Distribution and transport of sedimentary trace metals in the tidal portions of the Kennebec/Androscoggin River system, Maine, USA

Previous investigations suggest that contaminant transport from the large Kennebec/Androscoggin watershed is an important large-scale process in mid-coast Maine. To investigate this phenomenon, we determined the concentrations of Cd, Cr, Cu, Ni, Pb, Sn and Zn in the surface sediments of 47 stations in the tidal Kennebec/Androscoggin system. Most stations exhibited elevated metal concentrations. Highest levels were found in the main stem of the system. Distribution patterns lead to the conclusion that metals enter the system from the watershed and are transported to the nearshore Gulf of Maine. The coarse-grained, ebb tide dominated flow prevents the accumulation of contaminants in the estuary. This supports the hypothesis of Larsen and Gaudette (1995) that the Kennebec and Androscoggin watersheds are sources for contaminants observed in the nearshore Gulf of Maine.     

Long term monitoring for oil in the Exxon Valdez spill region

In the aftermath of the 1989 Exxon Valdez oil spill, a Long Term Environmental Monitoring Program (LTEMP) has been regularly sampling mussels (and some sediments) for polycyclic aromatic and saturated hydrocarbons (PAH and SHC) at sites in Port Valdez, Prince William Sound, and the nearby Gulf of Alaska region. After 1999, a decreasing trend appears in total PAH (TPAH) in tissues at all sites with current values below 100 ng/g dry weight (many below 50 ng/g). Currently, most samples reflect a predominantly dissolved-phase signal. This new low in TPAH likely represents ambient background levels. Synchrony in TPAH time-series and similarities in the hydrocarbon signatures portray regional-scale dynamics. The five inner Prince William Sound sites show similar composition and fluctuations that are different from the three Gulf of Alaska sites. The two Port Valdez sites represent a unique third region primarily influenced by the treated ballast water discharge from the Alyeska Marine Terminal. Prince William Sound has reverted to a stable environment of extremely low level contamination in which local perturbations are easily detected.     

Earth tides observed by gravity and GPS in southeastern Alaska

We analyzed gravity data obtained in Juneau and global positioning system (GPS) data obtained from three PBO sites in southeastern Alaska (SE-AK), which are part of a US research facility called ‘EarthScope’, and we compared the obtained tidal amplitudes and phases with those estimated from the predicted tides including both effects of the body tide and ocean tide. Global tide models predict the ocean tides in this region of complex coastline and bathymetry. To improve the accuracy of prediction, we developed a regional ocean tide model in SE-AK.Our comparison results suggest: (1) by taking into account the ocean tide effect, the amplitude differences between the observation and the predicted body tide is remarkably reduced for both the gravity and displacement (e.g. for the M₂ constituent, 8.5–0.3 μGal, and 2.4–0.1 cm at the AB50 GPS site in Juneau in terms of the vector sum of three components of the north–south, east–west and up–down), even though the ocean tide loading is large in SE-AK. (2) We have confirmed the precise point positioning (PPP) method, which was used to extract the tidal signals from the original GPS time series, works well to recover the tidal signals. Although the GPS analysis results still contain noise due to the atmosphere and multipath, we may conclude that the GPS observation surely detects the tidal signals with the sub-centimeter accuracy or better for some of the tidal constituents. (3) In order to increase the accuracy of the tidal prediction in SE-AK, it is indispensable to improve the regional ocean tide model developed in this study, especially for the phase.     

Faroe Shelf Water

Faroe Shelf Water (FSW) is the water mass that occupies the shallow parts of the Faroe Shelf, surrounding the Faroe Islands (62°N, 7°W). Intensive tidal mixing induces a high degree of homogeneity and the circulation system allows a partial isolation from surrounding waters. This water mass, therefore, supports a unique ecosystem of great importance for commercial fish stocks and studies have shown a clear dependence of the ecosystem on the physical processes that maintain this system and control the exchange between the FSW and the off-shelf waters. In order to identify and quantify these processes, a large observational dataset has been analysed and related to alternative theories. From this analysis, the extent and properties of the FSW have been quantified and the degree of stratification explained in terms of the Simpson–Hunter theory. The residual clockwise circulation system, which is responsible for the partial isolation from off-shelf waters, is shown to be mainly generated by tidal rectification. The typical exchange rate of water between the FSW and the off-shelf regimes has been determined by the use of simple models based on the heat and the salt budgets but the actual exchange rate is found to vary considerably in time and space. These results support earlier suggestions that this exchange is the main limiting factor for the phytoplankton spring bloom on the Faroe Shelf and that variations in exchange rate are responsible for the large inter-annual variation in spring bloom timing and intensity. The observations indicate that the on-shelf/off-shelf exchange intensity is not symmetrically distributed around the shelf, but rather concentrated around the narrow southern tip of the Faroe Shelf, where off-shelf waters during intensive exchange events may be imported all the way to the shore.     

