Large Quantities Of Sand Research Articles

Surface and Airborne Arsenic Concentrations in a Recreational Site near Las Vegas, Nevada, USA.

Elevated concentrations of arsenic, up to 7058 μg g-1 in topsoil and bedrock, and more than 0.03 μg m-3 in air on a 2-week basis, were measured in the Nellis Dunes Recreation Area (NDRA), a very popular off-road area near Las Vegas, Nevada, USA. The elevated arsenic concentrations in the topsoil and bedrock are correlated to outcrops of yellow sandstone belonging to the Muddy Creek Formation (≈ 10 to 4 Ma) and to faults crossing the area. Mineralized fluids moved to the surface through the faults and deposited the arsenic. A technique was developed to calculate airborne arsenic concentrations from the arsenic content in the topsoil. The technique was tested by comparing calculated with measured concentrations at 34 locations in the NDRA, for 3 periods of 2 weeks each. We then applied it to calculate airborne arsenic concentrations for more than 500 locations all over the NDRA. The highest airborne arsenic concentrations occur over sand dunes and other zones with a surficial layer of aeolian sand. Ironically these areas show the lowest levels of arsenic in the topsoil. However, they are highly susceptible to wind erosion and emit very large amounts of sand and dust during episodes of strong winds, thereby also emitting much arsenic. Elsewhere in the NDRA, in areas not or only very slightly affected by wind erosion, airborne arsenic levels equal the background level for airborne arsenic in the USA, approximately 0.0004 μg m-3. The results of this study are important because the NDRA is visited by more than 300,000 people annually.

Large freshwater and sediment impoundments between the Mississippi River and the Louisiana coastline

Abstract. An innovative system-level sediment and freshwater management plan is proposed for the coastal regions of Louisiana, USA. It involves the construction of large sediment and freshwater impoundments between the river and coastline fed periodically through large spillway structures during the rising hydrograph of the river when the highest concentration of sediment is in the water column. Sediment directing and trapping technologies are proposed for the river channel and spillways to capture the coarser-grained sediments. The embankments can be constructed from dredging and then enlarged by land-based harvesting of coarse-grained sediments from the traps. These impoundments will permit the continuous introduction of freshwater and finer-grained sediments to coastal marshlands for vegetation, land augmentation, protection from storm surges and salt water intrusion, while removing large amounts of sand from the river and decreasing annual maintenance dredging costs.

Aeolian Activity on the Northern Coast of Lake Peipsi, North-Eastern Estonia

ABSTRACT Ratas, U.; Raukas, A.; Rivis, R., and Tavast, E., 2015. Aeolian activity on the northern coast of Lake Peipsi, north-eastern Estonia. Lake Peipsi is one of the largest inland water bodies in Europe. In the geological past, it was much bigger, flooding vast areas to the north of the contemporary lake. In the proglacial lakes formed behind the retreating glacier, large amounts of sand and silt accumulated, providing source material for various aeolian deposits and landforms, such as coversand hillocks, blowouts, deflation hollows, foredunes, inland and coastal dunes, and wind-eroded plains. Because of land uplift they are of different age (from the Late Glacial up to the present) and structure. The oldest dunes in the area were formed in severe climatic conditions of the Younger Dryas and the Early pre-Boreal. Near the contemporary shoreline of Lake Peipsi, the rhythmically changing water level has strongly influenced the aeolian redistribution of sediments. Here specific “basket-trap” dunes were f...

NOWADAYS PROBLEMS OF SEDIMENT TRANSPORT MODELING IN THE COASTAL ZONE

The ultimate purpose of sediment transport studies is the prediction of bottom relief in the zone of active wave effect accompanied by transport of significant sand volumes. The energetic longshore currents induced by the oblique wave approach, transport large amounts of sand lifted by waves from the sea bottom. This mass sediment transport and its variations finally determine the shore-line configuration and the location of accumulative and erosion areas on the underwater slope. Because of great practical significance, the problem of sediment transport has attracted much attention. When constructing theoretical models of suspended sediment mass transport by water flows, investigators have to face a number of difficulties. Modeling of the sediment transport is limited by the absence of clear physical mechanisms of sediment suspension. The main difficulties of the modeling are discussed in this report.

