Derivation of Critical Loads by Steady-State and Dynamic Soil Models

1999 ◽  
pp. 213-234 ◽  
Author(s):  
M. Posch ◽  
W. De Vries
Keyword(s):  
Steady State ◽  
Critical Loads

scholarly journals Present and potential nitrogen outputs from Norwegian soft water lakes – an assessment made by applying the steady-state First-order Acidity Balance (FAB) model

2002 ◽  
Vol 6 (1) ◽  
pp. 101-112 ◽  
Author(s):  
Ø. Kaste ◽  
A. Henriksen ◽  
M. Posch
Keyword(s):  
Steady State ◽  
Critical Loads ◽  
N Deposition ◽  
Soft Water ◽  
N Leaching ◽  
First Order ◽  
Fab Model ◽  
The Future ◽  
N Immobilisation

Abstract. The steady-state First-order Acidity Balance (FAB) model for calculating critical loads of sulphur (S) and nitrogen (N) is applied to 609 Norwegian soft-water lakes to assess the future nitrate (NO3‾) leaching potential under present (1992-96) S and N deposition. The lakes were separated into five groups receiving increasing levels of N deposition (<25, 25-49, 50-74, 75-99 and 100-125 meq m-2yr-1). Using long-term sustainable N sink rates presently recommended for FAB model applications, N immobilisation, net N uptake in forests, denitrification and in-lake N retention were estimated for each group of lakes. Altogether, the long-term N sinks constituted 9.9 ± 3.2 to 40.5 ± 11.4 meq m-2yr-1 in the lowest and highest N deposition categories, respectively. At most sites, the current N deposition exceeds the amount of N retained by long-term sustainable N sinks plus the NO3‾ loss via the lake outlets. This excess N, which is currently retained within the catchments may, according to the FAB model, leach as acidifying NO3‾ in the future. If these predictions are fulfilled, NO3‾ leaching at sites in the various N deposition categories will increase dramatically from present (1995) mean levels of 1-20 meq m-2yr-1, to mean levels of 7-70 meq m-2yr-1 at future steady state. To illustrate the significance of such an increase in NO3‾ leaching, the mean Acid Neutralising Capacity (ANC) at sites in the highest N deposition category may decrease from -18 ± 15 μeq L-1 at present, to -40 ± 20 μeq L-1. Under present S and N deposition levels, the FAB model predicts that 46% of the Norwegian lakes may experience exceedances of critical loads for acidifying deposition. In comparison, the Steady-State Water Chemistry model (SSWC), which considers only the present N leaching level, estimates critical load exceedances in 37% of the lakes under the same deposition level. Thus far, there are great uncertainties regarding both the time scales and the extent of future N leaching, and it is largely unknown whether the FAB model predictions will ever be fulfilled. Hence, long-term monitoring and further studies on N immobilisation processes under varying N deposition levels and ecosystem types seem necessary to make better predictions of future NO3‾ leaching. Keywords: Lakes, hydrochemistry, nitrogen, nitrate, sinks, leaching, acidification, critical loads, FAB model

Calculating critical loads for acidification for five forested catchments in China using an extended steady state function

2007 ◽  
Vol 387 (1-3) ◽  
pp. 54-67 ◽  
Author(s):  
Yu Zhao ◽  
Lei Duan ◽  
Thorjorn Larssen ◽  
Jan Mulder ◽  
Lanhua Hu ◽  
...  
Keyword(s):  
Steady State ◽  
Critical Loads ◽  
State Function ◽  
Forested Catchments

scholarly journals Quantification of nitrate leaching from forest soils on a national scale in The Netherlands

2004 ◽  
Vol 8 (4) ◽  
pp. 813-822 ◽  
Author(s):  
J. Kros ◽  
A. Tietema ◽  
J. P. Mol-Dijkstra ◽  
W. de Vries
Keyword(s):  
Steady State ◽  
Regression Model ◽  
Nitrogen Deposition ◽  
Dynamic Model ◽  
Critical Loads ◽  
Forest Ecosystems ◽  
Dynamic Models ◽  
National Scale ◽  
Regional Variability ◽  
Nitrate Concentrations

