The Truncated Discovery Process Model

The purpose of this paper is to describe a mathematical and computer model that has been developed by TransCanada for TransCanada Pipelines (TCPL) and for the Canadian Gas Potential Committee (CGPC) for future Canadian natural gas resource assessment work. It was developed in the contexts of developing a gas supply model for forecasting future Canadian gas supply for TCPL and of improving the CGPC's assessment methodologies and software. The model developed in this paper integrates two discovery process models used by the CGPC and solves the economic truncation problem for semi-mature to mature plays. It is based on applying techniques developed by G. M. Kaufman and J. D. Fuller and colleagues in new ways which extends the work of these authors. This model has a number of important advantages including: fast computational speed, integration of parametric and nonparametric statistical approaches, integration of the Kaufman and others model and the Arps-Roberts model, overcoming a PETRIMES limitation of a maximum of 1000 samples, providing a finding rate forecast for economic analysis and providing a fresh look at solving the economic truncation problem. The details of the new Modified Arps-Roberts Model (now known as the Truncated Discovery Process Model or TDPM for short) are discussed in this paper.     

Nitrate sources and sinks in Elkhorn Slough,California: Results from long-term continuous in situ nitrate analyzers

Nitrate and water quality parameters (temperature, salinity, dissolved oxygen, turbidity, and depth) were measured continuously with in situ NO₃ analyzers and water quality sondes at two sites in Elkhorn Slough in Central California. The Main Channel site near the mouth of Elkhorn Slough was sampled from February to September 2001. Azevedo Pond, a shallow tidal pond bordering agricultural fields further inland, was sampled from December 1999 to July 2001. Nitrate concentrations were recorded hourly while salinity, temperature, depth, oxygen, and turbidity were recorded every 30 min. Nitrate concentrations at the Main Channel site ranged from 5 to 65 μM. The propagation of an internal wave carrying water from ≈100 m depth up the Monterey Submarine Canyon and into the lower section of Elkhorn Slough on every rising tide was a major source of nitrate, accounting for 80–90% of the nitrogen load during the dry summer period. Nitrate concentrations in Azevedo Pond ranged from 0–20 μM during the dry summer months. Nitrate in Azevedo Pond increased to over 450 μM during a heavy winter precipitation event, and interannual variability driven by differences in precipitation was observed. At both sites, tidal cycling was the dominant forcing, often changing nitrate concentrations by 5-fold or more within a few hours. Water volume flux estimates were combined with observed nitrate concentrations to obtain nitrate fluxes. Nitrate flux calculations indicated a loss of 4 mmol NO₃ m^?2 d^?1 for the entire Elkhorn Slough and 1 mmol NO₃ m^?2 d^?1 at Azevedo Pond. These results suggested that the waters of Elkhorn Slough were not a major source of nitrate to Monterey Bay but actually a nitrate sink during the dry season. The limited winter data at the Main Channel site suggest that nitrate was exported from Elkhorn Slough during the wet season. Export of ammonium or dissolved organic nitrogen, which we did not monitor, may balance some or all of the NO₃ flux.     

Evaluating salt marsh restoration in Delaware Bay: Analysis of Fish response at former salt hay farms

In a continuing effort to monitor the fish response to marsh restoration (resumed tidal flow, creation of creeks), we compared qualitative and quantitative data on species richness, abundance, assemblage structure and growth between pre-restoration and post-restoration conditions at two former salt hay farms relative to a reference marsh in the mesohaline portion of Delaware Bay. The most extensive comparison, during April–November 1998, sampled fish populations in large marsh creeks with otter trawls and in small marsh creeks with weirs. Species richness and abundance increased dramatically after restoration. Subsequent comparisons indicated that fish size, assemblage structure, and growth of one of the dominant species,Micropogonias undulatus, was similar between reference and restored marshes 1 and 2 yr post-restoration. Total fish abundance and abundance of the dominant species was greater, often by an order of magnitude, in one of the older restored sites (2 yr post-restoration), while the other restored site (1 yr post-restoration) had values similar to the reference marsh. The success of the restoration at the time of this study suggests that return of the tidal flow and increased marsh area and edge in intertidal and subtidal creeks relative to the former salt hay farms contributed to the quick response of resident and transient young-of-the-year fishes.     

