You are looking at 41-50 of 102 articles
The Mississippi River, the longest in North America, is really two rivers geophysically. The volume is less, the slope steeper, the velocity greater, and the channel straighter in its upper portion than in its lower portion. Below the mouth of the Ohio River, the Mississippi meanders through a continental depression that it has slowly filled with sediment over many millennia. Some limnologists and hydrologists consider the transitional middle portion of the Mississippi, where the waters of its two greatest tributaries, the Missouri and Ohio rivers, join it, to comprise a third river, in terms of its behavioral patterns and stream and floodplain ecologies.
The Mississippi River humans have known, with its two or three distinct sections, is a relatively recent formation. The lower Mississippi only settled into its current formation following the last ice age and the dissipation of water released by receding glaciers. Much of the current river delta is newer still, having taken shape over the last three to five hundred years.
Within the lower section of the Mississippi are two subsections, the meander zone and the delta. Below Cape Girardeau, Missouri, the river passes through Crowley’s Ridge and enters the wide and flat alluvial plain. Here the river meanders in great loops, often doubling back on itself, forming cut offs that, if abandoned by the river, forming lakes. Until modern times, most of the plain, approximately 35,000 square miles, comprised a vast and rich—rich in terms of biomass production—ecological wetland sustained by annual Mississippi River floods that brought not just water, but fertile sediment—topsoil—gathered from across much of the continent. People thrived in the Mississippi River meander zone. Some of the most sophisticated indigenous cultures of North America emerged here. Between Natchez, Mississippi, and Baton Rouge, Louisiana, at Old River Control, the Mississippi begins to fork into distributary channels, the largest of which is the Atchafalaya River. The Mississippi River delta begins here, formed of river sediment accrued upon the continental shelf. In the delta the land is wetter, the ground water table is shallower. Closer to the sea, the water becomes brackish and patterns of river sediment distribution are shaped by ocean tides and waves. The delta is frequently buffeted by hurricanes.
Over the last century and a half people have transformed the lower Mississippi River, principally through the construction of levees and drainage canals that have effectively disconnected the river from the floodplain. The intention has been to dry the land adjacent to the river, to make it useful for agriculture and urban development. However, an unintended effect of flood control and wetland drainage has been to interfere with the flood-pulse process that sustained the lower valley ecology, and with the process of sediment distribution that built the delta and much of the Louisiana coastline. The seriousness of the delta’s deterioration has become especially apparent since Hurricane Katrina, and has moved conservation groups to action. They are pushing politicians and engineers to reconsider their approach to Mississippi River management.
David I. Stern
The environmental Kuznets curve (EKC) is a hypothesized relationship between environmental degradation and GDP per capita. In the early stages of economic growth, pollution emissions and other human impacts on the environment increase, but beyond some level of GDP per capita (which varies for different indicators), the trend reverses, so that at high income levels, economic growth leads to environmental improvement. This implies that environmental impacts or emissions per capita are an inverted U-shaped function of GDP per capita. The EKC has been the dominant approach among economists to modeling ambient pollution concentrations and aggregate emissions since Grossman and Krueger introduced it in 1991 and is even found in introductory economics textbooks. Despite this, the EKC was criticized almost from the start on statistical and policy grounds, and debate continues. While concentrations and also emissions of some local pollutants, such as sulfur dioxide, have clearly declined in developed countries in recent decades, evidence for other pollutants, such as carbon dioxide, is much weaker. Initially, many understood the EKC to imply that environmental problems might be due to a lack of sufficient economic development, rather than the reverse, as was conventionally thought. This alarmed others because a simplistic policy prescription based on this idea, while perhaps addressing some issues like deforestation or local air pollution, could exacerbate environmental problems like climate change. Additionally, many of the econometric studies that supported the EKC were found to be statistically fragile. Some more recent research integrates the EKC with alternative approaches and finds that the relation between environmental impacts and development is subtler than the simple picture painted by the EKC. This research shows that usually, growth in the scale of the economy increases environmental impacts, all else held constant. However, the impact of growth might decline as countries get richer, and richer countries are likely to make more rapid progress in reducing environmental impacts. Finally, there is often convergence among countries, so that countries that have relatively high levels of impacts reduce them more quickly or increase them more slowly, all else held constant.
