Showing papers in "Water Air and Soil Pollution in 1993"

Riverine Transport of Atmospheric Carbon: Sources, Global Typology and Budget

Abstract: Atmospheric C (TAC) is continuously transported by rivers at the continents’ surface as soil dissolved and particulate organic C (DOC, POC) and dissolved inorganic C (DIC) used in rock weathering reactions. Global typology of the C export rates (g.m-2.yr-1) for 14 river classes from tundra rivers to monsoon rivers is used to calculate global TAC flux to oceans estimated to 542 Tg.yr-1, of which 37% is as DOC, 18% as soil POC and 45% as DIC. TAC originates mostly from humid tropics (46%) and temperate forest and grassland (31%), compared to boreal forest (14%), savannah and sub-arid regions (5%), and tundra (4%). Rivers also carry to oceans 80 Tg.yr-1 of POC and 137 TG.yr-1 of DIC originating from rock erosion. Permanent TAC storage on land is estimated to 52 Tg.yr-1 in lakes and 17 Tg.yr-1 in internal regions of the continents.

Boreal forests and tundra

Abstract: The circumpolar boreal biomes cover ca. 2 109 ha of the northern hemisphere and contain ca. 800 Pg C in biomass, detritus, soil, and peat C pools. Current estimates indicate that the biomes are presently a net C sink of 0.54 Pg C yr-1. Biomass, detritus and soil of forest ecosystems (including ca. 419 Pg peat) contain ca. 709 Pg C and sequester an estimated 0.7 Pg C yr-1. Tundra and polar regions store 60-100 Pg C and may recently have become a net source of 0.17 Pg C yr-1. Forest product C pools, including landfill C derived from forest biomass, store less than 3 Pg C but increase by 0.06 Pg C yr-1. The mechanisms responsible for the present boreal forest net sink are believed to be continuing responses to past changes in the environment, notably recovery from the little ice-age, changes in forest disturbance regimes, and in some regions, nutrient inputs from air pollution. Even in the absence of climate change, the C sink strength will likely be reduced and the biome could switch to a C source. The transient response of terrestrial C storage to climate change over the next century will likely be accompanied by large C exchanges with the atmosphere, although the long-term (equilibrium) changes in terrestrial C storage in future vegetation complexes remains uncertain. This transient response results from the interaction of many (often non-linear) processes whose impacts on future C cycles remain poorly quantified. Only a small part of the boreal biome is directly affected by forest management and options for mitigating climate change impacts on C storage are therefore limited but the potential for accelerating the atmospheric C release are high.

Heavy metals in street and house dust in Bahrain

Abstract: A total of 106 street and household dusts have been sampled throughout Bahrain and analyzed for Pb, Zn, Cd, Ni and Cr using the atomic absorption spectrophotometric method. The sampling sites were divided into seven categories, including the control site. Results showed that dust samples contained significant levels of the metals studied compared with the control values. The mean values for Pb, Zn, Cd, Ni and Cr in street dust were 697.2, 151.8, 72.0, 125.6 and 144.4 μg g−1 respectively, whereas for household dust they were 360.0, 64.4, 37.0, 110.2 and 144.7 μg g−1. These values suggest that motor vehicles form a major source of these metals in dust samples. The values of heavy metals in dust samples in this study were compared with values found in other investigations in various countries. With respect to Ni, elevated concentration could be attributed to smoke from the burning of Kuwait oil fields. Also correlations between metal levels in dust samples for all the metals were investigated. Our results show that heavy metal levels in various sites in Bahrain are similar, which indicate that Bahrain can be considered as one big urban center with high population and traffic density.

