In this, the third part of the Mpofana River Report, Penny Rees writes about Alien Invasive Plants.
It was extremely encouraging to see the sterling job that the Balgowan Conservancy and some landowners have done by clearing invasive plants in the 32 metre buffer along the Mpofana River. Thus far a total of 6 kilometres (both sides of the river for three km in total) have been cleared of Bugweed,
and some bramble.
This is only the beginning as there are still many more areas that have been targeted. This will go a long way towards improving the health of the river, and all those concerned are heartily congratulated. Of the eight rivers that DUCT staff have walked, this is the largest private invasive control effort we have seen. Well done to all concerned.
Sadly, that’s where the good news ends!
Some of the negative impacts on the Mpofana are found along the entire length of the river. These include pastures, timber, gardens and lawns – not only in the buffer but often up to the rivers edge.
Thriving in the buffer are also invasive alien plants: bramble, self seeded wattle and bugweed
Construction of two different types was observed in the buffer – Downstream of the outfall this was undertaken by a landowner,
whilst upstream of the outfall, construction was for the new Mooi uMngeni Transfer Scheme pipeline at river and wetland crossings.
At these points, the meagre mitigation measures seen during the walk did not raise our hopes that enough care was being taken to minimise impacts on the Mpofana.
Of concern is the potential lack of post pipeline construction rehabilitation and monitoring which could lead to silt loads entering the Mpofana in places where up to now there have been no siltation impacts.
Additionally, the disturbed soils will be an ideal sprouting ground for invasive species such as wattle and bug weed
On the other hand, upstream of the outfall cattle trampling of river bank and wetland edge was far more prevalent
There were plenty of signs of nutrification:
Algal blooms – 5 sites: 4 on livestock farms, 1 residential
Oxygen weed – 10 sites: 2 in dams, 2 near residential, 6 at livestock watering points
Seen only upstream of the outfall: one rubbish pit only metres from the river
And the highly invasive Pickerel Weed – 2 sites: dams
Finally there were two impacts which were clearly different up and downstream of the outfall. They are as follows:
Upstream of outfall: The first water extraction point on the Mpofana is approximately 100 metres below the source spring. This is followed by dams which do not release any water into the stream,
plantations across the stream that have dried up the water,
water extraction pumps,
extraction for the pipeline construction
and a small non-permanent irrigation furrow for subsistence vegetable farming.
All of which, combined with the lack of rainfall over the last few months, have caused the river level to be either non–existent or very low.
Downstream of outfall: the amount of water slowly increases downstream as water from tributaries enters the Mpofana and the number of dams and plantations are fewer.
Siltation of river bed and submerged rocks:
Upstream of outfall: Occasional areas of elevated silt in the river from cattle trampling and erosion from paths accessing the river.
Mpofana banks are extremely vulnerable to water or wind erosion at pipeline construction points due to insufficient cover on exposed river banks.
Downstream of outfall: Almost constant elevated silt levels on the river bed and submerged rocks have the effect of smothering the life in the Mpofana.
As this was not observed upstream of the outfall, we have concluded that the silt is a direct result of the erosion caused by the inter catchment transfer.