Occurrence of jejunojejunal and ileocecal intussusceptions in a thoroughbred stallion

A 4-year-old, 600.4 kg stallion horse of German thoroughbred breed was presented at the Tehran University Veterinary Medicine Teaching Hospital, Iran, with a history of weakness of 2-3 days duration. The stallion died of unknown cause on the previous day. Abnormal findings during physical examination included an estimated dehydration of 3% to 5%, dark red oral mucous membranes, elevated heart and respiratory rates, stiffened feces, and absence of intestinal motility on auscultation. Postmortem examination indicated the presence of a jejunojejunal and ileocecal intussusceptions, 46 cm in length; a torsion of jejunum proximal to the intussusceptions was also noted. An ulcerative lesion, 6 cm in diameter, was found on the mucosa of duodenum. Large amounts of sand, coat hair, and hay mantling in bloody discharge were observed in a colonic impaction. It was an acute case that was evident by the involvement of intussusception and ulceration, indicating desquamation of the necrotic epithelial cells with edema and distinct infiltration of neutrophils. Histopathological examination confirmed that the ileum was the intussiscipiens to the jejunum that subsequently passed through into the caecum, and the mesentery probably tore as a result of the intussusception.

Restoration of Destroyed Land due to Building of Water Reservoir

In order to obtain adequate water resources, the decision to build water reservoirs is unavoidable. However, the large amount of sand and rocks washed out from upstream shortens the lifespan of the water reservoirs. Therefore, the sediment needs to be cleared away to prolong the lifespan of the reservoirs, secure the water storage in the water reservoirs and improve their efficiency to achieve the best economic benefits. This research aimed to discuss the reasons for geographical and environmental change, as well as natural ecological destruction due to construction of water reservoirs. The findings could serve as a reference to further ecological engineering projects to restore ecological and geographical conditions, and to improve the land degradation situation caused by the construction of water reservoirs.

Recent Advance of Horizontal Drainage Cushion in Vacuum Preloading Method

Horizontal drainage cushion plays a key role in vacuum preloading projects. The traditional horizontal drainage cushion is sand blanket which consumes large amount of sand and is not enviromentally friendly. Several improvements or modifications of horizontal drainage cushion were developed in engineer practices in recent years. Drainage net was used as horizontal drainage cushion in ultra-soft soil improving projects in order to solve the laying problem of sand blanket. Sand ditch was used to deduce the consumption of sand. Direct vacuum preloading method linked the PVDs and filer tubes together in order to improving the transfer efficiency of pressure and canceled the sand blanket at the same time. Low position vacuum preloading method set horizontal drainage cushion below the surface of the ground in order to cancel the sealing membrane.

The impact of silt trapping in large reservoirs on downstream morphology: the Yangtze River

The sediment load of the Yangtze River (China) is decreasing because of construction of dams, of which the Three Gorges Dam (TGD) is the best known example. The rate of the decline in sediment load is well known, but changes in the sediment grain size distribution have not been given much attention. The TGD mostly traps sand and silt while clay is flushed through the reservoir. A large amount of sand is available in the Yangtze River downstream of the reservoir, and therefore the pre-dam sand concentration is not substantially reduced. The availability of silt on the Yangtze River bed is limited, and it is expected that most silt will be removed from the riverbed within one to two decades. In order to evaluate the impact of the change in grain size distribution on the tidal flats of the Yangtze Estuary, a highly schematized tidal flat model is setup. This model broadly reveals that the observed deposition rates are exceptionally large because of the high sediment concentration, the abundance of silt, the seasonal dominance of waves (shaping a concave profile), and the offshore tidal asymmetry. The model further suggests that deposition rates will be limitedly influenced by reductions in clay or fine silt but strongly impacted by reductions in median to coarse silt. The response of the downstream morphology to reservoir sedimentation therefore strongly depends on the type of trapped sediment. As a consequence, silt-dominated rivers, such as the Yangtze River and the Yellow River may be more strongly impacted than sand-dominated systems.

