Steady State Mass Balance Method Research Articles

Assessment of Critical Loads of Nitrogen Deposition in Natural Ecosystems of China

Excessive nitrogen (N) deposition causes a series of environmental problems, including biodiversity loss. Therefore, assessing current N deposition thresholds of natural ecosystems is critical for regional N management and pollution control. In this study, the critical loads of N deposition in mainland China were estimated using the steady-state mass balance method, and the spatial distribution of ecosystems that exceeded the critical load was evaluated. The results showed that areas with critical loads of N deposition higher than 56, in the range of 14-56, and lower than 14 kg·(hm2·a)-1 accounted for 6%, 67%, and 27% of that in China, respectively. The areas with higher critical loads of N deposition were mainly distributed in the eastern Tibetan Plateau, northeastern Inner Mongolia, and parts of south China. Lower critical loads of N deposition were mainly distributed in the western Tibetan Plateau, northwest China, and parts of southeast China. Moreover, the areas where N deposition exceeded the critical loads accounted for 21% of that in mainland China, being mainly distributed in southeast and northeast China. The exceedances of critical loads of N deposition in northeast China, northwest China, and the Qinghai-Tibet Plateau were generally lower than 14 kg·(hm2·a)-1. Therefore, the management and control of N in these areas that exceeded the critical load of deposition is more worthy of future attention.

Nitrogen budget and critical load determination at a Sahelian grazed grassland site

Based on rare and original in situ measurements together with published data, we estimate a complete nitrogen (N) budget for a semi-arid Sahelian grazed grassland located in Dahra (Senegal) in 2014 and 2017. Nitrogen inputs include biological fixation, dry and wet atmospheric deposition, and input from livestock manure. Nitrogen outputs include nitric oxide (NO) and nitrous oxide (N2O) emissions from soils, NO and ammonia (NH3) emissions from biomass burning, NH3 volatilization from manure, ingestion from livestock grazing, uptake by trees and soil leaching. Nitrogen inputs ranged between 11.7 ± 0.5 and 34.4 ± 0.5 kg N ha−1 yr−1 for low and high estimates respectively, and N outputs ranged between 16.4 ± 1.5 and 45.7 ± 1.5 kg N ha−1 yr−1 for low and high estimates respectively, on average for both years. Nitrogen depletion was estimated between 4.7 ± 2.0 and 11.3 ± 2.0 kg N ha−1 yr−1, which involves N mining from soils. The budget is dominated by the impact of livestock through grazing (63% of the outputs), NH3 volatilization (15% of the outputs), manure (68% of the inputs) and atmospheric deposition (19% of the inputs). The N critical load (Steady State Mass Balance method) ranged from 16.7 ± 0.8 to 47.5 ± 1.7 kg N ha−1 yr−1, showing that the grazed grassland of Dahra was not yet threatened by an excess of N. The assessment of the critical load in Sahelian landscapes depends heavily on livestock participation to the ecosystem equilibrium.

Estimation and analysis of ventilation rates in schools in Indian context: IAQ and Indoor Environmental Quality

The prolonged exposure to indoor air pollution may affect the health, comfort and performance of the occupants. Failing to address Indoor Air Quality (IAQ) problems may lead to short-term and long-term health problems. The health effects may vary for different individuals depending on factors like age and medical conditions, children being young and sensitive to the environment, are more susceptible to the same. The primary focus of this research is to estimate the ventilation rates in schools in Ahmedabad by using carbon dioxide (CO2) exhaled by the occupants, using steady state mass balance method. The air flow in the naturally ventilated classrooms was between 61.5 l/s per person to 15.6 l/s per person. The air flow in air-conditioned classrooms was 0.9 l/s per person and 1.0 l/s per person. The air flow in naturally ventilated classrooms are excessively high, more than meeting prescribed rates, while air flow in air-conditioned classrooms is far below the prescribed outdoor air rate per person as provided in ASHRAE 62.1: 2016 [1] and in the Bureau of Indian Standards [2].

