A GIS-based groundwater travel time model to evaluate stream nitrate concentration reductions from land use change

Excessive nitrate-nitrogen (nitrate) loss from agricultural watersheds is an environmental concern. A common conservation practice to improve stream water quality is to retire vulnerable row croplands to grass. In this paper, a groundwater travel time model based on a geographic information system (GIS) analysis of readily available soil and topographic variables was used to evaluate the time needed to observe stream nitrate concentration reductions from conversion of row crop land to native prairie in Walnut Creek watershed, Iowa. Average linear groundwater velocity in 5-m cells was estimated by overlaying GIS layers of soil permeability, land slope (surrogates for hydraulic conductivity and gradient, respectively) and porosity. Cells were summed backwards from the stream network to watershed divide to develop a travel time distribution map. Results suggested that groundwater from half of the land planted in prairie has reached the stream network during the 10 years of ongoing water quality monitoring. The mean travel time for the watershed was estimated to be 10.1 years, consistent with results from a simple analytical model. The proportion of land in the watershed and subbasins with prairie groundwater reaching the stream (10–22%) was similar to the measured reduction of stream nitrate (11–36%). Results provide encouragement that additional nitrate reductions in Walnut Creek are probable in the future as reduced nitrate groundwater from distal locations discharges to the stream network in the coming years. The high spatial resolution of the model (5-m cells) and its simplicity may make it potentially applicable for land managers interested in communicating lag time issues to the public, particularly related to nitrate concentration reductions over time.     

A comparative study of Monte Carlo simple genetic algorithm and noisy genetic algorithm for cost-effective sampling network design under uncertainty

This study evaluates and compares two methodologies, Monte Carlo simple genetic algorithm (MCSGA) and noisy genetic algorithm (NGA), for cost-effective sampling network design in the presence of uncertainties in the hydraulic conductivity (K) field. Both methodologies couple a genetic algorithm (GA) with a numerical flow and transport simulator and a global plume estimator to identify the optimal sampling network for contaminant plume monitoring. The MCSGA approach yields one optimal design each for a large number of realizations generated to represent the uncertain K-field. A composite design is developed on the basis of those potential monitoring wells that are most frequently selected by the individual designs for different K-field realizations. The NGA approach relies on a much smaller sample of K-field realizations and incorporates the average of objective functions associated with all K-field realizations directly into the GA operators, leading to a single optimal design. The efficacy of the MCSGA-based composite design and the NGA-based optimal design is assessed by applying them to 1000 realizations of the K-field and evaluating the relative errors of global mass and higher moments between the plume interpolated from a sampling network and that output by the transport model without any interpolation. For the synthetic application examined in this study, the optimal sampling network obtained using NGA achieves a potential cost savings of 45% while keeping the global mass and higher moment estimation errors comparable to those errors obtained using MCSGA. The results of this study indicate that NGA can be used as a useful surrogate of MCSGA for cost-effective sampling network design under uncertainty. Compared with MCSGA, NGA reduces the optimization runtime by a factor of 6.5.     

Quaternary palynology of the Pacific slope of Washington

Quaternary deposits on the Pacific slope of Washington range in age from the earliest known interglaciation, the Alderton, through the Holocene. Pollen stratigraphy of these deposits is represented by 12 major pollen zones and is ostensibly continuous through Zone 8 over more than 47,000 radiocarbon yr. Before this, the stratigraphy is discontinuous and the chronology less certain. Environments over the time span of the deposits are reconstructed by the comparison of fossil and modern pollen assemblages and the use of relevant meteorological data. The Alderton Interglaciation is characterized by forests of Douglas fir (Pseudotsuga menziesii), alder (Alnus), and fir (Abies). During the next younger interglaciation, the Puyallup, forests were mostly of pine, apparently lodgepole (Pinus contorta), except midway in the interval when fir, western hemlock (Tsuga heterophylla), and Douglas fir temporarily replaced much of the pine. Vegetation outside the limits of Salmon Springs ice (>47,00034,000 yr BP) varied chiefly between park tundra and forests of western hemlock, spruce (Picea), and pine. The Salmon Springs nonglacial interval at the type locality records early park tundra followed by forests of pine and of fir. During the Olympia Interglaciation (34,00028,000 yr BP), pine invaded the Puget Lowland, whereas western hemlock and spruce became manifest on the Olympic Peninsula. Park tundra was widespread during the Fraser Glaciation (28,00010,000 yr BP) with pine becoming more important from about 15,000 to 10,000 yr BP. Holocene vegetation consisted first of open communities of Douglas fir and alder; later, closed forests succeeded, formed principally of western hemlock on the Olympic Peninsula and of western hemlock and Douglas fir in the Puget Lowland. Over the length of the reconstructed environmental record, climate shifted between cool and humid or relatively warm, semihumid forest types and cold, relatively dry tundra or park tundra types. During times of glaciation, average July temperatures are estimated to have been at least 7°C lower than today. Only during the Alderton Interglaciation and during the Holocene were temperatures higher for protracted periods that at present.     