Photochemical production of low-molecular-weight carbonyl compounds in seawater and surface microlayer and their air-sea exchange

Coastal and oceanic surface microlayer samples were collected using a stainless steel screen, along with subsurface bulk seawater, and were analyzed for low-molecular-weight (LMW) carbonyl compounds, including formaldehyde, acetaldehyde, propanal, glyoxal, methylglyoxal, glyoxylic acid and pyruvic acid. The enrichment factor in surface microlayer compared to corresponding subsurface seawater ranged from 1.2 to 21. A time-series measurement at a coastal site showed strong diurnal variations in concentrations of the LMW carbonyl compounds in the surface microlayer and in the enrichment factor, with maxima in the early afternoon and minima in the early morning. Exposure of samples to sunlight resulted in the higher yields of these compounds in the surface microlayer than in the bulk seawater, by a factor of 1.1–25, suggesting that the higher photoproduction rate of LMW carbonyl compounds in the surface microlayer accounts for the majority of the observed enrichment in these samples. Potential sinks include biological uptake and mixing. Air-sea exchange may be a source for soluble compounds and a sink for less soluble compounds. The enrichment of the LMW carbonyl in surface microlayer may alter their net air-sea exchange direction e.g., from the ocean as a potential sink to a source for atmospheric acetaldehyde and acetone. The residence times of the LMW carbonyl compounds in the microlayer were estimated to be on the order of tens of seconds to minutes using a modified two-layer model. However, to maintain the observed microlayer enrichment factor, the residence time should be on the order of ˜ 1 hour. This prolonged residence time may be due to organic enrichment in the surface microlayer (‘organic film’) which inhibited molecular transfer of carbonyl compounds into and out of the microlayer. The deviated behavior from model prediction may also be due to changes in the apparent partition coefficients of these species as a result of thier physical and chemical interactions with organic matrix in the surface microlayer.     

A simple new bioassay based on echinochrome synthesis by larval sea urchins

A simple, rapid and quantitative embryo-larval bioassay that uses changes in echinochrome pigment synthesis as an indicator of seawater toxicity has been developed to allow increased use of sensitive sea urchin bioassays where time, resources and technical expertise may be limited. Several 48 h embryo-larval tests were conducted with lowered salinity and increased concentrations of copper as the potential toxicants. At 48 h the larvae were examined for echinochrome pigment level (E), the number of embryos that had gastrulated (G) and the percentage of gastrulas that had developed to prisms (P). Relationships between the pigment levels (E) and morphological parameters (G and P) were investigated using simple and partial correlation analysis. Reductions in echinochrome levels were correlated with both G and P, and partial correlation analysis showed that changes in echinochrome levels are associated with G, P, or G and P, depending on the experimental conditions. The echinochrome measurement procedure appears to be as good as or better than the morphological examination technique since it is as sensitive, less variable and takes about 25% of the time required for morphological examination.     

Amphipod prey of gray whales in the northern Bering Sea: Comparison of biomass and distribution between the 1980s and 2002–2003

The ampeliscid amphipod community in the Chirikov Basin of the northern Bering Sea was a focus of study during the 1980s because they were a major food for the Eastern North Pacific (ENP) population of gray whales Eschrichtius robustus. Information from the 1980s benthic investigations, published accounts of ENP gray whale population trends and the occurrence in 1999–2000 of an unusual number of gray whale mortalities prompted concern that the whale population may have exceeded the carrying capacity of its food base. Therefore, during two cruises per year between June and September, 2002 and 2003, we resampled the 20 stations occupied during the 1980s, to determine if there had been any significant changes in ampeliscid abundance and biomass. During 2002–2003, average ampeliscid dry weight biomass was about 28±10 g m⁻² (95% confidence interval), a decline of nearly 50% from maximum values in the 1980s. Amphipod length measurements indicated that the declines were due mainly to the absence of the larger animals (20–30 mm length). Two hypotheses were considered regarding the amphipod declines: gray whale predation and climate. Ampeliscid production (105 kcal m⁻² yr⁻¹) and gray whale energy requirements (1.6×10⁸ kcal individual⁻¹ yr⁻¹) indicated that as little as 3–6% of the current estimate of the ENP gray whale population could remove 10–20% of the annual ampeliscid production from the study site in 2002–2003, a finding consistent with the hypothesis that top-down control by foraging whales was the primary cause of the observed declines. A 10-yr time series of temperature near the bottom in the Bering Strait and northward transport did not reveal a consistent trend between 1990 and 2001, suggesting that climate influences were not the major cause of the observed declines. Arctic ampeliscids have slow growth rates and long generation times; therefore the ampeliscid community may require decades to recover to densities observed in the 1980s. Predicted warming trends in the northern Bering Sea could impact ampeliscid recovery by lowering primary production or altering the community composition of the benthos.     

