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Hoveton Great Broad Restoration Project: Seasonal Comparative Fish Areas

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Hoveton Great Broad Restoration Project: Seasonal Comparative Fish Areas a) Ecological condition of Hoveton Great Broad and Hudson's Bay The notified features for Hoveton Great Broad and Hudson’s Bay are: • H3140 Hard oligo-mesotrophic waters with benthic veg of Chara spp Aerial view of algal blooms on Hoveton • Great Broad and Hudson’s Bay. H3150 Natural eutrophic lakes with Magnopotamion or Hydrocharition b) • S1355 Otter, Lutra lutra © Mike Page. They are currently classified as ‘unfavourable – no change’ and ‘poor ecological status’ under the Habitats Directive and the Water Framework Directive respectively due to high turbidity, low macrophyte diversity and abundance, and the associated impact on aquatic fauna. Theses conditions can be directly attributed to historic eutrophication, in particular phosphate from sewage treatment The Hoveton Wetlands Restoration Project aims to deliver the works (Moss 1983). In the Broads, as with many other shallow lakes in north west Europe, this has resulted in: Figure 1: Macrophyte abundance (a) and diversity (b) of key lakes in the Broads 2014-2018, Hoveton Great Broad highlighted. Broads Authority water plant monitoring (Tomlinson et al. 2019). restoration of Hoveton Great Broad and Hudson’s Bay. These Aerial view of Hoveton Great Broad and Hudson’s Bay • high levels of phytoplankton production (often including blooms of blue green algae) lakes are situated in Norfolk, UK within The Broads National Park. • a reduction and eventually almost complete loss of aquatic plant cover and diversity They form part of the Bure Broads and Marshes, the Broadland SPA and the Broads SAC, and Broadland Ramsar Site. • high rates of sedimentation • dominance by small open water zooplankton species and loss of plant-associated invertebrates The project is using a combination of sediment removal and biomanipulation of the fish community to restore clear water • simplification of the structure of the fish community and dominance by a small number of age classes of and macrophytes to these lakes, restoring their natural ecological function. The project is financially supported by LIFE planktivores and benthivores. (the Bure LIFE Project - LIFE14 NAT/UK/000054) and is also supported by the National Lottery through the Heritage Lottery Fund. These changes in ecological function and condition are evident in Hoveton Great Broad and Hudson’s Bay, as shown in the graphs (right), and indeed often they compare badly even to other degraded lakes in the Broads. Figure 2: Overall mean density (ind. m-2) (a) and biomass (g m-2) (b) of roach (ro), bream (br), and all species (all sp) in key River Bure lakes incl. Hoveton Great Broad and Hudson’s Bay (HGB/HB), summer 2016. (Hindes 2017) These biomanipulations provide some key lessons for re- Biomanipulation establishing ecological functioning and internal stabilizing Water quality on Legislation and in the Broads mechanisms. These include : • Abundance of macrophytes can establish rapidly within the River Bure stakeholders There is a long history of biomanipulation in the Broads and around 5 years. Hoveton Great Broad and Hudson’s Bay are work here, and elsewhere, has shown that whilst • Diversity of not isolated lakes, and are directly The Habitats Directive and the Water Framework Directive biomanipulation of a sufficient magnitude almost inevitably macrophytes can take connected to the wider Broads system via are the key drivers for restoring natural function to produces clear water, the difficulty has been in maintaining this longer to establish, 15- the River Bure. Therefore water quality in Hoveton Great Broad and Hudson’s Bay. However, despite change. Maintaining low phosphate levels, management of fish 20 years at some sites the River Bure is key to their restoration. these strong legislative drivers, the project has faced many Macrophytes on the successfully biomanipulated populations, and the establishment of macrophytes are key to obstacles to restoration of these sites: Ormesby Broad • Stability of Figure 5: Modelled Source appointment of the long term sustainability. biomanipulation There has been control on the phosphorus phosphorus within the river Bure catchment. • Monitoring has shown Hoveton Great Broad and Hudson’s Bay are spawning sites for several sub- improves with discharged to the River Bure since 1986 populations of bream within the Broads. This has raised concerns of the impact of the site restoration macrophyte diversity, with standards improving through the Urban Waste Water Treatment Directive on the fishery and it’s local economic benefits. with more than 10 91/271/EEC (Council Directive 1991) and Water Framework Directive (WFD). • Ubiquitous bream are considered an integral part of