Isoprenoid hydrocarbons produced by thermal alteration of Nostoc muscorum and Rhodopseudomonas spheroides

Cells of Nostoc muscorum and Rhodopseudomonas spherodes have been subjected to thermal alteration over varying periods of time. Experiments were conducted using both unextracted and extracted cells in the absence and presence of montmorillonite. The isoprenoid hydrocarbons produced in these experiments have been examined. The major hydrocarbons produced were phytane and five isomeric phytenes. Phytane was observed to form faster from the unextracted cells than from the extracted cells. Montmorillonite increased the amount of phytane formed from the unextracted cells of Nostoc muscorum but not from the cells of Rhodopseudomonas spheroides. No phytadienes, pristane or pristenes were detected in the products of any of these experiments.     

Obliquity and precessional forcing of continental snow fall and melt: implications for orbital forcing of Pleistocene ice ages

Milankovitch theory posits that Earth's orbital cycles were the primary forcing of Pleistocene ice-age cycles through their strong influence on summer insolation at high latitudes. Accordingly, Milankovitch theory predicts ice volume should vary at both obliquity and precessional periods. However, early Pleistocene global ice volume varied mainly at the obliquity period with weak variability at the precessional period suggesting that Milankovitch theory is not sufficient to explain the ice-age cycles. Here we describe the results from a series of coupled ocean-atmosphere general circulation model experiments, using the Fast Ocean Atmosphere Model, that systematically investigate the influence of precession and obliquity on continental snowfall and potential ablation.Our model results identify three factors that magnify the influence of obliquity forcing on the global ice volume: First, high-latitude snowfall variability is dominated by changes in Earth's axial tilt. Second, hemispheric changes in net snowfall due to Earth's precession are out-of-phase, and largely cancel to produce a very small global snowfall change. Third, snowmelt variability over Antarctica responds greatly to changes in obliquity that intensify accumulation over obliquity cycle. We discuss the implications of these factors for existing hypotheses that account for the variability in the ice volume record.     

ASIANS,PACIFIC ISLANDERS,AND ETHNOBURBS IN AUCKLAND,NEW ZEALAND

ABSTRACT. Recent work on Asian ethnic minority immigrants to cities in the Anglophone Pacific Rim argues that their settlement patterns do not conform to those of earlier migrant streams. Instead of concentrating in high‐density, low‐quality, inner‐city housing, these new residents are moving directly to suburban areas where they form much less intensive concentrations—ethnoburbs—than has been typical of other culturally distinct migrant groups. We evaluate this thesis for Asian migrants in the Auckland metropolitan area, whose numbers more than quadrupled between 1991 and 2006. Their residential pattern is compared with that of Pacific Islanders also resident there, providing supporting evidence for the ethnoburb hypothesis.     

Turbidite deposition and the development of canyons through time on an intermittently glaciated continental margin: The Bonanza Canyon system,offshore eastern Canada

Bonanza Canyon is a complex canyon system on the slope from the intermittently glaciated Grand Bank on the south side of Orphan Basin. A 3D seismic reflection volume, 2D high-resolution seismic reflection profiles and ten piston cores were acquired to study the evolution of this canyon system in relation to glacial processes on the continental shelf and the effects of different types of turbidity currents on the development of deep water channels. Mapped reflector surfaces from the 3D seismic volume show that the Bonanza Canyons developed in a depression created by a large submarine slide of middle Pleistocene age, coincident with the onset of glacigenic debris flows entering western Orphan Basin. Two 3–5 km wide, flat-floored channels were cut into the resulting mass-transport deposit and resemble catastrophic glacial meltwater channels elsewhere on the margin. Both channels subsequently aggraded. The eastern channel A became narrower but maintained a sandy channel floor. The western channel, B, heads at a spur on the continental slope and appears to have been rather passively draped by muds and minor sands that have built 1500-m wave length sediment waves.Muddy turbidites recorded by piston cores in the channel and on the inter-channel ridges are restricted to marine isotope stage (MIS) 2 and were deposited from thick, sheet-like, and sluggish turbidity current derived from western Orphan Basin that resulted in aggradation of the channels and inter-channel ridges. Sandy turbidites in channels and on inner levees were deposited throughout MIS 2–3 and were restricted to the channels, locally causing erosion. Some coincide with Heinrich events. Channels with well-developed distributaries on the upper slope more readily trap the sediments on Grand Bank to form sandy turbidity currents. Channel B dominated by muddy turbidity currents has wide and relatively smooth floor whereas channel A dominated by sandy turbidity currents has a sharp geometry.