The new clay mud and its improvement effects of tunnels

During tunneling process by earth pressure balance (EPB) shield, the strata containing large amounts of sand and gravel are often encountered. The excavated soil in the shield chamber has poor plastic flow and larger permeability, so it leads to the difficult construction of the EPB tunnel. In order to ensure tunneling advance successfully, the excavated soil must be improved by adding modified materials to change its physical and mechanical properties, and make it to have a good plastic flow state, low friction angle and low permeability. Soil improvement techniques can guarantee the stability of excavation face, achieve the balance advance of shield tunnel, reduce machinery load and the ground settlement, and improve the excavation speed. The existing mud used in engineering practice is the dispersing mud and water system whose compositions are bentonite and water. Both the composition and function are simple. The existing mud has various problems, such as large amounts of waste mud emission, difficulties in controlling mud indicators, large areas for mud treatment and large uses of new mud materials and environmental pollution. In this paper, a kind of environmentally friendly clay mud was developed, and the laboratory and field tests were conducted to verify its adaptability and superiority.

Sand on Demand: A Laboratory Investigation on Improving Productivity in Horizontal Wells Under Heavy-Oil Primary Production—Part II

Summary The cold-production-recovery process, also known as cold heavy-oil production with sand (CHOPS), is a method for enhancing primary heavy-oil production by aggressively producing sand. It is successful in vertical (or slanted or deviated) wells in western Canada. In this process, large amounts of sand are produced on a continuing basis along with heavy oil. Attempts at cold production in horizontal wells have not been particularly successful. When sand production has been generated in horizontal wells, these wells have tended to become plugged with sand. This paper presents the results of experiments performed to assess the feasibility of applying cold heavy-oil production in horizontal wells that have been completed with slotted liners using less-aggressive (i.e., managed) sand-production strategies. Specifically, the effects of slot size, confining stress, fluid velocity, and sand-grain sorting on sand production were investigated. The results indicate that slot-size selection is critical for establishing "sand on demand." From the experiments, a correlation between slot size and controlled sand production was found for well-sorted sands. This correlation should allow for the specification of appropriate slot sizes for target reservoirs containing well-sorted sands. In the experiments, when flow rates resulted in low but persistent sand production, channels and/or elliptical dilated zones were created that greatly enhanced the effective permeability near the slot. This observation suggests that producing at low and steady sand cuts for a long period of time might bring two benefits: a way to transport the sand out of the well without causing plugging and the creation of high-permeability channels or zones that can improve production from the reservoir. To summarize, if the appropriate slot size were combined with the right drawdown rates, controlled sand production could be achieved, with attendant significant increases in permeability. This suggests that substantially increased oil-production rates could be achieved from horizontal wells if sand-production rates could be maintained at low but persistent levels.

Characteristics of the Shoreline Change along Florida Sandy Beaches with an Example for Palm Beach County

This paper introduces the recently developed resource “Characteristics of the Shoreline Change along the Sandy Beaches of the State of Florida: An Atlas” (available on the web). The shoreline positions on which the Atlas is based encompass 25 coastal counties extending over 1162 km of shoreline and averages over almost 140 years. The data were analyzed over three different periods (early, recent, and total) to distinguish mainly beach nourishment and sand bypassing projects, primarily in the recent period. The east and west coastlines of Florida have advanced significantly in the recent period relative to the early period, with the recent and early period average shoreline change rates being 23 cm/y and 18 cm/y on the east coast and 27 cm/y and −7 cm/y on the west coast, respectively. This improvement is attributable to, in part, the large quantities of sand placed during nourishment and sand bypass projects. Shoreline changes in the vicinity of the 58 inlets were examined, and it was found that shoreline fluctuations decreased significantly with increasing distance from the inlets, and that sand bypass and nourishment projects reduced the shoreline variability during the recent period.

