Brownsea
Castle in
Poole Harbour at high tide
Poole Harbour is acknowledged to be a beautiful place, enjoyed by those
who visit and those who live nearby, it is also an area of exceptional
ecological importance.
The waters of Poole Harbour are regularly flushed by the ebb and flow of the tide through the entrance at Sandbanks, unfortunately for Poole the amount of fresh sea water flowing in and out is comparatively small due to a low tidal range and a local phenomenon called the "Shallow Water Effect". At Neap tides the water flow is much further reduced, harbour reclamation carried out in recent years has reduced flow even further.
This small quantity of water replacement makes Poole Harbour particularly sensitive to pollution and studies on this have been carried out since 1974, probably well before then.
It does not help the harbour's delicate balance that many rivers flowing through Dorset countryside, the Frome and the Piddle in particular, carry agricultural chemicals from the farms and fields miles around depositing them straight into the harbour. Now add to this that the Sewerage Treatment Works at Dorchester, Wareham and Poole all discharge into Poole Harbour it seems almost pointless to mention the further burden of thousands of pleasure craft discharging raw effluent into the harbour each summer.
All
this pollution adds up to far too many Nitrates and some Phosphates entering
the waters of the harbour, these excellent fertilizer's make Poole Harbour
what it is today - "Eutrophic"!
Poole Harbour is breaking under the strain!
The
Environment Agency carried out extensive studies and designated Poole
Harbour as polluted (eutrophic) in 1996, it has since been designated
as an NVZ (Nitrate Vulnerable Zone) recommending that reductions in undesirable
chemical run off from land adjacent to rivers was reduced along with improved
water quality discharges from Sewerage Treatment Works.
Unfortunately, by the time reports had been prepared by the Environment
Agency, written, received and discussed by the Department for Environment,
Food and Rural Affairs and then forwarded to the Secretary of State to
designate Poole Harbour eutrophic and needing control under the various
directives, Pollution in the waters of Poole Harbour had continued to
escalate.
The
excess nutrient pollution in Poole harbour causes the horrid brown diatom
bloom which looks like raw sewerage, it reduces the oxygen levels in the
water which sustain underwater life, it produces excess Algae and above
all Ulva (Ulva lactuca). This Ulva continues to grow and rot turning
areas of once virgin mud into rotting masses of evil smelling vegetation.
The Holes Bay area of Poole Harbour is well on its way to this state,
other areas of shoreline also now turning visibly green.
