Intensive Field Sampling Research Articles

Evaluation of LAI-2000 for leaf area index monitoring in paddy rice

Leaf area index (LAI) is a variable of primary importance for crop monitoring and it is usually measured by labor intensive destructive field sampling. Indirect non-destructive estimates by optical instruments are a competitive alternative to direct methods for frequent measurements and over large areas. The work presented here evaluated the adequacy and the range of reliability of the LAI-2000 estimates for rice ( Oryza sativa L.) by comparison with LAI measurements derived by destructive sampling. Field data were collected in 2004 for an Indica type variety grown under different levels of nitrogen fertilization. The comparison showed that LAI-2000 estimates and destructive LAI measurements are well correlated ( R 2 > 0.8) whereas the correlation decreases when LAI values are lower than one ( R 2 < 0.6). Moreover, when LAI > 1, the estimates derived by discarding the wide angle reading (fifth ring) of the optical instrument are closer to the actual LAI values compared to the standard LAI-2000 outputs. The regression line is, in fact, not statistically different ( P = 0.25) from the 1:1 line. In these application conditions, LAI-2000 estimates are correct within ±32%. Therefore, if the range of applicability is restricted to LAI values greater than one and the wide angle readings are discarded, LAI-2000 is an appropriate instrument for in situ LAI estimation in paddy rice fields.

Real-time streaming of environmental field data

Field measurements in the environmental sciences still depend upon the pencil and paper notebook for data collection. Although robust, this method is labor-intensive and susceptible to recording and georeferencing errors during transcription. Recent advances in mobile computing and wireless communications allow the geoscientist to process and transmit data while still in the field, thereby minimizing human errors and time delays. We describe an integrated system developed for environmental and geolocation data acquisition that is intended to streamline the collection process. The system consists of software applications and hardware components that enable wireless, mobile and Internet computing during field campaigns. In particular, two-way transfer and display of collected data is achieved between the field site and a remote location, a concept referred to as field data streaming. A prototype system has been tested in field trials in Cambridge, Massachusetts, USA and Newcastle, New South Wales, Australia. Field studies demonstrate the noticeable gains in efficiency and precision achieved with the use of the field streaming technology. Potential applications include biogeochemical and hydrologic studies, water quality monitoring, emergency response to water-borne disasters and intensive field sampling campaigns.

A heavy‐duty time domain reflectometry soil moisture probe for use in intensive field sampling

Mapping soil water content for site‐specific management of farm fields is commonly achieved through grid soil sampling. This effort frequently requires intensive soil coring, which is destructive and time consuming. Precision farming and research can be facilitated if sampling techniques are improved and made cost effective. We designed and constructed a heavy‐duty time domain reflectometry (TDR) probe of simple design that fits a hydraulic soil sampling machine. The design is simple enough to be adapted to the TDR equipment and hydraulic sampler that a researcher or practitioner may already possess. The probe consists of a housing and adapter that can be fabricated in a local machine shop from materials that are easily obtainable. Probe schematics and summary soil water maps obtained using the new design are presented. As with conventional TDR probe designs, stony or indurate soils may present particular problems in effective insertion of the probe.

A heavy-duty time domain reflectometry soil moisture probe for use in intensive field sampling

A heavy-duty time domain reflectometry soil moisture probe for use in intensive field sampling

Aerosol radiative, physical, and chemical properties in Beijing during June 1999

Beijing experiences air pollution such that the sky overhead is gray much of the time even on cloudless days. In order to understand the cause of this problem, the aerosol light scattering coefficient σsp and absorption coefficient σap were measured under dry conditions (instrumental relative humidity &lt;40%) during a 1‐week intensive field sampling period in June 1999 in Beijing, China. Additional measurements included the aerosol mass size distribution, chemical composition of the aerosol mass having particle diameters less than 2.5 μm (PM2.5) as well as the chemical composition of the total suspended particulate matter. The mean (and standard deviation) for hourly averages of σsp, σap, and the single‐scattering albedo ω were 488 Mm−1 (370 Mm−1), 83 Mm−1 (40 Mm−1), and 0.81 (0.08), respectively, which is significantly higher than values reported in urban regions of the United States. The relatively high values of σsp were accompanied by a daily mean value for the PM2.5 mass concentration of 136 μg m−3 (48 μg m−3), which is significantly higher than the proposed U.S. 24‐hour average mean National Ambient Air Quality Standard of 65 μg m−3. The visual range during the field study, based on measurements of σsp and σap, was typically less than 6 km. For several days that did not have rain or fog, there was a clear diurnal trend in σsp, σap, and ω, with peak values in the early morning and minima that occur in the evenings. The peaks correspond to minima in ambient temperature and maxima in relative humidity. Mass size distribution measurements indicate that although ∼80% of the aerosol mass was located in the coarse particle mode (Dp &gt; 1.0 μm), the submicron aerosol was responsible for ∼80% of the light scattering at 530 nm. The largest contribution to the PM2.5 aerosol mass was due to organic compounds, which accounted for ∼30% of the mass. The contributions of sulfate, ammonium, and nitrate to the PM2.5 mass concentration were ∼15%, 5%, and 8%, respectively. Mineral aerosol contributed ∼16% to the PM2.5 aerosol mass. These data show that combustion‐related particles rather than wind‐blown dust dominated the light extinction budget during June 1999.

