Geology topics

D. Wells

Publications and source records attributed to D. Wells.

4 recordsLinked to original sources

USGS2011

Effects of planting method and seed mix richness on the early stages of tallgrass prairie restoration

Tallgrass prairie restoration has been practiced for more than 75. years, yet few studies have systematically tested restoration methods over large geographic regions with the intent of refining methodology. In this study, we used three planting methods (dormant-season broadcast, growing-season broadcast and growing-season drill) fully crossed with three levels of seed species richness (10, 20, and 34 spp). We replicated the study on nine former agricultural fields located from east-central Iowa (Neal Smith National Wildlife Refuge) to northwestern Minnesota (Litchfield, Fergus Falls and Morris Wetland Management Districts), USA, within the northern tallgrass prairie biome. Objectives were to evaluate the relative influences of planting method, seed mix richness, and their interactions, on (1) planted cover (both total and by guild) and richness, (2) exotic species cover, and (3) non-planted native species cover. Optimal techniques varied between the two study areas: the dormant broadcast method produced greater cover of planted species at the Minnesota sites and the growing-season drill method produced greater cover of planted species at Iowa sites. The dormant broadcast method strongly favored establishment of perennial forbs while the growing-season drill favored warm-season grasses. Although increasing richness of the seed mix produced greater planted species richness, this did not result in greater resistance to exotic invasion. We conclude that, if planting during the growing season, drilling seed is preferable to broadcasting, but if the choice is between broadcasting seed in the dormant or growing season, the dormant season is preferred. ?? 2011.

Biological Conservation↗

USGS2006

The Hayward fault

This field guide consists of eleven stops at sites that illustrate the geological, geophysical, geographic, and engineering aspects of the Hayward fault in the East Bay. Section I (Stops 1–4) consists of stops that are part of the University of California at Berkeley (UC-Berkeley), including research facilities, retrofit of campus buildings, and geomorphic features along the fault. Section II (Stops 5 and 6) consists of stops along the Hayward fault north of the UC-Berkeley main campus, and Section III (stops 7–11) consists of stops related to the Hayward fault south of the UC-Berkeley main campus (Fig. 1 ). Stops are designed to illustrate geomorphic features of the fault, the effects of fault creep on structures sited on the fault, and retrofit design of structures to mitigate potential future deformation due to fault rupture.

California↗

USGS1999

Ten years of studies on Maryland's inner Continental Margin and coastal bays

During the past ten years of the Association of American State Geologists-Mineral Management Service Continental Margins Program, the Maryland Geological Survey investigated the sedimentological, paleontological, stratigraphical and geophysical character of Maryland's inner continental shelf. Based on seismic records and sedimentological analyses completed during the first four years, a late Quaternary stratigraphic model was developed. Five distinct stratigraphic units were identified and described on the Maryland inner shelf. These units represent late Pleistocene interglacial deposits, the oldest of which corresponds to pre-Illinoian (oxygen-isotope stages 7 and/or 9) transgressive shelf sands. Overlying the Q1 unit, the Q2 unit is a 6-meter thick mud sequence of oxygen-isotope stage 5 (128-75 ka) age. Units Q3 and Q4 representing fluvial and leading edge estuarine deposits (oxygen-isotope stages 4, 3 and 2) filled numerous paleochannels that were incised into units Q2 and Q1. Modern trailing-edge transgressive shelf shoals (Unit Q5) discontinuously cap the sequence. The 5th and 6th years studies reported on the economic minerals of surficial and cored sediments. Vibracores collected off the Maryland's shelf during previous studies were analyzed for mineral types and abundances, weight percent of general size fractions, and heavy mineral (HM) content. Mineralogic maturity indices were compiled to correlate the THM and economic heavy minerals (EHM) abundances with position offshore, sediment type, and the indices themselves. For the 7th year, the Maryland Geological Survey re-examined geophysical records and lithological data originally collected by the Army Corps of Engineers to locate and assess beach fill borrow areas for the Ocean City Beach Replenishment Project. Data from 163 vibracores and over 300 kilometers of high-resolution seismic profile records collected off Ocean City, Maryland, supported the stratigraphic model developed by MGS during the first four years of the AASG-MMS program. The Maryland coastal bays became the focus of study during the 8th and 9th years during which seismic records, cores and surficial sediment were collected in Isle of Wight and Assawoman Bays. Shallow pretransgression surface was mapped, relating the existing streams to offshore paleochannels. The tenth year study focused on developing a repository for vibracores collected on Maryland's inner continental shelf.During the past ten years of the Association of American State Geologists-Mineral Management Service Continental Margins Program, the Maryland Geological Survey investigated the sedimentological, paleontological, stratigraphical and geophysical character of Maryland's inner continental shelf. Based on seismic records and sedimentological analysis completed during the first four years, a late quaternary stratigraphic model was developed. Five distinct stratigraphic units were identified and described on the Maryland inner shelf. These units represent late Pleistocene interglacial deposits, the oldest of which corresponds to pre-Illinoian transgressive shelf sands.

Marine Georesources and Geotechnology↗

USGS1981

On the use of the nephelometer in estuarine waters

A study of the problems encountered in nephelometric determinations of suspended sediment loads in the Chesapeake Bay estuary has led to development of a technique which uses nephelometer readings as a guide for sampling at vertical profiles in an estuary. This permits optimum sampling for concentration profiles and allows one to use nephelometer/load ratios to characterize particles.

Chesapeake Bay↗