Small-scale Spatial Variability Research Articles

Radial distribution of Ni in stemwood of Quercus ilex L. trees grown on serpentine and sandy loam (umbric leptosol) soils of NE-Portugal

Concentrations of Ni were determined in xylem and phloem of Quercus ilex trees growing on serpentine and sandy loam soils of northeast Portugal. Radial distribution patterns of Ni in stemwood were compared to variations in annual growth increments of the trees. Concentrations of Ni in xylem and phloem were higher in Q. ilex from serpentine soil, when compared with Q. ilex of a sandy loam soil. The radial distributions of Ni showed large variations among the trees, although they all grew in the same area within a short distance from each other. These differences can be caused by small-scale spatial variations in the soil. Therefore, the use of such radial Ni distributions for a retrospective biomonitoring of the Ni pollution of larger areas appears questionable.

Impact of small-scale spatial rainfall variability on runoff modeling

Rainfall and wind data obtained from a dense raingage network on a 4.4 ha semiarid catchment were used as input to a distributed rainfall-runoff model. It was shown that the wind direction and velocity have a relatively small impact on peak rate and runoff volume for this low relief watershed. However, even at this small scale, spatial variability of precipitation can translate into large variations in modeled runoff. When five model runs were conducted using input from one of five recording raingages, one at a time, the coefficient of variation for peak rate and runoff volume ranged from 9 to 76%, and from 2 to 65%, respectively, over eight observed storm events. By using four well distributed gages the variations in modeled runoff volume approach the sampling resolution of the raingages as well as the estimated accuracy of runoff volume and peak rate observations. The results of this study indicate that if distributed catchment modeling is to be conducted at the 5 ha scale in an environment dominated by convective air-mass thunderstorm rainfall, knowledge of the spatial rainfall variability on the same scale is required. A single raingage with the standard uniform rainfall assumption can lead to large uncertainties in runoff estimation.

Seabed dynamics of the inner Amazon continental shelf: temporal and spatial variability of surficial strata

The continental shelf southeast and northwest of the Amazon River mouth is overlain by a sediment layer of about a meter in thickness, characterized by 210Pb profiles consisting of one or more segments with nearly-uniform excess activity. Uniform 210Pb activity profiles in shelf environments commonly are a result of intense biological reworking of sediments; however, biological activity is minimal in this area. Hence, this surficial layer (SL) is a result either of physical reworking of the sediments, or of rapid (possibly episodic) deposition of sediment. Factors controlling the formation of the SL were examined during the AmasSeds project between August 1989 and October 1991. Primarily using 210Pb ( t 1/2 = 22.3 yr) activity profiles and X-radiography, the thickness and character of the SL were assessed at four locations reoccupied during four seasonal periods corresponding to various riverine and oceanographic conditions (e.g., discharge stage, wind stress); one of these stations was reoccupied during semidiurnal and fortnightly periods. Additionally, replicate sediment cores were obtained at stations in order to assess small-scale spatial variability of geochemical and sedimentological characteristics in the seabed. The SL thicknesses in replicate sediment cores obtained at each site were found to vary within ±5 cm. Normalized thickness of the SL decreased by an average of 17 cm between August 1989 and February 1990, a period of increasing wind stress during falling-to-rising river discharge. The SL thickness subsequently increased slightly (8 cm) from February to May 1990, and increased again (27 cm) between May 1990 and October 1991. The maximum SL thicknesses were observed in October, a period of low wind stress and minimal river input, suggesting that the observed seasonal changes are dictated by oceanographic conditions as well as by sediment discharge. Variations in SL thickness are reflected by changes in suspended sediment (mostly as fluid muds), as the highest suspended sediment inventories and most extensive fluid muds are observed during the period when SL thickness is at a minimum. Although a significant SL was present during all of the sampling periods, changes in the character of 210Pb profiles at two of the stations suggest that substantial, perhaps complete, removal and redeposition of the SL occurred some time between February and May. Preserved strata (i.e., below the SL) is characterized by greater evidence of bioturbation and increased sand content, but otherwise is similar to that of the SL. Long-term preservation of strata is thought to occur through episodic suspension and redeposition of the SL, with net accumulation of decimeter-thick, hiatus-bounded layers.

