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Ecological monitoring in the Steenbras Catchment

Baseline Monitoring for the City of Cape Town’s New Water Programme

Recently Umvoto’s Cole Grainger (Junior Freshwater Ecologist) and Fahad Aziz (Junior Water and Environmental Scientist) visited the Steenbras catchment as part of our quarter-annual ecological monitoring that forms part of the City of Cape Town’s New Water Programme. It is important to do this freshwater ecological monitoring to ensure that the wellfield development and groundwater abstraction do not negatively impact surface water.

South African Scoring System and River Health

In order to monitor this system, the team makes use of the SASS scoring system which refers to the South African Scoring System that looks at the assemblage of aquatic macroinvertebrates to derive River Health. The River Health classes range from class A (pristine condition) to F (critically deteriorated condition). Each aquatic taxon used in SASS is assigned a SASS sensitivity score ranging from 1-15, with 1 meaning the taxon is insensitive to water pollution and 15 meaning very sensitive to water pollution.

SASS represents a subcomponent of South African aquatic ecological monitoring known as the River Ecostatus Monitoring Programme (REMP) and is conducted to gauge baseline water quality and river biotope availabilities to establish reference conditions against which to compare future assessments, especially where there has been anthropogenic activity (e.g., groundwater abstraction at Steenbras).

Class A in the Steenbras Catchment

The Blephariceridae has a SASS score of 15/15 meaning river water quality is of a very high standard which will likely support other sensitive taxa that collectively meet the biological index requirements associated with a river health A class. Blephariceridae are a rare occurrence in the Steenbras catchment and as such cannot reliably be used to indicate riverine impacts. Blephariceridae interestingly did not follow the typical aquatic evolutionary path of proficient swimming, and instead have strategized their specialised ventral suckers that enable them to clasp to cobbles and bedrock to resist oncoming flows as they scrape benthic algae for nourishment. This evolutionary strategy allows them to inhabit aquatic biotopes that physiologically exclude other taxa so that they avoid predation and competition for food sources.

Cole explains the significance of the rare Blephariceridae that he and Fahad came across on their latest ecological monitoring survey.
Close up image of the Blephariceridae found in the Steenbras River Catchment near Cape Town, South Africa
Close up image of the Blephariceridae [Photo taken by Cole Grainger].

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