Shoreline Exposure Research Articles

Effect of environmental DNA sampling resolution in detecting nearshore fish biodiversity compared to capture surveys.

Sampling and sequencing marine environmental DNA (eDNA) provides a tool that can increase our ability to monitor biodiversity, but movement and mixing of eDNA after release from organisms before collection could affect our inference of species distributions. To assess how conditions at differing spatial scales influence the inferred species richness and compositional turnover, we conducted a paired eDNA metabarcoding and capture (beach seining) survey of fishes on the coast of British Columbia. We found more taxa were typically detected using eDNA compared to beach seining. eDNA identified more taxa with alternative habitat preferences, and this richness difference was greater in areas of high seawater movement, suggesting eDNA has a larger spatial grain influenced by water motion. By contrast, we found that eDNA consistently missed low biomass species present in seining surveys. Spatial turnover of communities surveyed using beach seining differed from that of the eDNA and was better explained by factors that vary at small (10-1000s meters) spatial scales. Specifically, vegetation cover and shoreline exposure explained most species turnover from seining, while eDNA turnover was not explained by those factors and showed a distance decay pattern (a change from 10% to 25% similarity from 2 km to 10 km of distance), suggesting unmeasured environmental variation at larger scales drives its turnover. Our findings indicate that the eDNA sample grain is larger than that of capture surveys. Whereas seining can detect differences in fish distributions at scales of 10s-100s of meters, eDNA can best summarize fish biodiversity at larger scales possibly more relevant to regional biodiversity assessments.

Wind Effects on Small‐Scale River and Creek Plumes

AbstractIn contrast to large river plumes, Coriolis effects are weak, and inertia is quickly depleted so that the fate and structure of small‐scale plumes are more sensitive to tide and wind. Advected alongshore by reversing tidal currents in absence of wind forcing, small buoyant plumes are persistently deflected downwind in presence of alongshore winds and exhibit little tidal variability. The effect of different upwelling/downwelling winds on buoyant outflows ∼10 m3 s−1 is explored. With increasing wind, tidal variability decreases, as does asymmetry in plume characteristics—for strong winds upwelling/downwelling plume structure is similar as the plume is retained closer to the shore. Wind forcing is exerted directly by wind stress on the surface of the plume and indirectly by wind‐driven currents that deflect the upwind boundary of the plume. While inertia and buoyancy dominate the inner plume, and wind dominates the outer plume, the mid‐plume responds to an interaction of wind and buoyancy forcing that can be indexed by a Plume Wedderburn Number Wpl (wind stress vs. density gradients): for weaker winds (Wpl < 1) surface stress enhances stratification through straining, lengthening the reach of low‐salinity waters, whereas for stronger winds (Wpl > 1) surface stress mixes the plume vertically, shortening the reach of low‐salinity waters. However, dilute plume waters extend furthest in strong winds, passively advected several kilometers downwind. Shoreline exposure to outflow transitions from a quasi‐symmetrical tide‐averaged zone of impact under zero‐wind to a heavily skewed zone with persistent weak wind and a one‐sided zone for strong wind.

Rapid coastal erosion of ice-bonded deposits on Pelly Island, southeastern Beaufort Sea, Inuvialuit Settlement Region, western Canadian Arctic

This paper quantifies rates of shoreline change and investigates the influence of surficial geology on shoreline dynamics between 1950 and 2018 on Pelly Island, located 10 km off the Mackenzie Delta. Long-term changes in shoreline position were calculated using imagery analysis and Analysing Moving Boundaries Using R (AMBUR). The influence of shoreline exposure to predominant storm direction and influence of surficial geology were examined for northwestern and southeastern zones. The average annual linear regression rate (LRR) rate during the 1950–2018 observation period was −3.8 m·a−1. The end point rate (EPR) was calculated for seven observation periods: 1950–1972, 1972–1985, 1985–2000, 2000–2018, 2000–2013, 2013–2018, and 1950–2018. A mean EPR of −5.5 ± 0.7 m·a−1 was calculated for the 2000–2018 period, and a maximum retreat rate of 46.7 ± 2.1 m·a−1 was recorded during the 2013–2018 observation period. By comparing the rate of change for sections of historical shorelines with differing surficial geology and exposure to storms, it was possible to draw conclusions on why Pelly Island continues to have the highest retreat rates in the Mackenzie–Beaufort region. Greater retreat rates were observed in lacustrine deposits (5.3 m·a−1) compared with moraine deposits (2.7 m·a−1). In addition, shoreline exposure to the predominant storm direction from the northwest was found to be a major influence on rates of shoreline change in all observation periods.

