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A warmer than normal winter and heavy early season rains contributed to the highest levels of water hyacinth on the St. Johns River and Lake Okeechobee since 1986.

A warmer than normal winter and heavy early season rains contributed to the highest levels of water hyacinth on the St. Johns River and Lake Okeechobee since 1986. (Photo by USACE)

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Posted 1/8/2013

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By Annie Chambers


The year 2012 brought many challenges for the Invasive Species Management (ISM) Branch to tackle. Multiple factors led to the highest levels of water hyacinth on Lake Okeechobee since 1986.

Water hyacinth invades lakes, ponds, rivers, marshes and other types of wetland habitats. According to the Early Detection and Distribution Mapping System website, water hyacinth can reproduce and quickly form dense floating mats of vegetation, sometimes doubling in size over a two week period. These dense mats reduce light and deplete oxygen levels for submerged plants and aquatic invertebrates.

Biologist Jon Lane explained the myriad factors that led to the explosion of aquatic plant growth this year.

“The warmer than normal winter did not kill back the water hyacinth as usual and the heavy early season rains flushed those plants out of the nursery areas and into the St. Johns River and Lake Okeechobee; and the abundance of snail kite nests prevented treatment in certain areas on Lake Okeechobee,” said Lane.

About 8,350 acres of floating vegetation were removed from the St. Johns River and 11,961 acres from Lake Okeechobee. This is much higher than last year. Typically 500 acres are removed monthly. In 2012, almost 2,000 acres were removed each month.

The ISM team worked with the Florida Fish & Wildlife Commission and the U.S. Fish and Wildlife Service to conduct aquatic plant management within pre-determined buffers on Lake Okeechobee.  Although the snail kites are often found in the Lake Okeechobee area, this is the first year there’s been a large-scale impact. The snail kite nests were located precisely where contractors needed to spray to manage aquatic plant growth.

November brought the first sightings of the old world climbing fern in St. Johns and Duval counties. Prior to this year, this aggressive, exotic plant grew primarily in south Florida, so the migration to north Florida was alarming.

The Invasive.org website describes old world climbing fern as a perennial that can reach lengths of more than 90 feet and often invades swamps, glades and hammocks. It forms dense mats that smother underwater vegetation and native shrubs and trees and increases fire risks. Thick mats of dead fronds that grow into trees act as fire ladders, bringing the fires into the tree canopies.

The ISM team is currently working with the First Coast Invasive Working Group (FCIWG) to eradicate the fern in dredge management areas along the St. Johns River. The FCIWG is a five-county task force that works to prevent and control invasive species in Baker, Clay, Duval, Nassau & St. Johns Counties.

Alligatorweed is an emergent, or rooted, floating plant that invades aquatic areas and adjoining uplands throughout the southern United States. The thick mats often displace native vegetation and wildlife habitat, clog waterways, restrict water oxygen levels, increase sedimentation, interfere with irrigation and prevent drainage.

Jacksonville District undertakes a yearly collection of alligatorweed flea beetles from local waters for shipment to locations where alligatorweed is becoming a problem. In May, the Aquatic Plant Control Operation Support Center collected and sent 49,799 alligatorweed flea beetles to six different states.

The hearty appetites of these effective bio-control agents have significantly decreased the use of chemicals to control alligatorweed. Three years after the release of the alligatorweed flea beetle in Florida, the Corps suspended herbicide spraying of alligatorweed.

Jacksonville District is the only district in the U.S. Army Corps of Engineers with an Invasive Species Management Branch. It is also host to the Aquatic Plant Control Operation Support Center, which assists the entire Corps with invasive species management issues. Jacksonville District team members travel around the country to assist in aquatic plant removal.

Jeremy Crossland, biologist, assisted the Great Lakes and Mississippi River Interbasin Study (GLMRIS) technology team to complete the Aquatic Nuisance Species Control Paper titled Inventory of Available Controls for Aquatic Nuisance Species of Concern – Chicago Area Waterway System.

The GLIMRIS team is a regional, collaborative effort that includes various Corps district and division offices, as well as centers of expertise and research laboratories.

The control paper will explore options and technologies that could be applied to prevent aquatic nuisance species transfer through aquatic pathways between the Great Lakes and Mississippi River basins. Recently the team began a risk assessment process to test the technologies proposed in the control paper. The proposed technological controls will be presented to Congress by January 2014.

alligatorweed alligatorweed flea beetle aquatic plant aquatic plant growth biologist biology everglades First Coast Invasive Working Group Florida Florida Fish and Wildlife Commission GLIMRS Great Lakes and Mississippi River Interbasin Study invasive species Lake Okeechobee old world climbing fern snail kite St. Johns River U.S. Fish and Wildlife Service water hyacinth