Climate change impacts on U.S. Coastal and Marine Ecosystems

Increases in concentrations of greenhouse gases projected for the 21st century are expected to lead to increased mean global air and ocean temperatures. The National Assessment of Potential Consequences of Climate Variability and Change (NAST 2001) was based on a series of regional and sector assessments. This paper is a summary of the coastal and marine resources sector review of potential impacts on shorelines, estuaries, coastal wetlands, coral reefs, and ocean margin ecosystems. The assessment considered the impacts of several key drivers of climate change: sea level change; alterations in precipitation patterns and subsequent delivery of freshwater, nutrients, and sediment; increased ocean temperature; alterations in circulation patterns; changes in frequency and intensity of coastal storms; and increased levels of atmospheric CO₂. Increasing rates of sea-level rise and intensity and frequency of coastal storms and hurricanes over the next decades will increase threats to shorelines, wetlands, and coastal development. Estuarine productivity will change in response to alteration in the timing and amount of freshwater, nutrients, and sediment delivery. Higher water temperatures and changes in freshwater delivery will alter estuarine stratification, residence time, and eutrophication. Increased ocean temperatures are expected to increase coral bleaching and higher CO₂ levels may reduce coral calcification, making it more difficult for corals to recover from other disturbances, and inhibiting poleward shifts. Ocean warming is expected to cause poleward shifts in the ranges of many other organisms, including commercial species, and these shifts may have secondary effects on their predators and prey. Although these potential impacts of climate change and variability will vary from system to system, it is important to recognize that they will be superimposed upon, and in many cases intensify, other ecosystem stresses (pollution, harvesting, habitat destruction, invasive species, land and resource use, extreme natural events), which may lead to more significant consequences.     

Hypoxia in the northern Gulf of Mexico: Does the science support the Plan to Reduce,Mitigate, and Control Hypoxia?

We update and reevaluate the scientific information on the distribution, history, and causes of continental shelf hypoxia that supports the 2001 Action Plan for Reducing, Mitigating, and Controlling Hypoxia in the Northern Gulf of Mexico (Mississippi River/Gulf of Mexico Watershed Nutrient Task Force 2001), incorporating data, publications, and research results produced since the 1999 integrated assessment. The metric of mid-summer hypoxic area on the LouisianaTexas shelf is an adequate and suitable measure for continued efforts to reduce nutrients loads from the Mississippi River and hypoxia in the northern Gulf of Mexico as outlined in the Action Plan. More frequent measurements of simple metrics (e.g., area and volume) from late spring through late summer would ensure that the metric is representative of the system in any given year and useful in a public discourse of conditions and causes. The long-term data on hypoxia, sources of nutrients, associated biological parameters, and paleoindicators continue to verify and strengthen the relationship between the nitratenitrogen load of the Mississippi River, the extent of hypoxia, and changes in the coastal ecosystem (eutrophication and worsening hypoxia). Multiple lines of evidence, some of them representing independent data sources, are consistent with the big picture pattern of increased eutrophication as a result of long-term nutrient increases that result in excess carbon production and accumulation and, ultimately, bottom water hypoxia. The additional findings arising since 1999 strengthen the science supporting the Action Plan that focuses on reducing nutrient loads, primarily nitrogen, through multiple actions to reduce the size of the hypoxic zone in the northern Gulf of Mexico.     

Geochronology of a polymetamorphic and anatectic gneiss region: The moldanubicum of the area Lam-Deggendorf,eastern Bavaria,Germany

