Enrique Muñoz-Arcos

Wetlands are delicate ecosystems that host diverse species and face ongoing environmental stress. The “Carlos Anwandter” Ramsar Site in Valdivia, Chile, is the world’s main breeding ground for the black-necked swan, which strongly relies on the aquatic plant Egeria densa. This area has been impacted by anthropogenic activities that have increased particulate iron (Fe) and zinc (Zn) deposition. However, standard protocols for metal analysis encourage eliminating any particles on the plant’s surface, neglecting the contribution of deposited particulate contaminants. Appropriate sample treatment is therefore essential to quantify metal concentrations and the potential impact on herbivore species. This study aimed to evaluate how sample treatments and plant sectioning affect Fe and Zn concentrations in E. densa. Samples were collected from both the Ramsar site (Cruces River) and a control site (Calle-Calle River). Results showed that washing samples (both in the field and lab) significantly reduced reported metal concentrations, underscoring the importance of standardised sampling and pre-treatment protocols. Fe concentrations were notably higher at the Ramsar site (11,155 mg kg⁻¹) compared to the control (3783 mg kg⁻¹). The same is true for Zn (108 mg kg⁻¹ and 60 mg kg⁻¹, respectively). Over time, Fe concentrations remained stable, while Zn concentrations declined, suggesting a consistent Fe input and a decreasing Zn trend in the wetland. These findings are crucial for interpreting metal pollution and understanding spatial–temporal variability in aquatic plant contamination.

Wetlands are delicate ecosystems that host diverse species and face ongoing environmental stress. The “Carlos Anwandter” Ramsar Site in Valdivia, Chile, is the world’s main breeding ground for the black-necked swan, which strongly relies on the aquatic plant Egeria densa. This plant has been impacted by deposition of particulate iron (Fe) and zinc (Zn). However, current methodological approaches typically remove particulate matter during sample pre-treatment through washing, following agricultural plant-tissue protocols. This study aimed to evaluate how sample treatments and plant sectioning affect Fe and Zn concentrations in E. densa. Samples were collected from both the Ramsar site (Cruces River) and a control site (Calle-Calle River). Results showed that washing samples (both in the field and lab) significantly reduced reported metal concentrations, underscoring the importance of standardized sampling and pre-treatment protocols. Fe concentrations were notably higher at the Ramsar site (11,155 mg kg^-1) compared to the control (3,783 mg kg^-1). The same is true for Zn (108 mg kg^-1 and 60 mg kg^-1, respectively). Over time, Fe concentrations remained stable, while Zn concentrations declined, suggesting a consistent Fe input and a decreasing Zn trend in the wetland. These findings are crucial for interpreting metal pollution and understanding spatial-temporal variability in aquatic plant contamination.

Wetlands are fragile ecosystems that support diverse habitats and are under constant environmental pressure. The "Carlos Anwandter" Ramsar Site located in Valdivia, Chile, is home to many waterfowl species, and it is the main reproductive site for black-necked swan in the world. The main food source for these swans, Egeria densa , has been affected by sediment deposits with high iron (Fe) and zinc (Zn) concentrations, however the methodology for the evaluation of such concentrations has not been standardised. In fact, results obtained from commercial labs showed significant differences in metal concentrations highlighting the need to develop better assessment protocols for improved reproducibility and comparability of metal content in aquatic plants. The study aimed to understand the effects of different sample treatments and plant section subsampling on Fe and Zn concentrations in E. densa . To address this aim, samples were collected at the Ramsar site and a control site. Results indicated that washing the samples in the field and in the laboratory significantly reduced reported Fe and Zn concentrations. These findings highlighted the need for stablishing standard protocols for sampling and sample pre-treatment and their influence in interpreting metal pollution.

This chapter provides an overview of nuclear tools used in sediment source apportionment studies, summarising essential information about the use of fallout radionuclides, elemental geochemistry, and compound-specific stable isotopes. Exemplar studies are described to show how the method can inform decision making at farm and basin scales to control diffuse water pollution by agriculture.

Fine sediment plays an important role in the healthy functioning of river ecosystems providing nutrients and contributing to habitat functioning. However, excessive sediment supply into rivers has several detrimental impacts on water quality and it causes sedimentation in river channels, reservoirs and estuaries. In addition, silts and clays are geochemically active and consequently are responsible for the transport of contaminants, including trace metals, phosphorus, pesticides and radionuclides among others which have high sorptive affinity for fine-grained particles. Hence, quantifying the timescales of sediment transfer throughout a river system is critical for understanding river basin sediment dynamics and the fate of their associated pollutants.Fallout radionuclides (7Be, 210Pbex and 137Cs) have been used to assess sediment travel distances, sediment age and sediment residence times in a variety of landscapes. An advantage of using these radionuclides as sediment chronometers is their half-lives which can be used to model sediment residence time from days to decades in different catchment compartments.The River Avon (Devon, UK) is a 40 km long gravel-bed river, draining rough moorland and with a catchment area of 110 km2. The mean annual flow is 3.7 m3 s-1 and is moderated by managed discharges from a reservoir upstream. Suspended and channel bed sediments were sampled in a 5 km section of the river during four seasonal surveys (January, March, July and November 2022) and suspended sediments during a stormflow event were also sampled.Radionuclide activity concentrations of channel deposited sediments varied substantially within and between river bars and seasonally. Suspended sediment activity concentrations varied within the stormflow hydrograph and seasonally. Relationships between radionuclide activity concentrations and sediment storage, particle size, total organic carbon and C:N ratios were also evaluated. Channel sediment residence times obtained using 7Be/210Pbex activity ratios ranged between 0 to 110 days, reproducing the high variability found in activity concentrations. Future research will assess the influence of sediment sources on 7Be/210Pbex ratios and the relationship between sediment storage dynamics and sediment-bound contaminants. Sediment residence time modelling will allow an improved understanding of sediment dynamics in gravel-bed rivers which is essential to inform management decisions and prediction of the timescales of transfer and fate of associated contaminants.