Bridging gaps across macronutrient cycles

Effects of an aluminum-based chemical remediator on the cyanobacteria population: a study in the northeast of Brazil

Water sources destined to human supply are increasingly threatened worldwide due to various sources of pollution, either point or diffuse. In this sense, the objective of this work was to evaluate the efficiency of an aluminum-based chemical remediator in the Joanes River. An statistical analysis of physical, chemical, biological, and hydraulic monitoring data was performed relying on a 2013-2018 recording period, provided by the local sanitation service provider and the environmental agency. The results showed that even with the use of aluminum-based chemical remediators, the key parameters for controlling flowering events remained high with mean values of 0.18 mg P L^-1, 176.155 cells mL^-1 of cyanobacteria and peaks of 1.56 μg L^-1 and 4.02 μg L^-1 for microcystin and saxitoxin, respectively. At the end of this study, it was verified that the aluminum-based chemical remediator showed low effectiveness in the reduction of phosphorus and cyanobacteria, opposing to expectations of the sanitation provider.

Phosphorus and nitrogen limitation and impairment of headwater streams relative to rivers in Great Britain: A national perspective on eutrophication

This study provides a first national-scale assessment of the nutrient status of British headwater streams within the wider river network, by joint analysis of the national Countryside Survey Headwater Stream and Harmonised River Monitoring Scheme datasets. We apply a novel Nutrient Limitation Assessment methodology to explore the extent to which nutrients may potentially limit primary production in headwater streams and rivers, by coupling ternary assessment of nitrogen (N), phosphorus (P), and carbon (C) depletion, with N:P stoichiometry, and threshold P and N concentrations. P limitation was more commonly seen in the rivers, with greater prevalence of N limitation in the headwater streams. High levels of potential P and N co-limitation were found in the headwater streams, especially the Upland-Low-Alkalinity streams. This suggests that managing both P and N inputs may be needed to minimise risks of degradation of these sensitive headwater stream environments. Although localised nutrient impairment of headwater streams can occur, there were markedly lower rates of P and N impairment of headwater streams relative to downstream rivers at the national scale. Nutrient source contributions, relative to hydrological dilution, increased with catchment scale, corresponding with increases in the extent of agricultural and urban land-use. The estimated nutrient reductions needed to achieve compliance with Water Framework Directive standards, and to reach limiting concentrations, were greatest for the Lowland-High-Alkalinity rivers and streams. Preliminary assessments suggest that reducing P concentrations in the Lowland-High-Alkalinity headwater streams, and N concentrations in the Upland-Low-Alkalinity rivers, might offer greater overall benefits for water-quality remediation at the national scale, relative to the magnitude of nutrient reductions required. This approach could help inform the prioritisation of nutrient remediation, as part of a directional approach to water quality management based on closing the gaps between current and target nutrient concentrations.