Showing papers on "Ecosystem published in 1974"

The export of nutrients and recovery of stable conditions following deforestation

Abstract: We report the effects of deforestation on the export of particulate matter, erodi- bility of the ecosystem, and the relative importance of dissolved substances and particulate matter in exported materials. The mature forested ecosystem is little affected by erosion, with an average annual particulate matter export of only 2.5 MT (metric tons) km-2 yr-1. Defor- estation and repression of growth for 3 yr increased export to a maximum of 38 MT km-2 yr-1, but the increase in export was exponential with rather minor increases in the first 2 yr after cutting and a sharp increase in the 3rd yr. This resulted because the ecosystem continued to exercise considerable control over erodibility for 2 yr after cutting without annual renewal of biotic regulation by primary productivity. Increases in particulate matter export are pri- marily due to increases in erodibility rather than increased flow rates. In the mature ecosystem, the average ratio of annual net export of dissolved substance to particulate matter is 2.3. Deforestation shifts this ratio to > 8.0 during the first 2 yr after cutting. This shift results because the export trends, for dissolved substances and particu- late matter following deforestation, are not synchronous. The first response to deforestation is mobilization of nutrients from the available nutrient and organic matter compartments and leakage in stream water. After 2 yr, particulate matter output rises sharply as biotic control of erodibility weakens, while dissolved substance export declines, probably because of diminu- tion of readily available nutrients stored within the system. This nonsynchrony, coupled with the action of natural species adapted to take advantage of the abundance of nutrients and water that results immediately after disturbance, may be considered as part of a homeostatic mechanism that allows rapid recovery of a forest ecosystem while minimizing the effects of erosion.

The Export of Nutrients and Recovery of Stable Conditions Following Deforestation at Hubbard Brook

Abstract: We report the effects of deforestation on the export of particulate matter, erodibility of the ecosystem, and the relative importance of dissolved substances and particulate matter in exported materials. The mature forested ecosystem is little affected by erosion, with an average annual particulate matter export of only 2.5 MT (metric tons) km—2 yr—1. Deforestation and repression of growth for 3 yr increased export to a maximum of 38 MT km—2 yr—1, but the increase in export was exponential with rather minor increases in the first 2 yr after cutting and a sharp increase in the 3rd yr. This resulted because the ecosystem continued to exercise considerable control over erodibility for 2 yr after cutting without annual renewal of biotic regulation by primary productivity. Increases in particulate matter export are primarily due to increases in erodibility rather than increased flow rates. In the mature ecosystem, the average ratio of annual net export of dissolved substance to particulate matter is 2.3. Deforestation shifts this ratio to >8.0 during the first 2 yr after cutting. This shift results because the export trends, for dissolved substances and particulate matter following deforestation, are not synchronous. The first response to deforestation is mobilization of nutrients from the available nutrient and organic matter compartments and leakage in stream water. After 2 yr, particulate matter output rises sharply as biotic control of erodibility weakens, while dissolved substance export declines, probably because of diminution of readily available nutrients stored within the system. This nonsynchrony, coupled with the action of natural species adapted to take advantage of the abundance of nutrients and water that results immediately after disturbance, may be considered as part of a homeostatic mechanism that allows rapid recovery of a forest ecosystem while minimizing the effects of erosion. Thus, following destruction of the vegetation, the ecosystem maintains a residual resistance to erosion and has a high potential for repair through successional productivity. Nutrient flux and erosion losses return to previous levels as the intrasystem aspects of the hydrologic—nutrient cycle interaction and erodibility are increasingly regulated by biotic factors. These results relative to stable conditions and their reestablishment following disturbance may have applicability to a wide range of terrestrial ecosystems.

