Regional analysis of groundwater nitrate concentrations and trends in Denmark in regard to agricultural influence

[摘要] The act of balancing between an intensive agriculture with a high potentialfor nitrate pollution and a drinking water supply almost entirely based ongroundwater is a challenge faced by Denmark and similar regions around theglobe. Since the 1980s, regulations implemented by Danish farmers havesucceeded in optimizing the N (nitrogen) management at farm level. As aresult, the upward agricultural N surplus trend has been reversed, and the Nsurplus has reduced by 30–55% from 1980 to 2007 depending on region. Thereduction in the N surplus served to reduce the losses of N fromagriculture, with documented positive effects on nature and the environmentin Denmark. In groundwater, the upward trend in nitrate concentrations wasreversed around 1980, and a larger number of downward nitrate trends wereseen in the youngest groundwater compared with the oldest groundwater.However, on average, approximately 48% of the oxic monitored groundwaterhas nitrate concentrations above the groundwater and drinking waterstandards of 50 mg l⁻¹. Furthermore, trend analyses show that 33% of allthe monitored groundwater has upward nitrate trends, while only 18% ofthe youngest groundwater has upward nitrate trends according to data sampledfrom 1988–2009. A regional analysis shows a correlation between a high levelof N surplus in agriculture, high concentrations of nitrate in groundwaterand the largest number of downward nitrate trends in groundwater in thelivestock-dense northern and western parts of Denmark compared with thesoutheastern regions with lower livestock densities. These results indicatethat the livestock farms dominating in northern and western parts of Denmarkhave achieved the largest reductions in N surpluses. Groundwater rechargeage determinations allow comparison of long-term changes in N surplus inagriculture with changes in oxic groundwater quality. The presented dataanalysis is based on groundwater recharged from 1952–2003, but sampled from1988–2009. Repetition of the nitrate trend analyses at five-year intervalsusing dating of the groundwater recharged in the coming years and a longertime series of the nitrate analyses can reveal the evolution in nitrateleaching from Danish agriculture during the past 10 yr. Similar analysescan be carried out to compare with other regions internationally.

[学科分类] 地球化学与岩石