Carlos Bonetto

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.

Insecticide toxicity to Hyalella curvispina in runoff and stream water within a soybean farm (Buenos Aires, Argentina)

Toxicity to the locally dominant amphipod Hyalella curvispina was assessed in a first-order stream running through a cultivated farm. Cypermethrin, chlorpyrifos, endosulfan and glyphosate were sprayed throughout the studied period. Toxicity was assayed under controlled laboratory conditions with runoff and stream water samples taken from the field under steady state and flood conditions. Ephemeral toxicity pulses were observed as a consequence of farm pesticide applications. After pesticide application, runoff water showed 100% mortality to H. curvispina for 1 month, but no mortality thereafter. Toxicity persistence was shortest in stream water, intermediate in stream sediments and longest in soil samples. Runoff had a more important toxicity effect than the exposure to direct aerial fumigation. The regional environmental features determining fast toxicity dissipation are discussed.

Litter decomposition of emergent macrophytes in a floodplain marsh of the Lower Paraná River

Abstract The role of litter decomposition on organic matter accumulation and nutrient cycling was studied in a floodplain marsh of the Lower Parana River by means of in situ litterbag experiments. The effect of waterborne nutrients on decomposition rates was studied through a laboratory litterbag experiment. Litter decomposition was rather slow, remaining 40–50% of the initial mass after 2 years incubation. Similar decomposition rates were observed in laboratory and field experiments. Water fertilization did not significantly affect decomposition rates. Since organic matter production is faster than decomposition a net accumulation takes place in the upper layers of the marsh soil. N and P litter concentration increased during the decomposition experiment. Floodplain marshes represent effective sinks of nutrients through litter accumulation.

Factors influencing biomass and nutrient content of the submersed macrophyte Egeria densa Planch. in a pampasic stream

We identified factors influencing biomass and nutrient content in E. densa in an enriched pampean stream of Argentina. Physical (current velocity, temperature), chemical (pH, conductivity, dissolved oxygen, nutrient content in water and sediments), and biological variables (biomass and nutrient content of E. densa, biomass of periphyton and other macrophytes) were estimated at each sampling occasion, and mean monthly values estimated. Biomass and nutrient content in E. densa were correlated with these physical-chemical and biological variables. Biomass was positively correlated with ammonium in stream water (P<0.05) and sediment total nitrogen (P<0.01). Nitrogen showed a positive relationship with ammonium (P<0.01), and a negative one with nitrate and periphyton biomass (P<0.05). Phosphorus was positively correlated with soluble reactive phosphorus (P<0.01). The growth of other macrophyte species in the stream seemed to influence E. densa biomass, probably through competition for light. Current velocity was low and not significantly related with E. densa biomass, however, a flood at the beginning of the study washed the macrophyte stand downstream.

The nitrogen cycle in shallow water sediment systems of rice fields. Part 1: The denitrification process

Denitrification causes important losses of N-fertilizer in rice-fields, where high temperature and high production of organic matter favour denitrification losses. Two techniques have been used to quantify the denitrification losses: the 15N technique, which can be used to quantify the amount finally incorporated, and the acetylyne inhibition technique which is a direct measure of the quantities lost.Both techniques were applied in enclosures (diameter = 44 cm) in the field while moreover bio-assays in 3 l glass beakers were carried out. In all experiments where nitrate was added we found a rapid decrease of nitrate; usually about 30–50% of the nitrate that disappeared was recovered as N2O. As in one experiment, in which we measured the N2O disappearance rate as well, the N2O itself decreased at a rather constant rate of 20% per day, a correction must be made for this N2O decrease in the calculations of the nitrate disappearance rate. Although we have only one series in which the decrease of N2O was measured, the mathematical analysis indicates that as much as 80% of the N-fertilizer is actually lost. This figure is in full agreement with the 15N experiments; if the 15N was applied early only about 7% was recovered in soil and plants, while if it was applied later (after 7 weeks) about 20% was incorporated.Denitrification rate could be fitted on an negative exponential regression line; the rate constant increased during the summer. It is suggested that organic matter caused this increase.During denitrification considerable quantities of nitrite appear, which later on disappear again by processes still unknown; the nature of the available organic matter may be important for this nitrite production.With N-serve we tried to inhibit NH3 oxidation. In this way we tried to prevent the considerable N losses and to demonstrate that the nitrite produced in our experiments was not derived from NH3 oxidation. N-serve, however, had very little influence. It is probably inactivated by absorption onto the sediments.From these results it is suggested that the efficiency of N-application may be considerably increased by using low doses of N-fertilizer, but applied late in the growing season, e.g. 7 weeks after sowing. This favours environmental protection as well.