Development of some lake ecosystems in tropical africa, with special reference to the invertebrates

Abstract: Summary 1. The flooding of a lake basin initiates a series of changes leading eventually to a more stable climax situation after some years. Sequential physical and chemical changes in the mud and water and related changes in the animal and plant populations of three types of tropical African lakes are considered. The giant man-made lakes, Kariba and Volta, both several thousand square kilometres in area, provide the bulk of the material for this review. Two other kinds of tropical lake, the annual storage-reservoirs like Jebel Aulia and Sennar in the Sudan, and natural lakes subject to periodic droughts, like Lake Chilwa in Central Africa, are also considered. Evidence is often patchy but suggests a number of generalizations regarding the course and causes of the developmental changes in these tropical ecosystems. 2. On the evidence available, the course of development appears to fall conveniently into two periods based on water level changes, the filling phase and the post-filling phase. The former is characterized by sudden appearances of organisms and explosive growths of animal and plant populations. This unstable behaviour, especially characteristic of tropical lakes, is associated with the destruction of old habitats and the creation of new ones, the increasing area and volume of the new lake environment and the introduction of materials to the system at the advancing shore-line. By the time that filling is complete, the situation has stabilized to a large extent and the ecosystem enters a new phase. 3. This post-filling phase is characterized by the development and exploitation of existing habitats. Examples considered here are: the development of the mud habitat under the influence of processes like sedimentation and beach formation; the development of submerged woodland as a habitat for bottom dwelling animals; the spread of rooted aquatic plants and their effect on the mud; and the role of fluctuation in water-level on the post-filling phase. All four phenomena result in a modification of the substrata originally flooded, in a way that directly effects the associated fauna and flora. Apart from influencing the first three processes, water-level fluctuations also result in an interaction between the aquatic and terrestrial ecosystems which brings about important changes in itself. 4. The relative importance of these two phases varies with the type of lake, filling-phase phenomena obviously dominating in the annual storage reservoirs while post-filling phase characteristics are fully expressed in the large lakes made by man. 5. In contrast to the development of temperate lake ecosystems, succession of species in these tropical examples is not so much interrupted by major annual temperature changes. In addition, both the course of succession and the climax communities achieved are different. This may be largely due to the more rapid decomposition of organic matter in the muds which has two main consequences. In the first place, extraneous organic material brought in to the system during flooding, is rapidly broken down. Early filling stages, therefore, are associated with anoxic conditions and development of conspicuous communities of algae and large aquatic plants. The result is an overlapping of what in temperate systems are two distinct episodes: the early extraneous and later self-contained systems. Secondly, the replacement of chironomids by an oligochaete climax in the mud as seen in temperate lakes does not normally occur, apparently because of the lack of accumulated organic material. The presence in Africa of the may-fly Povilla adusta, on the other hand, provides an extra stage in the colonization of submerged woodland, replacing the earlier chironomid communities.

Barrier Island Forest Ecosystem: Role of Meteorologic Nutrient Inputs

Abstract: The Sunken Forest, located on Fire Island, a barrier island in the Atlantic Ocean off Long Island, New York, is an ecosystem in which most of the basic cation input is in the form of salt spray. This meteorologic input is sufficient to compensate for the lack of certain nutrients in the highly weathered sandy soils. In other ecosystems these nutrients are generally supplied by weathering of soil particles. The compensatory effect of meteorologic input allows for primary production rates in the Sunken Forest similar to those of inland temperate forests.

Estimates of Above-Ground Biomass and Primary Productivity in a Missouri Forest

Abstract: For the ecologist, forest primary production and biomass have somewhat different connotations than they have for the forester. Ecologists are concerned with total forest primary production and biomass, whereas foresters, at least in the past, were concerned only with primary production of the merchantable portion of the forest (Ovington 1965). However, the forester's views have somewhat diversified as a result of the tremendous pressures put upon our remaining forests (Young 1968). They recognize that ecology is basic to forest land management and that all forest processes must be considered for optimization of forest productivity and biomass. Total dry matter production is considered to be a measure of the forest's efficiency to fix energy in all components of the ecosystem. Total dry matter production is also a measure of total energy input to the system with its subsequent dissipation of energy by respiring organisms. To maximize primary production and biomass accretion for fibre production, it is logical to consider all energy pathways of the ecosystem. The material presented in this paper is part of the data collected from June 1968 to June 1971 in order to gain some insight into ecosystem dynamics of an oak-hickory forest in central Missouri, U.S.A. Data are given for net primary productivity (NPP) and biomass of herbaceous vegetation, shrubs, saplings and trees. Root NPP and biomass are not considered here.

