Abstract
Fecal contamination of waterbodies due to poorly managed human and animal waste is a pervasive problem that can be particularly costly to address, especially if mitigation strategies are ineffective at sufficiently reducing the level of contamination. Identifying the most worrisome sources of contamination is particularly difficult in periurban streams with multiple land uses and requires the distinction of municipal, agricultural, domestic pet, and natural (i.e., wildlife) wastes. Microbial source-tracking (MST) methods that target host-specific members of the bacterial order Bacteroidales and others have been used worldwide to identify the origins of fecal contamination. We conducted a dry-weather study of Onondaga Creek, NY, where reducing fecal contamination has been approached mainly by mitigating combined sewer overflow events (CSOs). Over three sampling dates, we measured in-stream concentrations of fecal indicator bacteria; MST markers targeting human, ruminant, and canine sources; and various physical–chemical parameters to identify contaminants not attributable to CSOs or stormwater runoff. We observed that despite significant ruminant inputs upstream, these contaminants eventually decayed and/or were diluted out and that high levels of urban bacterial contamination are most likely due to failing infrastructure and/or illicit discharges independent of rain events. Similar dynamics may control other streams that transition from agricultural to urban areas with failing infrastructure.
Highlights
Improper disposal or inadequate containment of fecal waste has well-documented, detrimental effects on human [1] and environmental health [2]
Physicochemical measurements from this study are, for the most part, in agreement with extensive surveys conducted on the creek in recent years ([3,28,29]; Table 1). pH significantly decreased in the downstream direction as a function of latitude (p < 0.001; Table 2; Map S1) presumably due to surficial changes in geology; with the upper, rural watershed comprised of alkaline limestone bedrock, and the lower, urban reaches predominantly lined with concrete and relatively disconnected from the natural geology of the lower watershed [30]
While ruminant markers were occasionally identified in urban areas, we found that high levels of ruminant contaminants upstream were not present at downstream, urban locations, suggesting that these contaminants may have been significantly degraded, diluted, or deposited during in-stream transport
Summary
Improper disposal or inadequate containment of fecal waste has well-documented, detrimental effects on human [1] and environmental health [2]. Runoff from agricultural and residential areas, as well as aging infrastructure (e.g., septic systems), sewer overflows, and illicit discharges have all been identified as potential sources of fecal contamination. In areas with combined sewer systems, urban creeks receive human fecal contaminants from combined sewer overflows (CSO) during rain events only, while failing infrastructure and illicit discharges contribute contaminants during both wet and dry weather. Urban stream reaches may receive contaminants from rural sources upstream, as well as from domestic pets and wildlife in both the rural and urban reaches. This multiplicity of potential fecal contamination sources can make identifying, prioritizing, and remediating major inputs of bacterial contamination challenging
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