Browsing by Author "Bolstad, Paul V."
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- Can small stream solute-land cover relationships predict river solute concentrations?Webster, Jackson R.; Jackson, C. Rhett; Knoepp, Jennifer D.; Bolstad, Paul V. (Wiley, 2023-01)Most studies of land use effects on solute concentrations in streams have focused on smaller streams with watersheds dominated by a single land-use type. Using land cover as a proxy for land use, the objective of this study was to determine whether the hydrologically-driven response of solutes to land use in small streams could be scaled up to predict concentrations in larger receiving streams and rivers in the rural area of the Little Tennessee River basin. We measured concentrations of typically limiting nutrients (nitrogen, phosphorus), abundant anions (chloride, sulfate), and base cations in 17 small streams and four larger river sites. In the small streams, total solute concentration was strongly related to land cover -- highest in streams with developed watersheds, lowest in streams with forested watersheds, and streams with agricultural watersheds were in between. In general, the best predictor of solute concentrations in the small streams was forest land cover. We then predicted solute concentrations for the river sites based on the solute--land cover relationships of the small streams using multiple linear regressions. Results were mixed -- some of the predicted river concentrations were close to measured values, others were greater or less than measured concentrations. In general, river concentrations did not scale with land cover-solute relationships found in small tributaries. Measured values of nitrogen solutes in the river sites were greater than predicted, perhaps due to the presence of waste water treatment plants. We attributed other differences between measured and predicted river concentrations to the heterogeneous geochemistry of this mountainous region. The combined complexity of hydrology, geochemistry, and human land-use of this mountainous region make it difficult to scale up from small streams to larger river basins.
- Canopy, terrain, and distance effects on Global Positioning System position accuracyDeckert, Christopher J. (Virginia Tech, 1994-04-15)A number of tests were conducted to determine the realizable accuracies of the Global Positioning System for natural resource conditions. The effects of terrain, forest canopy, number of consecutive position fixes, and PDOP on accuracy were evaluated. Position accuracies were determined for a total of 27 sites: three replicate sites selected for each of nine distinct conditions: three canopy (deciduous, coniferous, open) and three terrain (ridge, slope, valley) in all possible combinations. Each site was visited ten times over a span of eight months to collect position data, for ten replicates of 60, 100, 200, 300, and 500 position fixes. The mean differentially corrected positional accuracy for all sites was 4.35 meters with 95 percent of the positions estimated within 10.2 meters of the true value. The least accurate differential position data were observed at coniferous sites. Positional accuracy was higher for deciduous sites and the most accurate differential position data was collected at open sites. Accuracy increased with increasing number of position fixes. When the number of position fixes increased from 60 to 500, mean accuracy increased 46.7% at deciduous sites, 32.8% at coniferous sites, and 44.5% at open sites. The average time required by the GPS receiver to lock onto four satellites and begin collecting positions varied from one to two minutes. The most time was spent collecting position fixes at coniferous sites. No correlation was found between accuracy and the receiver's distance from the base-station. Nine replicates of 300 position fixes were averaged for six sites, which ranged from 43 kilometers to 247 kilometers from a Virginia Tech base-station. Mean accuracy ranged from 1.48 meters to 2.43 meters. GPS position data were evaluated for ease of conversion to GIS formats. Conversion was accomplished without problems.