Seasonal and long-term temporal patterns in the chemistry of Adirondack lakes

Abstract: There is considerable interest in the recovery of surface waters from acidification by acidic deposition. The Adirondack Long-Term Monitoring (ALTM) program was established in 1982 to evaluate changes in the chemistry of 17 Adirondack lakes. The ALTM lakes exhibited relatively uniform concentrations of SO42−. Lake-to-lake variability in acid neutralizing capacity (ANC) was largely due to differences in the supply of basic cations (Ca2+, Mg2+, K+, Na+; CB) to drainage waters. Lakes in the western and southern Adirondacks showed elevated concentrations of NO3−, while lakes in the central and eastern Adirondacks had lower NO3− concentrations during both peak and base flow periods. The ALTM lakes exhibited seasonal variations in ANC. Lake ANC was maximum during the late summer or autumn, and lowest during spring snowmelt. In general Adirondack lakes with ANC near 100 Μeq L−1 during base flow periods may experience decreases in ANC to near or below 0 Μeq L−1 during high flow periods. The ALTM lakes have exhibited long-term temporal trends in water chemistry. Most lakes have demonstrated declining SO42−, consistent with decreases in SO2 emissions and SO42− in precipitation in the eastern U.S. Reductions in SO42− have not coincided with a recovery in ANC. Rather, ANC values have declined in some ALTM lakes. This pattern is most likely due to increasing concentrations of NO3− that occurred in most of the ALTM drainage lakes.

Phenols and nitrophenols as tropospheric pollutants: Emissions from automobile exhausts and phase transfer in the atmosphere

Abstract: Motor exhaust gas from an automobile motor, operated under stationary conditions with unleaded gasoline, was sampled with two different impinger bath methods. The samples were analyzed by gas chromatography/mass spectrometry (GC/MS) for phenol, cresols and nitrated phenols. Phenol and cresols were measured in the range of 80–220 nmol/L of exhaust gas from a noncatalyst engine, and nitrated phenols were found in the range of 9–36 nmol/L. A large reduction of total phenols down to 7% and less was observed when the engine was operated with a regulated three-way catalytic converter. The result of this study shows that exhaust gas sampling of phenols with alkaline aqueous impinger solutions leads to an underestimation of phenol emissions, since phenols are not stable under high-pH conditions.

The global terrestrial carbon cycle

Abstract: There is great uncertainty with regard to the future role of the terrestrial biosphere in the global carbon cycle. The uncertainty arises from both an inadequate understanding of current pools and fluxes as well as the potential effects of rising atmospheric concentrations of CO2 on natural ecosystems. Despite these limitations, a number of studies have estimated current and future patterns of terrestrial carbon storage. Future estimates focus on the effects of a climate change associated with a doubled atmospheric concentration of CO2. Available models for examining the dynamics of terrestrial carbon storage and the potential role of forest management and landuse practices on carbon conservation and sequestration are discussed.

Modeling the effects of climatic and co2 changes on grassland storage of soil C

Abstract: We present results from analyses of the sensitivity of global grassland ecosystems to modified climate and atmospheric CO2 levels. We assess 31 grassland sites from around the world under two different General Circulation Models (GCM) double CO2 climates. These grasslands are representative of mostly naturally occurring ecosystems, however, in many regions of the world, grasslands have been greatly modified by recent land use changes. In this paper we focus on the ecosystem dynamics of natural grasslands. The climate change results indicate that simulated soil C losses occur in all but one grassland ecoregion, ranging from 0 to 14% of current soil C levels for the surface 20 cm. The Eurasian grasslands lost the greatest amount of soil C (~1200 g C m-2) and the other temperate grasslands losses ranged from 0 to 1000 g C m-2, averaging approximately 350 g C m-2. The tropical grasslands and savannas lost the least amount of soil C per unit area ranging from no change to 300 g C m-2 losses, averaging approximately 70 g C m-2. Plant production varies according to modifications in rainfall under the altered climate and to altered nitrogen mineralization rates. The two GCM’s differed in predictions of rainfall with a doubling of CO2, and these differences are reflected in plant production. Soil decomposition rates responded most predictably to changes in temperature. Direct CO2 enhancement effects on decomposition and plant production tended to reduce the net impact of climate alterations alone.

Remediation of oil polluted soils: 1. effect of organic and inorganic nutrient supplements on the performance of maize ( Zea may L)

Abstract: Percentage germination, plant height, leaf area, relative dry matter yield, plant nutrient concentration, soil chemical characteristics and source/sink relationship were assessed for maize (Zea mays L TZ-SR-Y) planted in a soil polluted with 3% (v/w) crude oil or 0% (untreated soil), after remediation of soil with different organic (Poultry manure, peptone water, sawdust and yeast extract) and inorganic (NPK, KNO3, NH4H2PO4 and (NH4)2SO4) nutrient supplements applied 7 days after oil treatment. Germination of maize in oil polluted soil was not significantly affected by nutrient supplementation (P=0.05). Maize performance in terms of other studied parameters was highest in the oil polluted soil supplemented with poultry manure, and least in oil polluted soil supplemented with sawdust. Oil treatment correlated significantly with organic C, N, Na, Mg and ferrous in the soil (P=0.05) and with nutrient composition in maize plant tissues (P=0.05). For nutrient uptake, significant correlation was only established between soil N and plant N. Population of petroleum hydrocarbon tolerant microbes increased initially but decreased with time. There is every indication that nutrient supplementation of oil polluted soil especially with organic nutrient sources is beneficial for maize growth, because the C/N ratio is narrowed while the rate of biodegradation of oil and soil recovery is also enhanced. Poultry manure is recommended, however sawdust is not recommended since it tends to impose adverse effect by widening the C/N ratio in soil.

