Main Sand Research Articles

The Lutzomyia longipalpis species complex: does population sub-structure matter to Leishmania transmission?

Leishmania chagasi causes visceral leishmaniasis and, to a lesser extent, atypical cutaneous leishmaniasis in Central and South America. Its main sand fly vector, Lutzomyia longipalpis s.l. (Diptera: Psychodidae) displays a complex population structure that might contribute to the observed clinical pleomorphism and to recent major urban epidemics. This article summarises our understanding on reproductive barriers and hybridisation among this vector's sibling incipient species. Identifying genes important for sand fly ecological adaptability and sand fly-Leishmania genetic co-variation could be helpful for interrupting Leishmania transmission.

The Orange River, southern Africa: an extreme example of a wave-dominated sediment dispersal system in the South Atlantic Ocean

Sediments delivered to the South Atlantic Ocean by the Orange River are fractionated and dispersed northwards and westwards by a vigorous longshore drift system and a number of ocean currents. Gravels are accreted to the coastline for a distance >300 km north from the Orange River mouth. Sands are transported alongshore for >700 km but are, in places along this transport path, returned onshore by coastal winds to form the main Namib Sand Sea and other smaller dune fields. Mud is more widely dispersed westwards, northwards and southwards, probably by slow-moving, ocean-scale currents into basins on the shelf and onto the continental shelf edge. This dispersal system, operating since at least Eocene times, is believed to have originated during a time when there was a Late Cretaceous–Early Cenozoic uplift of southern Africa, which resulted in: (1) intensification of the existing southerly wind system; (2) incision of the Orange River, which, coupled with a shift in climate, resulted in a coarsening of its sediment load delivered to the coast; (3) a broad, weakly subsiding or mildly uplifting inner continental shelf with little accommodation space for the sediment load of the incising Orange River.

Tahiti: Development-Strategy Assessment

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 100656, "Tahiti: Development-Strategy Assessment Using Design-of-Experiments and Response-Surface Methods," by P.E. Carreras, SPE, S.E. Turner, SPE, and G. Wilkinson, SPE, Chevron, prepared for the 2006 SPE Western Regional/AAPG Pacific Section/GSA Cordilleran Section Joint Meeting, Anchorage, 8-10 May. The Tahiti field in the deepwater Gulf of Mexico (GOM) is a three-way anticlinal structure trapped against salt. The discovery well was drilled in 2002, and two appraisal wells were drilled soon afterward. Because of significant uncertainties remaining after appraisal, probabilistic methods were used to assess development alternatives. A classical experimental-design method was applied, and reasonable reservoir-simulation models were designed and validated. The proposed workflow enhances use of experimental design by combining the technique with response-surface methods and rational engineering judgement. Introduction Tahiti field is in more than 4,000 ft of water in the Green Canyon area of the GOM, approximately 190 miles southwest of New Orleans. The field was discovered in April 2002 with the drilling of Well GC 640-1. Results from the exploratory well indicated the presence of high-quality reservoir sand with more than 400 ft of total net pay distributed in three main Miocene turbidite sheet sands at depths ranging from 24,000 to 27,000 ft true vertical depth. In 2003, two appraisal wells were drilled simultaneously. One of the appraisals encountered more than 1,000 ft of net pay in high-quality sandstones, confirming one of the most significant net-pay accumulations in the history of the deepwater GOM. The field will be developed in phases. The first development phase was sanctioned in August 2005 by Tahiti joint-venture partners Chevron, Statoil, and Shell at a cost of more than U.S. $1.8 billion. Total capital costs for the project are anticipated to be approximately U.S. $3.5 billion. The field is expected to come on line in mid-2008. Because of significant uncertainties, probabilistic methods were used to assess development alternatives during Phases 2 and 3 of Chevron's project-management process. The main purpose of this study, part of Phase 3 (Develop Preferred Alternatives), was to assess a mature predevelopment strategy. Reservoir Description The Tahiti prospect was identified by use of advanced subsalt 3D-seismic imaging technology, along with geologic-data interpretation to identify the presence of reservoir-sand development, hydrocarbon charge, and migration into a geologic trap. The trap tested by the discovery well is a three-way anticlinal closure truncated against a salt feeder/weld system buried beneath an 11,000-ft-thick subsalt canopy (Fig. 1). On the basis of seismic data and appraisal wells, the trap is estimated to extend approximately 5 miles in a north-to-south direction and 1.5 miles in a west-to-east direction. Main reservoirs are Lower to Middle Miocene. DOE Methodology Design of experiments (DOE) is a methodology that reduces the number of reservoir-simulation runs that must be generated to develop equations for response variables. The response variables usually are economics parameters such as oil recovery or net present value (NPV). DOE provides not only a systematic framework for unbiased decisions but also technical continuity to the study. The understanding of field dynamics increases as the project evolves. The DOE workflow applied in this study comprises nine steps.