The measurement of nitrous oxide emissions from soil by using chambers

Small flux chambers are widely used to measure emissions of nitrous oxide, N 2 O , from soil, the gas being determined by gas chromatography with an electron capture detector. The technique is relatively cheap, and is adaptable to a wide range of site conditions and emission rates: from the order of 1 µg m -2 h -1 to more than 10 mg m -2 h -1 . Increasingly, systems are being automated, to get more information on short-term temporal variability and to collect data over long periods to improve estimates of total annual emissions. Such systems are being used in the field and with soil monoliths installed in a greenhouse. Large chambers 50-60 m 2 in area, with gas analysis by long-path infrared spectrometry, offer a way of overcoming small-scale spatial variability, and are useful in conditions where micrometeorological methods may not be applicable, or when long runs of data are needed from the same site. In studies with small closed chambers, we have measured N 2 0 emissions from grassland ranging from negligible values to about 4 mg N 2 O -N m -2 h -1 (nearly 1 kg N 2 O-N ha -1 d -1 ), with total losses in the range 0.14-5.1% of the nitrogen applied as fertilizer, depending on factors such as soil structure, water potential and temperature, and the chemical form of the fertilizer. Reasonable agreement can be obtained between chamber and micrometeorological flux measurements on homogeneous sites.

Ultraviolet observations of the structure and dynamics of an active region at the limb

The structure and dynamics of active region NOAA 7260 at the limb have been studied using ultraviolet spectra and spectroheliograms obtained during the eighth rocket flight of the Naval Research Laboratory's High Resolution Telescope an Spectrograph (HRTS). The instrument configuration included a narrow-bandpass spectroheliograph to observe the Sun in the lines of C IV lambda 550 and a tandem-Wadsworth mount spectrograph to record the profiles of chromospheric transition region and coronal lines in the 1850-2670 A region. The combination of high spatial resolution and high spectral purity C IV slit jaw images with ultraviolet emission-line spectra corresponding allows examination of a variety of active region phenomena. A time series of spectroheliograms shows large-scale loop systems composed of fine-scale threads with some extending up to 100 Mm above the limb. The proper motion of several supersonic features, including a surge were measured. The accelerated plasmas appear in several different geometries and environments. Spectrograph exposures were taken with the slit positioned at a range of altitudes above the limb and provide a direct comparison between coronal, transition region and chromospheric emission line profiles. The spectral profiles of chromospheric and transition region emission lines show line-of-sight velocities up to 70 km/s. These lower temperature, emission-line spectra show small-scale spatial and velocity variations which are correlated with the threadlike structures seen in C IV. Coronal lines of Fe XII show much lower velocities and no fine structure.

Use of the euryhaline bivalve Potamocorbula amurensis as a biosentinel species to assess trace metal contamination in San Francisco Bay

