Suitability of phytoliths as a quantitative process tracer for soil erosion studies

<p>Phytoliths are a plant microfossil commonly used as qualitative archive markers in archaeological and paleoecological studies. Their potential uniqueness to the vegetation cover, robustness to weathering, and lack of chemical alteration along the paths make them a potentially suitable tracer for quantitative erosion studies.<br>In this pilot study, we explore the potential of phytoliths in a sediment fingerprinting study in the Ceguera catchment (28 km2) in NE Spain. The phytolith concentrations and morphologies of four land cover classes (agricultural land, badland, forest, and shrubland) were analyzed, and their contributions to four sediment mixture samples along the river course were modelled. Phytoliths concentrations allowed us to discriminate sources sufficiently, albeit with limited sample size. The performance of the phytoliths as the tracer was tested by reproducing the sources of artificial sediment mixture samples with satisfactory recall ratio. Results identified badlands to be the main contributor, with 84–96% of the sediment load to the sinks, followed by shrublands (median 5%) and agricultural lands (median 2%). Additionally, an intensively used agricultural area in the SW of the catchment was well indicated. These major findings can be reproduced by other conventional erosion studies from this area, indicating that phytoliths are suited to quantifying erosion patterns in mesoscale catchments.</p>

The Study of Phosphate Release from Artificial Sediment into Water Body Using Diffusive Gradient in Thin Film (DGT) Device in Oxic Condition

The phenomenon of phosphate release in sediments into water bodies under oxic environment has been investigated using the Diffusive Gradient in Thin Film (DGT) technique. This research consists of several stages: polymer synthesis and DGT probe assembly, sediment sampling, DGT deployment in oxic conditions, and phosphate analysis from DGT adsorption results. Acrylamide polymer was successfully synthesized with a composition 15% acrylamide; N-N'-methylenebisacrylamide 0.1% and ferrihydrite as binding gels. DGT probes were assembly by placing a 16 x 3.2 cm polyacrylamide gel, binding gels and filter membranes on the DGT probes. The sediment sample was taken from the Bogor Botanical Gardens at the coordinates 6°36’00.6” S; 106°47’51.0” E. The DGT probe was placed in sediment samples for 1, 3 and 7 days in oxic conditions. After the prescribed time, the binding gel was removed and cut every 1 cm depth, then eluted using 0.25 M H2SO4 and the phosphate concentration was measured using spectrophotometry method. The results showed that the phosphate concentration tends to be higher with the increasing incubation time and depth. Maximum CDGT phosphate released on day 1, day 3 and day 7 were 1.00 µg/L at a depth of 14 cm, 6.61 µg/L at a depth of 14 cm, and 20.92 µg/L at a depth of 11 cm respectively. This ensures that the phosphate in water bodies comes from biogeochemical processes that occur in sediments and is successfully measured through DGT techniques.

Geomorphic effects of gravel augmentation on the Old Rhine River downstream from the Kembs dam (France, Germany)

During the last 30 years, river restoration activities aiming to improve the functionality of degraded fluvial ecosystems increased markedly. For large rivers, it remains difficult to evaluate restoration efficiency and sustainability due to the lack of standardized monitoring metrics. From 2010 to 2016, three gravel augmentations were performed on the Old Rhine, a by-passed reach downstream from the Kembs dam (France- Germany). A geomorphic monitoring combining topo-bathymetric surveys, bedload tracking and hydraulic modelling allows to evaluate the successfulness of these actions. Results show that, to be mobilized, artificial sediment deposit should be located in concavity rather than convexity areas, due to higher shear stresses for moderate floods (Q2). Sediment starvation appeared rapidly on the restored reaches once the sediment wave moved downstream, as a consequence of limited upstream sediment supply. Bathymetric homogenization was observed along and downstream from the restored reaches without creation of new fluvial forms. This research highlights that future actions should include channel enlargement downstream of gravel augmentations, which would promote sediment deposition and habitat diversification. Sediments excavated during artificial widening could be stored and injected progressively into the upstream part of the Old Rhine to benefit the downstream sections.

Single-walled carbon nanotubes toxicity to the freshwater amphipod Hyalella azteca: influence of sediment and exposure duration

Carbon nanomaterials are present in various industrial applications and therefore their release into the environment including freshwater ecosystem is expected to increase. The aim of the present study was to investigate the influence of several parameters on the toxicity of single-walled carbon nanotubes (SWCNT) to the freshwater amphipod, <em>Hyalella</em> <em>azteca</em>. The effect of period of exposure, sediment presence and possible impurities released during SWCNT preparation on survival and/or growth of such organism was evaluated. We measured a reduction of survival at concentrations ranging from 10 to 40 mg/L after 96-h exposure, while no mortality was observed with the same concentrations and in the presence of artificial sediment after 14 days of exposure. It is possible that SWCNT are adsorbed on the organic matter from the artificial sediment leading to a decrease of SWCNT bioavailability. The survival and growth toxicity tests revealed a stronger effect at 28 days compared to the 14 days of exposure, and full mortality of organisms at 1000 mg/L for both exposure times. The presence of SWCNT in the gut of survived organisms was observed. The present study demonstrates that the interaction with sediment should be considered when carbon nanotubes toxicity through water exposure is investigated.