The role of catchment characteristics in determining surface water nitrogen in four upland regions in the UK

Abstract

Hydrochemical and catchment data from 80 upland moorland sites in four regions with contrasting climate, soils, geology and geomorphology have been analysed to assess the key catchment attributes that influence enhanced leaching of soluble nitrogen to surface waters. The regions are the South Pennines of northern England, the Snowdonia National Park in north Wales, the Galloway region of south-west Scotland and the Mourne Mountains in Northern Ireland, all highly acidified, with median pH values of <5.5. Linear regression of mean summer and winter concentrations for nitrate (NO 3 ), ammonium (NH 4 + ), dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) were expressed as functions of catchment attributes. Nitrate concentrations in waters draining catchments dominated by peaty soils (large C pool) were much less than those in catchments dominated by mineral soils (small C pool). Hence, if future N deposition levels are maintained or increase, high-altitude catchments with small carbon pools are potentially more susceptible to NO 3 leaching. All N species exhibit seasonality; this is most marked in Galloway and least marked in the South Pennines, which implies that the South Pennines have reached an advanced stage of N saturation. Surface water inorganic N concentrations and the ratio of dissolved organic carbon (DOC) to dissolved organic N (DON) can be related to deposition inputs, although relationships differ throughout the year. If the DOC/DON ratio is indicative of catchment N saturation, levels of N retention are at least partially determined by deposition levels. This study identifies N deposition as a major interregional control on the degree of catchment N saturation and on N leaching to surface waters; it stresses the importance of catchment factors in modifying the relationship between N deposition and leaching in acid sensitive UK upland catchments.

Catchment features controlling nitrogen dynamics in running waters above the tree line (central Italian Alps)

“…Previous studies (e.g. Helliwell et al, 2007;Evans et al, 2006, aimed at analysing control on NO 3 leaching in mountain freshwaters, reached similar conclusions about the importance of soil carbon pool in controlling N retention. Nonetheless, our findings suggest that in homogenous environments as those above the tree line, the percentage of soil cover may be sufficient for predicting N water concentrations independently of the carbon pool contents that are often rather difficult to obtain.…”

“…Recent studies on the microbiology of alpine soils suggest an important role of bacterial communities in controlling N cycling and NO 3 export in these basins (Lipson et al, 1999;Nemergut et al, 2005). Physical features of the catchment strongly influence the chemical composition of stream water, and may control ecosystem responses to global perturbations, such as atmospheric N deposition and/or changes in climate (Clow and Sueker, 2000;Lovett et al, 2000;Sickman et al, 2002;Lewis, 2002;Kopaceck et al, 2005;Helliwell et al, 2007). The importance of physical landscape components in the amplification and attenuation of biogeochemical processes has been recently highlighted in a conceptual model for high-elevation ecosystems named "Landscape Continuum Model" (Seastedt et al, 2004).…”

Application of a simple multiplicative spatio-temporal stream water quality model to the river Conwy, North Wales

“…The combination of class groups used in the landscape 9 definition is shown in Table 3. 10 This choice of grouping is also supported by evidence from other studies of enhanced 2 atmospheric deposition of some water quality variables, differences in soil processes in 3 different soil types, particularly between peat and mineral soils, and the strong 4 association between water quality and farming, where the fertility of the soil is 5 artificially influenced by farming practices 12,21,11 . 6 7 The three classifications do not explicitly include a number of covariates which are likely 8…”

Relationship between critical load exceedances and empirical impact indicators at Integrated Monitoring sites across Europe

“…Hence changes in N deposition may not always directly correlate with changes in inorganic N leaching. The variation in the relationship between N concentrations and fluxes and exceedances of critical loads may be expected, since N leaching depends on landscape characteristics, site history, soil fertility and organic matter pool, vegetation type and hydrological processes (Helliwell et al, 2007;Rothwell et al, 2008). However, continued high N deposition may result in N saturation of terrestrial ecosystems in the long run and excess NO 3 leaching to surface waters (e.g.…”