『Abstract
　A reliable and economical method for the estimation of nutrient export (e.g. phosphorus) in stream flow from catchments is necessary to quantify the impact of land use or land use change upon aquatic systems. The transport of phosphorus (P) from soil to water is known to impact negatively on water quality. A key observation from studies is that most P export occurs during high stream flow. However, it is not yet clear how flood-antecedent conditions affect the P export during flood events. In this study, the P loss from soil to water as represented by soluble reactive phosphorus (SRP) in stream waters from three different catchments, varying in land use, scale and location in Ireland was monitored over 1 year. This study examined the role of antecedent stream flow conditions on SRP export and identifies a catchment-specific relationship between SRP flood event load (EL) and a flow ratio (FR). The FR is defined as the ratio of the flood event volume (EV) to the pre-event volume (PEV). The latter is the cumulative flow volume for a number of days preceding the event. This PEV period was found to be longer (average 81 days) in the grassland catchments which were known to be saturated with soil P than in the forested catchments (average 21 days) with minimal soil P. This FR ratio is a measure of the antecedent hydrological state (wet or dry) of the catchment. For SRP for each catchment, a specific relationship between with the concentration/discharge (C/Q) method. The new flow ratio method was used with data from 12 flood events during the year to estimate an annual export of SRP. For the two grassland catchments in the study, using the FR method, we estimated an SRP export of 1.77 and 0.41 kg ha^-1 yr^-1. Using the C/Q method, for the same sites, our estimate of SRP export was 1.70 and 0.50 kg ha^-1 yr^-1 respectively. The C./Q method used SRP concentrations covering 40％ of the year while the FR method used only 12 flood events covering less than 2％ of the year. This new method which takes account of the antecedent flow state of the river is an alternative to and may be more promising than the traditional C/Q method, particularly when short duration or flood sampling of water quality is carried out.

Keywords: Water quality; Phosphorus; Runoff; Model; Loads; Ireland』

Introduction
Methods
　Study catchments
　　Dripsey river
　　Oona river
　　Douglas forested catchments
　Data collection
　　Stream flow
　　Water chemistry
　Estimation of phosphorus export
　　C/Q method
　　Flow ratio method
　　　Event load estimation
　　　Correlation of event load with the flow ratio
　　　Using correlations to estimate annual loads
　Dripsey and Oona events
Results
　Comparison of water quality results
　Comparison of antecedent periods
　Comparison of PEVs and ELs
　Testing the event selection used in the correlations
　Comparison of annual loads from C/Q method and FR method
Discussion
Conclusions
Acknowledgments
References