Insecticide concentrations in stream sediments of soy production regions of South America.

Concentrations of 17 insecticides were measured in sediments collected from 53 streams in soy production regions of South America (Argentina in 2011-2014, Paraguay and Brazil in 2013) during peak application periods. Although environmental regulations are quite different in each country, commonly used insecticides were detected at high frequencies in all regions. Maximum concentrations (and detection frequencies) for each sampling event ranged from: 1.2-7.4 ng/g dw chlorpyrifos (56-100%); 0.9-8.3 ng/g dw cypermethrin (20-100%); 0.42-16.6 ng/g dw lambda-cyhalothrin (60-100%); and, 0.49-2.1 ng/g dw endosulfan (13-100%). Other pyrethroids were detected less frequently. Banned organochlorines were most frequently detected in Brazil. In all countries, cypermethrin and/or lambda-cyhalothrin toxic units (TUs), based on Hyalella azteca LC50 bioassays, were occasionally>0.5 (indicating likely acute toxicity), while TUs for other insecticides were <0.5. All samples with total insecticide TU>1 were collected from streams with riparian buffer width<20 m. A multiple regression analysis that included five landscape and habitat predictor variables for the Brazilian streams examined indicated that buffer width was the most important predictor variable in explaining total insecticide TU values. While Brazil and Paraguay require forested stream buffers, there were no such regulations in the Argentine pampas, where buffer widths were smaller. Multiple insecticides were found in almost all stream sediment samples in intensive soy production regions, with pyrethroids most often occurring at acutely toxic concentrations, and the greatest potential for insecticide toxicity occurring in streams with minimum buffer width<20 m.

Cd, Cu and Zn concentrations in sediments and the invasive bivalves Limnoperna fortunei and Corbicula fluminea at the Río de la Plata basin, Argentina

Cd, Cu and Zn content in sediments and bivalves (Limnoperna fortunei and Corbicula fluminea) were studied in the lower 500 km stretch of the Paraná River and in the right margin of the Río de la Plata Estuary. Both bivalves species showed higher metal contents at the Paraná River, possibly related to water chemistry. The Paraná water is circumneutral and soft, while the Río de la Plata coastal water is alkaline, hard, with a higher organic content. Bivalves sampled at the thermal effluent of the Atucha Nuclear Power Plant, at the Paraná River, showed the highest metal content, either from increased absorption at the higher water temperatures (12 °C higher than the river water) or from metal corrosion of the power plant cooling system. L. fortunei and C. fluminea appeared to be successful biomonitor organisms for Cd pollution in the basin, while Cu and Zn content in bivalve tissues was apparently not related to metal load.

