The effects of an artificial wetland dominated by free‐floating plants on the restoration of a subtropical, hypertrophic lake

Abstract

Lake Rodó (Montevideo, Uruguay) is a small, urban, hypertrophic lake undergoing restoration. In this study, we evaluated the nutrient removal efficiency and water quality improvement attributable to a water recirculation system, consisting of the lake and three connected pools converted to artificial wetlands dominated by free-floating hydrophytes. Eichhornia crassipes and Spirodela intermedia dominated the hydrophyte community during summer and winter, respectively, with the biomass production being maintained throughout the year. The maximum production values of E. crassipes were 11.3 and 5.6 g DW m -2 d -1 in the summers of 1998 and 2000, respectively, while those of S. intermedia were 2.7 and 0.8 g DW m -2 d -1 in the summers of 1999 and 2000, respectively. The aquatic plant community reduced the concentration of nutrients in the water column but did not significantly affect the sediment concentrations. Harvesting the hydrophytes removed the equivalent of 58-88% and 39-78% of the nitrogen (N) and phosphorus (P) load associated with the water column, respectively. In contrast, the harvests accounted for only 1-2% of the N and P load associated with the sediments. In the pools, the combination of water recirculation and hydrophytes generally diminished the algal biomass and the associated N and P, compared to that observed for the lake. The combined use of adequate aquatic plant harvests and hydraulic management increased the efficiency of the system and, therefore, seems to be a useful tool for restoring small, shallow lakes in tropical and subtropical regions.

Seasonal-dependence in the responses of biological communities to flood pulses in warm temperate floodplain lakes: implications for the “alternative stable states” model

“…5) and chlorophyll a consequently diminished to values in correspondence to clear waters (Tables 2, 3). Our results are especially relevant for nutrient rich shallow lakes from warm to warm-temperate climates, where cyanobacteria or free-floating plants become very abundant (Rodríguez-Gallego et al 2004;Bicudo et al 2007;O'Farrell et al 2011;Giblin et al 2014). Notwithstanding, the dominance by either free-floating plants or cyanobacteria is predicted to expand even to cooler regions because of climate warming (Paerl and Huisman 2009;Kosten et al 2011;Scheffer et al 2003;Netten et al 2011), which is an undesirable scenario due to their known harmful effects on water quality, ecosystem functioning and biodiversity, among others (Paerl et al 2001;de Tezanos et al 2007;Ibelings and Havens 2008;O'Farrell et al 2009;Fontanarrosa et al 2010).…”

Succession and collapse of macrozoobenthos in a subtropical hypertrophic lake under restoration (Lake Rodó, Uruguay)

“…The accumulation of organic matter in Lake Rodo´was conditioned by the sedimentation originating from an excessive algal biomass, in turn determined by high nutrient inputs (from nitraterich groundwater and deciduous vegetation on the margins), and the almost continuously low grazing pressure by zooplankton (Scasso et al 2001;Kruk et al 2002;Meerhoff et al 2003). The termination of the groundwater supply after the summer of 1998 and the recirculation of lake water through an artificial wetland, led to a reduction of the nutrient input but promoted the accumulation of organic matter in the sediment (Rodrı´guez-Gallego et al 2004). This was caused by a longer residence time and the decrease of the oxidizing agent nitrate (Rodrı´guez-Gallego et al 2004).…”

“…The termination of the groundwater supply after the summer of 1998 and the recirculation of lake water through an artificial wetland, led to a reduction of the nutrient input but promoted the accumulation of organic matter in the sediment (Rodrı´guez-Gallego et al 2004). This was caused by a longer residence time and the decrease of the oxidizing agent nitrate (Rodrı´guez-Gallego et al 2004). …”

“…The following measures were implemented: (1) diversion of the main inlet and drying out of the lake, (2) removal of ca. 1 m of upper sediment, which almost exposed the sandy bottom, (3) pumping of groundwater to refill the lake and to maintain the water level, (4) construction of an artificial wetland and implementation of a water recirculation system in the lake to reduce the internal nutrient load and (5) removal of omnivorous -planktivorous fish and introduction of piscivores (Scasso et al 2001;Rodrı´guez-Gallego et al 2004). Measures 4 and 5 have been repeatedly applied since 2000.…”

Producing Liquid Organic Fertilizer from Water Hyacinth; A Case of Lake Victoria, Kenya

“…Water hyacinth's uptake capacity has been validated in several field studies as well. It has a high nutrient uptake rate compared to other macrophytes [37]. It therefore has the potential to significantly reduce nutrient concentrations in the water body depending on the extent of cover and density (Pinto-Coelho & Greco, 1999).…”