6
Hydrological Units and
Selenium Criteria
Introduction
The hydrological pathways that transport selenium across the landscape, as well as the presence of different habitat types (wetlands,
streams, rivers, lakes; reservoirs) within many watershed basins, have
important implications for setting water quality criteria for this trace
element. In the time since the USEPA established the current United
States national criteria (EPA 1987), there have been several field-documented cases of toxic effects to wetland biota occurring while waterborne concentrations of selenium were below the criterion value for
chronic exposure (5 !lg SelL) (eg, Skorupa and Ohlendorf 1991;
Stephens et al. 1992; Hallock and Hallock 1993; Lemly 1995; Hamilton
et al. 1996; Skorupa 1998). There have also been observations which
suggest that the criterion is too restrictive for some rivers and streams
(Canton and Van Derveer 1997; Van Derveer and Canton 1997). This
has led several states, the USFWS, and local municipalities to pursue
development and implementation of criteria on a site-specific basis
(eg, Guglielmone 1995). Although this is a logical course of action, the
approaches used to derive criteria are often seriously flawed, because
certain components of the selenium cycle are overlooked or underestimated, especially the potential for bioaccumulation and toxic
impacts downstream of the "site" under consideration (Hamilton and
Lemly 1999).
Because of selenium's propensity to bioaccumulate in aquatic
food chains, it is important to carefully assess the entire selenium
cycle-including down-gradient transport, transformation, and
bioaccumulation-at locations where site-specific criteria are being
considered. This is essential because it is possible for 2 adjacent aquatic
systems (eg, a river and an off-channel wetland) to have largely different selenium cycling dynamics (Lemly and Smith 1987). A waterquality criterion that is appropriate for one system may not be sufficient
for another, particularly if the two are hydrologically connected. The
103
Hydrological Units and
Selenium Criteria
Introduction
The hydrological pathways that transport selenium across the landscape, as well as the presence of different habitat types (wetlands,
streams, rivers, lakes; reservoirs) within many watershed basins, have
important implications for setting water quality criteria for this trace
element. In the time since the USEPA established the current United
States national criteria (EPA 1987), there have been several field-documented cases of toxic effects to wetland biota occurring while waterborne concentrations of selenium were below the criterion value for
chronic exposure (5 !lg SelL) (eg, Skorupa and Ohlendorf 1991;
Stephens et al. 1992; Hallock and Hallock 1993; Lemly 1995; Hamilton
et al. 1996; Skorupa 1998). There have also been observations which
suggest that the criterion is too restrictive for some rivers and streams
(Canton and Van Derveer 1997; Van Derveer and Canton 1997). This
has led several states, the USFWS, and local municipalities to pursue
development and implementation of criteria on a site-specific basis
(eg, Guglielmone 1995). Although this is a logical course of action, the
approaches used to derive criteria are often seriously flawed, because
certain components of the selenium cycle are overlooked or underestimated, especially the potential for bioaccumulation and toxic
impacts downstream of the "site" under consideration (Hamilton and
Lemly 1999).
Because of selenium's propensity to bioaccumulate in aquatic
food chains, it is important to carefully assess the entire selenium
cycle-including down-gradient transport, transformation, and
bioaccumulation-at locations where site-specific criteria are being
considered. This is essential because it is possible for 2 adjacent aquatic
systems (eg, a river and an off-channel wetland) to have largely different selenium cycling dynamics (Lemly and Smith 1987). A waterquality criterion that is appropriate for one system may not be sufficient
for another, particularly if the two are hydrologically connected. The
103