Phosphorus in sediments: Controlling factors for release or burial of P and the role of sediment P in controlling trophic structure and productivity in shallow freshwater and marine ecosystems.
The figure above was on the front cover of my Ph.D. thesis in 1991. It illustrates how much the P release from an aerobic sediment surface contributes to P availability in the photic zone in summer in a shallow lake. An extreme case that shows the importance of understanding the sediment P cycle. (I will translate the figure from Danish in the presentation J)
Mechanisms of P’s coupling to the lakes iron cycle, the role of external P-loading in lake eutrophication, and the role of internal P-loading (P release from lake sediments) in delaying lakes recovery from eutrophication, have roughly been known since 19361, 19702, and 19803, respectively. While the mechanisms controlling P-release from lake sediments have been studied by many, the opposite process, the mechanisms that control permanent P-retention in lake sediments, has received much less interest. In oceanography it is quite the opposite. Here P burial and the potential phosphorite formation in the ocean floor have been the primary targets of marine geological studies. In between are estuaries and shallow coastal waters where both questions have received attention. There is inspiration to gain from working with the same processes in different environments and I hope to be able to communicate some of this in my presentation.
I will have to take you through the very laborious (did I say tedious?) chemical extraction of P from soils and sediments4 because it for decades has been the most powerful tool for studying P biogeochemistry - a viewpoint that I share with my host at IGB, Dr. Michael Hupfer. With this method we discriminate between sinks and potential sources for P for instance when we amend the sediment with aluminum in order to stop the internal P-loading. But we know well that there are plenty of exceptions from our interpretation.
One such exception is when extractable organic P-forms are not being mineralized in eutrophic lake sediments. Probably this is due to lack of quality electron acceptors for microbial respiration, but will the mineralization of (otherwise) buried organic P then increase when you oxygenate the hypolimnion in a stratified lake? And will mineralization of (otherwise) buried organic P increase when the water gets warmer due to climate change? Another exception is when tropical seagrasses growing in carbonate sands actually dissolves the solid matrix of the sediment to gain P that is bound in apatite5. Is there a parallel to this in carbonate rich lakes and wetlands?
Finally, as lake restoration has been my main research topic for the past ten years, I will discuss how food web manipulations may alter P cycling in the sediment and increase P burial in shallow lakes.
Looking forward to seeing you, Henning
1 Einsele W., 1936. Über die Beziehungen des Eisenkreislaufs zum Phosphatkreislauf im Eutrophen See. Arch. Hydrobiol., 29, 664–686.
2 Schindler D. W., Carpenter S. R., Chapra S. C., Hecky R. E., Orihel D. M., 2016. Reducing phosphorus to curb lake eutrophication is a success. Environ. Sci. Technol., 50, 8923–8929; DOI 10.1021/acs.est.6b02204.
3 Boström B., Jansson M., Forsberg C., 1982. Phosphorus release from lake Sediments. Arch. Hydrobiol. Beih. Ergebn. Limnol. 18, 5–59.
4 Psenner, R., R. Pucksko, and M. Sager 1984. Fractionation of organic and inorganic phosphorus compounds in lake sediments. An attempt to characterize ecologically important fractions. (In German). Arch. Hydrobiol/Suppl. 70(1): 111-155.
5 Jensen, HS, KJ McGlathery, R Marino & RW Howarth 1998: Forms and availability of sediment phosphorus in carbonate sand of Bermuda seagrass beds. Limnology and Oceanography 43(5), 799-810.
6 Jensen HS, OI Nielsen, MS Koch & I de Vicente 2009. Phosphorus release with carbonate dissolution coupled to sulfide oxidation in Florida Bay seagrass sediments. Limnology and Oceanography 54(5): 1753-1764.
Host: Michael Hupfer