Gonzalo L. Pérez

EFFECTS OF THE HERBICIDE ROUNDUP ON FRESHWATER MICROBIAL COMMUNITIES: A MESOCOSM STUDY

The impact of the widely used herbicide glyphosate has been mainly studied in terrestrial weed control, laboratory bioassays, and field studies focusing on invertebrates, amphibians, and fishes. Despite the importance of phytoplankton and periphyton communities at the base of the aquatic food webs, fewer studies have investigated the effects of glyphosate on freshwater microbial assemblages. We assessed the effect of the commercial formulation Roundup using artificial earthen mesocosms. The herbicide was added at three doses: a control (without Roundup) and two treatments of 6 and 12 mg/L of the active ingredient (glyphosate). Estimates of the dissipation rate (k) were similar in the two treatments (half-lives of 5.77 and 7.37 d, respectively). The only two physicochemical parameters showing statistically significant differences between treatments and controls were the downward vertical spectral attenuation coefficient kd(lambda), where lambda is wavelength, and total phosphorus concentration (TP). At the end of the experiment, the treated mesocosms showed a significant increase in the ratio kd(490 nm)/k(d)(550 nm) and an eightfold increase in TP. Roundup affected the structure of phytoplankton and periphyton assemblages. Total micro- and nano-phytoplankton decreased in abundance in treated mesocosms. In contrast, the abundance of picocyanobacteria increased by a factor of about 40. Primary production also increased in treated mesocosms (roughly by a factor of two). Similar patterns were observed in the periphytic assemblages, which showed an increased proportion of dead: live individuals and increased abundances of cyanobacteria (about 4.5-fold). Interestingly, the observed changes in the microbial assemblages were captured by the analysis of the pigment composition of the phytoplankton, the phytoplankton absorption spectra, and the analysis of the optical properties of the water. The observed changes in the structure of the microbial assemblages are more consistent with a direct toxicological effect of glyphosate rather than an indirect effect mediated by phosphorus enrichment.

New evidences of Roundup® (glyphosate formulation) impact on the periphyton community and the water quality of freshwater ecosystems

Argentina is the second largest world producer of soybeans (after the USA) and along with the increase in planted surface and production in the country, glyphosate consumption has grown in the same way. We investigated the effects of Roundup® (glyphosate formulation) on the periphyton colonization. The experiment was carried out over 42xa0days in ten outdoor mesocosms of different typology: “clear” waters with aquatic macrophytes and/or metaphyton and “turbid” waters with great occurrence of phytoplankton or suspended inorganic matter. The herbicide was added at 8xa0mgxa0L−1 of the active ingredient (glyphosate) in five mesocosms while five were left as controls (without Roundup® addition). The estimate of the dissipation rate (k) of glyphosate showed a half-life value of 4.2xa0days. Total phosphorus significantly increased in treated mesocosms due to Roundup® degradation what favored eutrophication process. Roundup® produced a clear delay in periphytic colonization in treated mesocosms and values of the periphytic mass variables (dry weight, ash-free dry weight and chlorophyll a) were always higher in control mesocosms. Despite the mortality of algae, mainly diatoms, cyanobacteria was favored in treated mesocosms. It was observed that glyphosate produced a long term shift in the typology of mesocosms, “clear” turning to “turbid”, which is consistent with the regional trend in shallow lakes in the Pampa plain of Argentina. Based on our findings it is clear that agricultural practices that involve the use of herbicides such as Roundup® affect non-target organisms and the water quality, modifying the structure and functionality of freshwater ecosystems.

Phytoplankton and primary production in clear-vegetated, inorganic-turbid, and algal-turbid shallow lakes from the pampa plain (Argentina)