Controls of grain-size distribution on geomechanical properties of reservoir rock—A case study: Cretaceous Khafji Member, Zuluf Field, offshore Arabian Gulf

The Khafji Member of the Cretaceous Wasia Formation in Zuluf Field, offshore Saudi Arabia is an important siliciclastic hydrocarbon reservoir. The reservoir consists of a lower Main Sand and an upper Stringer Sand. The present study investigated the relationships between the geomechanical attributes (Young's modulus and Poisson's ratio) of the reservoir and its grain size distribution. In addition, an attempt was also made to relate the reservoir quality with the depositional environments deduced from factor analysis of the grain size distribution data. The Young's modulus for the Khafji reservoir range from a low of 8.43×10 5 psi at 1000 psi confining pressure (1.13×10 6 psi at 2900 psi confining pressure) to a high of 1.27×10 6 psi at 1000 psi (1.91×10 6 psi at 2900 psi). The study shows that there is no significant relationship between grain size parameters (mean, median, skewness, and kurtosis) and geomechanical properties. However, a good correlation was observed between geomechanical parameters and sands deposited in different environments. The clean sand showing moderate to good sorting and interpreted as beach sand showed low Young's modulus (average 1.07×10 6 psi) and Poisson's ratio (average 0.16), while the parameters were higher (average of 1.57×10 6 psi Young's modulus and 0.204 Poisson's ratio) for the fine-grained sediments representing possible lagoonal or offshore environment.

Periodic accumulation and destruction of aeolian erg sequences in the Permian Cedar Mesa Sandstone, White Canyon, southern Utah, USA

AbstractThe Permian Cedar Mesa Sandstone represents the product of at least 12 separate aeolian erg sequences, each bounded by regionally extensive deflationary supersurfaces. Facies analysis of strata in the White Canyon area of southern Utah indicates that the preserved sequences represent erg‐centre accumulations of mostly dry, though occasionally water table‐influenced aeolian systems. Each sequence records a systematic sedimentary evolution, enabling phases of aeolian sand sea construction, accumulation, deflation and destruction to be discerned and related to a series of underlying controls. Sand sea construction is signalled by a transition from damp sandsheet, ephemeral lake and palaeosol deposition, through a phase of dry sandsheet deposition, to the development of thin, chaotically arranged aeolian dune sets. The onset of the main phase of sand sea accumulation is reflected by an upward transition to larger‐scale, ordered sets which represent the preserved product of climbing trains of sinuous‐crested transverse dunes with original downwind wavelengths of 300–400 m. Regularly spaced reactivation surfaces indicate periodic shifts in wind direction, which probably occurred seasonally. Compound co‐sets of cross strata record the oblique migration of superimposed slipfaced dunes over larger, slipfaceless draa. Each aeolian sequence is capped by a regionally extensive supersurface characterized by abundant calcified rhizoliths and bioturbation and which represents the end product of a widespread deflation episode whereby the accumulation surface was lowered close to the level of the water table as the sand sea was progressively cannibalized by winds that were undersaturated with respect to their potential carrying capacity.Aeolian sequence generation is considered to be directly attributable to cyclical changes in climate and related changes in sea level of probable glacio‐eustatic origin that characterize many Permo‐Carboniferous age successions. Sand sea construction and accumulation occurred during phases of increased aridity and lowered sea level, the main sand supply being former shallow marine shelf sediments that lay to the north‐west. Sand sea deflation and destruction would have commenced at, or shortly after, the time of maximum aridity as the available sand supply became exhausted. Restricted episodes of non‐aeolian accumulation would have occurred during humid (interglacial) phases, accumulation and preservation being enabled by slow rises in the relative water table. Subsidence analysis within the Paradox Basin, together with comparisons to other similar age successions suggests that the climatic cycles responsible for generating the Cedar Mesa erg sequences could be the product of 413 000 years so‐called long eccentricity cycles. By contrast, annual advance cycles within the aeolian dune sets indicate that the sequences themselves could have accumulated in just a few hundred years and therefore imply that the vast majority of time represented by the Cedar Mesa succession was reserved for supersurface development.

