Suction Samplers Research Articles

Faunal Description of an Irish Cobble Site Using Airlift Suction Sampling

SHORT COMMUNICATION FAUNAL DESCRIPTION OF AN IRISH COBBLE SITE USING AIRLIFT SUCTION SAMPLING A. Linnane, B. Ball, B. Munday, R. Browne and J.P. Mercer INTRODUCTION One of the pnrmary goals in marine ecology is to understand themechanisms that control population dynamics in benthic habitats. One such habitat type is cobble (32-256mm particle diameter, Phi scale range = - 5 to - 8, (Wentworth 1922)), a substratum that is particularly common at the base of many subtidal reefs off the west coast of Ireland. Due to the interstitial nature of cobble, such sites have long been considered an important nursery area formany organisms (Hudon 1987; Able et al. 1988). Quantitative descriptions are sparse, however, as conventional sampling methods such as cores and grabs are unsuitable for gravel and cobble substrata. This problem was addressed with the development of the airlift suction sampler, which was first used in the 1960s (Brett 1964; Barnett and Hardy 1967) and later developed specifically for cobble areas in the United States as a means of identifying benthic recruitment habitats and nursery grounds of juvenile American lobsters Homarus americanus (Incze and Wahle 1991; Wahle and Steneck 1991). The advantages of suction dredging over manual sampling are that divers are not constrained by low visibility and replicate samples are easily achieved. Furthermore, tests indicate that sampling efficiency ranges from 70 -80% (R.Wahle, pers. comm.). As a result, suction samplers have had considerable success quantifying recruitment densities of juvenile lobsters and other benthic crustaceans within cobble substrata (Wahle and Incze 1997; Palma et al. 1998; Robinson and Tully 2000a,b). The aim of this study was to obtain both qualitative and quantitative data on the fauna of an Irish subtidal cobble site. This was achieved by standardised airlift suction sampling over a five-day period at four sites in Galway Bay. MATERIALS AND METHODS Field sampling was carried out on the west coast of Ireland in September 1997 at an area known as Aughinish Shoal in inner Galway Bay. The experimental ground was discovered through a series of reconnaissance dives from the MRV Connemara. Visual observations by two divers confirmed that an apparently homogenous cobble habitat existed. The cobble area was situated along the base of a reefwhere thewater depth ranged from 9m to 14m. The underlying substratum consisted of sand and bedrock. Benthic sampling of cobble habitat was conducted using a diver-operated airlift suction sampler (Incze andWahle 1991; Wahle and Steneck 1991). The airlift consisted of a 170cm length of 7cm diameter black PVC tube, with a scuba cylinder supplying air, fitted 10cm above the mouth of the tube. The other end of the tube was affixed to a 1mm mesh nylon bag that could be removed, closed and replaced underwater. The suction sampler was operated by two divers and was used in conjunction with a 0.5m2 quadrat constructed from buoyant PVC piping, a30cm high sheet of lnmmmesh curtain and a heavy chain base. This design prevented the escape ofmobile decapods from the quadrat. The cobble area was sampled at four sites; ten quadrats were sampled in each of two sites, while nine quadrats were sampled in the remaining two, giving a total sample area of 19m2.On sampling, the quadrat was placed randomly on a suitable cobble patch. One diver then removed the cobble stones by hand, while the second diver operated the airlift, ensuring that themouth of the tube reached into the interstitial spaces of the substratum. The divers worked slowly until all of the interstitial spaceswere exposed and sampled. Periodically, sample bagswere returned to the surface where they were analysed immediately or preserved for future examination. Prior to identification, samples were preserved by freezing or storage in 70% alcohol. All animals were identified at least to class level. RESULTS In total, 74 families of animals were sampled across the four sites (Table 1). The molluscan gastropods were the numerically dominant group (Fig. 1)with A. Linnane (corresponding author; email: adrian.linnane@ nuigalway.ie); B. Ball, B. Munday and J.P. Mercer, Martin Ryan MarineScience Institute, National University of Ireland, Galway R. Browne, National University of Ireland, Galway, Martin Ryan Institute Laboratories, Carna, Co Galway. Received 30 April2002. Read7October2002. Published 31 July 2003. BIOLOGY...