Tropical forests : their past, present, and potential future role in the terrestrial carbon budget

Abstract: In this paper we review results of research to summarize the state-of-knowledge of the past, present, and potential future roles of tropical forests in the global C cycle. In the pre-industrial period (ca. 1850), the flux from changes in tropical land use amounted to a small C source of about 0.06 Pg yr−1. By 1990, the C source had increased to 1.7 ± 0.5 Pg yr−1. The C pools in forest vegetation and soils in 1990 was estimated to be 159 Pg and 216 Pg, respectively. No concrete evidence is available for predicting how tropical forest ecosystems are likely to respond to CO2 enrichment and/or climate change. However, C sources from continuing deforestation are likely to overwhelm any change in C fluxes unless land management efforts become more aggressive. Future changes in land use under a “business as usual” scenario could release 41–77 Pg C over the next 60 yr. Carbon fluxes from losses in tropical forests may be lessened by aggressively pursued agricultural and forestry measures. These measures could reduce the magnitude of the tropical C source by 50 Pg by the year 2050. Policies to mitigate C losses must be multiple and concurrent, including reform of forestry, land tenure, and agricultural policies, forest protection, promotion of on-farm forestry, and establishment of plantations on non-forested lands. Policies should support improved agricultural productivity, especially replacing non-traditional slash-and-burn agriculture with more sustainable and appropriate approaches.

Assessment of C budget for grasslands and drylands of the world.

Abstract: Intergovernmental Panel on Climate Change (IPCC) estimates indicate that potential changes in seasonal rainfall and temperature patterns in central North America and the African Sahel will have a greater impact on biological response (such as plant production and biogeochemical cycling) and feedback to climate than changes in the overall amount of annual rainfall. Simulation of grassland and dryland ecosystem responses to climate and CO2 changes demonstrates the sensitivity of plant productivity and soil C storage to projected changes in precipitation, temperature and atmospheric CO2. Using three different land cover projections, changes in C levels in the grassland and dryland regions from 1800 to 1990 were estimated to be -13.2, -25.5 and -14.7 Pg, i.e., a net source of C due to land cover removal resulting from cropland conversion. Projections into the future based on a double-CO2 climate including climate-driven shifts in biome areas by the year 2040 resulted in a net sink of +5.6, +27.4 and +26.8 Pg, respectively, based upon sustainable grassland management. The increase in C storage resulted mainly from an increase in area for the warm grassland sub-biome, together with increased soil organic matter. Preliminary modeling estimates of soil C losses due to 50 yr of regressive land management in these grassland and dryland ecoregions result in a 11 Pg loss relative to current conditions, and a potential loss of 37 Pg during a 50 yr period relative to sustainable land-use practices, an average source of 0.7 Pg C yr-1. Estimates of the cost of a 20 yr rehabilitation program are 5 to 8 x 109 US$ yr-1, for a C sequestering cost of approximately 10 US$ per tC.

Review of impact of heavy metals on stream invertebrates with special emphasis on acid conditions

Abstract: Studies of the accumulation and toxicity of Cd, Zn, Fe, Pb and Cu under acid conditions to stream invertebrates are reviewed. The influence of pH on metal speciation decreases in the following order: Cu > Pb > Cd > Zn. The free metal ion is one of the most toxic species and is generally taken up directly from the water by organisms. The role of food in the uptake of metals depends mainly on feeding habits of the species, body size, life span and duration of the exposure. Surface adsorption can be regarded as a form of metal ‘uptake’ which increases at high pH. Biomagnification of metals along aquatic trophic food chains has not been proved for many metals. Toxicity of Cd, Fe, Zn and Pb increases at low pH, however not for all invertebrates. More knowledge is needed concerning sublethal effects of metals on invertebrates at different pH values and uptake, bioconcentration and biomagnification of metals at different pH values. Future studies should include experiments in artificial streams or in the field instead of short term tests and simple recording of field data.

