A method to assess instream water quality – the role of nitrogen entries in a North German rural lowland catchment

Abstract

Abstract. The objective of this study was the detection and assessment of nutrient entry pathways in a complex mesoscale lowland catchment. The central aim was the development of a transferable method for an efficient estimation of instream water quality in rural environments. The investigated Kielstau catchment with a size of approximately 50 km 2 is located in the North German lowlands. Land use is dominated by agriculture as well as pasture and is characterised by extensive artificial drainage systems. Additionally wastewater treatment plants influence the river water quality.Six measuring campaigns were carried out over the period of one year. Each time, water quality was assessed at 16 locations along a 12 km longitudinal transect of the stream to consider the influence of each tributary or inflow. The results showed that the applied measuring method was useful to assess nutrient entry pathways into surface waters from diffuse and point sources. Some tributaries increased the main stream NO 3 -N concentrations especially in autumn. Using a German classification system (LAWA, 1998), the NO 3 -N results can mostly be assigned to water quality class III (heavily contaminated). Water balance and nitrate loads were modelled with the river basin scale model SWAT (Soil and Water Assessment Tool, Arnold et al., 1998). The measured and modelled discharges showed a good correlation. While nitrate load range and dynamics are well represented during the summer periods, they show a poor correlation during the winter period.

Modelling of discharge, nitrate and phosphate loads from the Reda catchment to the Puck Lagoon using SWAT

“…They also found a strong correlation between N-NO 3 concentration and discharge explaining the underestimation of loads in winter season occurring in Kielstau catchment due to lower peak fl ows simulated by the model. Similar results were presented by Schmalz et al (2008) for the same catch-FIGURE 5. Plot of two uncertainty measures (p-factor against r-factor) for different model outputs in calibration and validation periods.…”

Incorporating landscape depressions and tile drainages of a northern German lowland catchment into a semi‐distributed model

“…SWAT has been applied to various regions and within a multitude of projects all over the world (Arnold and Fohrer, 2005;Gassman et al, 2007). It is suitable for the application in lowland catchments as the implemented processes have been successfully tested in watersheds with flat topography, low hydraulic gradients, shallow groundwater, a high potential for water retention in peatland and lakes (Schmalz et al, 2008b), for tile drained sites (Ahmad et al, 2002;Fohrer et al, 2007) and potholes in the landscape (Du et al, 2005). The model can simulate the water balance, nutrients and pesticides, field erosion, plant growth cycles, management practices and water bodies on a daily time step for continuous simulations over long time periods (Neitsch et al, 2005a).…”

O desafio do manejo do nitrogênio no contexto da produtividade agricola e da vulnerabilidade ambiental

“…La contaminación de las aguas por NO 3 -asociada a la agricultura de regadío, es un problema mundial ampliamente investigado (CAVERO et al, 2003;NEAL et al, 2006;CHERRY et al, 2008;HOWDEN e BURT, 2008;PEREIRA et al, 2009;BOURAOUI e GRIZZETTI, 2011;JACKSON et al, 2008;SILEIKA et al, 2006;SCHMALZ et al, 2008;KRONVANG et al, 2008;IITAL et al, 2005;LAM et al, 2011), Sin embargo, son pocos los trabajos que muestran éxito en la reducción de los niveles de contaminación, entre los cuales se destacan los trabajos de KRONVANG et al (2008), IITAL et al (2005) y POTT et al (2012. De acuerdo con a KRONVANG et al (2008), el éxito en la reducción de la contaminación del N en Dinamarca se debe a tres principales instrumentos implementados: (i) los requisitos obligatorios para mejorar el tratamiento de aguas residuales (Estaciones de tratamiento -ETARS), incluyendo la eliminación de N en ETARS mayores, (ii) los planes necesarios para la fertilización y rotación de cultivos, considerando los requerimientos de los cultivos, y (iii) establecimiento del nivel máximo de N disponible aplicado desde estiércol.…”