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Title: Using Macrophytes for the Environmental Assessment of Rivers: The Role of Sediment Nutrients
Author: S J Clarke
Author: G Wharton
Author: Environment Agency
Document Type: Monograph
Annotation: Environment Agency Project ID:EAPRJOUT_1431, Representation ID: 602, Object ID: 2586
A study of the inter-relationship between submerged aquatic macrophytes and sediment characteristics in lowland British rivers is described. The research was focused on the variability of nutrient concentrations in river sediments, in which macrophytes are rooted, and the relationship between macrophyte species and sediment characteristics. The overall research aim was to further develop understanding of the role of sediments in determining macrophyte community composition in order that sediment-macrophyte relationships may be incorporated into methods using macrophytes as tools for the biological assessment of pollution. A review of the role of abiotic factors controlling and determining macrophyte growth and community composition is presented with particular reference to river sediments. The role of sediments in macrophyte nutrition and flowing water nutrient dynamics is described. This review of research in the fields of macrophyte ecology, sediment chemistry and hydrology concludes that the study of sediment nutrients and the relationship with macrophytes in flowing waters has been neglected. Seventeen lowland rivers in England were visited and sediment samples were collected from beneath macrophyte stands and unvegetated areas. The sediment samples were analysed for total phosphorus, inorganic phosphorus, total nitrogen, organic carbon, silt/clay content and organic matter content. Variability of these nutrient concentrations and sediment characteristics both within river reaches and between rivers were explored. The relationships between these physical and chemical sediment variables were considered through the use of linear regression and principal components analysis. Sediments were found to exhibit a high degree of variability both w ithin 100m river reaches and between the different rivers. Sediment phosphorus concentrations were found to differ greatly between rivers yet sediment nitrogen and organic carbon contents were similar for all rivers, with the exception of particularly organic-rich sediments. Total and inorganic phosphorus concentrations were closely related in all sediments although the relationship was not linear. There were also significant relationships between total nitrogen and organic carbon, both of which were related to the organic matter content of the sediment. Relationships between mean values for sediment parameters and mean water chemistry parameters indicated that the relationship between water column and sediment nutrient concentrations is complex and is not apparent from time- and space-integrated samples. The significance of the sediment variables as a control on macrophyte community structure was investigated graphically and through the use of canonical ordination (redundancy analysis) and discriminant analysis. Macrophyte species showed broad tolerances to all sediment variables and it was difficult to separate the influence of sediment nutrients from other sediment parameters or differences between rivers. Ordination indicated that Base Flow Index (which reflects catchment geology), the degree of channel shading and sediment total nitrogen concentrations (possibly a surrogate for organic matter content which was closely related to total nitrogen and organic carbon) were important in explaining the variability in macrophyte species distributions. Discriminant analysis indicated that macrophyte species were not well distinguished by the sediments upon which they were growing. R and D TECHNICAL REPORT E1-S01/TR i Finally, the results of this study are discussed with reference to more general questions concerning the role of different abiotic and biotic factors on the distribution and ecology of submerged aquatic macrophyte species. Suggestions are made for further research and for future methodological advances. R and D TECHNICAL REPORT E1-S01/TR ii CONTENTS page EXECUTIVE SUMMARY i 1.
Publisher: Environment Agency
Subject Keywords: River; Sediment; Macrophyte; Nutrient; Phosphorus; Biological analysis
Extent: 97
Total file downloads: 3

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