NFEPA Atlas 5.3_20111025_FINAL.indd - Biodiversity GIS - SANBI

4.4 Wetland conditionWetland condition describes the extent to which a wetland has been modified by humanactivity. There are many approaches to assessing wetland condition in the field. However,in the absence of field survey data for most wetlands across the country, wetlandcondition was modelled by NFEPA to serve as a relative measure for informing choices inselecting wetland FEPAs. As explained in Section 2.2, choices in the selection of wetlandFEPAs were made using wetland ranks, which were based on a combination of specialfeatures and wetland condition. Wetlands with known special features (e.g. presence ofrare plants and animals, extensive intact peat wetlands) were selected as the first choicefor achieving biodiversity targets for wetland ecosystem types. Any remaining targets wereachieved first in wetlands of good condition, proceeding only if necessary to wetlands ofprogressively modified condition (Table 4.2). Wetland FEPAs did not have to be in a goodcondition to be chosen as a FEPA, but those wetland FEPAs currently in less than goodcondition should be rehabilitated to the best attainable ecological condition.Wetlands that had the majority of their area coinciding with 1:50 000 artificial water bodies(Department of Land Affairs: Chief Directorate Surveys and Mapping 2005-2007) wereassigned a heavily- to critically-modified wetland condition (equivalent of D, E or Fecological category for rivers: Table 4.1). For the remaining wetlands, the percentagenatural land cover in and around the wetland was used as a surrogate measure of wetlandcondition. The same land cover data as used for modelling condition of tributaries wasapplied (Section 4.2). Percentage natural land cover was calculated within four areas:the wetland itself, and the wetland surrounded by GIS buffers of 50 m, 100 m and 500 mfrom the edge of the wetland. The lowest of these four resulting percentages of naturalland cover was used to guide the condition category of the wetland (Table 4.2; Figure 4.9),using the following rules:Natural or goodModerately modifiedHeavily to critically modified• Non-riverine wetlands were considered to be in a good, moderately modified orheavily modified condition if the lowest percentage natural land cover in and aroundthe wetland was 75% or more, 25-75%, or less than 25% respectively.• This same rule was applied to riverine wetlands associated with natural or moderatelymodified rivers (i.e. in an A, B, or C ecological category) because in such cases thesurrounding land use is more likely to be a driver of wetland ecosystem degradationthan the condition of the associated river.• Riverine wetlands associated with a largely modified, seriously modified or criticallymodified river (i.e. in a D, E or F ecological category) were assigned a heavily modifiedcondition irrespective of the surrounding natural land cover.• Several riverine wetlands are associated with rivers too small to be included onthe 1:500 000 river network GIS layer – in these instances, the river condition wasunknown and the wetland was assigned a condition based on the lowest percentagenatural land cover.It is very difficult to assess accurately how much of South Africa’s wetland area hasalready been irreversibly lost. However, we know it is substantial, especially in urbanareas and intensively cultivated areas. Over and above this irreversible loss that hasalready taken place, approximately 45% of our remaining wetland area in South Africa isin a heavily or critically modified condition, owing to human impacts such as damming,draining and bulldozing of wetlands. This is of immense concern given the importantregulating ecosystem services that healthy wetlands provide, such as purifying water andregulating floods.Figure 4.been accentuated to make them more visible.500 kmTable 4.2: Wetland condition categoriesWetland condition Assessment criteria * % of total wetland area **Good Natural land cover ≥ 75% 44Moderately modified Natural land cover 25-75% 18Heavily modified Riverine wetland associated with a D, E, F or Z category river 9Critically modified Wetland where the majority of its area coincides with a 1:50 000artificial inland water body, or where natural land cover < 25%* Percentage natural land cover was calculated within four areas: the wetland itself, and the wetland surrounded byGIS buffers of 50 m, 100 m and 500 m from the edge of the wetland. The lowest of these four percentages wasused.** Note that this excludes the extent of wetlands that have already been irreversibly lost due to draining, ploughingand concreting.36Input data layers - 53 -