Uncertainty analysis of critical loads for terrestrial ecosystems in Russia

The goal of this study is to give a comprehensive and quantitative estimation of the uncertainty of computed in different scale nitrogen (N) and sulphur (S) critical loads (CL) values for terrestrial ecosystems of the Northern Asia, European part and the North-Western regions of Russia. The CL values are used to set goals for future deposition rates of acidifying compounds so that the environment is protected. In this research CL values for terrestrial ecosystems are determined using the expert-modelling geoinformation system (EM GIS) approach. UNCSAM software package is used as the tool for uncertainty analysis. The analysis presented here focuses on the estimation and effect of the input source uncertainties and sensitivities on the CL values in various regions under study. In spite of the region, nitrogen uptake by vegetation, nitrogen leaching from terrestrial ecosystems and the difference between deposition and uptake by plants of base cations (BC) are the most influential factors for all terrestrial ecosystems of Russia.     

Assessing significant harm to terrestrial ecosystems from contaminated land

Abstract. Terrestrial ecosystem risk assessment remains in its infancy by comparison with the aquatic discipline, yet it is advancing quickly in response to increasing concerns surrounding soil quality and the sustainable use of soil. Several international frameworks have been developed during the last decade to aid decision-makers as the need for scientifically derived tools for determining ecological risk from land contamination has been recognized. From the regulatory viewpoint, the priority is establishing what to protect in order to prevent ecological harm. This is a complex issue requiring clear objectives in a risk assessment context. The most important factor in assessing ecological harm is whether or not ecosystem function is altered as a result of land contamination and, if it is, judging the significance. A consensus is developing that ecological risk assessment should aim to protect populations rather than individuals. This paper critically reviews recent developments in risk assessment for terrestrial ecosystems and land contamination in the UK, with emphasis on deriving a measure of ecological harm to assess ecosystem function. We seek to further justify the use of earthworms as a favoured indicator species for protecting ecological function. Guidance on how to measure harm in relation to ecological function is, however, still lacking.     

Parameters of the productivity of soil algae in terrestrial ecosystems

A review is presented of the recent state of the problem of soil algae productivity in terrestrial ecosystems on the basis of literature data and our own research. It is shown that the organic matter accumulated by soil algae is highly mobile. The following parameters were analyzed: the biological production, the time of the biomass turnover, and the rate of the algal organic matter renewal in the soil. The average monthly production of algae ranged from 0.9 to 765 g/m², the rate of the organic matter renewal ranged from 0.03 to 25.5 g/m² per day, and the time of the algal biomass renewal ranged from 0.1 to 7 days.     

Microclimate and moisture dynamics of wood decomposing in terrestrial ecosystems

The theoretical relationship between microclimate, temperature and moisture in decaying branchwood is considered and methods of expressing moisture content discussed. Field measurements were obtained over a 1-yr period. The annual pattern of branch temperature and moisture contents consisted of a cold wet winter period when branch moisture contents are at or above saturation, low temperatures and high rainfall prevent drying. When temperatures rise in spring the trend is for branches to begin gradually to dry. During the summer months moisture contents are not constant and vary considerably from day to day with fairly rapid drying following periods of wetting. Moisture contents only rarely fell below the fibre saturation point. With the approach of autumn and winter the overall trend is for a gradual increase in moisture content but with periods of slow drying occurring whilst temperatures are still high enough to allow this.     

Humus forms in terrestrial ecosystems: a framework to biodiversity

Humus forms are the seat of most biological transformations taking place in terrestrial ecosystems, being at the interface between plants, animals and microbes. The diversity of terrestrial humus forms (mor, moder and mull) can be attributed to the existence of different patterns (strategies) for the capture and use of resources by ecosystems, in ascending order of biodiversity and bioavailability. Arguments are found in the parallel development of humus forms and terrestrial ecosystems, in exclusion mechanisms between organisms living in different humus forms, and in palaeontological studies. The diversification of terrestrial life forms in the course of Earth history, concomitant with an improvement in resource availability due to the development of sedimentary layers at the surface of continents, may explain the successive appearance of more active humus forms enabling the co-existence of an increasing number of organisms. Contradictory reports about the relationships between biodiversity and stability of ecosystems can be explained by the existence of different belowground pathways making ecosystems more stable.     