The simultaneous immunological detection of four stress-70 protein isoforms in Mytilus edulis

Organisms exposed to adverse environmental conditions exhibit a stress-70 protein response which is highly conserved from bacteria to man. Immunological analysis of the stress-70 response in mussels is of interest for its potential use in marine biomonitoring. We have analysed the gill tissues of Mytilus edulis individuals for changes in stress-70 complement after exposure to 48 h of temperature stress. Using a commercially available monoclonal antibody raised against human hsp70 and epitope mapped to a conserved ATP binding region, the authors were able to detect by western analysis constitutively-expressed 72kDa and 78kDa isoforms in control animals acclimated at normal temperatures. After 48 h of heat stress, induction of a 70kDa protein was clearly seen along with an increase in the level of the 72kDa protein. Western analysis using two-dimensional gel electrophoresis indicated that the antibody recognised four stress-70 isoforms (70, 72, 72 and 78kDa). This simultaneous detection of four members of the stress-70 family will permit studies on the differential regulation of each of the four members of the multigene family in response to a variety of environmental Stressors.     

The nearshore western Beaufort Sea ecosystem: Circulation and importance of terrestrial carbon in arctic coastal food webs

The nearshore shelf of the Beaufort Sea is defined by extreme physical and biological gradients that have a distinctive influence on its productivity and trophic structure. Massive freshwater discharge from the Mackenzie River, along with numerous smaller rivers and streams elsewhere along the coast, produce an environment that is decidedly estuarine in character, especially in late spring and summer. Consequently, the Beaufort coast provides a critical habitat for several species of amphidromous fishes, some of which are essential to the subsistence lifestyle of arctic native populations. Because of its low in situ productivity, allochthonous inputs of organic carbon, identifiable on the basis of isotopic composition, are important to the functioning of this arctic estuarine system. Coastal erosion and river discharge are largely responsible for introducing high concentrations of suspended sediment from upland regions into the nearshore zone. The depletion in the ¹³C content of invertebrate and vertebrate consumers, which drops about 4–5‰ eastward along the eastern Alaskan Beaufort Sea coast, may reflect the assimilation of this terrestrial organic matter into local food webs. In addition, the large range in ¹³C values of fauna collected in the eastern Beaufort (nearly 8‰) compared to the same species in the northeastern Chukchi (3‰), indicate a lower efficiency of carbon transfer between trophic levels in the eastern Beaufort. The wider spread in stable isotope values in the eastern Beaufort may also reflect a decoupling between benthic and pelagic components. Isotopic tracer studies of amphidromous fishes in the Simpson Island barrier island lagoon revealed that terrestrial (peat) carbon may contribute as much as 30–50% of their total dietary requirements. On the eastern Alaska Beaufort Sea coast, the δ¹³C values of arctic cod collected in semi-enclosed lagoons were more depleted, by 3–4‰, compared to fish collected in the coastal Beaufort Sea. Calculations from isotopic mixing equations indicate cod from lagoons may derive 70% of their carbon from terrestrial sources. The δ¹⁵N values of lagoon fish were also 4‰ lower than coastal specimens, reflective of the lower δ¹⁵N values of terrestrially derived nitrogen (0–1.5‰ compared to 5–7‰ for phytoplankton). The role of terrestrial carbon in arctic estuarine food webs is especially important in view of the current warming trend in the arctic environment and the role of advective processes that transport carbon along the nearshore shelf. Biogeochemical studies of the arctic coastal estuarine environment may provide more insights into the function of these biologically complex ecosystems.     

Effects of salinity and clay type on oil-mineral aggregation

Effects of salinity and clay type on the aggregation process of crude oil and clay particles (oil-mineral aggregates--OMA) were studied in the laboratory. OMA were generated by shaking various oil/clay mixtures in water at 20 degrees C and at a pre-determined energy level. Shape, median and maximum sizes, size distribution and concentration of oil droplets forming OMA were measured using epi-fluorescence microscopy. Results showed that the median and maximum sizes and the concentration of mineral-stabilized droplets increase rapidly when salinity increases from zero to a critical aggregation salinity in the range of 1.2-3.5 ppt. The magnitude of the increase of droplet size is controlled by clay type, while the increase of droplet concentration is influenced by oil type. Size distributions of oil droplets are self-similar, but their magnitudes depend on salinity and oil type. The effect of salinity on droplet size distribution is strongly influenced by clay type. Empirical relationships are derived to calculate concentration and size distribution of mineral-stabilized droplets.