An information systems approach to the preservation of biological diversity

Abstract

Although biological diversity has emerged in the 1980s as a major scientific and political issue, efforts at scientific assessment have been hampered by the lack of cohesive sets of data. We describe, in concept, a comprehensive national diversity information system, using geographical information system (GIS) techniques to organize existing data and improve spatial aspects of the assessment. One potential GIS analysis, to identify gaps in the network of nature reserves for California, is discussed in greater detail. By employing an information systems approach, available data can be used more effectively and better management strategies can be formulated.     

Modelling spatially and temporally distributed phenomena: new methods and tools for GRASS GIS

Abstract

The concept of GRASS (Geographic Resources Analysis Support System) as an open system has created a favourable environment for integration of process based modelling and GIS. To support this integration a new generation of tools is being developed in the following areas: (a) interpolation from multidimensional scattered point data, (b) analysis of surfaces and hypersurfaces, (c) modelling of spatial processes and, (d) 3D dynamic visualization. Examples of two applications are given-spatial and temporal modelling of erosion and deposition, and multivariate interpolation and visualization of nitrogen concentrations in the Chesapeake Bay.     

Evaluating field-based GIS for environmental characterization,modelling and decision support

ABSTRACT

This paper examines the potential of using GIS (Geographical Information Systems) in the field for environmental characterization, modelling and decision support particularly in isolated areas where data collection is difficult. Observations are based on experiences gained during two Anglo-Russian expeditions to the Altai Mountains of south central Siberia aimed at evaluating proposals for a new national park in the Katunsky Ridge area of the Belukha Massif. The use of GIS together with GPS (Global Positioning Systems) for primary data collection and verification/update of existing data is described and the use of field-based systems for on-the-spot environmental modelling and decision support is evaluated.     

Rinded iron‐oxide concretions: hallmarks of altered siderite masses of both early and late diagenetic origin

Iron‐bearing concretions are valuable records of oxidation states of subsurface waters, but the first concretions to form can be altered drastically during later diagenetic events. Distinctive concretions composed of heavy rinds of iron oxide that surround iron‐poor, mud‐rich cores are common along bases of fluvial cross‐bed sets of the Cretaceous Dakota Formation, Nebraska, USA. Concretion rinds thicken inward and cores contain 46 to 89% void space. Millimetre‐scale spherosiderites are abundant in palaeosols that developed in floodplain facies. Evolution of rinded concretions began when intraformational clasts were eroded from sideritic soils, transported, abraded and deposited in river channels. Alteration of siderite and formation of rinds occurred much later, perhaps in the Quaternary when sandstone pore waters became oxic. Dakota concretions are analogous to ‘rattlestones’ in Pleistocene fluvial channels of The Netherlands, and their rinded structure is analogous to that of iron‐rich concretions in the aeolian Navajo Sandstone of Utah. In all three deposits, rinded concretions formed when pre‐existing, siderite‐cemented concretions were oxidized within a sand matrix. Unlike fluvial examples, siderite in the Navajo Sandstone was autochthonous and of late diagenetic origin, having precipitated from carbon dioxide and methane‐enriched waters moving through folded and jointed strata. Iron‐rich rinds formed in all these strata because concretion interiors remained anaerobic, even as oxygen accumulated in the pore waters of their surrounding, permeable matrix. Iron oxide first precipitated at redox boundaries at concretion perimeters and formed an inward‐thickening rind. Acid generated by the oxidation reaction drove siderite dissolution to completion, creating the iron‐poor core. Iron‐oxide rinds are indicators of the former presence of siderite, a mineral that forms only under reducing conditions, during either early or late diagenesis. Siderite is vulnerable to complete oxidation upon exposure, so the distinctive rinded concretions are valuable clues that aid in deciphering diagenetic histories and for recognizing methanic floodplain palaeoenvironments and wet palaeoclimate.     