A preliminary assessment of coastal vulnerability for Ngazidja Island, Comoros Archipelago, Western Indian Ocean

In previous studies, an emphasis on the particular vulnerability of small island states to future sea-level rise and the intensity of increasing storm surges have been discussed. This preliminary assessment develops a Coastal Vulnerability Index (CVI) along the 202 km-long coastline of Ngazidja Island (formerly Grande Comore, Comoros Archipelago), using fieldwork, remote sensing, and geographic information system tools (GIS). The CVI considers nine variables: geology (a), geomorphology (b), topography (c), shoreline change (d), shoreline exposure (e), relative sea-level rise (f), significant wave height (g), mean tide range (h), and land-use (i). The land-use variable was added in this analysis to highlight the human asset exposure in the surrounding areas. Each variable was ranked based on local physical and hydrodynamic conditions and their vulnerability contribution to sea-level rise. The CVI was computed in 270 sections. According to the vulnerability index, approximately 57.5% of the coastline is under low and moderate vulnerability. High and very high vulnerabilities refer specifically to beaches and shores with old volcanic lava flows located mainly in the northern, northeastern, and southeastern parts of the island, approximately 42.5% of the coastline. The lowest value of CVI is 9.2 on high, rocky cliffs and the highest value is 160 on beaches. This vulnerability partition along the coastline is consistent with in situ indicators of coastal erosion and flooding. In a sea-level rise context, it is of prime importance to integrate coastal vulnerability maps with planning and sustainable management of the coastal zone.

What's ‘SUP’ with paddlers? Integrating spatial, social, and ecological data to understand behavior among paddlesport users at a popular lake destination

Non-motorized, water-based recreation (e.g., paddlesports) represents one of the most sought after outdoor activities in U.S. Parks and Protected Areas (PPA). Among paddling options, stand-up paddleboarding represents the activity with the highest levels of growth. However, stand-up paddleboarding has yet to be spatially examined in a PPA setting. This research paired GPS-tracking data of paddlesport users with corresponding social and environmental information to build a robust understanding of paddlesport behavior and experience in PPA. Statistical classification procedures revealed distinctions in movement across paddling activity types, highlighting implications for resource protection and visitor flow management. Integrating spatial and non-spatial data identified numerous drivers and impacts of paddlesport use: the motivation to escape corresponded to traveling further distances, while higher group sizes and prolonged shoreline exposure aligned with concentrated use levels near parking lots and facilities. Results broaden our knowledge of recreationist movement and experience, and add to a growing body of PPA research that incorporates mixed method spatial approaches to research designs. Furthermore, these findings contribute novel information on paddlesport spatial behavior in PPAs, especially given the emergent introduction of stand-up paddleboarding.

Multi-decadal planform changes on coral reef islands from atolls and mid-ocean reef platforms of the equatorial Pacific Ocean: Gilbert Islands, Republic of Kiribati