Susceptibility of Forests in the Northeastern USA to Nitrogen and Sulfur Deposition: Critical Load Exceedance and Forest Health

The objectives of this study were to assess susceptibility to acidification and nitrogen (N) saturation caused by atmospheric deposition to northeastern US forests, evaluate the benefits and shortcomings of making critical load assessments using regional data, and assess the relationship between expected risk (exceedance) and forest health. We calculated the critical loads of nutrient N and of sulfur (S) + N using the steady-state mass balance method at >4,000 regional and national vegetation and soil monitoring network plots in the northeastern USA. Regional calculations of critical loads necessitate use of soil maps which provide a range for each soil characteristic resulting in a broad range of critical load of S + N and exceedance values. For the scenario most representative of regional conditions, over 80 % of the critical loads fell into the range of 850–2050 eq ha−1 yr−1; at 45 % of the plots, deposition exceeded the critical load. In contrast, the critical load for nutrient N, 200–300 eq ha−1 yr−1, was lower. Site measurements, especially to estimate soil weathering, would increase the certainty of the critical load. We observed significant negative correlations between critical load exceedance and growth (17 species) and crown density (4 species); we observed significant positive correlations of exceedance with declining vigor (four species), with crown dieback (six species) and crown transparency (seven species). Among the species which demonstrate the most significant detrimental responses to atmospheric deposition are balsam fir, red spruce, quaking aspen, and paper birch. These results indicate that significant detrimental responses to atmospheric deposition are being observed across the northeastern USA.

Simultaneous Assessment of Deposition Effects of Base Cations, Sulfur, and Nitrogen Using an Extended Critical Load Function for Acidification

Base cations (BC) play an important role to prevent soil acidification. In certain acid sensitive areas, such as China, BC deposition is high and a considerable fraction is of anthropogenic origin. BC deposition might decrease in the future with the implementation of air pollution control measures. The effect of changes in BC deposition, however, has seldom been considered in critical load calculations based on the steady-state mass balance (SSMB) method. In order to better quantify the importance of the BC deposition for acid deposition mitigation policy, an extension of the SSMB method for critical load calculation for soil acidification is presented. The BC deposition is taken into account as a variable along with sulfur (S) and nitrogen (N) deposition, creating an S-N-BC critical load function. As a case study, critical loads of S and N for the Tie Shan Ping catchment in Chongqing in southwest China under variable BC deposition were calculated. Results indicate that abatement of BC deposition has significant impact on the critical loads of S and N. A 75% reduction in BC of assumed anthropogenic origin decreases the critical loads of acids by 58%. The current deposition does not exceed the critical loads, but if BC deposition from anthropogenic sources was controlled, then the exceedance would be considerable. Uncertainty analysis show that the size of the BC deposition of natural origin is the single parameter contributing the most to the steady-state S and N critical load. The extended critical load function can be used by policy makers to set more reasonable acidity control strategies in the future. The method also highlights for policymakers the "competition" between emission control of particulate matter driven by human health targets and potential increase of net acid load from such measures.

Critical Loads for Cd and Pb in the Province of Bologna

Atmospheric deposition represents a significant source of heavy metals entering soil and aquatic ecosystems. The evaluation of their vulnerability can be carried out by the Critical Load criterion. In this work we focus the attention on the terrestrial ecosystems in the Province of Bologna, estimating the maximum tolerable load of cadmium and lead they are able to bear without sustain the occurrence of harmful ecotoxicological effects. To this aim the Steady-State Mass Balance method is applied on a small scale (10 x 10 Km EMEP grids) and the more suitable approach to define critical limits for the Province condition, effect-base or stand-still, is discussed. The opportunity of simplifying the input data collection is also considered, trying to deduce soil properties from geological information. Finally, the environmental risk due to the present deposition of Pb and Cd on provincial soils is described as exceedances over the critical loads.