Origin and significance of lateral meltwater channels formed along a temperate glacier margin, Glacier Bay, Alaska

Pleistocene lateral meltwater channels are commonly used as evidence of cold-based or polythermal ice. However, lateral meltwater channel formation has been observed for >40 years along the margins of a rapidly thinning temperate glacier in Glacier Bay, Alaska. Flights of nested linear lateral meltwater channels and in-and-out channels have formed on the sides of emerging nunataks. Nested channels at Burroughs Glacier are up to 200 m long; they are good proxies for the slope of the ice margin along the land surface and are terminated by subglacial chutes. A perched water table associated with precipitation and high ablation rates in the temperate ice causes surface meltwater to flow toward the margin above less permeable ice. The water flows along the margin and erodes lateral meltwater channels until a subglacial chute carries the water into the subglacial water system. Rates of channel formation range from 0 to 8 channels/year. Spacing and rates of channel formation are controlled by the land-surface slope, ablation rate, erodibility of the substrate and stream discharge. Because lateral meltwater channels have been observed forming along a temperate glacier margin, care must be exercised when using the presence of lateral meltwater channels as definitive evidence of cold-based or polythermal ice.     

Relationship of diagenetic chlorite rims to depositional facies in Lower Cretaceous reservoir sandstones of the Scotian Basin

The relationship between diagenetic chlorite rims and depositional facies in deltaic strata of the Lower Cretaceous Missisauga Formation was investigated using a combination of electron microprobe, bulk geochemistry and X‐ray diffraction data. The succession studied comprises several stacked parasequences. The delta progradational facies association includes: (i) fluvial or distributary channel sandstones (some with tidal influence); (ii) thick‐bedded delta‐front graded beds of sandstone interpreted as resulting from fluvial hyperpycnal flow during floods and storms; and (iii) more distal muddier delta‐front and prodeltaic facies. The transgressive facies association includes lag conglomerate, siderite‐cemented muddy sandstone and mudstone, and bioclastic sandy limestone. Chlorite rims are absent in the fluvial facies and best developed in thick sandstones lacking mudstone baffles. Good quality chlorite rims are well correlated with Ti in bulk geochemistry. Ti is a proxy for Fe availability, principally from the breakdown of abundant detrital ilmenite (FeTiO₃). Under conditions of sea floor diagenesis, the abrupt decrease in sedimentation rate at transgressive surfaces caused progressive shallowing of the sulphate‐depletion level and of the overlying Eh‐controlled diagenetic zones, resulting in conditions suitable for diagenetic formation of berthierine to migrate upwards through the packet of reservoir sandstones. This early diagenetic berthierine suppressed silica cementation and later recrystallized to chlorite. Thick euhedral outer chlorite rims were precipitated from formation water in sandstone lacking muddy baffles on this chlorite substrate and inhibited late carbonate cementation. This study thus shows that the preservation of porosity by chlorite rims is a two‐stage process. Rapidly deposited delta‐front turbidite facies create early diagenetic conditions that eventually lead to the formation of chlorite rims, but the best quality chlorite rims are restricted to sandstones with high permeability during burial diagenesis.     

The Biotite Isograd and the Lower Greenschist Facies in the Dalradian Rocks of Scotland

Analyses of a series of coexisting minerals and their host rocks,from the Aberfoyle area, indicate that previously proposed biotite-formingreactions are inadequate to account for the appearance of biotitein the Dalradian greywackes and pelites. Initially biotite isformed as a product of the breakdown of the assemblage chlorite+microcline+phengiticmuscovite in greywackes of suitable bulk composition. With increasein grade the stability field of the biotite-bearing assemblageis enlarged through the reduction in the amount of celadonitesubstitution that can be tolerated by the white micas. The stabilityfield increases so that it includes progressively more aluminousrocks. The sequence of biotile-forming reactions is used to definethree zones of increasing metamorphic grade in the Dalradiangreywackes and pelites. The interrelationships of the assemblagesdeveloped in these zones are considered in detail. The assemblagesdeveloped in the Green Beds are explained on the assumptionthat the fugacity of CO₂ is a third intensive variable.     

Spatial autocorrelation in marine birds

All marine organisms exhibit some degree of spatial autocorrelation, which is the tendency for high (or low) densities to occur in proximity, rather than at random in the ocean. Autocorrelation occurs at scales ranging from the length of the organism to thousands of kilometres. Autocorrelation results from a wide variety of mechanisms, many of which act at characteristic scales. Consequently, some insight into causal mechanisms can be obtained from exploratory analysis of the scale and intensity of autocorrelation of abundance or behaviour, and the scale and intensity (coherence) of cross-correlation with environmental variables such as water temperature or prey abundance. This paper uses seabird counts along extended transects to illustrate standard measures of autocorrelation and cross-correlation. A brief discussion of exploratory and confirmatory analysis of autocorrelated data on marine birds follows.