Constructed of poorly lithified carbonate sediments with elevations of <3–5 m above MSL, coral reef islands are considered extremely vulnerable to the effects of anthropogenic climate change, particularly sea-level rise. While some studies have shown islands are dynamic landforms with the ability to physically adjust their shape and position on the reef platform, large geographical gaps still exist in reef island change records. This study presents a multi-decadal analysis of shoreline changes and planform geomorphic adjustments across coral reef islands in the equatorial Pacific from the Gilbert archipelago, Republic of Kiribati. Shoreline positions of 71 islands from 3 atolls and 4 mid-ocean reef platforms were analysed by comparing historical aerial photographs (from 1940s and 1960s) and recent satellite imagery covering a period of local sea-level rise rate of ~2.2 mm/year. Results show ~47% of the shorelines were characterised by statistically significant accretion leading to a net increase of 274.07 ha (2.45%) of planform land area. A comparative examination of changes on platform-islands and atoll-islands revealed platform-islands were relatively more stable (mean rate of 0.01 m/year) with significantly less variability in shoreline change rates, while atoll-islands were characterised by a higher mean rate of accretion (0.09 m/year). Further analysis of change rates across various shoreline exposure categories, demonstrate high dynamism across atoll-island shorelines is a function of distinctive local-scale processes occurring within atoll settings; lagoon-facing shorelines were characterised by the highest rate of accretion (0.14 m/year), spits were found to be highly dynamic and embayment infilling accounted for ~9% of the net increase in land area across the study islands. Results are instructive in defining styles of morphological change across various geomorphic settings to inform projections of future island adjustments, assessments of attribution of island change and formulation of adaptation responses across atoll nations.

Quantified Exposures from Potential Deepwater Releases for Comparative Risk Assessment of Oil Spill Response Options Including Dispersant Use

ABSTRACT The goal of oil spill response is to mitigate the overall impacts of spilled oil on ecological and socioeconomic resources. Surface and subsea dispersant applications are effective tools that remain controversial after decades of research and discussion. The tradeoff that dispersants potentially increase effects on water column and benthic communities while reducing floating and nearshore/shoreline oil exposure is recognized, but inevitably are qualitatively considered when subjectivity and stakeholder interests prevail. To be objective and transparent, we developed a quantitative approach using oil spill modeling to evaluate response alternatives in a Comparative Risk Assessment (CRA) framework where the fractions of resources potentially exposed are compared, along with their recovery potential. The model quantifies exposure as water surface area, shoreline area and water volume exposed above thresholds of concern, multiplied by duration of exposure, in each environmental compartment. These exposure metrics (i.e., area-days or volume-days) are multiplied by relative densities across the environmental compartments to evaluate the fractions of the resources exposed in each modeled scenario. The fractions of resources exposed, along with their recovery potential, inform decisionmakers using a Spill Impact Mitigation Assessment (SIMA) approach with quantitative estimates of potential consequences, which they may consider along with stakeholder values. Previously, we evaluated a deepwater blowout in the Gulf of Mexico, assuming no intervention or various response options (mechanical recovery, in-situ burning, surface dispersant application, and subsea dispersant injection [SSDI]). The findings were that inclusion of SSDI reduced human and wildlife exposure to volatile organic compounds; dispersed oil into a large water volume at depth; enhanced biodegradation; and reduced surface water, nearshore and shoreline exposure to floating oil and entrained/dissolved oil in the upper water column. Tradeoffs included increased exposures at depth. However, since organisms are less abundant at depth, overall exposure of valued ecosystem components was minimized by use of SSDI. Follow-up modeling shows the benefits of SSDI are due to reduction of the oil droplet sizes released to the water column. Droplet sizes are sensitive to oil and gas release rates, release depth, orifice size and dispersant-to-oil ratio. The exposure metrics resulting from a matrix of scenarios varying these inputs and response actions are expected to be generally representative of the fate and behavior of oil and gas blowouts in the offshore areas of the Gulf of Mexico, as well as other regions with similar oceanographic conditions.

Relationship of Coastline and Mangrove Area in West Rangsang - Indonesia

The coastal zone of West Rangsang is part of the Kepulauan Meranti regency, which directly faces Malacca Strait, which is one of the most crowded channels in the world. However, its shoreline is an open coast, which mostly undergoes local erosion as the defensive areas, encompassing coral rock and mangrove forest, are fragmented by nature and human exploitation. Therefore, this study aimed to investigate the relationship between the damaged coastline and the mangrove area changes in West Rangsang for the past 20 years. We propose a remote sensing method by satellite imagery to evaluate the coastline changes and the mangrove. Each year, the coastline positions were obtained using data processing involving geometric calibration, image cutting, and extraction. The changes were analyzed by inter-crossing the images of 1997 and 2017, further divided for four periods, i.e., 1997–2002, 2002–2007, 2007–2012, and 2012–2017. The results showed that varying erosion and accretion rates were due to shoreline exposure, strongly associated with the mangrove forests' devastation. However, this caused the physical function loss as an anchor against the coast's wear-out and as a breaker of waves and current approaching the island from the ocean. The stakeholder may use these research results to appropriate measures, such as replanting and creating mangrove-care societies, to conserve and maintain the coast.

