Jon C. Boothroyd

A depositional model for outwash, sediment sources, and hydrologic characteristics, Malaspina Glacier, Alaska: A modern analog of the southeastern margin of the Laurentide Ice Sheet

The Malaspina Glacier on the southern coast of Alaska is a partial analog of the late Wisconsinan Laurentide Ice Sheet that occupied New England and adjacent areas. Ice lobes of the Malaspina are similar in size to end moraine lobes in southern New England and Long Island. Estimated ablation rates, surface slopes, and meltwater discharge per unit of surface area for the Laurentide Ice Sheet are comparable to measured ablation rates, surface slopes, and meltwater discharge rates for the Malaspina Glacier. Meltwater moves from the surface of the Malaspina down-glacier and toward the bed of the glacier along intercrystalline pathways and through a series of tunnels. Regolith beneath the glacier, which is eroded and transported to the margin of the glacier by subglacial and englacial streams, is the source of essentially all fluvial and lacustrine deposits on the Malaspina Foreland. By analogy, a similar hydrologic system existed at the southeastern margin of the Laurentide Ice Sheet. Subglacial regolith, which was eroded from beneath the ice sheet by meltwater, was the source of most stratified sediment deposited in New England and adjacent areas during the late Wisconsinan. Similarly, Wisconsinan ice-contact landforms in New England were built by the same processes that are constructing landforms composed of stratified sediments in contact with the Malaspina Glacier. For the Malaspina Glacier and the Laurentide Ice Sheet, therefore, we reject the concept of the “dirt machine” by which debris near the base of the glacier is carried to the surface of the glacier along shear planes and then washed off the surface to form ice-contact stratified deposits.

Geology of microtidal coastal lagoons: Rhode Island

Abstract The coastal lagoons of Rhode Island are contained behind narrow (200–300 m wide) barrier spits in a microtidal, wave-dominated environment. The major depositional environments within the lagoons are: (1) flood tidal deltas; (2) subtidal storm-surge platforms; and (3) back-lagoon, low-energy basins. The pathways of sediment influx into the coastal lagoons are: (1) tidal inlets (breachways); (2) temporary storm-surge channels cut through the barrier spits; and (3) overwash transport of sand that crosses the spits and builds into the lagoons. Sediment transport in the lagoons is caused by currents generated by windshear within the lagoon basins and by storm-surge generated flow, both of which may be additive to tidal currents. Lagoonal sedimentation was initiated in Ninigret Pond approximately 4100 B.P. (based on radiocarbon dating) as low-energy basins developed on an uneven Pleistocene glaciofluvial surface. Tidal-delta sedimentation began approximately 2500 B.P. The continued existence of the lagoons is dependent on rate of infill and barrier retreat versus rate of sea-level rise. Based on long-term sea-level rise (past 2500 years), calculations indicate that the lagoons will decrease in size as sediment influx exceeds the rate of inundation.

Seagrass-sediment dynamics of a flood-tidal delta in Rhode Island (U.S.A.)

Abstract Interactions between seagrasses and sediment dynamics were examined on a flood-tidal delta of a coastal lagoon in southern Rhode Island from 1978 to 1980. Serial aerial photographs combined with site visits showed that Zostera marina L. appeared on a stable portion of the delta in the springs of 1978 through 1980 and also on a new, incipient lobe during 1980. The population of an annual form of Z. marina increased rapidly from June (100 plants m−2) to late July and early August (1000 plants m−2), after which it rapidly decreased. In vegetated plots in both areas current measurements fell to zero near the substrate, while in experimentally denuded plots (64 m2) they simultaneously reached 8 cm s−1 in the stable and 14 cm s−1 in the unstable portion of the tidal delta. At the margin of the lobe in August 1980 the sediment accreted 2.5 cm in vegetated plots and eroded 1.5 cm in denuded plots. On the stable site short frames (0.25 m2) protruding 5 cm from the sediment surface prevented sediment removal and prolonged plant life, but these frames set at the margin of a lobe either made no difference or increased the rate of plant burial and subsequent plant loss. Rooted plants trapped dense red algal mats. Where Z. marina had been removed in the stable area, Ruppia maritima L. appeared. Benthic diatoms quickly covered all denuded areas. This work shows that, even as an ephemeral, Z. marina can encourage sediment accumulation by slowing water current on a moderate-energy tidal delta; but the degree to which this factor becomes important depends upon the density of the plant bed.

Mapping Shallow Coastal Ecosystems: A Case Study of a Rhode Island Lagoon

Abstract In order to effectively study, manage, conserve, and sustain shallow-subtidal ecosystems, a spatial inventory of the basic resources and habitats is essential. Because of the complexities of shallow-subtidal substrates, benthic communities, geology, geomorphology, and water column attributes, few standard protocols are fully articulated and tested that describe the mapping and inventory processes and accompanying interpretations. In this paper, we describe a systematic approach to map Rhode Islands shallow-subtidal coastal lagoon ecosystems, by using, integrating, and reconciling multiple data sets to identify the geology, soils, biological communities, and environments that, collectively, define each shallow-subtidal habitat. We constructed maps for these lagoons via a deliberate, step by step approach. Acoustics and geostatistical modeling were used to create a bathymetric map. These data were analyzed to identify submerged landforms and geologic boundaries. Geologic interpretations were verified with video and grab samples. Soils were sampled, characterized, and mapped within the context of the landscape and geologic boundaries. Biological components and distributions were investigated using acoustics, grab samples, video, and sediment profile images. Data sets were cross-referenced and ground-truthed to test for inconsistencies. Maps and geospatial data, with Federal Geographic Data Committee (FGDC)-compliant metadata, were finalized after reconciling data set inconsistencies and made available on the Internet. These data allow for classification in the revised Coastal and Marine Ecological Classification Standard (CMECS). With these maps, we explored potential relationships among and between physical and biological parameters. In some cases, we discovered a clear match between habitat measures; in others, however, relationships were more difficult to distinguish and require further investigation.

