 |
| Titel |
Timescales and controls on phosphorus loss from a grassland hillslope following a cessation in P application. |
| VerfasserIn |
Rachel Cassidy, Donnacha Doody, Catherine Watson |
| Konferenz |
EGU General Assembly 2016
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250133264
|
| Publikation (Nr.) |
 EGU/EGU2016-13853.pdf |
|
|
|
|
|
| Zusammenfassung |
| Despite the implementation of EU regulations controlling the use of fertilisers in agriculture,
reserves of phosphorus (P) in soils continue to pose a threat to water quality. Mobilisation and
transport of legacy P from soil to surface waters has been highlighted as a probable cause of
many water bodies continuing to fail to achieve targets under the Water Framework
Directive. However, the rates and quantities lost from farmland, and the timescales for
positive change to water quality, following cessation of P inputs, remain poorly
understood.
Monitoring data from an instrumented grassland research site in Northern Ireland provide
some insights. The site is located in a hydrologically ‘flashy’ landscape characterised by steep
gradients and poorly drained soils over impermeable bedrock. Between 2000 and 2005 soil
Olsen P concentrations were altered in five 0.2 ha hydrologically isolated grazed grassland
plots through chemical fertiliser applications of 0, 10, 20, 40, 80 kg P ha−1yr−1. By 2004 this
had resulted in soil Olsen P concentrations of 19, 24, 28, 38 and 67 mg P L−1 across the
plots, after which applications ceased.
Subsequently, until 2012, changes in soil Olsen P across the plots and losses to overland
flow and drainage were monitored, with near-continuous flow measurement and water
samples abstracted for chemical analysis. Runoff events were sampled at 20 minute intervals
while drainage flows were taken as a weekly composite of 4-hourly samples. Overland
flow events were defined by at least 24 hours without flow being recorded at the
respective plot outlets. Drainage flow was examined on a weekly basis as it was
continuous except during prolonged dry periods. To examine the hydrological drivers
of overland flow and drainage losses the dissolved reactive P (DRP) and total P
(TP) time series were synchronised with rainfall data and modelled soil moisture
deficits.
Results demonstrated that from 2005-2012 there was no significant difference among
plots in the recorded TP and DRP time series for either overland flow or drainage flow despite
the large variation in soil Olsen P. Flow-weighted mean concentrations for overland flow
losses declined slightly over the period but remained in excess of the chemical
Environmental Quality Standard in all plots (EQS; 0.035 mg/L). In individual events the plot
receiving zero P fertiliser inputs since 2000 often lost as much, or more, P than
the plot which received 80 kg ha−1 yr−1 up to 2005. Annual loads also reflect
this. Drainage losses showed no decline over the period. The hydrological drivers,
particularly the antecedent dry period and soil moisture, were observed to have a greater
influence on P loss from the plots than soil P status. Given that Olsen P often forms the
basis of nutrient management advice this raises questions on the environmental
sustainability of current nutrient advice for some soil types under similar geoclimatic
conditions. |
|
|
|
|
|
|