Pagham Lagoon Water Quality Investigations

Descriptions

Pagham Lagoon (Unit 1 of Pagham Harbour SSSI) has been reported as having poor water quality by an external stakeholder, who provided water quality data showing significantly elevated levels of E. coli, total coliforms, and Enterococci. While these parameters are not typically assessed by Natural England, the concentrations reported are of potential ecological concern. No other water quality data for the lagoon is currently available.

Following further desk-based investigation, the source of the pollutants is still unknown. Natural England are therefore seeking to obtain a baseline understanding of the water quality condition at Pagham Lagoon and identify the sources of pollutants.

This will allow Natural England to determine the best course of action to address the water quality issues within Pagham Lagoon. We will then use this baseline knowledge to implement targeted interventions to ensure SSSI condition improvement.

The requirements for the investigation are:

1. Desk based review of known/mapped outfalls into the lagoon, and any other existing evidence.

2. Mapping of surface water drainage system that feeds into the lagoon, to identify key potential sources.

3. Testing of the water quality within the lagoon is expected to include a broad range of parameters to establish baseline conditions and identify potential sources of pollution. The following parameters should be assessed as a minimum:

• Dissolved Oxygen

• Biochemical Oxygen Demand (BOD)

• Turbidity

• Nitrogen (likely Dissolved Inorganic Nitrogen due to the saline nature)

• Phosphorus (preferably soluble reactive phosphorous)

• Ammonia

• Conductivity

• Temperature

• Sulphate

• Soluble reactive phosphorous

Additional parameters of concern will include:

• E. coli

• Enterococci

• Consideration will also be given to possible sediment sampling, subject to confirmation of lagoon connectivity and sediment deposition processes.

• Sampling will be undertaken under various weather conditions to determine whether water quality fluctuations are linked to storm events.

• Final written report compiling findings from the desk based and on the ground investigation, identifying and distinguishing sources of pollution, and recommendations for actions to improve water quality review of the information suppliers would need to decide whether they would be interested in an opportunity.

This is to be completed by 31st March 2026