Bison and Cattle Grazing Impacts on Baseflow Suspended Sediment Concentrations within Grassland Streams

Abstract

Prior to European colonization and the introduction of cattle, bison were the prominent grazing ungulates throughout North American grasslands. Yet, relative zoogeomorphic impacts between bison and cattle on grassland streams remain largely unknown. Utilizing a paired watershed study design, we compared baseflow suspended sediment concentrations across ten watersheds and four grazing treatments (ungrazed, bison-grazed, moderately stocked cattle-grazed, and intensively stocked cattle-grazed) in the Flint Hills subregion of the Great Plains. Additionally, we determined whether periods of increased thermal stress led to higher sediment concentrations within each treatment. Water samples were analyzed for total suspended solids (TSS, mg/L), nonvolatile suspended solids (NVSS, mg/L), and percentage organic matter (POM, percent). Intensively stocked cattle-grazed treatments produced significantly higher TSS and NVSS concentrations relative to ungrazed (TSS p = 0.012, NVSS p < 0.01) and bison-grazed treatments (TSS p = 0.082, NVSS p < 0.01). Moderately stocked cattle-grazed treatments contained significantly higher NVSS concentrations relative to bison-grazed treatments (p = 0.057). Bison-grazed and ungrazed treatments contained similar sediment concentrations (TSS and NVSS p > 0.10). Additionally, intensively and moderately stocked cattle-grazed treatments showed a significant increase in sediment concentrations with increasing temperature (p = 0.024 and p = 0.08, respectively), whereas bison-grazed and ungrazed treatments did not (p > 0.10). At the subdaily timescale, the highest sediment concentrations within cattle-grazed treatments and the greatest difference in sediment concentrations between cattle-grazed and ungrazed treatments coincided with the hottest daily temperatures, further highlighting that cattle-grazing impacts are influenced by thermal conditions.

在欧洲殖民和引入牧牛之前, 北美野牛是遍佈北美草原的放牧蹄类动物。但草原溪流上的北美野牛与牧牛之间的亲属动物地理学之影响仍鲜为人知。我们运用配对的分水岭研究设计, 比较北美大平原的弗林特次区域中, 十大流域与四大放牧方法 (未放牧、北美野牛放牧、适中的储备牧牛放牧, 以及密集的储备牧牛放牧) 之基流悬浮沉积的集中度。此外, 我们判定热应力增加的时期, 是否导致各方法中较高的沉积集中。我们分析水体採样的总悬浮固体 (TSS, mg/L), 非挥发性悬浮固体 (NVSS, mg/L), 以及百分比有机物 (POM, 百分比)。集约的储备牧牛放牧方法, 相较于未放牧 (TSS p = 0.012, NVSS p < 0.01) 与北美野牛放牧方法 (TSS p = 0.082, NVSS p < 0.01), 生产显着较高的 TSS 与NVSS 集中度。适中的储备牧牛放牧方法, 较北美野牛放牧方法 (p = 0.057) 而言, 包含了显着较高的 NVSS 集中度。北美野牛放牧与非放牧方法, 则具有相似的沉积集中度 (TSS and NVSS p > 0.10)。此外, 密集与适中的储备牧牛放牧方法, 随着温度升高展现出显着的沉积集中之增加 (分别为 p = 0.024 与 p = 0.08), 而北美野牛放牧与非放牧方法则否 (p > 0.10)。在每日中的时间尺度中, 牧牛放牧方法中的最高沉积集中度, 以及牧牛放牧与非放牧方法之间最大的沉积集中度差异, 与每日最热的气温相符, 进一步凸显出牧牛放牧受到热应力条件的影响。

