Salinity and temperature increase impact groundwater crustaceans

Abstract

Anthropogenic impacts in groundwater ecosystems remain poorly known. climate change is omnipresent, while groundwater salinization poses serious long-term environmental problems in arid and semi-arid regions, and is exacerbated by global warming. Both are present threats to the conservation of groundwater ecosystems, which harbour highly specialized species, with peculiar traits and limited geographic distributions. We tested the temperature and salinity tolerance of groundwater-adapted invertebrates to understand the effect of global warming and salinization in groundwater ecosystems. We used species representative of groundwater-adapted crustaceans: two copepods (harpacticoid and cyclopoid) and one syncarid, endemic to Australia. our results show that 50% of the populations died at salt concentrations between 2.84 to 7.35 g NaCl/L after 96 h, and at 6.9 °C above the ambient aquifer temperature for copepods and more than 10 °C for syncarids. Both copepods were more sensitive to temperature and NaCl than the syncarid. We calculated a salinity risk quotient of 9.7 and predicted the risk of loss of 10% of syncarid and 20% of copepod population abundances under a worst-case scenario of global warming predictions for 2070. These results highlight that both salinity and temperature increases pose a risk to the ecological integrity of groundwater ecosystems. Groundwater comprises 97% of the freshwater global resources available for direct human consumption 1. It harbours a unique ecosystem, composed of groundwater-adapted species, mostly crustaceans, which provide ecosystem functions linked with nutrient recycling and water purification 2. The biota, and their ecosystem services, are under increasing threat from anthropogenic activities causing changes to the aquifer environment 3. Salinization is a process in which the mobilization and/or fractionation of salts causes an increase salt concentration in water and soils 4. Human activities can induce salinization of groundwater in multiple ways, such as seawater intrusion into coastal aquifers caused by rising sea levels and excessive groundwater pumping 5,6 , inland salinization caused by rising and lowering the water tables through saline sediment layers 4 or by direct salt application, e.g., to prevent ice formation on roads 7. Salinization processes associated with human activities are notably intensified in arid and semi-arid regions which, at the same time, are expected to be very sensitive to climate change effects, particularly, increased temperatures due to global warming 8,9. Australia has the world's highest proportion of salt-affected soils, and with that, the sum of salts in groundwaters reach as high as 19.32 g/L 10,11 (sea salt concentrations around 30 g/L 10). Large increases in salinity (e.g., EC ranged from 7,000 to 27,000 µS/cm or 600 to 17,000 µS/cm) have been observed over the last 50 years, especially in shallow aquifers 11. High salinities in some parts of Australia are due to the geological history of the continent, much of which was subject to pe...

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