Calibration of regional pollen data to construct maps of former forest types in southern Sweden

A method was developed to construct maps of former forest types based on regional pollen data in southern Sweden. The considered species were Alnus, Betula, Carpinus, Corylus, Fagus, Fraxinus, Juniperus, Picea, Pinus, Populus, Quercus, Salix, Tilia and Ulmus. A network of 37 regional pollen sites with high data quality from lakes and peat deposits were selected from Sweden south of 60 ° N. Pollen percentage values were calculated and converted into estimates of tree composition. For controlling the reliability of the reconstruction, the estimates from the core-tops were compared with present day forest inventory data, and local pollen diagrams were compared with the regional pollen diagrams. An inverse distance weighted interpolation algorithm was used to generate maps for each tree species distribution at 2000 BP, 1500 BP, 1000 BP, 500 BP and 0 BP. A supervised classification routine was implemented to generate nine different forest types common to the five studied time intervals. The maps show that the amounts and patterns of distribution of the species and the forest types have varied in a significant but systematic manner through time. The changes are due to human activities, migrational patterns and changes in climate. These maps will be of value as a basis for future landscape planning, forestry and conservation of biodiversity.This is the 20th in a series of papers published in this special AMQUA issue. These papers were presented at the 1994 meeting of the American Quaternary Association held 19–22 June, 1994, at the University of Minnesota, Minneapolis, Minnesota, USA. Dr Linda C. K. Shane served as guest editor for these papers.     

Microphytobenthos: The ecological role of the “secret garden” of unvegetated,shallow-water marine habitats. II. role in sediment stability and shallow-water food webs

The microphytobenthos form an important component of all shallow-water ecosystems where enough light reaches the sediment surface to support appreciable primary production. Although less conspicuous than macroalgae or vascular plants, the microphytobenthos can contribute significantly to primary production and can modify habitat characteristics. The microphytobenthos alter sediment properties (e.g., erodibility) both directly, in the extreme forming a mat or scum on the sediment surface, and indirectly by modifying the activities of benthic infauna (e.g., pelletization, burrowing, tube building, and sediment tracking). Carbon dioxide fixed by the microphytobenthos supports higher, grazing trophic levels. These include deposit-feeding and suspension-feeding macrofauna as well as meiofauna and microfauna. Quantitative relations between the feeding and growth rates of macrofauna and the abundance of microphytobenthos and suspended organic matter (i.e., functional responses) are reviewed. Given the current state of knowledge of the direct and indirect interactions involving trophic dynamics, sediment properties, and benthic microalgae, we argue for reductionist studies of particular interactions as distinct entities. This is a prerequisite for the emergence of a comprehensive picture of unvegetated ecosystems and the ability to predict their responses to man’s activities. *** DIRECT SUPPORT *** A01BY074 00005     

Some applications of paleoecology to the management of tidal marshes

The shallow-water habitat is under increasing environmental pressures from accelerated sea-level rise and continual urban sprawl and will require well-informed management decisions to maintain its health into the future. One of the keys to the effective management of the shallow-water habitat is understanding the processes responsible for its development. Paleoecology has the potential to provide much insight into the development of the system, particularly when the impacts of accelerated sea-level rise on vegetation and sedimentation dynamics in tidal marshes is being considered. For example, a paleoecological comparison of tidal salt marshes to tidal freshwater marshes shows that rates of development will dictate the system's response to accelerated sea-level rise, with tidal freshwater marshes capable of transgressing landward more rapidly than their saline counterparts. Such information implies that management of the adjacent uplands is as important to the future of the system as management of the marsh itself. Therefore, it is important to consult paleoecological research when management strategies are being considered. *** DIRECT SUPPORT *** A01BY074 00010     

Hydraulic properties of groundwater systems in the saprolite and sediments of the wheatbelt, Western Australia

Hydraulic properties of deeply weathered basement rocks and variably weathered sedimentary materials were measured by pumping and slug-test methods. Results from over 200 bores in 13 catchments, and eight pumping-test sites across the eastern and central wheatbelt of Western Australia were analysed. Measurements were made in each of the major lithological units, and emphasis placed on a ubiquitous basal saprolite aquifer. Comparisons were made between alternative drilling and analytical procedures to determine the most appropriate methods of investigation.

