SINKHOLES AND THEIR RIPARIAN BUFFERS INFLUENCE WATER CHEMISTRY IN THE BLUE RIVER, SOUTHERN INDIANA

Sinkholes often are surficial entry points to underground flow paths that can transport contaminants directly from landscape to river. As such, conservation in and around sinkholes in karst topography is of importance. To improve understanding of karstic landscape effects on streams in an agricultural watershed, we examined the effects of sinkhole density on nutrient chemistry and macroinvertebrate communities in the Blue River in south-central Indiana, much of which flows through a karst plain. Further, we assessed the water-quality effects of riparian buffer zones surrounding sinkholes in the watershed. Field methods included sampling at 16 sites along the stream channel for water chemistry. Geospatial analysis was used to identify sinkholes, estimate percent agricultural land cover, and measure riparian width. Statistical analysis showed that greater prevalence of sinkholes containing ponds and wetlands reduced macroinvertebrate richness and abundance. Riparian buffers served to reduce nitrate loading to the river and, therefore, are a useful conservation measure for nutrient management in agricultural karstic watersheds. Surprisingly, however, we also found that having a greater proportion of sinkholes that were vegetated rather than devoid of plants increased nitrate in the stream. Farmland with fertilized row crops tended have vegetation in and around sinkholes, whereas rangeland used for livestock did not. This suggests that despite vegetation, the fertilized row crops are a net source of nitrate, whereas pasture lands are not producing as high of a nitrate load. These results are being used by The Nature Conservancy and partners to foster positive land stewardship in the watershed that protects the Blue River, a biodiverse steam in the Mitchell Karst Plain of Indiana.