Attribution of Particulate Sulfur in the Grand Canyon to Specific Point Sources Using Tracer-Aerosol Gradient Interpretive Technique (TAGIT)

ABSTRACT Since aerosol particulate sulfur is generally a secondary airborne pollutant, most source attribution techniques require many assumptions about the transport and chemistry of sulfur dioxide (SO2) emissions. Uncertainties in our understanding of these processes impair our ability to generate reliable attribution information that is necessary for designing cost-effective pollution control policies. A new attribution technique using artificial tracer is presented in hopes of reducing the uncertainty of secondary aerosol source attribution. The Tracer-Aerosol Gradient Interpretive Technique (TAGIT) uses tracer data from a monitoring network to distinguish sites impacted by a source tagged with tracer from nonimpacted sites. Sites determined not to be influenced by the plume are considered to represent background particulate sulfur concentrations. The particulate sulfur attributable to the source at sites within the plume is calculated as the difference between observed and background particulate sulfur. TAGIT is applied to measurements made in the vicinity of the east and west ends of the Grand Canyon in order to attribute particulate sulfur to the sources within the Eastern Colorado River Valley (ECRV) and the Mohave Power Project (MPP), respectively. TAGIT results indicate that during the winter intensive field sampling experiment (January 15–February 13, 1992), an average of 59 + 12% of the particulate sulfur at Marble Canyon, AZ, was attributable to ECRV sources. Similarly, during the summer field sampling experiment (July 13–August 30, 1992), MPP is estimated to have contributed an average of 7 + 3% of the particulate sulfur at Meadview, AZ. Uncertainties associated with the assumptions of TAGIT are discussed and quantified. The attribution results suggest that SO2-to-sulfate conversion rates are highly variable from day to day in this region.

RNA content of copepods as a tool for determining adult growth rates in the field

We propose a method to determine growth rates of adult copepods based on their nucleic acid contents. We investigated the suitability of this method on the marine copepod Acartia gruni in a range of food concentrations and temperatures. There was a good linear relationship between growth rate (estimated as egg production) and RNA contents of the adult copepods. The slope of the relationship was dependent on temperature. We also built a multiple regression model to predict egg production rates of A. grani as a function of RNA contents and temperature. This method allows very intensive field sampling and does not require incubations onboard. Samples are preserved frozen and analyzed in the laboratory using a very sensitive fluorometric technique that allows working with small numbers of individuals of the desired species.