Review of denitrification in tropical and subtropical soils of terrestrial ecosystems

Purpose

Denitrification has been extensively studied in soils from temperate zones in industrialized countries. However, few studies quantifying denitrification rates in soils from tropical and subtropical zones have been reported. Denitrification mechanisms in tropical/subtropical soils may be different from other soils due to their unique soil characteristics. The identification of denitrification in the area is crucial to understand the role of denitrification in the global nitrogen (N) cycle in terrestrial ecosystems and in the interaction between global environmental changes and ecosystem responses.

Materials and methods

We review the existing literature on microbially mediated denitrification in tropical/subtropical soils, attempting to provide a better understanding about and new research directions for denitrification in these regions.

Results and discussion

Tropical and subtropical soils might be characterized by generally lower denitrification capacity than temperate soils, with greater variability due to land use and management practices varying temporally and spatially. Factors that influence soil water content and the nature and rate of carbon (C) and N turnover are the landscape-scale and field-scale controls of denitrification. High redox potential in the field, which is mainly attributed to soil oxide enrichment, may be at least one critical edaphic variable responsible for slow denitrification rates in the humid tropical and subtropical soils. However, soil pH is not responsible for these slow denitrification rates. Organic C mineralization is more important than total N content and C/N in determining denitrification capacity in humid subtropical soils. There is increasing evidence that the ecological consequence of denitrification in tropical and subtropical soils may be different from that of temperate zones. Contribution of denitrification in tropical and subtropical regions to the global climate warming should be considered comprehensively since it could affect other greenhouse gases, such as methane (CH₄) and carbon dioxide (CO₂), and N deposition.

Conclusions

Tropical/subtropical soils have developed several N conservation strategies to prevent N losses via denitrification from the ecosystems. However, the mechanisms involved in the biogeochemical regulation of tropical and subtropical ecosystem responses to environmental changes are largely unknown. These works are important for accurately modeling denitrification and all other simultaneously operating N transformations.     

Carbon dioxide emissions and net primary production of Russian terrestrial ecosystems

 Determination of the C balance is of considerable importance when forecasting climate and environmental changes. Soil respiration and biological productivity of ecosystems (net primary production; NPP) are the basic components of the terrestrial C cycle. In this study, a previously made assessment of the annual CO₂ flux from Russian soils was improved upon. CO₂ emissions from Russian soils during the growing period were shown to represent, on average, 53–82% of the annual CO₂ flux from Russian soils. The total annual CO₂ flux from Russian soils was estimated at 4.50 Gt C (C source). The NPP of Russian ecosystems was estimated at 4.81 Gt C year^–1 (C sink). Our calculations showed values of CO₂ emissions and the C sink to be very close. This shows that, in general, terrestrial ecosystems are under steady state. Received: 1 December 1997     

Atmospheric deposition in maritime environments and its impact on terrestrial ecosystems

Seasalts are the dominant chemical constituents of precipitation in maritime regions. Dry deposition of these salts is also an important process and consequently, canopy interception by forest ecosystems greatly augments wet deposition. The separation of seasalt from non-seasalt sulphur is usually accomplished by reference to the concentration ratio of other major component ions of seawater, such as sodium-, chloride-, or magnesium-to sulphate. Biogenic sulphur, from the oceans or from terrestrial ecosystems is sometimes of importance in maritime regions. Seasalts, which dominate atmospheric deposition in maritime regions can induce short-term acidification in surface waters as a result of ion-exchange reactions following storm events. The results of one large storm in western Ireland in 1991 and the recovery process in a peat soil were clearly discernible in soil water analysis. The seasalt impact on acid mineral soils can be seen in the exchangeable sodium levels and the degree of base saturation of these soils.     

