Thesis (M. Ag.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 69-71). Also available on the World Wide Web.

Thesis (M.S.)--Humboldt State University, 2010. / Includes bibliographical references (leaves 59-60). Also available via Humboldt Digital Scholar.

Dectes texanus LeConte (Coleoptera: Cerambycidae) is a longhorn beetle species endemic to eastern United States. Originally described as a pest of weeds from the family Asteraceae, D. texanus has expanded its host range and is found infesting the stems of soybeans, Glycine max (L.) through the southwestern and middle United States. Female D. texanus chews a hole in the epidermis of a petiole and oviposits on it. Then, the D. texanus larva depletes all the pith of the stem making a tunnel down to the base of the plant and girdle the stem about 5 cm above the soil line. When a force is applied to the girdling point, generally weather related (i.e. strong winds), the plant lodges. While D. texanus phenology has been described for some states, this topic has yet to be explored in Kentucky. The objectives of this study were: 1) to describe the life cycle and behavior of D. texanus in soybeans in Western Kentucky, 2) to study the effect of the stem diameter on the incidence of D. texanus infestations, 3) to evaluate the susceptibility of full-season and double-crop soybeans to D.texanus infestations, 4) investigate the efficacy of seed treatment in reducing D. texanus infestations, 5) to determine effects of D. texanus larval feeding in the physiological yield of soybeans. The results of these studies showed that: 1) there was no distinct peak of D. texanus emergence detected in the 2018 and 2019 growing seasons and pupation period varied with year and location; the best sampling period for D. texanus population should occur between 1000 and 1600 hours during the peak season with either a 5-gallon white plastic bucket or sweep net; 2) the probability of finding D. texanus infesting soybeans was higher when the stem diameter is larger than 9 mm, and smaller than 11 mm; 3) double-crop soybeans had reduced infestations of D. texanus because these soybean plants are not a suitable host when D. texanus was active ovipositing and the pith was not fully developed; 4) seeds treated with imidacloprid did not influence D. texanus infestation on soybeans, larvae presence in main and lateral stems, and parasitism occurrences; and 5) D. texanus did not affect seeds and pods attributes (pod width, length, height and weight), and yield. The latter may occur because feeding of D. texanus larva does not interfere on photosynthesis or nutrient transportation during seed fill.

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 50-52). Also available on the World Wide Web.

Thesis (M.S.)--California State University, Chico. / Includes abstract. "Located in the Chico Digital Repository." Includes bibliographical references (p. 67-73).

River-groundwater exchange (hyporheic exchange) influences temperature, water chemistry, and ecology within rivers and alluvial aquifers. Rates and patterns of hyporheic exchange depend on riverbed permeability, pressure gradients created by current-obstacle interactions, and river stage fluctuations. I demonstrate the response of hyporheic exchange to three examples of these driving forces: fine-scale permeability structure in cross-bedded sediment, current interactions with large woody debris (LWD), and anthropogenic river stage fluctuations downstream of dams. Using numerical simulations, I show that cross-bedded permeability structure increases hyporheic path lengths and modifies solute residence times in bedforms. The tails of residence time distributions conform to a power law in both cross-bedded and internally homogeneous riverbed sediment. Current-bedform interactions are responsible for the decade-scale tails, rather than permeability heterogeneity. Like bedforms, wood debris interacts with currents and drives hyporheic exchange. Laboratory flume experiments and numerical simulations demonstrate that the amplitude of the pressure wave (and thus hyporheic exchange) due to a channel-spanning log increases with channel Froude number and blockage ratio (log diameter : flow depth). Upstream from LWD, downwelling water transports the river’s diel thermal signal deep into the sediment. Downstream, upwelling water forms a wedge of buffered temperatures. Hyporheic exchange associated with LWD does not significantly impact diel surface water temperatures. I tested these fluid and heat flow relationships in a second-order stream in Valles Caldera National Preserve (NM). Log additions created alternating zones of upwelling and downwelling in a reach that was previously losing throughout. By clearing LWD from channels, humans have reduced hydrologic connectivity at the meter-scale and contributed to degradation of benthic and hyporheic habitats. Dams also significantly alter hydrologic connectivity in modern rivers. Continuous water table measurements show that 15 km downstream of the Longhorn dam (Austin, Texas), river stage fluctuations of almost 1 m induce a large, unsteady hyporheic exchange zone within the bank. Dam-induced hyporheic exchange may impact thermal and geochemical budgets for regulated rivers. Together, these three case studies broaden our understanding of complex drivers of hyporheic exchange in small, natural streams as well as large, regulated rivers. / text

Periodic releases from an upstream dam cause rapid stage fluctuations in the Colorado River near Austin, Texas. These daily pulses modulate fluid exchange and residence times in the hyporheic region, where biogeochemical reactions are pronounced. We installed two transects of wells perpendicular to the river to examine in detail the reactions occurring in this zone of surface-water and groundwater exchange. One well transect recorded physical water level fluctuations and allowed us to map hydraulic head gradients and fluid movement. The second transect allowed for water sample collection at three discrete depths. Samples were collected from 12 wells every 2 hours for a 24-hour period and were analyzed for nutrients, carbon, major ions, and stable isotopes. The results provide a detailed picture of biogeochemical processes in the bank environment during low flow/drought conditions in a regulated river. Findings indicate that a pulse that causes a change in river stage of approximately 16-centimeters does not cause significant mixing in the bank. Under these conditions, the two systems act independently and exhibit only slight mixing at the interface. / text