The Role of Birds in Nutrient Cycling in a Northern Hardwoods Ecosystem

Abstract: Birds collected from the forested watershed—ecosystems of the Hubbard Brook Experimental Forest in central New Hampshire were analyzed for Ca, N, P, S, K, Na, Mg, Fe, Zn, Cu, and Mn. The nutrients bound in avain biomass (mg/ha) were calculated and compared to the nutrient budgets for these watersheds. Although birds contain but a tiny percentage of the standing crop of nutrients, they contribute to nutrient flux by removing small quantities of nutrients through losses during migration. Their impact on the turnover and distribution of nutrients within ecosystems is probably small but requires further study. See full-text article at JSTOR

Community structure, modelling and simulation of the Cladophora ecosystem in the Baltic sea.

Abstract: Community structure, modelling and simulation of the Cladophora ecosystem in the Baltic sea.

Water in the nutrient cycle of a Papuan rain forest

Abstract: INTEGRATED ecosystem studies of nutrient cycling on a catchment basis1 for tropical rain forest areas are few2–4, but information on the effects of nutrient cycling in these ecosystems on soil development, hydrology, and variations in stream water quality is needed, since rain forested areas in many developing tropical countries are rapidly being cleared to provide agricultural land5.

Human impact on transportation and diversity in ecosystems. How far is extrapolation valid

Abstract: Firts International Congress of Ecology, Structure, functioning and management of ecosystems, 8-14 September 1974, The Hague : Primer Congreso Internacional de Ecologia, 8-14 de septiembre 1974, La Haya.-- 5 pages

Tropical Ecosystem Structure and Function

Abstract: Conventionally, an ecosystem is defined as an integrated set of biological components making up a biotic community plus its abiotic environment (Odum, 1953). The basic biotic components of an ecosystem include (a) producers—the photosynthetic organisms that convert solar energy into chemical energy, (b) consumers that serve as ecosystem regulators, and (c) decomposers that recycle finite material resources. These components, in turn, are composed of species populations. The differences that one observes among ecosystem types can be studied and interpreted in terms of the storages and flows associated with each component, the role that each component assumes in the overall maintenance of that ecosystem and the response of the system to various forcing functions.

Nitrogen Accumulation in Successions

Abstract: Nitrogen in ecosystems has been determined as a function of time of plant succession in the entire ecosystem, in its biomass, and in its soil alone.

Distribution of copper, lead, and zinc in selected components of a pond ecosystem

Abstract: Concentrations of copper, lead, and zinc in several components of an aquatic ecosystem were determined by atomic absorption spectrophotometry. Concentrations of all metals were found to be lowest in the water and greatest in the sediments and biota. No increase in the amount of metals could be associated with increasing trophic levels. Domestic ducks and tree leaves from the pond's perimeter contributed heavy metals to the pond ecosystem.

Carbon Flux through a Coral-Reef Ecosystem: a Conceptual Model

Abstract: The potential application of modeling techniques to sedimentological studies of modern carbonate environments is demonstrated by a suggested conceptual model of the carbon system in a coral-reef ecosystem. A graphic model is employed to delineate the locations and characteristics of carbon flow patterns in the reef ecosystem. Modeling is thought to be a valid tool of geological research which should be considered a necessary first step in studies of systems such as the one described. The given model is intended to stimulate discussion about the usefulness of modeling in geological investigations of coral reefs, particularly in identifying the geological priorities in coral-reef research. This model will also form the basis for future simulation analyses.