the Broads fishery by anglers, in part probably species normally Much of this investment in phosphate removal was done in partnership with and due to shifting baseline syndrome. required for stable clear Figure 4 (right) : Relationship between by negotiation with Anglian Water. • Conflict for partner organisations with statutory duties under the Water Framework Directive and water and macrophyte fluctuations in macrophyte cover and duties to ‘enhance and maintain’ the fishery under national legislation. richness (Phillips et al. 2018) -1 community Phosphate levels within the River Bure are ~60μgl . Modelling indicates to reach • No WFD tool for assessing the fish status has been adopted for English lakes. This has prevented the the target of 30μgl-1, set by WFD and expected to deliver natural recovery of the • Manipulation of the fish community throughout project from categorially demonstrating a change in fish community is required to meet WFD system, would require large scale land-use change. Such change is unlikely in the macrophyte recovery increases the prospects of achieving objectives for fish. short-medium term. However, modelling indicates 52μgl-1 is likely to be achieved • the desirable end community, a high piscivore:planktivore WFD fish status, using the precautionary principle, has therefore been perversely used to try to by 2030 through agreed reductions from sewage treatment works alone, below ratio, which is a feature of macrophyte- prevent the biomanipulation required to restore the site to favourable condition and good ecological the 55μgl-1 identified as key to stable biomanipulation in the Broads. In addition, dominated systems. status. work through agri-environment schemes and sustainable development should • • Annual mean total Phosphorus concentrations of <55μgl-1 Difficulty ‘selling’ the angling interest of a healthy naturally functioning fishery to anglers. Figure 3: Species stability index for biomanipulated lakes in the Broads reduce phosphates from agriculture and urban sources respectively. • Assessment tools and evidence base mainly from isolated lakes, not interconnected systems. (Phillips et al. 2018) are likely to be required to maintain a stable system. Sediment Biomanipulation of Hoveton Great Broad Project Contacts removal and Hudson’s Bay Scott Hardy, Science Officer Email: [email protected] Hoveton Great Broad and Hudson’s Bay are not isolated lakes, and their connections to the Chris Terry, Project Manger High rates of sedimentation, with wider system undoubtably play an important role in the natural functioning of their trophic Email: [email protected] rich fine sediment, as a result of dynamics. Therefore, their isolation from the River Bure to enable biomanipulation will be eutrophication had reduced the Experimental biomanipulation enclosure temporary (~10 year) and when a stable and diverse macrophyte community is achieved they depth of Hoveton Great Broad and References on Hoveton Great Broad © Mike Page. will be reconnect to the River Bure. Hudson’s Bay to less than 0.5m in Figure 7: Relative biomass and numbers of fish species within Hindes, A. (2017) Hoveton Great Broad Restoration project: Seasonal comparative fish areas. surveys summary report. Fishtrack report to Natural England Biomanipulation of Hoveton Great Broad and Hudson’s Bay will take the following steps: turbid and macrophyte dominated Norfolk broads (Kelly 2008) New fen area created in Hoveton • Installation of temporary (~10 years) permeable barriers to prevent fish movement but maintain hydraulic connectivity to the River Bure. Kelly, A. (2008) Lake restoration strategy for the Broads. Broads Authority. Sediment removal was undertaken Great Broad. © Mike Page. Original data: Perrow, M.R., Jowitt, A.J.D., Leigh, S.A.C. Hindes, A.M. & Rhodes, J.D. • Removal of >75% of the fish biomass focusing on planktivores and benthivores. to return the lakes to a depth of (1999). The stability of fish communities in shallow lakes undergoing restoration: • Further fish removals every 3 years to prevent recruitment of planktivores and benthivores in the remain fish community. ~1.1m, achieving a more favourable depth for macrophyte expectations and experiences from the Norfolk Broads (UK). Hydrobiologia, 408/409, • Manipulation of the fish community to increase the prospects of achieving a favourable fish community, a high piscivore:planktivore diversity and exposure of propagules. 85-100. ratio, as seen in macrophyte dominated lakes in the Broads (figure 7). Moss, B., (1983). THE NORFOLK BROADLAND: EXPERIMENTS IN THE • Removal of fish barrier and reconnection to the River Bure once a stable and This sediment was used to create new in lake fen areas RESTORATION OF A COMPLEX WETLAND. Biological Reviews 58:521-561 diverse macrophyte community has established. (methodology shown in figure 6). This method
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