Coastal Processes

Bioprotection and Disturbance: seaweed, microclimatic stability and weathering in the intertidal zone.

by Martin Coombes

MA. Coombes, LA. Naylor, HA Viles, RC Thompson (accepted). Bioprotection and Disturbance: seaweed, microclimatic stability and weathering in the intertidal zone. Geomorphology.

Plants, animals, and microorganisms can contribute to geomorphology and ecology through their direct or indirect... more Plants, animals, and microorganisms can contribute to geomorphology and ecology through their direct or indirect bioprotective roles, which can reduce weathering and erosion. For example, indirect bioprotection can operate via biotic influences on microclimate, whereby weathering processes associated with fluctuations in temperature and moisture are limited. As a consequence, bioprotective organisms moderate physical disturbance at a range of spatial and temporal scales. The microclimatic influence of organisms can also improve environmental conditions for other species, and thus acts as an agent of biodiversity maintenance.
In the intertidal zone, the spatial and temporal distribution of macroalgae (seaweeds) is patchy, related to physical and ecological conditions for colonization and growth, and the nature and frequency of disturbance (both natural and anthropogenic). We examined the influence of seaweed canopies (Fucus spp.) on near-surface microclimate and, by implication, on weathering and ecology. Monitoring on hard artificial coastal structures in South West England, UK built from limestone and concrete showed that both the range and maxima of daily summertime temperatures were significantly lower (by an average of 56% and 25%, respectively) in areas colonized by seaweed compared to experimentally cleared areas. Short-term microclimatic variability (minutes–hours) was also significantly reduced (by an average of 78% for temperature and 71% for humidity) under algal canopies during low tide events.
Using seaweed as an example, we develop a conceptual model of the relationship between biological cover and microclimate in the intertidal zone. Disturbance events which remove or drastically reduce seaweed cover mediate shifts between relatively stable and unstable states with respect to both weathering and ecological stress associated with heat and desiccation. In urbanized coastal environments, where disturbance may be frequent, facilitating the establishment and recovery of canopy-forming species on rocks and engineered structures may enhance the durability of construction materials as well as support conservation, planning, and policy targets for biodiversity enhancement.

The significance of the major variables that control the formation and evolution of the Hellenic beach zones.

by George Alexandrakis

Alexandrakis G., Poulos S.E. 10th Greek Symposium in Oceanography and fisheries.

This study aims to investigate the significance of 14 principal variables (sedimentological, oceanographical and... more This study aims to investigate the significance of 14 principal variables (sedimentological, oceanographical and morphodynamic) that control the formation and evolution of the Hellenic beach zones. Thus, data from sixteen beach zones, characterized by different geomorphological settings, were collected and inserted to a properly organized database that allowed the application of factor analysis. The results of the statistical analysis showed that the wave characteristics appear to have a leading role in the evolution of the beach zone, followed by the sea level rise rate and the granulometry of the surf zone. In particular, for pocket beaches, the profile length and the riverine sediment influx are the most significant variables, whilst for the other beach zones that host active river systems, the dominant factor, apart from riverine sediment flux, is wave characteristics.

The anticipated spatial loss of microtidal beaches in the next 100 years due to sea level rise.

