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Water 2019, 11(3), 538; https://doi.org/10.3390/w11030538

Periods of Extreme Shallow Depth Hinder but Do Not Stop Long-Term Improvements of Water Quality in Lake Apopka, Florida (USA)

1
National Demonstration Center for Experimental Fisheries Science Education, CREEFN of the Ministry Agriculture and Shanghai Universities Key Laboratory of Marine Animal Taxonomy and Evolution, Shanghai Ocean University, Shanghai 201306, China
2
Florida Sea Grant College Program, University of Florida Institute of Food and Agricultural Sciences, Gainesville, FL 32611, USA
*
Author to whom correspondence should be addressed.
Received: 17 December 2018 / Revised: 7 February 2019 / Accepted: 11 March 2019 / Published: 15 March 2019
(This article belongs to the Special Issue Trophic Interactions in Warm Freshwater Ecosystems)
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Abstract

We recently documented that during times of extreme shallow depth, there are severe effects on the water quality of one of the largest shallow lakes in the southeastern USA—Lake Apopka. During those times, total phosphorus (TP), total nitrogen (TN), chlorophyll-a (Chl-a) and toxic cyanobacteria blooms increase, and Secchi transparency (SD) declines. The lake recovers when water levels rise in subsequent years. In this paper, we determined whether extreme shallow depth events, particularly when they re-occur frequently, can stop the long-term recovery of a shallow eutrophic lake undergoing nutrient reduction programs. Apopka is an ideal location for this case study because the State of Florida has spent over 200 million USD in order to reduce the inputs of P to the lake, to build large filter marshes to treat the water, and to remove large quantities of benthivorous fish that contribute to internal P loading. We obtained data from 1985 to 2018, a period that had relatively stable water levels for nearly 15 years, and then three successive periods of extreme shallow depth, and we examined the long-term trends in TP, TN, Chl-a, and SD. There were significant decreasing trends in all of these water quality variables, and even though water quality deteriorated during periods of extreme shallow depth, and reduced the slope of the long-term trends, it did not stop the recovery. However, in the future, if climate change leads to more frequent shallow depth events, which in lakes such as Apopka, result in the concentration of water and nutrients, it is unclear whether the resilience we document here will continue, vs. the lake not responding to further nutrient input reductions. View Full-Text
Keywords: shallow lakes; depth; water quality; climate change; nutrients; lake management shallow lakes; depth; water quality; climate change; nutrients; lake management
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Ji, G.; Havens, K. Periods of Extreme Shallow Depth Hinder but Do Not Stop Long-Term Improvements of Water Quality in Lake Apopka, Florida (USA). Water 2019, 11, 538.

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