Freshwater Umbrella Presentations

Relationship between Nitrogen leaching, Nitrogen limitation and landscape-scale predictors in upland catchments

Martin Kernan, Gavin L. Simpson, Stephen Maberly, Chris J. Curtis and Mike J. Hughes

Abstract

Phosphorus has traditionally been seen as the primary nutrient limiting the productivity of unproductive lakes in upland areas or where there is no significant catchment nutrient source. However, in some unproductive upland lakes, both phytoplankton and periphyton have been found to be limited as much by nitrogen as phosphorus and co-limitation frequently occurs (Maberly et al., 2002). The relationships between catchment characteristics and water chemistry, phytoplankton and periphyton biomass, and phytoplankton and periphyton nutrient limitation were examined for 30 upland lakes used in the earlier study on nutrient limitation (Maberly et al., 2003).

A regression model was used to establish relationships between P and N limitation and a series of land cover variables. The present study uses these relationships as the basis to explore the possibility of producing national maps of N limitation in upland areas showing vulnerability to nutrient enrichment from elevated levels of N deposition. The sampling of a further 12 lakes for N and P phytoplankton bioassays provided a dataset of N and P limitation in 42 lakes, which on a national scale is still too few sites to establish whether systems are N, P or co-limited. However, analyses of the 42 upland lakes showed that dissolved inorganic nitrogen (DIN) was found to be strongly related to N / P limitation.

Thus, to upscale the approach nationally DIN can be used as a surrogate for nutrient limitation. DIN data are available for ca. 1600 sites from the UK Freshwater Umbrella database. Data relating to catchment morphology, land cover and soil are also available for these sites. A screening exercise was undertaken to remove those sites likely to exhibit significant terrestrial inputs of nitrogen and phosphorus from fertiliser applications or point source emissions. On a sub-set of these sites, statistical techniques (e.g. multivariate adaptive regression splines and classification trees) were used to identify catchment attributes which could explain statistically significant levels of variation in DIN. From this calibration dataset it was possible, using DIN as a surrogate, to identify both regions and specific instances where N limitation was dominant in standing waters in the UK uplands. The predictive model produced can be further developed so that DIN can be predicted from catchment characteristics for sites with no water chemistry data. The ultimate aim is a tool which enables identification of all sites where nutrient enriching effects of N deposition in the uplands are most likely.

Presentation

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References

  • Maberly S.C., King L., Dent M.M., Jones R.I. and Gibson C.E. (2002) Nutrient limitation of phytoplankton and periphyton growth in upland lakes. Freshwater Biology 47, 2136–2152. [ article ]
  • Maberly S.C., King L., Gibson C.E., May L., Jones R.I., Dent M.M., and Jordan C. (2003) Linking nutrient limitation and water chemistry in upland lakes to catchment characteristics. Hydrobiologia 506–507, 83–91. [ article ]