Implication of lake water residence time on the classification of norwegian surface water sites into progressive stages of nitrogen saturation

摘要: Seasonal behaviour of NO3 - in surfacewater is often used as an indicator on a catchment's ability toretain N from atmospheric deposition. In this paper, weclassify 12 pristine sites (five streams and seven lakes) insouthernmost Norway according to the saturation stageconcept. All examined were acid-sensitive had annualmean concentrations range 6–36 μeqL-1. At lake with relatively long water residencetimes, hydrology will have damping effect seasonalNO3 - oscillations outlet streams. Under givenrunoff conditions (1.0–2.2 m yr-1), pattern was clearly affected when lake:catchmentarea ratios exceeded 0.15 total residence time lakesin catchments 0.3 yr. such cases, concentration rather than seasonalvariations may be better saturation. Toaccount for we propose set supplementary criteria forsuch systems, defining limit values annual meanNO3 - within each stage class. Beforebeing applied broader scale, however, recommend anexamination additional lake-dominated catchmentsrepresenting larger gradient ecosystem types, depositionlevels hydrologic regimes. When applying supplementarycriteria Norwegian sites, two classified 0(no saturation), five 1 (early saturation)and 2 (saturated – moderate loss). No siteswere showing symptoms 3, which characteriseswatersheds that are net sources N, sinks. Theresults indicate great variability retention capacity inthe study region, despite fact many catchmentsexperience uniform deposition amounts climaticconditions. This suggests much must bedue specific catchment characteristics e.g. soil type,soil depth, vegetation cover.