Forest Sector Carbon Offset Projects: Near-Term Opportunities to Mitigate Greenhouse Gas Emissions

Abstract: The Framework Convention on Climate Change separately recognizes sources and sinks of greenhouse gases and provides incentives to establish C offset projects to help meet the goal of stabilizing emissions. Forest systems provide multiple opportunities to offset or stabilize greenhouse emissions through a reduction in deforestation (C sources), expansion of existing forests (CO2 sinks) or production of biofuels (offset fossil fuel combustion). Attributes and dimensions of eight forest-sector C offset projects, established over the past three years, were examined. The projects, mostly established or sponsored by US or European electric utilities, propose to conserve/sequester over 30 x 106 Mg C in forest systems at an initial cost of $1 to 30 Mg C. Given the relative novelty and complexity of forest sector C offset projects, a number of biogeochemical, institutional, socio-economic, monitoring, and regulatory issues merit analysis before the long-term potential and cost effectiveness of this greenhouse gas stabilization approach can be determined.

Trace metals in roof runoff

Abstract: In this paper we present the concentration of heavy metals (Cd, Cu, Pb, Zn) in runoff from five different roofs (tar felt, pantiles, asbestos cement, Zn sheet, gravel) during two rainfall events. The heavy metal load of roof runoff is assessed and the different processes influencing the fate of heavy metals on roof surfaces and in roof runoff are discussed. The extent of contamination with heavy metals of runoff from different roofing material has the following sequence: zinc sheet>tar felt>pantiles>asbestos cement>gravel. The hazard of infiltration of roof runoff with respect to heavy metals is discussed by comparison with concentrations in rain.

ALKALINITY GENERATION BY Fe(III) REDUCTION VERSUS SULFATE REDUCTION IN WETLANDS CONSTRUCTED FOR ACID MINE DRAINAGE TREATMENT

Abstract: Despite the widespread use of wetlands for acid mine drainage (AMD) treatment, alkalinity generating mechanisms in wetlands and their abiotic and biotic controls are poorly understood. While both dissimilatory sulfate reduction and Fe(III) reduction are alkalinity-generating mechanisms, only the former has been considered as important in wetlands constructed for AMD treatment. This study was conducted to determine the extent to which Fe(III) reduction occurs and the extent to which sulfate reduction versus Fe(III) reduction contributes to alkalinity generation in 5 wetlands constructed with different organic substrates (Sphagnum peat with limestone and fertilizer, Sphagnum peat, sawdust, straw/ manure, mushroom compost) that had been exposed to the same quality and quantity of AMD for 18–22 months. These substrates had Fe oxyhydroxide concentrations of 250–810 μmol Fe g−1 dry substrate. Flasks containing 100 g of wet substrate along with either 150 mL of wetland water or 130 mL of wetland water and 20 mL of 37 % formalin were incubated at 4 °C in January and 25 °C in May. On days 0, 2, 4, 8, 12 and 16, the slurry mixtures were analyzed for concentrations of H+, Fe2+ and SO42−. The bulk of the evidence indicates that for all except the mushroom compost wetland, especially at 25 °C, biologically-mediated Fe(II) reduction occurred and generated alkalinity. However, in none of the wetlands, regardless of incubation temperature, was there evidence to support net biological sulfate reduction or its attendant alkalinity generation. Sulfate reduction and concurrent Fe(III) oxyhydroxide accumulation may be important in the initial stages of wetland treatment of AMD, both contributing to effective Fe retention. However, as Fe(III) oxyhydroxides accumulate over time, Fe(III) reduction could lead not only to decreased Fe retention, but also to the potential net release of Fe from the wetland.

