Critical Loads of Acid Deposition for Wilderness Lakes in the Sierra Nevada (California) Estimated by the Steady-State Water Chemistry 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 19761999. 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·m2·year1. As a result of the declining deposition, the portion of lakes with critical load exceedances has dropped substantially, from 7482% in the four sensitive regions in 1976 to 1126% 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·m2·year1 (11 kg S·ha1·year1) to prevent critical load exceedance.

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A critical review of mass balance methods for calculating critical loads of nitrogen for forested ecosystems

Environmental Reviews ◽

10.1139/a93-011 ◽

1993 ◽

Vol 1 (2) ◽

pp. 145-156 ◽

Cited By ~ 2

Author(s):

L. H. Pardo ◽

C. T. Driscoll

Keyword(s):

Steady State ◽

Atmospheric Deposition ◽

Water Chemistry ◽

Critical Load ◽

Mass Balance ◽

Critical Loads ◽

Balance Method ◽

Mass Balance Method ◽

Basic Cation ◽

State Water

Critical loads are used in the assessment of air pollution and regulation of the causative emissions to prevent or mitigate ecological damage. We critically review four mass balance methods for calculating critical loads for nitrogen deposition: the steady-state water chemistry method, the nitrogen mass balance method, the basic cation mass balance method, and the steady-state mass balance method. The critical loads may be calculated with respect to effects of acidification associated with nitrate leaching or effects of elevated nitrogen such as eutrophication, excess nitrate loss, and nutrient imbalances. The most useful method for calculating the critical load for nitrogen with respect to effects of elevated atmospheric deposition of nitrogen is the nitrogen mass balance method. The steady-state water chemistry method can be readily applied for regional-scale calculations because it requires only water chemistry data from synoptic surveys of surface waters and does not explicitly consider biogeochemical processes. Both of the other approaches are severely limited by lack of quantitative information on rates of mineral weathering. If weathering data were available, the steady-state mass balance method could be more effectively used to assess critical loads with respect to acidification. Similarly, the basic cation mass balance method could be used to calculate critical loads for both acidity and elevated nitrogen effects. Because of the complexity of the nitrogen cycle, it is not possible to obtain a single critical load for the whole ecosystem. Rather, one should analyze and synthesize several values of critical loads that reflect different components of the ecosystem and different ecological effects of elevated nitrogen deposition (e.g., acidification and eutrophication effects).Key words: atmospheric deposition of nitrogen, acidification, critical loads, nitrogen cycling.

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Critical loads of sulphur and nitrogen for freshwaters in Great Britain and assessment of deposition reduction requirements with the First-order Acidity Balance (FAB) model

Hydrology and Earth System Sciences ◽

10.5194/hess-4-125-2000 ◽

2000 ◽

Vol 4 (1) ◽

pp. 125-140 ◽

Cited By ~ 18

Author(s):

C. Curtis ◽

T. Allott ◽

J. Hall ◽

R. Harriman ◽

R. Helliwell ◽

...

Keyword(s):

Great Britain ◽

Water Chemistry ◽

Critical Load ◽

Acid Deposition ◽

Critical Loads ◽

Freshwater Ecosystems ◽

Acid Neutralizing Capacity ◽

First Order ◽

Fab Model ◽

S Deposition

Abstract. The critical loads approach is widely used within Europe to assess the impacts of acid deposition on terrestrial and freshwater ecosystems. Recent work in Great Britain has focused on the national application of the First-order Acidity Balance (FAB) model to a freshwaters dataset of 1470 lake and stream water chemistry samples from sites across Britain which were selected to represent the most sensitive water bodies in their corresponding 10 km grid square. A ``Critical Load Function" generated for each site is compared with the deposition load of S and N at the time of water chemistry sampling. The model predicts that when catchment processes reach steady-state with these deposition levels, increases in nitrate leaching will depress acid neutralizing capacity (ANC) below the critical threshold of 0 μeql-1 at more than a quarter of the sites sampled, i.e. the critical load of acid deposition is exceeded at these sites. The critical load exceedances are generally found in upland regions of high deposition where acidification has been previously recognised, but critical loads in large areas of western Scotland are also exceeded where little biological evidence of acidification has yet been found. There is a regional variation in the deposition reduction requirements for protection of the sampled sites. The FAB model indicates that in Scotland, most of the sampled sites could be protected by sufficiently large reductions in S deposition alone. In the English and Welsh uplands, both S and N deposition must be reduced to protect the sites. Current international commitments to reduce S deposition throughout Europe will therefore be insufficient to protect the most sensitive freshwaters in England and Wales. Keywords: critical loads; acidification; nitrate; FAB model; acid deposition

