Response to Cllr Brett to question: “Considerable complaints about the Algae choking off Wildlife in Broomfield Park. When will the lakes be cleaned and the boating pond reinstated?”
Response:
The cause of the algae in the waterbodies in Broomfield Park (the lakes and the new wetlands) is due to high nutrient loading of the inflows into these water bodies. As part of the wetland creation project at Broomfield Park we have been carrying out water quality monitoring of the surface water flows alongside our delivery partner Thames21. It was found that the readings for nitrogen and phosphate were classed as “poor” (according to Water Framework Directive (WFD) values), and at levels which would cause algal blooms. It seems that we are seeing a process known as eutrophication, with algal blooms becoming more pronounced in the summer.
The source of these nutrients in the catchment is likely to be misconnections from the foul network to the surface water in the catchment, this is an issue that Thames Water are aware of in the upstream catchment. A plus point to consider is that the readings for the same nutrients (nitrogen and phosphate) are much lower at the outfall of the wetlands, indicating that they appear to be functioning in respect to reducing nutrient loads. However at the wetlands are downstream of the lakes this does not solve the problem directly (just more generally for the water flowing onwards to Pymmes Brook).
For the lakes to be meaningfully “cleaned” they would need to be desilted. This would carry a high cost and is not a job that I am aware of being programmed at this point.
The boating pond is a slightly separate matter as the inflow has traditionally been through a ground water pump. This pump has been investigated, it is very aged infrastructure and does not appear to be functioning. We have been ruling out the reasons for this one by one. Including blockages on the line, the working of the pump itself and the absence of reliable ground water in the well. Due to a lot of remaining uncertainty regarding this asset and potential spiralling costs we are now exploring other means of providing water input into the boating pond. I believe the cleaning of sediment from the at present dry boating pond is currently in-hand with Parks Operations. @Marcus Harvey should be able to update on this.