Effects of nitrogen deposition on the acidification of terrestrial and aquatic ecosystems

The concentration of ammonium and nitrate in precipitation has increased during this century. The deposition of N compounds (wet + dry) is reaching 30 to 40 kg ha^?1yr^?1 in many areas in Central Europe and above 20 kg in the southern parts of Scandinavia. In extreme situations throughfall data indicate depositions above 60 kg ha^?1yr^?1 in Central Europe and above 40 kg ha^?1yr^?1 in south Sweden. Very high depositions are observed on slopes at forest edges and adjacent to areas with animal farms and manure spreading. In areas with low N deposition almost all deposited N (>95%) will be absorbed in the tree canopies or in the soil. In areas with high deposition an increased outflow is observed which in some cases reach 10 to 15 kg ha-lyr-1. The increased output is an indication of N saturation of the ecosystem and it leads to acidification effects in soils, soilwater, groundwater and surface waters.     

Large predators and trophic cascades in terrestrial ecosystems of the western United States

Large predators potentially can help shape the structure and functioning of terrestrial ecosystems, yet strong evidence of top-down herbivore limitation has not been widely reported in the scientific literature. Herein we synthesize outcomes of recent tri-trophic cascades studies involving the presence and absence of large predators for five national parks in the western United States, including Olympic, Yosemite, Yellowstone, Zion, and Wind Cave. Historical observations by park biologists regarding woody browse species and recently compiled age structure data for deciduous trees indicate major impacts to woody plant communities by ungulates following the extirpation or displacement of large predators. Declines in long-term tree recruitment indexed additional effects to plant communities and ecological processes, as well as shifts towards alternative ecosystem states. The magnitude and consistency of vegetation impacts found within these five parks, in conjunction with other recent North American studies, indicate that broad changes to ecosystem processes and the lower trophic level may have occurred in other parts of the western United States where large predators have been extirpated or displaced. Thus, where ungulates have significantly altered native plant communities in the absence of large predators, restoration of native flora is urgently needed to recover former ecosystem services. Following the reintroduction of previously extirpated gray wolves Canis lupus into Yellowstone National Park, a spatially patchy recovery of woody browse species (e.g., aspen Populus tremuloides, willow Salix spp., cottonwood Populus spp.) has begun, indicating that large predator recovery may represent an important restoration strategy for ecosystems degraded by wild ungulates.     

Reduced carbon sequestration in terrestrial ecosystems under overcast skies compared to clear skies

There is still no consensus on the impact of cloud on terrestrial carbon sequestration. Nevertheless, the fraction of sky irradiance which is diffuse (fDIF) is close to half as a global annual average, owing mainly to the presence of clouds. Furthermore, as a consequence of human-induced perturbations, the occurrence and opacity of cloud is changing both regionally (due to deforestation and drainage) and globally (shortwave “solar” dimming). In this study, we quantify the impact of cloud on carbon assimilation at an unprecedented number of FLUXNET sites (38) and for six plant functional types (PFTs). We compare results from previously established empirical and statistical methods with novel land-surface and three-dimensional (3D) radiative-transfer (RT) simulations that take explicit account of diffuse sunlight. We record a much lower enhancement in canopy light-use efficiency (LUE) under diffuse sunlight relative to direct sunlight (factor 1.12–1.80) compared to previous authors (factors 2–3). Increased radiation-sharing, due to varied leaf orientation within the canopy, is the primary cause of LUE-enhancement rather than beam penetration within an open crown structure. Under cloud, we consistently record a decrease in primary productivity (≥10–40%) and an unequivocal decline in daily carbon sequestration (60–80%), owing to the dramatic reduction in total (direct plus diffuse) irradiance that occurs when clouds obscure the solar disk (≥60% attenuation). A cooling-induced reduction in ecosystem respiration offsets the decline in primary productivity by about one third.     

