Geology topics
Austin Reed
Publications and source records attributed to Austin Reed.
Anthropocene streams and base-level controls from historic dams in the unglaciated mid-Atlantic region, USA
Recently, widespread valley-bottom damming for water power was identified as a primary control on valley sedimentation in the mid-Atlantic US during the late seventeenth to early twentieth century. The timing of damming coincided with that of accelerated upland erosion during post-European settlement land-use change. In this paper, we examine the impact of local drops in base level on incision into historic reservoir sediment as thousands of ageing dams breach. Analysis of lidar and field data indicates that historic milldam building led to local base-level rises of 2–5 m (typical milldam height) and reduced valley slopes by half. Subsequent base-level fall with dam breaching led to an approximate doubling in slope, a significant base-level forcing. Case studies in forested, rural as well as agricultural and urban areas demonstrate that a breached dam can lead to stream incision, bank erosion and increased loads of suspended sediment, even with no change in land use. After dam breaching, key predictors of stream bank erosion include number of years since dam breach, proximity to a dam and dam height. One implication of this work is that conceptual models linking channel condition and sediment yield exclusively with modern upland land use are incomplete for valleys impacted by milldams. With no equivalent in the Holocene or late Pleistocene sedimentary record, modern incised stream-channel forms in the mid-Atlantic region represent a transient response to both base-level forcing and major changes in land use beginning centuries ago. Similar channel forms might also exist in other locales where historic milling was prevalent.
North American Brant: Effects of changes in habitat and climate on population dynamics
We describe the importance of key habitats used by four nesting populations of nearctic brant (Branta bernicla) and discuss the potential relationship between changes in these habitats and population dynamics of brant. Nearctic brant, in contrast to most geese, rely on marine habitats and native intertidal plants during the non-breeding season, particularly the seagrass, Zostera, and the macroalgae, Ulva. Atlantic and Eastern High Arctic brant have experienced the greatest degradation of their winter habitats (northeastern United States and Ireland, respectively) and have also shown the most plasticity in feeding behavior. Black and Western High Arctic brant of the Pacific Flyway are the most dependent on Zostera, and are undergoing a shift in winter distribution that is likely related to climate change and its associated effects on Zostera dynamics. Variation in breeding propensity of Black Brant associated with winter location and climate strongly suggests that food abundance on the wintering grounds directly affects reproductive performance in these geese. In summer, salt marshes, especially those containing Carex and Puccinellia, are key habitats for raising young, while lake shorelines with fine freshwater grasses and sedges are important for molting birds. Availability and abundance of salt marshes has a direct effect on growth and recruitment of goslings and ultimately, plays an important role in regulating size of local brant populations. ?? 2005 Blackwell Publishing Ltd.
Description and identification of American Black Duck, Mallard, and hybrid wing plumage
We developed a key to identify wings of hybrids between American Black Ducks (Anas rubripes) and Mallards (A. platyrhynchos). Material for analysis included review of historical descriptions dating from the late 1700's, older museum collections in Europe and North America, wings collected from hunters in North America and Great Britain, birds banded in Canada and the United States, and a flock of propagated hybrids. All first filial generation (F1) American Black Duck - Mallard hybrids were identified correctly with the key. A lower proportion of other hybrid cohorts (i.e., backcrosses of F1 to parental forms (P1), and second and third filial generations (F2, F3, etc.) were identified. We successfully identified a larger portion of male than female hybrids for all hybrid progeny cohorts examined except F1. The new key identified 2.37 times more hybrids in the 1977 U.S. Fish and Wildlife Service Parts Collection Survey (annual determination of the species, age, and sex composition of the waterfowl harvest using detached wings contributed by hunters) than were identified by standard techniques. The proportion of American Black Duck - Mallard hybrids to the American Black Duck parental population (the ratio: hybrids/[hybrids + American Black Ducks]) may therefore be closer to 0.132 than 0.056, the historically reported value. The hybrid key is suggested for use from North Carolina north in the Atlantic Flyway and Arkansas and Tennessee north in the Mississippi Flyway (areas where other members of the Mallard group will not confound assessment). We provide suggestions for further research that would assist identification of wings in parts collection surveys and permit estimation of the proportional representation of Mallard genes in the American Black Duck gene pool.
Autumn use of Izembek Lagoon, Alaska, by brant from different breeding areas
Thirty-three adult brant ( Branta bernicla ) were radiomarked at 4 widely separated areas of the western Canadian arctic and 1 area in western Alaska during June-August 1987. Their use of the Izembek Lagoon on the Alaska Peninsula was monitored through the 1987 fall staging period (Sep-Dec). Eighty percent of the brant (n = 33), including ≥50% of individuals from each of the marking areas, were located at Izembek Lagoon. The mean arrival time for brant marked nearest to Izembek (the Yukon-Kuskokwim Delta [YK], Alas. [900 km away]) was 18 September, followed by those from the Mackenzie Delta, Northwest Territories, (3,500 km away) on 26 September, and brant from Victoria, Melville, and Prince Patrick islands, Northwest Territories [NT], (approx 4,500 km away) on 3 October. The mean duration of their stay at Izembek was 49 days. Within the 48-km-long lagoon there was considerable segregation between black brant ( B. b. nigricans ) and gray-bellied brant (intermediate between black brant and B. b. hrota ).