Freshwater Umbrella Resources

Final report of the 2004–2007 research programme


Final Report Front CoverIn upland areas of the UK located away from direct human disturbance through agriculture, industrial activities and urban pollution, atmospheric pollution poses one of the major threats to the chemical and biological quality of lakes and streams. One of the most important groups of pollutants is nitrogen (N) compounds, including oxidised forms of N called NOx, generated mainly by fossil fuel combustion especially in motor vehicles, and reduced forms of N (ammonia gas or dissolved ammonium compounds) generated mainly from agricultural activities and livestock. These nitrogen compounds may dissolve in rain or soilwater to form acids, or may be taken up as nutrients by plants and soil microbes in upland catchments, and then subsequently released in acid form associated with nitrate leaching at a later date. It is well established that nitrate leaching contributes to acidification of upland waters, with damage to aquatic ecosystems including plants, invertebrates and fish. However it has recently been suggested that nitrate leaching may also be associated with nutrient enrichment of upland waters that contain biological communities adapted to very low nutrient levels.

Issues of acidification, nutrient enrichment and biological controls on nitrate leaching are therefore intrinsically linked and need to be understood in order to determine current and future impacts of N deposition on water quality and ecological status of upland waters. The Freshwater Umbrella programme was specifically designed to tackle these scientifically challenging problems, with key objectives and methods to:

  • assess the importance of inorganic forms of N (i.e. nitrate and ammonium) as nutrients in upland lakes through a combination of literature review, lake sediment studies and experimental work;
  • improve understanding of nitrate leaching pathways and controls using complementary isotopic tracer and dual isotope approaches. The first approach allows N compounds to be marked and then tracked through the environment, while the second uses naturally occurring isotopic differences between atmospherically deposited nitrate that is leached unchanged from catchments and nitrate produced from ammonium by the microbial process of nitrification in soils;
  • develop models for predicting which nutrient (N or phosphorus) is the major control of biological productivity in upland waters from catchment characteristics and other nationally available datasets, including studies of catchment soils and mosses as possible controlling factors;
  • assess the impacts of climate change on effects of atmospheric pollutants in upland catchments through literature review and experimental work; and
  • review and develop models linking deposition loads to ecological effects (with a quantified biologically relevant threshold or critical load) for acidity in UK freshwaters and review the case for application of nutrient N critical loads.

Chris Curtis and Gavin L. Simpson

Publication Date:

July 2007




Adobe pdf icon Final Report (9.6 MB | PDF)

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