The Bourne Stream, which takes
its route through Poole and Bournemouth, finally joins the sea from an
outfall pipe at Bournemouth beach.
These are bathing waters under strict compliance with the Bathing
Water Directive 76/160/EEC.
Historically, the stream has had high levels of bacterial contamination,
which has caused problems with regards to lack of compliance with the
Constructed wetlands were
built in 2000 using Common Reed Phragmites australis
and Cattail Typha latifolia as part of a water quality improvement
measure. These emergent
macrophytes are well known for their ability to clean waters, which
contain organic pollutants and heavy metals.
A study was conducted over a
6-month period to assess how effective the wetland system was in improving
the water quality of the Bourne Stream. Variables tested for were pH, temperature, BOD, dissolved
oxygen, conductivity, nitrates, phosphates, turbidity, E. Coli, Total
Coliforms and various heavy metals.
Significant improvements were
not found. However, some
reductions were made in the levels of turbidity, nitrates, phosphates and
E.coli. The plants performance was not as well as expected.
This was mainly due to the timing of the sampling schedule, which
continued into the winter months when plant productivity was becoming
lower and dieback becoming prevalent.
There is also the possibility of non-point sources of pollution
which could be affecting the efficiency of the system.
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