|Programmatic Coordination Newsletter||contact: Paul T. Jacobson (pjacobson@LangheiEcology.com)|
|Volume 3, March 23, 2001|
|Microbiological Assessment of a Baltimore Metropolitan Watershed||
contact: Kellogg J. Schwab,
Surface waters in the greater Baltimore region are heavily impacted by contamination from a variety of sources, including leaking sewage pipelines, on-site septic waste treatment discharges, and land run-off from urban, agricultural and natural areas. Human fecal contamination of water is of public health concern because of the possibility of microbial disease transmission. The microbial quality of waters used for potable supply, recreation, irrigation and shellfish harvesting is currently based on the level of total coliform and fecal coliform (which include E. coli) bacterial indicators. However, the use of these standard indicators to assess human fecal contamination can be problematic because total coliforms and fecal coliforms are not associated exclusively with human feces but can be shed in the feces of many warm-blooded animals including dogs and cats. In addition, many of the important human pathogens of fecal origin are enteric viruses and protozoa. Enteric viruses and protozoa are more persistent in natural waters and more resistant to water and wastewater disinfection processes than bacteria.
Therefore, the use of bacteria as indicators of human fecal contamination may result in inaccurate estimates of the level of human feces (and thus the level of human pathogens in the feces) present by detecting bacteria from other animals. In addition, the absence of bacterial indicators may lead to a false sense of confidence that water absent of indicator bacteria does not contain enteric viruses and protozoa.
To address these problems, we are evaluating the use of F+ coliphages as an indicator that would be more predictive of the presence of human feces. F+ coliphages are viruses that infect and are specific for E. coli. A gene probe method has recently been developed that can differentiate between F+ coliphages originating from human waste and the waste from other animals. Using this method we will attempt to determine the level of human fecal contamination present in urban streams. Having an indicator that is both specific for human contamination and a better indicator of human viruses will provide much needed information on the level of human fecal contamination present in urban streams. For example, F+ coliphage could be used as a marker to determine if sewer line repairs have reduced human fecal loads in an urban stream even in the presence of background levels of fecal contamination from other animals.
Diazinon in the Urban Environment
The Center for Watershed Protection recently completed a literature review for EPA regarding the Impacts of Urbanization on Receiving Waters. This short article on diazinon was adapted from the pesticide section because of its potential importance in the Chesapeake Bay region.
Diazinon is one of the most widely used pesticides in the urban and suburban environment. It is used primarily to control insects such as grub, roaches and ants. Frequently it is being found in urban streams at concentrations lethal to aquatic life. Diazinon has been banned for a number of years from golf courses as it has been known to kill birds. On December 5, 2000, EPA announced that diazinon would be voluntary phased out by the manufacturer over a four year time period. Since it is used so frequently by homeowners who may still have a supply and as it will continue being marketed and sold until supplies run out, its use is expected to continue affecting urban streams unless public awareness is improved.
Diazinon has been detected in 75% of the NAWQA urban baseflow samples and in 92% and 100% of stormflow samples from Texas and King County, Washington respectively (Brush et. al., 1995, USGS, 1999). USGS reports that diazinon concentrations generally increase during urban stormflow (Ferrari et al., 1997). Stormflow samples in Texas were 22 times higher in concentration than the national baseflow samples (Brush et. al., 1995). Diazinon is also reported to attach fairly readily to organic carbon consequently it is likely being resuspended during storm events. Diazinon also is the pesticide most frequently measured at concentrations greater than chronic toxicity levels in urban stormwater.
A study of pesticides in King County, WA stormwater can be found at: http://wa.water.usgs.gov/pugt/fs.097?99/
Another Article on Diazinon can be found on the Center's New Stormwater Website: www.stormwatercenter.net as well as 150 other articles on urban watershed management under the library section.
|Urban Reference Index||
EA Engineering, Science, and Technology is assisting the City of Baltimore in revising and enhancing biomonitoring programs for the City's streams. As part of this process, a special measure of biological condition was developed called the "Urban Reference Index." This index is based on standard biomonitoring protocols called the Index of Biological Integrity (IBI) developed by the Department of Natural Resources Maryland Biological Stream Survey (MBSS) for fish and benthic invertebrates. These indices are created by scoring a site according to a number of measures (metrics) involving species composition, trophic status, and abundance of either fish or benthic communities. Based on a fish (or benthic) sample from a given site, each metric is assigned a score of 1, 3, or 5, and the average of all scores is calculated, which is a value between one and five. Based on prior analyses of unaffected reference sites in Maryland by the MBSS, biological condition of either fish or benthic communities was related to IBI scores as follows: Good condition (IBI=4 to 5); Fair (IBI=3 to 3.9); Poor (IBI=2 to 2.9); and Very Poor (IBI=1 to 1.9).
Although the IBI protocols developed by the MBSS can be used directly on urban streams, it introduces a bias related to the nature of urban watersheds. Even under the best of circumstances, urban streams cannot achieve the biological condition possible in un-impacted rural reference streams. The best-managed urban areas exert stresses on aquatic environments that are unavoidable. Therefore an approach was sought that would permit comparison of biological condition of urban watersheds to realistic reference conditions. The solution was the Urban Reference Index.
The Urban Reference Index is an IBI score deemed to be near the best achievable in an urban environment. The MBSS statewide database was accessed, and nearly 50 sampling stations were identified that had 50 % or greater urban land use in their upstream watershed areas. These stations were located primarily in the Greater Baltimore and Washington, DC areas. For both fish and benthic invertebrates, the IBI scores were ranked, and the 90th percentile identified. This value was designated as the Urban Reference Index-a value greater than 90 % of urban IBI scores in Maryland and a value close to the best achievable in an urban environment. For fish, the Urban Reference Index was calculated as IBI=3.25. Whereas this value is only "Fair" on a statewide basis, it is a high-end urban value that represents the most appropriate target for restoration and biomonitoring of urban streams. In practice, IBI scores for urban sampling locations will be calculated just as done by MBSS. The resulting scores will be divided by the Urban Reference Index. For example, a fish sample at an urban stream location results in an IBI score of 2.9. Whereas this is in the "Poor" category statewide, it is nearly 90 percent of the Urban Reference Index of 3.25. Thus, the result would be close to the best achievable condition in an urban environment.