Buenos Aires, Argentina)

Environ Monit Assess (2018) 190:99 https://doi.org/10.1007/s10661-017-6448-7 The effects of hydraulic works and wetlands function in the Salado-River basin (Buenos Aires, Argentina) M. E. Bazzuri & N. A. Gabellone & L. C. Solari Received: 3 November 2016 /Accepted: 28 December 2017 # Springer International Publishing AG, part of Springer Nature 2018 Abstract Man-made activities exert great influences on salinization that threatens the economic exploitation of fluvial ecosystems, with lowland rivers being substan- the region. The wetlands present in this study acted as tially modified through agricultural land use and popu- service environments not only helping to reduce salt, lations. The recent construction of drainage canals in the nutrient, and suspended-solid concentrations down- upper stretch of the Salado-River basin caused the mo- stream but also contributing a plethora of species and bilization of huge amounts of salts formerly stored in the plankton biomass into the Salado-River main course. groundwater. The main aim of this work was to analyze the effect of the discharges of those canals into the Keywords Lowland river. Canalizations . Wetlands . Salado-River water, under different hydrologic condi- Saline waters . Salinization . Argentine pampas tions, and the role of the wetlands and shallow lakes placed along the canals’ system. Physicochemical variables were measured and water samples were taken Introduction during times of high water, mean flows, drought, and extreme drought. The environmental variables and the The dynamics of fluvial ecosystems are largely depen- plankton development were related to the hydrologic dent on the hydrologic regime and the seasonal variation regime and reached minimum values during floods be- in the physicochemical variables (de Cabo et al. 2003). cause of low temperatures and dilution. Local effects on According to Junk et al. (1989), the pulsing of a river’s the water’s ionic composition became pronounced dur- discharge acts as an influential forcing agent for the ing droughts because of groundwater input. Nutrient aquatic biota, sustaining the hydrologic connectivity concentrations were mainly associated with point waste- and continuity between the river’s course and the flood- water discharges. Conductivity, ion concentrations, total plain. Accordingly, floods, like droughts, are considered plankton biomass, and species richness increased in the as hydrologic disturbances, characterized by a particular Salado-River downstream site, after the canals’ dis- timing, duration plus magnitude, and associated shifts in charges. The artificial-drainage system definitely pro- the environmental variables (Poff et al. 1997;Schagerl motes the incorporation of salts into the Salado-River et al. 2009). In addition, ecological theories applied to basin. In this scenario, a careful hydraulic management low-order watercourses consider that stream-corridor is needed to take into account this issue of secondary ecosystems are compounds of concentric subsystems : : (i. e., superficial, hyporheic, parafluvial, riparian), that M. E. Bazzuri (*) N. A. Gabellone L. C. Solari are spatially separated but hydrologically connected. Instituto de Limnología Dr. Raúl A. Ringuelet, CONICET. The arrangement of those landscape patches, referred FCNyM (UNLP), Boulevard 120 y 62, (1900) La Plata, Buenos ’ Aires, Argentina to as their configuration, is closely linked to the system s e-mail: [email protected] response to disturbance and overall resilience (Fisher 99 Page 2 of 23 Environ Monit Assess (2018) 190:99 et al. 1998). River ecosystems are increasingly threat- environments, since salinity represents a key biologic ened by civilization (Margalef 1983), and as a conse- parameter (Williams 1999; Cañedo-Argüelles et al. quence, their hierarchical organization and functional 2016a) and a potential toxicant as well (Kefford et al. properties are often disrupted (Sparks 1995). 2002). In lotic systems, salinity acts as an additional The anthropic impact on freshwater environments selective force for unidirectional flow and as such can be separated into two categories: chemical alteration creates novel environments, consequently leading to of water quality through pollutant emission and physical new research (Kefford et al. 2016). Accordingly, salin- degradation through human activities—e. g.,deforesta- ity appears as a pressing disturbance for stream com- tion, urbanization, and canalization—that modify the munities, acting at the physiologic level of the constit- hydrologic and biogeochemical cycles (Zalewski uent biota so as to enable a species to withstand the 2007). Among these anthropic influences, hydraulic impending stress (Schäfer et al. 2011). In view of the works may represent an additional disturbance factor effects of salinization on the aquatic biota present; that modifies the river’s drainage network, morphologic wetlands, streams, and riparian vegetation are the prin- aspects, and hydrologic dynamics (Weilhoefer et al. cipal ecosystems at risk (Hart et al. 2003). 