Geology topics

Gail V. Irvine

Publications and source records attributed to Gail V. Irvine.

7 recordsLinked to original sources

USGS2013

Sampling design for long-term regional trends in marine rocky intertidal communities

Probability-based designs reduce bias and allow inference of results to the pool of sites from which they were chosen. We developed and tested probability-based designs for monitoring marine rocky intertidal assemblages at Glacier Bay National Park and Preserve (GLBA), Alaska. A multilevel design was used that varied in scale and inference. The levels included aerial surveys, extensive sampling of 25 sites, and more intensive sampling of 6 sites. Aerial surveys of a subset of intertidal habitat indicated that the original target habitat of bedrock-dominated sites with slope ≤30° was rare. This unexpected finding illustrated one value of probability-based surveys and led to a shift in the target habitat type to include steeper, more mixed rocky habitat. Subsequently, we evaluated the statistical power of different sampling methods and sampling strategies to detect changes in the abundances of the predominant sessile intertidal taxa: barnacles Balanomorpha, the mussel Mytilus trossulus, and the rockweed Fucus distichus subsp. evanescens. There was greatest power to detect trends in Mytilus and lesser power for barnacles and Fucus. Because of its greater power, the extensive, coarse-grained sampling scheme was adopted in subsequent years over the intensive, fine-grained scheme. The sampling attributes that had the largest effects on power included sampling of “vertical” line transects (vs. horizontal line transects or quadrats) and increasing the number of sites. We also evaluated the power of several management-set parameters. Given equal sampling effort, sampling more sites fewer times had greater power. The information gained through intertidal monitoring is likely to be useful in assessing changes due to climate, including ocean acidification; invasive species; trampling effects; and oil spills.

Alaska↗

USGS2013

Geomorphic factors related to the persistence of subsurface oil from the Exxon Valdez oil spill

Oil from the 1989 Exxon Valdez oil spill has persisted along shorelines of Prince William Sound, Alaska, for more than two decades as both surface and subsurface oil residues. To better understand the distribution of persistent subsurface oil and assess the potential need for further restoration, a thorough and quantitative understanding of the geomorphic factors controlling the presence or absence of subsurface oil is required. Data on oiling and geomorphic features were collected at 198 sites in Prince William Sound to identify and quantify the relationships among these geomorphic factors and the presence and absence of persistent subsurface oil. Geomorphic factors associated with the presence of subsurface oil were initial oil exposure, substrate permeability, topographic slope, low exposure to waves, armoring on gravel beaches, tombolos, natural breakwaters, and rubble accumulations. Geomorphic factors associated with the absence of subsurface oil were impermeable bedrock; platforms with thin sediment veneer; fine-grained, well-sorted gravel beaches with no armor; and low-permeability, raised bay-bottom beaches. Relationships were found between the geomorphic and physical site characteristics and the likelihood of encountering persistent subsurface oiling at those sites. There is quantitative evidence of more complex interactions between the overall wave energy incident at a site and the presence of fine-scale geomorphic features that may have provided smaller, local wave energy sheltering of oil. Similarly, these data provide evidence for interactions between the shoreline slope and the presence of angular rubble, with decreased likelihood for encountering subsurface oil at steeply sloped sites except at high-angle sheltered rubble shoreline locations. These results reinforce the idea that the interactions of beach permeability, stability, and site-specific wave exposure are key drivers for subsurface oil persistence in exposed and intermittently exposed mixed gravel beach and rocky shoreline environments.

Alaska↗

USGS2010

Development of monitoring protocols to detect change in rocky intertidal communities of Glacier Bay National Park and Preserve

Glacier Bay National Park and Preserve in southeastern Alaska includes extensive coastlines representing a major proportion of all coastlines held by the National Park Service. The marine plants and invertebrates that occupy intertidal shores form highly productive communities that are ecologically important to a number of vertebrate and invertebrate consumers and that are vulnerable to human disturbances. To better understand these communities and their sensitivity, it is important to obtain information on species abundances over space and time. During field studies from 1997 to 2001, I investigated probability-based rocky intertidal monitoring designs that allow inference of results to similar habitat within the bay and that reduce bias. Aerial surveys of a subset of intertidal habitat indicated that the original target habitat of bedrock-dominated sites with slope less than or equal to 30 degrees was rare. This finding illustrated the value of probability-based surveys and led to a shift in the target habitat type to more mixed rocky habitat with steeper slopes. Subsequently, I investigated different sampling methods and strategies for their relative power to detect changes in the abundances of the predominant sessile intertidal taxa: barnacles -Balanomorpha, the mussel Mytilus trossulus and the rockweed Fucus distichus subsp. evanescens. I found that lower-intensity sampling of 25 randomly selected sites (= coarse-grained sampling) provided a greater ability to detect changes in the abundances of these taxa than did more intensive sampling of 6 sites (= fine-grained sampling). Because of its greater power, the coarse-grained sampling scheme was adopted in subsequent years. This report provides detailed analyses of the 4 years of data and evaluates the relative effect of different sampling attributes and management-set parameters on the ability of the sampling to detect changes in the abundances of these taxa. The intent was to provide managers with information to guide design choices for intertidal monitoring. I found that the coarse-grained surveys, as conducted from 1998 to 2001, had power ranging from 0.68 to 1.0 to detect 10 percent annual changes in the abundances of these predominant sessile species. The information gained through intertidal monitoring would be useful in assessing changes due to climate (including ocean acidification), invasive species, trampling effects, and oil spills.