- A comparison of spatial interpolation techniques in temperature estimationCollins, Fred C. (Virginia Tech, 1995-11-05)Spatially distributed estimates of meteorological data are becoming increasingly important as inputs to spatially explicit landscape, regional, and global models. Accurate estimates of meteorological values such as temperature, precipitation, and evapotranspiration are required for a number of landscape scale models, including those of regeneration, growth, and mortality in forest ecosystems. Given a set of meteorological data, researchers are confronted with a variety of stochastic and deterministic interpolation methods to estimate meteorological variables at unsampled locations. Depending on the spatial attributes of the data, accuracies may vary widely among different spatial interpolation methods. The choice of spatial interpolator is especially important in mountainous regions where data are sparse and variables may change over short spatial scales. While there have been comparisons of interpolation methods, few research efforts have been directed towards comparing the effectiveness of different spatial interpolators in predicting temperature. Due to the additional effort kriging and cokriging entails, it was decided to compare the effectiveness of kriging and cokriging in estimating mean, maximum, and minimum temperature at unsampled locations with less computationally intensive interpolation techniques such as inverse distance weighted averaging, cubic splining, the fitting of a trend surface, polynomial regression, and the lapse rate method. Eight interpolation techniques (inverse distance squared, optimal inverse distance, cubic splining, trend surface analysis, regression, kriging, cokriging, and the lapse rate method) were compared in their ability to predict temperature at unsampled locations. Temperature data for two regions, two scales (minimum and maximum temperatures) and three temporal scales (10 year mean, seasonal, and daily) were prepared and the eight methods were compared on the basis of bias, MAE, and MSE. In addition, summary statistics of interpolated mean, minimum, and maximum temperatures were recorded to determine how well the interpolated data represented the original temperature values. This dissertation provides evidence that certain apriori data characteristics such as temperature range, temperature variance, and temperature correlation with elevation may influence interpolator choice. The dissertation results also indicate that spatial scale and the relative spatial density and distribution of sampling stations may influence interpolator choice. These results should be of interest to scientists studying global warming. The MAEs associated with interpolation techniques which did not use ancillary information were far greater than the 0.5°F to 1.0°F estimate of global warming over the past 100 years. The use of regression techniques which utilize the relationship between temperature and elevation as ancillary information offers significant improvement over the current inverse distance weighting methods. The dissertation also shows that when station elevations are not representative of regional elevations, bias occurs. In Region 2, stations were underrepresented for higher elevations. Interpolation techniques which did not use elevation as ancillary information were biased 1.0°F to 3.0°F above techniques which used elevation. While it is unclear what the extent of this effect is on a global scale, one would suspect the use of distance weighting techniques would bias global estimates upwards. These dissertation results should also be of interest to scientists who use kriging and cokriging to interpolate irregularly spaced data onto a rectangular grid. The results indicate that when data are isotropic, less subjective methods, such as optimal inverse distance, have lower MAE values. The semivariogram fitting methodology outlined in this dissertation demonstrates how to fit semivariograms iteratively using an indicative goodness of fit (IGF) metric. Semivariogram fitting using an IGF is less subjective and more accurate than traditional fit-by-sight methods. Despite its mathematical elegance, kriging and cokriging did not perform better than many other less computationally intensive methods. In addition, when there is a more intensely sample covariate which is highly correlated, polynomial regression gave far better results than kriging or cokriging. The results of this dissertation should also be of interest to users of geographic information systems (GISs). Because climatic data such as temperature is sampled from an irregular network, a number of interpolation techniques can be used to convert the data to a regular grid for use in visualization, models and GISs. This dissertation shows that the choice of spatial interpolator can influence the resulting data accuracy. In addition, data attributes influence the choice of interpolator. What is dissertation shows, is that through preliminary data analyses, an interpolator may be chosen which yields the most accurate grid for input into a GIS. It should be noted that this dissertation has wider ranging applications beyond the three examples mentioned above. The results should be of interest in any field where point data is interpolated onto a regular grid. Additional application areas include, but are not limited to, medical imaging, scientific visualization, weather forecasting, ecological modeling, forestry, petroleum exploration, and hydrological modeling.
- Modeling the diameter and locational distributions of branches within the crowns of loblolly pine treesDoruska, Paul F. (Virginia Tech, 1993-02-05)Crown structure for 9- to 30-year-old loblolly pine was quantified via analysis of branch diameters and location, both along and around the bole, using observational data from 68 trees. The trees analyzed ranged in size from 11.1 to 31.6 cm in DBH and from 8.30 to 25.67 m in height, and were growing in Piedmont and Atlantic Coastal Plain stands ranging from 70 to 200 sq. ft. BA/acre. A series of equations was used to describe the diameter distribution of branches. Circular statistics were used to examine branching patterns around the bole. A recursive system of 2 equations was developed in order to predict the total number of branches within a crown. A series of 3 equations was used to describe the average of and range in diameter within a whorl. Attempts at modeling the height above ground to branches (whorls) were unsuccessful; therefore, equidistant spacing was assumed. Similarly, predicting the number of branches within a whorl of a certain height was difficult, and overall percentages were employed. Analysis of branch azimuths on a whole tree basis indicated a uniform distribution was appropriate (and not a “circular normal” distribution). Finally circular correlation was used to analyze rotational patterns within and between whorls, and a strong positive correlation was found for consecutive whorls of the same number of branches. From this study it was concluded that modeling crown structure will be difficult, with much variation occurring among trees. More data are necessary to better refine the baseline work herein presented.
