Author
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Lerch, Robert |
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Submitted to: Journal of Cave and Karst Studies
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 12/6/2010 Publication Date: 8/15/2011 Citation: Lerch, R.N. 2011. Contaminant transport in two central Missouri karst recharge areas. Journal of Cave and Karst Studies. 73:99-113. DOI: 10.4311/jcks2010es0163. Interpretive Summary: About 25% of the land area in the United States is covered by karst topography. Karst occurs when surface water infiltrates limestone or dolomite bedrock, eventually forming sinkholes, caves, springs, and losing streams. Any land use that affects the quantity or quality of surface water can then also dramatically impact sub-surface watersheds. Examples include urban development, agricultural production, industrial activities, or wastewater treatment systems. This study was undertaken to establish non-urban baselines for Hunters Cave and Devils Icebox caves in the Bonne Femme watershed in central Missouri. These baselines included monitoring the concentration and annual mass of nutrients, herbicides, and sediment transported through the two cave streams. The watersheds of these two cave systems are rapidly urbanizing, and this study was initiated before significant development occurred. Both recharge areas were formed in the same limestone bedrock, and they were determined to be of similar size (about 13 square miles). Land uses in both recharge areas were about 80% grasslands and row crops. Despite these similarities, the quality of the water in the two cave streams was very different. The Devils Icebox watershed had greater concentrations and total amounts of nutrients, sediment, and herbicides than the Hunters Cave watershed. Within the Devils Icebox watershed, 94% of the row crop areas occurred on high runoff potential soils compared to only 57% of the row crop areas within Hunters Cave. These high runoff potential claypan soils are known to be especially problematic with respect to surface transport of contaminants. In both recharge areas, prevailing land management has significantly degraded water quality. Because of these findings, a stakeholder-led watershed plan for the Bonne Femme watershed, which includes the two cave watersheds, was developed with the primary goal of improving water quality. The plan has a number of detailed recommendations for protection of karst areas. The successful implementation of this plan will benefit local communities by improving or maintaining environmental quality, and therefore quality of life, as well as protecting the watershed’s water resources. Technical Abstract: Karst watersheds with significant losing streams represent a particularly vulnerable setting for ground water contamination because of the direct connection to surface water. Because of the existing agricultural land-use and future likelihood of urbanization, two losing stream karst basins were chosen for intensive monitoring in Boone County, MO: Hunters Cave (HC) and Devils Icebox Cave (DI). Both caves were formed in Burlington Limestone and have similar sized recharge areas (33-34 km2) and land uses. Year-round monitoring was initiated in April 1999 and completed in April 2002 with the objective of characterizing the water quality status of the main cave streams relative to herbicide, nutrient, and sediment contamination. Water sampling for contaminants entailed grab samples at regular intervals, and runoff event samples collected using automated sampling equipment. Total nitrogen, phosphorus, and sediment concentrations and loads were consistently higher in Devils Icebox recharge area compared to HC. Median total N fluxes were 96 g/km2/d at DI and 30 g/km2/d at HC while median total P fluxes were 8.5 g/km2/d in DI and 3.3 g/km2/d in HC. Herbicides or their metabolites were detected in >80% of the samples from both cave streams, and herbicide concentrations and areal loss rates were generally similar between sites. Overall, the greater loads and mass flux of contaminants in the DI recharge area compared to HC was a result of both greater stream discharge and the occurrence of most cropped fields on high runoff potential claypan soils. Prevailing land management has significantly degraded the water quality in both recharge areas, but a watershed plan has been developed for the Bonne Femme watershed, which encompasses these two recharge areas. With the data collected from this study, the impact of changing land uses and the implementation of management practices or new ordinances designed to improve water quality can be documented. |