MEASUREMENT OF DARCY AND FORCHHEIMER COEFFICIENTS FOR SILICA SAND BEADS

High Breaking Capacity fuses are widely used to withdraw the energy brought by an electric fault current. One of the main constituent elements of a HBC fuse is the arc quenching material, silica sand in our case. During the arc quenching by the fuse, a plasma is generated due to the fusion and the vaporization of the fuse element (Ag) and the silica sand (SiO2). The plasma resulting from the dissociation of Ag and SiO2 is surrounded by a fused silica viscous sheath itself surrounded by silica sand grains. In this study it is showed that the main silica sand morphometric properties - granulometry, porosity, Darcy and Forchheimer coefficients - strongly influence the fuse operation. The measurements of the Darcy and Forchheimer coefficients are described, and the results are given for silica sand beads and glass sphere beads. The influence of the morphometric properties is discussed taking into consideration already published data concerning pressure, temperature and electron density of the plasma generated during the fuse operation.

Provenance of Late Cretaceous to Paleocene submarine fan sandstones in the Norwegian Sea: Integration of heavy mineral, mineral chemical and zircon age data

This paper describes a strategy for effective discrimination and provenance evaluation of sandstones transported by different sediment dispersal systems using an integrated programme of heavy mineral analysis, mineral chemistry and zircon age dating. Sandstones derived from different source regions are initially discriminated using provenance–sensitive heavy mineral parameters (ratios of abundances of stable, hydraulically equivalent minerals). Differences between the heavy mineral populations are reinforced by single-grain mineral chemical analysis, which also provides further information on the nature of the source terrains. Zircon age dating of representative samples places further constraints on the location of the source areas, by identifying the main crust-forming events. In addition, the validity of the mineralogical discrimination can be tested by the zircon age data. The value of this integrated approach is illustrated by a case study of deep marine Late Cretaceous–Paleocene sandstones in the Norwegian Sea. Potential sources of coarse clastic sediment lie both to the east, in mid-Norway, and the west, in East Greenland. Three main sand types (MN1, MN2 and MN3) have been identified, each of which has a unique combination of heavy mineral ratios (rutile/zircon, monazite/zircon, chrome spinel/zircon and apatite/tourmaline) and mineral chemistry (garnet and tourmaline). Sand type MN1 has a simple zircon age spectrum, with a large Early–Middle Proterozoic group and a small Early Paleozoic group, indicating derivation from northern mid-Norway. Sand type MN2 has a complex age structure including Archaean and early Proterozoic zircons. It can be divided into two subtypes, MN2a and MN2b, and can be ascribed to a source in East Greenland. Sand type MN3 has a simple age structure dominated by Middle Proterozoic zircons, and it was sourced from southern mid-Norway. Since reservoir presence is a major area of uncertainty in the deep water Norwegian Sea, the use of heavy mineral, mineral chemical and zircon age data to discriminate sandstones of eastern and western origin is crucial to hydrocarbon exploration of the area.

Acoustic seafloor discrimination with echo shape parameters: A comparison with the ground truth

Features extracted from echosounder bottom returns are compared with the ground truth in a North Sea survey area. The ground truth consists of 50 grab samples for which the grain size distribution, and the gravel and shell contents were determined. Echo envelopes are analysed for two single-beam echosounders, operated at frequencies of 66 and 150 kHz. It is shown that a set of six energetic, statistical, spectral and fractal parameters carries useful information that can be exploited for seafloor characterization and classification purposes. A quantitative comparison of the individual features with the grab sample mean grain size reveals significant correlations. The echo features are also subjected to a principal component analysis in tandem with a cluster analysis. Four sediment classes with different geo-acoustic properties are examined and compared with the grab samples and existing geological information. A subtle difference between the two sounder frequencies is observed in the rendition of an isolated trench with a soft infill of clay and Holocene channel deposits. The acoustic transition from the valley to neighbouring sand and gravel fields occurs more rapidly at the lower of the two examined frequencies. A direct comparison of the acoustic sediment classes with the ground truth reveals that the main sediment types mud, sand, and gravel are more clearly separated at 150 kHz. The acoustic bottom classification scheme also appears particularly sensitive to the presence of gravel at this sounder frequency.