Interaction of acid rain and global changes: Effects on terrestrial and aquatic ecosystems

Both acid deposition and changes in the global atmosphere and climate affect terrestrial and aquatic ecosystems. In the atmosphere sulphate aerosols tend to increase haze, altering the global radiation balance. Increased nitrogen deposition to N-limited systems such as boreal forests results in increased growth and increased sequestration of atmospheric CO₂, slowing the increase in CO₂ levels in the atmosphere. Future reduction in S and N emissions may result in a trade-off -- better with respect to some effects of acid deposition and greenhouse warming, but worse with respect to others. Global warming may cause the incidence and severity of drought to increase. Mineralisation of N and oxidation of organic S compounds release pulses of SO₄, acid and Al to surface waters. Effects in lakes may include reduced deep water refugia for cold stenotherms, lower nutrient concentrations, and greater penetration of harmful UV radiation. Longer water renewal times cause declines in SO₄ and NO₃, due to increased in situ removal, but increases in base cations. The net result is increased internal alkalinity production. In areas characterised by cold winters, global warming may result in a major shift in hydrologic cycle, with snowmelt episodes occurring during the winter rather than the typical pattern of accumulation in the winter and melting in the spring. Increased storm frequency predicted for the future will cause increased frequency and severity of sea salt episodes in coastal regions. Predicting the interactions of regional and global environmental factors in the coming decades poses new challenges to scientists, managers and policy-makers.     

Changes in C storage by terrestrial ecosystems: How C-N interactions restrict responses to CO2 and temperature

A general model of ecosystem biogeochemistry was used to examine the responses of arctic tundra and temperate hardwood forests to a doubling of CO₂ concentration and to a 5°C increase in average growing season temperature. The amount of C stored in both ecosystems increased with both increased CO₂ and temperature. Under increased CO₂, the increase in C storage was due to increases in the C∶N ratio of both vegetation and soils. Under increased temperature, the increased C storage in the forest was due to a shift in N from soils (with low C∶N ratios) to vegetation (with high C∶N ratios). In the tundra, both a shift in N from soils to vegetation and an increase in C∶N ratios contributed to increased C storage under higher temperatures. Neither ecosystem sequestered N from external sources because the supply rate was low.     

Consistent responses of microbial C and N metabolic processes to elevated CO2 across global terrestrial ecosystems

Journal of Soils and Sediments - Elevated CO2 contributes greatly to global warming, playing a pivotal role in terrestrial ecosystem processes, in particular microbially regulated C and N cycling....     

SOCRATES—A simple model for predicting long-term changes in soil organic carbon in terrestrial ecosystems

The maintenance of soil organic carbon (SOC) in terrestrial ecosystems is critical for long-term productivity. Simulation models of SOC dynamics are valuable tools in predicting the impacts of climate on carbon storage and developing management strategies for the mitigation of greenhouse gas emissions, however, their utility is generally reduced due to need for specific data. The SOCRATES model is a simple process based representation of soil SOC dynamics in terrestrial ecosystems, which requires minimal data inputs and specifically designed to examine the impact of land use and land use change on soil carbon storage. SOCRATES was successful in predicting SOC change at eighteen long-term crop, pasture and forestry trials from North America, Europe and Australasia. These trials ranged from 8 to 86 years in duration, over a wide range of climates and soil types with annual changes in SOC ranging from −3.0 to 4.2%.     

The role of lysimeters in the development of our understanding of soil water and nutrient dynamics in ecosystems

This paper considers the development of lysimeters and their role in the evolution of our understanding of the dynamics of water and plant nutrients in ecosystems. Lysimeters are delineated volumes of soil. They can be divided into those filled with repacked soil, and those enclosing an undisturbed monolith. The original repacked lysimeter was developed to investigate the concept that all life stems from water, and is considered to be the first quantitative experiment in history. It focussed on the growth of a willow tree and how much of the increment was derived from the soil solids. From this start some 360 years ago lysimeters quickly contributed to the quantification of the transpiration stream and the differentiation of water loss by evaporation from the soil from loss via the leaves of plants. Chronologically, further development began about 210 years ago with the exploration of whether precipitation could account for all the water moving from the land to the oceans, and was the origin of springs. In part, this required a careful quantification of soil evaporation, runoff and deep drainage. This in turn led to the quantification of the soil water balance. As a result, we are able to predict indices, such as crop water use efficiency, drainage and irrigation requirements, contributions to stream flow, groundwater recharge and nutrient loss by leaching. Recognition that the quantification of drainage and leaching required soils of natural structure and profile integrity resulted in the building of the first monolith lysimeter and the development of ‘pan’ or ‘Ebermayer’ lysimeters. Improved technology allowed a better understanding of the role of soil in the regional water balance through the development of small diameter lysimeters that could be transported to a central location subject to the same climatic variables. In contrast, other technological changes allowed the impact of typical soil management operations carried out using regular machinery to be applied on field‐scale lysimeters. The contribution of the different types of lysimeter to the development of our understanding of soil use and management is considered.     