Ceramic suction samplers: A reliable method for extracting soil solutions for analysis

Ceramic samplers are used to extract soil solutions at different depths from the soil profile for chemical analysis. The advantage of this method is that samples can be taken at any time provided that the soil water potential is high enough to allow extraction of the water from the soil. An investigation was conducted to determine to what extent the CEC (cation exchange capacity) and selectivity coefficients of the samplers might influence the chemical composition of the water samples collected. This was due to criticism that the accuracy of the method may be influenced by the CEC of the samplers. The CEC of four Soil Moisture ceramic cup soil water samplers was determined. Two of these samplers had previously been installed in the field and two were new. The CEC of the sampiers did not vary much, although the used samplers had higher CEC values, which were ascribed to the contribution of clay particles contaminating the ceramic material. Selectivity coefficients for different cation combinations were calculated using the Vanselow equation. The selective adsorption of certain cations requires that negligibly small amounts of extracted soil solution be discarded. This makes the ceramic soil water samplers suitable for solution cation analysis.

Novel use of soil moisture samplers for studies on anaerobic ammonium fluxes across lake sediment-water interfaces.

Small soil suction samplers have been used for several years to sample soil solution for chemical analysis in laboratory and glasshouse experiments. They are very cheap, effective and convenient. Here we describe for the first time their use in studies on sediment porewater. Bulk sediment from West Lake, a shallow hypereutrophic lake in Hangzhou, Zhejiang Province, China, was placed in laboratory microcosms and incubated in the dark at 25 degrees C for 182 days to evaluate the feasibility of using the samplers to extract sediment porewater and to estimate NH4+ flux across the sediment-water interface under anaerobic conditions. The results show that the samplers were capable of sequentially extracting sediment porewater, 15 ml of which could be readily extracted for analysis within 30-45 min by vacuum applied using a plastic syringe. The NH4+ flux under laboratory conditions was characterized by a fast phase during the initial 18 days of incubation followed by a slower linear phase, with average release rates of 11.6 and 3.6 mg N m(-2) d(-1), respectively.

Coupled vertical and lateral preferential flow on a forested slope

Coupling of vertical and lateral preferential flow paths was examined on a forested slope with thin soil cover during artificial irrigations. Point‐scale infiltration was measured at sites with differing soil macroporosities using vertical profiles of time domain reflectometry probes and suction samplers. Lateral fluxes of water and solutes from the slope were determined at a through flow trench. Sites with greater macroporosities tended to exhibit vertical preferential flow, while infiltration at sites with relatively small macroporosities was largely by vertical propagation of a well defined wetting front through the soil profile. Generation of vertical preferential flow at sites with relatively large macroporosities increased with input intensity. Lateral macropores made a minor contribution to slope runoff. Instead, runoff largely occurred in a thin saturated layer at the soil‐bedrock interface, both in a highly conductive zone at the bedrock surface and in the overlying saturated soil matrix. Some assumptions underlying the use of isotopic and geochemical tracers to study runoff generation are called into question by complex mixing of event and pre‐event water in this saturated layer. Soil depth, bedrock topography, and antecedent soil wetness determine the thickness, connectivity, and upslope extent of the pre‐event saturated layer above the bedrock surface. These, in turn, control whether vertical preferential and matrix flow reaching the bedrock surface participate in slope runoff.

A quantitative technique for sampling motile macroinvertebrates in beds of the seagrass <i>Posidonia oceanica</i> (L.) Delile

Techniques for sampling motile macroinvertebrates associated with Posidonia oceanica seagrass meadows have mainly involved the use of hand-nets and suction samplers or collection by hand. These techniques give unreliable quantitative estimates or have practical difficulties. A large cylindrical saw-rimmed corer was designed and used successfully to obtain quantitative samples of macroinvertebrates from both foliage and root-rhizome matrix of a Posidonia oceanica meadow in Malta (central Mediterranean). Choice of the appropriate sample unit size was assessed by comparing the relative accuracy, precision and efficiency of three different core diameters: 25 cm, 35 cm and 45 cm. The results suggest that for comparison of macrofaunal species richness and abundance between different meadows/sites the 25 cm diameter corer is recommended. For surveys aimed at estimating total diversity within a particular site, the 35 cm diameter corer is more appropriate.