Synergistic Application of Optical and Radar Data for Archaeological Exploration in the Talakadu Region, Karnataka

Talakadu is a well known historic place situated on bank of the river Cauvery in Mysore district of Karnataka. The place is close to concave side of a prominent meander where large amount of sand has accumulated. It is believed that after construction of a reservoir upstream, sand was exposed to wind action burying the structures of Ganga dynasty and other later kingdoms. A number of buried sites have been identified by archaeological excavations conducted so far. Presently the area forms sand dunes with thick plantation cover. Analysis of RADAR data (fine beam RADARSAT and ENVISAT ASAR) led to identifying a hitherto unknown buried channel through the Old Talakadu town adjoining the excavated archaeological sites. The study suggests that RADAR penetration through the plantation canopy seems to have occurred as observed by comparing with corresponding optical data of LISS-IV. Below the canopy, sand and shrubs on top of the channel (topographically low area) are acting as smooth surface providing dark tone on radar imagery. During field validation GPS was extensively used to navigate through the forest canopy and locate the buried channel, excavated archaeological sites as well as other anomalous patterns. Synergistic application of optical (RESOURCESAT-1 LISS-IV and CARTOSAT-1 & 2) and radar (fine beam RADARSAT and ENVISAT ASAR) data led to identifying remote sensing based guides for archaeological exploration. Integration of known archaeological sites with the identified anomalous patterns was done in GIS environment. This study adds on to the knowledge base of the site and compliments already known information and suggested new areas for further archaeological exploration.

Bar structure in an arid ephemeral stream

This study describes the structure of gravel bars in Nahal Zin, an ephemeral stream in the Negev desert. The internal structure of the bars was examined along trenches and in shallow pits. Gravel sheets and unit bars form during transporting flow events in the main channel, on intra-bar channels and near bar heads. Unit bars are dominated by the Go facies. Compound bars develop from accretion around, and modification of, unit bars. Compound bars are active under the current flow regime and the average depth of the fill layer is about 35 cm. The structure of compound bars is dominated by Gm (massive), containing large amounts of sand. The second most common facies is clast-supported, openwork, and well sorted sediments of the Go (pebbles) facies. Bar formation, and the development of the range of facies evident in the bars is controlled by sediment supply, particularly the high volumes of sand-sized sediment, the passage of gravel sheets and bedforms during floods, and the lateral and vertical instability of the channel. Repeated scour and fill events have produced a diverse arrangement of facies, with numerous erosional contacts between depositional units. Lateral and downstream shifts in the pattern of scour and fill due to flow and antecedent conditions shape the channel morphology and bar internal structure. Ephemeral river bars differ from those of humid and proglacial rivers in terms of the dominant facies present, the arrangement of the facies within the bars, and the sedimentary structures developed within the depositional units and on the bar surface.