Shallow lakes often alternate between two possible states: one clear with submerged macrophytes, and another one turbid, dominated by phytoplankton. A third type of shallow lakes, the inorganic turbid, result from high contents of suspended inorganic material, and is characterized by low phytoplankton biomass and macrophytes absence. In our survey, the structure and photosynthetic properties (based on 14C method) of phytoplankton were related to environmental conditions in these three types of lakes in the Pampa Plain. The underwater light climate was characterized. Clear-vegetated lakes were more transparent (Kd 4.5–7.7xa0m−1), had high DOC concentrations (>45xa0mgxa0l−1), low phytoplankton Chl a (1.6–2.7xa0μgxa0l−1) dominated by nanoflagellates. Phytoplankton productivity and photosynthetic efficiency (αxa0~xa00.03xa0mgCxa0mgChla−1xa0h−1xa0W−1xa0m2) were relatively low. Inorganic-turbid lakes showed highest Kd values (59.8–61.4xa0m−1), lowest phytoplankton densities (dominated by Bacillariophyta), and Chl a ranged from 14.6 to 18.3xa0μgxa0l−1. Phytoplankton-turbid lakes showed, in general, high Kd (4.9–58.5xa0m−1) due to their high phytoplankton abundances. These lakes exhibited the highest Chl a values (14.2–125.7xa0μgxa0l−1), and the highest productivities and efficiencies (maximum 0.56xa0mgCxa0mgChla−1xa0h−1xa0W−1xa0m2). Autotrophic picoplankton abundance, dominated by ficocianine-rich picocyanobacteria, differed among the shallow lakes independently of their type (0.086xa0×xa0105–41.7xa0×xa0105xa0cells ml−1). This article provides a complete characterization of phytoplankton structure (all size fractions), and primary production of the three types of lakes from the Pampa Plain, one of the richest areas in shallow lakes from South America.

Effects of Herbicide Glyphosate and Glyphosate-Based Formulations on Aquatic Ecosystems

Public awareness of worldwide increase herbicides use and their adverse effects on ecosystems has been growing over the past decades. Herbicides may reach water bodies via agricultural runoff and leaching processes, as well as by direct applications to control noxious aquatic weeds. Once in the aquatic ecosystems, herbicides may reduce environmental quality and influence essential ecosystem functioning by reducing species diversity and community structures, modifying food chains, changing patterns of energy flow and nutrient cycling and changing the stability and resilience of ecosystems. The aim of this chapter is to provide a general notion of the current knowledge concerning the direct and indirect effects of glyphosate and commercial formulations of glyphosate on aquatic ecosystems. Glyphosate based products are the leading post-emergent, systemic and nonselective herbicides for the control of annual and perennial weeds in the world. Here, we present a revision of their toxicity to non-target species of algae, aquatic plants, protozoa, crustaceans, molluscs, fish and amphibians. In addition, we describe the importance of each group of organisms in the functioning and health of aquatic ecosystems. With this information, a conceptual framework can be developed contributing to enhance our attention and concern about human impacts on ecosystems.

Seasonal Variability of Optical Properties in a Highly Turbid Lake (Laguna Chascomús, Argentina)

We study the underwater light field seasonality in a turbid lake, Laguna Chascomús (Buenos Aires, Argentina). We report (1) relationships between optical properties (OPs) and optically active substances (OASs); (2) relationships between inherent (IOPs) and apparent (AOPs) optical properties; and (3) the seasonal variability in OASs and OPs. Light absorption was dominated by the particulate fraction. The contributions of phytoplankton pigments and unpigmented components were similar. The best predictors of total particulate absorption, unpigmented particulate absorption, turbidity and vertical attenuation coefficient were total suspended solids or their ash content. Many OASs and OPs varied seasonally. The concentrations of OASs were higher during spring and summer, resulting in lower transparency and higher turbidity. However, mass‐specific absorption coefficients displayed lower values during spring and summer. Thus, the higher light attenuation observed during spring and summer resulted from higher concentrations of relatively less absorptive OASs. Collectively, these results suggest that: (1) light extinction is enhanced during spring and summer; (2) the enhanced light extinction is due to changes in the particulate fraction; (3) the enhanced light extinction is mostly due to an increase in the amount of particulate material; and (4) the increase of particulate matter also enhanced light extinction through increased scattering.

Planktonic ciliates from an oligotrophic South Andean lake, Morenito Lake (Patagonia, Argentina)

In this contribution we have studied the planktonic ciliates from Morenito Lake, an oligotrophic lake situated in the South Andes of Argentina. Six species that are new records for South America or Argentina are described and illustrated. Besides, population dynamics of the ciliate species were studied during a spring-summer period. Strobilidium lacustris and Balanion planctonicum were the most abundant species, showing a maximum in mid summer. Paradileptus elephantinus was present all over the period while Urotricha furcata was observed in late summer samples. Strobilidium lacustris and S. humile were found to be occasional species during the studied period. The recorded ciliate assemblage with oligotrichs and prostomates as dominant indicate the oligotrophic condition of the lake.

The relationship between light attenuation, chlorophyll a and total suspended solids in a Southern Andes glacial lake

The light climate of oligotrophic lakes is normally characterised by high transparency, leading to deep euphotic zones. However, inputs of allochthonous particles to oligotrophic lakes can affect verticallight attenuation, and, consequently, influence phytoplankton communities. Glacial lakes frequently receive inputs o f finely ground rock particles of glacial origin; thus, upper glaciallakes often have a grey o r whitish appearance. In contrast, the lower lakes in a series of glaciallakes can be blue because all partides have settled out of the water column.