Use of chemical concentration changes in coastal sediments to compute oil exposure dates

Oil spills can result in changes in chemical contaminant concentrations along coastlines. When concentrations are measured along the Gulf of Mexico over time, this information can be used to evaluate oil spill shoreline exposure dates. The objective of this research was to identify more accurate oil exposure dates based on oil spill chemical concentrations changes (CCC) within sediments in coastal zones after oil spills. The results could be used to help improve oil transport models and to improve estimates of oil landings within the nearshore. The CCC method was based on separating the target coastal zone into segments and then documenting the timing of large increases in concentration for specific oil spill chemicals (OSCs) within each segment. The dataset from the Deepwater Horizon (DWH) oil spill was used to illustrate the application of the method. Some differences in exposure dates were observed between the CCC method and between oil spill trajectories. Differences may have been caused by mixing at the freshwater and sea water interface, nearshore circulation features, and the possible influence of submerged oil that is unaccounted for by oil spill trajectories. Overall, this research highlights the benefit of using an integrated approach to confirm the timing of shoreline exposure.

Comparative Risk Assessment of spill response options for a deepwater oil well blowout: Part 1. Oil spill modeling

Oil spill model simulations of a deepwater blowout in the Gulf of Mexico De Soto Canyon, assuming no intervention and various response options (i.e., subsea dispersant injection SSDI, in addition to mechanical recovery, in-situ burning, and surface dispersant application) were compared. Predicted oil fate, amount and area of surfaced oil, and exposure concentrations in the water column above potential effects thresholds were used as inputs to a Comparative Risk Assessment to identify response strategies that minimize long-term impacts. SSDI reduced human and wildlife exposure to volatile organic compounds; dispersed oil into a large water volume at depth; enhanced biodegradation; and reduced surface water, nearshore and shoreline exposure to floating oil and entrained/dissolved oil in the upper water column. Tradeoffs included increased oil exposures at depth. However, since organisms are less abundant below 200 m, results indicate that overall exposure of valued ecosystem components was minimized by use of SSDI.

Impact of climate change and seasonal trends on the fate of Arctic oil spills

We investigated the effects of a warmer climate, and seasonal trends, on the fate of oil spilled in the Arctic. Three well blowout scenarios, two shipping accidents and a pipeline rupture were considered. We used ensembles of numerical simulations, using the OSCAR oil spill model, with environmental data for the periods 2009–2012 and 2050–2053 (representing a warmer future) as inputs to the model. Future atmospheric forcing was based on the IPCC’s A1B scenario, with the ocean data generated by the hydrodynamic model SINMOD. We found differences in “typical” outcome of a spill in a warmer future compared to the present, mainly due to a longer season of open water. We have demonstrated that ice cover is extremely important for predicting the fate of an Arctic oil spill, and find that oil spills in a warming climate will in some cases result in greater areal coverage and shoreline exposure.

Ecological impacts of winter water level drawdowns on lake littoral zones: a review

Freshwater littoral zones harbor diverse ecological communities and serve numerous ecosystem functions that are controlled, in part, by natural water level fluctuations. However, human alteration of lake hydrologic regimes beyond natural fluctuations threaten littoral zone ecological integrity. One type of hydrologic alteration in lakes is winter water level drawdowns, which are frequently employed for hydropower, flood control, and macrophyte control, among other purposes. Here, we synthesize the abiotic and biotic responses to annual and novel winter water level drawdowns in littoral zones of lakes and reservoirs. The dewatering, freezing, and increased erosion of exposed lakebeds drive changes in the littoral zone. Shoreline-specific physicochemical conditions such as littoral slope and shoreline exposure further induce modifications. Loss of fine sediment decreases nutrient availability over time, but desiccation may promote a temporary nutrient pulse upon re-inundation. Annual winter drawdowns can decrease taxonomic richness of macrophytes and benthic invertebrates and shift assemblage composition to favor taxa with r-selected life history strategies and with functional traits resistant to direct and indirect drawdown effects. Fish assemblages, though less directly affected by winter drawdowns (except where there is critically low dissolved oxygen), experience negative effects via indirect pathways like decreased food resources and spawning habitat. We identify eight general research gaps to guide future research that could improve our understanding about the complex effects of winter drawdowns on littoral zone ecology.