Cold Flow: A Multi-Well Cold Production (CHOPS) Model

Abstract A multi-well cold production (CHOPS) model, developed at the Saskatchewan Research Council, was used in conjunction with a commercial reservoir simulator, to predict the effect of well spacing and in-filling on oil recovery in cold production. The oil and sand production from the Lindbergh/Frog Lake cold production wells was history matched initially. The comparative economics of five different well spacings (10 acre, 20 acre, 40 acre, 60 acre and 80 acre) was estimated. The 20 acre spacing was the most economic overall for heavy oil prices varying between C$251/m3 (C$40/barrel) and C$502/m3 (C$80/barrel). The multi-well model was used to estimate the additional oil recovery from in-fill wells at different in-fill times. In-filling a 40 acre spacing well with 10 acre spacing wells was not economic for a Lindbergh/Frog Lake type of reservoir. In-filling the same well with 20 acre spacing wells was economic at higher oil prices in the C$502/m3 range (C$80/barrel). Introduction The main mechanisms which contribute to the success of the cold production process are solution gas drive and sand production. Maini(1) argued that the greater oil recovery for heavy oil compared to light oil was due to the formation of a gas in oil dispersion which he called "foamy oil." This dispersion would have a greater compressibility which would maintain the reservoir pressure for longer times. Firoozabadi(2), based on a series of solution gas drive experiments performed at reservoir-type oil velocities, attributes the greater oil recovery for heavy oil to a higher critical gas saturation and to reduced gas flow leading to reservoir pressure maintenance. Three basic scenarios were proposed in the literature to explain how sand production leads to greater oil recovery:a limited dilated sand region around the wellbore(3),a dilated sand region around the wellbore with wormholes extending into the formation(4) andonly wormholes extending out into the formation(5, 6). The third scenario can best explain the rapid (within a few hours) travel time of a fluorescein tracer dye between an injector and a producer, observed by Amoco in a tracer test(5). Since the concentration of this dye, which is known to adsorb on the surface of a porous medium, did not change at the producer, Squires(5) concluded that an open (sand-free) channel connected the injector and producer. This observation contradicts scenarios 1 and 2 since these scenarios preclude the existence of an open channel throughout the length of the wormholes. Field engineers have observed that they sometimes lose fluid circulation while drilling into cold produced reservoirs. The location at which fluid loss occurs can help in mapping the wormhole network in the field. For example, when Nexen Inc. drilled two horizontal wells in a field after cold production, they observed lost circulation to neighbouring wells at the locations indicated by the ? marks in Figure 1. These 40 acre spacing cold production wells had produced large quantities of sand.

Surgical management of sand colic impactions in horses: a retrospective study of 41 cases

A retrospective review of the medical records of 41 horses requiring abdominal surgery for sand colic. The diagnosis of sand colic was made when sand was found to be the cause of impaction of the gastrointestinal tract during surgical exploration. The most common clinical signs at presentation were abdominal pain, abdominal distension and diarrhoea. A statistically significant association was found between the respiratory rate on arrival and short-term survival. Sand impaction at multiple locations was detected in one-third of the horses. Concurrent pathology was detected in half of the horses. Four horses were euthanased during surgery; of those that recovered from surgery, 35/37 (95%) were discharged from hospital. Short- and long-term complications were similar to those previously reported. Long-term (1 year) survival of the horses discharged was 100%. The good prognosis for horses undergoing surgery for the treatment of sand impaction supports early surgical intervention in cases where large amounts of sand are suspected.

Jejunojejunal Intussusception and Colonic Impaction in a 12-Day-Old Orphan Foal

A 12-day-old, 14.4-kg, female foal of Australian Miniature Pony breed was presented at the National Chung Hsing University Veterinary Medicine Teaching Hospital, Taiwan, with a history of weakness of 2 days’ duration. The mare died of unknown cause on the previous day. Abnormal findings during physical examination included an estimated dehydration of 3 to 5%, dark red oral mucous membranes, elevated heart and respiratory rates, stiffened feces, and absence of intestinal motility on auscultation. Continual nursing care was followed by intravenous fluid therapy and nonsteroidal anti-inflammatory drug and antibiotic treatment. The foal's condition deteriorated rapidly, and feeding was refused. Subsequently, she developed signs of pyrexia and panting. In spite of oxygen supplement, she died 18 hours after admission. Postmortem examination revealed the presence of a jejunojejunal intussusception, 20 cm in length; a torsion of jejunum proximal to the intussusception also was noted. An ulcerative lesion, 3 cm in diameter, was found on the mucosa of duodenum. Large amounts of sand, coat hair, and hay mantling in bloody discharge were observed in a colonic impaction. That it was an acute case was evident by the involvement of intussusception and ulceration, indicating desquamation of the necrotic epithelial cells with edema and distinct infiltration of neutrophils. These results suggested that a practical management strategy for nursing an orphan foal should be performed to avoid a similar case in the future.

南九十九里浜の侵食と堆積の実態

Beach erosion and accretion of the south Kujukuri coast was investigated based on the aerial photographs and field observation. The sand supply by northward longshore sand transport has been decreasing on this coast, causing erosion of the south part of the coast close to the sand source (sea cliff). In contrast, on the north end of the coastline, a long breakwater of the Katakai fishing port was extended and a large amount of sand has been deposited in the wave shelter zone. Furthermore, the ground subsidence up to 60cm occurred along the coastline due to the pumping-up of the ground water to obtain the water-soluble gas. The coastal situation of the south Kujukuri coast has devastated year by year due to all these impacts. To save the coast, full scale sand nourishment is required.

