Water depth and water quality in Lake Apopka KARL HAVENS DIRECTOR, - - PowerPoint PPT Presentation

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Feb 05, 2023 207 likes •426 views

Water depth and water quality in Lake Apopka KARL HAVENS DIRECTOR, FLORIDA SEA GRANT PROFESSOR, UNIVERSITY OF FLORIDA / IFAS HARRIS CHAIN OF LAKES RESTORATION COUNCIL, SEPT 2018 1999-2016 SJRWMD data from Harris Chain Intent: determine

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Water depth and water quality in Lake Apopka

KARL HAVENS DIRECTOR, FLORIDA SEA GRANT PROFESSOR, UNIVERSITY OF FLORIDA / IFAS HARRIS CHAIN OF LAKES RESTORATION COUNCIL, SEPT 2018

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1999-2016 SJRWMD data from Harris Chain
Intent: determine if variation in depth can

affect limnology of shallow FL lakes

Dataset originally used to examine

zooplankton and phytoplankton

First, all Harris Chain lakes, then focus on

Apopka

Study was not a test of efficacy of restoration

program; it was a case study of climate variability effects

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Havens, Ji, Beaver, Fulton et al. (2017) Hydrobiologia

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Based on 1999-2016 data from the SJRWMD

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Havens and Ji (2018) Inland Waters

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Havens and Ji (2018) Inland Waters

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Conclusions 1: Droughts and extreme low water resulted in markedly reduced water quality in Lake Apopka during 1999-2016, as well as in the other Harris Chain of Lakes. Similar results have been obtained in

ther shallow lakes world-wide

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Drought Depth and Volume Decline Fish, nutrients and algae are concentrated / fish effects are magnified Blooms more severe

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Wet Years Depth and Volume Increase Fish, nutrients and algae are diluted / fish effects are weakened Blooms less severe

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A Longer Historical Context

With additional data provided by the SJRWMD from the onset of routine water quality monitoring in 1985

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Start: 230 End: 113 Change: 51% down Significant: yes, <0.001 Start: 5.6 End: 4.2 Change: 26% down Significant? Yes, <0.001 Mann-Kendall non-parametric trend tests

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Start: 101 End: 56 Change: 44% down Significant: yes, <0.001 Start: 0.22 End: 0.33 Change: 54% up Significant: yes, <0.001

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Last three values significantly lower, and by 40%

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Last three values significantly lower, and by 58%

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Last three values significantly lower, and by 32%

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Last three values significantly higher, and by 73%

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Conclusions 2: Statistically-significant long-term declines in TP, TN and Chl-a in the 1985-2018 dataset, and increased Secchi depth Comparing high water periods only, improved water quality during last three high water periods compared to earlier high water period. Reiterating – severe lows are a problem. Why are they happening?

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