Monitoring nutrient losses from arable land
Losses of nitrogen and phosphorus from arable land contribute to the eutrophication of lakes and coastal waters. Two sub-programs within the Swedish Environmental Monitoring program provide data to support the evaluation of mitigation programs that have been initiated in the agricultural sector to reduce nutrient losses.
In both sub-programs (‘Arable fields’ and ‘Agricultural catchments’, see more information below), nitrogen and phosphorus concentrations are monitored in water discharging from arable land: one focuses on water draining from individual arable fields (ca. 4-34 hectares in size), while the second is carried out at a larger scale, focusing on streams draining agricultural catchments ranging from 200 to 3500 hectares in size.
The work is carried out by the Department of Soil and Environment at SLU and is financed by the Swedish Environmental Protection Agency.
Monitoring arable fields
Maria Blomberg at a monitoring station in Jämtland, Sweden. Photo: Göran Johansson.
Monitoring of arable fields was established in different parts of the country in 1972 to study how farming affects the nutrient leaching in field drainage. The runoff from 12 fields is recorded continuously by a Campbell logger and drainage water samples are collected every two weeks using flow proportional sampling. The flow proportional samples are analysed for total nitrogen, nitrate nitrogen, total phosphorus, particulate bound phosphorus, suspended solids and total organic carbon and used to calculate nutrient fluxes.
In addition grab samples are collected every two weeks and analysed for pH, conductivity and alkalinity. Groundwater sampling is conducted in 9 arable fields (nitrate nitrogen, pH, conductivity and alkalinity). Information on the cultivation of the field in terms of crops, fertilization, tillage, etc. is collected annually from the farmers. The monitoring fields are part of the farm's typical crop rotation and therefore they do not undergo any special treatment. The specific locations of the farms are not revealed, to maintain farmers' voluntary participation in the monitoring program.
The monitoring is part of the national environmental monitoring program commissioned by the Swedish Environmental Protection Agency.
Monitoring agricultural catchments
Lovisa Stjernman Forsberg takes a water sample in an arable field in Uppland. Photo: Katarina Kyllmar.
21 small agricultural catchments are monitored within the Swedish Environmental monitoring program. The purpose of the program is to increase knowledge about the link between the agricultural land use and water quality in runoff water and their changes over time.
The catchments are part of the farm's typical crop rotation and therefore they do not undergo any special treatment. The monitoring data are related to national farming census data. The program was reorganized in 2002 with monitoring of eight catchments transferred to a national program (intensive monitoring catchments) carried out by Department of Soil and Environment at SLU and financed by the Environmental Protection Agency.
The investigations are mainly focused on nitrogen and phosphorus losses from agricultural land to surface water. The water flow is measured continuously in the streams and water samples are collected every two weeks and analyzed for nitrogen, phosphorus, suspended sediments etc. In the eight intensive monitoring catchments additional groundwater monitoring is conducted and information on the cultivation of the field in terms of crops, fertilization, tillage, etc. is collected annually from the farmers. The specific locations of the farms are not revealed, to maintain farmers' voluntary participation in the monitoring program.
In four of the catchments pesticide leaching is also monitored.