Changes in the ecology of the Norfolk Broads

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Abstract
Summary: The Norfolk Broads have recently shown a marked loss of both floral and faunal diversity. To detect any recent changes and to provide a baseline for future research, twenty‐eight broads were visited in 1972–73. Samples of aquatic flora and benthic fauna were taken and a number of physical parameters were measured.In the private broads a good inverse correlation between chlorophyll‐a concentration and Secchi disc readings was found, suggesting that phytoplankton was largely responsible for the turbidity of the water. The relationship did not hold for the public broads where erosion and the stirring of sediments by motor launches is intense.Eleven broads were completely devoid of macrophytes. A macrophyte flora was well developed only in Upton and in the five Thurne broads and in these latter there was evidence of a recent loss in diversity. The sudden loss of formerly abundant species of macrophyte has been recorded frequently from the broads. The benthic fauna was poorly developed in most broads and was dominated by Limnodrilus hoffmeisteri and/or Potamothrix hammoniensis. Valvata piscinalis was the only regularly occurring gastropod in the benthos. Most of those broads with a diverse benthic fauna also had an abundant growth of macrophytes.Possible reasons for the recent changes in the ecology of the broads are discussed.