by George Alexandrakis

G. Alexandrakis and S. Poulos. Geophysical Research Abstracts Vol. 14, EGU2012-5560, 2012, EGU General Assembly 2012

The anticipated sea level rise is expected to influence on a global scale the earth coast in the near future and it is... more The anticipated sea level rise is expected to influence on a global scale the earth coast in the near future and it is considered to be a main factor related to coastal retreat, with beach zones being among the most vulnerable coastal landforms. Records for the period 1890-1990 have shown that sea level has already risen by 18cm (min: +10cm, max: +25cm), while the projected to 2100 sea level rise has estimated to be 20 to 50cm (IPCC, 2007). It has to be highlighted that a small rise of few tens of meters would cause shoreline retreat of a few to tens meters in the case of low lying coasts, i.e. beach zones (e.g. Bruun 1962, Nichol and Letherman, 1995, Ciavola and Corbau, 2002). Within the concept of climate change, sea level rise could also being related, in regional scale, to changes of meteorological factors such as intensity, duration and direction of the onshore blowing winds, variation in atmospheric pressure. In the microtidal Greek waters temporary changes in sea level exceeds the 1 m (HHS, 2004) This work investigates the impact of sea level rise to sixteen beach zones along the Greek coast. More specifically, shoreline retreat has been estimated for time periods of 10, 20, 50 and 100 years for the corresponding sea level rise of 0,038, 0,076m, 0,19m and 0,38m, according to the A1B scenario of IPCC (2007) and utilizing Dean’s (1991) equation; the latter includes in the calculations both the effects of the anticipated sea level rise and the associated storm surge The appropriate morphodynamic and sedimentological data used for the estimation of beach retreat has been deduced from field measurements. Finally, the percentage of the sub-aerial area lost for each beach zone, under investigation, has been estimated. The results show that coastline retreat follows a liner increase in the case of eleven out of the 16 beach zones, for a time period of 100 years. Santava beach zone (inner Messiniakos Gulf) undergoes most of erosion in the first period of 20 years, meeting a new state of equilibrium when land loss reaches the 68.67% of its initial width. Similarly, the beach zones of Ag. Petros (Isl. Andros), Korission Lagoon (Isl. Corfu), Marathon bay (Attica) and Alfios river delta (west Peloponnese) a reduced rate of retreat after the first 50 years, attaining a new state of equilibrium but when already have lost more than 85% of their current width.

A method to evaluate metal enrichment in marine sediments

by Eric Alfaro

Lizano, O., E. Alfaro y A. Salazar, 2012. Un método para evaluar el enriquecimiento de metales en sedimentos marinos en Costa Rica. Rev. Biol. Trop. 60(Supl. 2). 197-211.

Abstract: In order to evaluate metal enrich-
ment in sediments , a method is proposed and tested in Bahia Culebra... more Abstract: In order to evaluate metal enrich-
ment in sediments , a method is proposed and tested in Bahia Culebra and the Golfo de Nicoya, Costa Rica
through the normalization of the elements against aluminum, and by linear regression of the logarithm of the
concentrations of different elements respect to aluminum. The distributions of the elements manganese, and
strontium of Bahía Culebra did not satisfy the tests of normalization and linear regression, indicating a non-
natural distribution or enrichment of these elements in this region. In the Golfo de Nicoya the elements copper
, zinc , rubidium and the strontium did not satisfy the test of normality or the linear regression with respect
to aluminum, indicating a possible enrichment of these elements. The majority of the concentrations of the ele-
ments in two sample sites, with the exception of chromium, are within the natural ranges in rocks or clays of
marine sediments, and within the concentration ranges of other studies done in these same regions. Chromium
has average values beyond the natural concentrations, the values of some samples in the Golfo de Nicoya are up
to 10 times greater than the concentration value of a typical bay with high contamination of this element. Rev.
Biol. Trop. 60 (Suppl. 2): 197-211.

Lithological heterogeneity in a back-barrier sand island: Implications for modelling hydrogeological frameworks

by Stephen McLoughlin

Reference:
Hodgkinson, J., Cox, M.E. & McLoughlin, S., 2008. Lithological heterogeneity in a back-barrier sand island: Implications for modelling hydrogeological frameworks. Sedimentary Geology 203: 64-86.

Sediment mineralogy, quartz-grain surface-textures, grain-size analysis, bore-hole logging and ground penetrating... more Sediment mineralogy, quartz-grain surface-textures, grain-size analysis, bore-hole logging and ground penetrating radar are combined to develop a three dimensional stratigraphic model of a back-barrier sand island in southeast Queensland, Australia. The island consists of an unconsolidated sedimentary pile above an erosional bounding surface at the top of the underlying bedrock. The stratigraphy is complex, recording the shift in depositional environments from fluvio-deltaic to strandplain, via estuarine stages of evolution. The back-barrier island deposits are correlated with the stratigraphy of the adjacent coastal plain to the west and the barrier island to the east. Extrapolation of optically stimulated luminescence dates obtained from the barrier island combined with direct dating of the back-barrier island sediments is used to constrain the depositional age and chronology of the back-barrier island stratigraphy. The modern depositional environment evolved from a chenier plain into a barrier island system by the flooding of an interdune swale and development of a shore-parallel back-barrier tidal lagoon. The lithological heterogeneity of the back-barrier island succession was controlled by the presence of a bedrock incised palaeovalley and changes in relative sealevel.
Sedimentary facies associations constrain the spatial distribution of hydraulic properties controlled by lithological heterogeneity. Postdepositional alteration horizons are integrated with the facies model to account for the effects of weathering and diagenesis on hydraulic behaviour. The derived hydrostratigraphy describes a vertically stacked, dual aquifer, island groundwater system consisting of a semi-confined palaeovalley aquifer overlain by an unconfined strand-plain aquifer.
Hydrostratigraphic analysis based on sedimentary facies associations, integrated with post-depositional alteration characteristics reveals great complexity of groundwater systems within small island settings. The facies modelling approach employed in this study more accurately estimates the distribution of lithological heterogeneity and the associated variations in hydraulic properties in the sedimentary pile.