Saharan dust and the atmospheric inputs of elements and alkalinity to mediterranean ecosystems

Abstract: Saharan dust delivered by so-called ‘red rains’ strongly influences precipitation chemistry in the Mediterranean region We show here that at rural sites in eastern Spain, red rains have much higher ion concentrations than non-red rains, and they account for up to 50% of the mean annual input of dissolved elements in bulk precipitation, though they make up only a minor part of the annual rainfall The mean annual input of alkalinity in red rains is enough to neutralize the input of free acidity in acidic precipitation Transport of Saharan dust is thus a major ecological force in Mediterranean ecosystems through its effects on the acid neutralizing capacity of the atmosphere and the atmospheric deposition of elements

Ligand effect on the adsorption of heavy metals: The sulfate — Cadmium — Goethite case

Abstract: Complexing ligands may alter the adsorption behaviour of heavy metals compared to a ligand free system, either by changes in solution speciation, or by interactions at the adsorbing mineral surface. In this paper the effect of sulfate on the adsorption of cadmium onto goethite has been studied. Adsorption experiments under defined conditions revealed the following effects: Cadmium adsorption from sulfate containing solutions by goethite was higher than from pure NaNO3-solutions. Simultaneously sulfate adsorption increased, indicating synergic effects. Increasing the ionic strength of the metal-sulfate solutions caused a decrease both in heavy metal and in sulfate adsorption. Model calculations on simultaneous adsorption of cadmium and sulfate lead to the following conclusions: 1.) Sulfate adsorption reduces the surface potential so that the surface becomes more attractive to heavy metals. 2.) In addition, new, so called ternary surface complexes (SOCd+-SO4 2−) between reactive surface sites, heavy metals and sulfate-anions must be assumed in order to get agreement between observed and calculated effects.

Chemical characteristics and temporal trends in eight streams of the Catskill Mountains, New York

Abstract: Discharge to concentration relationships for eight streams studied by the U.S. Geological Survey (USGS) as part of the U.S. Environmental Protection Agency's (U.S. EPA) Long-Term Monitoring Project (1983–89) indicate acidification of some streams by H2SO4 and HNO3 in atmospheric deposition and by organic acids in soils. Concentrations of major ions in precipitation were similar to those reported at other sites in the northeastern United States. Average concentrations of SO4 2− and NO3 − were similar among streams, but base cation concentrations differed widely, and these differences paralleled the differences in acid neutralizing capacity (ANC). Baseflow ANC is not a reliable predictor of stream acidity at high flow; some streams with high baseflow ANC (>150 Μeq L−1) declined to near zero ANC at high flow, and one stream with low baseflow ANC (<50 Μeq L−1) did not approach zero ANC as flow increased. Episodic decreases in ANC and pH during peak flows were associated with increased concentrations of NO3 − and dissolved organic carbon (DOC). Aluminum concentrations exceeding 300 Μg L−1 were observed during peak flows in headwater streams of the Neversink River and Rondout Creek. Seasonal Kendall Tau tests for temporal trends indicate that SO4 2− concentrations in streamwater generally decreased and NO3 − concentrations increased during the period 1983–1989. Combined acid anion concentrations (SO4 2− + NO3 −) were generally unchanged throughout the period of record, indicating both that the status of these streams with respect to acidic deposition is unchanged, and that NO3 − is gradually replacing SO4 2− as the dominant acid anion in the Catskill streams.

Agricultural sources and sinks of carbon

Abstract: Most existing agricultural lands have been in production for sufficiently long periods that C inputs and outputs are nearly balanced and they are neither a major source nor sink of atmospheric C. As population increases, food requirements and the need for more crop land increase accordingly. An annual conversion of previously uncultivated lands up to 1.5 x 107 hectares may be expected. It is this new agricultural land which suffers the greatest losses of C during and subsequent to its conversion. The primary focus for analysis of future C fluxes in agroecosystems needs to be on current changes in land use and management as well as on direct effects of CO2 and climate change. A valid assessment of C pools and fluxes in agroecosystems requires a global soils data base and comprehensive information on land use and management practices. A comprehensive effort to assemble and analyze this information is urgently needed.

