1. A weighted averaging (WA) regression and calibration model for diatoms a
nd total phosphorus (TP) was developed from a dataset of 45 surface-sedimen
t samples from Swedish lakes. Jack-knifed error statistics were comparable
with those for similar diatom-TP datasets: r(jack)(2) = 0.47, root mean squ
ared error of prediction (RMSEP) = 0.24 log(10) mug TP L-1 and mean bias =
-0.002 log(10) mug TP L-1 for the simple WA model; r(jack)(2) = 0.36, RMSEP
= 0.27 log(10) mug TP L-1 and mean bias = 0.017 log(10) mug TP L-1 for WA
with tolerance downweighting.
2. The model was used to estimate TP concentrations for the Ekoln basin of
Lake Malaren using a Pb-210-dated sediment core record. Highly eutrophic co
nditions developed in the basin in the 1960s as a result of nutrient inputs
from cultivated land and the city of Uppsala. A reduction in the supply of
phosphorus from sewage outlets in the late 1960s resulted in less eutrophi
c conditions.
3. The model results indicated levels of 50-60 mug TP L-1 prior to 1900. Th
e rapid eutrophication of the lake basin after the 1950s and the subsequent
recovery were evident from the diatom data.
4. Diatom-inferred TP (DI-TP) values were validated by comparison with moni
tored data for the period 1966-95. The diatom model tended to underestimate
TP at high levels (> 80 mug L-1) but overestimate at lower concentrations.
5. A good agreement was observed between the trends in TP concentration and
the DI-TP concentration and the timing of the maximum was well reflected b
y the diatom-based reconstruction. A significant correlation (r(2) = 0.69,
P < 0.01) was found between DI-TP and measured TP at this site.