Coupling mineral analysis with conceptual groundwater flow modelling: The source and fate of iron, aluminium and manganese in a back-barrier island

by Stephen McLoughlin

Reference:
Hodgkinson, J., Cox, M.E. & McLoughlin, S., 2008. Coupling mineral analysis with conceptual groundwater flow modelling: The source and fate of iron, aluminium and manganese in a back-barrier island. Chemical Geology 251: 77-98.

Mineral and aqueous geochemical data are combined with a conceptual groundwater flow model, to establish the origin... more Mineral and aqueous geochemical data are combined with a conceptual groundwater flow model, to establish the origin and fate of iron, aluminium and manganese in the groundwater system of a small backbarrier island. The flow model domain consists of an unconfined island fresh groundwater lens overlying a semi-confined hypersaline aquifer. The two aquifers are separated by a discontinuous, clay-rich aquitard and both contain diffusion governed variable density flow fields. High concentrations of dissolved iron and manganese are associated with brackish to hypersaline groundwater, although there is no systematic relationship with salinity. Calculation of S2_/SO4 2_ and Fe2+/Fe3+ redox couples and the results of thermodynamic modelling show that redox disequilibrium in the groundwater is widespread. Groundwater samples containing aqueous sulphide and ferric iron complexes are supersaturated with respect to pyrite, goethite and haematite but the prevailing state of redox disequilibrium controls mineral dissolution and precipitation. Aqueous iron in the deeper regions of both aquifers is derived from the dissolution of iron oxide–hydroxides in lateritic palaeosols controlled by seasonal fluctuations in groundwater redox state. Aqueous manganese is potentially derived from the dissolution of ilmenite and amorphous oxide– hydroxides. The oxidation of iron sulphides contributes to the aqueous iron concentration and sulphuric acid production in the shallow groundwater. The solubility of aluminium is also limited by this process, governed by acidity regulation. A significant proportion of aqueous iron is transmitted from the semi-confined to the overlying unconfined aquifer through discontinuities in the aquitard layer. Movement of metals in solution outside the island groundwater system is restricted by the presence of diffusion boundaries within variable density transition zones.

Using the Landsat Archive for the Monitoring of Mediterranean Coastal Wetlands: Examples from the GlobWetland-II Project

by Julia Reschke

A conceptual model of depositional, rather than erosional, tidal channel development in the rapidly prograding Skagit River Delta (Washington, USA)

by Greg Hood

The origin and growth of blind tidal channels is generally considered to be an erosional process. This paper describes... more The origin and growth of blind tidal channels is generally considered to be an erosional process. This paper describes a contrasting depositional model for blind tidal channel origin
and development in the Skagit River delta, Washington, USA. Chronological sequences of historical maps and photos spanning the last century show that as sediments accumulated at the river mouth, vegetation colonization created marsh islands that splintered the river into distributaries. The marsh islands coalesced when intervening distributary channels gradually
narrowed and finally closed at the upstream end to form a blind tidal channel, or at mid-length to form two blind tidal channels. Channel closure was probably often mediated through gradient reduction associated with marsh progradation and channel lengthening, coupled with large woody debris blockages. Blind tidal channel evolution from distributaries was common in the Skagit marshes from 1889 to the present, and it can account for the origin of very small modern blind tidal channels. The smallest observed distributary-derived modern blind tidal channels have mean widths of 0·3 m, at the resolution limit of the modern orthophotographs. While channel initiation and persistence are similar processes in erosional systems, they are different processes in this depositional model. Once a channel is obstructed and isolated from distributary flow, only tidal flow remains and channel persistence becomes a function of tidal prism and tidal or wind/wave erosion. In rapidly prograding
systems like the Skagit, blind tidal channel networks are probably inherited from the antecedent distributary network. Examination of large-scale channel network geometry of such
systems should therefore consider distributaries and blind tidal channels part of a common channel network and not entirely distinct elements of the system. Finally, managers of tidal
habitat restoration projects generally assume an erosional model of tidal channel development. However, under circumstances conducive to progradation, depositional channel development may prevail instead.