Abstract. To evaluate the effects of nitrogen (N) emission policies, reliable information on nitrate concentrations and leaching fluxes from forest ecosystems is necessary. Insight into the regional variability of nitrate concentrations, to support local policy on emission abatement strategies is especially desirable. In this paper, three methods for the calculation of a spatial distribution of soil nitrate concentrations in Dutch forest ecosystems are compared. These are (i) a regression model based on observed nitrate concentrations and additional data on explanatory variables such as soil type, tree species and nitrogen deposition (ii) a semi-empirical dynamic model WANDA, and (iii) a process-oriented dynamic model SMART2. These two dynamic models are frequently used to evaluate the effects of reductions in nitrogen deposition at scales ranging from regional to countrywide. The results of the regression model evaluated the performance of the two dynamic models. Furthermore, the results of the three methods are compared with the steady-state approach currently used for the derivation of nitrogen critical loads. Both dynamic models, in the form of cumulative distribution functions, give similar results on a national scale. Regional variability is predicted differently by both models. Discrepancies are caused mainly by a difference in handling forest filtering and denitrification. All three methods show that, despite the high nitrogen inputs, Dutch forests still accumulate more N than they release. This implies that, in respect of groundwater quality, presently acceptable nitrogen deposition is higher than the (long-term) critical loads. However, in areas with high atmospheric nitrogen input, all three methods indicate that the EU standard for nitrate in groundwater (50 mg NO3 l–1) is exceeded. Steady-state with nitrogen deposition seems to have been reached in about 10% of the forested area, with a nitrate concentration greater than 50 mg NO3–1. Keywords: soil modelling, up-scaling, model validation, critical load

Critical loads of acidity for surface waters in south-central Ontario, Canada: regional application of the Steady-State Water Chemistry (SSWC) model

2002 ◽  
Vol 59 (8) ◽  
pp. 1287-1295 ◽  
Author(s):  
A Henriksen ◽  
P J Dillon ◽  
J Aherne
Keyword(s):  
Steady State ◽  
Water Chemistry ◽  
Critical Load ◽  
Critical Loads ◽  
Lake Chemistry ◽  
Sulphur Deposition ◽  
South Central ◽  
State Water ◽  
Critical Loads Of Acidity ◽  
Sswc Model

Critical loads of acidity and the amount by which these critical loads are exceeded by atmospheric deposition (termed "exceedances") were estimated for 1469 lakes from five regions in south-central Ontario, Canada, using single lake chemistry measurements and sulphur deposition data for the period 1976–1999. Based on the Steady-State Water Chemistry (SSWC) model, four of the five regions had low critical loads, which is consistent with the underlying geology (silicate bedrock) and the thin glacial soils in these regions. Sulphur deposition in the study area showed a clear downward trend over the time period, with a decrease of approximately 50% to current levels of approximately 44 meq·m–2·year–1. As a result of the declining deposition, the portion of lakes with critical load exceedances has dropped substantially, from 74–82% in the four sensitive regions in 1976 to 11–26% in 1999. The pentile critical load is typically used as a regional target to account for uncertainties, but also to ensure that a sufficient percentage of lakes are protected (95%). This suggests that further reductions in emissions are required to reduce depositions to approximately 34 meq·m–2·year–1 (11 kg S·ha–1·year–1) to prevent critical load exceedance.

scholarly journals Long-term modelling of nitrogen turnover and critical loads in a forested catchment using the INCA model

2002 ◽  
Vol 6 (3) ◽  
pp. 395-402 ◽  
Author(s):  
J.-J. Langusch ◽  
E. Matzner
Keyword(s):  
Steady State ◽  
Critical Load ◽  
Mass Balance ◽  
Critical Loads ◽  
Forest Ecosystems ◽  
N Deposition ◽  
N Saturation ◽  
Negative Consequences ◽  
Hydrological Conditions

Abstract. Many forest ecosystems in Central Europe have reached the status of N saturation due to chronically high N deposition. In consequence, the NO3 leaching into ground- and surface waters is often substantial. Critical loads have been defined to abate the negative consequences of the NO3 leaching such as soil acidification and nutrient losses. The steady state mass balance method is normally used to calculate critical loads for N deposition in forest ecosystems. However, the steady state mass balance approach is limited because it does not take into account hydrology and the time until the steady state is reached. The aim of this study was to test the suitability of another approach: the dynamic model INCA (Integrated Nitrogen Model for European Catchments). Long-term effects of changing N deposition and critical loads for N were simulated using INCA for the Lehstenbach spruce catchment (Fichtelgebirge, NE Bavaria, Germany) under different hydrological conditions. Long-term scenarios of either increasing or decreasing N deposition indicated that, in this catchment, the response of nitrate concentrations in runoff to changing N deposition is buffered by a large groundwater reservoir. The critical load simulated by the INCA model with respect to a nitrate concentration of 0.4 mg N l–1 as threshold value in runoff was 9.7 kg N ha–1yr–1 compared to 10 kg ha–1yr–1 for the steady state model. Under conditions of lower precipitation (520 mm) the resulting critical load was 7.7 kg N ha–1yr–1 , suggesting the necessity to account for different hydrological conditions when calculating critical loads. The INCA model seems to be suitable to calculate critical loads for N in forested catchments under varying hydrological conditions e.g. as a consequence of climate change. Keywords: forest ecosystem, N saturation, critical load, modelling, long-term scenario, nitrate leaching, critical loads reduction, INCA

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