Laura de Cabo

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.

Phytoremediation of two types of sediment contaminated with Zn by Schoenoplectus americanus

The effect of different sediments on growth, Zn uptake, Zn plant distribution, and morphometric variables of Schoenoplectus americanus were investigated under controlled conditions. Two types of sediments were assayed: from a large natural levee (LS) and alluvial sediments (AS), the former with lower organic matter (OM) and nutrients content than AS, without and with added Zn (2500 μg Zn/g air-dry sediment). Zinc partition in sediment was determined. Increases in water conductivity and Zn concentrations in water and sediments were observed in artificially contaminated treatments. Plants showed a lower aboveground growth rate, height, and width of shoots, and a higher Zn concentration in shoots and rhizomes. In the contaminated treatments, AS treatment showed lower Zn concentration in water and higher Zn concentration in sediments (total, exchangeable, and OM fractions) than LS treatment, due to Zn displacement from floodwater to sediments. The presence of a high level of OM and nutrients also increased aboveground biomass growth, whereas it decreased Zn concentration in shoots. Although the translocation factor increased with Zn addition, it was lower in AS treatment. Sediments of AS treatments are a suitable environment for growth of S. americanus, which partially compensates the toxic effects of Zn. Our results provide an encouraging basis for planning larger scale experiments to test the role of OM and nutrients in improving phytoremediation.

Measured Copper Toxicity to Cnesterodon decemmaculatus (Pisces: Poeciliidae) and Predicted by Biotic Ligand Model in Pilcomayo River Water: A Step for a Cross-Fish-Species Extrapolation

In order to determine copper toxicity (LC50) to a local species (Cnesterodon decemmaculatus) in the South American Pilcomayo River water and evaluate a cross-fish-species extrapolation of Biotic Ligand Model, a 96 h acute copper toxicity test was performed. The dissolved copper concentrations tested were 0.05, 0.19, 0.39, 0.61, 0.73, 1.01, and 1.42 mg Cu L−1. The 96 h Cu LC50 calculated was 0.655 mg L−1 (0.823 − 0.488). 96-h Cu LC50 predicted by BLM for Pimephales promelas was 0.722 mg L−1. Analysis of the inter-seasonal variation of the main water quality parameters indicates that a higher protective effect of calcium, magnesium, sodium, sulphate, and chloride is expected during the dry season. The very high load of total suspended solids in this river might be a key factor in determining copper distribution between solid and solution phases. A cross-fish-species extrapolation of copper BLM is valid within the water quality parameters and experimental conditions of this toxicity test.

Impact of the Moron stream on water quality of the Reconquista River (Buenos Aires, Argentina)

The Reconquista River basin is located in an urban area where 2.5 10 6 inhabitants and 4,242 industries are settled. The confluence with the Moron stream shows the largest anthropogenic impact. The effect of the Moron stream on the water quality of the Reconquista River was evaluated in relation to its organic, mineral and metal contribution. Bimonthly samplings were carried out in the Reconquista River upstream (GOR), and downstream (SMT) from the confluence with the Moron stream and in the latter (MOR). Dissolved oxygen, pH, conductivity, temperature, transparency, nutrients, major ions, suspended solids, particulate and total organic carbon, Kjeldahl nitrogen, total phosphorus and heavy metals were determined in water samples. Discharge ratios between the Reconquista and Moron streams were estimated based on chloride concentrations. The samplings were ordered from the Principal Component Analysis in: GOR, SMT and MOR according to a growing gradient of organic and mineral contamination. This gradient has a spatial component (related to the discharge point of the Moron stream) and one related with the flow of the Reconquista River. Mean levels of heavy metals were higher than the thresholds for aquatic life protection. The most important were: lead, zinc, copper and mainly chromium, all of them related to industrial activity. Their concentrations responded to an irregular and intermittent discharge. Sometimes, metal levels at SMT and GOR were higher than at MOR, indicating other sources of contamination besides the Moron stream.

Tidal exchange of water between a coastal marsh and the Río de la Plata estuary: the effect on the main physical and chemical variables

At Punta Blanca, a Schoenoplectus californicus marsh of about 1,190 m long and 175 m wide is separated from the Rio de la Plata estuary by a sand bar interrupted at one extreme by a channel through which tidal exchange of water occurs. Water movement in and out the marsh was estimated by installing a water stage height meter and following stage height variations through complete tidal cycles. Incoming river water was sampled twice and outcoming marsh water three times along six tidal cycles, and main physical and chemical variables were determined. The marked decrease of the suspended matter concentration in the outcoming water points out the large retention of sediments by the marsh. Oxygen concentration and water pH decreased in the outcoming water in four over six samplings. Higher concentrations of soluble reactive phosphorus in the outcoming tidal water suggest P release related with riverine suspended matter transformation upon sedimentation, in response to acidification and reduction within the marsh environment. Nitrate impoverishment in the outcoming water suggests denitrification losses. Since ammonium concentration in the outcoming water was larger than in the incoming water, a net flux from the sediments is suggested. Nevertheless, as a result of nitrate depletion and ammonium release, a net loss of inorganic nitrogen took place.