From intermittent to persistent cyanobacterial blooms: identifying the main drivers in an urban tropical reservoir

Abstract

Eutrophication has impacted water bodies around the world. Knowledge on how to manage and restore these systems is urgently needed in order to of this work was to analyze the evolution of the eutrophication process in an urban tropical reservoir, using a 15-year time series (with occasional interruptions). The dataset comprised monthly sampling of several environmental variables and the phytoplankton community. We found a continuous process of water quality deterioration, mainly related to increasing levels of nutrient and phytoplankton biomass, as well as decreasing water transparency, even after the installation of a municipal wastewater treatment plant. The ongoing eutrophication resulted in a steep trend of increasing cyanobacteria biomass that turned from a seasonal appearance into more persistent blooms in the most recent decades, while the relative contribution of other algal phyla to total phytoplankton biomass declined, which resulted in a loss of phytoplankton diversity. Phosphorus was the major determinant of the persistent blooms. Even though nitrogen concentrations were very high in this system

Potential effects of mechanically removing macrophytes on the phytoplankton community of a subtropical reservoir

“…Resuspending sediment promotes the bioavailability of phosphorus and nitrogen from the bottom; thus, providing an additional nutrient source for phytoplankton (Shaw & Prepas 1990). This process has significant implications in subtropical water bodies, such as the Piraquara II reservoir, as phosphorus is the main factor promoting phytoplankton growth at these latitudes (Aubriot et al 2000;Downing et al 2001;Perkins & Underwood 2001;Horn 2003;Figueredo et al 2016). Phosphorus concentrations in sediments can reach up to 100 times that in the water column (Sondergaard et al 2003), and harmful cyanobacteria usually constitute the most favored group (Bakker & Hilt 2015), posing a serious threat to aquatic organisms and human beings, either by producing secondary metabolites, such as toxins and allelopathic compounds (Leflaive & Ten-Hage 2007;Pearl & Huisman 2009) or by drastically changing the physical and chemical parameters, including the sediment-water interface (Zhu et al 2013).…”

Impact of Urban Stormwater Runoff on Cyanobacteria Dynamics in A Tropical Urban Lake

“…Lower PO 4 3− concentration in the water column in scenarios -waster_water and -phosphorus limited the build-up of cyanobacteria biomass leading to smaller and delayed cyanobacteria peaks. The relationship between cyanobacteria biomass and TP in Lake Pampulha had already been highlighted in previous studies [32,36]. Figueredo et al [32] observed a long-term continuously increasing trend for TP from 1996 to 2011 which was identified as a major driver of persistent blooms of cyanobacteria while no significant correlation was found between cyanobacteria and NO 3 nor with NH 4 + .…”

“…The relationship between cyanobacteria biomass and TP in Lake Pampulha had already been highlighted in previous studies [32,36]. Figueredo et al [32] observed a long-term continuously increasing trend for TP from 1996 to 2011 which was identified as a major driver of persistent blooms of cyanobacteria while no significant correlation was found between cyanobacteria and NO 3 nor with NH 4 + . According to the authors, this TP increasing trend may be related to increasing wastewater disposal in Lake Pampulha tributaries and the associated inefficiency of the fluvial waste water treatment plant.…”

Dissolved organic N in shallow tropical lakes and reservoirs: Contribution to total dissolved N and relationships with eutrophication

“…The Pampulha Reservoir, an exclusively urban reservoir larger than the other investigated lentic system, was the only exception. Considering the rapid urbanization processes occurring in many tropical, developing countries, the Pampulha reservoir, receiving sewage from 13 municipalities (Giani, 1994), represents a typical endpoint of the eutrophication process (Figueredo et al, 2016;Pinto-Coelho, 2012), and we, therefore, considered it important to include this reservoir into our study. It has high ammonium and TP concentrations, and high algal biomass, including cyanobacterial blooms (Figueredo et al, 2016).…”

“…Considering the rapid urbanization processes occurring in many tropical, developing countries, the Pampulha reservoir, receiving sewage from 13 municipalities (Giani, 1994), represents a typical endpoint of the eutrophication process (Figueredo et al, 2016;Pinto-Coelho, 2012), and we, therefore, considered it important to include this reservoir into our study. It has high ammonium and TP concentrations, and high algal biomass, including cyanobacterial blooms (Figueredo et al, 2016). The humid subtropical climate of the region is characterized by two distinct seasons, a mild dry winter between April and September, and a warm and rainy summer between October and March.…”