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 124:129-142 (1995) - doi:10.3354/meps124129 Use of the euryhaline bivalve Potamocorbula amurensis as a biosentinel species to assess trace metal contamination in San Francisco Bay Brown CL, Luoma SN Potamocorbula amurensis was assessed as a biosentinel species in San Francisco Bay, California, USA. Uptake of metal in both the laboratory and field showed that P. amurensis was sufficiently responsive to Ag, Cd, Cr, Ni and V to detect environmental differences in exposure. It was less suitable as an indicator of Cu and Zn contamination. Concentration factors for P. amurensis were: Ag, 386000; Cd, 50200; Cr, 36600; Cu, 12200; Ni, 5200; and Zn, 115500. Samples were collected from 6 stations throughout the bay at near-monthly intervals from January 1991 to March 1992. Variability within a collection was influenced by gut content and animal size. Other sources of variability were time [coefficient of variation (CV) = 10 to 21%], small-scale spatial variability (within 3 km, CV = 10 to 25%), and large-scale spatial variability (CV = 3.3 to 12.4%). Depuration for 48 h was necessary to mitigate bias from gut content. Precision was improved by analyzing large numbers of individuals (60 to 120) separated into several (5 to 14) composites at each collection and by determining, from regression, the mean and variance for samples with significant correlations between metal concentration and shell length. Repeated monthly sampling increased the accuracy of long-term site characterizations. Temporal variability was small because of drought. The grand means of the concentrations of Ag, Cd, Cr, Ni, and V in the tissues of P. amurensis at each station for the 15 mo period revealed persistent contamination from industrialized Suisun Bay to the mouth of San Francisco Bay. Demonstration of responsiveness, precision and accuracy should be a prerequisite for the optimal use of biosentinels. Potamocorbula amurensis . Biosentinel . Trace metals . San Francisco Bay . Size . Gut content . Variability Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 124. Publication date: August 10, 1995 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1995 Inter-Research.

Disappearance of spatial variability and structure in forest floors ? A distinct effect of air pollution?

Small-scale spatial structure and variability are characteristic features of soils and are also of ecological importance. A few investigations show that predictability of the edaphic environment, at spatial distances relevant for the vegetative proliferation of plants, is essential for survival. The relevant scale for forest field layer vegetation would be from 0.1m to a few meters.

Small-scale spatial and temporal variations in mid-ocean ridge crest magmatic processes

Data from a suite of closely spaced lava flows recovered within the axial summit caldera and on the crestal plateau of the East Pacific Rise around lat 9°31′N indicate that eruptions on this fast-spreading part of the mid-ocean ridge occur throughout the crestal region and are not restricted to the axis. These eruptions contribute to a complex distribution of basalts of various ages and a significant thickening of seismic layer 2A away from the axis in our study area. Small-scale (<600 m) diversity and nonsystematic distribution of lava types may reflect rapid changes in magma chemistry that occur during crystallization and replenishment in small magma lenses, coupled with the effects of frequent low-volume eruptions both within and outside of the axial summit caldera.

Relationships between denitrification rate and determinant soil properties under barley

To better understand environmental regulation of denitrification, we examined relationships between denitrification rate and six determinant soil properties: moisture content, air-filled porosity, NO3− content, respiration rate, mineralizable-C concentration and denitrifying enzyme activity (DEA). Soil cores were collected on 27 sampling dates over a growing season at a site seeded to barley (Hordeum vulgare). Denitrification rate was measured using a static core technique and acetylene blockage. Moisture content and air-filled porosity and, to a lesser extent, mineralizable-C concentration and respiration rate were more strongly related to denitrification rate than was DEA. Denitrification rate was unrelated to NO3− content. On most sampling dates, mean denitrification rate increased substantially only below an air-filled porosity of 0.3. Moreover, the distribution of individual measurements of denitrification rate was less skewed at lower air-filled porosities. Approximately 60% of variation in mean values of denitrification rate for each sampling date could be accounted for by measurements of bulk soil properties, of which moisture content and air-filled porosity were most important. Measurements of bulk soil properties did not account for nil values of denitrification rate at low air-filled porosities or for small-scale spatial variability. Such measurements were better indicators of temporal variation — that is, when denitrification occurred — than of actual rates. Key words: Denitrification, air-filled porosity, denitrifying enzyme activity

Spatial variability of urban precipitation chemistry and deposition: Statistical associations between constituents and potential removal processes of precursor species

