We modified a five step sequential extraction scheme originally developed tot. phosphorus (P) in lake and marine sediments for use in a Danish freshwater wetland rich in organic matter. In contra.st to the original scheme, the modification suggests isolation of P associated with aluminum (A1) and iron (Fe) in bumic acid complexes. As in the original scheme, discrimination also was obtained between inorganic P associated with reducible forms of Fe and inorganic P associated with AI oxides. This is important because only iron-bound P is likely to be mobilized when wetland sediments become anoxic. ExUaetion of ironbound P was performed by use of bicarbonate-buffered dithionite and was followed by a NaOH treatment that extracted most organic bound P together with P adsorbed onto clays and AI oxides. The NaOH extract was dark brown, but upon acidihcation (pH~ 1), we produced a precipitate of presumeably humic acids (HA) and a clear supematant. The precipitate contained up to 30% of the total sediment P and significant fractions of sediment A1 and Fe. Ratios of ~12 between HA-At and HA-P and of ~2.5 between HA Fe and HA-P suggest that most HA-P was associated with A1 in the humic acid complexes. Comparison with sediment from an acid-bog lake suggests that the HA-P traction might also be important in other li-eshwater sediments. A similar AhP and Fe:P ratio was found in the humic acid precipitate fi-om the lake sediment, indicating that the same mechanism was responsible for binding inorganic P in the humic acid complex as in the wetland sediment. When wet sediments were sieved through a 2-mm mesh and handled under N2, the method was highly reproducible, and no further precision could be obtained by grinding the wet sediment prior to extraction.

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Seven regions with coastal eutrophication problems in the Baltic Sea, including the Kattegat, constitute the BERNET project (Baltic Eutrophication Regional Network). To counteract eutrophication and associated severe biological conditions the countries around this large brackish water body must all cooperate. The regions are characterized by large differences in land use, e.g. agricultural intensity, and losses of retention capacity in the catchments due to wetland reclamation. Initially it has been necessary to identify nutrient sources--especially nitrogen--and technical, economical and even administrative obstacles to initiate eutrophication management measures. Nitrogen retention in different types of wetlands in the Baltic Sea Region has been analysed. The wetlands generally have a positive effect on reduced nitrogen transport to aquatic environments and it is generally accepted that measures leading to decreased losses of nutrients to the aquatic environment must be combined with measures leading to increased retention of nutrients in catchments. Data analysed in the BERNET project show that the potential for such a measure is large. Therefore, conservation and restoration initiatives for wetlands is an essential part of the work in the BERNET project. Wetlands have been drained or totally eliminated due to intensive agriculture in some regions while large scale rehabilitation of wetlands occurs in regions with less intensive agriculture. Based on land use data from the seven regions, the working group for wetland management within the BERNET project has identified the possible use of wetlands as building blocks as a contribution to the management of the Baltic Sea eutrophication. Several recommendations are presented on the wise use of existing and constructed wetlands for water quality management in relation to non-point nutrient pollution.

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