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

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.

Impacts of extreme precipitation events in water quality: a scientometric analysis in global scale

“…There is not a concept that fully defines what extreme weather events are, but the most common approach to defining extreme weather events is by using historical data and climate expectations. Typically, events occurring in the lowest 5% of a frequency curve are considered extreme (Ji & Havens, 2019;Camuffo et al, 2020;Stockwell et al, 2020). This analysis requires at least 20 years of daily, continuous monitoring data from historical time-series (IPCC, 2012;Peterson et al, 2012;WMO, 2016).…”

“…The drastic changes in water volume trigger alterations in various physical and chemical parameters, such as suspended solids and nutrient concentrations, turbidity, transparency, temperature, and pH (Stockwell et al, 2020;Mosley, 2015;Marengo et al, 2018;Santos et al, 2021). These changes in light and nutrient conditions directly impact the phytoplankton community, thereby influencing trophic dynamics and overall ecosystem functioning (Guo et al, 2018;Ji & Havens, 2019;Lisboa et al, 2020). Scientometric studies focusing on aquatic systems provide a valuable framework for investigating variations in water quality patterns and understanding the underlying mechanisms that govern the responses of water bodies (Costa et al, 2018;Stockwell et al, 2020).…”

Common Wetland and Aquatic Plants of Lake Apopka, Florida (USA)

“…After decades of water quality degradation and associated decline of fisheries in Lake Apopka, restoration efforts have contributed to habitat improvement within the lake. Actions include establishment of a marsh flow way that removes nutrient-rich sediment (Dunne et al 2012), restoration of surrounding marshes (Bowen and Slater 2016), and reductions in nutrient inputs (Coveney et al 2005), all of which have contributed to long-term improvements in water quality (Ji and Havens 2019). Subsequently, characteristic aquatic plants have returned to Lake Apopka, via both natural colonization and planting; their persistence is a sign of habitat recovery, but also these plants will help consolidate floating suspended sediments, sequester nutrients and continue to improve water quality.…”