Environmental Engineering Reference
In-Depth Information
services, such as primary production or plant density if the habitat is relatively
uniform, such as a mangrove swamp or Spartina spp. salt marsh.
Selecting a currency that is indicative of the health of a habitat is another
approach that can be useful for some habitats. For example, the density of
grass shrimp ( Palaemonetes pugio ), considered a key species by local experts,
is highly correlated with many and diverse services provided by marsh
habitats (NOAA 1997). Thus, grass shrimp population density can serve as
the currency in HEA because it is indicative of the services provided by the
environmental resource under consideration and can ultimately be used to
calculate ecological debit and credit in a NEBA approach.
An advantage of HEA is that the service can be replaced without replacing
the actual habitat lost. For example, at the Blackbird mine site, the salmon
population was severely damaged by water quality and habitat alteration
resulting from the disposal of waste in Panther Creek, a tributary to the
Snake River in Idaho (Ray 2007). The damage to the fish had occurred over a
long time, and compensation for years of damage could not be achieved by
simply restoring the river to the pre-waste disposal value. The value had to
be increased over baseline conditions to achieve the target of supporting at
least 200 naturally spawning salmons each year to make up for years of loss
productively. The value was increased by a number of enhancements includ-
ing: creating a new off-channel habitat, establishing a salmon hatchery to
restock the creek, fencing off several kilometers of land along the creek to
keep livestock out of riparian habitat, and restoration of the natural mean-
dering of the creek. The HEA demonstrated that these measures increased
the value to a level that offset the decades of damage created by the waste
disposal.
The selection of the currency to be used is frequently a combination of envi-
ronmental attributes and negotiation among stakeholders. A proposed currency
can be strongly defended if it demonstrates several of the following attributes:
r Indicative of multiple environmental functions such as the grass
shrimp discussed above
r Integrates multiple functions such as nutrient cycling that depends
on a suitable chemical and physical structure and the presence or
absence of a full suite of organisms involved in decomposition and
remineralization
r Indicative of high social and/or recreational value such as hunting/
birdwatching species density or habitat requirement
r A service in limiting or short supply for the area/regional ecosystem
(e.g., food, shelter, and water)
r A service that would make a substantial contribution to a threatened
or endangered species, such as isolating and protecting nesting sites
for bald eagles
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