Evaluation of Effectiveness of Beach Nourishment using Dredging Sediment on Hazaki Coast

Hazaki fishing port is located at the south end of the Hazaki coast with a 16 km length and facing the Pacific Ocean. A large amount of sand accumulated in the wave shelter zone of this fishing port after the extension of the breakwater, whereas beach erosion occurred at the beaches north of the fishing port. In this area, wave direction seasonally varies, while generating southward and northward longshore sand transport alternately. The effect of these changes in wave direction to beach changes was modeled using the contour-line-change model considering grain size changes. The effectiveness of beach nourishment using dredging material from the port was also investigated. The optimum location for effective beach nourishment was predicted under the wave condition with periodically changing wave directions.

Critical events in the Ariake Bay ecosystem: Clam population collapse, red tides, and hypoxic bottom water

Ariake Bay is located off the west coast of Kyushu, western Japan, and is a typical enclosed coastal sea of approximately 1,700 km2 in area. The tidal amplitude reaches approximately 6 m in the inner parts of the bay at the spring tide, and consequently approximately 20,000 ha of tidal flats appear along the coast of the bay at ebb tide. The tidal flats and the shallow waters offshore from the tidal flats are extremely productive areas, and utilized for various fisheries. However, the ecosystem of Ariake Bay is now in critical condition. The abundance of benthic animals has decreased markedly on the sandy tidal flats in the bay. This phenomenon is represented by the drastic decrease in the harvest of the most popular short neck clam, Ruditapes philippinarum, on the sandy tidal flats of Kumatoto Prefecture facing Ariake Bay. The annual harvest on the sandy tidal flats exceeded 50,000 tons until 1980, but decreased to only around 400 tons between 1995 to 1997. On the sandy tidal flats where the dense clam population collapsed, very few macro-benthic animals occurred. Since the 1960s, a large amount of sand and gravel has been collected from the rivers that flow into Ariake Bay. It is apparent that the marked decrease in newly deposited sand on the sandy tidal flats is one of the main causes of the collapse of the dense population of the short neck clam and marked decrease of other macro-benthic animals on the sandy tidal flats, and thus it appears that the only effective measure to recover the benthic communities on the sandy tidal flats is creating sand covers with natural sands collected from the sea floor offshore of the bay.In the subtidal areas of the bay, the scale of the autumn bloom of phytoplankton has increased markedly and red tides have covered almost the entire inner bay area since 1998, although the nutrient input from the land to the bay through the major rivers has fluctuated stably over the past three decades. The nori culture was seriously damaged by the occurrence of a large-scale autumn red tide on two occasions (2000 and 2002). In early summer, hypoxic bottom water has occurred in the wide areas of the inner parts of the bay since at least 2001, causing a serious environmental disturbance to the benthic ecosystem. Both of these phenomena commonly occurred when the water was stratified mainly due to the decrease of salinity in the surface layers. These facts indicate that the stratification of the water was enforced in the inner parts of the bay from the end of the 1990s. In Isahaya Bay, an inner bay of the west side of Ariake Bay, a big reclamation project of the tidal flats to create land and a fresh water pond of approximately 3,500 ha in total area has been conducted since 1986, and the gates of the dike were closed to lower the water levels inside the dike for reclamation in April 1997. A decrease in the tidal current was recently observed in some parts of the west coast of the bay. It is very likely that the changes of the hydrographical conditions caused by the modification of the topography of Isahaya Bay are responsible for the development of the water stratification in the inner parts of Ariake Bay, following the occurrence of the large-scale autumn red tides without any increase in the nutrient input from the land and the hypoxic bottom water in the summer.

