Spatial distribution of soils determines export of nitrogen and dissolved organic carbon from an intensively managed agricultural landscape

[摘要] The surrounding landscape of a stream has crucial impacts on the aquaticenvironment. This study pictures the hydro-biogeochemical situation of theTyrebækken creek catchment in central Jutland, Denmark. The intensivelymanaged agricultural landscape is dominated by rotational croplands. Thesmall catchment mainly consist of sandy soil types besides organic soilsalong the streams. The aim of the study was to characterise the relativeinfluence of soil type and land use on stream water quality. Nine snapshotsampling campaigns were undertaken during the growing season of 2009. Totaldissolved nitrogen (TDN), nitrate (NO₃⁻), ammonium nitrogen and dissolvedorganic carbon (DOC) concentrations were measured, and dissolved organicnitrogen (DON) was calculated for each grabbed sample. Electricalconductivity, pH and flow velocity were measured during sampling.Statistical analyses showed significant differences between the northern,southern and converged stream parts, especially for NO₃⁻ concentrations withaverage values between 1.4 mg N l⁻¹ and 9.6 mg N l⁻¹.Furthermore, throughout the sampling period DON concentrations increased to2.8 mg N l⁻¹ in the northern stream contributing up to 81% toTDN. Multiple-linear regression analyses performed between chemical data andlandscape characteristics showed a significant negative influence of organicsoils on instream N concentrations and corresponding losses in spite of theiroverall minor share of the agricultural land (12.9%). On the other hand,organic soil frequency was positively correlated to the corresponding DOCconcentrations. Croplands also had a significant influence but with weakercorrelations. For our case study we conclude that the fractions of coarsetextured and organic soils have a major influence on N and DOC export in thisintensively used landscape. Meanwhile, the contribution of DON to the total Nlosses was substantial.

[学科分类] 地球化学与岩石