George Morris and Patrick Saunders
Most people today readily accept that their health and disease are products of personal characteristics such as their age, gender, and genetic inheritance; the choices they make; and, of course, a complex array of factors operating at the level of society. Individuals frequently have little or no control over the cultural, economic, and social influences that shape their lives and their health and well-being. The environment that forms the physical context for their lives is one such influence and comprises the places where people live, learn work, play, and socialize, the air they breathe, and the food and water they consume. Interest in the physical environment as a component of human health goes back many thousands of years and when, around two and a half millennia ago, humans started to write down ideas about health, disease, and their determinants, many of these ideas centered on the physical environment.
The modern public health movement came into existence in the 19th century as a response to the dreadful unsanitary conditions endured by the urban poor of the Industrial Revolution. These conditions nurtured disease, dramatically shortening life. Thus, a public health movement that was ultimately to change the health and prosperity of millions of people across the world was launched on an “environmental conceptualization” of health. Yet, although the physical environment, especially in towns and cities, has changed dramatically in the 200 years since the Industrial Revolution, so too has our understanding of the relationship between the environment and human health and the importance we attach to it.
The decades immediately following World War II were distinguished by declining influence for public health as a discipline. Health and disease were increasingly “individualized”—a trend that served to further diminish interest in the environment, which was no longer seen as an important component in the health concerns of the day. Yet, as the 20th century wore on, a range of factors emerged to r-establish a belief in the environment as a key issue in the health of Western society. These included new toxic and infectious threats acting at the population level but also the renaissance of a “socioecological model” of public health that demanded a much richer and often more subtle understanding of how local surroundings might act to both improve and damage human health and well-being.
Yet, just as society has begun to shape a much more sophisticated response to reunite health with place and, with this, shape new policies to address complex contemporary challenges, such as obesity, diminished mental health, and well-being and inequities, a new challenge has emerged. In its simplest terms, human activity now seriously threatens the planetary processes and systems on which humankind depends for health and well-being and, ultimately, survival. Ecological public health—the need to build health and well-being, henceforth on ecological principles—may be seen as the society’s greatest 21st-century imperative. Success will involve nothing less than a fundamental rethink of the interplay between society, the economy, and the environment. Importantly, it will demand an environmental conceptualization of the public health as no less radical than the environmental conceptualization that launched modern public health in the 19th century, only now the challenge presents on a vastly extended temporal and spatial scale.
The animal world is under increasing pressure, given the magnitude of anthropogenic environmental stress, especially from human-caused rapid climate change together with habitat conversion, fragmentation, and destruction. There is a global wave of species extinctions and decline in local species abundance. To stop or even reverse this so-called defaunation process, in situ conservation (in the wild) is no longer effective without ex situ conservation (in captivity). Consequently, zoos could play an ever-greater role in the conservation of endangered species and wildlife—hence the slogan Captivity for Conservation.
However, the integration of zoo-based tools and techniques in species conservation has led to many conflicts between wildlife conservationists and animal protectionists. Many wildlife conservationists agree with Michael Soulé, the widely acclaimed doyen of the relatively new discipline of conservation biology, that conservation and animal welfare are conceptually distinct, and that they should remain politically separate. Animal protectionists, on the other hand, draw support from existing leading accounts of animal ethics that oppose the idea of captivity for conservation, either because infringing an individual’s right to freedom for the preservation of the species is considered as morally wrong, or because the benefits of species conservation are not seen as significant enough to overcome the presumption against depriving an animal of its liberty.
Both sides view animals through different lenses and address different concerns. Whereas animal ethicists focus on individual organisms, and are concerned about the welfare and liberty of animals, wildlife conservationists perceive animals as parts of greater wholes such as species or ecosystems, and consider biodiversity and ecological integrity as key topics. This seemingly intractable controversy can be overcome by transcending both perspectives, and developing a bifocal view in which zoo animals are perceived as individuals in need of specific care and, at the same time, as members of a species in need of protection.
Based on such a bifocal approach that has lately been adopted by a growing international movement of “Compassionate Conservation,” the modern zoo can only achieve its conservation mission if it finds a morally acceptable balance between animal welfare concerns and species conservation commitments. The prospects for the zoo to achieve such a balance are promising. Over the past decade or so, zoos have made serious and sustained efforts to ensure and enhance animal welfare. At the same time, the zoo’s contribution to species conservation has also improved considerably.
