138
8. Setting Ecosystem Loading Limits
eggs, and aquatic bird eggs (convert fish/bird tissue values to egg values using a conversion factor if no eggs are available; that is, bird liver
selenium x 0.33 = approximate bird egg concentration; fish wholebody selenium x 3.3 = approximate fish egg concentration; Lemly and
Smith 1987). If bird eggs or fish eggs cannot be obtained (if only one of
these two is available), a 4-component assessment can be done. Collect a minimum of 10 samples of each component in each major habitat type present in the HU (stream, river, off-channel bay, wetland,
lake, reservoir, other impoundment). This number of samples is sufficient to reveal the range of concentrations likely to be encountered
(Lemly 1993, 1997). Make sure to designate sampling sites throughout
the HU to provide adequate spatial coverage. Some of the required
measurements for waterborne selenium may be available from the
screening-level assessment done in Step 1. Maintain high quality
assurance/quality control in all sampling and analysis; document QA/
QC procedures for future reference. Evaluate selenium concentrations
with the Protocol (see Chapter 4) to determine the hazard rating. A
rating of low, moderate, or high hazard indicates that the TMDL process should continue. A rating of either minimal or no hazard indicates that TMDL calculations are not necessary, but the HU should be
monitored by applying the Protocol to selenium measurements made
at 3-year intervals. If monitoring reveals that hazard has increased
above the minimal level, TMDL reductions are needed.
Step 3: Determine Selenium Sources,
Concentrations, and Volumes
Identify all possible sources of selenium (agricultural, industrial, petrochemical, mining, etc.) and map them in the HU, noting their proximity/
discharge to specific habitat types, that is, wetlands, streams, rivers, reservoirs, and other HU habitats. Determine/verify selenium concentrations from each source, using existing data or analyzing new samples.
Determine/estimate average discharge volume from each source. Calculate total existing selenium loading rate for the HU (kg Se/day).
Step 4: Estimate the Retention Capacity
of the Hydrological Unit for Selenium
A key part of the TMDL process for selenium is to estimate retention capacity (RC). The RC will reflect the propensity of the HU to accumulate
selenium and, thereby, serve as an indicator of how much selenium the
system will likely retain and potentially cycle into bioaccumulation pathways. For the purposes of this chapter, the RC is defined as the natural
ability of a system to accumulate and conserve selenium. Components of
8. Setting Ecosystem Loading Limits
eggs, and aquatic bird eggs (convert fish/bird tissue values to egg values using a conversion factor if no eggs are available; that is, bird liver
selenium x 0.33 = approximate bird egg concentration; fish wholebody selenium x 3.3 = approximate fish egg concentration; Lemly and
Smith 1987). If bird eggs or fish eggs cannot be obtained (if only one of
these two is available), a 4-component assessment can be done. Collect a minimum of 10 samples of each component in each major habitat type present in the HU (stream, river, off-channel bay, wetland,
lake, reservoir, other impoundment). This number of samples is sufficient to reveal the range of concentrations likely to be encountered
(Lemly 1993, 1997). Make sure to designate sampling sites throughout
the HU to provide adequate spatial coverage. Some of the required
measurements for waterborne selenium may be available from the
screening-level assessment done in Step 1. Maintain high quality
assurance/quality control in all sampling and analysis; document QA/
QC procedures for future reference. Evaluate selenium concentrations
with the Protocol (see Chapter 4) to determine the hazard rating. A
rating of low, moderate, or high hazard indicates that the TMDL process should continue. A rating of either minimal or no hazard indicates that TMDL calculations are not necessary, but the HU should be
monitored by applying the Protocol to selenium measurements made
at 3-year intervals. If monitoring reveals that hazard has increased
above the minimal level, TMDL reductions are needed.
Step 3: Determine Selenium Sources,
Concentrations, and Volumes
Identify all possible sources of selenium (agricultural, industrial, petrochemical, mining, etc.) and map them in the HU, noting their proximity/
discharge to specific habitat types, that is, wetlands, streams, rivers, reservoirs, and other HU habitats. Determine/verify selenium concentrations from each source, using existing data or analyzing new samples.
Determine/estimate average discharge volume from each source. Calculate total existing selenium loading rate for the HU (kg Se/day).
Step 4: Estimate the Retention Capacity
of the Hydrological Unit for Selenium
A key part of the TMDL process for selenium is to estimate retention capacity (RC). The RC will reflect the propensity of the HU to accumulate
selenium and, thereby, serve as an indicator of how much selenium the
system will likely retain and potentially cycle into bioaccumulation pathways. For the purposes of this chapter, the RC is defined as the natural
ability of a system to accumulate and conserve selenium. Components of