The precipitation chemistry of Greater Manchester, a Metropolitan County in the northwest of England, has been examined for small scale spatial variability using a network of 18 bulk precipitation collectors. Significant spatial variability was found for concentrations of non-marine SO 4 2−, NO 3 −, NH 4 +, Ca 2+ and H + ions. The statistical associations between the data were investigated using correlation, partial correlation and principal components analyses. It was found that zero-order correlation coefficients were inadequate for the interpretation of the data and that the computation of first, and higher order partial correlation coefficients was necessary in order to explain the interrelationships between the data and their spatial variability. The statistical associations between the data suggest relationships between Ca 2+ and non-marine SO 4 2−, and NO 3 + in precipitation which are discussed in terms of their possible precursor species. Potential source effects were examined in conjunction with atmospheric removal processes. The dry deposition of SO 4 particles, rather than the dry deposition of SO 2, may explain the spatial variability of non-marine SO 4 2−. The erosion of CaSO 4 formed from the reaction of SO 2 with CaCO 3 on urban surfaces with subsequent resuspension is thought to be the basis of the relationship between Ca 2+ and non-marine SO 4 2− concentrations in precipitation. The wet and dry deposition of CaCO 3 particles from local sources may be partially responsible for the spatial variability of H +, and dry deposition and scavenging of NH 3, in conjunction with the predominant wind direction may explain the spatial variability of NO 3 − and NH 4 + ions. Ammonia is thought to originate from sources both outside the study area and within it.

Spatial variability of energy fluxes in suburban terrain

Energy fluxes over an area of “homogeneous” suburban residential land-use in Vancouver, B.C., Canada are shown to vary by up to 25–40% within horizontal scales on the order of 102–103 m. Previously, variability of this magnitude has been expected to occur only at larger scales, between land-use zones or as urban-rural differences. In view of these findings, it is recognized that microadvective interaction between surface types at small scales may be important and can affect the energy balance even at larger scales. The present study discusses the small-scale spatial variability of energy fluxes and shows that it varies greatly for each term in the surface energy balance.

Large-scale distribution of metal contamination in the fine-grained sediments of the Clark Fork River, Montana, U.S.A.

Historic discharges from the mining and smelting complex at the head-waters of the Clark Fork River have resulted in elevated Ag, Cd, Cu, Pb and Zn concentrations in the <60 μm fraction of both bed and flood-plain sediments of the river. Processes affecting the trends in longitudinal distributions of these metals were investigated by repeated sampling over a 380 km river reach between August 1986 and July 1989. At the most upstream site, bed-sediment metal concentrations were enriched 18–115 times above least enriched tributaries, depending on the metal. All metals decreased exponentially with distance downstream away from mining. The exponential model predicts that elevated metal concentrations should occur over 550 km downstream, in Lake Pend Oreille. Longitudinal trends, obvious on a scale of hundreds of kilometers, were obscured by small-scale spatial variability when shorter stretches of the river were considered. Longitudinal dispersion appeared to be controlled largely by physical dilution with less-contaminated sediments. Evidence suggests that erosion of contaminated flood-plains contributes to metal contamination in the bed sediments. Tributary input appeared to have little influence on the large-scale, downstream distribution of metals; however, it did contribute to local variability in bed-sediment metal concentrations. Association of metals with specific mineral grains, as well as variability in total organic C and Fe concentration, appeared also to contribute to variability. Some year-to-year variability in bed-sediment metal concentrations was observed, however, trends in longitudinal dispersion were not significantly different between at least two of the years sampled.

Variation in estuarine littoral nematode populations over three spatial scales

The population characteristics of the nematode fauna from five replicate cores taken over four seasons at nine sites within mangroves, at three different estuaries on the south-east coast of Australia, are compared. Using cluster analysis, principal co-ordinate analysis and other statistical techniques, the variation in nematode populations is identified as arising from several sources: temperature changes between the more northerly and southerly estuaries (5%); changes in grain size and organic content of the sediment between sites (22%); changes between sites in the frequency of samples containing certain types of food, particularly associated with pools of water and surface topography (30%); stochastic changes in nematode populations within individual samples, probably caused by small scale spatial and temporal variability in food sources (35%); and seasonal changes at all the sites and estuaries (8%). The implications of this pattern of variation for the biology of the nematodes is discussed.

