Modeling Sensitivity to Accuracy in Classified Imagery: A Study of Areal Interpolation by Dasymetric Mapping*

Areal interpolation is the process by which data collected from one set of zonal units can be estimated for another zonal division of the same space that shares few or no boundaries with the first. In previous research, we outlined the use of dasymetric mapping for areal interpolation and showed it to be the most accurate method tested. There we used control information derived from classified satellite imagery to parameterize the dasymetric method, but because such data are rife with errors, here we extend the work to examine the sensitivity of the population estimates to error in the classified imagery. Results show the population estimates by dasymetric mapping to be largely insensitive to the errors of classification in the Landsat image when compared with the other methods tested. The dasymetric method deteriorates to the accuracy of the next worst estimate only when 40% error occurs in the classified image, a level of error that may easily be bettered within most remote sensing projects.     

Water and organic carbon fluxes from an irregularly flooded brackish marsh on the upper Texas coast,U.S.A.

Water flows, concentrations of total (TOC), dissolved (DOC), and particulate (POC) organic carbon and seston were monitored for 52 diel periods in the single creek draining a 270-ha Spartina patens-Distichlis spicata marsh on the upper Texas coast. Rainfall, creek water flows, and water levels in the creek and on the marsh were measured by recording instruments.Rainfall accounted for most marsh flooding, and water outflow was significantly correlated with both rainfall and marsh water level. Creek flows were predominantly outward because microtopographic features and dense vegetation restricted overmarsh water flows and thereby reduced tidal flooding while extending the time of precipitation runoff. Concentrations of organic carbon in water leaving the marsh were highest in spring and summer and averaged 25·62, 21·41 and 3·35 mg l^?1 of TOC, DOC and POC, respectively. These were 9·34, 9·93 and 0·04 mg l^?1, respectively, higher than bay water. Most POC was 0·3–28 μm in diameter. Seston > 28μ leaving the marsh was 95% amorphous material; the rest was plankton, grass particles and fecal pellets. Loss of organic carbon was directly correlated with net water flux, and thus rainfall accounted for most carbon loss. Net carbon loss averaged 196 kg TOC, 150 kg DOC and 32 kg POC per day. Net annual loss was 2·4–5·5% of net aerial primary productivity (NAPP), or 21·55-30·09 g TOC m^?2 year^?1.Export from this marsh falls within the range found for other marshes and the data collectively indicate that coastal marshes are not losing as much organic carbon as has been suggested by indirect measurements. The discrepancy between potential and realized export is explained by the fact that export is not a simple removal of excess detritus by tidal action but is a more complicated process mediated by the interaction of additional factors such as rainfall, vegetation structure, microtopographic variation and decomposition, which can serve to reduce the amount and quality of NAPP exported.     

Multimedia Reporting of the Results of Natural Resource Surveys

For most of the twentieth century Natural Resource Surveys were executed for particular geographical regions and for each region a paper map was produced together with a written report. Those conducting the survey and preparing the report have used that report to convey much information to the user, which would otherwise be lost. To the authors the report is the real product, and the map a view onto it. To most users, however, it has always been the map that was important because many lack the knowledge to comprehend the report in any detail: the report, therefore, being an adjunct to the map. Increasing production costs combined with the advances in computer systems and especially the widespread use of this information within GIS have resulted in a shift from paper to digital as the publication medium for the map and the report (when it is produced at all). Currently, many different models of presentation of natural resource survey results are apparent, ranging from those which only contain the map (spatial information) to those combining the report and the map on CD‐ROM to those presenting a more integrated view of the map and the equivalent of the report. None has yet reached the full spatial multimedia solution which is now possible with computer technology. Such an approach will make it possible to interrogate the map for the report information, and vice versa, and to access and visualize tabular information. The current diversity of approaches means the potential loss of the valuable knowledge of the surveyors and report‐writers other than as it is expressed in the map, but the integration of the report with the map in a multimedia presentation may save the report, and make that information available to more people than ever before.     

Anisotropy of magnetic susceptibility studies of depositional processes in the Campanian Ignimbrite,Italy

The late Pleistocene trachytic Campanian Ignimbrite underlies much of the Campanian Plain near Naples, Italy, and occurs in valleys in the mountainous area surrounding the plain out to about 80 km from its source, the Campi Flegrei caldera. At sites within 15 km of the Campi Flegrei, anisotropy of magnetic susceptibility (AMS) principal directions indicate that, in the absence of significant topography, deposition came from a flow moving in a roughly radial direction. AMS studies of the more distal ignimbrite reveal downhill and/or downvalley flow directions prior to deposition, even where these directions are at high angles to a generally radial transport direction from the vent. On the flanks of Roccamonfina Volcano, flow was directly downhill, as if the source of the ignimbrite was the summit of the volcano. In most localities, the ignimbrite consists of a single massive deposit. In a few localities in the Apennine Mountains, however, the confluence of multiple drainage systems off mountains resulted in multiple local flow units that cannot be correlated between valleys. A detailed study of the ignimbrite in the flat Titerno River valley near Massa shows that the AMS fabrics are not due to late-stage creeping during deposition or compaction. Well-defined, but non-parallel AMS fabrics from vertical and lateral sections in the Massa area are best explained by the merging of gravity currents flowing down the valley and steep valley sides to form a single aggradational deposit. Clast compositions and AMS axes at Mondragone indicate that the pyroclastic flow encountered the Monte Massico massif and was partially blocked, so that flow during deposition was toward the Campi Flegrei. Similar AMS data from sites along the edge of the Campanian Plain indicate back-flow off the first ridge of the Apennine Mountains reached at least 5 km from their base. The Campanian Ignimbrite was deposited from a density-stratified pyroclastic flow. The depositional system consisted of the lower, denser portion of the current, and was controlled by topography. The grouping of the AMS axes is interpreted to indicate that deposition occurred under laminar flow conditions.     