- Positional accuracy in a natural resource database: comparison of a single-photo resection versus affine registrationCombs, Russell G. (Virginia Tech, 1995-04-05)Positional and area accuracies were calculated for digitized data taken from 1:20,000 scale aerial photographs and United States Geological Survey (USGS) 1:24,000 scale topographic maps. Positional accuracy was determined as the Euclidian distance between the digitized coordinate and the reference ground coordinate collected with global positioning systems (GPS). Area accuracy was the acreage difference between the digitized area and GPS calculated area. Three methods were employed to collect the digitized data: manual digitizing from topographic maps and aerial photographs followed by an affine transformation, and manual digitizing from aerial photographs while applying a single-photo space resection. Two study sites, one in low terrain relief and one in high terrain relief, were used to examine the effects of terrain on positional accuracies. The single-photo space resection technique provided the most accurate positional data on both study sites. The single-photo space resection produced mean positional accuracies of 5.0 to 6.0 meters. In comparison, the uncorrected digitized photo data produced mean positional accuracies of 7.0 to 26.0 meters. The effects of terrain displacement were evident in these data sets, as the mean positional accuracy at the low-relief study site was 18.96 meters less than the corresponding accuracy at the high-relief study site. The uncorrected digitized photo data set from the high-relief study site provided the highest mean positional accuracy, 25.86 meters. The topographic map digitized data from both study sites provided mean positional accuracies below 12.0 meters, but failed to meet National Map Accuracy Standards (NMAS) for 1:20,000 scale or smaller maps. The average area accuracy from both study sites proved to be not significantly different, regardless of the digitizing technique or terrain conditions. The average area accuracy between the two study sites differed by at most 0.05 hectares. Average percent area errors ranged from 9.96% to 11.74% on the low-relief study site and from 11.84% to 12.65% on the high-relief study site.
- Premigratory movements of a long-distance migratory species: the Wood Thrush (Hylocichla mustelina)Rivera, Jorge H. Vega (Virginia Tech, 1997-01-05)The postbreeding period in migratory bird species is an important, but often neglected,area of knowledge. From May-October of 1993-95, I studied the breeding andpostbreeding ecology of 61 adults and postfledging movement of 43 juveniles in aradio-tagged population of Wood Thrushes (Hylocichla mustelina) on the U. S. MarineCorps Base, Quantico, Virginia (38 30' N, 77 25' W). Fledglings became independent 0 0from their parents at 28-36 days post hatching and dispersed 307-5300 m from their natalsites to join flocks of conspecifics. About half (46%) of the young birds stayed in onedispersal site until migrating, but the rest visited other sites. In 40 instances, 15fledglings moved up to 6 km out of the dispersal site and, after 1-5 days, returned to thelocality occupied before initiating the movement. After dispersal, fledglings' positions(n = 556) occurred in (1) second growth and sapling stage sites at the edge of forested areas [52%], (2) gypsy moth (Lymantria dispar) damaged deciduous forest [21.8%], (3)Virginia pine (Pinus virginianus) forest that had a heavy understory of young deciduous trees and an open canopy [15.6%], and (4) mature mixed forest [10.6%]. Most fledglings(73%) left the Marine Base in September at the mean age of 81 days. After finishing breeding, adult Wood Thrushes underwent molt that extended from late July to early October. Flight-feather molt lasted on average 38 days and may have impaired flight efficiency in some individuals. Of 30 observed adults, 15 molted in the same area where they nested, and 15 moved 545 to 7290 m from their nesting sites. Molting sites were located in areas with a larger number of pines, less canopy cover, fewer trees with dbh>38 cm, and a denser understory strata than nesting sites (P < 0.1). My data suggest that a conservation strategy that focuses on identifying and protecting nesting habitat in the temperate region, although important, is incomplete at best if the events and needs during the post reproductive and post fledging periods are not considered.