Elevated Magnesium Concentrations Altered Freshwater Assemblage Structures in a Mesocosm Experiment

Abstract

Magnesium (Mg) is a mining-related contaminant in the Alligators Rivers Region of tropical northern Australia. A mesocosm experiment was used to assess Mg toxicity to aquatic freshwater assemblages. Twenty-five 2700-L tubs were arranged, stratified randomly, on the bed of Magela Creek, a seasonally flowing, sandy stream channel in the Alligator Rivers Region of northern Australia. The experiment comprised 5 replicates of 4 nominal Mg treatments, 2.5, 7.5, 23, and 68 mg L −1 , and a control. Phytoplankton biomass, and diatom, zooplankton, and macroinvertebrate assemblages present in the treatment tubs were sampled before and after Mg addition. A significant negative relationship between phytoplankton biomass and Mg was observed 4 wk after Mg addition as measured by chlorophyll a concentrations (r 2 = 0.97, p = 0.01). This result was supported by reductions in some major phytoplankton groups in response to increasing Mg concentrations, in the same experiment and from independent field studies. There was a significant negative relationship between zooplankton assemblage similarity (to control) and Mg concentrations (r 2 = 0.96, p = 0.002). Seven weeks after Mg addition, macroinvertebrate assemblages were dominated by 3 microcrustacean groups (Ostracoda, Cladocera, and Copepoda), each reaching maximum abundance at intermediate Mg concentrations (i.e., unimodal responses). The responses of phytoplankton and zooplankton were used to derive assemblage effect concentrations (Mg concentrations resulting in x% of the assemblage change [ECx]). Magnesium concentrations resulting in assemblage EC01 values were <3 mg L −1. Together with candidate guideline values from other laboratory-and field-based lines of evidence, the mesocosm EC01 values were incorporated into a weight-of-evidence framework for a robust regulatory approach to environmental protection.

Long-Term Survivability of Tardigrade Paramacrobiotus experimentalis (Eutardigrada) at Increased Magnesium Perchlorate Levels: Implications for Astrobiological Research

“…experimentalis as a model species for Martian research. Importantly, it cannot be excluded that the toxicity observed in the present study partially resulted from the elevated magnesium concentration and not only from the action of perchlorate ion, as elevated levels of this element have been shown to affect freshwater invertebrates adversely [ 46 , 47 ]. Nevertheless, Martian regolith contains perchlorate in the form of salts, including magnesium perchlorate [ 4 , 6 ].…”

Application of a vulnerability assessment framework to assess environmental risks of solutes at Ranger Mine, Northern Territory, Australia

“…Under the baseline closure strategy there is a high likelihood that the persistent elevated Mg concentrations would have ongoing, direct effects to sensitive phytoplankton and invertebrate species, resulting in long-term changes to community structure relative to reference sites. This is supported by operational phase monitoring results, with high Mg concentrations at CB coinciding with alterations in macroinvertebrate, zooplankton, phytoplankton and fish communities (Humphrey & Chandler 2018;Mooney et al 2020). The changes observed at CB during the operational phase may be a response to multiple stressors (i.e.…”

Freshwater salinisation: a research agenda for a saltier world

“…Composition and relative ion concentrations Salinisation effects depend on ion composition and concentrations, both in terms of background salinity and the 'chemical cocktails' of ions created by anthropogenic activities [14,45]. The combination of different ions (e.g., Na + , K + , Cl -, CO 3 2-, SO 4 2-) and the mobilisation of other elements or ions (e.g., Cu, Mn, Zn, Sr, NH 4+ , PO 4 3-) can lead to extremely different and complex habitat-specific consequences [10,14,46]. The interrelationships between these consequences and the chemical, biological, and geological properties of an environment are termed the freshwater salinisation syndrome [10,14].…”