Environmental Engineering Reference
In-Depth Information
develop ongoing collaborations with other efforts that
meet multiple needs (e.g., global change, urban sprawl, and
changing-land-use issues).
Therefore, based on the discussion above, the follow-
ing criteria for site location (Schmeltz et al., 2011) can be
listed in order of importance. The chosen sites should, most
importantly, be those sites with (Harris et al., 2007a) exist-
ing longer-term Hg data (atmospheric and ecosystem data)
and supporting information on site characteristics and
ancillary measurements; if possible, sites that are expected
to be sensitive to Hg inputs and to exhibit large changes
in response to changes in Hg deposition should also be
included. Sites should preferably refl ect a particular ecosys-
tem type (e.g., forest, lake, wetland, urban, of coastal) and/
or ecoreg ions a nd shou ld be chosen to spa n ecosystems w it h
a range of characteristic response times to changes in depo-
sition (e.g., rapid-perched seepage lakes and slow sites with
substantial groundwater input) and should also include
reference sites (i.e., those that are currently impacted only
minimally by anthropogenic sources). In addition, prefer-
ence should be given to sites with existing facilities and
infrastructure to support the overall monitoring program.
Given the importance of modeling, sites that are useful test
beds for evaluation of atmospheric and watershed Hg mod-
els should be targeted, and these should include sites where
a clearly defi ned response to changes in Hg emissions and
deposition is anticipated (i.e., sites whose response will not
be confounded by other disturbances and which are remote
from point source inputs). Finally, some sites should be near
point emission sources to evaluate the importance of and
response to local deposition from elevated Hg inputs.
Although it is not clear to what extent anthropogenic
inputs within the United States have impacted offshore
open ocean waters (Sunderland and Mason, 2007; Selin
et al., 2008), especially the Pacifi c Ocean, it is clear that
human activity and local inputs have impacted many U.S.
estuaries and the associated coastal zones, for example.
Therefore, a monitoring program cannot ignore these saline
waters (Evers et al., 2008a) and should not focus exclusively
on freshwater environments. These environments are
complex, given the potential impact of local point source
inputs and the legacy of past inputs that are in estuarine
sediments. However, with the proper choice of locations,
and with the careful selection of the indicator species to
be monitored, the impact of changes in Hg inputs can be
ascertained. Indeed, the usefulness of using estuarine/
coastal organisms in a monitoring program is exemplifi ed
by the National Oceanic and Atmospheric Administration
(NOAA) Mussel Watch program (NCCOS, 2008), which has
been tracking contaminants in the coastal zone for many
years already, and total Hg is one of the analytes included
in this program.
In ascertaining ecosystem response in the United States,
the modeling efforts of NOAA, EPA, and others (Bullock
and Brehme, 2002; Cohen et al., 2004; Seigneur et al., 2004;
Selin et al., 2008; Bullock and Jaegle, 2009) can be used to
evaluate the relative change across the continent. At pres-
ent, these model outputs suggest that the largest decreases
in atmospheric deposition, given current projected regula-
tory impact, would be in the eastern states, while there may
be increases in the western states, refl ecting overall changes
in U.S. and global emissions (Dastoor and Davignon, 2009;
Jaegle et al., 2009; Jung et al., 2009; Seigneur et al., 2009;
Travnikov and Ilyin 2009). An initial evaluation of poten-
tial sites within the United States has found up to 40 can-
didate locations with approximately 50% in the Eastern
United States (east of the Mississippi), ~25% in the Great
Lakes/Midwest region and ~25% in the Western United
States (Schmeltz et al., 2011). Clearly, this initial evalua-
tion, based on existing Hg monitoring locations, does not
cover all the requirements outlined above. Reference (i.e.,
low-impact) sites would likely include higher-elevation
locations, islands, or forested, undeveloped regions in the
Western United States. Finally, efforts such as the U.S. Hg
sensitivity maps, developed by the United States Geological
Survey (USGS) (Myers et al., 2007), can provide the infor-
mation needed to target sensitive ecosystems and those
that are likely to show the largest biogeochemical response
to changes in Hg inputs. There is also an effort within the
EPA to collate and provide maps showing the locations of
ongoing and longer-term measurements of Hg and MeHg
in water, sediments, and various biota (fi sh and wildlife)
and these efforts at summarizing the existing information
and databases will provide the necessary background and
assist in site selection. Thus, substantial effort and prog-
ress is currently underway to identify potential monitoring
sites, to coalesce the information from current efforts, and
to move toward a consensus on the location of the inten-
sive monitoring sites (Schmeltz et al., 2011).
Proposed Indicators
Choice of suitable measurements for the network is the key
to the success of the overall program. Suitable indicators
are those that are: (1) comparable across ecosystems or, for
biota, have a large geographic distribution; (2) able to inte-
grate variability in space and time; (3) relatively simple to
interpret, and for biologic indicators, relevant in terms of
human and ecologic health; (4) easy to sample, process, and
quantify analytically; (5) already measured or part of an
existing database, and ideally have historical data available;
(6) able to show a response to Hg loading on a relatively
short timescale without infl uence from confounding fac-
tors; (7) able to detect, or refl ect, changes in MeHg produc-
tion and bioaccumulation; and (8) theoretically and empir-
ically sound. In addition, indicators should refl ect changes
in exposure to humans and wildlife (Harris et al., 2007).
Such criteria allow the determination of the relative value
of each metric within any study design, given a balance
between fi nancial resources and scientifi c rationale. Based
on this rationale, the indicators that are most suitable for
both the intensive and cluster sites are shown in Table 6.1.