MACROPOROSITY AFFECTS WATER MOVEMENT AND PORE WATER SAMPLING IN PEAT SOILS

The measurement of chemical concentration profiles in pore water is a starting point for the analysis of biogeochemical processes in waterlogged peat soils. Concentration patterns may be obscured when macroporosity causes preferential flow in column experiments and when pore water is retrieved from the peat by suction. To investigate the magnitude of such effects, we used LiBr as a tracer in peat columns at outflow rates of 0, 2–3, and 8 mm d−1. The results were compared with modeled advective-diffusive migration rates. Twenty to fifty percent of the tracer was recovered from depths at which the tracer would have been absent if preferential flow had not occurred. At the high flow rate, the preferential flow was stronger, and the retrieved pore-water was probably in disequilibrium with the matrix. When pore water was retrieved by suction, linear concentration gradients decreased by about 30% through the recovery of water from different depths, and the quality of fitted linear gradients decreased from R2 = 0.99 to R2 = 0.82. When flow rates are low (<3 mm d−1) and pore water concentration values from samplers are aggregated or regressed, the obtained concentration profiles seem to represent the vertical distribution of chemical species reasonably well. The use and interpretation of pore water profiles in peat soils is problematic if flow rates are higher and if vertical gradients are based on individual or few data points that have been obtained by suction samplers.

Uranium and phosphate behavior in the vadose zone of a fertilized corn field

Phosphate fertilizers contain approximately 200 mg.kg-1 of uranium. The uranium and phosphate can move through the vadose zone and reach groundwater. Therefore, the knowledge of the ways in which these two elements are distributed, their partition relationships and their mobility behavior is of great interest. In order to study the latter, suction cup samplers, intended to collect soil water at different depths, were installed in an experimental site in a high plain of Mexico, where corn is cultivated and phosphate fertilizers are systematically applied. It was observed that the vadose zone contains high concentrations of uranium (1-50 mg.kg-1) and phosphates (22-33 mg.kg-1), which decrease at greater depths. Uranium concentration in the soil water varies between 10 and 3 mg.l-1 and phosphates between 1 and 0.3 mg.l-1. Their evolution throughout the profile of the vadose zone is determined by the decrease in concentrations, due to the physico-chemical processes involved.

Investigating preferential flow in a large intact soil block under pasture

Abstract. A large soil block was constructed to determine the importance of preferential flow routes compared with matric flow pathways at a pasture site in mid‐Devon. The sandy loam soil was well structured and uniform. The soil block measured 5 m×3 m×1 m and was instrumented with an array of 54 tensiometers, TDR wave guides and suction samplers connected to an in situ chloride analysis system. Four steady state irrigation experiments were conducted with a range of rainfall intensities. During each experiment chloride and nitrate tracers were applied and the patterns of movement were observed. Although the application of tracer was uniform and the soil was relatively homogeneous, there was large variability across the block in terms of time taken to reach the peak concentration (TPC) and the peak concentration itself. About 44 samplers operated at the greatest intensities (10–2 mm h−1) and only 35 at the smallest (1 mm h−1). No relationship was found between TPC and depth. The fastest TPC and largest concentrations were associated with the greatest rainfall intensities. Relative importance of the individual water pathways was a function of soil heterogeneity: parts of the soil block were highly active with several pathways having short TPCs and conductivities in excess of 4 m day−1 whereas other areas had longer TPCs and conductivities of 1–2 m day−1. The pattern was also dynamic, with conductivities of the pathways changing through time, though most of the faster pathways maintained their greater conductivities for more than one year.

Timing of Nitrate Leaching from Turfgrass after Multiple Fertilizer Applications

Abstract The leaching of nitrogen from surface-applied fertilizer to groundwater is an environmental concern. Nitrogen fertilizer is routinely applied to turfgrass from spring to late autumn in Canada. The main objective of this study was to determine the contribution of N applied in May, July and September to leaching. The leaching of applied chloride (May and September only) was also monitored and the transport of nitrate and chloride were simulated using the model LEACHM (within EXPRES) to assist in fulfilling the main objective. The accuracy of the model simulation for transport, not nitrogen losses, was also addressed. Field lysimeters (Guelph, Ontario) were packed with a three-horizon profile of a sandy loam soil, topped with Kentucky bluegrass (Poa pratensis) sod and monitored for 1 year. Based on soil water samples taken from suction samplers placed at depths of 10, 17, 29, 43, 54, 64 and 85 cm, part of the solute from spring/summer applications remained in the soil during the unusually dry summer. This residual solute was later transported downward with the ensuing infiltration front in late autumn, building upon the autumn application, resulting in excessive concentrations. Predictions by LEACHM of solute concentration profiles generally were similar to field measurements.