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Calculating critical loads of acid deposition with PROFILE ? A steady-state soil chemistry model

Water Air & Soil Pollution ◽

10.1007/bf00475626 ◽

1992 ◽

Vol 63 (1-2) ◽

pp. 119-143 ◽

Cited By ~ 141

Author(s):

Per Warfvinge ◽

Harald Sverdrup

Keyword(s):

Steady State ◽

Acid Deposition ◽

Critical Loads ◽

Soil Chemistry

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Estimating calcium weathering rates and future lake calcium concentrations in the Muskoka–Haliburton region of Ontario

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f07-196 ◽

2008 ◽

Vol 65 (5) ◽

pp. 821-833 ◽

Cited By ~ 47

Author(s):

Shaun A Watmough ◽

Julian Aherne

Keyword(s):

Steady State ◽

Water Chemistry ◽

Timber Harvesting ◽

Mineral Weathering ◽

Drainage Basins ◽

Weathering Rates ◽

South Central ◽

Model Predictions ◽

State Water ◽

Hydrochemical Model

Calcium (Ca) concentrations in surface waters on the Precambrian Shield are determined primarily by the Ca weathering rate in soil, which requires extensive soil data that generally do not exist. From a water chemistry database comprising approximately 550 lakes in south-central Ontario, Canada, 130 lakes were selected with low Ca concentrations (Ca < 75 µmol·L–1). Calcium weathering is primarily dominated by silicate minerals such as plagioclase and hornblende, allowing the use of Ca–sodium (Na) ratios in lake water to estimate Ca weathering rates. Soil profile data at seven sites indicated that the Ca–Na ratio from mineral weathering is 0.86; correspondingly, Ca weathering rates in lakes ranged from 0.04 to 0.24 kmol·ha–1·year–1 (median of 0.09 kmol·ha–1·year–1). This compares with a range of 0.06–0.24 kmol·ha–1·year–1 (median of 0.14 kmol·ha–1·year–1) obtained using the steady-state water chemistry model. Using these methods to bound potential weathering rates, Ca concentrations in individual lakes at steady state are predicted to decline by 10%–40% compared with current values. Dynamic soil hydrochemical model predictions indicate that Ca concentrations in lakes will be considerably lower than these steady-state predictions within decades if timber harvesting occurs in the drainage basins.

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Testing the steady-state water chemistry model predictions of pre-industrial lake pH with paleolimnological data from northern Sweden☆

The Science of The Total Environment ◽

10.1016/j.scitotenv.2008.10.007 ◽

2008 ◽

Vol 407 (1) ◽

pp. 723-729 ◽

Cited By ~ 7

Author(s):

K BISHOP ◽

L RAPP ◽

S KOHLER ◽

T KORSMAN

Keyword(s):

Steady State ◽

Water Chemistry ◽

Northern Sweden ◽

Model Predictions ◽

State Water

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Surface water acidification and critical loads: exploring the F-factor

Hydrology and Earth System Sciences ◽

10.5194/hess-13-2191-2009 ◽

2009 ◽

Vol 13 (11) ◽

pp. 2191-2201 ◽

Cited By ~ 8

Author(s):

L. Rapp ◽

K. Bishop

Keyword(s):

