Transient small boats as a long-distance coastal vector for dispersal of biofouling organisms

Alaska is at the northern end of an apparent latitudinal trend of decreasing coastal marine introductions on the West Coast of North America. Historical propagule supply may have played a role in forming this trend, but few studies have evaluated propagule supply to northern latitudes. Here, we examined the role of small boat traffic as a mechanism of long-distance spread for nonindigenous species (NIS) into coastal Alaska. We used a combination of public records, marina surveys, and boater interviews to characterize vessel traffic patterns and boater behaviors. In-water SCUBA sampling of recently arrived transient boats provided data on extent, richness, composition, and biogeography of biofouling incursions to Alaska from outside of the state. We documented a striking seasonality and directionality of vessel traffic, and most vessels were on voyages of >900 km. Most transient vessels sampled had few organisms, although one third had >100 organisms on submerged surfaces. Several NIS were recorded, including two that are not known to be established in Alaska (Watersipora subtorquata and Amphibalanus improvisus). The seasonal northward pulse of vessels and their cumulative biofouling species represent an important incursion mechanism for species yet to establish at the northern edge of a marine bioinvasion front in the northeastern Pacific. The low numbers of NIS sampled in this study coincide with the low number of marine NIS known from Alaska, which suggests that an opportunity remains to promote awareness and management of the vector to limit NIS influx to the region. This may be particularly relevant for future scenarios of increased vessel traffic and ocean warming, which are likely to interact to increase establishment success of invaders from the south.     

Objective definition of rainfall intensity–duration thresholds for the initiation of post-fire debris flows in southern California

Rainfall intensity–duration (ID) thresholds are commonly used to predict the temporal occurrence of debris flows and shallow landslides. Typically, thresholds are subjectively defined as the upper limit of peak rainstorm intensities that do not produce debris flows and landslides, or as the lower limit of peak rainstorm intensities that initiate debris flows and landslides. In addition, peak rainstorm intensities are often used to define thresholds, as data regarding the precise timing of debris flows and associated rainfall intensities are usually not available, and rainfall characteristics are often estimated from distant gauging locations. Here, we attempt to improve the performance of existing threshold-based predictions of post-fire debris-flow occurrence by utilizing data on the precise timing of debris flows relative to rainfall intensity, and develop an objective method to define the threshold intensities. We objectively defined the thresholds by maximizing the number of correct predictions of debris flow occurrence while minimizing the rate of both Type I (false positive) and Type II (false negative) errors. We identified that (1) there were statistically significant differences between peak storm and triggering intensities, (2) the objectively defined threshold model presents a better balance between predictive success, false alarms and failed alarms than previous subjectively defined thresholds, (3) thresholds based on measurements of rainfall intensity over shorter duration (≤60 min) are better predictors of post-fire debris-flow initiation than longer duration thresholds, and (4) the objectively defined thresholds were exceeded prior to the recorded time of debris flow at frequencies similar to or better than subjective thresholds. Our findings highlight the need to better constrain the timing and processes of initiation of landslides and debris flows for future threshold studies. In addition, the methods used to define rainfall thresholds in this study represent a computationally simple means of deriving critical values for other studies of nonlinear phenomena characterized by thresholds.     

Oxygen and Ethene Biostimulation for a Persistent Dilute Vinyl Chloride Plume

Contamination of groundwater with chlorinated ethenes is common and represents a threat to drinking water sources. Standard anaerobic bioremediation methods for the highly chlorinated ethenes PCE and TCE are not always effective in promoting complete degradation. In these cases, the target contaminants are degraded to the daughter products DCE and/or vinyl chloride. This creates an additional health risk, as vinyl chloride is even more toxic and carcinogenic than its precursors. New treatment modalities are needed to deal with this widespread environmental problem. We describe successful bioremediation of a large, migrating, dilute vinyl chloride plume in Massachusetts with an aerobic biostimulation treatment approach utilizing both oxygen and ethene. Initial microcosm studies showed that adding ethene under aerobic conditions stimulated the rapid degradation of VC in site groundwater. Deployment of a full‐scale treatment system resulted in plume migration cutoff and nearly complete elimination of above‐standard VC concentrations.     

Continental-scale patterns in soil geochemistry and mineralogy: Results from two transects across the United States and Canada

In 2004, the US Geological Survey (USGS) and the Geological Survey of Canada (GSC) initiated a pilot study that involved collection of more than 1500 soil samples from 221 sites along two continental transects across Canada and the United States. The pilot study was designed to test and refine protocols for a soil geochemical survey of North America. The two transects crossed a wide array of soil parent materials, soil ages, climatic conditions, landforms, land covers and land uses. Sample sites were selected randomly at approximately 40-km intervals from a population defined as all soils of the continent. At each site, soils representing 0 to 5 cm depth, and the O, A, and C horizons, if present, were collected and analyzed for their near-total content of over 40 major and trace elements. Soils from 0–5 cm depth were also collected for analysis of organic compounds. Results from the transects confirm that soil samples collected at a 40-km spacing reveal coherent, continental- to subcontinental-scale geochemical and mineralogical patterns that can be correlated to aspects of underlying soil parent material, soil age and climate influence. The geochemical data also demonstrate that at the continental-scale the dominance of any of these major factors that control soil geochemistry can change across the landscape. Along both transects, soil mineralogy and geochemistry change abruptly with changes in soil parent materials. However, the chemical influence of a soil’s parent material can be obscured by changing climatic conditions. For the transects, increasing precipitation from west to east and increasing temperature from north to south affect both soil mineralogy and geochemistry because of climate effects on soil weathering and leaching, and plant productivity. Regional anomalous metal concentrations can be linked to natural variations in soil parent materials, such as high Ni and Cr in soils developed on ultramafic rocks in California or high P in soils formed on weathered Ordovician limestones in central Kentucky. On local scales, anomalous metal concentrations recognized in soil profiles, such as high P in soils from animal confinement sites, are consistent with local anthropogenic disturbances. At a larger scale, the distribution of Hg across the west to east transect demonstrates that it can be difficult to distinguish between natural or anthropogenic contributions and that many factors can contribute to an element’s spatial distribution.Only three samples in a subset of seventy-three 0–5 cm depth soil samples from the north to south transect had organochlorine pesticides values above the method detection limit, apparently related to historic usage of the pesticides DDT and dieldrin.     