Simultaneous Determination of Oxygen Consumption Rate and Volumetric Oxygen Transfer Coefficient in Pneumatically Agitated Bioreactors

A new approach is proposed for the simultaneous determination of the volumetric oxygen transfer coefficient (KLa) and the oxygen uptake rate (OUR) in bioreactors. The methodology is based on modifications of the classical dynamic gassing-in method and the steady-state mass balance method for obtaining the values KLa and OUR, respectively. A polarographic dissolved oxygen electrode is used to monitor the oxygen concentration during a switch of aeration gas composition. The flow rate of the gas phase is not altered so that the hydrodynamics of the bioreactor are not affected during the measurement. Data obtained with this method are compared with the classical methods to show that the proposed technique is robust and reproducible. At a 95% confidence level, the proposed method produced results that were statistically identical to data obtained with the traditional methods. The proposed technique was reproducible to within 4% of the mean value at a 95% confidence level. The proposed method was further proved...

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

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

Deriving critical loads for the Agra region in India

A steady state mass balance (SMB) method was used to calculate the critical load of S and N for soil. The present load of sulphur (160.6 Eq ha−1 year−1), nitrogen (49.6 Eq ha−1 year−1) and ammonium (172.4 Eq ha−1 year−1) were calculated from wet and dry depositions collected from the Agra region. The values of the critical load of S and N for soil with respect to Cenchrus ciliaris (Anjan grass) were 309.2 and 381.8 Eq ha−1 year−1, respectively. The present loads are lower than the critical loads in this region. The critical loads calculated by the SMB method from the experimental data are in agreement with the results obtained from the RAINS-Asia model for this region.

Assessment of critical loads in liuzhou, China using static and dynamic models

The project Comprehensive Control and Demonstration for Acid Deposition in Liuzbou area is a national key project in the 8th Five-year-plan, and the study on critical loads will provide scientific and quantitative accordance for formulating control strategy. In this paper, critical loads of acid deposition to soil in Lirzhou area, China, were calculated using the Steady State Mass Balance method (SMB and PROFILE) and dynamic modeling methods(MAGIC), based on data obtained from field investigations and physiochemical properties measured through experiments such as the organic content, cation exchange capacity, base saturation, sulfate adsorption capacity, gibbsite coefficient, biomass base cation uptake and selectivity coefficient for cations. Weathering rates necessary to calculate soil chemistry in applying SMB and MAGIC model were determined by computation with PROFILE using independent geophysical properties such as soil texture and mineralogy as the input data, or by the total soil base cation content correlation. The results have shown that the critical loads of acidity in this area are in the range of 0.7–6.0 keq ha−1 yr−1, indicating sulfur deposition should be cut down by 50–90 percent of the present level. The upper soil layer is the most sensitive. The maximum allowable deposition loading of this area is also presented in the paper.

The use of critical loads in emission reduction agreements in Europe

Critical loads have been used in the revision of the Sulphur Protocol of the Convention on Long Range Transboundary Air Pollution (LRTAP) of the United Nations Economic Commission for Europe (UN/ECE). Critical loads, i.e. maximum allowable depositions which do not increase the probability of damage to forest soils and surface waters, have been computed and mapped for Europe by means of the Steady-state Mass Balance Method, using national data and, if national data were unavailable, using a European database. Results show that areas with low critical loads are located mostly in northern and central Europe. The reduction of the excess of sulfur (S) deposition over critical loads was a starting point for negotiations leading to the Oslo Protocol on Further Reduction of Sulphur Emissions (the “Second Sulphur Protocol”). The new protocol protects about 81%, 86% and 90% of the ecosystems' area in 2000, 2005 and 2010, respectively. In addition, the total European area in which sulphur deposition exceeds critical loads by more than 500 eq ha−1 yr−1 will be reduced from about 19% in 1980 to practically zero in 2010. Besides these results, a methodology is presented which allows the combined assessment of the acidifying effects of S and N as well as the eutrophying effects of N deposition on ecosystems (so-called critical load functions and the protection isolines derived from them). This methodology is well suited to integrate ecosystem sensitivities into future negotiations on the reductions of nitrogen (N) compounds, taking into account present or anticipated S emissions.

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

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.