Time Series ◽

Surface Water ◽

Water Chemistry ◽

Acid Deposition ◽

Critical Loads ◽

Base Cations ◽

Recovery Phase ◽

Biogeochemical Model ◽

Lake Chemistry ◽

F Factor

Abstract. As acid deposition decreases, uncertainties in methods for calculating critical loads become more important when judgements have to be made about whether or not further emission reductions are needed. An important aspect of one type of model that has been used to calculate surface water critical loads is the empirical F-factor which estimates the degree to which acid deposition is neutralised before it reaches a lake at any particular point in time relative to the pre-industrial, steady-state water chemistry conditions. In this paper we will examine how well the empirical F-functions are able to estimate pre-industrial lake chemistry as lake chemistry changes during different phases of acidification and recovery. To accomplish this, we use the dynamic, process-oriented biogeochemical model SAFE to generate a plausible time series of annual runoff chemistry for ca. 140 Swedish catchments between 1800 and 2100. These annual hydrochemistry data are then used to generate empirical F-factors that are compared to the "actual" F-factor seen in the SAFE data for each lake and year in the time series. The dynamics of the F-factor as catchments acidify, and then recover are not widely recognised. Our results suggest that the F-factor approach worked best during the acidification phase when soil processes buffer incoming acidity. However, the empirical functions for estimating F from contemporary lake chemistry are not well suited to the recovery phase when the F-factor turns negative due to recovery processes in the soil. This happens when acid deposition has depleted the soil store of BC, and then acid deposition declines, reducing the leaching of base cations to levels below those in the pre-industrial era. An estimate of critical load from water chemistry during recovery and empirical F functions would therefore result in critical loads that are too low. Therefore, the empirical estimates of the F-factor are a significant source of uncertainty in the estimate of surface water critical loads and related calculations for quantifying lake acidification status, especially now that acid deposition has declined across large areas of Europe and North America.

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The development of an approach to assess critical loads of acidity for woodland habitats in Great Britain

Hydrology and Earth System Sciences ◽

10.5194/hess-8-355-2004 ◽

2004 ◽

Vol 8 (3) ◽

pp. 355-365 ◽

Cited By ~ 8

Author(s):

S. J. Langan ◽

J. Hall ◽

B. Reynolds ◽

M. Broadmeadow ◽

M. Hornung ◽

...

Keyword(s):

Air Pollution ◽

Steady State ◽

Critical Load ◽

Acid Deposition ◽

Critical Loads ◽

Balance Model ◽

Mass Balance Model ◽

Simple Mass ◽

The Uk ◽

Simple Mass Balance Model

Abstract. Alongside other countries that are signatories to the UNECE Convention Long Range Transboundary on Air Pollution, the UK is committed to reducing the impact of air pollution on the environment. To advise and guide this policy in relation to atmospheric emissions of sulphur and nitrogen, a critical load approach has been developed. To assess the potential impact of these pollutants on woodland habitats a steady state, simple mass balance model has been parameterised. For mineral soils, a Ca:Al ratio in soil solution has been used as the critical load indicator for potential damage. For peat and organic soils critical loads have been set according to a pH criterion. Together these approaches have been used with national datasets to examine the potential scale of acidification in woodland habitats across the UK. The results can be mapped to show the spatial variability in critical loads of the three principal woodland habitat types (managed coniferous, managed broadleaved/ mixed woodland and unmanaged woodland). The results suggest that there is a wide range of critical loads. The most sensitive (lowest) critical loads are associated with managed coniferous followed by unmanaged woodland on peat soils. Calculations indicate that at steady state, acid deposition inputs reported for 1995–1997 result in a large proportion of all the woodland habitats identified receiving deposition loads in excess of their critical load; i.e. critical loads are exceeded. These are discussed in relation to future modelled depositions for 2010. Whilst significant widespread negative impacts of such deposition on UK woodland habitats have not been reported, the work serves to illustrate that if acid deposition inputs were maintained and projected emissions reductions not achieved, the long-term sustainability of large areas of woodland in the UK could be compromised. Keywords: critical loads, acid deposition, acidification, woodland, simple mass balance model, sustainability

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