Abstract At biome-scale, terrestrial carbon uptake is controlled mainly by weather variability. Observational data from a global monitoring network indicate that the sensitivity of terrestrial carbon sequestration to mean annual temperature ( T ) breaks down at a threshold value of 16°C, above which terrestrial CO 2 fluxes are controlled by dryness rather than temperature. Here we show that since 1948 warming climate has moved the 16°C T latitudinal belt poleward. Land surface area with T > 16°C and now subject to dryness control rather than temperature as the regulator of carbon uptake has increased by 6% and is expected to increase by at least another 8% by 2050. Most of the land area subjected to this warming is arid or semiarid with ecosystems that are highly vulnerable to drought and land degradation. In areas now dryness-controlled, net carbon uptake is ~27% lower than in areas in which both temperature and dryness ( T < 16°C) regulate plant productivity. This warming-induced extension of dryness-controlled areas may be triggering a positive feedback accelerating global warming. Continued increases in land area with T > 16°C has implications not only for positive feedback on climate change, but also for ecosystem integrity and land cover, particularly for pastoral populations in marginal lands.
Possible impacts of an 800-MW coal-fired power plant to be built near Atikokan, Ontario were evaluated. It is feared that the emissions of SO/sub 2/ will lead to the deposition of sulfuric acid and result in the acidification of freshwaters in nearby parks and wilderness areas. The most obvious biological effects of acidification are damages to populations of fish. Less conspicuous but no less severe damages also occur to other organisms. It appears that all trophic levels are affected: species numbers are reduced, biomasses are altered, and primary production and decomposition are impaired. Field experiments and laboratory experiments indicate that microbial activity is reduced and that the recycling of materials is greatly impeded at low pH. This may interfere with nutrient supplies to plants and decrease the microbial biomass available to higher trophic levels. Phytoplankton densities decrease in acidified lakes and there is a reduction in some species of macrophytes. On the other hand, Sphagnum and benthic filamentous algae greatly increase in acidified conditions. The total primary productivity of lakes and streams may actually increase because of such dense growths on the bottom. Zooplankton and benthic invertebrate communities become less complex as acidity increases. This may in part be due to reduced food supplies, but direct inhibition by H/sub 2/SO/sub 4/ has also been demonstrated. This removal of fish food organisms may exacerbate damage to fisheries, especially in the pH range of 5 to 6. When a lake loses all fish because of low pH, a few species of invertebrates may become very abundant. The salamanders Ambystoma jeffersonium and A. maculatum, sensitive to acidity below pH 7.0 and 5.0 respectively, are being eliminated from small ponds or temporary pools in the region around Ithaca, NY because of the impact of acid precipitation. Species of frogs in some lakes are also being eliminated because of acidification. (ERB)
Three watershed–lake systems of the Integrated Lake–Watershed Acidification Study (ILWAS) were investigated to determine the effects of atmospheric deposition on the chemical compositions of oligotrophic lakes in the Adirondack Mountains of New York. Using the principles of watershed mass balance and electroneutrality of solutions, the following conclusions were drawn. (1) Annually, about 90% of the NH 4 + and 50% of the NO 3 − from atmospheric deposition were retained in the systems. (2) In the Woods system, Cl − was in steady state with respect to atmospheric deposition although both Panther and Sagamore systems had net losses, indicating watershed sources of Cl − . (3) The losses of base cations from Panther and Sagamore were substantially greater than from the Woods system, reflecting the shallow soils of the latter. (4) The concentrations of SO 4 2− in the waters of the three systems were controlled by the atmospheric deposition of anthropogenic sulfur; in Woods and Panther, inputs (atmospheric deposition) equalled outputs (discharges from the lake outlets); in Sagamore, outputs exceeded inputs. (5) In 1978–80, concentrations of SO 4 2− were four to five times higher than historical values. These increased concentrations had caused either decreased alkalinities of surface waters or increased concentrations of base cations (Ca 2+ , Mg 2+ , Na + , K + ) or both. The former directly affects aquatic ecosystems; the latter directly affects terrestrial ecosystems because of increased rates of loss of the nutrients Ca, Mg, and K in the absence of resupply from primary weathering.
Over the past few decades the acidity of lakes and rivers has been increasing in several areas of the world. In southern Norway, western Sweden, the Canadian Shield, and the northeastern United States, acidification of fresh waters has become a major environmental problem. It has been clearly established that acid precipitation is the cause of decreasing pH levels in waters of the affected areas. Over most all of northern Europe, southern Scandinavia, and essentiallly all of the U.S. east of the Mississippi River, the mean annual H/sup +/ concentrations in precipitation, expressed as pH, are below 5.0. Furthermore, the regions affected by very acid precipitation (pH < 4.5) are rapidly expanding. The effects of acid precipitation on aquatic ecosystems depend primarily on the geology of the region, but also on the evaluation (orographic precipitation). The regions now known to be the most seriously affected are mountainous districts of southern Scandinavia and the northeastern United States which are located hundreds of kilometers from SO/sub 2/ and NO/sub x/ emissions sources. Regions of the United States which are potentially sensitive to acid inputs because of their geology and surface water alkalinity are also found in the western United States. Local acid precipitation problems are now known on the West Coast, and some lakes in the Puget Sound region appear to be acidified aquatic flora and fauna at all ecosystem levels are greatly impoverished in acidified freshwaters. The numbers of species are reduced and changes in the biomass of some groups of plants and animals have been observed. Decomposition of leaf litterand other organic substrates is hampered, nutrient recycling appears to be retarded, and nitrofication inhibited at pH levels frequently observed in acid-stressed waters.