Benthic Geologic Habitats of Shallow Estuarine Environments: Greenwich Bay and Wickford Harbor, Narragansett Bay, Rhode Island, U.S.A

Abstract Oakley, B.A.; Alvarez, J.D., and Boothroyd, J.C., 2012. Benthic geologic habitats of shallow estuarine environments: Greenwich Bay and Wickford Harbor, Narragansett Bay, Rhode Island, U.S.A. An integrated mapping approach using high-resolution side-scan sonar, surface sediment grab samples, digital aerial and orthophotography, and underwater video imagery was used to map Holocene sediment cover and Late Wisconsinan glacial outcrop in two shallow embayments in Narragansett Bay, Rhode Island, U.S.A. The use of side-scan sonar to characterize the seafloor has become common in a variety of different marine environments. Challenges remain in classifying side-scan or other acoustic data into a naming convention that is useful to scientists and managers. We characterize the benthic geologic habitats of these areas utilizing a flexible naming convention that combines information about geologic processes, morphologic form, particle size, biota, and anthropogenic impacts. Benthic geologic habitats were separated into three habitat groups (depositional environments) (estuarine bayfloor, estuarine cove, and estuarine marginal habitats), and further divided on the basis of morphologic form, surface sediment texture, geologic features, biologic characteristics, and anthropogenic impacts. There is a general trend of decreasing grain size with increasing distance from the open water of Narragansett Bay; however, the types and distribution of facies is complicated, and this work adds to the developing sedimentary models of estuaries. The methods outlined in this paper have been successfully applied in other estuarine, lagoon, and shoreface environments, providing a concise method of imaging and characterizing benthic geologic habitats on the seabed.

Harnessing the Power of Relational Databases for Managing Subsurface Geotechnical and Geologic Data

Knowledge of surface and subsurface geology as well as geotechnical properties is fundamental to the planning and development of transportation systems. Through dynamic linkage of readily available spatial geographic information system data and subsurface borehole data stored in a relational database, we have created a spatially referenced, digital catalog of borehole data for two pilot areas in Rhode Island. The borehole database is populated with data from Rhode Island Department of Transportation geotechnical reports and supplemental data from the U.S. Geological Survey groundwater site inventory system as well as local storm-water and sewer projects. Most of these data were previously stored in paper format, making historical or inter-project data comparisons very difficult, if not impossible. Consolidation of these data in a single relational database yields two primary benefits: Historical data are readily accessible for review and, therefore, can be easily incorporated into the planning stages of new projects, and sophisticated analysis of the region becomes possible with access to data from multiple projects with both spatial and temporal layers. Geologic data include bedrock geology, surface outcrops, unconsolidated materials, soil type, topographic and orthophotographic base maps, and location of boreholes and wells. Subsurface data include land-surface elevation, depth to water table, depth to bedrock, and presence or absence of fill, high and low blow-count zones, and organic sediment. The digital catalog is distributed on a CD-ROM that includes ArcView project files and an Access relational database. The borehole data are also accessible through the Internet (http://geo.uri. edu/borehole/index.asp), with public retrieval access for all users but data entry restricted to registered users only.

Geographic Information System-Based Digital Catalog for Managing Subsurface Geotechnical and Geologic Data

Knowledge of surface and subsurface geology and geotechnical properties is fundamental to planning, developing, and modernizing transportation systems. Through dynamic coupling of readily available areal geographic information system coverages and subsurface borehole data stored in a relational database, a spatially referenced digital catalog of borehole data was created for two pilot areas in Rhode Island. The borehole database was populated with data derived from Rhode Island Department of Transportation geotechnical reports and supplemental data from the U.S. Geological Survey groundwater site inventory system and local storm water and sewer projects. Most of these data were previously maintained in paper format, making historical or interproject data comparisons virtually impossible. Unification of these data in a single relational database yields two primary benefits: (a) historical data are readily accessible for review and therefore can be incorporated easily into the planning stages of new projects and (b) sophisticated analysis of the region becomes possible with access to data from multiple projects with both spatial and temporal coverage. Geologic data include bedrock geology, surface outcrops, unconsolidated materials, soil type, topographic and orthophotographic base maps, and location of boreholes and wells. Subsurface data include land surface elevation, depth to water table, depth to bedrock, presence of fill, high and low blow-count zones, and organic sediment. The digital catalog is distributed on a CD-ROM that includes ArcView project files and an Access relational database. The borehole data are also accessible through the Internet, with retrieval access for all users and data entry privileges for registered users.