Effect of rehabilitation activities on ecological integrity and flow regulation function of wetlands in a gauged catchment

Abstract

Wetland ecosystems provide essential hydrological and ecological ecosystem services ranging from flow regulation, water quality improvement to biodiversity support. These systems face various pressures from surrounding land uses, and their ability to function optimally and provide ecosystem services is heavily dependent on the condition of the wetland. In a developing country like South Africa where land-use change is prevalent to support development agenda, wetlands and rivers are severely impacted. It is estimated that approximately 45% of wetlands are being heavily modified, which compromises the regulatory services that healthy wetlands can provide. This study seeks to respond to a perceived need for increased knowledge of the contribution that rehabilitation activities have made towards improving wetland health (ecological integrity) and flow regulation capacity in support of the country’s investment made towards wetland rehabilitation. The study focuses on two wetland catchments which consist of two wetland systems, Kgaswane and Rietfontein wetland systems. Both wetland systems are located in the North West Province, and wetland rehabilitation work was completed in both systems. Additional criteria of selection included the presence of the streamflow gauge at the outlet of the rehabilitated wetland catchment for flow data analysis. The study found that in general, the implementation of rehabilitation interventions on both wetlands (Kgaswane and Rietfontein) has shown improvement in ecological conditions. Kgaswane wetland system had shown a statistically insignificant improvement (i.e. little improvement) in the ecological conditions ranging from 3% to 8% with regard to rehabilitation activities. Rietfontein wetland system has shown a significant improvement in ecological conditions of 30%. The analysis of flow data at the outlet of the wetland catchments at streamflow gauges A2H038 (Kgaswane wetland) and A2H053 (Rietfontein wetland) shows an increase in the magnitude of high flows and a decrease in low flows as compared to our current knowledge that wetlands increase or maintain baseflows. The conclusion is that rehabilitation efforts in both of Kgaswane and Rietfontein systems did not contribute positively to flow regulation, particularly with regards to improvement and maintenance of baseflows; the variability of flow between high and low flows increased following rehabilitation. All the wetland interventions are performing under the dry period for Rietfontein and an average rainfall period for Kgaswane. The cost-effectiveness of implementing rehabilitation activities for the Kgaswane wetland system is low and for Rietfontein wetland system is intermediate. The projects that yield high return on investments and are cost effective turned to be high priority in terms implementation. This is not the case for the two wetland systems assessed in this report. There are various limitations identified in all aspects (ecological integrity, flow regulation and cost-effectiveness) that can be addressed in future studies in similar projects. There is scope for future work to address issues raised on the limitations and to provide on-going improvements to the results on an assessment of this nature. The assessment is predominantly developmental to encourage versatile administration, reformist learning and persistent improvement of our understanding of the effects of rehabilitation activities. The purpose of the assessment is to provide some direction that can be developed and refined as adequate information becomes available