The primary objective of this study is to estimate CO{sub 2} fluxes (F{sub CO{sub 2}}) under ambient and elevated atmospheric CO{sub 2}, and varying environmental conditions. Additional objectives are to: (2) quantify canopy conductance and evaluate the hypothesis that canopy conductance will not be altered by elevated atmospheric CO{sub 2} because reduction in leaf conductance is compensated by increased leaf area index, and (3) quantify the effect of elevated CO{sub 2} on aboveground production and apparent allocation of carbon below ground. In order to achieve the primary objective, the authors propose a modification to a methodology proposed earlier which emphasized leaf level measurements.
The study of root growth and development in soil has been intellectually and technically challenging. In response to concern about increasing levels of atmospheric carbon dioxide (CO2), resulting from increase in global energy use, the cycling of carbon has become the object of many intensive investigations.. Terrestrial ecosystems are a huge, natural biological scrubber for CO2 currently sequestering, directly from the atmosphere, about 22% of annual anthropogenic carbon emissions. It is assumed that a significant fraction of this carbon uptake goes into roots. Presently, there are no means by which root morphology, distribution, and mass can be measured without serious sampling artifacts that alter these properties. This is because the current methods are destructive and labor intensive. A non-invasive, imaging procedure for examining roots in situ would be a powerful tool quantifying subsurface storage, as well as for documenting changes in root structure. Preliminary results using a high frequency, 1.5 Ghz, impulse Ground Penetrating Radar (GPR) for nondestructive imaging of tree root systems in situ are presented. Two 3D reconstructed images taking advantage ofthe polarization effect are used to assess root morphology and dimensions. The constraints, limitations, and potential solutions for using GPR for tree root systems imaging and analysis are discussed.
One of the key uncertainties relative to future increases in atmospheric CO{sub 2} is the extent to which growth in future emissions will be accommodated by increased uptake by terrestrial vegetation, the so-called fertilization'' effect. Research on this issue is currently pursued by many research groups around the world, using various experimental protocols and devices. These range from leaf cuvettes to various types of enclosures and glass-houses to various types of open-field gas enrichment or fumigation systems. As research priorities move from crops to forests and natural ecosystems, these experimental devices tend to become large and enrichment gas (i.e., CO{sub 2}) requirements and costs become a major factor in experimental design. This paper considers the relative efficiencies of gas usage for different types of systems currently in use. One of these is the Free Air CO{sub 2} Enrichment System (FACE) designed and developed at Brookhaven National Laboratory (BNL). In this paper, we develop some nondimensional groups of parameters for the purpose of characterizing performance, i.e., enrichment gas usage. These nondimensional groups are then used as figures of merit and basically allow the required flow rates of CO{sub 2} to be predicted based on the geometry of the device, wind speed,more » and the incremental gas concentration desired. The parameters chosen to comprise a useful nondimensional group must not only have the correct dimensions, they must also represent an appropriate physical relationship.« less
The FACTS II (Aspen FACE) infrastructure including 12 FACE rings, a central control facility, a central CO{sub 2} and O{sub 3} receiving and storage area, a central O{sub 3} generation system, and a dispensing system for CO{sub 2} and O{sub 3} was completed in 1997. The FACE rings were planted with over 10,000 plants (aspen, birch and maple). The entire system was thoroughly tested for both CO{sub 2} and O{sub 3} and was shown to be effective in delivering elevated CO{sub 2} and/or O{sub 3} on demand and at predetermined set points. The NCASI support to date has been extremely helpful in matching support for federal grants.
Lakes Findley, Chester Morse and Sammamish, Washington, are characterized by one major outburst of phytoplankton productivity and biomass (mainly diatoms) with usually no or low fall activity. Vernal outbursts were often delayed in the monomictic lakes by inadequate light because of unfavorable climate and/or a lack of thermal stratification. Strong inhibition by light (probably u.v.) was observed in Findley such that average maximum productivity occurred at 10% of surface intensity while maximum was customarily at 60% in the other lakes. Annual productivity was 369C/m2 in Findley, 479C/m2 in Chester Morse and 1989C/m2 in Sammamish. The range in mean chlorophyll a content was 0.8 to 10 ug/,for the same lakes respectively. Although more than three fourths of the productivity in the four lakes was contributed by nanoplankton (5-50u), a tendency for increased contribution from netplankton was observed with increasing trophic state. In vitro experiments during all parts of the growing season show that nitrogen (N) and phosphorus (P) were simultaneously limiting productivity increase in the three lakes. Growth rate kinetics experiments showed increasing half-saturation constants for P (0.17 to 2.8pgP/A) for the natural phytoplankton progressing from oligotrophy to eutrophy. Growth rate models using these parameters were evaluated in Findley Lake subsequent to iceout in 1973. The best agreement was obtained with a model using light (with a function that included inhibition) N and P in contrast to several other combinations of those variables. Light was the most important factor and adaptation problems to low experimental light necessitated increasing the maximum growth rate by a factor of 10 in order to obtain the best agreement with in situ growth rate.
