Nutrient concentrations before and after the Focus on Phosphorus project in E23 catchment

Abstract: Between 2007-2014, as part of the Greppa Näringen, there was a subproject on phosphorus losses called Focus on Phosphorus (FoP; Greppa Fosforn). Previous measures on eutrophication mainly focused on nitrogen leakage, whilst the purpose of FoP was to test already known mitigation methods against phosphorus losses in the field. The aim of this study is to evaluate the impact of the measures in one of the three pilot areas in FoP, catchment E23 in Östergötland. The three main measures implemented during the project were: structure liming, construction of a two-stage ditch and a sedimentation pond along with modernising the drainage in the entire catchment. Several hydrochemical parameters (Total Phosphorus, TP, Phosphate Phospho-rus, PO4-P, Particulate Phosphorus, PP, Total Nitrogen, TN, Nitrate Nitrogen, NO3-N, Ammonium Nitrogen, NH4-N, Total Organic Carbon, TOC and Total Suspended Solids, TSS) were studied with both flow proportional and manual measurements. Discharge, temperature, precipitation and run off data were obtained from the Swe-dish Meteorological and Hydrological Institute (SMHI). The flow proportional, compared to the manual measurements showed higher concentrations of all parameters except NH4-N and TOC. In both flow proportional and manual measurements, the concentrations of TP and PP are lower after FoP whereas the concentrations of TN, and especially NO3-N have increased. TOC is significantly lower after the project. In addition to the flow proportional and manual sampling, the synoptic measurements also showed that the concentrations of TP are lower in all sampling points along the main stream. Moreover, a distinct increase of NO3-N in all sampling points can be observed. The monthly mean temperature was slightly higher after FoP, while precipitation, run off and discharge were slightly lower after FoP. With a lower discharge after FoP, nutrient concentrations would have been slightly lower even without measures. The results show that selection of measurement method can affect the evaluation of the effectiveness of the mitigation measures. The measurement methods all have pros and cons and to achieve any viable conclusions, measurements must span a long period of time. The analysis shows an unexpected increase in N concentrations. Hence, further work needs to be done to establish whether there is any correlation between P reduction and N in-crease.