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A COMPARATIVE ANALYSIS OF LAKE ALICE AND LAKE ISLAND FORD: METHODS AND RESULTS OF A LOW-COST DIAGNOSTIC LAKE ASSESSMENT PROTOCOL

David Eilers, Jim Griffin, Sarah Koenig Florida Center for Community Design and Research, University of South Florida Tampa, Florida

A five-year research effort is currently underway to conduct diagnostic assessments of 150 lakes located within Hillsborough County. The Florida Center for Community Design and Research (FCCDR), with support from the Hillsborough County and the Southwest Florida Water Management District, uses a revised approach to assess the ecological health and morphology of lakes. The primary goals of the lake assessments are: (1) to determine the current state of each lake in terms of trophic state, vegetative cover, and presence of nuisance vegetation and (2) to determine the potential for future changes to the trophic state from stormwater runoff and lake management practices. The data collected from these assessments are summarized in reports and made available to stakeholders at WaterAtlas.org.

The use of new, low-cost spatial technology allows for the diagnostic assessment of a lake with one day of field work and minimal pre- and post-processing. This paper examines this revised assessment approach and includes results from Lake Island Ford and Lake Alice. Lake Island Ford and Lake Alice are located in the Brooker Creek Watershed in the Keystone Lakes

Region of Northwestern Hillsborough County. urbanization in recent years.

This region has experienced significant

Bathymetric data is collected with a Lowrance LCX 26C HD Wide Area Augmentation System enabled Global Positioning System (WAAS-GPS) with fathometer (bottom sounder) to determine the boat’s position and bottom depth in a single measurement. The advantages of this low-cost ‘fish finder’ include its ability to collect hard (bottom depth) and soft (vegetation) returns and a dual geographical / sonar display. This data is used to understand the morphology (perimeter, volume, bathymetry, etc.) of the lake and to determine the percent area covered (PAC) and percent of the available volume of the lake infested (PVI) with submerged vegetation. GIS is used both in the field and office to increase the effectiveness of data collection and reduce the post-processing of field-derived data. Additionally, shoreline vegetation is surveyed for species abundance and the presence of pest plants, a water column profile is conducted to determine changes in physicochemical parameters, and water column chemistry samples are collected.

Lake Island Ford and Lake Alice were assessed during the 2006 field season, the first year the revised approach was employed in Hillsborough County. The approach was successful, and Alice and Island Ford yielded differing results regarding their general health and primary concerns for lake management. Our water physicochemical survey supported the upward trend in Trophic State Index (TSI) values that can be seen in both lakes from the latest data from LAKEWATCH and other sources. The substantial increase in phosphorus and 85% PAC in Lake Alice is of primary concern. Moreover, the recent increase in phosphorous and high

Session 2 – Page 6

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