Evaluation of Oil Fate and Exposure from a Deep Water Blowout With and Without Subsea Dispersant Injection Treatment as Well as Traditional Response Activities

ABSTRACT The goals of subsea dispersant injection (SSDI) into a deep water oil and gas blowout are to increase effectiveness of dispersant treatment over that achievable at the water surface; decrease the volume of oil that surfaces; reduce human and wildlife exposure to volatile organic compounds (VOCs); disperse the oil over a large water volume at depth; enhance biodegradation; and reduce surface, nearshore and shoreline exposure to floating and surface-water entrained/dissolved oil. Potential tradeoffs include increased water column and benthic resource exposures to oil at depth. In order to better understand the implications of SSDI use, we modeled a hypothetical blowout in the northern Gulf of Mexico to predict oil fate and compare the environmental exposure for no intervention to various response options (i.e., mechanical recovery, in-situ burning (ISB), surface dispersant application, and SSDI). Probabilistic modeling was used to evaluate the influence of variable metocean conditions (i.e., wind, currents, temperature). The results showed that even with a substantial capacity of equipment applied, mechanical and ISB removed only a small fraction of the oil that would otherwise be floating or evaporate. Compared to cases without use of SSDI, SSDI reduced the size of oil droplets by an order of magnitude, substantially decreased the amount of oil on the water surface and on the shoreline, increased dissolution and degradation rates of hydrocarbons at depth, increased weathering rate of rising oil such that floating oil contained much lower content of soluble and semi-soluble hydrocarbons, decreased surface water concentrations of dissolved hydrocarbons, and decreased VOC emissions to the atmosphere and, therefore, reduced human and wildlife exposures to VOCs. The tradeoff was that with SSDI there was greater exposure to hydrocarbons in deep water. However, densities of biota are much lower in deep water than near the water surface, where sensitive early life history stages of fish and invertebrates are most abundant. This approach provides decision makers with quantitative environmental exposures with which they may evaluate risk tradeoffs regarding appropriate response strategies for mitigating impacts from oil and gas released during a deep water blowout.

Assessing shoreline exposure and oyster habitat suitability maximizes potential success for sustainable shoreline protection using restored oyster reefs.

Oyster reefs provide valuable ecosystem services that contribute to coastal resilience. Unfortunately, many reefs have been degraded or removed completely, and there are increased efforts to restore oysters in many coastal areas. In particular, much attention has recently been given to the restoration of shellfish reefs along eroding shorelines to reduce erosion. Such fringing reef approaches, however, often lack empirical data to identify locations where reefs are most effective in reducing marsh erosion, or fully take into account habitat suitability. Using monitoring data from 5 separate fringing reef projects across coastal Louisiana, we quantify shoreline exposure (fetch + wind direction + wind speed) and reef impacts on shoreline retreat. Our results indicate that fringing oyster reefs have a higher impact on shoreline retreat at higher exposure shorelines. At higher exposures, fringing reefs reduced marsh edge erosion an average of 1.0 m y−1. Using these data, we identify ranges of shoreline exposure values where oyster reefs are most effective at reducing marsh edge erosion and apply this knowledge to a case study within one Louisiana estuary. In Breton Sound estuary, we calculate shoreline exposure at 500 random points and then overlay a habitat suitability index for oysters. This method and the resulting visualization show areas most likely to support sustainable oyster populations as well as significantly reduce shoreline erosion. Our results demonstrate how site selection criteria, which include shoreline exposure and habitat suitability, are critical to ensuring greater positive impacts and longevity of oyster reef restoration projects.

