Subsequent to a proposed development being constructed, or an activity such as a mine being established it may be evident that there will be considerable negative impact on the receiving aquatic environment that should be remediated. This is usually determined during the initial Environmental Impact Assessment (EIA) phase of a project when specialist studies and impact assessments are conducted. The outcomes of which, and subsequent to the implementation of the Department of Environmental Affairs (2013) mitigation hierarchy, may present that rehabilitation of impacts will be required. The mitigation hierarchy aims to first avoid negative impacts, but if this is not possible the next tier is to minimise these impacts. Effective minimisation can eliminate some impacts and reduce others allowing for sustainability targets to be met. The next consideration is restoration, or rehabilitation which takes place where minimisation efforts have failed to reach the required remediation target. At this stage, the exact quantity of functional aquatic habitat (hectare equivalents) that may be lost as a result of a proposed development, or activity must be calculated. This will inform the level of rehabilitation that should be considered for the project.
Based on the perceived loss of direct area (Hectares) and the calculated hectare equivalent (ha equiv.) loss of functional aquatic habitat, appropriate mitigation and rehabilitation measures must be formulated in an effort to remediate the impacts within a specific hydrogeomorphic (HGM) Unit (i.e. wetland) and improve the state of the systems back to a near-natural, or pre-development condition. HGM unit-specific rehabilitation goals, objectives, and targets are formulated to guide the required rehabilitation of each at-risk system.
To calculate the theoretical effect of the proposed rehabilitation measures on the integrity of the at-risk HGM unit, the ENVASS specialist will determine the pre- and post-development Present Ecological State (PES) scores, otherwise referred to as the integrity, of the aquatic habitat using legislated and best-practice methodologies and tools. In terms of wetland rehabilitation, this would be the WET-Health tool (MacFarlane et al., 2009), which uses three modules, namely; hydrology, geomorphology, and vegetation, to calculate the PES score of a specific HGM unit. The pre-and post-development PES scores are then converted into a ha equiv. score, which is essentially a representation of the integrity of an HGM unit expressed as an area, to compare the pre and post-development scenarios.
If the difference between the pre-and post-development has equiv. scores are positive, it indicates that the theoretic rehabilitation measures proposed have the potential to remediate the perceived impacts of the proposed development, or activity on the receiving aquatic environment, and thus ensure a ‘no net loss of biodiversity’ in the post-development scenario. However, if the difference is recorded to be negative there will be a residual impact on the receiving aquatic environment, and further steps within the DEA mitigation hierarchy must be applied.
The ENVASS in-house specialists have conducted numerous conceptual rehabilitation and monitoring programs for various proposed development and activities and would be well-suited to assist with any rehabilitation needs your organisation may require.
FRAI (Fish Response Assessment Index)
The purpose of the Fish Response Assessment (FRAI) is to provide a habitat-based, cause-and-effect underpinning fish communities and habitats to interpret the deviation of the fish assemblage from a Fish Reference Frequency of Occurrence (FROC) database in accordance with the SQR fish data from DWS (2013) and is implemented by the National River Health Programme (Kleynhans et al., 2007). The FRAI methodology was implemented to evaluate the existing state of the fish communities. This community metric measure allows for the evaluation of a range of metrics (flows, cover feature availability, migration impacts, water quality impacts, and alien invasive fish’s impacts) that are known to affect fish community conditions (Kleynhans et al., 2007).
Effective fish sampling included an electro-fishing apparatus (SAMUS 1000®) for 45 minutes per site. Stunned fish is then collected, photographed, identified, and released. All fish sampled were identified using Skelton (2001). Fish data was collected using the protocol prescribed for velocity/depth-categorised habitats (Kleynhans et al., 2007). Undercut banks and riparian vegetation were identified, and their coverage was estimated and scored. The fish and environmental data collected during this study were used to determine the ecological integrity of the fish communities. The reference frequency of occurrence developed by Kleynhans et al. (2007) was used in conjunction with the fish species list per quaternary reach in the SQR data provided by DWS to determine the reference fish species list in order to calculate the FRAI.
The FRAI was used to address specific information requirements regarding the response of fish assemblages to changes in the environment (Kleynhans et al, 2007). These ecosystem variables usually include physical and chemical variables, which are referred to as “ecological driver components”.
An assessment of the responses of the species metrics to changing environmental conditions may be done either through direct measurement (surveys) or concluded from the change in environmental conditions (habitat) (Kleynhans et al., 2007). Evaluation of the derived response of species metrics to habitat changes is based on knowledge of the ecological requirements of species. Changes in environmental conditions are related to fish stress and form the basis of ecological response interpretation (Kleynhans et al., 2007). These metric groups include the available habitats or velocity and depth; a cover metric that considers the preferences of overhanging vegetation, aquatic vegetation, water column, substrata as well as undercut banks and root wads; flow modifications in terms of volume, timing, and the duration of flows; migration and introduced species. As a result, expected and actual patterns can be evaluated to achieve an Ecological Category (EC) rating as seen in the table below.
Category A: Unmodified, natural | Score 90-100
Category B: Largely natural with few modifications. A small change in natural habitats and biota may have taken place but the ecosystem functions are essentially unchanged. | Score 80-90
Category C: Moderately modified. A loss and change of natural habitat and biota have occurred but the basic ecosystem functions are still predominantly unchanged. | Score 60-79
Category D: Largely modified. A large loss of natural habitat, biota, and basic ecosystem functions has occurred. | Score 40-59
Category E: The loss of natural habitat, biota, and basic ecosystem functions is extensive. | Score 20-39
Category F: Modifications have reached a critical level and the lotic system has been modified completely with an almost complete loss of natural habitat and biota. In the worst instances, the basic ecosystem functions have been destroyed and the changes are irreversible. | Score 0