Conservation problems in the norfolk broads and rivers of East Anglia, England—Phytoplankton, boats and the causes of turbidity

Abstract

The Norfolk Broads and rivers of eastern England (Fig. 1) comprise an area hitherto farmed for the diversity of its wildlife and submerged aquatic plant communities. The latter have progressively disappeared since the early 1950s, until only four sites currently retain more than remnants of the original sub-aquatic macrophyte flora and its associated invertebrate fauna. Increases in turbidity of the water have been associated with the loss of macrophytes, and these increase have been variously attributed to phytoplankton and to disturbance of sediment by the many boats of visiting tourist and residents. Synoptic surveys of turbidity were carried out in the navigable waterways of Broadland in summer and winter 1973, and of phytoplankton in summer 1973. The differential distribution of phytoplankton is discussed in terms of the nutrient loadings on, and flushing coefficients of, the waterway. Highly significant correlations were obtained between phytoplankton numbers and turbidity in the system as a whole and Broads and rivers considered separately. A very weak correlation between boat activity and turbidity was shown to be non-causative. It is concluded that increase in turbidity is a function of increased nutrient loading from human activities in the catchment area and that boat disturbance does not contribute significantly to the sustained turbidity.