Abstract
Abstract. The surrounding landscape of a stream has crucial impacts on the aquatic environment. This study pictures the hydro-biogeochemical situation of the Tyrebækken creek catchment in central Jutland, Denmark. The intensively managed agricultural landscape is dominated by rotational croplands. The small catchment mainly consist of sandy soil types besides organic soils along the streams. The aim of the study was to characterise the relative influence of soil type and land use on stream water quality. Nine snapshot sampling campaigns were undertaken during the growing season of 2009. Total dissolved nitrogen (TDN), nitrate (NO3−), ammonium nitrogen and dissolved organic carbon (DOC) concentrations were measured, and dissolved organic nitrogen (DON) was calculated for each grabbed sample. Electrical conductivity, 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 with average values between 1.4 mg N l−1 and 9.6 mg N l−1. Furthermore, throughout the sampling period DON concentrations increased to 2.8 mg N l−1 in the northern stream contributing up to 81% to TDN. Multiple-linear regression analyses performed between chemical data and landscape characteristics showed a significant negative influence of organic soils on instream N concentrations and corresponding losses in spite of their overall minor share of the agricultural land (12.9%). On the other hand, organic soil frequency was positively correlated to the corresponding DOC concentrations. Croplands also had a significant influence but with weaker correlations. For our case study we conclude that the fractions of coarse textured and organic soils have a major influence on N and DOC export in this intensively used landscape. Meanwhile, the contribution of DON to the total N losses was substantial.
Highlights
Agricultural land use has been found responsible for major nutrient losses from land to river systems and estuaries worldwide (Vitousek et al, 1997)
We investigated the fractions of dissolved inorganic nitrogen (DIN) and dissolved organic nitrogen (DON) within total dissolved nitrogen (TDN) concentrations and fluxes in the stream water, respectively
Organic soils contain a high proportion of degradable organic matter that can be eventually released by different physicochemical processes into streams (Kennedy et al, 1996). These observations coincide with the results of our study where we find a higher proportion of organic soils in the southern stream part along with higher dissolved organic carbon (DOC) concentrations and loads
Summary
Agricultural land use has been found responsible for major nutrient losses from land to river systems and estuaries worldwide (Vitousek et al, 1997). Nitrate (NO−3 ) is described as the main source of nitrogen (N) losses from cultivated land, because it is the most important growth regulating nutrient and is often applied in excess to guarantee optimal crop yields (van Kessel et al, 2009; Martin et al, 2004; Randall and Mulla, 2001; Ruiz et al, 2002a; Steenvoorden et al, 2002). The amount of NO−3 leaching into water bodies depends on dry and wet climatic cycles (Randall, 1998). During dry periods NO−3 accumulates in soils before being released under wet conditions, even after many years (Randall and Mulla, 2001).
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