Reconstructing past lake water total phosphorus concentration using sediment geochemical records

To understand current phosphorus (P) cycling, which encompasses disturbances caused by human activity, it is necessary to quantify the long-term natural P cycles on which modern drivers act. The shortness of monitored P records renders this difficult by only covering the post-disturbance period and therefore fail to capture pre-disturbance baselines. Target driven management of sensitive ecosystems suffering from eutrophication uses baselines for P that cannot be reliably quantified at present. Recovery will only be possible if P loadings can be brought under control and this requires an understanding of what water quality targets are both desirable and achievable on a site-specific basis. This matters because a well-functioning ecosystem will be more resilient under future climate change and increasing human pressure on the landscape.

Where lakes are present in the landscape, there is the opportunity to use the sediment archive to provide long records of past P concentration.  At present, these reconstructions rely on diatoms or related microfossil indicators. These require time and resource intensive tailored training sets and furthermore the records do not preserve in all lakes. Here we present a novel geochemical method for reconstructing water P concentrations based on lake sediment P burial fluxes, which in principle is universally applicable.

Tested at six published lake sites, the method produces results that agree very well with overlapping monitoring data for those lakes (r² = 0.8). We want to share our method with the research community to identify additional sites to further verify the general applicability.

To illustrate the value of this approach to site-specific management, we compare past lake water total P reconstructions at Crosemere (UK) with a record of Holocene land cover change to identify the drivers of acceleration in the P cycle. Wider application of this lake sediment geochemical method will allow more critical evaluation of the human and natural drivers of the P cycle and be of benefit to ‘systems understanding’ spanning terrestrial and aquatic ecosystems.