The Vegetation of Irish Machair

Machair is a highly specialised and complex sand dune habitat that is confined globally to the north west coasts of Ireland and Scotland. It comprises a flat or gently undulating sandy plain that develops in an oceanic location with a cool, moist climate. Machair systems are highly calcareous, the sediments usually containing a high percentage of shell fragments and having pH values in excess of 7. The vegetation is herbaceous, with low frequency of typical sand-binding species such as Ammophila arenaria. Irish machair is designated as a priority habitat under the EU Habitats Directive and as such Ireland has special responsibility for its conservation. The quality and extent of machair in Ireland is increasingly under threat from human pressures such as housing developments, recreation and changes in agricultural practice. This paper describes the vegetation of Irish machair and examines how climatic, edaphic, geographic and anthropogenic factors not only influence the distribution and formation of machair, but the plant communities present. A comparison between the vegetation of Irish and Scottish machair reveals a high degree of similarity, with some variation that can be explained by different land-use and/or management practices. Karen Gaynor (e-mail: karen. gaynor@environ.ie), Research Branch, National Parks and Wildlife Service, 7 Ely Place, Dublin 2. INTRODUCTION Machair is a distinct geomorphological and ecological habitat that forms as a result of a unique combination of climatic, geographic, edaphic and anthropogenic factors. Irish machair is designated as a priority habitat under the EU Habitats Directive (Commission of the European Communities 1992) (code: 21 AO). It is described therein as a 'complex habitat comprised of a sandy coastal plain resulting partially from grazing and/or rotational cultivation, in an oceanic location with a cool moist climate'. The system is highly calcareous, the sediment containing high shell fragment contents and pH values in excess of 7. The vegetation is herbaceous, with low frequency of sand-binding species. Machair is unique in that it is considered a natural landscape that is the product of cultural activities. The features of a typical machair system are presented in Fig. 1. In most cases, a small escarpment or dune ridge fronts the system. The true machair plain represents that area where wind erosion has eroded the original dune system down to a level just above the water table, where the wet consistency of the sand prevents further erosion (Pl. I). In general, the degree of flatness depends on the age of the system, as well as the underlying topography, geology, outcropping of local rocks and historical management. The machair plain is often terminated on the landward side by a lake or associated marsh/fen. There are a number of exceptions to this typical sequence. Flat machair like surfaces may form over rock platforms by the sea, bypassing the dune building phase. Where the wind is particularly strong and the direction suitable, large quantities of sand can even be deposited on the seaward face of hills inland to form hilly machair (e.g. Garter Hill, Co. Mayo) (Bassett and Curtis 1985). Scottish machair was first identified as a distinct habitat in the 1940s (Wilmott 1945; Darling 1947; MacLeod 1949) and has since been extensively described (Ranwell 1974a, 1974b; 1977; 1981; Dargie 1993; 2000; Angus 2004). Although Tansley (1939) described machair vegetation from Dog's Bay, County Galway, the habitat was not formally recognised in Ireland until 1980, when the first account of Irish machair on the Mullet Peninsula was published (Akeroyd and Curtis 1980). The criteria used to define Scottish machair were tested on a number of sites in the west of Ireland, revealing a close similarity between Irish machair sites and those found in Scotland. Further research subsequently supported this assessment (Bassett 1983; Bassett and Curtis 1985; Crawford et al. 1996). The most recent inventory of Irish sandy systems lists a total of 50 machair sites (Curtis 1991a). Following on from the work of Ritchie (1976), Curtis (1991b) used the following five criteria to define Irish machair: 1. A mature coastal sandy plain, with a more or less level surface. 2. A significant proportion of shell fragments in the sand producing a lime-rich soil (pH > 7.0). Biology and Environment: Proceedings of the Royal Irish Academy, Vol. 106B, No. 3, 311-321 (2006). ? Royal Irish Academy 311 This content downloaded from 157.55.39.225 on Thu, 09 Jun 2016 05:16:57 UTC All use subject to http://about.jstor.org/terms Biology and Environment 4-Mobile Dune-^ ^-Machair Foredune Strandline : Hummocky machair