Zooplankton Distribution in Three Estuarine Bayous with Different Types of Anthropogenic Influence

Zooplankton was sampled in three tributaries of the Calcasieu Estuary: one flowing through an area of petrochemical industries, one through a municipal area, and one through an agricultural area. Synoptic comparisons among the bayous were made on eight trips over a two-year period. Additionally, each bayou was sampled intensively for small-scale distribution on four occasions. Numbers of all zooplankton taxa were consistently higher in the agricultural bayou than in either of the other bayous. Patterns of small-scale spatial variability also differed among the bayous. The agricultural bayou appeared to be a relatively healthy estuarine tributary. The municipal bayou was probably subjected to chronic environmental stress that is very severe in the vicinity of the municipal sewage and storm-drain outfalls. Evidence indicated that the industrial bayou suffered from frequent, but not continuous, episodes of environmental stress throughout its length.

Intertidal and Shoal Benthic Community Metabolism in a Temperate Estuary: Studies of Spatial and Temporal Scales of Variability

Variability in benthic community metabolism, sediment chlorophyll and sediment organic carbon attributable to substrate type and season were examined. Substrate types included intertidalSpartina alterniflora marsh, mudflat, and sandflat and subtidal eelgrass (Zostera marina) and bare sand bottoms. Significant differences in parameter estimates were found among the different substrate types for each specific sampling data. When estimates were pooled over the entire study period, significant differences were found only for respiration rate and sediment pigment concentrations. The data indicate no obvious ranking in magnitude for any parameter that can be attributed to substrate type or season. Small-scale spatial variability and rapid temporal changes (turnover) are postulated as the principal reasons governing the overall results.

Determination of sea ice motion using digital SAR imagery

Using digital SEASAT synthetic aperture radar (SAR) imagery, high-precision densely sampled maps of ice motion have been derived by tracking ice features to determine the small-scale spatial variability of ice deformation. The digital SAR imagery was processed to remove geometric distortions and located on the Earth to an accuracy of about 100 m utilizing an algorithm based on the spacecraft orbital data and the characteristics of the SAR data collection system, independent of attitude information or ground reference points. Radiometric enhancement of the imagery using a variable linear stretch algorithm was performed to remove a system-related gradient and improve the identification of sea ice features. Using ice features common to an overlapping pair of images, vector plots of ice motion were then produced. Examples of ice motion are shown in the marginal ice zone and in the central ice pack where mean displacements of 15.3 km/day and 5.0 km/day were measured, respectively. Considering errors in Earth location with those in feature identification an overall error of 150-200 m in displacement measurements was estimated. The ice motion vector plots indicate a high degree of spatial deformation, demonstrating the potential value of spaceborne SAR data for production of precision large-scale maps of ice displacement with a spatial resolution of ice deformation on scales much less than 100 km.

Temporal and Small-scale Spatial Variability of Algal Abundance on an Intertidal Rocky Shore

Variation saisonniere de 6 Algues principales sur une plateforme rocheuse de la Nouvelle-Galles du Sud

Estimates of particle flux and reworking at the deep-sea floor using 234Th/ 238U disequilibrium

Because of high specific activities of excess 234Th ( t 1/2 = 24.1 days) on suspended particles in the deep sea, this nuclide is potentially an extremely sensitive indicator of particle inputs and dynamics at the seafloor. Measurements were made at two deep-sea sites in order to examine this potential. Inventories of excess 234Th at a low-current hemipelagic mud site (3990 m) in the Panama Basin were ∼ 1.5 (September, ′81) and ∼ 2.5 (June, ′82) dpm/cm 2. The steady state fluxes to the seafloor calculated from these inventories are in rough agreement with radionuclide fluxes measured in sediment traps. Small-scale ( ∼ 100m) spatial variability in inventories implies biologically significant heterogeneity in particle inputs. Sediment from the continental rise site in the northwest Atlantic (2800 m), a site with higher current velocities than the Panama Basin, had an inventory of ∼ 1.9dpm/cm 2 . This inventory is also in rough agreement with predictions made on the basis of nearby sediment trap data. Particle mixing coefficients of ∼ 30cm 2/yr calculated at the Pacific and Atlantic sites are similar to those in shallow water deposits but could reflect disturbance during handling. Based on 210Pb data from the Panama Basin, sediment from below ∼ 6cm is mixed at a rate ∼ 10 × slower than the near-surface sediment to a depth of at least 20 cm. Agreement between 234Th predicted mixing rates at the Panama Basin site with 210Pb profiles and in-situ experiments with glass bead tracers implies that these rates are real. Although the diffusion of dissolved 234Th into deep-sea sediments complicates interpretations, 234Th xs distributions in bottom sediments offer a useful adjunct to sediment traps for investigation of particle dynamics near the deep-sea floor.