History of Indo-Pacific coral reef systems since the last glaciation: Development patterns and controlling factors

History of Indo-Pacific coral reef systems since the last glaciation: Development patterns and controlling factors

DISTRIBUIÇÃO ESPACIAL E CARACTERIZAÇÃO GEOLÓGICA DOS ARENITOS ASFÁLTICOS DA BORDA LESTE DA BACIA DO PARANÁ NO ESTADO DE SÃO PAULO

This paper focuses on the spatial distribution of the main tar sand occurrences in the Eastern Border of the Paraná Basin, São Paulo State. The spatial analysis of these occurrences was performed according to geological features present in the area. Field data, geocronological data, airborne magnetometrics und remote sensing data have provided information for structural maps, lineament maps and magnetometric maps. Based on the regional and field data it was described the main elements and processes related to the genesis of the tar sand occurrences in the area. It was concluded that the best genetic model relates oil generation to the intrusion of sills of the Serra Geral Formation in the black shales of the Irati Formation Formation; migration through faults and dike walls and accumulation in the sandstones of Pirambóia Formation, trapped by argillaceous layers of the interdune and fluvial facies of Pirambóia Formation and by basic dikes.

Distribuição espacial e caracterização geológica dos arenitos asfálticos da borda leste da Bacia do Paraná no estado de São Paulo

This paper focuses on the spatial distribution of the main tar sand occurrences in the Eastern Border of the Parana Basin, Sao Paulo State. The spatial analysis of these occurrences was performed according to geological features present in the area. Field data, geocronological data, airborne magnetometrics and remote sensing data have provided information for structural maps, lineament maps and magnetometric maps. Based on the regional and field data it was described the main elements and processes related to the genesis of the tar sand occurrences in the area. It was concluded that the best genetic model relates oil generation to the intrusion of sills of the Serra Geral Formation in the black shales of the Irati Formation; migration through faults and dike walls and accumulation in the sandstones of Piramboia Formation. trapped by argillaceous layers of the interdune and fluvial facies of Piramboia Formation and by basic dikes.

Reservoir geology of the Utsira Formation at the first industrial-scale underground CO 2 storage site (Sleipner area, North Sea)

Abstract At the Sleipner fields in the North Sea, CO 2 is being injected into sands of the Miocene-Pliocene Utsira Formation, which is overlain by thick Pliocene shales. The highly porous (35%–40%) and extremely permeable (approximately 2 D) Utsira sands are organized into approximately 30 m thick packages. These packages are separated by thin (predominantly 1 m thick), low-permeability shale layers, which are assumed to contain potential fluid pathways of erosive or deformational origin. A 6.5 m thick shale layer close to the top of the sands separates an eastward thickening sand wedge from the main sand package below. Migration simulations indicate that the migration pattern of CO 2 below the shale layer would differ strongly from that within the sand wedge above. Time-lapse seismic data acquired prior to the start, and after three years, of injection confirmed a reservoir model based on these findings and showed that the thin shale layers act as temporary barriers and that the 6.5 m thick shale layer does not fully inhibit upward migration of CO 2 .

An Intensive Mongolian Cyclone Genesis Induced Severe Dust Storm

In this paper, a severe dust storm which occurred in northern China is presented and its associated physics investigated. The main sand source regions of this storm were from the Badanjilin Desert in western Inner Mongolia (IM), western Hunshandakend sand lands and the Gobi Desert in southern Mongolia. This dust storm process was a typical cyclonic dust storm, induced mainly by intensive development of a Mongolian cyclone rather than any other weather system. The formation of the strong surface winds was caused not only by the intensive development of a cyclone, and the passage of a cyclonic cold front, but also by a strong meso-scale pressure gradient. The former closely accorded with the severe dust storm while the latter induced the severe prefrontal dust storm. The dust raising mechanism could be described in the following manner: after obtaining much momentum from strong surface winds, the dust was raised upward by strong turbulence in the PBL and then by the systemic ascending motion of a cyclonic system. In addition, divergence-pumping in the upper troposphere indirectly transplanted dust upward.

La evaluación de los recursos territoriales turísticos de carácter básico : el caso de las playas del norte de la Comunidad Valenciana

Las playas de arena con calibres granulométricos bajos de las costas valencianas se caracterizan en general por ser recursos básicos ya que han provocado la atracción de la demanda, configurando, al desarrollar los elementos del «sistema turístico», el principal producto de la Comunidad Valenciana, el de «sol y playa». Este sistema participa de dos subsistemas, el físico-natural y el social, actuando generalmente con falta de simbiosis, lo que repercute negativamente tanto en el medio como en la rentabilidad socio-económica. En este sentido intentamos aplicar una metodología de carácter analítico que nos permita evaluar y comparar la situación actual de esa relación entre ambos subsistemas en las playas del norte de la Comunidad Valenciana.