Laboratory measurement of suspended sediment concentration using an Acoustic Concentration Profiler (ACP)

Vertical profiles of suspended sediment concentration have been gathered in a laboratory flume using a 2.25 MHz acoustic transducer. The acoustic concentration profiler (ACP) was calibrated in a vertical duct for homogeneous concentrations of two uniformly sized sediments. The transducer was then transferred to a 6 m horizontal flume where concentration profiles were measured in steady and unsteady flows. For the steady flow tests, concentration measurements made with the ACP and with suction samplers are compared. The results demonstrate that the ACP provides an accurate method of non-intrusively measuring sediment concentrations of more than 2.5% by volume.

Development of a Protocol for Sampling Faecal Coliform Bacteria Originating from Manure in the Vadose Zone

Abstract Contamination of water resources with components of manure is a significant concern in Ontario. One aspect is the potential for bacterial transport through the vadose zone to groundwater following field application of manure. One obstacle to characterizing the movement of faecal bacteria in the vadose zone is the sampling of soil solution for bacteria. Porous-cup suction samplers are commonly used in estimating solute transport through this zone. However, there is little information on the calibration of such samplers for estimating numbers of bacteria in soil solution. This paper reports an attempt to make such a calibration. Tests were carried out under laboratory conditions which simulated the sampling of soil solution under field situation. As the suction applied was less than the air entry value for the ceramic porous cups used, the saturation status of the medium surrounding the cups was only important in terms of the number of colonies-forming units collected and not whether they were detected. The results indicated that although there were limitations in the use of the porous-cup suction samplers for bacterial sampling because of filtration effects, such samplers could be used for field collection of faecal bacteria from soil solution in situations with contrasting initial boundary conditions.

LATERAL BROMIDE DISTRIBUTION IN A VERTIC CLAY SOIL

In order to control the transport oftoxic elements, dissolved salts, and nutrients in agricultural areas, information on the spatial variability of field-scale transport properties is needed. To evaluate this for an unsaturated layered clayey soil, tracer tests were conducted at the Cherfech experimental field research station in Tunisia. Bromide-tagged water was infiltrated under ponding conditions on a 21.7-m 2 horizontal field plot equipped with 60 solute samplers, 15 neutron probe access tubes, and 15 piezometers. Volumetric soil water content was measured by means of a neutron probe at five depths, and soil moisture samples were withdrawn through ceramic soil water samplers at four depths, each with 15 suction samplers. The results showed typical evidence of preferential flow, with a wide variety of travel times with depth. This was noted especially for deeper soil layers, which displayed a large horizontal variation. In two tracer experiments, the groundwater tracer concentration increased up to twice the concentration of the water in the unsaturated zone withdrawn from different depths. This shows that bypass directly to the groundwater, initially at 1.5 m depth, occurred under ponding with chemigation.

Soil Solution Electrical Conductivity Measurements under Transient Conditions Using Time Domain Reflectometry

AbstractSeveral studies have shown that time domain reflectometry (TDR) can be used to measure water content and solute concentration during steady‐state experiments with constant soil water content. Few studies have been carried out to identify the relationship between bulk electrical conductivity (σa) and soil solution electrical conductivity (σw) to be used for transient conditions with varying water content. In this study, a single TDR probe was calibrated and found to accurately measure water content and σa. The σa measurements were fitted to σw using several previously published models. The accuracy of the σa and σw measurements increased with σa; however, the error in the σw estimation was &lt;10% for σa higher than 5.7 mS m−1. The calibration was verified in a large sand column; σa measurements were fitted to σw measured in soil solution extracted with suction samplers. The calibration was also used in a transient solute transport experiment. If not accounted for, the temperature effects of the water content measurement introduce significant errors in the σw estimations.