Pore water N and P concentration in a floodplain marsh of the Lower Paraná River

Inorganic nitrogen and soluble reactive phosphate (o-P) concentrations were measured in the water of a marsh and in its interstitial water at two sites, and in the river water of a floodplain marsh of the Lower Paraná River. These values were compared with the N and P concentration in sediments and macrophyte biomass in order to assess nutrient availability, fate and storage capacity. High variability was found in the interstitital water using a 1 cm resolution device. Nitrate was never detected in the pore water. Depth averaged NH4+ concentrations in the upper 30 cm layer often ranged from N = 1.5 to 1.8 mg l-1, but showed a pronounced minimum (0.5–0.7 mg l-1), close to (March 95), or relatively soon after (May 94) the end of the macrophyte growing season. Soluble phosphate showed a large variation between P = 0.1–1.1 mg l-1 without any discernible seasonal pattern. NH4+ depletion in the pore water concentration and low N/P ratios (3.7 by weight) within the macrophyte biomass at the end of the growing period suggest that available N limits plant growth. NH4+ and o-P concentrations were 35 and 7 times higher, respectively, in the pore water than in the overlying marsh, suggesting a permanent flux of nutrients from the sediments. o-P accumulate in the marsh leading to higher concentrations than in the incoming river. NH4+ did not accumulate in the marsh, and no significant differences were observed between the river and the marsh water, while the NO3- contributed by the river water was depleted within the marsh, caused probably by coupled nitrification-denitrification at the sediment–water interface. Although an order of magnitude smaller, the pore water pool can supply enough nutrients to build up the macrophyte biomass pool, but only if a fast turnover is attained. The Paraná floodplain marsh retains a large amount of nutrients being stored mainly in the sediment compartment.

Abnormalities in amphibian populations inhabiting agroecosystems in Northeastern Buenos Aires Province, Argentina.

The occurrence of abnormalities in amphibians has been reported in many populations, and its increase could be related to environmental pollution and habitat degradation. We evaluated the type and prevalence of abnormalities in 5 amphibian populations from agroecosystems with different degrees of agricultural disturbance (cultivated and reference areas). We detected 9 types of abnormalities, of which the most frequent were those occurring in limbs. The observed prevalence of abnormality in assessed populations from cultivated and reference areas was as follows: Rhinella fernandezae (37.1 and 10.2%, respectively), Leptodactylus latrans adults (28.1 and 9.2%) and juveniles (32.9 and 15.3%), and Hypsiboas pulchellus (11.6 and 2.8%). Scinax granulatus populations did not show abnormalities. Pseudis minuta, which was only detected in the reference area, exhibited a prevalence of 13.3%. For R. fernandezae, L. latrans, and H. pulchellus, generalized linear mixed models showed that prevalence of abnormalities was significantly higher (p < 0.05) in cultivated than in reference areas. L. latrans juveniles were more vulnerable to abnormalities than adults (p < 0.05). The presence of abnormalities in some species inhabiting different agroecosystems suggests that environmental stress factors might be responsible for their occurrence. While we detected pesticides (endosulfan, cypermethrin, and chlorpyrifos) and lower dissolved oxygen levels in ponds of the cultivated area, no data are currently available on how other factors, such as injuries from predators and parasite infections, vary by land use. Further research will be necessary to evaluate possible causes of abnormalities detected in the present study mainly in the context of factor interactions.

Trace metal concentrations in coastal marshes of the Lower Paraná River and the Río de la Plata Estuary

Cu, Cr, Pb, Zn and Fe in water, sediment and tissue of the emergent macrophyte Schoenoplectus californicus were studied in three coastal environments differing in aquatic chemistry and tide amplitude: a deltaic floodplain marsh, a coastal vegetated strip of the river and a tidal marsh at the south margin of the Río de la Plata Estuary. Metal content in water was not significantly different between the river and the floodplain marsh. Metal content in sediments showed higher values in the marshes than in the river, suggesting a retention in the marsh. Except for Cu, the highest metal content in sediments and water was observed in the tidal marsh. Pb in plants was undetectable. Metal content was higher in rhizomes, except Cr, which was mainly stored in stems. Rhizome metal content was higher in the river, probably related to the higher redox potential of its sediments. Inflorescence metal content was higher in the marshes: the highest Zn, Cr and Fe contents were measured in the tidal marsh; the highest Cu content was in the floodplain marsh, together with the highest organic matter content of the sediments. Zn, Cr and Fe increased in standing drying stems and in inflorescences in late fall. Inflorescences showed the highest metal content after seeds had been released.