This post was written by guest blogger Emily Nodine, a PhD candidate in FIU's Periphyton Lab (http://algae.fiu.edu/research/).

When people think about today’s Everglades or the “River of Grass,” they generally think of Lake Okeechobee, Everglades National Park, and the canals and water control structures in between.  But the watershed is actually much larger than that.  Lake Okeechobee does serve as the headwaters of the Everglades; prior to human alteration, Lake Okeechobee would slowly overflow southward during very wet periods, forming the shallow, slow-flowing sheet of water that earned it the title “River of Grass.”  Today, the Hoover Dike prevents this and the water flow is strictly controlled, mostly released to the east and west coasts via the St. Lucie and Caloosahatchee Rivers, but also southward to the Everglades through an extensive system of canals and water control structures.  But the water in Lake Okeechobee came from somewhere else, too.

Lake Okeechobee sits at the mouth of the Kissimmee River and several smaller creeks that drain much of highlands central Florida as far north as Orlando.  Much like Lake Okeechobee and the Everglades, the Kissimmee River has also been through dramatic hydrological alteration and subsequent restoration efforts.  Once a meandering 103-mile waterway with a floodplain 1 to 3 miles across, the Kissimmee River was transformed during the 1960s to a 56-mile canal 300 feet wide and 30 feet deep.  Within the next couple of years, the South Florida Water Management District and U.S. Army Corps of Engineers plan to complete backfilling of a large section of the canal and removing water control structures in order to restore ecological integrity to 40 square miles of the river-floodplain system and 12,000 acres of wetlands.  Already, flora and fauna that disappeared following the canalization have begun to return.  Additional details about the restoration project can be found at http://my.sfwmd.gov/portal/page/portal/xweb%20protecting%20and%20restoring/kissimmee%20river.

Little of the Everglades watershed has been left untouched by hydrological alterations.  While restoration efforts such as the one-mile bridge on Tamiami Trail aim to deliver more water southward to the Everglades, estuaries at the outflows of the St. Lucie and Caloosahatchee Rivers  suffer from the effects of too much freshwater.  Historically, the Caloosahatchee River’s headwater was a small wetland pond west of Lake Okeechobee called Lake Hicpochee.  During early efforts to drain the Everglades for farmland in the late 1800s, a canal was dug connecting Lake Hicpochee to Lake Okeechobee, allowing the Caloosahatchee to become a major outflow for the larger lake.  Through subsequent canalization and installation of water control structures, the Caloosahatchee, like the Kissimmee River, was transformed.  Today, freshwater is released through a series of lock and dam structures down the Caloosahatchee to relieve pressure on the aging Hoover Dike that surrounds Lake Okeechobee, causing an influx of eutrophic water to the Charlotte Harbor estuary that results in adverse effects on seagrasses, oyster beds, and water quality.

My research is focused on the Charlotte Harbor watershed, which sometimes feels peripheral to the work of FCE LTER scientists in the Everglades, but I remind myself how important this region is as part of the Greater Everglades Ecosystem.  There are three major inflows into Charlotte Harbor, and they couldn’t be more different.  The Caloosahatchee, which is near my home, is highly managed and cut off from marine influence by water control structures (except during severe storms, when these are occasionally breached); the Peace River, which is naturally enriched in phosphorus and has been extensively mined for fertilizer; and the Myakka River, which is relatively pristine, with much of its watershed set aside as conservation lands and parks.

My goal is to understand the differences among these systems and how they influence inputs to Charlotte Harbor over time.  I am studying the diatom communities across this watershed in order to interpret long term changes from sediment cores taken from the estuary.  Diatoms are single-celled algae that provide clues about past environments because they are indicators of specific environmental conditions and they preserve in sediments, allowing us to determine what past conditions were based on which diatoms are present.  Specifically, I am interested in how they are distributed along environmental gradients, and how this changes in response to a disturbance such as a tropical storm or hurricane.  By studying what diatoms occur in these waterways before and after storms, I hope to identify a signal of hurricane activity that can be detected in sediment cores and help us to understand how these types of storms have affected south Florida ecosystems on large time scales.

Tropical Storm Debby, in June 2012, provided an excellent opportunity to investigate changes across the watershed.  During the dry season, diatom assemblages are strongly related to a salinity gradient across the watershed.   But following the storm, diatom communities changed in different ways across the various regions of the watershed.   Next, I hope to identify patterns in these differences to help us understand drivers of the type or direction of changes, such as whether anthropogenic alteration causes a different response to disturbance compared to more pristine areas.