Hoveton Great Broad and Hudson’s Bay form part of the Bure Broads and Marshes SSSI which itself is a component of the Broadland SPA and The Broads SAC.

Currently both Broads are in ‘unfavourable’ condition with respect to Habitats Directive targets and fail to reach ‘good’ ecological status under WFD classifications. With recent improvements in the water quality within the River Bure, the focus has now shifted to internal nutrient release as the main reason for the poor condition of these waterbodies. Natural England is therefore developing a restoration plan in partnership with the EA, to restore the Broads by removing a significant proportion of the nutrient-rich upper sediments from both sites. In so doing, it is hoped that internal nutrient loads will fall and clear water conditions return. Clear water conditions will be facilitated if submerged aquatic plants are re-established in the sites. The ultimate goal of biomanipulation is to significantly alter the zooplankton and phytoplankton community (through the reduction of predation on zooplankton). It is therefore important to record the changes in these communities as the project progresses. ENSIS is currently working with Natural England to determine pre-eutrophication conditions at these sites.

Objectives:

The objective of the project is to to determine pre-eutrophication aquatic plant communities in Hoveton Great Broad and Hudson’s Bay and to determine seed and oospore viability in the sediments of the two broads

Methods:

ENSIS met with NE to agree survey/sampling techniques, particularly for zooplankton, as those proposed are either unsuitable for shallow lakes (ECN protocols) or have not been fully documented (EA protocols). The ECN zooplankton method was replaced by tube sampling of whole water columns, with multiple tubes pooled to account for spatial patchiness of zooplankton populations. ECN Phytoplankton sampling methods were also amended to ensure volumetric consistency in these shallow waters. Samples were preserved using alcohol as opposed to the formaldehyde suggested in published protocols.

An initial baseline survey was undertaken in May 2014, and thereafter monthly surveys at the same geo-referenced survey point(s) in each of Hoveton Great Broad and Hudson’s Bay were undertaken, using the same agreed methodologies to ensure consistency of data collection.

Water sampling At each geo-referenced biological sample point, and on each sampling visit, open-water samples were taken

Laboratory analyses Phytoplankton analyses and data enumeration follow the methods of the Environment Agency; zooplankton analysis follow an adaptation of standard techniques.

Light Extinction Co-efficient, pH and redox During field sampling Light Extinction Co-efficient readings were taken at the sample points using a Sky submersible light meter. Further, measurements were made of the pH and redox of the interstitial phase (top 2 cm of sediments). This provided was done to provide valuable information that would give a clearer picture of how zooplankton and sediment surface redox and temperature (a data logger is already in place for those measurements) associate with seasonal variations in Total P and water clarity. It will also allow the depth at which PAR is likely to be beneath that required to sustain or stimulate macrophyte growth to be extrapolated.

Results:

The project is still ongoing

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HGB1
Hoveton Great Broad, Norfolk
Daphnia photo
Daphnia with Volvox colonies