Juha Merilä and Ary A. Hoffmann
Changing climatic conditions have both direct and indirect influences on abiotic and biotic processes and represent a potent source of novel selection pressures for adaptive evolution. In addition, climate change can impact evolution by altering patterns of hybridization, changing population size, and altering patterns of gene flow in landscapes. Given that scientific evidence for rapid evolutionary adaptation to spatial variation in abiotic and biotic environmental conditions—analogous to that seen in changes brought by climate change—is ubiquitous, ongoing climate change is expected to have large and widespread evolutionary impacts on wild populations. However, phenotypic plasticity, migration, and various kinds of genetic and ecological constraints can preclude organisms from evolving much in response to climate change, and generalizations about the rate and magnitude of expected responses are difficult to make for a number of reasons.
First, the study of microevolutionary responses to climate change is a young field of investigation. While interest in evolutionary impacts of climate change goes back to early macroevolutionary (paleontological) studies focused on prehistoric climate changes, microevolutionary studies started only in the late 1980s. The discipline gained real momentum in the 2000s after the concept of climate change became of interest to the general public and funding organizations. As such, no general conclusions have yet emerged. Second, the complexity of biotic changes triggered by novel climatic conditions renders predictions about patterns and strength of natural selection difficult. Third, predictions are complicated also because the expression of genetic variability in traits of ecological importance varies with environmental conditions, affecting expected responses to climate-mediated selection.
There are now several examples where organisms have evolved in response to selection pressures associated with climate change, including changes in the timing of life history events and in the ability to tolerate abiotic and biotic stresses arising from climate change. However, there are also many examples where expected selection responses have not been detected. This may be partly explainable by methodological difficulties involved with detecting genetic changes, but also by various processes constraining evolution.
There are concerns that the rates of environmental changes are too fast to allow many, especially large and long-lived, organisms to maintain adaptedness. Theoretical studies suggest that maximal sustainable rates of evolutionary change are on the order of 0.1 haldanes (i.e., phenotypic standard deviations per generation) or less, whereas the rates expected under current climate change projections will often require faster adaptation. Hence, widespread maladaptation and extinctions are expected. These concerns are compounded by the expectation that the amount of genetic variation harbored by populations and available for selection will be reduced by habitat destruction and fragmentation caused by human activities, although in some cases this may be countered by hybridization. Rates of adaptation will also depend on patterns of gene flow and the steepness of climatic gradients. Theoretical studies also suggest that phenotypic plasticity (i.e., nongenetic phenotypic changes) can affect evolutionary genetic changes, but relevant empirical evidence is still scarce. While all of these factors point to a high level of uncertainty around evolutionary changes, it is nevertheless important to consider evolutionary resilience in enhancing the ability of organisms to adapt to climate change.
Agriculture has been the principal influence on the physical structure of the English landscape for many thousands of years. Driven by a wider raft of demographic, social, and economic developments, farming has changed in complex ways over this lengthy period, with differing responses to the productive potential and problems of local environments leading to the emergence of distinct regional landscapes. The character and configuration of these, as much as any contemporary influences, have in turn structured the practice of agriculture at particular points in time. The increasing complexity of the wider economy has also been a key influence on the development of the farmed landscape, especially large-scale industrialization in the late 18th and 19th centuries; and, from the late 19th century, globalization and increasing levels of state intervention. Change in agricultural systems has not continued at a constant rate but has displayed periods of more and less innovation.
Fisheries science emerged in the mid-19th century, when scientists volunteered to conduct conservation-related investigations of commercially important aquatic species for the governments of North Atlantic nations. Scientists also promoted oyster culture and fish hatcheries to sustain the aquatic harvests. Fisheries science fully professionalized with specialized graduate training in the 1920s.