Con anterioridad a la colonización europea y la introducción del ganado vacuno, los bisontes eran los prominentes ungulados herbívoros de los pastizales norteamericanos. Sin embargo, los relativos impactos zoogeomórficos de bisontes y vacunos sobre las corrientes de las dehesas permanecen en gran medida desconocidos. Utilizando un diseño de estudio pareado de cuenca, comparamos las concentraciones de sedimentos en suspensión de la base del flujo en diez cuencas y cuatro tratamientos de pastoreo (sin pastoreo, pastoreo con bisonte, pastoreo con ganado moderadamente poblado, y pastoreo con ganado intensamente poblado) en la subregión de Flint Hills de los Grandes Llanos. Además, determinamos si los períodos de estrés térmico incrementado conducían a mayores concentraciones de sedimento dentro de cada tratamiento. Se analizaron muestras de agua para el total de los sólidos suspendidos (TSS, mg/L), sólidos no volátiles suspendidos (NVSS, mg/L), y porcentaje de materia orgánica (POM, por ciento). Los tratamientos de pastoreo con vacunos intensamente poblados produjeron concentraciones de TSS y NVSS significativamente más altas relativas a los tratamientos sin pastoreo (TSS p D 0.012, NVSS p < 0.01) y de pastoreo con bisonte (TSS p D 0.082, NVSS p < 0.01). Los tratamientos con pastoreo de vacunos moderadamente poblados contenían concentraciones NVSS significativamente más altas relativas a los tratamientos de pastoreo con bisonte (p D 0.057). Los tratamientos de pastoreo con bisonte y los sin pastoreo contenían similares concentraciones de sedimento (TSS y NVSS p < 0.10). Adicionalmente, los tratamientos de pastoreo con ganado intensivamente poblados y los moderadamente poblados mostraron un incremento significativo de las concentraciones de sedimento con una mayor temperatura (Pd0.024 y Pd0.08, respectivamente), en tanto que los tratamientos de pastoreo con bisonte y sin pastoreo no lo tuvieron (p > 0.10). A la escala subdiaria, las concentraciones de sedimento más altas en los tratamientos de pastoreo con ganado y la más grande diferencia de concentraciones de sedimento en tratamientos pastoreados con ganado y sin pastoreo coincidieron con las temperaturas diarias más altas, destacando aún más que los impactos del pastoreo con vacunos están influidos por las condiciones térmicas.

Key Words:

• bison
• cattle
• grassland
• stream
• suspended sediment

关键词;:

• 北美野牛, 牧牛, 草原, 溪流, 悬浮沉积。

Palabras clave:

• bisonte, corriente, ganado, pradera, sedimento suspendido

Acknowledgments

The authors are thankful to Katie Costigan, Bryce Marston, and Nick Patch, who assisted in fieldwork. We are also appreciative of feedback provided by Heidi Mehl, William Renwick, and two anonymous reviewers on an earlier version of the article.

Additional information

Funding

Support was provided by the Konza Prairie LTER program (NSF-DEB Grant #0823341), the National Science Foundation (DDRI Grant #BCS1303108), and the KSU Department of Geography.

Notes on contributors

Bartosz Grudzinski

BARTOSZ GRUDZINSKI is an Assistant Professor in the Department of Geography at Miami University, Oxford, OH 45056. E-mail: [email protected]. His research interests include examining how natural and anthropogenic variables interact to influence fluvial structure and function.

Claire M. Ruffing

CLAIRE M. RUFFING is a Postdoctoral Research Fellow in the Department of Forest and Conservation Sciences at the University of British Columbia, Vancouver, BC V6T 1Z4, Canada. E-mail: [email protected]. Her research interests focus on how geomorphic and riparian properties interact to filter the effects of disturbances on stream ecosystem function.

Melinda D. Daniels

MELINDA R. DANIELS is an Associate Research Scientist at the Stroud Water Research Center, Avondale, PA 19311. E-mail: [email protected]. Her research interests focus on examining the fluvial geomorphology, hydrology, and stream ecosystem ecology of both “natural” and human-modified river systems from reach to watershed scales.

Michael Rawitch

MICHAEL RAWITCH is a Consultant at Ramboll, Overland Park, KS 66210. E-mail: [email protected]. His primary research interests include the application of geospatial technologies to solve environmental problems specifically related to fate and transport analysis, characterization, and remediation of contaminated soil and groundwater.