2008;Lairetal.2009). As a consequence, natural flow Wetlands represent diverse aquatic environments that pulses are altered with a resulting reduction in the spatial exhibit a high spatial heterogeneity and biologic rich- heterogeneity and connectivity of the floodplain envi- ness. In addition, periodic floods influence the structure ronments (Amoros and Bornette 2002). Moreover, can- and function of these ecosystems (Zalewski et al. 1998; alizations may also accelerate the downstream transport Kiedrzyńska and Zalewski 2012). Valuable environ- of water, nutrients, and suspended materials, with a mental functions—such as the retention of nutrients consequential effect on the storage and loading capacity and organic matter, and the processes of degradation of fluvial ecosystems (Kronvang et al. 1999). and transformation into biomass—take place in these The entrance of suspended solids, dissolved nutri- unique areas, shortening the spiraling nutrient loop ents, and organic matter may lead to the eutrophication (Reddy et al. 1999;Heinetal.2005;Zalewski2007). of aquatic environments (Ensign and Doyle 2006). Fur- As a consequence, wetlands are fundamental regulators thermore, nutrient enrichment degrades water quality of biogeochemical cycles, yet are strongly shaped by and perturbs biogeochemical cycles, thus becoming an hydrology and hydrologic inputs (Reddy and De Laune increasing problem in many rivers (Jarvie et al. 2002, 2008;Wolfetal.2013). In recent years, natural and 2008). In this regard, agriculture and urban activities are constructed wetlands have been successfully imple- considered the major sources of P and N input into mented with the objective of retaining P in agricultural aquatic ecosystems (Carpenter et al. 1998). Excesses landscapes (Kröger et al. 2013). of P added to cropland may accumulate in soils, there- Plankton exerts a key role in lotic ecosystems, since after reaching lotic systems by means of erosion that biota represents a food supply for many consumers (Carpenter 2008). In the water, the particulate P is and a quality source of organic carbon. The structure dissolved, thus becoming available for algal growth and dynamics of the phytoplankton and zooplankton (Garnier et al. 2005). communities are believed to be largely controlled by The salinization of freshwater ecosystems is a global physicochemical conditions such as temperature, pho- issue that is mainly a result of human activities (e. g., toperiod, turbulence, water velocity, and turbidity mining, irrigation, road-deicing agents, resource extrac- (Thorp et al. 1994;BasúandPick1996). In addition, tion). Salt concentrations are being increased in rivers the geomorphological features of the river basin and the around the world; and according to some predictions, ongoing hydrologic condition may also regulate plank- this situation will worsen in the future because of ton growth and development (de Ruyter van Steveninck climate change, global warming, and the increasing et al. 1992;DescyandGosselain1994). As a conse- demands on water (Cañedo-Argüelles et al. 2013). quence, chlorococcal chlorophytes, diatoms, rotifers, Secondary salinization—another man-made distur- and small cladocerans are frequently the dominant bance—is a hazard for terrestrial and aquatic systems, groups of the river plankton because of their particular exerting irreversible adverse effects on arable lands and adaptations to those physical limitations (Reynolds and ecosystem services (Herczeg et al. 2001). That pertur- Descy 1996). Moreover, plankton is considered as a bation constitutes a major issue in freshwater resilient community owing to that biota’sspecial Environ Monit Assess (2018) 190:99 Page 3 of 23 99 characteristics such as microscopic dimensions, quick to measure the physicochemical characteristics of the growth, short life cycles, and the production of resting water in the drainage canals; (b) to assess the effect of eggs and other resistant structures that enable the organ- the drained wetlands and shallow lakes present within isms to cope with disturbances (Fisher et al. 1998; the study area on the water from the canals; (c) to Rossetti et al., 2009). examine the influence of the canals’ allochthonous dis- The study area—located in the northwestern portion charges on the Salado River’s main course; (d) to ana- of the Salado-River basin (Buenos Aires, Argentina)— lyze the structure, dynamic, and richness of the plankton is generally known as the sandy pampa (or western

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