Rb-Sr isotopic analyses of whole-rocks and biotite and U-Th-Pb analyses of zircon and monazite reveal regional metamorphic events for the Ordovician (Caledonian metamorphism) and the Carboniferous (Variscan=Hercynian orogeny), both accompanied by anatexis. The extent of the Caledonian and Variscan anatexis, however, cannot be evaluated, so far, because the field petrographic criteria are not sufficient to distinguish clearly between early and late Paleozoic anatexites. Evidence for a Precambrian metamorphism has not been found. Rb-Sr whole-rock isochrons obtained on leucosomes and melanosomes of partially molten paragneisses are interpreted as a minimum age of the second, early Variscan anatexis. The alternative explanation of the isochrons as a result of local Sr isotopic redistribution without a melt involved is considered less likely. Concordant and nearly concordant zircon ages (318–335 m.y.) of a coarse-grained granite and of diatexites are regarded as evidence for an intensive early Variscan granitization and palingenesis. Concordant zircon ages of diorite dykes, crosscutting the anatexites, establish a lower time limit of 309–312 m.y. for the Variscan anatexis. Rb-Sr ages of biotite (310-290 m.y.) indicate the end of the Variscan metamorphism. Estimates of the time of sedimentation or diagenesis based on Rb-Sr whole-rock analyses for some metasediment series in the north of the area yield maximum ages of 550 m.y., provided that Rb and Sr migration did not exceed substantially the extent of the outcrops (30–500 m) between the time of diagenesis and the Ordovician metamorphism. Otherwise, an upper limit of 2000–2300 m.y., which is the primary age of detrital zircon populations, can be established. Zircon populations of paragneisses and their anatectic derivatives were separated into size and shape fractions. From morphologic studies and U-Pb isotopic analyses, they were found to be composites of young concordant (318–325 m.y.) and old, highly discordant zircon components, with more than fifty per cent of young crystals in some anatexites. The apparent ages of the composites are 320–750 m.y. The U concentrations of the newly formed crystals can be higher, equal, or lower than those of the inherited zircon component. Some peculiarities in the concordia plot of the zircon data of paragneisses and migmatites (curved pattern; inversion of the generally observed systematics with respect to U concentration, grain size, degree of discordance) are interpreted as the result of polyepisodic disturbances of the inherited crystals in connection with new zircon growth. In the concordia diagram, the data points of the individual zircon grains containing inherited components appear to plot in band or wedgelike areas, and not on lines as the patterns of size fractions of the same zircon populations could pretend. Consequently, ages obtained by extrapolation of the regression curves to the concordia are not necessarily meaningful and require verification by other methods.     

Greenhouse Gas Dynamics of an Increased Use of Wood in Buildings in Switzerland

Long-living wood products contribute to the mitigation of climate change in many ways. They act as a carbon pool during their service life, as they withdraw CO₂ from its natural cycle. After their service life, they can stitute for fossil fuels if they are incinerated in adequate furnaces. Furthermore, wood products can stitute for more energy-intense products made of ‘conventional’ materials. This paper quantifies the stitution and pool effects of an increased use of wood in the building sector in Switzerland for the years 2000–2130. Life cycle data on greenhouse gas (GHG) emissions of 12 wood products and their stitutes are used as proxies for relevant building products; this data is linked to the forecasted wood flows for each group of building products in a cohort-model. For the political assessment, GHG effects occurring abroad and in Switzerland are distinguished. The results show that the pool effect of an increased use of long-living wood products is of minor importance, whereas the energetic and material stitution effects are much more relevant, especially on a long-term. For construction products, the Swiss share of the GHG effect related to the material stitution is relatively high, as mainly nationally produced materials are stituted for. For interior products, the Swiss share of the GHG effect related to the material stitution is rather small because mainly imports are stituted for. The results must be considered as rough estimates. Nonetheless, these calculations show that an increased use of wood in the building sector is a valid and valuable option for the mitigation of greenhouse gas emissions and for reaching GHG emission targets in a mid- to long-term. Still, the pool and stitution capacity of an increased use of wood is relatively small compared to the overall GHG emissions of Switzerland.     

Challenges and opportunities for science in reducing nutrient over-enrichment of coastal ecosystems

Nutrient over-enrichment has resulted in major changes in the coastal ecosystems of developed nations in Europe, North America, Asia, and Oceania, mostly taking place over the narrow period of 1960 to 1980. Many estuaries and embayments are affected, but the effects of this eutrophication have been also felt over large areas of semi-enclosed seas including the Baltic, North, Adriatic, and Black Seas in Europe, the Gulf of Mexico, and the Seto Inland Sea in Japan. Primary production increased, water clarity decreased, food chains were altered, oxygen depletion of bottom waters developed or expanded, seagrass beds were lost, and harmful algal blooms occurred with increased frequency. This period of dramatic alteration of coastal ecosystems, mostly for the worse from a human perspective, coincided with the more than doubling of additions of fixed nitrogen to the biosphere from human activities, driven particularly by a more than 5-fold increase in use of manufactured fertilizers during that 20-year period. Nutrient over-enrichment often interacted synergistically with other human activities, such as overfishing, habitat destruction, and other forms of chemical pollution, in contributing to the widespread degradation of coastal ecosystems that was observed during the last half of the 20th century. Science was effective in documenting the consequences and root causes of nutrient over-enrichment and has provided the basis for extensive efforts to abate it, ranging from national statutes and regulations to multijurisdictional compacts under the Helsinki Commission for the Baltic Sea, the Oslo-Paris Commission for the North Sea, and the Chesapeake Bay Program, for example. These efforts have usually been based on a relatively arbitrary goal of reducing nutrient inputs by a certain percentage, without much understanding of how and when this would affect the coastal ecosystem. While some of these efforts have succeeded in achieving reductions of inputs of phosphorus and nitrogen, principally through treatment of point-source discharges, relatively little progress has been made in reducing diffuse sources of nitrogen. Second-generation management goals tend to be based on desired outcomes for the coastal ecosystem and determination of the load reductions needed to attain them, for example the Total Daily Maximum Load approach in the U.S. and the Water Franmework Directive in the European Union. Science and technology are now challenged not just to diagnose the degree of eutrophication and its causes, but to contribute to its prognosis and treatment by determining the relative susceptibility of coastal ecosystems to nutrient over-enrichment, defining desirable and achievable outcomes for rehabilitation efforts, reducing nutrient sources, enhancing nutrient sinks, strategically targeting these efforts within watersheds, and predicting and observing responses in an adaptive management framework.     