Open-File Report↗

USGS2009

High-resolution sclerochronological analysis of the bivalve mollusk Saxidomus gigantea from Alaska and British Columbia: techniques for revealing environmental archives and archaeological seasonality

The butter clam, Saxidomus gigantea, is one of the most commonly recovered bivalves from archaeological shell middens on the Pacific Coast of North America. This study presents the results of the sclerochronology of modern specimens of S. gigantea, collected monthly from Pender Island (British Columbia), and additional modern specimens from the Dundas Islands (BC) and Mink and Little Takli Islands (Alaska). The methods presented can be used as a template to interpret local environmental conditions and increase the precision of seasonality estimates in shellfish using sclerochronology and oxygen isotope analysis. This method can also identify, with a high degree of accuracy, the date of shell collection to the nearest fortnightly cycle, the time of day the shell was collected and the approximate tidal elevation (i.e., approx. water depth and distance from the shoreline) from which the shell was collected. Life-history traits of S. gigantea were analyzed to understand the timing of growth line formation, the duration of the growing season, the growth rate, and the reliability of annual increments. We also examine the influence of the tidal regime and freshwater mixing in estuarine locations and how these variables can affect both incremental structures and oxygen isotope values. The results of the sclerochronological analysis show that there is a latitudinal trend in shell growth that needs to be considered when using shells for seasonality studies. Oxygen isotope analysis reveals clear annual cycles with the most positive values corresponding to the annual winter growth lines, and the most negative values corresponding to high temperatures during the summer. Intra-annual increment widths demonstrate clear seasonal oscillations with broadest increments in summer and very narrow increments or no growth during the winter months. This study provides new insights into the biology, geochemistry and seasonal growth of S. gigantea, which are crucial for paleoclimate reconstructions and interpreting seasonality patterns of past human collection.

Alaska;British Columbia↗

USGS2008

Development of a Monitoring Protocol to Detect Ecological Change in the Intertidal Zone of Sitka National Historical Park, Alaska

A pilot study to develop and test a probability-based intertidal monitoring protocol for Sitka National Historical Park was conducted from 1999 to 2003. In 1999, the basic design, with a focus on sampling the whole of the designated intertidal was created, and sampling was conducted for sessile species and large mobile invertebrates by point-intercept sampling of vertical transects and band surveys along transects, respectively. In 2002 and 2003, the same types of sampling were conducted, but quadrat sampling for small mobile invertebrates was added and then modified. This project has produced basic data on the presence, abundance, and spatial distribution of substrates and intertidal biota. Additionally, statistical power analyses conducted on the biological data have allowed assessment of the ability of the sampling to detect trends in the abundance of the predominant species. Current sampling has an 80 percent probability to detect +10 percent annual changes in abundance of all targeted species with an a = 0.05; the ability to detect -10 percent trends is not as uniformly high. Various options are discussed for decreasing the spatial variance of the data. The information presented provides a basis for discussion of the major questions being asked, how the sampling design might be reconfigured to be consistent in approach, and how the intertidal monitoring should interface with other potential intertidal monitoring.

Scientific Investigations Report↗

USGS2006

Persistence of 10-year old Exxon Valdez oil on Gulf of Alaska beaches: The importance of boulder-armoring

Oil stranded as a result of the 1989 Exxon Valdez spill has persisted for >10 years at study sites on Gulf of Alaska shores distant from the spill's origin. These sites were contaminated by "oil mousse", which persists in these settings due to armoring of underlying sediments and their included oil beneath boulders. The boulder-armored beaches that we resampled in 1999 showed continued contamination by subsurface oil, despite their exposure to moderate to high wave energies. Significant declines in surface oil cover occurred at all study sites. In contrast, mousse has persisted under boulders in amounts similar to what was present in 1994 and probably in 1989. Especially striking is the general lack of weathering of this subsurface oil over the last decade. Oil at five of the six armored-beach sites 10 years after the spill is compositionally similar to 11-day old Exxon Valdez oil. Analysis of movements in the boulder-armor that covers the study beaches reveals that only minor shifts have occurred since 1994, suggesting that over the last five, and probably over the last 10 years, boulder-armors have remained largely unmoved at the study sites. These findings emphasize the importance of particular geomorphic parameters in determining stranded oil persistence. Surface armoring, combined with stranding of oil mousse, results in the unexpectedly lengthy persistence of only lightly to moderately weathered oil within otherwise high-energy wave environments.

Alaska↗

USGS1999

Multi-year persistence of oil mousse on high energy beaches distant from the Exxon Valdez spill origin

For at least 5 yr after the Exxon Valdez spill, relatively unweathered oil mousse has persisted on the exposed rocky shores of Shelikof Strait 500 km from Prince William Sound, Alaska. Previously it was thought that oil would be rapidly removed from such geomorphic settings by wave action. Oil mousse persists at sites in Katmai National Park and Preserve (NP&P) where it was stranded high in the intertidal zone under a lag of large boulders. These boulders armor the beach, preventing waves from disturbing the substrate and its included oil. Weathering of this stranded mousse has been slight – mousse sampled in 1989, 1992 and 1994 show negligible changes in polynuclear aromatic hydrocarbons compared to 11-day old Exxon Valdez crude. The preservation of this oil is due to its transport as mousse boli whose interiors largely escape weathering, followed by its sheltering in the interstices of boulder-armored beaches. The transport of mousse may allow for the long distance dispersal of less weathered, and hence still toxic oil. Our findings suggest that the low ecological sensitivity ratings previously applied to exposed, rocky shorelines need to be modified. The biological threat posed by oil stranded on the Katmai NP&P coast probably is slight because of its small amount and sequestered state. However, it still possesses the ability to be chemically toxic and could be released through disturbance of the armoring boulders by unusually high wave events.

Alaska↗