Assessment of Egypt’s Red Sea coastal sensitivity to climate change

A coastal sensitivity index (CSI) was developed to assess the response of the Red Sea coast in Egypt to climate change in terms of sea level rise and global warming. Six different variables pertaining to the intrinsic characteristics of the coast that extends to 1200 km were utilized, notably: coastal geomorphology, coastal slope, width of the coastal plain, shoreline exposure, fauna/flora and land use. Data have been extracted, manipulated and presented using remote sensing and GIS analysis. The resulting coastal sensitivity map depicts the susceptibility levels of the Red Sea coastal plain to climate change. The most severely sensitive segments (very high CSI) account for 31 % (365 km) of the coast. They occur across unconsolidated, flat, wide, exposed, ecologically effective and/or inhabited coasts. On the other hand, the least sensitive (low CSI) coastal segments total 245 km (20 %) and are mainly rocky, steep, narrow, barren and/or inaccessible shores. Eustatic sea level rise by 1 m should inundate a coastal area of 106 km2, whereas a sudden tsunami of 5 m height should overwhelm 724 km2, particularly at the southern section near Shalateen. Global warming of seawater should impact the coastal zone between Hurghada and Marsa Alam (270 km long) due to the occurrence of fringing coral reef systems. The coastal sensitivity index provides a synoptic overview that could help prioritize emergency plans and protection strategies to reduce the ramifications of climate change.

Facies analysis and depositional environments of the Taulanne Limestone Formation in the South Alpine Foreland Basin (Oligocene, southeastern of France)

The Taulanne Limestone Formation of the Castellane region (South Alpine Foreland Basin of France) represents an Oligocene lake depositional system developed above the marine Nummulitic succession. A sedimentological analysis of the Taulanne limestone allows the identification of nine marine, lacustrine, and palustrine facies. The spatial and temporal distribution of these facies records five depositional sequences that are correlated between the Sant Peire section (edge of the lake) and the Pres section (central lake). Water-level variations highlight the high-frequency balance between drying and wetting periods under fluctuating climatic conditions. Lacustrine facies developed during more humid periods while palustrine facies correspond to more arid conditions and longer lake shoreline exposure. At the basin scale, the lateral changes in accommodation space are attributed to differential subsidence between the Pres and the Sant Peire sections, which permitted the deposition of a thicker succession in the central part of the lake (Pres section). The Taulanne limestone records a marine to continental transition. The progressive filling of the basin is related to the regional tectonic activity, namely the emplacement of the Embrun-Ubaye nappes to the northeast of the study area at about 30–32 Ma. This final regressive trend represents the transition between the underfilled flysch stage (marine Nummulitic succession) of a foreland-basin cycle to the overfilled stage (alluvial Red Molasse deposits) during the primary exhumation of the Internal Alps.

Assessing vulnerability to sea-level rise using a coastal sensitivity index: a case study from southeast Australia

Many of the world’s coasts appear vulnerable to the impacts of climate change and sea-level rise. This paper assesses the application of a coastal sensitivity index (CSI) to the Illawarra coast, a relatively well-studied shoreline in southeast Australia. Nine variables, namely (a) rock type, (b) coastal slope (c) geomorphology (d) barrier type (e) shoreline exposure (f) shoreline change (g) relative sea-level rise (h) mean wave height and (j) mean tide range, were adopted in calculation of the CSI (the square root of the product of the ranked variables divided by the number of variables). Two new variables, shoreline exposure and barrier type, were trialled in this analysis and the extent to which these increased the discriminatory power of the index was assessed. Four iterations of the CSI were undertaken using different combinations of ranked variables for each of 105 cells in a grid template, and the index values derived were displayed based on quartiles, indicating sections of coast with very high, high, moderate and low sensitivity. Increasing the number of variables increased the discriminatory power of the index, but the broad pattern and the rank order were very similar for each of the iterations. Rocky and cliffed sections of coast are least sensitive whereas sandy beaches backed by low plains or dunes record the highest sensitivity. It is difficult to determine shoreline change on this coast, because individual storms result in substantial erosion of beaches, but there are prolonged subsequent periods of accretion and foredune rebuilding. Consequently this variable is not a good indicator of shoreline sensitivity and the index is unlikely to provide a clear basis for forecasting future recession of beaches. The results of this study provide a framework for coastal managers and planners to prioritize efforts to enhance the resilience or consider adaptation measures in the coastal zone within a study region. Sensitivity of the coast if considered in conjunction with other social factors may be an input into broader assessments of the overall vulnerability of coasts and their communities.

