Norfolk has few large natural bodies of standing freshwater but has some of the most important human-made freshwater wetlands in the lowlands of the UK. Among these the Norfolk Broads stand out. Dug from the Middle Ages, principally for peat, the Broads are around forty shallow lakes in the east of the county, in the low-lying and readily flooded catchments of the Waveney, Yare, Bure, Ant and Thurne. They are of international importance as sites for rare pondweeds and stoneworts and as wintering sites for migrant waterfowl. They are also of local importance for otters, scarce dragonflies, and innumerable other species. The vegetated marsh habitats of the Broads, including fen and reed-bed, are discussed here
and information on Broadland’s freshwater grazing marshes may be found here
In the twentieth century, the open water habitats of the Norfolk Broads suffered greatly from eutrophication, namely the over-abundance of nutrients in the water, caused by nitrates from agricultural fertilisers and phosphates from sewage. Among the common results of eutrophication is the blooming of algae which often starve other plants of light. Thus the famously gin-clear waters of the Broads, which were historically celebrated as a site for rare pondweeds and stoneworts, became murky and green with resultant impacts on countless other species. Recently much greater control has been exerted over agricultural run-off and sewage, so the county’s rivers are in better health. However in standing water bodies, where mud has accumulated nitrates and phosphates, the problem persists. At NWT Cockshoot Broad
and NWT Barton Broad
large-scale experiments have been undertaken into the removal of nitrate-rich sediments with very encouraging results in terms of water chemistry and biodiversity.
Of much more recent origin than the Broads are the county’s many gravel and sand pits. These may be found throughout the county but there are concentrations of them in the Wensum, Nar and Gaywood valleys. Whereas the low-nutrient, acid waters of the greensands in the Gaywood mean that the sand pits here are relatively poor in animal life, the chalky waters of the upper Wensum and the Nar are rich in nutrients and biological diversity. The gravel pits here support a high diversity of plants and invertebrates and are consequently rich in fish and birds.