The timing of climbing dune formation in southwestern Niger: fluvio-aeolian interactions and the rôle of sand supply

Contemporary gully erosion has exposed sections in a climbing dune which is banked up against ferricrete terraces along the southern bank of the Niger River in southwestern Niger. The main sand transport direction in this area is from northeast to southwest, and the immediate source of the dune sand is the Niger River. Dune stratigraphy contains evidence of episodic, fluvially controlled accretion, separated by two palaeosols. Channel fills and stone stringers suggest occasional alluvial and colluvial reworking. Infra-red stimulated luminescence dating of the aeolian sands shows that dune development occurred episodically during the African Humid Period (15–5 ka), probably in response to an increase in sediment supply from the Niger River. Soil development occurred during the relatively short-lived period of enhanced aridity associated with the Younger Dryas, driven by weakening of the southwesterly monsoon circulation. Climate-driven dune accretion and further soil development occurred during the Holocene period.

A Case Study of Foamy Oil Recovery in the Patos-Marinza Reservoir, Driza Sand, Albania

Abstract With a current recovery of only 5%, Albania's largest oilfield, Patos-Marinza, (first commercially produced in 1939) still contains potentially more than 100 MMbbl of reserves of 10 to 12 ° API oil at a depth of 1,600 m. A consortium consisting of Albpetrol Albania, Preussag Energie (Germany), Premier Oil (Britain), and the IFC (the private sector arm of the World Bank) are making plans to improve oil recovery in the area. Test wells producing 1 to 2 m3/d yielded large rate improvements to over 30 m3/d using "progressive cavity pumps" up to 30 m3/d with producing sand cuts around 10 to 35%. PVT analysis of the oil, with a relatively high solution GOR of 31 m3/m3, shows a strong tendency to foam (gas in microbubbles without forming a continuous gas phase) below the bubble point, near the initial reservoir pressure. Core tests with different depletion rates resulted in primary oil recoveries of greater than 30%. This paper discusses the detailed suite of laboratory measurements used to examine the Driza crude oil, in the context of present theories of foamy oil and cold heavy oil production with sand (CHOPS). Introduction The Patos-Marinza oilfield is an onshore field located east of the city of Fier in South Central Albania (Figure 1). It occupies an area of approximately 24,000 hectares and was discovered in 1926, with commercial oil production starting in the early 1930s. Development to the north continued with drilling of over 2,300 wells, reaching the boundaries of the field in the late 1980s. The main sandstone reservoirs dip at 8 ° to 13 ° from an outcrop in the South containing mineable tar sands to the original oil water contacts at 1,800 m in the north. There are multiple stacked sand reservoirs of Upper Miocene (Messinian) age, the most important ones being the Gorani, Driza, and Marinza (top to bottom). The Driza reservoir contains the majority of the OOIP and reserves. It consists of up to six sand layers numbered from top to bottom, with D1 being the main sand continuous throughout the field. The Driza is a suite of unconsolidated sandstones with porosity of 25 - 28% and net pay varying areally from 7 to 95 m (south to north). Oil gravity also varies throughout the field depending on the depth of the reservoir and the type of formation. The Marinza oil (north) has a gravity up to 825 kg/m3 (40 ° API) due to greater depths and a closer position areally to the source rock. The oil gravity in the Patos area (southern half of the field) is about 998 kg/m3 (11 ° API) with dead oil viscosity over 9,000 mPa.s under reservoir conditions. Due to the unfavourable fluid properties, oil recovery to date in the entire reservoir amounts to less than 5% under depletion drive. The wells with a 2.5 acre spacing generally produce less than 1 M3/d of oil with tubing insert pumps landed halfway to bottom due to equipment limitations.

The Use of Microscopic Bitumen Froth Morphology for the Identification of Problem Oil Sand Ores

Oil sand, which is found in various deposits around the world, consists mostly of sand, surrounded by up to 18 wt% bitumen. The largest deposits known are situated in northern Alberta, Canada, where reserves of bitumen are estimated to be 1.7 trillion barrels. Bitumen is similar to heavy oil, but with much higher viscosity and density. The two main commercial oil sand operations in Alberta are surface mines and use aqueous flotation of the bitumen to separate it from the rest of the oil sand. Under optimal conditions up to 95% of the bitumen can be recovered, but occasionally ores are mined that create problems in extraction, and recovery can drop to 70% or less. This article discusses the microscopic morphologies of various bitumen and heavy oil streams and their relationship to processing problems. The results of extensive microscopic work have demonstrated that the bitumen in an oil sand ore is the phase most susceptible to oxidation and that the resulting changes manifest themselves in particular microscopic structures. The presence and type of these structures can be related to the processing behavior of oil sand ores. Morphological features found in froths from commercial operations are similar to those found in froths from laboratory-prepared samples. The morphological features found in froths of oxidized ores have been categorized and quantified for a variety of samples and are referred to as degraded bitumen structures. Experiments in which fresh oil sand ores were subjected to low-temperature oxidation showed that bitumen froth morphology changed dramatically compared to that of nonoxidized ores for identical bulk compositions and extraction water chemistries.

