Rivers Under Threat: Assessing the Ecological Impact of Macrolitter in the Leça River, Portugal

Ecological Impact of Macrolitter in the Leça River

Abstract

Rivers Under Threat: Assessing the Ecological Impact of Macrolitter in the Leça River, Portugal

Rivers provide vital ecosystem services for populations. However, these ecosystems face several anthropogenic threats, including macrolitter pollution, and their impacts remain inadequately understood. This study aimed to evaluate the ecological status of Leça River (northern Portugal) according to elements defined by the Water Framework Directive (WFD) and to assess the marginal macrolitter evaluation as a new ecological tool for rivers water quality assessment. Physical, chemical, and biological (benthic macroinvertebrates) elements were quantified to evaluate the ecological status, along the Leça River, in seven sites (P1 to P7) and in four seasons (autumn/23, winter/24, spring/24, summer/24). Macrolitter was collected in the riverbank of each site and was quantified and categorized according to the European marine macrolitter reports “Joint List”, “Master List” and “OSPAR”. Physical and chemical elements consistently achieved an ecological status of Good in P1, and Moderate in P4 to P7 (mainly due to nutrient enrichment) with P2 and P3 varying between Good and Moderate. The ecological status according to the macroinvertebrate community varied between: Good and Moderate in P1; Moderate and Poor in P2 and P3; Poor in P4 and P5; and Poor and Bad in P6 and P7. The 1717 macrolitter items belonging to 86 categories were collected, with artificial polymer/plastic items being more frequent (56.67%). More abundance and diversity of items were collected in sites P3 to P7, coinciding with the increasing anthropic presence. A multivariate analysis revealed that items originating from recreational activities were associated with fewer alterations in the macroinvertebrate community, while items originating from the deposition of domestic, industrial, and commercial residues were associated with more degraded conditions. The results suggest that the evaluation of macrolitter can be used to indicate anthropogenic activities that threaten aquatic ecosystems.