Sediment depth attenuation of biogenic phosphorus compounds measured by 31P NMR.
Being a major cause of eutrophication and subsequent loss of water quality, the turnover of phosphorus (P) in lake sediments is in need of deeper understanding. A major part of the flux of P to eutrophic lake sediments is organically bound or of biogenic origin. This P is incorporated in a poorly described mixture of autochthonous and allochthonous sediment and forms the primary storage of P available for recycling to the water column, thus regulating lake trophic status. To identify and quantify biogenic sediment P and assess its lability, we analyzed sediment cores from Lake Erken, Sweden, using traditional P fractionation, and in parallel, NaOH extracts were analyzed using 31P NMR. The surface sediments contain orthophosphates (ortho-P) and pyrophosphates (pyro-P), as well as phosphate mono- and diesters. The first group of compounds to disappear with increased sediment depth is pyrophosphate, followed by a steady decline of the different ester compounds. Estimated half-life times of these compound groups are about 10 yr for pyrophosphate and 2 decades for mono- and diesters. Probably, these compounds will be mineralized to ortho-P and is thus potentially available for recycling to the water column, supporting further growth of phytoplankton. In conclusion, 31P NMR is a useful tool to asses the bioavailability of certain P compound groups, and the combination with traditional fractionation techniques makes quantification possible.
Ahlgren
Joakim
J
Department of Analytical Chemistry, Uppsala University, 751 24 Uppsala, Sweden. Joakim.Ahlgren@kemi.uu.se
Tranvik
Lars
L
Gogoll
Adolf
A
Waldeback
Monica
M
Markides
Karin
K
Rydin
Emil
E
D004784:Environmental Monitoring; D005068:Eutrophication; D009682:Magnetic Resonance Spectroscopy; D017553:Phosphorus Compounds / Q000032:analysis*; D010759:Phosphorus Isotopes / Q000032:analysis; D013548:Sweden; D014881:Water Supply
D017553:Phosphorus Compounds; D010759:Phosphorus Isotopes