Typical Coastal Vegetation of Korea

It was found that 14 coastal habitats in South Korea have comparetively natural vegetation. The habitats were classified into three types - intertidal flats, sand dunes, and estuaries. There were four intertidal flats, five sand dunes and five estuaries. Except for Cynodon dactylon and Tetragonia tetragonoides, all of the main halophytes and sand dune plants were found in the habitats. These two species were mainly distributed on the southern coast. This study identified coastal vegetation, such as pure stands of Suaeda japonica on intertidal flats, mixed halophyte communities around the high-water mark, pure stands of Vitex rotundifolia on stable sand dunes, mixed communities dominated by Carex kobomugi on unstable sand dunes, and pure stands of Phragmites communis in estuaries. The types of coastal vegetation may depend on sediment types, the inundation time of seawater and the stability of sediments.

4-D time lapse reservoir monitoring of Nelson Field, Central North Sea: Successful use of an integrated rock physics model to predict and track reservoir production

Nelson Field, in the U.K. sector of the Central North Sea approximately 180 km east of Aberdeen in 280 ft of water, is on the Forties-Montrose ridge and forms a broad, low relief anticline with four-way dip closure (Figure 1). Figure 1. Nelson Field in relation to Forties-Montrose trend and established infrastructure. 4-D seismic data, acquired using conventional towed streamers, have been successfully applied to the Paleocene reservoirs of the North Sea. Importantly, AVO applications enhance the 4-D difference signal in this reservoir. We tested a new multivariate solution to predict shear-wave slowness against field data, and used this to establish an integrated rock physics model of the Forties Sandstone. This formed the basis for full elastic inversion of the AVO data sets. Full elastic inversion results demonstrate that quantifiable seismic differences can be detected and that they are of similar magnitude to those estimated independently from core and log data. Our study found that the predicted, simulated, drainage pattern and the actual time-lapse seismic difference signal are in good agreement. The 4-D is detecting OWC movements as small as 15–20 ft within the main sand channel fairways. 4-D seismic may provide a valuable tool to monitor reservoir drainage patterns for areas characterized by low net-to-gross sand ratios, but the method clearly works best within main sand fairways to target potential upside areas. The field was discovered in 1988. An extensive appraisal campaign by Enterprise and Shell/Esso followed. By 1990 13 appraisal wells had been drilled. The field began producing in February 1994 from eight wells. To date, 27 development wells have been drilled from a single central platform: 23 oil producers and 4 water injectors. In addition, four subsea producers exploit the southern satellite area. Plateau production was maintained during 1994–1996 at 150 000 b/d. Top Reservoir is relatively shallow at …

Extracellular enzyme activities during slow sand filtration in a water recharge plant

Activities of the extracellular enzymes β-glucosidase and phosphatase and bacterial densities were investigated during the filtration process at several sites in a groundwater recharge plant at the Ruhr river (Hengsen recharge plant in Schwerte, Germany). Low numbers of microorganisms and low levels of activity in this type of habitat, compared to most surface waters, caused methodological problems when determining microbial activity. In this study, fluorigenic model substrates, which enable hydrolytic rates as low as 1 nmol ( L× h) −1 to be measured, were used to determine extracellular enzyme activities. Highest activities were determined in surface water (107 nmol ( L× h) −1 for β-glucosidase and 252 nmol ( L× h) −1 for phosphatase), which decreased during the filtration process in the gravel prefilter and the main sand filter until the end of subsurface flow (1.6 nmol ( L× h) −1 and 6.8 nmol ( L× h) −1, respectively). Similarly, bacterial numbers decreased from 3.4×10 6 to 0.29×10 6 cells mL −1. These data showed that microbial activity within the prefilter and the shallow layers of the sand filter had the greatest impact on water quality. In addition to its involvement in the continuous purification of surface water, the microbial community in the sand filter probably acts as a biological buffer against ephemeral increases in the loads of organic matter and nutrients in the recharge plant.