Malta water table ‘fails’ test due to high nitrates

Nitrates mostly derived from agricultural activities such as pesticides have resulted in all of Malta’s groundwater resources now failing to reach good quality status, as required by EU law, recent studies have shown.

All Malta’s underground water sources failed the EU parameters due to nitrates from agriculture, or because too much water is being abstracted out of the underground wells faster than they get charged through rainfall.

Save for the Gozo and Comino mean sea level aquifers, and the Mellieħa perched groundwater body, all of Malta’s groundwater bodies failed quality objectives due to nitrate content in excess of the 50mg per litre limit.

The studies show the limit was surpassed in all other 12 groundwater bodies, including the Malta Mean Sea Water aquifer that spans over 217 square kilometres.

The river basin management plan, which regulates the inland water systems in EU states, assessed each of Malta’s 15 aquifers – bodies of groundwater that are either stored underground, above levels of impermeable rock, or floating above sea water seeping into the rocks.

These perched aquifers are a vital source for irrigation that also provided one-third of the national drinking water supply. Groundwater used for drinking purposes is mixed with desalinated water, to ensure that it is safe to drink.

But the third river basin management plan classified as “poor” all but one of Malta’s 15 aquifers, due to the presence of nitrates – primarily attributed to contamination from agricultural sources.

Additionally, the two most extensive bodies – the Malta and Gozo mean sea level aquifers – which are a freshwater lens floating on sea water, are now losing more water to abstraction, than they are gaining from rainfall. These were classified as having poor quantitative status.

When both quantitative, as well as qualitative assessments are taken in consideration, all of Malta’s aquifers were deemed to be in a poor condition.

Compared to the previous plan published in 2015, no progress in achieving good quality status for any of the aquifers has been achieved. As regards the smaller Pwales and Marfa Coastal groundwater bodies, the main objective remains that of preventing further deterioration in their status.

The plan targeted “good quality” status for most aquifers by 2027, but still acknowledging this could be missed due to the long percolation time for water to enter the aquifer, and other natural conditions.

The current plan admits that while the objective remains that of achieving good quality status for most aquifers, longer timeframes that go beyond the EU’s 2027 deadline are required. This is again attributed to the long, natural response time of groundwater bodies from the percolation of water infiltrating the aquifer.

And that also means that pesticides released in the past could still be percolating down the aquifer today.

Nitrate contamination traced to fertilisers

The main source of groundwater contamination are nitrates from agricultural activities, but an increased presence of urban contaminants, such as pharmaceuticals and derivatives of personal care products, as well as industrial contaminants, are also contributing to the increase in water contamination.

Groundwater in the Maltese islands is highly vulnerable to human activities occurring within its surface catchment area. A high population density and mixed uses on land across all of Malta, places potentially contaminating activities operating side by side.

Malta’s main aquifer – a lens of fresh water that floats over a mass of sea water that spans over 217sq.km – is now losing over 3.3 million cubic metres of water each year. Gozo’s aquifer, also floating over sea water, loses 1.2 million cb.m each year.

All other perched aquifers where water is stored above impermeable clay levels are receiving more water than they are losing, together gaining 7.97 million cubic metres annually.

The quantitative assessment, based on a ‘water balance model’, compares mean annual inflow through natural and artificial recharge, with outflows through abstraction and natural discharge.

Over-abstraction mainly affects the mean sea-level aquifers: as more groundwater is taken out of these aquifers through unmetered pumps and industrial plants pumping out this water, more sea water is allowed to accumulate into the aquifer. This rising level of saline water is replacing abstracted groundwater faster than it the aquifers’ recharge, leading to the progressive salinisation of the aquifer systems.