Transport of Dissolved Organic Matter through a Sandy Forest Soil

AbstractWe assessed the transport of dissolved organic matter (DOM) through a sandy, Ultisol forest soil on the southeastern U.S. Coastal Plain, and contrasted the results with similar studies from other forest regions, to test the hypothesis that DOM transport is greater through sandy Ultisols than finer textured Ultisols and Spodosols. Within a small headwater catchment, concentrations of dissolved organic carbon (DOC), a measure of DOM, were measured in soil solution at three depths (10, 30, and 90 cm) in sand A and E horizons of soil profiles, and in sand along the valley bottom at 198‐ to 264‐cm depth in shallow groundwater. Water samples were collected after every rainfall event for 21 mo using zero‐tension lysimeters, suction samplers, and piezometers. Mean concentration of DOC in soil water decreased from 25.5 mg C L‐1 at 10‐cm depth to 13.7 mg C L‐1 at 30 cm, and to 1.8 mg C L‐1 at 76 to 99 cm, before contacting clayenriched horizons. All valley bottom stations consistently averaged between 0.3 and 2.1 mg C L‐1. We did not find significant seasonal patterns, nor a correlation between DOC concentration and magnitude of rainfall events. We estimate that the flux of DOC decreased more sharply with soil depth than concentration due to attenuation of water transport through the soil profile. Compared with literature data from other forest regions, our results do not support the hypothesis that there is greater DOM transport through sandy upland soils on the Coastal Plain. Our results suggest that this is due to strong DOM retention within deep sand E horizons of these soils. Thus, strong DOM retention in forest soils appears to occur across a broader range of soil types than those exhibiting podzolization or having high clay content.

The influence of artificial macropores on water and solute transport in laboratory soil columns

The role of macropores in infiltration through a sandy loam was studied using laboratory columns pretreated with water possessing a δ 18O signature of −8.7% and 15 mg l −1 Cl −. A simulated snowmelt pulse of δ 18O-depleted water containing 1100 mg l −1 Cl − was added to a control column and two columns containing a single vertical macropore, one continuous and the other discontinuous. Macropores were formed in situ by disintegration of a biodegradable foam thread inserted during column packing. Macropores were 2 mm in diameter, which has been suggested to be the threshold for significant macropore flow given the soil's mean textural pore diameter of 0.41 mm. Meltwater was flushed from the columns by adding two pore volumes of isotopically enriched water containing 15 mg l −1 Cl − at a rate of 17.2 mm day −1. Tensiometers, time domain reflectometry probes and suction samplers were used to monitor matric potential, soil water content and soil water chemistry at 0.1 m intervals down the columns. Column effluent was sampled daily for δ 18O and Cl −. Mobile soil water contents ( θ m) and dispersivities (ϵ) were estimated by fitting a one-dimensional analytical solution of the convection-dispersion equation to Cl − breakthrough curves (BTCs). θ m increased with depth in all columns, whereas only the discontinuous macropore column showed an increase in ϵ with flow length. Cl − and δ 18O breakthrough occurred earlier at all depths in the macropore columns relative to the control, resulting in larger ϵ values for macroporous soil. ϵ for a given flow length tended to be greatest in the discontinuous macropore column, reflecting the role of internal catchment processes. Macropore presence was associated with decreased θ m during infiltration and bimodal BTCs in column effluent. The threshold ratio of macropore-to-micropore diameters at which macropores exert a detectable influence on water transport must be less than that examined here.

Operator Safety and Plant Deposits when using Pesticides in Greenhouses

Operator exposure and plant deposits have been measured while spraying ind greenhouses using handheld spraying equipment. Suction samplers and static samplers (rods and pads) were used. Rubidium Chloride (RbCl) was added to the spray as a tracer. Spray application was carried out with a knapsack sprayer (CP-20), a knapsack mist blower (Solo Master), a high pressure spray gun (Wanjet 200 spray gun with four nozzles), and a hot aerosol fogger (Igeba TF-30). Average dermal exposure was over ten times higher than respiratory exposure. Both dermal and respiratory exposure were reduced when the operator walked backwards away from the spray. When using a knapsack mist blower, the dermal exposure of the operator working forwards was 20 times higher than when he worked backwards. Respiratory exposure was also greater. Working forwards using a knapsack sprayer gave a dermal exposure almost four times greater than when working backwards. A high pressure spray gun used while working backwards gave the lowest dermal exposure. A hot aerosol fogger also gave a low dermal exposure, but the respiratory exposure was very high. Pesticide deposit on the operators face and hands after 8 h spraying was in the worst case more than 2500 times greater than the plant deposit. When applying the same dose, a hot aerosol fogger and knapsack mistblower gave lower plant deposits than a high pressure spray gun and knapsack sprayer.

