(Virtual Showroom): Aquatic ecosystems play a crucial role in supporting life on Earth. South Africa, with its vast coastline and numerous inland watercourses, is home to a diverse range of aquatic ecosystems. These ecosystems are influenced by a variety of drivers and respond to these drivers in unique ways. In this article, we will explore the drivers and responses of aquatic systems in South Africa and the methodologies and techniques used to monitor these changes.

Drivers of Aquatic Systems in South Africa:

The drivers of aquatic systems in South Africa can be broadly categorised into natural and anthropogenic factors. Natural factors include climate change, hydrology (flow regime), and geology, while anthropogenic factors include land use change, pollution (water quality), and invasive species. These factors drive changes that may occur to the aquatic ecosystems we so heavily rely on.

Climate change is a significant driver of aquatic systems in South Africa, with rising temperatures and changing precipitation patterns leading to changes in river flows, water quality, and the distribution of species. Precipitation is a key driver in South Africa, which has an average rainfall of 420 Millimetres (mm) below the world average. Hydrology, or the study of water movement and distribution, is another critical driver of aquatic systems, with changes in rainfall patterns, dam construction, and water abstraction impacting aquatic ecosystems.

Anthropogenic drivers, such as land use change and pollution, have also had a significant impact on aquatic systems in South Africa. Agricultural expansion, urbanization, and mining activities have led to habitat destruction and altered nutrient and sediment loads in rivers and estuaries. This has been exasperated by the significant abstraction of water needed to support these anthropogenic activities, which results in the reduction of surface and groundwater flows sustaining the valuable water resources. The direct and indirect impacts of these land use changes may lead to alterations in water quality within the downstream environment. In addition to this, the introduction of invasive species has also led to significant changes in aquatic ecosystems, with species like Eichhornia crassipes (Water Hyacinth) and Cyprinus carpio (Common Carp) displacing native species.

Responses of Aquatic Systems in South Africa:

Aquatic systems in South Africa respond to these drivers in a variety of ways, with some responding rapidly and others over more extended periods. Two (2) response classes are typically associated with aquatic ecosystems, namely: 1) Biota and 2) Habitat (Physical structure and vegetation). Alterations in water quality caused by land use change, for example, can impact on the growth and survival of aquatic organisms and alter the structure and function of ecosystems. Changes in hydrology, such as altered river flows, can lead to changes in the distribution of aquatic species and the connectivity of ecosystems, as well as erosion and thus alteration to instream habitats and quality. Invasive species can displace native species and alter ecosystem processes, while land use change can lead to habitat loss and fragmentation. Activities within the catchment for example mining, may lead to drawdown of the groundwater table, increased sediment and concentration of chemical constituents, as well as the direct destruction of aquatic habitat, which results in changes to the overall ecosystem and biota taking refuge therein.

The alteration (response) of aquatic ecosystems as a result of the various natural and anthropogenic drivers leads to the reduced ability of the systems to provide regulatory, provisioning and cultural Ecosystem Services (ESS). These include inter alia: Flood attenuation, streamflow regulation, water quality enhancement, carbon storage, maintenance of biodiversity, provision of water for human use, harvestable resources and cultivated foods, as well as cultural benefits such as tourism and recreation, education and research and cultural heritage. It is therefore vital that the aquatic ecosystems be monitored and sustainably managed to ensure that a reduction in the supply of ESS is not realised as a result of the broader aquatic ecosystem drivers.

Monitoring Techniques:

Monitoring the drivers and responses of aquatic systems is crucial for understanding their dynamics and informing management strategies. A variety of methodologies and techniques are used to monitor aquatic systems in South Africa, including water quality monitoring, hydrological monitoring, and ecological monitoring. The mechanisms used for monitoring will depend on a variety of factors, including but not limited to: Legislative requirements, type of activity/development, classification of the at-risk water resource/s and characteristics thereof. A broad list of monitoring techniques that could be used on riverine and wetland habitats is presented below. These are typically used to monitor water resources within South Africa, however this list is not exhaustive as additional methods of assessment are available.