Ecosystem simulation through use of models of subsystem response structures

Abstract: Every system has specific kinds and levels of re sponses to conditions as they exist and change in the environment in which the system is immersed. Each response can be expressed quantitatively by a structure in N-dimensional space, where N refers to the number of different environmental factors which operate together to determine the level of that response, and each dimension represents one of the determinative environmental factors. Examination via this response structure of the relationship between environmental factor levels and the system's response permits analysis and modeling of the system's dynamics and allows accurate evaluation of its relationships to other systems. This paper in cludes examples of use of this approach in the modeling of the ecological processes of population growth, competition, predation, and evolution, and it presents a model of a simple hierarchical eco system. Suggestions are made concerning the utiliza tion of this analytical and heueristic approach to examine other, very different systems; brief examples from economics, public health, and social psychology are given.

Walker Branch Watershed: a study of terrestrial and aquatic system interaction

Abstract: In Environmental Sciences Division annual progress report for period ending September 30, 1973. Retention and transport of elements and materials in forested landscapes are being investigated in the Walker Branch Watershed project in order to better understand ecosystem function and assess the impact of controlled and accidental releases of elements to similar ecosystems. The project emphasizes interactions between the terrestrial and aquatic components of the watershed ecosystem and therefore concentrates research on the two dominant element carrier systems, water and biomass. Less than 5% of the total amount of elements cycling within a forest is lost to streams through water movement. A dominant mechanism for preventing greater loss of elements has been shown to be the dynamics of root death and decomposition, with microbial immobilization and subsequent plant uptake during new root growth. Precipitation which produces large increases in streamflow has been shown to be of overriding importance in the annual transport of water and elements from the landscape. Approximately 20% of the annual water loss on Walker Branch Watershed occurs during the week of peak annual discharge. Element concentrations in streamflow change during these storm periods according to the mobilities of elements, but transport in both dissolved and suspendedmore » form increases. The movement of suspended organic and inorganic material, which predominates at high discharge rates, accounts for the major transport to aquatic systems of many trace elements which are generally present in very low concentrations in dissolved form. Application of results from this watershed study was used to evaluate economic and environmental considerations associated with land disposal of nitraterich industrial effluents, using extant data from the Walker Branch project to provide less critical variables needed for construction of mathematical simulation models. These models predicted ecosystem stability and longevity before detrimental effects would be incurred due to effluent nitrate additions, and thus provided the basis for cost-benefit analysis of this disposal practice. (auth)« less

Dynamics of Playa lakes in the Texas High Plains. [correlation of ERTS-1 imagery signatures with water balance ecosystem and geology]

Abstract: This study shows that satellite imagery can be used for a census of the thousands of lake basins which commonly exist in semi-arid areas, and which sporadically contain water at various times of the year. Storm paths and runoff collected by such lake basins can also be closely monitored, the accuracy dependent on periodicity of the orbits and the size of the basins. Study of the relationships between spectral differences (obtained from ERTS-1 imagery) and the water balance ecosystem of the lake basins is in a preliminary stage. However, examination of ERTS-1 MSS frames show that Band 4 has the poorest tonal contrast in semi-arid West Texas, Band 5 is best for definition of vegetation, Band 6 is best for defining larger water areas, and Band 7 is best for counting small lake basins with water. Ground-truth studies reveal significant differences between test sites, the relative importance of which will be reflected by the hydrologic balance of each lake basin.

Morphological Studies of Two Pristigasterinae Larvae from Southern Brazil

Abstract: This study is a part of the Sardine Project SOL to investigate the spawning and early life history of the Brazilian sardine and its relatives, and includes beam-trawl samplings in Southern Brazil, from Cabo de Sao Tome (22°00′S) to Cabo de Sta. Marta Grande (28°35′S). The purpose is to demonstrate differences among very similar larvae and juveniles of clupeoid fishes. Even though the species studied may not be of direct commercial value, morphological and ecological studies of these fishes are necessary for an understanding of the interrelationships of the different forms and their place in the ecosystem. In this paper the larval stages of Pellona harroweri, (Fowler) and Chirocentrodon bleekerianus (Poey) are described and compared, with a discussion of the systematic status of the latter. Comments are also made about the position of Chirocentrodon within the family Clupeidae.