The Agencies worked cooperatively and conducted multiple studies to assess
resource injuries caused by the spill and to determine restoration needs. The
injury assessment process considered the spill’s effects on freshwater
wetlands, fish, crab & shrimp, surface waters, benthic invertebrates,
oysters and mussels, birds and recreational fishing. The results of this work
are summarized in the Final Damage Assessment and
Restoration Plan, and Environmental Assessment, for the December 7,
1997 Alafia River Spill. The Agencies determined that the release injured
freshwater wetlands, fish, crab & shrimp, surface waters, freshwater
benthic invertebrates, oysters and mussels, as described below:
Freshwater Wetlands
The Agencies undertook remote sensing and systematic field sampling to
determine the extent and nature of injuries to freshwater wetlands.
Approximately 377 acres of wetland vegetation situated between the site of the
release and the Keysville Bridge were inundated by and experienced some
observable die-off due to the release, including 315.3 acres of ground cover,
53.75 acres of sub canopy, and 7.99 acres of mature hardwoods (canopy).
Studies: An Initial Assessment of the
Impacts to Vegetation Resulting from the Alafia River Acid Spill, 1998.
Fish
The release-induced acidity in the surface waters of the river caused an
instantaneous fish, crab and shrimp kill in the river. The majority of smaller
fish killed included bay anchovy, menidia, hog choker and sand sea trout.
Striped mojarra, gar, sheepshead and hardhead catfish comprised the majority of
the larger fish killed. The Agencies used smaller animal seine and trawl data,
larger animal visual survey data and dead fish and larger animal clean-up data
to determine the extent and nature of the injury. They also used a biological
model to determine the lost future biological production of the animals killed.
The total biomass lost (including the loss of future growth) was estimated at
64,892 kilograms.
Studies:
Assessment of Fish, Blue Crab, and Pink Shrimp Mortality in the Tidal Portion
of the Alafia River Following the December 1997 Process Water Spill,
December 10, 1998.
Surface Water
The release injured the physical and chemical quality of surface
waters in the Alafia River by reducing pH levels in the river below water
quality criteria established under both federal and state law for the support
of aquatic life and recreation. This injury was evidenced by instantaneous
losses of fish, oysters and benthic invertebrates. The release also added
nutrients such as phosphorous and nitrogen to the system in amounts sufficient
to cause or contribute to an imbalance in the natural populations of aquatic
flora and fauna in the Alafia River and portions of Tampa Bay over a several
month period. This change was documented by comparing surface water samples
collected from a variety of stations to historic long-term water quality data.
Although phosphorus is also a nutrient contributing to algal growth, nitrogen
has been identified as the limiting or controlling nutrient in Tampa Bay in
prior work examining the health of the Tampa Bay Estuary. The Agencies,
therefore, quantified the injury in terms of the total amount of nitrogen
contributed to the Bay system by the release. The release added an estimated
656,775 pounds of nitrogen to the system.
Studies: Water Quality Impacts on
Alafia River and Tampa Bay, May 29, 1998.
Freshwater Benthic Invertebrates
Biological and chemical sampling following the release demonstrated
reduced benthic species abundance and diversity in freshwater reaches of the
river compared to pre-release conditions. However, changes in benthic community
structure in response to short-term changes in environmental conditions are
often of short duration, as benthic recolonization and recruitment can occur
rapidly. As a result, the Agencies determined losses were likely minimal.
Because of the minimal injury and the high cost of additional studies, this
injury was not quantified. This decision also reflected the fact that
restoration projects to benefit marsh, riverine, and oyster reef habitat would
also serve to indirectly compensate for the injury to freshwater benthic
invertebrates.
Oysters and Mussels
Following the release, the Hillsborough County
Environmental Protection Commission (EPC)
conducted reef surveys and found approximately 30 percent mortality on an
oyster reef in the lower Alafia River. EPC also photo documented that the
mussel population that had been growing on I-75 Bridge pilings had died as a
result of the release. However, the agencies determined further work to assess
these losses was not warranted. This decision took into account, among other
things, that oyster and mussel populations typically recruit and recover
relatively quickly from temporary adverse changes in environmental conditions,
the cost and time required to further quantify these losses , and the size or
amount of restoration that would be expected to compensate for the relatively
small injury.
Other Resources Considered:
Birds
Although no bird mortalities were observed, the U.S.
Fish and Wildlife Service (FWS) searched historical wildlife data and
GIS databases, inspected the affected area and consulted with experts to
evaluate the potential for spill-related injuries to birds. A primary concern
was the potential for reduced survival, growth and reproduction in some species
of birds due to the loss of fish in the river, since many of the fish species
killed represent a main food source for bird s in the affected area. The FWS
found, however that additional studies would need to be conducted to confirm
any change in bird health and/or abundance and to link these effects to the
release. The FWS considered several strategies for collecting additional data
but all approaches involved costly studies, potentially inconclusive results,
and greatly expand the time to complete the assessment of resource injuries for
the spill. For these reasons, and because restoration actions to increase fish
abundance (marsh and oyster reef restoration) would indirectly compensate for
any potential bird injury, the Agencies took no further action to investigate
potential indirect harm to birds.
Recreational Fishing
The acidity of the river’s surface waters, the fish kill and post-release
warnings about use of the river reported in the news and posted at boating
access points prompted the Agencies to investigate whether recreational fishing
activity was adversely affected by the spill. Such factors can result in fewer
angler trips, or diminish the value of trips due to reduced catch rates. To
investigate, the Agencies obtained information on sales during and preceding
the release from bait and tackle shop owners along the Alafia River as well as
law enforcement data on vessel intercepts in the area before and after the
release. While these records indicated recreational fishing activity was
reduced in December 1997, the Agencies could not determine the extent to which
this effect was caused by the spill versus the record rainfall in the region
that occurred that same month. Because further work to confirm losses due to
the spill would have necessitated expensive and potentially inconclusive
studies, the Agencies elected to end their investigation. This decision also
recognized that restoration projects planned to compensate for the fish injury
would also indirectly compensate for any potential recreational losses.
