Diffuse: phosphorus (P) loads to a small lake, Friary Lough, in a 1 km(2) a
gricultural subcatchment were quantified over 90 years using a palaeolimnol
ogical model. The model assumes that lake total phosphorus (TP) is lost to
the sediments and to the lake outflow du(r)ing periods of steady-state or i
s also stored within the water column during periods of non-steady-state be
havior. Reconstructed TP loads during the 1991-1995 time interval of 2.05-2
.53 g m(-2) yr(-1) are verified by hydrochemical monitoring results from th
e lake inflow during 1997-1998. This provides evidence for the accuracy of
the palaeolomnological model and also that TP loads to the lake dan be acco
unted for from external catchment runoff. An analysis of the TP load data i
n terms of-catchment exports shows that there was a linear rate of increase
from ca. 1946 to 1995 of 1.20- 1.56 kg km(-2) yr(-1). The rate of increase
is similar to river P load data in the larger 1480 km(2) catchment tal;en
over 17 years, The; rate of TP increase to the lake is interpreted with reg
ard to current soil P models that propose increasing and threshold soil P c
oncentrations as the cause for increasing diffuse P loss-in runoff.