The earliest stage, involving inventory science, trawling surveys, and natural history studies continued to dominate into the 1930s within the European colonial diaspora. Meanwhile, scientists in Scandinavian countries, Britain, Germany, the United States, and Japan began developing quantitative fisheries science after 1900, incorporating hydrography, age-determination studies, and population dynamics. Norwegian biologist Johan Hjort’s 1914 finding, that the size of a large “year class” of juvenile fish is unrelated to the size of the spawning population, created the central foundation and conundrum of later fisheries science. By the 1920s, fisheries scientists in Europe and America were striving to develop a theory of fishing. They attempted to develop predictive models that incorporated statistical and quantitative analysis of past fishing success, as well as quantitative values reflecting a species’ population demographics, as a basis for predicting future catches and managing fisheries for sustainability. This research was supported by international scientific organizations such as the International Council for the Exploration of the Sea (ICES), the International Pacific Halibut Commission (IPHC), and the United Nations’ Food and Agriculture Organization (FAO).
Both nationally and internationally, political entanglement was an inevitable feature of fisheries science. Beyond substituting their science for fishers’ traditional and practical knowledge, many postwar fisheries scientists also brought progressive ideals into fisheries management, advocating fishing for a maximum sustainable yield. This in turn made it possible for governments, economists, and even scientists, to use this nebulous target to project preferred social, political, and economic outcomes, while altogether discarding any practical conservation measures to rein in globalized postwar industrialized fishing. These ideals were also exported to nascent postwar fisheries science programs in developing Pacific and Indian Ocean nations and in Eastern Europe and Turkey.
The vision of mid-century triumphalist science, that industrial fisheries could be scientifically managed like any other industrial enterprise, was thwarted by commercial fish stock collapses, beginning slowly in the 1950s and accelerating after 1970, including the massive northern cod crisis of the early 1990s. In the 1980s scientists, aided by more powerful computers, attempted multi-species models to understand the different impacts of a fishery on various species. Daniel Pauly led the way with multi-species models for tropical fisheries, where the need for such was most urgent, and pioneered the global database FishBase, using fishing data collected by the FAO and national bodies. In Canada the cod crisis inspired Ransom Myers to use large databases for fisheries analysis to show the role of overfishing in causing that crisis. After 1980 population ecologists also demonstrated the importance of life history data for understanding fish species’ responses to fishery-induced population and environmental change.
With fishing continuing to shrink many global commercial stocks, scientists have demonstrated how different measures can manage fisheries for species with different life-history profiles. Aside from the need for effective scientific monitoring, the biggest ongoing challenges remain having politicians, governments, fisheries industry members, and other stakeholders commit to scientifically recommended long-term conservation measures.
Hans Keune and Timo Assmuth
This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Environmental Science. Please check back later for the full article.
Framing and dealing with complexity is of crucial importance in environmental health science, policy, and practice. Complexity is a key feature of most environmental health issues, as they by definition include aspects of environmental and human health, both of which constitute complex phenomena. The factors that may play a role in an environmental health issue are many, and the issues also have a multitude of characteristics and consequences. Framing this complexity is crucial because it will involve key decisions about what to take into account when addressing environmental health issues and how to deal with these. This is not merely a technical process of scientific framing but also a methodological decision-making process with both scientific and societal implications. Mostly, the benefits and burdens related to such issues cannot be generalized or objectified and will be distributed unevenly, resulting in health inequalities. Even more generally, framing is crucial as it reflects cultural factors and historical contingencies, perceptions and mind-sets, and political processes and associated values and worldviews. Framing is at the core of how we relate to and deal with environmental health, as scientists, policymakers, and practitioners, with models, policies, or actions.
David E. Clay, Sharon A. Clay, Thomas DeSutter, and Cheryl Reese
Since the discovery that food security could be improved by pushing seeds into the soil and later harvesting a desirable crop, agriculture and agronomy have gone through cycles of discovery, implementation, and innovation. Discoveries have produced predicted and unpredicted impacts on the production and consumption of locally produced foods. Changes in technology, such as the development of the self-cleaning steel plow in the 18th century, provided a critical tool needed to cultivate and seed annual crops in the Great Plains of North America. However, plowing the Great Plains would not have been possible without the domestication of plants and animals and the discovery of the yoke and harness. Associated with plowing the prairies were extensive soil nutrient mining, a rapid loss of soil carbon, and increased wind and water erosion. More recently, the development of genetically modified organisms (GMOs) and no-tillage planters has contributed to increased adoption of conservation tillage, which is less damaging to the soil. In the future, the ultimate impact of climate change on agronomic practices in the North American Great Plains is unknown. However, projected increasing temperatures and decreased rainfall in the southern Great Plains (SGP) will likely reduce agricultural productivity. Different results are likely in the northern Great Plains (NGP) where higher temperatures can lead to increased agricultural intensification, the conversion of grassland to cropland, increased wildlife fragmentation, and increased soil erosion. Precision farming, conservation, cover crops, and the creation of plants better designed to their local environment can help mitigate these effects. However, changing practices require that farmers and their advisers understand the limitations of the soils, plants, and environment, and their production systems. Failure to implement appropriate management practices can result in a rapid decline in soil productivity, diminished water quality, and reduced wildlife habitat.
