Johnston Karina K, Dorsey John H, Saez Jose A
The Bay Foundation, 1 LMU Dr, Los Angeles, CA, 90045, USA,
Environ Monit Assess. 2015 Mar;187(3):58. doi: 10.1007/s10661-015-4314-z. Epub 2015 Feb 3.
Stratification and loading of fecal indicator bacteria (FIB) were assessed in the main tidal channel of the Ballona Wetlands, an urban salt marsh receiving muted tidal flows, to (1) determine FIB concentration versus loading within the water column at differing tidal flows, (2) identify associations of FIB with other water quality parameters, and (3) compare wetland FIB concentrations to the adjacent estuary. Sampling was conducted four times during spring-tide events; samples were analyzed for FIB and turbidity (NTU) four times over a tidal cycle at pre-allocated depths, depending on the water level. Additional water quality parameters measured included temperature, salinity, oxygen, and pH. Loadings were calculated by integrating the stratified FIB concentrations with water column cross-sectional volumes corresponding to each depth. Enterococci and Escherichia coli were stratified both by concentration and loading, although these variables portrayed different patterns over a tidal cycle. Greatest concentrations occurred in surface to mid-strata levels, during flood tides when contaminated water flowed in from the estuary, and during ebb flows when sediments were suspended. Loading was greatest during flood flows and diminished during low tide periods. FIB concentrations within the estuary often were significantly greater than those within the wetland tide channel, supporting previous studies that the wetlands act as a sink for FIB. For public health water quality monitoring, these results indicate that more accurate estimates of FIB concentrations would be obtained by sampling a number of points within a water column rather than relying only on single surface samples.
在巴洛纳湿地的主要潮汐通道中评估了粪便指示菌（FIB）的分层和负荷情况。巴洛纳湿地是一个城市盐沼，受潮汐流影响较小。此次评估旨在：（1）确定不同潮汐流情况下水柱内FIB浓度与负荷的关系；（2）确定FIB与其他水质参数之间的关联；（3）比较湿地FIB浓度与相邻河口的FIB浓度。在大潮期间进行了四次采样；在一个潮汐周期内，根据水位在预先确定的深度对样本进行四次FIB和浊度（NTU）分析。测量的其他水质参数包括温度、盐度、氧气和pH值。通过将分层的FIB浓度与对应于每个深度的水柱横截面积体积进行积分来计算负荷。肠球菌和大肠杆菌在浓度和负荷方面都存在分层现象，尽管这些变量在一个潮汐周期内呈现出不同的模式。最高浓度出现在表层至中层，在涨潮期间，受污染的水从河口流入时，以及在落潮期间，沉积物被悬浮时。负荷在涨潮时最大，在低潮期减小。河口内的FIB浓度通常明显高于湿地潮汐通道内的浓度，这支持了之前关于湿地作为FIB汇的研究。对于公共卫生水质监测而言，这些结果表明，通过在水柱内多个点采样，而不是仅依赖单一的表层样本，可以获得更准确的FIB浓度估计值。