Riverine Systems

River delineation:

• A practical field procedure for identification and delineation of wetlands and riparian areas (DWAF, 2008)

River classification:

• Classification system for wetlands and other aquatic ecosystems in South Africa (Ollis et al., 2013)

Water quality characteristics:

• Grab samples
• In situ water quality probe readings
• Electrical water quality monitoring station
• Physicochemical Driver Assessment Index (PAI)
• Diatom analyses: South African Diatom Index (SADI) (Harding & Taylor, 2011), Specific Pollution Sensitivity Index (SPI) (CEMAGREF, 1982) and Percentage of Pollution Tolerant Values (%PTV) (Kelley & Whitton, 1995)
• Environmental toxicity testing: Direct Estimate of Ecological Effect Potential (DEEEP) (Department of Water Affairs and Forestry (DWAF), 2003)

Hydrological flow volume and velocity in high and low flows:

• Flow meter
• Flow weir
• Community-based measurement techniques

Aquatic biota:

• South African Scoring System Version 5 (SASS5) (Dickens & Graham, 2002)
• Fish Response Assessment Index (FRAI) (Kleynhans, 2008)
• Macroinvertebrate Response Index (MIRAI) (Thirion, 2007)
• Dragonfly Biotic Index (DBI) (Samways & Simaika, 2016)

Aquatic habitat:

• Geomorphological Driver Assessment Index (GAI) (Rowntree, 2013)
• Index of Habitat Integrity Assessment (IHIA) (Kleynhans, 1996; Kleynhans et al., 2009)
• Integrated Habitat Assessment System (IHAS) (McMillan, 1998, Ollis et al., 2006) 
• Riparian Vegetation Response Index (VEGRAI) (Kleynhans et al., 2007)
• Ecological Importance and Sensitivity (EIS) assessment (Kleynhans & Louw, 2008)
• Buffer zone guidelines for rivers, wetlands and estuaries (Macfarlane & Bredin, 2016)

Wetland Systems:

Wetland delineation:

• A practical field procedure for identification and delineation of wetlands and riparian areas (DWAF, 2008)

Wetland classification:

• Classification system for wetlands and other aquatic ecosystems in South Africa (Ollis et al., 2013)

Water quality characteristics:

Grab samples

• In situ water quality probe readings
• Electrical water quality monitoring station
• Diatom analyses: South African Diatom Index (SADI) (Harding & Taylor, 2011), Specific Pollution Sensitivity Index (SPI) (CEMAGREF, 1982) and Percentage of Pollution Tolerant Values (%PTV) (Kelley & Whitton, 1995)
• Environmental toxicity testing: Direct Estimate of Ecological Effect Potential (DEEEP) (Department of Water Affairs and Forestry (DWAF), 2003)

Hydrological flow volume and velocity in high and low flows:

• Flow meter
• Flow weir
• Community-based measurement techniques

Wetland integrity:

• WET-Health (Version 2.0) (MacFarlane et al., 2020)
• Wetland Index of Habitat Integrity (IHI) (DWAF, 2007)

Wetland functionality:

• WET-EcoServices (Version 2.0) (Kotze et al., 2020)

Wetland ecological importance and sensitivity:

• Ecological Importance and Sensitivity (EIS) assessment (Rountree & Kotze, 2013)

Wetland buffer zone determination:

• Buffer zone guidelines for rivers, wetlands and estuaries (Macfarlane & Bredin, 2016)

Wetland rehabilitation and offset:

• WET-Prioritise (Rountree et al. 2019)
• WET-RehabPlan (Kotze et al. 2009)
• WET-RehabMethods (Russell, 2009)
• WET-RehabEvaluate (Version 2) (Walters et al., 2019)
• Wetland offsets: A best-practice guideline for South Africa (Macfarlane et al. 2016)

In conclusion, the aquatic systems of South Africa are influenced by a variety of natural and anthropogenic drivers, which can lead to diverse responses over different timescales. Monitoring these systems using a range of methodologies and techniques is critical for understanding their dynamics and informing management strategies. By working together to protect and manage these ecosystems, we can ensure their continued health and resilience for generations to come.