Distribution of Phytophthora spp. in Field Soils Determined by Immunoassay

ABSTRACT Populations of Phytophthora spp. were determined by enzyme-linked immunosorbent assay (ELISA) in field soils used for pepper and soybean production in Ohio. Soybean fields were sampled extensively (64 fields, n = 6 samples per field over 2 years) and intensively (4 fields, n = 64 samples per field in 1 year) to assess heterogeneity of P. sojae populations. Four pepper fields (n = 64), three of which had a history of Phytophthora blight (caused by P. capsici), also were sampled intensively during a 6-month period. Mean (m), variance (v), and measures of aggregation (e.g., variance-to-mean ratio [v/m]) of immunoassay values, translated to Phytophthora antigen units (PAU), were related to the disease history in each of the pepper and soybean fields. Mean PAU values for fields in which Phytophthora root rot (soybean) or blight (pepper) had been moderate to severe were higher than in fields in which disease incidence had been low or not observed. A detection threshold value of 11.3 PAU was calculated with values for 64 samples from one pepper field, all of which tested negative for Phytophthora by bioassay and ELISA. Seven of the eight intensively sampled fields contained at least some detectable Phytophthora propagules, with the percentage of positive samples ranging from 1.6 to 73.4. Mean PAU values ranged from 1 to 84 (extensive soybean field sampling), 6 to 24 (intensive soybean field sampling), and 4 to 30 (intensive pepper field sampling); however, variances ranged from 0 to 7,774 (extensive sampling), 30 to 848 (intensive soybean field sampling), and 5 to 2,401 (intensive pepper field sampling). Heterogeneity of PAU was high in most individual soybean and pepper fields, with values of v/m greater than 1, and log(v) increasing with log(m), with a slope of about 2.0. Spatial autocorrelation coefficients were not significant, indicating there was no relationship of PAU values in neighboring sampling units (i.e., field locations) of the intensively sampled fields. Combined results for autocorrelations and v/m values indicate that Phytophthora was highly aggregated in these fields but that the scale of the aggregation (e.g., average focus size) was less than the size of the sampling units. Because of the observed variability, we calculated that sample sizes of 20 or more would be needed to estimate precisely the mean density of Phytophthora in most cases.

Identifying wetland meadows in Grand Teton National Park using remote sensing and average wetland values

Six spectrally and ecologically distinct montane meadow community types were identified and mapped within Grand Teton National Park by analysis of Indian IRS-1B LISS-II imagery. A distinct to-xeric-hydric gradient among the meadow types was predicted by analysis of the satellite data. Thirty sites (five replicates for each of six meadow typ were selected for intensive field sampling. At each of the 30 sites, meadow vegetation was sampled in 20 m by 20 m square plots for canopy cover of all species. Using wetland indexes (on a scale of 1–5, where obligate wetland species = 1, facultative land = 2, facultative = 3, facultative upland = 4 and upland species = 5), average wetland values were calculated and ranged from 1.88 for A-type meadows and 2.86 for B meadows to 4.40, 4.49, 4.74, and 4.43 for C, D, E and F meadows, respectively. Because average wetland values of A and B meadows were < 3.00, they were determined to be indicative of wetlands. Eight out of ten obligate wetland plants had their greatest cover on A meadows (the wettest of the gradient) and had significant cover differe among meadow types using the non-parametric Kruskal-Wallis test. Average wetland values and plant species cover were used, in conjunction with remotely sensed data, to identify as wetlands 1,258 hectares of A meadows and 1,711 hectares of B meadows in Grand Teton National Park.

Modelling black fly production dynamics in blackwater streams

SUMMARY. 1. Two predictive models were employed along with intensive field sampling to estimate production of black flies (Simulium spp.) on snags (submerged wood) in three blackwater streams on the Georgia Coastal Plain of the southeastern U.S.A. One model predicts daily growth rate from temperature and hydrograph pattern; the other predicts habitat abundance (of snags) from river height.2. In the sixth order Ogeechee River, annual production was twice as high in 1982 (7.1 g dry mass [=DM] m−2 of snag surface) as in 1983 (3.6 g DM m−2). When converted to production per m2 of river bottom, values were 35–40% of the snag surface estimates. Annual production was much lower in fourth order Black Creek (1982, 1.3 g DM m−2 of snag surface) and much higher in the sixth order Satilla River (1975, 15.6–40.0 g DM m−2).3. There was a distinct bimodal pattern of black fly production in the Ogeechee River in both years, with peaks occurring in winter and summer. Similar bimodal patterns of production were found in Black Creek and in the Satilla River. Although there appears to be an intrinsic component to the bimodal pattern, production peaks (growth rate and biomass) appear to be associated with initial stages of flooding.4. Annual production/biomass ratios (37–85) are the highest reported for black fly populations. The variation of annual P/B ratios among sites was more strongly dependent on the temporal distribution of standing stock biomass than on differences in growth rates. Variation in production among sites appears to be due to differences in current velocity, hydro‐graph variability, and abundance of coexisting consumers.

