retention below it)” (p52). In order to resolve onsite impacts, the lowest functionality score of the onsite impacts is taken and adjusted according to the value of functionality scores for other onsite impacts. These adjustments are made through consultation with Table 12, which contains the values to be used to scale functionality scores in valley-bottom wetlands as determined for a range of catchment and onsite impacts.
As a hypothetical example, imagine a wetland which has functionality scores for two onsite impacts: 1.60 due to reduced surface roughness, and 1.80 due to flow impediment (for sediment trapping). Table 12 would have been consulted to determine the value to be subtracted from 1.60 (the lower of the two scores) by considering the additional onsite impact that is being resolved for (which in this case is flow impediment); the functionality score range (which is 1.2- 1.99 since the higher functionality score is 1.80), the ecosystem service for which the determination of functionality is being conducted (sediment trapping); and the wetland type (valley-bottom). By doing so, it is determined that a value of 0.1 should be subtracted from the lower functionality score of 1.60 on order to resolve the scores for impacts arising within the wetland. Therefore in this example, the final functional effectiveness score for sediment trapping based on impacts in the wetland is 1.5.
By applying this methodology, the functional effectiveness scores from impacts arising in the wetland (onsite impacts) for the other ecosystem services evaluated - phosphate trapping and toxicant removal - were calculated to equal 3.39 and 3.39 for Wetland FID 0.
4.3.2.3 Catchment and Onsite Impacts
For a given ecosystem service for a single wetland, the steps described thus far result in two functional effectiveness scores: one for impacts arising in the wetland’s catchment, and one for impacts arising in the wetland. As such, in much the same way that various onsite impacts were resolved in order to determine a single functional effectiveness score, scores for impacts
arising in the wetland’s catchment and for impacts arising within the wetland were compared and the lowest was chosen and scaled by subtracting the relevant value from Table 12.
Returning to the previous example, it has been determined thus far that for the ecosystem service of sediment trapping, Wetland FID 0 has a functional effectiveness score of 2.50 due to impacts arising in the wetland’s catchment, and 2.45 from impacts arising in the wetland.
Since the lower of these two values is 2.45, the value to be subtracted is retrieved from Table 12 based on the score of 2.50 for the catchment impact of decreased water inputs as previously determined using Table 17. For Wetland FID 0 the final functionality score is therefore determined as follows: 2.45 (functionality score due to impacts arising within the wetland) – 0 (decreased water input from the catchment has a functionality score between 2 and 2.99) = 2.45.
In exactly the same way, the final functionality scores for all the other ecosystem services were established. Taking nitrate removal as an added example, it was determined that due to impacts arising in the wetland’s catchment, Wetland FID 0 has a functional effectiveness score of 3.47 for nitrate removal, while the functional effectiveness score of Wetland FID 0 for nitrate removal based on impacts arising within the wetland was found to equal 3.39.
Through consultation with Table12, the final functionality score for nitrate removal of Wetland FID 0 was resolved to be 3.39, following the same logic as described in the previous example: 3.39 (functionality score due to onsite impacts) – 0 (decreased water input from the catchment has a functionality score between 3 and 4) = 3.39. Similarly, overall functionality with respect to phosphate trapping and toxicant removal for Wetland FID 0 were determined to be 3.39 and 3.39.
4.3.2.4 Calculating Functional Hectare Equivalents
Functional hectare equivalents were calculated by utilizing the following equation:
Functional hectare equivalents = (final functional effectiveness score / 4) * size of wetland (ha).
Therefore for the example of Wetland FID 0, the functional hectare equivalents of each ecosystem service evaluated were determined as follows:
Sediment Trapping: (2.45/4)*46.37 = 28.40 ha
Nitrate Removal: (3.39/4)*46.37 = 39.30 ha Phosphate Trapping: (3.39/4)*46.37 = 39.30 ha Toxicant Removal: (3.39/4)*46.37 = 39.30 ha
4.3.2.5 Determining Water Quality Enhancement Functionality
The functional effectiveness scores and hectare equivalents for the ecosystem services of sediment trapping, nitrate removal, phosphate trapping, and toxicant removal for each wetland in the Goukou Catchment was determined, and the mean of these values was taken to represent water quality enhancement functionality and hectare equivalents of water quality enhancement functionality. For example, for Wetland FID 0, water quality enhancement functionality was determined to be 3.16 ((2.45 + 3.39 + 3.39 + 3.39) / 4), while hectare equivalents of water quality enhancement functionality equalled 36.58 ((28.40 + 39.30 + 39.30 + 39.30) / 4).
4.3.3 Calculating the Magnitude of Impacts of Land-cover Change on Water Quality as