Assessing the age of relief growth in the Andes of northern Chile: Magneto-polarity chronologies from Neogene continental sections

The Andes of northern Chile currently experience a phase of relief rejuvenation as indicated by valleys that are >1000 m dissected into pediplains. However, it has been unclear when this phase of relief enhancement started. This paper discusses the use of palaeomagnetic chronologies from four sections in the Taracapá-Region (northern Chile) to assess this age. The sections are located in distal and proximal positions. Sediment accumulation occurred between c. 22.5 and 8/7.5 Ma with a hiatus that possibly spans a time interval between c. 19.5 and 11 Ma. The magnetic polarity chronologies suggest a preferred age between 8.0 and 7.5 Ma for the time when relief growth started. In proximal positions, however, alternative correlations suggest an age of 8.5 Ma. In addition, the palaeomagnetic data reveal no rotation of the analysed strata, suggesting a minimum age of c. 22.5 Ma for the tectonic block rotation south of the Arica deflection.     

A Conceptual Framework for Uncertainty Investigation in Map‐based Land Cover Change Modelling

Uncertainty research represents a research stream of high interest within the community of geographical information science. Its elements, terminology and typology are still under strong discussion and adopted methods for analysis are currently under intensive development. This paper presents a conceptual framework for systematic investigation of uncertainty which occurs in applications of land cover change modelling in Geographical Information Systems (GIS) based on historical map data. Historical, in this context, means the map is old enough to allow identification of changes in landscape elements of interest, such as vegetation. To date such analyses are rarely conducted or not satisfactorily carried out, despite the fact that historical map data represent a potentially rich information source. The general validity and practicability of the framework for related applications is demonstrated with reference to one example in which forest cover change in Switzerland is investigated. The conceptual model consists of three domains in which main potential sources of uncertainty are systematically exposed. Existing links between data quality research and uncertainty are investigated to access the complex nature of uncertainty and to characterise the most suitable concepts for analysis. In accordance with these concepts appropriate methods and procedures are suggested to assess uncertainty in each domain. One domain is the production‐oriented amount of uncertainty which is inherent in the historical map. Vagueness and ambiguity represent suitable concepts for analysis. Transformation‐oriented uncertainty as the second domain occurs owing to editing and processing of digital data. Thereby, the suitable concept of uncertainty is error. The third domain is the application‐oriented uncertainty which occurs in comparing semantically different data. This domain relates to multi‐temporal discord which assumes the assessment of ‘equi‐temporal’ ambiguity and is thus connected to the production‐oriented domain. The framework provides an estimation of the overall amount of uncertainty. This can be linked to subsequent assessment of ‘fitness for use’. Thus the model provides a practicable and systematic approach to access the complex nature of uncertainty in the scope of land cover change modelling.     

Dependence of fishery species on salt marshes: The role of food and refuge

Salt marshes are widely believed to serve as nurseries for many fishes and crustaceans of fishery value as a result of the high production of vascular plant detritus and the protection from predation offered by shallow, spatially complex habitats. Comparisons of the yields of species which reside in salt marsh habitats during critical life history stages (such as penaeid shrimp) with the area of such habitats and their greater densities in flooded marshes and associated tidal creeks support the premise that marshes enhance the yield of such species. A range of evidence, including the amount of detrital export from marshes, the poor nutritive value of vascular plant detritus, and natural diets, casts doubt on the notion that production of fishery species is based on the direct consumption of marsh grass detritus or predominantly on food chains based on this detritus. Vascular plants and associated algae may, however, contribute to the production of prey species. The limited observations available support the hypothesis that salt marshes offer significant escape from mortality due to predation, but there have been yet few experimental tests of this hypothesis. Knowledge of relative importance of the food and refuge functions in support of living resources is of practical value in marsh and fisheries management. Better understanding of these roles is important to the effective evaluation of the effects of coastal habitat modifications on fisheries resources and design of alterations to minimize the losses of these values.