Department of Agricultural and Biosystems Engineering, South Dakota State University, 1400 N Campus Drive, Ag & biosystems Engineering-Box 2120 University Station, Brookings, SD 57007, USA.
Department of Agricultural and Biosystems Engineering, South Dakota State University, 1400 N Campus Drive, Ag & biosystems Engineering-Box 2120 University Station, Brookings, SD 57007, USA.
J Contam Hydrol. 2021 Oct;242:103859. doi: 10.1016/j.jconhyd.2021.103859. Epub 2021 Jul 17.
E. coli is the number one cause for water quality impairments in rivers and streams in South Dakota and the United States. Stream bottom sediments can be a reservoir for bacteria, including pathogenic organisms and fecal indicator bacteria (FIB), due to the favorable conditions provided by sediments for survival. Despite this, little is known about the variability of E. coli in sediments which should be considered when developing a sampling regime. This study examines the spatial variability of E. coli in sediment across the stream cross-section, the temporal stability of E. coli in sediment samples, and the implications for sediment sampling and processing. Five locations were sampled for sediment E. coli along two tributaries to the Big Sioux River in eastern South Dakota, four along Skunk Creek (Sk1, Sk2, Sk3, and Sk4), and one in Sixmile Creek (SM). In Skunk Creek, site Sk1 has direct cattle access where the other three sites (Sk2, Sk3, and Sk4) are under Seasonal Riparian Area Management (SRAM), a strategy that limits the cattle access to the stream. E. coli concentrations in the sediment ranged from 4 to 997 CFU g (8.5 × 10 to 2.1 × 10 CFU 100 mL). The highest and lowest E. coli concentrations observed were at sites Sk1 and Sk4, respectively. The E. coli concentration decreased from the upstream cattle crossing site (Sk1) through the downstream SRAM sites. Analyzing the stream cross-section analysis revealed no significant difference in E. coli concentration between the edge and the middle of the stream. Sediment samples can be held up to 24 h after sample collection in refrigerated conditions (37 °F) in the majority of cases (80%) without significant changes in E. coli concentrations. The sample size analysis indicated the spatial variability of E. coli across the stream cross-section is high and a single grab sample may not be able to provide adequate representation of E. coli concentrations in sediment without substantial error. The findings provide insight for designing E. coli monitoring projects and promote the awareness of unconventional sources of microbiological water quality impairment which are often overlooked.
大肠杆菌是南达科他州和美国河流和溪流水质受损的首要原因。由于沉积物为细菌（包括病原体和粪便指示菌[FIB]）的生存提供了有利条件，溪流底部沉积物可能成为细菌的储库。尽管如此，对于沉积物中大肠杆菌的变异性知之甚少，在制定采样方案时应考虑这一点。本研究考察了河流横断面中沉积物中大肠杆菌的空间变异性、沉积物样品中大肠杆菌的时间稳定性，以及对沉积物采样和处理的影响。在南达科他州东部的大苏河的两条支流上，有五个地点采集了沉积物中的大肠杆菌样本，其中四个在臭鼬溪（Sk1、Sk2、Sk3 和 Sk4），一个在六英里溪（SM）。在臭鼬溪，Sk1 点有直接的牛通道，而其他三个点（Sk2、Sk3 和 Sk4）则受季节性河岸管理区（SRAM）的限制，该策略限制了牛进入溪流的机会。沉积物中大肠杆菌的浓度范围为 4 到 997 CFU g（8.5×10 到 2.1×10 CFU 100 mL）。观察到的最高和最低大肠杆菌浓度分别位于 Sk1 和 Sk4 点。大肠杆菌浓度从上游牛过境点（Sk1）到下游 SRAM 点逐渐降低。对河流横断面分析表明，在大多数情况下（80%），在冷藏条件（37°F）下采集样本后 24 小时内，大肠杆菌浓度在河流边缘和中间没有显著差异。在大多数情况下（80%），采集的沉积物样本在冷藏条件下（37°F）可保存长达 24 小时，而大肠杆菌浓度没有明显变化。样本量分析表明，河流横断面中大肠杆菌的空间变异性很高，单次抓样可能无法充分代表沉积物中大肠杆菌的浓度，而不会产生大量误差。这些发现为设计大肠杆菌监测项目提供了参考，并提高了对非常规微生物水质破坏源的认识，这些源通常被忽视。
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