Quantification of openness and wave activity in archipelago environments

Ecological and geomorphological processes in the littoral zone are greatly influenced by waves. Despite its importance wave exposure is not often quantified as a spatial parameter in coastal research. We present three GIS-based approaches for openness and wave exposure assessment in archipelago environments. First, we studied openness by fetch measurements: a theme map of sea area openness showing average fetch lengths for 1 km 2 study cells over the SW-Finnish archipelago area of 16 900 km 2 was produced. Second, we calculated wave exposure based on average wave power values for shoreline points to create a shoreline exposure classification within the same study areas. Finally, we made temporal graphs to study the variation in shoreline wave power and work at selected sites during a four-year period. The fetch and wave power calculations using GIS provide interesting possibilities for spatial studies concerning shoreline exposure in fragmented archipelago environments. Different kinds of numerical information of the shoreline exposure are required for diverse purposes in coastal regions: the average fetch maps assess effectively the sea area openness, and shoreline exposure and the temporal graphs quantify parameters relevant to littoral processes.

Insights from Stratigraphic Modeling: Mud-Limited Versus Sand-Limited Depositional Systems

Quantitative stratigraphic modeling provides new perspectives on the controls on basin-fill stacking patterns, gross lithology distributions, and submarine fan deposition in siliciclastic systems. Our modeling relates basin-fill geometries to the ratio of space creation vs. sediment supply. Facies components differentially distribute sand/mud mixtures below rising base-level surfaces across a basin profile. We model alluvial architecture, shoreline position, shelf width, and the occurrence of turbidite sands as a function of relative base-level rise and varying receiving-basin geometries. Slope unconformities and onlapping submarine fans are the erosional and depositional responses to changing basin physiography. Sediment budgeting reveals two types of siliciclastic systems. Sand-limited systems develop in shallow basins or on basin-margin platforms; have broad, muddy, wave-graded shelves; and are subject to exposure and major basinward shifts of shoreline with minor sea level falls. Mud-limited systems develop during progradation into deep-water basins, have narrow shelves with turbidites in a base-of-slope position, and are not particularly susceptible to major basinward shifts in facies. We emphasize the fundamental importance of basin physiography and lithology budgeting, as well as sea level, in contrast to eustatically based models. In addition to accommodation and sediment supply, alluvial architecture and basin depth also act as primary controls on shelf width, basin-fill geometry, and submarine fan deposition.

SHORELINE EXPERIMENTS AND THE PERSISTENCE OF OIL ON ARCTIC BEACHES

ABSTRACT Experiments associated with the oiling of beaches in an arctic environment show that fetch and wave-energy conditions at the shoreline are primary factors in determining the persistence of stranded oil. Five intertidal sections of coast were oiled, each of which differed in terms of shoreline exposure and fetch. The oil loadings of the test beaches that were oiled artificially were in the same range as those from an adjacent nearshore spill, so that the experimental results can be assumed to replicate real-world oiling conditions. On the most exposed beach (fetch 90 kilometers) all oil was removed naturally after 80 days of exposure to open-water conditions. At a semi-exposed location, 85 to 95 percent of the oil was removed within 40 days, and at the most sheltered test sites (fetch less than 2 km) between 5 and 30 percent of the oil remained after an observation period of 160 open-water days. Data collection to determine fates of oil at the different sites over a four-year period is continuing. In this relatively low-energy wave climate environment, with an open-water season of about 60 days, most exposed beaches would be cleaned naturally to levels less than 500 milligrams/kilogram within 100 days, but where the fetch is less than 10 to 25 km the expected persistence of oil stranded in the intertidal zone could be greater than 10 years.