Experimental field evidence of interspecific aggression between two species of kangaroo rat (Dipodomys).

The competitive coexistence of heteromyid rodents has been primarily ascribed to differential utilization of resources such as microhabitats and seeds. An examination of the use of space by the kangaroo rat Dipodomys merriami indicates this species is aggressively subordinate to a larger species, Dipodomys spectabilis and is excluded from the larger species home range during the crtical fall harvesting season. These experiments suggest that interspecific aggression may be involved in the coexistence of these species. Additional evidence is presented that small scale spatial variations in resource productivity may promote the coexistence of these two species.

Effect of Optical Inhomogeneities on Phase Matching in Nonlinear Crystals

Experimentally, we have observed variations in the phase-matching temperature (Tpm) for second harmonic generation (SHG) along the pull axis of lithium niobate (LiNbO3) crystals. We have related these to variations in the extraordinary index of refraction caused by changes in crystal stoichiometry occurring in the growth process. We have established a technique, for filtering pathological crystals, based upon a point-by-point mapping of the birefringence variations along the direction of interest. This provides information about the details of the large and small-scale spatial variations. Empirically we can get toleration limits on the birefringence variations for application to parametric oscillator design. We have studied several physical models (single step, multiple step, and linear ramp) for the manner in which monotonic changes in index, appropriate for LiNbO3, are introduced as a function of position. We have found that the usual quality criterion based upon the width of the central peak in an SHG scan versus temperature is misleading because this width is rather sensitive to the manner in which a given total variation in birefringence is introduced. A criterion based upon the ratio of the first sideband peak to the height of the center maximum is found to be only somewhat model dependent, but this test becomes less meaningful when the distortion causes asymmetry in the SHG scan. Asymmetries which are typical in SHG scans can be accounted for by our step model. The most significant result of the theory is a quality test which is independent of the models which we have considered and which is based upon an effective width defined to be the area under the SHG scan divided by the height of the central peak. We have further demonstrated that this area criterion is quite generally model independent and will be useful in gauging index distortion of any nature in any nonlinear material. This technique would allow one to estimate the nonlinear susceptibility in any phase-matchable ferroelectric crystal with multidomains. Such an evaluation of a scan of SHG power versus momentum mismatch can provide the only certain way to establish that a phase-matchable ferroelectric crystal which can be multidomained is indeed single domain throughout its volume. We have examined theoretically, periodic and rapidly varying index distortions in barium sodium niobate, Ba2NaNb5O15. We have considered a sinusoidal variation (first analyzed by Smith) and present birefringence mapping data which supports this representation of the growth striae and shows that this distortion may not significantly degrade SHG. In addition we have studied a step-function periodic distortion which might apply to propagation in a uniformly twinned crystal. The effects of periodic distortion are quite different from the monotonic and slowly varying distortion in LiNbO3, and the commonly employed evaluation criteria become useless. Finally we have considered two means by which one could either eliminate or get around the stoichiometric variations in LiNbO3. The first involves crystal growth at the maximum melting composition in the phase equilibrium diagram while the second concerns the choice of a suitable geometry in an ordinarily grown c axis boule.