Nutrients in soil solution following selective logging of a humid tropical ‘terra firme’ forest north of Manaus, Brazil

Sustainable use of the Amazon forest for timber production is conditioned by the effect of logging on the system's nutrient cycling. This paper reports the results of a soil moisture and soil water chemistry monitoring campaign before and immediately after a selective logging which removed 35 m(3) wood/ha. Soil moisture was measured using tensiometers, and soil water chemistry using suction samplers in five disturbance classes: tractor tracks, clearing centres, clearing edges, forest edges and untouched forest. The results show that the soil under the tractor tracks and clearings contained more moisture than under the untouched forest. The suction samplers extracted substantially more nitrate, ammonium, calcium, magnesium and potassium from the clearing centres, the tractor tracks and the clearing edges than from the forest sites. The results are explained in terms of altered microbial activity, changes in crown interception and uptake by roots.

Movement of water and the herbicides atrazine and isoproturon through a large structured clay soil core

A large (1.1 m × 0.8 m in diameter) core of strongly cracked clay soil was instrumented with eight suction samplers, ten zero-suction samplers and sixteen pressure transducer tensiometers. Results of three rainfall events labelled with potassium bromide, pentafluorobenzoic acid and 2,6-difluorobenzoic acid indicate rapid bypass flow, matrix advection and mixing of water between the soil macropores and the matrix all occurred. Generally, no sharp distinction was observed between crack flow and matrix advection; water flow was best described by a continuum of flow phenomena. Before rainfall application, the herbicides atrazine and isoproturon were applied to the soil surface at rates typically used in the field (2.475 kg active ingredient/ha). Rapid bypass flow in large cracks, by which some of the solutes were transported with limited contact with the soil, was mainly responsible for redistribution of the herbicides and their movement to depth in short time periods. Over the course of the experiments 0.23 pore volumes of rainfall were applied to the core but only 0.02 pore volumes were recovered by gravity drainage. Less than 1% of the herbicides applied was lost in water draining from the soil core.

A field-based spectrophotometric flow-injection system for automatic determination of chloride in soil water

The use of chloride as a tracer for soil water investigations is discussed. Limitations with laboratory based soil core and field based sampling are considered with respect to the poor suitability of the data for rigorous assessment of mechanistic models. Investigation of water movement in soil has been restricted by limitations in spatial and temporal sampling. Fine resolution sampling generates large numbers of samples which cause problems with post sampling laboratory analysis. This paper describes a field-based system for the analysis of chloride in soil water. There are three component parts to the system, (i) a custom sampling sub-system comprising of ceramic cup suction samplers and sample traps, (ii) a sample routing sub-system to channel sample to (iii) a sample analysis sub-system utilizing a flow injection method for sample analysis using a custom built photo-diode detector. The three sub-systems were controlled by a suitably equipped personal computer. A calibration procedure is described with a third order polynomial equation derived to convert millivolt response from the detector into chloride concentration. Field and laboratory data from a tracer experiment are presented and discussed, and it is concluded that the system is well suited to field-based applications. Finally it is noted that the photo-detector is suitable for colourimetric analysis of any tracer with suitable chemical determination.

Computer control for investigating water and chemical transport in a large isolated soil block

Abstract This paper describes the computer controlled data acquisition systems designed to obtain fine spatial and temporal resolution data of tracer in soil water within a large undisturbed soil block. Such information is desirable to help understand and model transport mechanisms in light of increasingly strict environmental pollution limits. The soil block was 5.4 × 3.4 × 1.2 m, instrumented in nine layers with time domain reflectometry (TDR) waveguides multiplexed using a PC; pressure transducer equipped tensiometers multiplexed using a datalogger and suction samplers connected to in situ flow-injection analysis systems controlled by a PC. A rainfall simulator capable of applying tracer to the block without altering the surface flux (which could range from 1 to 30 mm h −1 ) was controlled by a datalogger. Initial conditions when the soil block was subjected to a surface flux of 10 mm h −1 are presented along with an example of a chloride breakthrough curve to illustrate the nature of the data obtained from the soil block system. It is concluded that the integrated system described is a significant advance in working technology for field and plot scale tracer experiments because the spatial and temporal resolutions achieved are possible with a single person maintaining the system.