Are UK Rivers Getting Saltier and More Alkaline?

Abstract

River salinisation and alkalinisation have become one of the major environmental problems threatening the safety of global freshwater resources. With the accelerated climate change and aggravating anthropogenic influences, it is important to identify the trends and causes of river salinisation and alkalinisation so that better mitigation measures could be taken. This study has focused on the UK rivers because there has been insufficient investigation on this topic. To understand the salinisation and alkalinisation trends and causes of rivers in the UK over the past 20 years from a vertical (analysis of each river) and horizontal (comparison of all rivers) perspective, this study uses the Theil-Sen regression and Mann-Kendall test to deal with the trends of conductivity (proxy on salinisation) and pH (proxy on alkalinisation), obtains outliers of conductivity and pH by boxplot, and calculates the Pearson’s and the Kendall’s Tau correlation coefficients (α = 0.05) between the water quality data and the potential factors (potential road salting, normalized difference vegetation index (NDVI), river discharge, agricultural and urban lands). The results show that the UK rivers are becoming more alkaline with a median pH increase of 0.05 to 0.40, but less salty with a median conductivity decrease of 0.06 to 0.11 mS/cm. And the changes in conductivity and pH have seasonality and regionality, which shows that there are usually greater changes in trends and medians of them in winter or through reaches with more anthropogenic disturbance. Furthermore, from a vertical perspective, the conductivity of more than 50% of rivers in this study is negatively correlated with NDVI and river discharge, and positively correlated with potential road salting, and the pH of that is positively correlated with agricultural lands. While from a horizontal perspective, NDVI and agricultural lands are positively correlated with pH, and potential road salting and urban lands are positively correlated with conductivity. Therefore, road salting, urbanisation, agricultural lands, river discharge and vegetation cover can be considered to affect river salinisation and alkalinisation in the UK.

Pyridinium-furfuryl-modified granular agro-waste adsorbent for orthophosphate recovery

“…For the case of aqueous media in many river systems, pH conditions reside near 7-8, where anion adsorption by chitosan can become attenuated or negligible. 24,25 While chemical crosslinking addresses the aforementioned low mechanical strength and improves hydrostatic resilience, this introduces lower active site accessibility for adsorption and restricts expansion of the polymer network. Therefore reducing the adsorption capacity of the crosslinked composites.…”

“…For the case of aqueous media in many river systems, pH conditions reside near 7–8, where anion adsorption by chitosan can become attenuated or negligible. 24,25…”

A pyridinium-modified chitosan-based adsorbent for arsenic removal via a coagulation-like methodology

“…22 However, arsenic removal studies via chitosan-based adsorbents are limited by its pK a (ca. 6.5), where chitosan's arsenic removal efficacy drastically decreases at pH > 6, [23][24][25][26][27] where acidic conditions (pH < 6) are required for optimum uptake. 21 However, this is in contrast with the regularly encountered pH of natural water sources such as ground water with slightly alkaline pH conditions (ca.…”

“…pH 7-8). 26 Optimal chitosan-based adsorbents should be designed to obviate pH adjustments to afford more efficient water treatment. One such example for removal at pH 7 can be found in chitosan-loaded MgAl layered double hydroxides.…”

The use of zebrafish to assess water quality and remediation efforts.

“…This highlights the need for more efficient removal of pollutants from the aquatic environment since pollutants in different industries can be dispersed into localized water environments, potentially forming a considerable portion of wastewater that was seen to cause deformities in zebrafish in the present study. The acidification and alkalinisation of water systems as a result of climate change and other anthropogenic practices has become one of the serious environmental concerns globally (Oberholster et al,2017;Van Niekerk et al,2022;Jiang et al,2022). Acid rain and chemical waste pollution can cause the decrease of local fish population by shifting the natural water pH to acidic.…”