Incipient tunnel channels

Glaciated terrains in east-central Alberta and south-central Michigan contain channels that have hummocks and transverse ridges separating depressions along their floors. This association imparts a linked pothole appearance. Similar channels are often interpreted as tunnel channels or subaerial channels, partly filled with sediment from a subsequent glacial advance, a stagnating ice roof, or slumped sediment from the channel margins. However, the truncation of sedimentary packages in the channel walls and intrachannel hummocks indicates that they are erosional landforms, cut into glacial sediments (till), bedrock, or gravel. Eskers overlie and are found within a few channels, indicating that these channels formed before the final stagnation that produced the eskers. These two characteristics, combined with the observation that many channels have convex-up long profiles, indicate that the channels were eroded by pressurized, subglacial water. Because the formative mechanisms for this type of channel are not clear, and modern environments that could produce this type of landform are inaccessible, we draw on several morphologic analogues to propose mechanisms for channel erosion. We conclude that the erosion of these linked pothole channels (incipient tunnel channels) was the product of the complex interaction between complex turbulent flow structures and various scales of roughness elements.     

Holocene loess deposition and soil formation as competing processes, Matanuska Valley, southern Alaska

Although loess–paleosol sequences are among the most important records of Quaternary climate change and past dust deposition cycles, few modern examples of such sedimentation systems have been studied. Stratigraphic studies and 22 new accelerator mass spectrometry radiocarbon ages from the Matanuska Valley in southern Alaska show that loess deposition there began sometime after 6500 ¹⁴C yr B.P. and has continued to the present. The silts are produced through grinding by the Matanuska and Knik glaciers, deposited as outwash, entrained by strong winds, and redeposited as loess. Over a downwind distance of 40 km, loess thickness, sand content, and sand-plus-coarse-silt content decrease, whereas fine-silt content increases. Loess deposition was episodic, as shown by the presence of paleosols, at distances >10 km from the outwash plain loess source. Stratigraphic complexity is at a maximum (i.e., the greatest number of loesses and paleosols) at intermediate (10–25 km) distances from the loess source. Surface soils increase in degree of development with distance downwind from the source, where sedimentation rates are lower. Proximal soils are Entisols or Inceptisols, whereas distal soils are Spodosols. Ratios of mobile CaO, K₂O, and Fe₂O₃ to immobile TiO₂ show decreases in surface horizons with distance from the source. Thus, as in China, where loess deposition also takes place today, eolian sedimentation and soil formation are competing processes. Study of loess and paleosols in southern Alaska shows that particle size can vary over short distances, loess deposition can be episodic over limited time intervals, and soils developed in stabilized loess can show considerable variability under the same vegetation.     

Late Pleistocene mammoth remains from Coastal Maine, USA

Remains identified as those of a woolly mammoth (Mammuthus primigenius) dated at 12,200 ± 55 ¹⁴C yr B.P. were recovered while excavating in a complex sequence of glaciomarine sediments in Scarborough, Maine, USA. The mammoth was found in the top meter of a fossiliferous unit of mud and sand laminites. These sediments were deposited during a marine regressive phase following the transgression that accompanied northward retreat of the margin of the Laurentide ice sheet. A Portlandia arctica valve from the underlying transgressive unit provides a minimum age of 14,820 ± 105 ¹⁴C yr B.P. for local deglaciation. The mammoth, an adult female, died in midwinter with no evidence of human involvement. Tusk growth rates and oxygen-isotope variation over the last few years of life record low seasonality. The mammoth was transported to the site as a partial carcass by the late-glacial proto-Saco River. It sank in a near-shore setting, was subjected to additional disarticulation and scattering of elements, and was finally buried in sediments reworked by the shallowing sea.     

Bioavailability of sediment-bound metals to marine bivalve molluscs: An overview

Coastal marine sediments are commonly enriched in metals, including potentially toxic trace metals, by natural processes and human activities. These sediments have long been regarded as the final repositories of contaminants, but in recent years it has been recognized that they can also serve as potentially important sources of metal contaminants for benthic organisms and benthic food chains in general. The geochemical and biological factors governing the bioavailability of diverse metals (Ag, Cd, Co, Cr, Se, Zn) that are bound to different kinds of marine sediments are reviewed. Particular attention has been paid to those species of marine bivalve mollusks that are used as bioindicators of coastal contamination. Both deposit-feeding and suspension-feeding bivalves can accumulate metals appreciably by assimilating sediment-bound metals that are ingested, although important differences have been recognized between these two feeding modes as well as between metals. The properties of the digestive tracts of deposit and suspension-feeding bivalves that influence metal bioaccumulation from food are also discussed. Through kinetic modeling, the relative importance of ingestion as a route of metal uptake has been compared quantitatively with uptake from the dissolved phase, including from pore water and from overlying water, and has been shown to account for the high concentrations in bivalve tissues for a number of contaminant metals.