Lake Annie: Pristine headwaters

Introduction Lake Annie is a pristine, 90-acre sinkhole lake at the northern end of the Archbold main property. Purchased in 1983 as part of the Frances and Page Hufty Tract, the lake is of exceptional geological and ecological interest. The lake provides an opportunity to study not just a pristine lake, but also the uppermost water in a chain of connected lakes and streams. It lies at 111 feet (33.7 m) above mean sea level, and is the southernmost of a series of sinkhole lakes extending 200 miles north along and beyond the Lake Wales Ridge. The lake is 68 feet deep and contains at least 36 feet (11 m) of sediment. Pollen analysis and 14C dating of sediment cores reveal a continuous record of area vegetation for the past 50,000 years. The lake is fed by rainfall and groundwater and develops a thermocline during the summer.

Lake Annie is located as the southernmost of a linearly aligned series of lakes extending some 200 miles north along the axis of the peninsula. Lake Annie is located in Highlands County Florida (Fig 1A), approximately six miles from the Town of Lake Placid, (Lat 27˚ 12’ 35” Long. 81˚ 20’ 57”. It lies immediately south of State Road 70 and west of Old SR 8. Lake Annie lies at the north end of Archbold Biological Station (Fig 1C) about here ASK ro to give us jpegs of each of these figs. It was named Annie, after the wife of J.W. Childs, the US General Lands Office surveyor for this area in 1870. To protect this critically important lake for research and conservation, Archbold Biological Station purchased Lake Annie and the surrounding land from the Consolidated Tomoka Land Company in 1983.

Lake Annie is a 90-acre sinkhole lake; the bathymetric profile (Fig 1D about here ASK ro to give us jpegs of each of these figs) shows it is egg-shaped with its longest axis north east to south-west. To the SW it forms a relatively uniform, cone shaped deep basin tapering to a 67-68’ (21 m) “deep hole”. A shallow bay lies to the NE. It is a subtropical monomictic lake with a stable thermocline, typically mixing only during January to March, a rare phenomenon in Florida lakes. Lake Annie is one of the least modified by human influence of any water body in south Florida, with (1) its position at the head of the drainage system (2) a small drainage basin with little surface inflow, and (3) absence of development around the lake. The watershed of Lake Annie lies largely within the protected lands of Archbold Biological Station; surface inflow occurs only after high rainfall via two ditches on the south and east shores. US Geological Survey studies show that Lake Annie is fed primarily by groundwater inflow (seepage) from the south and west, and outflow to the north.

Lake Annie lies at about 111’ (33.7 m) above msl, the headwaters for a chain of lakes on the southern Lake Wales Ridge. A small outlet stream next to the dock flows north through what is known locally as the West Chain of Lakes - Lake Placid, Lake June, Lake Francis, and then draining north through Jack Creek, a tributary of Josephine Creek, and eventually, via Josephine Creek, to Lake Istokpoga, all part of the Northern Everglades ecosystem.

Lake Annie is best known for its 11 m, ~50,000 year sedimentary record from which Bill Watts, Eric Grimm and colleagues have reconstructed a climate and vegetation history of the region. The thick bed of sediments, deposited in the deeper part of its basin is best preserved in the 67-68’ bottom anoxic conditions of the 1-2-acre “deep hole”. Sediment cores reveal a record of changes in climate, pollen from surrounding vegetation, fire histories, algal communities, and more recent mercury levels.

Since 1982 detailed long-term monthly limnological studies have been conducted at Lake Annie by Archbold Biological Station, measuring light, temperature, conductivity, and oxygen vertical profiles as well as pH and sulphate levels. The lake ranges from clear and transparent with low rainfall levels, to dark colored and stained under high rainfall and groundwater conditions. Since 2000 Lake Annie has been part of the Florida’s Lakewatch program and, starting in 2005, the Southwest Florida Water Management District has collected regular data to monitor trends in nutrient levels. Lake level data go back to 1931. Between 1982 and 1992, rainfall was below-average and percolated into groundwater that moved through the sandy soils of the LWR before delivering nutrient-poor water to the lake. The annual mean Secchi depth in the lake during this period was 6-12 m and the thermocline depth ranged from 8-13 m. From 1993 onwards, rainfall was above-average, raising the height of the water table and causing increased surface water delivery to the lake. Total nutrient and chlorophyll a concentrations increased slightly, but remained within the oligo- to mesotrophic range. However, increased transport of colored organic materials from the watershed reduced the Secchi disk transparency to 1-3 m, increased the depth of the summer euphotic zone and thermocline, and caused a 1-month reduction in the duration of winter mixing. Models from the 22-year record were used to infer a longer history of lake water transparency from the 73-year lake stage and precipitation record. Resulting trends correspond roughly to the Atlantic Multi-decadal Oscillation, which is one of the drivers of long-term precipitation patterns in Florida.

Driving Directions from the Station. Turn left (north) from the entrance drive to Archbold Biological Station onto Old SR8. Go 1.8 miles to SR 70. Turn left (west). Within 100 yds you will cross the RR line on SR70, then approximately 100yds later, on the big bend, turn left (south) onto a small dirt track. There is a gate in front of you and a sign saying “Frances and Page Hufty” Tract. If you have a gate key go through and park by the gazebo (40 yds), if not just park outside the gate and walk in through gap to west of gate.

In 2006 Lake Annie became part of GLEON the Global Lakes Ecological Observatory Network sponsored by the National Science Foundation. A new instrumented buoy was deployed on the lake in February 2008 (link to new GLEON PAGE) in conjunction with the 6th international GLEON workshop. Integrated lake data from Lake Annie and other lakes around the world will be analyzed to examine global trends.