Vegetation redistribution: A possible biosphere source of CO2 during climatic change

Abstract: A new biogeographic model, MAPSS, predicts changes in vegetation leaf area index (LAI), site water balance and runoff, as well as changes in Biome boundaries. Potential scenarios of equilibrium vegetation redistribution under 2 x CO2 climate from five different General Circulation Models (GCMs) are presented. In general, large spatial shifts in temperate and boreal vegetation are predicted under the different scenarios; while, tropical vegetation boundaries are predicted (with one exception) to experience minor distribution contractions. Maps of predicted changes in forest LAI imply drought-induced losses of biomass over most forested regions, even in the tropics. Regional patterns of forest decline and dieback are surprisingly consistent among the five GCM scenarios, given the general lack of consistency in predicted changes in regional precipitation patterns. Two factors contribute to the consistency among the GCMs of the regional ecological impacts of climatic change: 1) regional, temperature-induced increases in potential evapotranspiration (PET) tend to more than offset regional increases in precipitation; and, 2) the unchanging background interplay between the general circulation and the continental margins and mountain ranges produces a fairly stable pattern of regionally specific sensitivity to climatic change. Two areas exhibiting among the greatest sensitivity to drought-induced forest decline are eastern North America and eastern Europe to western Russia. Drought-induced vegetation decline (losses of LAI), predicted under all GCM scenarios, will release CO2 to the atmosphere; while, expansion of forests at high latitudes will sequester CO2. The imbalance in these two rate processes could produce a large, transient pulse of CO2 to the atmosphere.

Toxic effect of landfill leachate on microalgae

Abstract: Leachates from two landfills, namely Junk Bay (JB) and Gin Drinkers' Bay (GDB), were assessed for their acute toxicity using four green algal species, Chlorella pyrenoidosa, C. vulgaris, Scenedesmus sp. and Dunaliella tertiolecta. JB leachate was more toxic to the four algal species tested than leachate from GDB landfill. The growth rates of all four species in 50% JB leachate, and two species (C. vulgaris and D. tertiolecta) in 50% GDB leachate were significantly lower (P<0.05) than those in the control (Bristol Medium only). Values of 96h-EC50 of JB leachate for all four species were lower than those of GDB. The high contents of ammoniacal-nitrogen and organic compounds (such as volatile fatty acids) seemed to be the factors governing the toxicity of leachate on algae. There were differential sensitivities to leachate exhibited by the tested algal species. Susceptibility to leachates in terms of cell number were in the ascending order of C. pyrenoidosa, Scenedesmus sp., C. vulgaris and D. tertiolecta.

Forest Management and Carbon Storage: An Analysis of 12 Key Forest Nations

Abstract: Forests of the world sequester and conserve more C than all other terrestrial ecosystems and account for 90% of the annual C flux between the atmosphere and the Earth’s land surface. Preliminary estimates indicate that forest and agroforest management practices throughout the world can enhance the capability of forests to sequester C and reduce accumulation of greenhouse gases in the atmosphere. Yet of the 3600 x 106 ha of forests in the world today, only about 10% (350 x 106 ha) are actively managed. The impetus to expand lands managed for forestry or agroforestry purposes lies primarily with nations having forest resources. In late 1990, an assessment was initiated to evaluate the biological potential and initial site costs of managed forest and agroforest systems to sequester C. Within the assessment, 12 key forested nations were the focus of a special analysis: Argentina, Australia, Brazil, Canada, China, Germany, India, Malaysia, Mexico, South Africa, former USSR, and USA. These nations contain 59% of the world’s natural forests and are representative of the world’s boreal, temperate, and tropical forest biomes. Assessment results indicate that though the world’s forests are contained in 138 nations, a subset of key nations, such as the 12 selected for this analysis, can significantly contribute to the global capability to sequester C through managed tree crops. Collectively, the 12 nations are estimated to have the potential to store 25.7 Pg C, once expanded levels of practices such as reforestation, afforestation, natural regeneration and agroforestry are implemented and maintained. Initial site costs based upon establishment costs for management practices are less than US$33/Mg C.

Nitrate assimilation and biomass production in Sesamum indicuml. Seedlings in a lead enriched environment

Abstract: Seed germination was delayed and seedling growth inhibited by 0.04 to 1.9 mM Pb+2 in Sesamum indicum L. var HT-I. In root, shoot and leaf Pb+2 accumulation increased with increasing Pb+2 concentration in the nutrient solution. In root and leaf tissues in vivo and in vitro nitrate reductase activity was inhibited significantly which was well correlated with the concentration of Pb+2 supplied and its accumulation in the plant parts. The inhibition of the NR enzyme activity could be, however, reversed by simultaneous treatment of Sesamum seedlings with K2HPO4, CaCl2 and KNO3 dissolved in nutrient solution. Total organic N and soluble protein of roots and shoots/leaves, on the other hand, increased with increasing concentration of Pb+2 while the same treatment caused a decrease in the N content of cotyledons. It appears therefore, that the increase in N and protein in the roots, shoots/leaves may be a result of increased translocation of N from the cotyledons to the roots and shoots/leaves during early seedling growth in a Pb+2 enriched environment.

