Changes in Shallow Groundwater Quality Beneath Recently Urbanized Areas in the Memphis, Tennessee Area¹

Abstract

Memphis, the largest city in the state of Tennessee, and its surrounding suburbs depend on a confined aquifer, the Memphis aquifer, for drinking water. Concern over the potential for downward movement of water from an overlying shallow aquifer to the underlying Memphis aquifer provided impetus for monitoring groundwater quality within the shallow aquifer. The occurrence of volatile organic compounds (VOCs), nitrate, and pesticides in samples from the shallow well network indicate a widespread affect on water quality from the overlying urban land use. Total pesticide concentration was generally higher in more recently recharged groundwater indicating that as the proportion of recent water increases, the occurrence of pesticides related to the current urban land use also increases. Groundwater samples with nitrate concentrations greater than 1.5 mg ⁄ l and detectable concentrations of the pesticides atrazine and simazine also had higher concentrations of chloroform, a VOC primarily associated with urban land use, than in other samples. The age of the water from these wells indicates that these concentrations are most likely not representative of past agricultural use, but of more recent urban use of these chemicals. Given that the median age of water represented by the shallow well network was 21 years, a lag time likely exists between changes in land use and the occurrence of constituents related to urbanization in shallow groundwater.(KEY TERMS: urbanization; land use ⁄ land cover change; nonpoint source pollution; organic chemicals; nutrients.)

Impact of Urban Growth and High Residential Irrigation on Streamflow and Groundwater Levels in a Peri‐Urban Semiarid Catchment

“…; Barlow et al. ; Whittemore ), as well as the emergence of peri‐urban catchments (i.e., catchments characterized by a high level of heterogeneity in which natural, rural, and urban areas are mixed (Santo Domingo et al. )).…”

“…Currently, more than half of the human population lives in urban areas; this proportion is expected to increase to 66% in the next 30 years (UN 2014). This development has changed land uses tremendously and led to a series of water resource problems (Xiao et al 2007; Barlow et al 2012;Whittemore 2012), as well as the emergence of peri-urban catchments (i.e., catchments characterized by a high level of heterogeneity in which natural, rural, and urban areas are mixed (Santo Domingo et al 2010)). These catchments are especially vulnerable to environmental changes, and their landscape and the connectivity of surface and subsurface flowpaths are likely to be significantly modified (Lee and Heaney 2003;Shuster et al 2005;Braud et al 2013).…”

The quality of our Nation's waters: water quality in the Mississippi embayment-Texas coastal uplands aquifer system and Mississippi River Valley alluvial aquifer, south-central United States, 1994-2008

“…(16,17,30) Pesticides were more frequently detected in the Memphis area likely because of the overlying urban land use, which is a source of chemicals, and the relatively young age of the groundwater. In this area, pesticide concentrations were related to the age of the groundwater (29) -the total concentration of pesticides in a sample was higher for those samples containing a higher proportion of recently recharged groundwater ( fig. 6-13).…”

“…Changes in concentrations of nitrate in groundwater may lag several years to decades behind changes in the amount of nitrogen input at land surface because of the length of time it takes water and contaminants to move through an aquifer. (11,28) The median age of shallow groundwater in the Memphis area was about 20 years, (29) and a similar lag time likely exists between changes in land use-such as urbanization-and a change in the occurrence of nitrate in shallow groundwater. The areas in which most of these wells are located had been developed for 20 or more years when samples were collected in 2006, so much of the observed increase in nitrate concentrations likely is related to sources associated with urban land use.…”

Status and trends of orthophosphate concentrations in groundwater used for public supply in California

“…In contrast to these studies are the long-term or continuing groundwater quality trend assessments conducted on regional or national spatial scales (e.g., Rosen 1999Rosen , 2001; Rosen and Lapham 2008), and these may reach century temporal scales (e.g., Hansen et al 2018). Groundwater quality trend studies may focus on only one or two waterquality constituents (Hantzsche and Finnemore 1992;Rosen 2003;Batlle Aguilar et al 2007;Burow et al 2007;Landon et al 2011;Kent and Landon 2013;Naranjo et al 2013;Hansen et al 2018) or several water-quality constituents (Stoline et al 1993;Rosen 1999; Barlow et al 2012;Lindsey and Rupert 2012;Kent and Landon 2016;Kent 2018). An understanding of how and why concentrations of water-quality constituents are changing over time is helpful to water resource managers as they plan for the future.…”