Study concludes that seagrass meadows exposed to effluents from wastewater treatment plants are healthier

English version: Diana Taborda

An international study involving the Department of Life Sciences of the Faculty of Sciences and Technology of the UC (DCV-FCTUC) has concluded that seagrasses in the Tagus and Sado estuaries exposed to effluents from a wastewater treatment plant (WWTP) and a food factory are healthier.

According to Arthur Veronez, researcher at the FCTUC Centre for Functional Ecology, this study aimed to "analyse the health of seagrass stands subject to varying concentrations of nitrogen and phosphorus as a consequence of anthropogenic additions to natural background levels. In this context, we reanalysed and compared studies previously carried out in different locations around the world (Brazil, Costa Rica, British Isles, Ireland and Italy) of different species with similar habitats and anthropogenic influences".

The research "Seagrasses benefit from mild anthropogenic nutrient additions" focused, in Portugal, on the seagrass meadows of Zostera noltei (a seagrass species) in the Centre and South of the country. "The meadows monitored in the Tagus and Sado estuaries and Ria Formosa have smaller seagrasses, an indication that they are healthier under moderate nutrient concentrations in the water," explains the co-author of the study.

Veronez adds that in the Tagus estuary, “the healthiest meadows were located exactly next to a WWTP and a food factory, where ammonia concentrations were similar to those observed for Ria Formosa meadows, when compared with sampling stations with an increased distance from the local WWTP”.

According to the DCV scientist, "under lower nutrient loads, the grass of Zostera noltei (Z. noltei) meadows increased, suggesting that they were under nutrient deprivation. These lower loads occurred in the Ria Formosa, Tagus and Sado meadows furthest away from the WWTPs. IFurthermore, the Sado meadows were even less healthy than the Tagus and Ria Formosa meadows under equivalently low ammonium loads, suggesting that the lack of phosphate worsened their condition."

This research further suggests that, under a higher nutrient load Z. noltei meadows also increased, suggesting that they were suffering from toxicity (found in meadows of the Ria Formosa located closer to the local WWTP). However, “Comparisons with Z. noltei meadows from other locations and reported in other studies show that the meadows from Ria Formosa and the Tagus estuary, under moderate anthropogenic nutrient additions, were among the healthier ever reported”, claims Arthur Veronez.

For the FCTUC researcher, the monitoring of Z. noltei in Portugal "was an unprecedented experiment, carried out during the summer of 2021", which included nine stations in the Tagus estuary and six stations in the Sado estuary (located in intertidal areas). “It is worth noting that this study - which uses a cosmopolitan, active and robust study methodology - provides a high-impact work for better scientific understanding of how seagrasses benefit from anthropogenic nutrient additions.”, he concludes.

The study involved over a dozen researchers from nine institutions worldwide. The scientific article is available here.