Potential for carbon sequestration in the drylands

Abstract: Non-forested drylands occupy 43% of the world’s land surface yet they are not currently regarded as important in sequestering carbon due to overuse and poor management. Seventy percent of drylands have already undergone moderate to severe desertification and an additional 3.5% drops out of economic production each year. Reversing the trend towards desertification through cultivation of halophytes on saline lands, revegetation of degraded rangelands and other innovative conservation measures could result in net C sequestration in dryland soils of 0.5-1.0 Gt yr-1 at a cost of $10–18 t-1 C, based on a 100 yr scenario. Investment in anti-desertification measures in the world’s drylands appears to be an economical method to mitigate CO2 buildup in the atmosphere while accomplishing a major international objective of restoring dryland productivity.

Carbon trends of productive temperate forests of the coterminous United States

Abstract: Carbon trends of U. S. timberlands reflect past and current harvesting patterns and forest growth. Using periodic forest inventory data coupled with the Carbon Budget Model, we estimate C inventory from 1952 to the present, and project future trends through 2070. Two sets of projections are presented, one based on economically derived harvest levels and the other assuming no harvests after 1990. Productive forests sequester an average of 250 Tg C yr-1 from 1952-1987, but projections under expected harvests assuming no changes in growing conditions indicate this rate will fall to 60 Tg C yr-1 from 1987 to at least 2050, and then become a C source by 2070. Carbon sequestered in products and landfills over the projection period average 75 Tg C yr-1. An estimated 328 Tg C yr-1 would be sequestered if harvesting ceased.

Effects of root exudates and humic substances on weathering kinetics

Abstract: The effect of complex natural organic ligands on the weathering kinetics of aluminum oxide was investigated in laboratory experiments. A peat-derived humic substance and root exudates obtained from ectomycorrhizal (Picea abies — Hebeloma crustuliniforme) and non-mycorrhizal Norway Spruce trees; and γ-Al2O3 were used as a model system. The experimental weathering rates are in accordance with a surface-controlled dissolution mechanism. The effect of the humic material on dissolution rates appears to depend on the degree of protonation of the humic (macro)molecules: we observed dissolution-enhancement or -inhibition at pH 3 and 4, respectively. Ectomycorrhizal exudates proved to be effective weathering agents at pH 4, as opposed to humic material and non-mycorrhizal exudates. Our results suggest that (i) the role of humic materials in mineral weathering and podzolization is different from what is commonly thought, and (ii) mineral weathering rates in the rhizosphere may be higher than in the bulk soil.

Average critical loads for nitrogen and sulfur and its use in acidification abatement policy in the Netherlands

Abstract: Atmospheric deposition of N and S on terrestrial and aquatic ecosystems causes effects induced by eutrophication and acidification. Effects of eutrophication include forest damage, NO3 pollution of groundwater and vegetation changes in forests, heathlands and surface waters due to an excess of N. Effects of acidification include forest damage, groundwater pollution, and loss of fish populations due to Al mobilization. Critical loads (deposition levels) for N and S on terrestrial and aquatic ecosystems in the Netherlands related to these effects have been derived by empirical data and steady-state acidification models. Critical loads of N generally vary between 500 and 1500 mol c ha−1 yr−1 for forests, heathlands and surface waters and between 1500 and 3600 for phreatic groundwaters. Critical loads of total acid (S and N) vary between 300 to 500 mol c ha−1 yr−1 for phreatic groundwaters and surface waters and between 1100 to 1700 mol ha−1 yr−1 for forests. On the basis of the various critical loads a deposition target for total acid of 1400 mol c ha−1 yr−1 has been set in the Netherlands from which the N input should be less than 1000 mol c ha−1 yr−1. This level, to be reached in the year 2010, implies an emission reduction of 80–90% in SO2, NO x and NH3 in the Netherlands and of about 30% in neighboring countries compared to 1980 emissions.