Coseismic stress parameter of three California Earthquakes derived from the stochastic finite fault technique

Stochastic finite fault modeling is used to derive the coseismic stress parameter distribution on the fault surface of three well-recorded California earthquakes: M7.0, 1989, Loma Prieta; M7.3, 1992, Landers; and M6.7, 1994, Northridge. Classical waveform inversion techniques are inherently more powerful than stochastic modeling as a means of deriving detailed source parameters. However, the application of stochastic methods to the source modeling problem is useful to: (1) explore and calibrate the limitations and boundaries of stochastic modeling, (2) understand its relationship to more deterministically based techniques, and (3) provide a view of the source radiation not available from deterministic modeling. The stress parameter distribution for the M7.0 1989 Loma Prieta earthquake fault shows a concentration of stress in the lower part of the northwest side of the fault and another concentration in the upper southeast side of the fault, with an average stress parameter of 80 bars over the fault surface. The stress parameter distribution for the M7.3 1992 Landers earthquake fault shows a gradual increase of stress starting from the southeast side of the fault, close to the hypocenter, towards the center. The maximum stress occurs in the lower central part of the modeled fault surface. The average stress parameter is 70 bars for the Landers earthquake. The stress parameter distribution of the M6.7 1994 Northridge earthquake shows a concentration at the lower southeast end of the fault surface, extending toward the center of the fault surface and stretching to the northwest end. The average stress parameter is 80 bars for Northridge earthquake. The stress parameter distributions derived in this study by stochastic finite-fault modeling of high-frequency motions show considerable similarity to many of the slip distributions provided by different research groups for the same earthquakes, suggesting that the derivation of stress parameter distribution on a fault surface by the method applied in this study is reliable and closely tied to slip on the fault.     

Leaf dipping as an environmental screening measure to test chemical efficacy against Bemisia tabaci on poinsettia plants

The screening of potential chemicals for control of Bemisia tabaci on poinsettia (Euphorbia pulcherrima c.v. Lilo Pink) plants using a leaf dipping technique was investigated. All relevant B. tabaci lifestages (eggs, larvae and adults) were investigated. In leaf dipping tests, Certis spraying oil was the only compound to show potential to be used as a control agent against B. tabaci eggs, with 81% obtained mortality. Oberon resulted in no mortality of B. tabaci eggs in the reported experiments. Leaf dipping against second instar and adult B. tabaci proved more effective for all chemical products. Dipping techniques using Majestik, Certis spraying oil and Agri- 50 E all resulted in high second instar larval mortality (93, 87 and 85.5 %, respectively). Certis spraying oil again resulted in a high efficacy against adult B. tabaci with 100 % mortality obtained. The potential of the various chemicals to be incorporated into integrated pest management strategies for the control of B. tabaci is discussed.     

Modeling changes in ice dynamics and subsurface thermal structure in Lake Michigan-Huron between 1979 and 2021

Ocean Dynamics - The world’s largest lakes, including the Laurentian Great Lakes, have experienced significant surface warming and loss of ice cover over the last several decades. Although...     

Exposure age and erosional history of an upland planation surface in the US Atlantic Piedmont

The upland planation surface in the Piedmont of central New Jersey consists of summit flats, as much as 130 km² in area, that truncate bedding and structure in diabase, basalt, sandstone, mudstone and gneiss. These flats define a low‐relief regional surface that corresponds in elevation to residual hills in the adjacent Coastal Plain capped by a fluvial gravel of late Miocene age. A Pliocene fluvial sand is inset 50 m below the upland features. These associations suggest a late Miocene or early Pliocene age for the surface. To assess exposure age and erosional history, a 4·4 m core of clayey diabase saprolite on a 3 km² remnant of the surface was sampled at six depths for atmospherically produced cosmogenic ¹⁰Be. The measured inventory, assuming a deposition rate of 1·3 × 10⁶ atoms cm⁻² a⁻¹, yields a minimum exposure age of 227 000 years, or, assuming continuous surface erosion, a constant erosion rate of 10 m Ma⁻¹. Because the sample site lies about 60 m above the aggradation surface of the Pliocene fluvial deposit, and itself supports a pre‐Pliocene fluvial gravel lag, this erosion rate is too high. Rather, episodic surface erosion and runoff bypassing probably have produced an inventory deficit. Reasonable estimates of surface erosion (up to 10 m) and bypassing (up to 50 per cent of total precipitation) yield exposure ages of as much as 6·4 Ma. These results indicate that (1) the surface is probably of pre‐Pleistocene age and has been modified by Pleistocene erosion, and (2) exposure ages based on ¹⁰Be inventories are highly sensitive to surface erosion and runoff bypassing. Copyright © 2000 John Wiley & Sons, Ltd.