The Chemistry of Phosphate and Nitrogen Compounds in Sediments

Phosphate and nitrogen compoundsare the two plant nutrients involved in the process of - trophication. In their cycles sediments are of paramount importance. In freshwater eutrop- cation remains the severest process of pollution, while coastal marine environments are now becoming seriously a?ected too (Orive, Elliot & De Jonge, 2002). Not only developed co- triesencountertheseproblems;developingcountrieshavealsobeguntosu?er. Foralongtime wetlands were almost not studied or even mentioned; this state of a?airs has nowadays much changed. Not only were wetlands, in the past, considered to be unimportant, but, moreover, the close contact between sediment and water owing to the shallowness of the water-layer kept theP-concentration in the water low by adsorption, thus delaying the consequences of loading. Since wetlands have been recognized not only by the happy few, but also by water managers, they receive more attention. Golterman & de Oude (1991) reviewed relevant literature on mechanisms and processes of eutrophication and paid some attention to the role of sediments, albeit only in their d- cussion concerningthe in?uence of sediment on the phosphate in- and output balance. A few equations were discussed, but not the chemical mechanisms by which sediment in?uences theP-cycle. Nitrogen has always receivedmuch less attention, althoughthe sediment layer in lakes and wetlands is the site of major changes and processes in theN-cycle. One of the most important processes is denitri?cation, by which nitrogen is lost from the system, for which reason it has been considered to be advantageous. It entails, however, a situation favourable for blue-green algal blooms.