Human influence on seagrass habitat fragmentation in NW Mediterranean Sea

by Matteo Vacchi

Estuarine, Coastal and Shelf Science 86, 2, 20; 292-298

The influence of coastal dynamics on the upper limit of the Posidonia oceanica meadow

by Matteo Vacchi

Marine Ecology 31 (4): 546-554

Underwater geomorphology of the rocky coastal tracts between Finale Ligure and Vado Ligure (western Liguria, NW Mediterranean Sea)

by Matteo Vacchi

Quaternary International 232: 187-200

Hydrodynamic constraints to the seaward development of Posidonia oceanica meadows

by Matteo Vacchi

Estuarine, Coastal and Shelf science 97, 58-65.

Sedimentary Dynamics of the Southern Shelf of Madeira (Portugal)

by Raúl Fonseca

by A. Rodrigues; A. Oliveira; R. Fonseca; R. Taborda and J. Cascalho. (2006) Journal of Coastal Research SI 39:454-458

In order to investigate the sedimentary dynamics of the Madeira's southern shelf several aspects of this North... more In order to investigate the sedimentary dynamics of the Madeira's southern shelf several aspects of this North Atlantic island shelf were studied. The principal goals of this work are: identification of the major sediment sources to the shelf; understand the sedimentary patterns and obtain further insight into the governing mechanisms of the shelf. To fulfil these objectives, high-resolution sea-floor mapping, heavy mineral distribution maps, wave and current information and sedimentary data were used. It was possible to identify four different sectors of the shelf, each one with different characteristics. Those characteristics are: sediment transport direction and magnitude; major suppliers of sediment (creeks and/or sea cliffs); distribution factors (currents, waves); and a energy gradient. The westernmost part of the shelf is very wide (9 km) and is characterized by high energy parallel to shore sediment transport. Sea cliff erosion plays a major role in supplying the shelf with sediment in this sector and creek contribution is negligible in comparison. The easternmost sector is narrow (about 1.5 km wide) and shows normal to shore sediment transport with a slight component towards the east. Wave energy is very low, thus, the transport gradient in this sector is also low. Creeks are the major suppliers of sediment in this sector, more so than sea cliffs. The mid-sectors show a high transport gradient, which is parallel to shore near the western end and tends to become normal to shore towards the eastern end. Sea cliffs and creeks have similar importance in shelf sediment supply.

Causes and Events of Atipic Washover Effects on the Pacific Coast of Colombia: the events of May and August 1997 on the El Choncho Island, San Juan River Delta.

by Gloria I. López

In Correa, I.D. and Restrepo, J.D. (Eds), Geology and Oceanography of the San Juan River Delta, Pacific Coast of Colombia. EAFIT University Editorial Found. EAFIT University – COLCIENCIAS, Medellín, Ant., Colombia, pp. 133-150 (ISBN 958- 9041-93-0; in Spanish).

Frequent Non-Storm Washover of Barrier Islands, Pacific Coast of Colombia.

by Gloria I. López

A 14,000 year-old-record from a coastal freshwater lake: Sedimentological evidence for tsunamigenic events on the west coast of Vancouver Island, British Columbia, Canada.

by Gloria I. López

Tsunamis and the Coastal Zone: A Geological Perspective.

by Gloria I. López

International Oceanographic Commission, IOCARIBE-UNESCO, Newsletter, 4: 12-15.

Characteristics of the burial environment related to Quartz SAR-OSL dating at St. Vincent Island, NW Florida, U.S.A.

by Gloria I. López

New Quartz-OSL ages for Beach Ridges on the St. Vincent Island Holocene Strandplain, Florida, U.S.A.

by Gloria I. López

Sedimentation patterns in the Río Cruces after the May 1960 Chilean earthquake and tsunami.

by Gloria I. López