US Geological Survey, Southeast Ecological Science Center Grant: Ecological Research on Canal Backfilling in South Florida

Goal 1 – Determine if complete backfilling is an ecological necessity for restoration.

The ecological rationale for the complete backfilling of canals is based on the hypothesis that the transport and redistribution of materials by flow is an important driver regulating the ridge & slough landscape pattern. It is hypothesized that without complete backfilling, canals that are oriented perpendicular to the direction of flow will alter the hydrodynamics of sheet flow and the advective transport of material with negative downstream consequences. Currently, the L-67 canals supports a highly prized and valued sport fishery; however, canals and levees also reduce the degree of contiguous landscape connectivity that may influence the natural dispersal patterns of flora and fauna or may serve as vectors for the dispersal of exotic, invasive, and nuisance species.

Goal 2 – Evaluate the hydrodynamic and ecological effects of different construction options for backfilling canals.

Alternatively, canals provide habitat for many socially important fauna and are refugia for native taxa during the dry-season or extreme droughts. Shifting the hydrologic driver from conveyance, the lateral flow of water through a canal, to sheet flow, perpendicular flow across the canal, will alter the within-canal hydrodynamics. It is not known if these hydrologic modifications will alter the physical (dissolved oxygen and temperature) environment within the canal or if these changes will alter patterns of density, standing crop, and relative abundance of fishes and macroinvertebrates at the local and landscape scale.

Specific objectives are detailed below:
This research centers on four fauna related hypotheses contained with the DPM Science Plan and to conduct large-scale hydrodynamics of surface water flows using sulfur hexafluoride (SF6) tracer methodology.

Objective 1- Test the hypothesis that habitat quality (oxygen and temperature depth profiles) will not differ among backfilling treatments. The greater water depths in canals relative to marsh depths may develop different vertical profiles of ecologically important physiochemical constituents (e.g., dissolved oxygen or temperature). Of special concern is the development of waters with low dissolved oxygen concentrations (hypoxia) which could be detrimental to aquatic fauna and influential to biogeochemical cycling.

In conjunction with faunal sampling, document the physical characteristics (e.g., dissolved oxygen, pH, temperature, and specific conductivity) with depth (0.5 m resolution) at monitoring stations within each backfilling treatment in the L-67C canal. Provide Annual report of results/findings by January 30, 2011.

Objective 2- Test the hypothesis that habitat quality (oxygen and temperature depth profiles) will not differ between canals used for conveyance versus hydrological modified canals. Canals used to convey water (e.g., L-67A) are more likely to be chemically well mixed whereas hydrologically modified canals that do not convey water (e.g., L-67C) are expected to mix less and develop vertical stratification. Of special concern is the development of waters with low dissolved oxygen concentrations (hypoxia) which could be detrimental to aquatic fauna and affect biogeochemical cycling.

In conjunction with faunal sampling, document the physical characteristics (e.g., dissolved oxygen, pH, temperature, and specific conductivity) with depth (0.5 m resolution) at monitoring stations within the L-67A canal. Provide Annual report of results/findings by January 30, 2011.

Objective 3- Test the hypothesis that fish assemblage structure and usage will not differ among backfilling treatments. Of special interest is the backfilling of canals on the sport fishery, chiefly bass (Micropterus spp.), that currently occupies the existing canal network. Canals may serve as valuable habitat for fish, being refuges during periods of high thermal stress or drought. Alternatively, canals may also serve as corridors that enable the spreading and harboring of non-native or exotic species. It is suspected that the canal fisheries are dependent, to some degree, on the marsh, readily moving from one habitat to the other.

Assess the fishery within the L-67C canal backfilling treatments at 5 intervals per year. Each treatment will be surveyed using electro-shocking including immediately before and after flows are manipulated.

Assess the extent that the fishery within the L-67C canal backfilling treatments utilizes and is dependent upon a connection to the adjacent marsh. Several techniques will be used. To capture fish movement, 20 large fish each of four species (two native, probably largemouth bass and Florida gar, and two non-native, probably Mayan cichlids and either oscars or jaguar guapote) will be tagged with radio transmitters and their positions determined at weekly intervals, again with extra intensity immediately before and after flow manipulations. Additionally, dual frequency identification sonar (DIDSON; http://www.soundmetrics.com) will be used to count the number fish crossing the canal-marsh interface. Provide Annual report of results/findings by January 30, 2011.

Objective 4- Test the hypothesis that aquatic fauna structure will not differ among backfilling treatments. Assuming that depth-related physiochemical differences will occur among canal backfilling options, it is likely that a pelagic and anaerobic benthic aquatic fauna will be present in the no backfill and partial backfill treatments. These differences may be reflected in spatial and temporal distributions of prey availability for higher trophic levels and trophic cascades.

Assess the macroinvertebrate assemblage within the L-67C canal backfilling treatments at 5 intervals per year. Concomitant measures of prey availability will obtained from marshes using sweep net sampling and periphyton. Provide Annual report of results/findings by
January 30, 2011.