Toby Dogwiler

Thermal Variations in the Hyporheic Zone of a Karst Stream

This investigation quantifies how temperatures in the streambed sediments of a karst stream fluctuate in relation to discharge, seasonal, and diurnal temperature variations as the stream passes through a karst window. Furthermore, the linkages between meteorological processes and temperature variation in the hyporheic zone are delineated. Examination of a high-resolution, three dimensional record of temperature variation in a karst stream substrate provides insight into thermal disturbances in the hyporheic zone. Temperatures in the upper portion of the hyporheic zone are strongly linked to air temperatures via the surface water. The variation is considerably less as depth increases. The annual temperature variation in the lower portion of the shallow hyporheic zone is reduced by one-third, relative to the variation observed in the surface water and upper substrate. During storm events, the upper portion (0-5 cm) of the shallow hyporheic zone is subject to a thermal regime very similar to surface stream water. However, below these depths the sharpest temperature fluctuations are effectively muted within the stream substrate. More frequent diurnal variations, particularly those associated with baseflow conditions, are also dampened within the substrate.

Estimating water quality effects of conservation practices and grazing land use scenarios

Conservation management practices such as reduced tillage, fertilizer management, and buffer strips are well-established means by which to control erosion and nutrient losses from fields planted in annual row crops. However, agricultural systems which include perennial plant cover, such as the perennial forages found in grazing systems, may represent an alternative way to reduce these losses. In this study, management intensive rotational grazing (MIRG) was tested as a means by which to improve water quality on highly vulnerable row crop land, compared to more traditional conservation management schemes in the south branch of the Root River Watershed (a karst-influenced watershed in Southeastern Minnesota). The effects of both sets of alternative scenarios were evaluated with a watershed-based modeling approach using the Soil and Water Assessment Tool. Alternative conservation management practices included conservation tillage, cover crops, and filter strips. Conversion of row crop production to management-intensive rotational grazing of beef cattle was selected to occur on 2.6% of the total watershed area. Both the conservation management practices and land use changes were targeted to reduce contributions of sediment and phosphorus (P) loads from cropped upland areas. Watershed-wide implementation of all conservation management practices resulted in the greatest reductions in sediment (52%) and total P (28%) loads from upland crop areas, but had the largest land area requirements to achieve these results. Cover crops or filter strips on areas of high slope also showed large cumulative reductions across the watershed and also had the greatest reductions per-unit treated area of all conservation management practices. However, changing land use from row crop production to pasture for grazing was most effective at reducing total sediment and P loads on those acres changed, reducing sediment and P by greater than 85% on targeted areas. Simulation results indicate that utilizing alternative conservation management practices or MIRG, when targeted to areas of steeper slope (greater than 4%), could appreciably reduce sediment and P loads in this watershed, with limited reductions in row crop agriculture acreage.

Longitudinal profile and sediment mobility as geomorphic tools to interpret the history of a fluviokarst stream system

Karst terrains, characterized by closed depressions, subsurface drainage, and caves, account for approximately 10-20% of Earth’s land area (Palmer, 1991; Gillieson, 1996). The degree of karst development varies from region to region as a result of climatic conditions and relief. Consequently, a land surface may exhibit gently rolling soil covered plains with slight depressions or it may include deep depressions, isolated towers, and pointed hills (White, 1988). Dissolution plays a more significant role in the development of karst landscapes than in other landscapes (Jennings, 1985). However, studies have shown that physical erosional processes may also play an important role in the formation of karst systems (Aley, 1965; Sanders, 1981; Palmer, 1991; Bosch & White, 2004; Dogwiler & Wicks, 2004). Regardless of the erosion process, the formation of karst in suitable rock types requires the movement Citation:

Approaching Cave Level Identification with GIS: A Case Study of Carter Caves

Cave passages that are found at similar elevations are grouped together and called levels. The current understanding is that passages within a level are speleogenetically linked to a common static baselevel or stratigraphic control. Cave levels have provided an interpretive framework for deciphering cave development, landscape evolution, and climatic changes. Cosmogenic dating has been successfully used to interpret levels in Mammoth Cave and the Cumberland Plateau; however, this technique is expensive and there are limited funding resources available. Geographic information systems may be used as preliminary procedures to identify cave levels and constrain the timing of level development. A GIS method is applied to the Carter Cave system in northeastern Kentucky. Cave entrance elevations along stream valleys were found by extracting elevation values from a  m digital elevation model. Using a histogram generated from the frequency of cave elevations and a natural breaks classifier, four cave levels were identified in the Carter Cave system. This work improves the understanding of the Carter Cave system evolution and contributes toa methodology that can be used to ascertain an erosion history of karst systems.

Identifying the stream erosion potential of cave levels in Carter Cave State Resort Park, Kentucky, USA

Cave levels, passages found at similar elevations and formed during the same constant stream base level event, reveal information about paleoclimates and karst geomorphology. The investigation presented here examines how Stream Power Index (SPI) relates to cave levels. The study area, Carter Caves State Resort Park (CCSRP), is a fluviokarst system in northeastern Kentucky containing multiple cave levels. SPI determines the erosive power overland flow based on the assumption that flow accumulation and slope are proportional to potential for sediment entrainment. Part of this digital terrain analysis requires the creation of a flow accumulation raster from a digital elevation model (DEM). In creating the flow accumulation raster, one has the option to fill depressions (also considered errors) within the DEM. Filling these depressions, or “sinks,” creates a well-connected stream network; however it also removes possible sinkholes from the DEM. This paper also investigates the effects a filled and an unfilled DEM have on SPI and what each reveals about erosion potential in the area. The data shows that low elevations within the filled DEM maintain a high SPI value when compared to the unfilled DEM. The filled DEM also created a stream network similar to reality. The unfilled DEM demonstrated similar SPI results between all levels, indicating a well-connected karst system. In order to truly understand the mechanics of this system, a combination of these two DEMs is required.