Optical properties of highly turbid shallow lakes with contrasting turbidity origins: the ecological and water management implications.

A comprehensive optical study of three highly turbid shallow lakes was presented. The lakes contained very high concentrations of optically active substances [OASs] with clear differences in total suspended solid [TSS] composition among them. Lakes presented elevated values of total absorption [at(λ)] and scattering coefficients [b(λ)], which translated into extremely high light attenuation coefficients [Kd(PAR)]. Differences among lakes in the estimation of Kd(PAR), using two typical estimators of light penetration (i.e., nephelometric turbidity [Tn] and Secchi disk [ZSD]), were analysed. Kirks optical model was used to model Kd(PAR) using inherent optical properties [IOPs]. Modelled values of Kd(PAR) agreed very well with those measured (R(2) = 0.95). In addition, optical properties and Kirks model were used to determine water quality targets for restoring submerged aquatic vegetation [SAV]. Based on a minimum light requirement for SAV of 10%, results showed that only an integrative remediation action, considering substantial reduction of TSS and Chl a (95%), and CDOM (50%), must be contemplated to improve maximum colonization depth for SAV to values higher than 0.7 m. On the other hand, phytoplankton absorptive characteristics were also studied. In these lakes, phytoplankton showed different responses to the nature of light competition. Some of the variation in specific phytoplankton absorption [aph(*)(λ)] was explained by differences in the ratio between unpigmented particulate absorption and phytoplankton absorption (up to R(2) = 0.48 for the blue band). Hydrologic optical results were discussed in terms of ecological and management implications.

CDOM and the underwater light climate in two shallow North Patagonian lakes: evaluating the effects on nano and microphytoplankton community structure

We performed an annual synchronous sampling in two oligotrophic shallow lakes to assess the influence of chromophoric dissolved organic matter (CDOM) on the underwater light climate, and its potential effects on the nano and microphytoplankton community structure. Lake Escondido showed higher CDOM concentration and light attenuation with a spectral composition of underwater light shifted towards green–yellow light, while Lake Morenito presented clearer waters and a dominance of green light. Temporal dynamics of CDOM absorption at 440xa0nm were consistently explained by differences in cumulative precipitation. Mixotrophic cryptophytes and chrysophytes dominated the phytoplankton of both lakes, although the prevalence of each algal group was different between lakes. The dominance of these groups was largely explained by differences in spectral composition of underwater light, estimated as the ratio between Kd(RED) and Kd(GREEN) [Kd(R)/Kd(G) ratio]. Cryptophytes prevailed in Lake Morenito and their biomass showed a positive strong relationship with Kd(R)/Kd(G) ratio. Chrysophyte biomass was comparatively more important in Lake Escondido showing an opposite relationship with the Kd(R)/Kd(G) ratio. These results underscore that higher relative green light availability allowed the dominance of cryptophytes, while changes in light spectral composition driven by CDOM allowed coexistence. We suggest that nano and microphytoplankton community structure in these lakes could be driven by changes in spectral composition of underwater light shaped by differences in CDOM, ultimately determined by precipitation/hydrological patterns.

Microbial abundance patterns along a transparency gradient suggest a weak coupling between heterotrophic bacteria and flagellates in eutrophic shallow Pampean lakes

The aim of this work was to study the components of the microbial food web and the degree of coupling between heterotrophic bacteria (HB) and heterotrophic flagellates (HF) in different shallow lakes of the Pampa Plain over a wide range of water transparency and nutrient levels. We hypothesized that not all microorganisms (i.e., HB, HF) equally increase with nutrient levels, thus, resulting in a weaker degree of coupling between HB and HF in more eutrophic waters. During the spring–summer 2009–2011, we sampled 40 Pampean lakes situated in different watershed of Buenos Aires Province. Abundances of most microbial components were very high, even higher than those reported in the literature. HB as well as picocyanobacteria (Pcy) increases with trophic state, while no clear relationship was found between protist (HF or ciliates) and Chl-a concentrations or nutrient levels. Photosynthetic picoplankton was generally dominated by phycocyanin-rich Pcy. Lakes with high HB and low HF were abundant, which suggest these components were weakly coupled. Based on the abundance of microorganisms, we do not accumulate enough evidence to segregate Pampean lakes into two discrete groups (clear vs turbid).