Distribution, population dynamics and estimates of production for the estuarine mysid, Rhopalophthalmus terranatalis

The biology of the mysid shrimp Rhopalophthalmus terranatalis is described from a warm temperate estuary in southern Africa. Intensive quantitative field sampling continued over 21 months while laboratory culture provided detailed information for production estimates. Three generations are produced annually and individual females produce multiple broods. The overwintering generation has a lifespan of 9–10 months and is characterized by low population density, but individuals are relatively large with females producing large broods. The summer generation survives for 6 months. Population density is high (maximum may exceed 4000 m −3 of water) but individuals attain a smaller size and produce fewer progeny. The spring generation has characteristics which may generally be described as intermediate between the other two generations. Daily production values of 2·69, 6·93 and 13·97 mg m −3 were calculated for the overwintering, spring and summer generations, respectively. Daily P B coefficients varied between 0·020 and 0·026. The P B ratio for the overwintering generation was 5·86; for the spring generation, 3·06 and for the summer generation 4·74. The annual P B ratio for the whole population was 7·85. Comparative values using a second method of population production are provided. The biology of R. terranatalis allows for rapid recovery of the population in a region where catastrophic aperiodic fresh-water flooding occurs.

Dry season wastewater assimilation by a North Florida hardwood swamp

Approximately 2650 m3/day of secondarily-treated effluent is currently discharged into a 206 ha mixed hardwood swamp located south of Jacksonville, Florida. In the early summer of 1981, a study was conducted to assess (1) whether the swamp was satisfactorily assimilating the present discharge, and (2) whether the swamp ecosystem was suffering significant adverse impacts due to the discharge. Intensive field sampling coincided with a period of extended drought. The study plan included examination of water chemistry and vegetation at the receiving swamp and at four nearby control swamps not receiving secondary effluent. The major outflow of the receiving swamp differed significantly from outflows of the control swamps in concentrations of total nitrogen, nitrate-nitrite nitrogen, total and dissolved phosphorus, and specific conductance. Based on flow measurements and mass balance calculations, the receiving swamp achieved nutrient “removal” rates of 87.0% (26.1 kg/day) for total nitrogen and 62.0% (8.8 kg/day) for total phosphorus. Data indicated that much of this removal occurred through infiltration. Field investigations indicated that swamp vegetation stresses were present at the receiving swamp and at one of the control swamps.

Some aspects of feeding in the Antarctic krill, Euphausia superba

The interaction between feeding activity, swarming behaviour and vertical migration in Antarctic krill, Euphausia superba Dana, was examined by a combination of laboratory physiology studies and intensive field sampling of a patch of krill located NE of South Georgia, in April 1980. The combined use of echolocation and a series of timed net hauls from discrete depth horizons revealed a diurnal rhythm of swarming behaviour, vertical migration and gut fullness. Laboratory physiological data showed that krill will filter feed throughout the 24 h but with peak activity by night, and that filtration rate is affected by krill density. Biochemical studies in vitro indicated that rates of lipid synthesis are generally highest at the surface and by night. These results are discussed in relation to other studies of krill feeding activity and suggestions made for further research.

Organic and inorganic gaseous chlorine concentrations in relation to the particle size distribution of chloride in the marine aerosol

An intensive field sampling program has been carried out over the ocean in which 56 gas samples and 172 aerosol particle samples were analyzed for total organic chlorine and total inorganic chlorine gas and for particulate chlorine as a function of particle size. Sampling was conducted for 13- to 21-hour periods, March 5–14, 1976, 4 km from the north Florida shore of the Gulf of Mexico at 10-m and 2-m heights. Replicate samples collected simultaneously showed agreement within analytical errors generally of a few percent for gases and for the sum of particle size fractions. Over the course of the experiment, 21 ambient measurements of organic chlorine averaged 3050 ng Cl/m3 STP of air, with a standard deviation of the distribution of measurements of 80 ng Cl/m3 STP. Also in 21 measurements the sum of particulate and inorganic chlorine averaged 3030±190 ng Cl/m3 STP. Thus the total chlorine concentration observed averaged 6070±220 ng Cl/m3 STP, of which 50% was organic gaseous. In contrast, the proportion of inorganic gaseous chlorine varied drastically, ranging from one half to one hundred times the observed particulate chlorine concentration. The variation depended at least in part on whether cascade impactors with Nuclepore backup filters or filters alone were used for particle sampling before the airstream passed through treated LiOH-impregnated gas absorption filters and charcoal absorbers. The results suggest that rapid interchange occurs between inorganic gaseous and particulate chlorine in the atmosphere but that organic gaseous chlorine is relatively decoupled from these forms.