According to the Center for Watershed Protection in Maryland, surface runoff of nutrients from lawns is minimal from well-managed lawns. However, many lawns have compacted soil, bare spots, steep slopes, and thin turf, all of which increase runoff. Subsurface leaching of nutrients into groundwater is greatest from lawns that are overfertilized and overwatered at the same time. In this situation, high nitrogen inputs are more susceptible to leaching because the over-watering sharply increases percolation through the soil (CWP, 2002).

In another study conducted by the U. S. Geological Survey (USGS) urban streams were found to have the second highest nitrate and total phosphorus levels, second only to agricultural streams (Smith et al., 1992 in CWP, 2002). Although the role of urban lawn care remains somewhat of a mystery, nutrient concentrations in urban streams are problematic, able to trigger eutrophication, or over-enrichment, in nutrient-sensitive surface waters.

Pesticides and herbicide migration from land applications into waterways is a better documented problem, particularly in storm water runoff. In 1991, the USGS began to implement a full scale National Water Quality Assessment (NAWQA) program to study the status and trends in a representative part of the nation’s surface and groundwater resources, and to provide a sound, scientific understanding of the primary and natural human factors affecting the quality of these resources. The Connecticut River was among the waters under investigation in the NAWQA program. In a study conducted between 1992 and 1995 in the Connecticut, Housatonic, and Thames river basins, insecticides were more commonly detected in urban than agricultural samples with pesticides rarely being detected in streams draining forested settings (Zimmerman, 1998). The highest estimated total daily loads of pesticides were associated with elevated stream flow in storm runoff during the late spring and early summer period, shortly following pesticide application. Some high loads, however, were also found later in the growing season. The USGS also found that the most heavily used pesticides are the ones found most often in streams and groundwater. The top 15 pesticides found in water are among those with the highest current usage today (USGS, undated in Glaser, 2006).

Documentation about the threat of pesticides and herbicides to human health and the environment are numerous including endocrine disruption in fish, amphibians, and humans. A study of sex hormones in carp indicates that pesticides may be affecting the ration of estrogen to testosterone in both male and female fish (Goodbred, 1997 in Glaser, 2006). Studies by researchers at the University of California Berkeley on atrazine, the most commonly used herbicide in the U.S., show that exposure to atrazine at levels found in the environment, even at levels far below EPA’s drinking water limits, demasculinizes tadpoles and turns developing frogs into hermaphrodites, having both male and female sexual characteristics (Hayes, 2002 in Glaser, 2006).

According to the USGS, insecticides in urban streams are a concern for downstream water suppliers and possibly for recreational users (USGS, 1999 in Glaser, 2006). In Kentucky, researchers discovered that in counties where drinking water is contaminated with triazine herbicides such as atrazine, there are increased numbers of breast cancer cases (Kettles, 1997 in Glaser, 2006). In southern Iowa, researchers found that the number of babies with low birth weights is linked to herbicide-contaminated drinking water (Munger, 1997 in Glaser, 2006). A study in Missouri found that men with lower sperm counts and quality also had higher concentrations of the pesticide metabolites alachlor, diazinon, and atrazine in their urine. Researchers believe that the men are ingesting these chemicals in their drinking water (Adams, 2003 in Glaser, 2006).


References:
Center for Watershed Protection. Article 4: Nutrient Movement from the Lawn to the Stream: Watershed Protection Techniques 2(1): 239-246

Center for Watershed Protection. Article 5: Urban Pesticides: From the Lawn to the Stream: Watershed Protection Techniques 2(1): 247-253

Glaser, Aviva, February 2006. Threatened Waters: Turing the Tide on Pesticide Contamination: Beyond Pesticides.

Zimmerman, M.J., 1998. Pesticides in Surface Water in the Connecticut, Housatonic, and Thames River Basins, 1992-95: USGS Water Resources Investigation Report 98-4247.