Abstract
Diffusive groundwater pollution caused by agricultural and atmospheric inputs is a pressing issue in environmental management worldwide. Various researchers have studied nitrate contamination since the substantial increase of nitrogen fertilization in agriculture starting in the second half of the 20th century. This study addresses large scale reactive solute transport in typical landscapes and aquifers exemplified by geological analogues of southwestern Germany.. Fate of nitrate and other solutes (e.g. agricultural nitrate, ammonium, natural sulfate and dissolved organic carbon) was studied in a typical small river floodplain. Reactive transport model of Ammer river floodplain shows that agriculture nitrate is reduced rapidly in the Ammer floodplain sediments. However, there is a potential for geogenic production of ammonium in sediment layers high in organic carbon and peat, which might be a major source of nitrate in the drains. Part of the nitrate in drains and creeks in the Ammer valley thus could be of geogenic origin. Such findings are relevant for regional land and water quality management.
Highlights
IntroductionIn temperate climates, they are typically comprised by Pleistocene sands and gravels as well as Holocene peat lenses and loams [1, 2] and normally considered as hotspots in the biogeochemical cycle due to high organic matter content [3]
This study addresses large scale reactive solute transport in typical landscapes and aquifers exemplified by geological analogues of southwestern Germany..Fate of nitrate and other solutes was studied in a typical small river floodplain
A 2-D fully coupled reactive transport model was set up aiming to answer following questions: 1) What is the fate of nitrate when it enters the sediments of the floodplain? Is it reduced in the sediments or collected by drainage channels? 2) What is the influence of the spatial distribution or organic carbon within the floodplain sediments on ammonification and denitrification? 3) What is the source of the nitrate observed in the drains? Is it agricultural nitrate or does it come from natural ammonium produced in organic carbon rich layers in the sediments? 4) Are there any other important reactions except the redox reactions affecting nitrate such as sulfate reduction, mineral precipitation, nitrogen gas trapping, etc.?
Summary
In temperate climates, they are typically comprised by Pleistocene sands and gravels as well as Holocene peat lenses and loams [1, 2] and normally considered as hotspots in the biogeochemical cycle due to high organic matter content [3]. Hillslopes formed of Gipkeuper mudstones confine the floodplain At the base, it starts with highly conductive base gravel layer, followed by a low-conductive clay layer and a layered system of calcareous sediments and peat. It starts with highly conductive base gravel layer, followed by a low-conductive clay layer and a layered system of calcareous sediments and peat These layers are overlain by alluvium silt and loam. A 2-D fully coupled reactive transport model was set up aiming to answer following questions: 1) What is the fate of nitrate when it enters the sediments of the floodplain? Is it reduced in the sediments or collected by drainage channels? 2) What is the influence of the spatial distribution or organic carbon within the floodplain sediments on ammonification and denitrification? 3) What is the source of the nitrate observed in the drains? Is it agricultural nitrate or does it come from natural ammonium produced in organic carbon rich layers in the sediments? 4) Are there any other important reactions except the redox reactions affecting nitrate such as sulfate reduction, mineral precipitation, nitrogen gas trapping, etc.?
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