Wim De Vries, Enzai Du, Klaus Butterbach Bahl, Lena Schulte Uebbing, and Frank Dentener
Human activities have rapidly accelerated global nitrogen (N) cycling since the late 19th century. This acceleration has manifold impacts on ecosystem N and carbon (C) cycles, and thus on emissions of the greenhouse gases nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4), which contribute to climate change.
First, elevated N use in agriculture leads to increased direct N2O emissions. Second, it leads to emissions of ammonia (NH3), nitric oxide (NO), and nitrogen dioxide (NO2) and leaching of nitrate (NO3−), which cause indirect N2O emissions from soils and waterbodies. Third, N use in agriculture may also cause changes in CO2 exchange (emission or uptake) in agricultural soils due to N fertilization (direct effect) and in non-agricultural soils due to atmospheric NHx (NH3+NH4) deposition (indirect effect). Fourth, NOx (NO+NO2) emissions from combustion processes and from fertilized soils lead to elevated NOy (NOx+ other oxidized N) deposition, further affecting CO2 exchange. As most (semi-) natural terrestrial ecosystems and aquatic ecosystems are N limited, human-induced atmospheric N deposition usually increases net primary production (NPP) and thus stimulates C sequestration. NOx emissions, however, also induce tropospheric ozone (O3) formation, and elevated O3 concentrations can lead to a reduction of NPP and plant C sequestration. The impacts of human N fixation on soil CH4 exchange are insignificant compared to the impacts on N2O and CO2 exchange (emissions or uptake). Ignoring shorter lived components and related feedbacks, the net impact of human N fixation on climate thus mainly depends on the magnitude of the cooling effect of CO2 uptake as compared to the magnitude of the warming effect of (direct and indirect) N2O emissions.
The estimated impact of human N fixation on N2O emission is 8.0 (7.0–9.0) Tg N2O-N yr−1, which is equal 1.02 (0.89–1.15) Pg CO2-C equivalents (eq) yr−1. The estimated CO2 uptake due to N inputs to terrestrial, freshwater, and marine ecosystems equals −0.75 (−0.56 to −0.97) Pg CO2-C eq yr−1. At present, the impact of human N fixation on increased CO2 sequestration thus largely (on average near 75%) compensates the stimulating effect on N2O emissions. In the long term, however, effects on ecosystem CO2 sequestration are likely to diminish due to growth limitations by other nutrients such as phosphorus. Furthermore, N-induced O3 exposure reduces CO2 uptake, causing a net C loss at 0.14 (0.07–0.21) Pg CO2-C eq yr−1. Consequently, human N fixation causes an overall increase in net greenhouse gas emissions from global ecosystems, which is estimated at 0.41 (−0.01–0.80) Pg CO2-C eq yr−1. Even when considering all uncertainties, it is likely that human N inputs lead to a net increase in global greenhouse gas emissions.
These estimates are based on most recent science and modeling approaches with respect to: (i) N inputs to various ecosystems, including NH3 and NOx emission estimates and related atmospheric N (NH3 and NOx) deposition and O3 exposure; (ii) N2O emissions in response to N inputs; and (iii) carbon exchange in responses to N inputs (C–N response) and O3 exposure (C–O3 response), focusing on the global scale. Apart from presenting the current knowledge, this article also gives an overview of changes in the estimates of those fluxes and C–N response factors over time, including debates on C–N responses in literature, the uncertainties in the various estimates, and the potential for improving them.