On the role of domain size and resolution in the simulations with the HIRHAM region climate model

We investigate the simulated temperature and precipitation of the HIRHAM regional climate model using systematic variations in domain size, resolution and detailed location in a total of eight simulations. HIRHAM was forced by ERA-Interim boundary data and the simulations focused on higher resolutions in the range of 5.5–12 km. HIRHAM outputs of seasonal precipitation and temperature were assessed by calculating distributed model errors against a higher resolution data set covering Denmark and a 0.25° resolution data set covering Europe. Furthermore the simulations were statistically tested against the Danish data set using bootstrap statistics. The results from the distributed validation of precipitation showed lower errors for the winter (DJF) season compared to the spring (MAM), fall (SON) and, in particular, summer (JJA) seasons for both validation data sets. For temperature, the pattern was in the opposite direction, with the lowest errors occurring for the JJA season. These seasonal patterns between precipitation and temperature are seen in the bootstrap analysis. It also showed that using a 4,000 × 2,800 km simulation with an 11 km resolution produced the highest significance levels. Also, the temperature errors were more highly significant than precipitation. In similarly sized domains, 12 of 16 combinations of variables, observation validation data and seasons showed better results for the highest resolution domain, but generally the most significant improvements were seen when varying the domain size.     

Nutrient Budgets and Management Actions in the Patuxent River Estuary,Maryland

Multi-year nitrogen (N) and phosphorus (P) budgets were developed for the Patuxent River estuary, a seasonally stratified and moderately eutrophic tributary of Chesapeake Bay. Major inputs (point, diffuse, septic, and direct atmospheric) were measured for 13 years during which, large reductions in P and then lesser reductions in N-loading occurred due to wastewater treatment plant improvements. Internal nutrient losses (denitrification and long-term burial of particulate N and P) were measured in tidal marshes and sub-tidal sediments throughout the estuary as were nutrient storage in the water column, sediments, and biota. Nutrient transport between the oligohaline and mesohaline zones and between the Patuxent and Chesapeake Bay was estimated using a salt and water balance model. Several major nutrient recycling terms were directly and indirectly evaluated and compared to new N and P inputs on seasonal and annual time-scales. Major findings included: (1) average terrestrial and atmospheric inputs of N and P were very close to the sum of internal losses plus export, suggesting that dominant processes are captured in these budgets; (2) both N and P export were a small fraction (13% and 28%, respectively) of inputs, about half of that expected for N based on water residence times, and almost all exported N and P were in organic forms; (3) the tidal marsh-oligohaline estuary, which by area comprised ~27% of the full estuarine system, removed about 46% and 74% of total annual upland N and P inputs, respectively; (4) recycled N and P were much larger sources of inorganic nutrients than new inputs during warm seasons and were similar in magnitude even during cold seasons; (5) there was clear evidence that major estuarine processes responded rapidly to inter-annual nutrient input variations; (6) historical nutrient input data and nutrient budget data from drought periods indicated that diffuse nutrient sources were dominant and that N loads need to be reduced by about 50% to restore water quality conditions to pre-eutrophic levels.     

Frequency of sediment movement on the Washington continental shelf: A note

Several independent sets of field data have been analyzed in order to estimate the frequency of sediment movement on the continental shelf off Washington over an annual period and to identify the major components of the bottom velocity field causing this motion. Sediment motions resulting from: (1) bottom currents caused by surface wind stress and tides, and (2) wave-induced oscillatory bottom currents have been investigated. Analysis of a 260-day current record from 3 m off the seabed at 80 m depth on the continental shelf and a 205-day open-ocean wave record collected on Cobb Seamount 465 km west of the Washington coast suggest that the threshold of sediment motion was exceeded for approximately 22 days per year as a result of mean currents (20 min time averaged) and approximately 53 days per year from wave-induced oscillatory currents. Substantial variations can be expected from year to year, so these values represent order of magnitude estimates.     

Place Perception and Social Interaction on an Exurban Landscape in Central Colorado*

An assumption commonly made in research on exurbanization is that the subdivision of land ownership necessarily creates a socially divisive landscape devoid of shared place perceptions and concerns. This article presents the results of an ethnography project undertaken in a former Colorado ranching valley that is currently exurbanizing. The study revealed not only the emergence of social networks and groups among new residents, but also the presence of distinct themes in place perception and assessment within these assemblages. In particular, the results indicated that concerns about natural hazards and environmental limitations have motivated new residents to interact with one another.