Aquifers with an average hydraulic conductivity of 0.55 m day⁻¹ occur in variably weathered Cainozoic sediments and poorly weathered saprolite grits (0.57 m day⁻¹). These aquifers are separated by an aquitard (0.065 m day⁻¹) comprising the mottled and pallid zones of the deeply weathered profile. Locally higher values of hydraulic conductivity occur in the saprolite aquifer, although after prolonged periods of pumping the values decrease until they are similar to those obtained from the slug-test methods. Hydraulic conductivities measured in bores drilled with rotary auger rigs were approximately an order of magnitude lower than those measured in the same material with bores drilled by the rotary air-blast method.

Wheatbelt aquifers range from predominantly unconfined (Cainozoic sediments), to confined (saprolite grit aquifer). The poorly weathered saprolite grit aquifer has moderate to high transmissivities (4–50 m² day⁻¹) and is capable of producing from less than 5 to over 230 kl day⁻¹ of ground water, which is often of a quality suitable for livestock. Yields are influenced by the variability in the permeability of isovolumetrically weathered materials from which the aquifer is derived.

The overlying aquitard has a low transmissivity (< 1 m² day⁻¹), especially when deeply weathered, indurated and silicified. The transmissivity of the variably weathered sedimentary materials ranges from less than 0.5 m² day⁻¹ to over 10 m² day⁻¹, depending on the texture of the materials and their position within the landscape. Higher transmissivity zones may occur as discrete layers of coarser textured materials. The salinity of the saprolite and sedimentary aquifers ranges from less than 2000 mgl⁻¹ to greater than 250000 mgl⁻¹ (total dissolved solids; TDS), depending on position within the landscape. Secondary soil salinization develops when groundwater discharge occurs from either saprolite or sedimentary aquifers.     

Volcanic geology and eruption frequency,lower east rift zone of Kilauea volcano,Hawaii

Detailed geologic mapping and radiocarbon dating of tholeiitic basalts covering about 275 km² on the lower east rift zone (LERZ) and adjoining flanks of Kilauea volcano, Hawaii, show that at least 112 separate eruptions have occurred during the past 2360 years. Eruptive products include spatter ramparts and cones, a shield, two extensive lithic-rich tuff deposits, aa and pahoehoe flows, and three littoral cones. Areal coverage, number of eruptions and average dormant interval estimates in years for the five age groups assigned are: (I) historic, i.e. A D 1790 and younger: 25%, 5, 42.75; (II) 200–400 years old: 50%, 15, 14.3: (III) 400–750 years old: 20%, 54, 6.6; (IV) 750–1500 years old: 5%, 37, 20.8; (V) 1500–3000 years old: <1%, 1, unknown. At least 4.5–6 km³ of tholeiitic basalt have been erupted from the LERZ during the past 1500 years. Estimated volumes of the exposed products of individual eruptions range from a few tens of cubic meters for older units in small kipukas to as much as 0.4 km³ for the heiheiahulu shield. The average dormant interval has been about 13.6 years during the past 1500 years. The most recent eruption occurred in 1961, and the area may be overdue for its next eruption. However, eruptive activity will not resume on the LERZ until either the dike feeding the current eruption on the middle east rift zone extends farther down rift, or a new dike, unrelated to the current eruption, extends into the LERZ.     

Case Histories of Shallow Time Domain Electromagnetics in Environmental Site Assessment

Time domain electromagnetic (TDEM) soundings were utilized in site assessment studies for the purpose of accomplishing two objectives: (1) measuring the migration of brines from oil and gas field evaporation pits, and (2) mapping the continuity of clay strata. Both case histories are representative of common objectives in site assessment. The data for both examples were analyzed by one-dimensional ridge regression inversions.
Both case histories illustrate that TDEM is an effective method for determining the lateral and vertical resistivity distribution (geoelectric section) of the subsurface in the depth range from about 5 m to 100 m, and it is known from other investigations that depths of investigations up to 2500 m can be achieved with TDEM.
Frequently, the lateral extent of contaminant plumes emanating from localized sources are of limited areal extent. The case history involving the use of TDEM to map a brine plume shows that a TDEM measurement has a relatively small zone of influence, so that meaningful information about the lateral and vertical extent of the plume can be obtained. Both case histories demonstrate the ability of TDEM to determine geoelectric sections below layers of low resistivity.