Contribution of Northern Forests to the Global C Cycle: Canada as a Case Study

Abstract: Boreal forests are exposed to periodic stand-replacing disturbances such as wildfire. Unchanging disturbance regimes in unmanaged forests result in an age-class structure in which the proportion of forest area is largest in the youngest age class and decreases exponentially in older age classes. The current (ca. 1970) age-class structure of Canadian forests contains a much smaller proportion of the forest area in each of the two youngest 20-yr age classes than in each of the next three age classes (i.e., the 40 to 99-yr age-classes). We hypothesize that more intensive disturbance regimes in the late 19th and early 20th centuries, compared to disturbances in the period 1920 to 1969, have resulted in this unusual age-class structure. The reduction in disturbance regimes has resulted in an increase of the average forest age and therefore an increase in total forest biomass carbon (C). This C sink is obtained without altering age-dependent growth or decomposition rates. If the average forest age of Canadian forests continues to increase, additional C sequestration of forests, (i.e., the C sink strength) will diminish. This result of a C sink in Canadian forest ecosystems is supported by more detailed C budget calculations for the year 1986.

The impact of cultivation on carbon fluxes in woody savannas of Southern Africa

Abstract: The rapid transition from miombo woodland and savanna to maize-based agriculture in Southern Africa results in a near universal loss of total system and biomass carbon. Forests and savannas occupy approximately 3.1 million km2 in southern Africa. Two natural ecosystems, a miombo woodland (Zimbabwe) and a broadleafed dry savanna (South Africa), contained 48 and 94 Mg C ha-1, respectively. Clearing of the miombo and establishment of maize-based agriculture on a sandy Alfisol resulted in a decline in total soil organic carbon from 28 to as little as 9 Mg ha-1. This decline is not related to the annual aboveground productivities which, in many cases is greater in the cropping system than in the savanna or forest. Severe declines in total soil organic matter resulting from shifting cultivation were also observed in coastal Mozambique. The CENTURY plant/soil simulation model was used to simulate long-term carbon dynamics a miombo woodland and maize-based cropping system in Marondera, Zimbabwe. The miombo woodland continues to accumulate total system C but shifting cultivation and commercial cultivation of maize result in annual carbon losses of 0.15 and 0.14 Mg ha-1 yr-1. Increases in temperature (2° C) accompanied by 25% increases in photosynthetic efficiency did not effect the decline in total system carbon, however, improved organic matter management within the agroecosystem reduced the losses in total system carbon within the agroecosystem by 57% under the climate change scenario.

Effect of crude oil on gas exchange functions of Juncus roemerianus and Spartina alterniflora

Abstract: The effect of crude oil on gas exchange functions of Juncus roemerianus and Spartina alterniflora, two important U.S. Gulf Coast plant species, were examined. Plants were exposed to petroleum hydrocarbons (Mexican Sour type) mixed with water at 4.4 mL L−1 (2 L m−2). Coating entire leaf with oil resulted in cessation of photosynthetic activity. Partial leaf exposure to oil resulted in net photosynthesis decrease in both species shortly after exposure. Net photosynthesis remained within 71 and 94% of control plants in J. roemerianus during the first four weeks of the experiment. In S. alterniflora, photosynthetic rates averaged between 53 to 80% of control plants during the same period. Four weeks following the partial oiling, net photosynthesis began to improve in both species. Partial oil coverage of leaves of both species resulted in reduction in normal photosynthetic activity with no lethal effects. By the end of the laboratory study, there was no significant reduction in production of new shoots or the overall growth of either species.

The Carbon Cycle and Global Forest Ecosystem

Abstract: Attempts to account for the fluxes by quantifying C sources and sinks have provided evidence of a missing C sink (Detwiler and Hall, 1988), which may be located somewhere in the temperate region of the northern hemisphere (Tans et al., 1990). Until recently, most estimates have concluded that the temperate forest is a small C source. Two recent papers (Sedjo, 1992; Kauppi et al., 1992) provided evidence that the temperate forests are substantial C sinks. This paper combines these earlier findings on temeperate forest carbon sequestration with a new estimate of the annual C releases due to tropical deforestation, 1.7 Gt, which is obtained using the FAO estimates of the rate of deforestation in the tropics over the decade of the 1980s and conservative estimates of C releases associated with this deforestation. Finally, to this is added the crude estimate of C export by the global river system found in Hall et al. (1992). Applying these estimates of the C sink function of both temperate and tropical forests to Detwiler and Hall’s alternative C budgets largely eliminates the “missing C” hypothesized by Detwiler and Hall, and Tans et al.