Compartmentalization of mercury in biotic components of terrestrial flood plain ecosystems adjacent to the South River AT Waynesboro,VA

Water, Air, & Soil Pollution - Aquatic Hg contamination extending more than 200 km along the South River, South Fork of the Shenandoah River, and Shenandoah River in western VA has been...     

Differential production of oxalate by mycorrhizal fungi in arid ecosystems

Oxalate crystals and elements binding to the surfaces of mycorrhizal fungal hyphae were examined using scanning electron microscopy coupled with X-ray analysis of elemental composition. Mycorrhizae from the arid zone vegetation types in southern California were examined including chaparral, riparian oak woodlands, coastal sage, grasslands, and deserts. Only mat-forming ectomycorrhizal hyphae, such as Hysterangium separabile, were found to produce oxalate crystals. None of the arbuscular mycorrhizal fungal hyphae (Glomus spp. and Acaulospora elegans) examined had crystal structures associated with them. The hyphae of Hysterangium separabile without crystals did not show the Ca peaks that were present when the crystals existed nor did the arbuscular mycorrhizal fungal hyphae have the Ca peaks. The elimination of arbuscular mycorrhizae using benomyl did not affect soil P or oxalate. These data indicate that there are some fundamental differences in chemical exudation between mycorrhizal fungi that could affect P uptake and cycling in arid ecosystems. Received: 7 December 1994     

Direct contribution by soil arthropods to nutrient availability through body and faecal nutrient content

Summary The direct contribution made by soil arthropods to nutrient dynamics was investigated in pine forests that differed in soil nutrient status. Nutrient concentrations (K⁺, Ca²⁺, Mg²⁺, PO ₄ ^3– , N, C) in the most abundant species and groups of arthropods in two Pinus nigra forests were compared, and distinct differences were found among taxonomic groups. In the rank order: collembolans, oribatides, isopods, diplopods, Ca²⁺ and Mg²⁺ concentrations increased, while N and C concentrations decreased. The nutrient concentrations in individuals of the same species but originating from the different forests were similar, except for the isopod Philoscia muscorum. The total and available nutrient concentrations in food and faeces of the collembolan Tomocerus minor and the isopod Philoscia muscorum were compared. The isopod faeces contained relatively less K⁺ and Mg²⁺, and more Ca²⁺, PO ₄ ^3– , and greater N availability, compared with the food material. The collembolan faeces showed a higher availability of all nutrients measured. The N species appeared to be changed by collembolans; their faeces contained high NO ₃ ^– concentrations, while their food contained relatively high concentrations of NH ₄ ⁺ . These findings were examined in relation to their significance for ecosystem functioning. It was concluded that about 12% of the total K⁺, PO ₄ ^3– , N and 2% of the Ca²⁺ in the organic layer was found in the mesofauna. It was calculated that faeces production by the collembolans resulted in a 2.4 times higher NO ₃ ^– availability in the forest floor.     

Dynamic aspects of nutrient requirements by intact plants

Abstract

When plant tissues are analyzed, the interpretation of the mineral composition depends on all the dynamic factors of mineral uptake, distribution, redistribution, and interactions. Each of these factors must be viewed in the proper perspective to insure a valid interpretation of the nutrient requirements of plants.

Since plant growth is dynamic, the factor which must be considered is the rate of nutrient supply to the rate of nutrient demand for growth. These rates vary throughout the life cycle of the plant.

In tissue analysis, the critical concentrations may vary throughout the plant depending on the plant part and nutrient element under consideration. Here, also, the dynamic factors should be considered to insure the proper applications of these critical concentrations.