Tiles, leaves and cotton strips for measuring river health

Rivers perform a vital role in environmental balance. Keeping them in good condition depends not only on water quality, but also on the life they host and the processes that take place within them: plant respiration, decomposition of organic matter, and transformation of nutrients, among others. “The good condition of a river means taking into account both the organisms that inhabit it and the way it functions,” explained Luz Boyero, an Ikerbasque Research Professor at the EHU. Human activity may alter this natural dynamic, so tools need to be available to enable its effects to be detected in a timely manner.

With the aim of standardising methods for assessing river health and providing a simple, accessible guide for environmental management bodies, the researcher in the EHU’s Stream Ecology group Diana Rojo analysed the performance of different materials that enable the decomposition processes and organic matter production to be measured in three streams located in agricultural areas in the Green Belt area of Vitoria-Gasteiz.

As Rojo explained, using various types of substrates, the team compared the differences between well-preserved sections and others more affected by agricultural activities. “We wanted to identify which ones best reflect the changes taking place in the river when there are human alterations,” the researcher pointed out.

The tests examined a wide variety of items, including marble tiles, alder and oak leaves, tongue depressors used in medicine, cotton strips, green and red tea bags, and even banana leaves, to determine which ones are most effective as ecological indicators.

Communities of invertebrates, fungi, algae, and decomposition

Once they had selected altered and unaltered stretches of various streams on the outskirts of Vitoria-Gasteiz, they put experimental units containing the aforementioned substrates in the water and kept them incubating for four weeks, “so they could compare them afterwards and decide which substrates indicate changes in the condition of these streams most efficiently and within a short space of time”, they explained. After collecting all the material, “we were able to analyse the communities of invertebrates, fungi and algae, as well as various decomposition variables, which indicate the state of the impacted areas compared with the unaltered stretches”, they added.

Broadly speaking, the researchers concluded that “to carry out efficient studies with limited resources, in terms of both time and money, alder is the best substrate for studying total decomposition and macroinvertebrate communities; banana leaves or cotton strips are very efficient for studying microbial decomposition; and finally, marble tiles are useful for studying algae or primary production. These three materials would provide us with a great deal of fairly immediate information about the state of the ecosystem”. At the end of the day, this is a set of recommendations not only for the research community, but also for the administration and management bodies. What is more, the materials proposed are also quite universal, which makes it easier for this study to be replicated globally in different locations.

In the view of the EHU researchers, “Water is a vital resource for human beings. Healthy river communities need to be maintained and ecosystem processes need to function as they should. It is essential to know how to assess the health of ecosystems in order to address pollution. “This is always the first step: seeing where the conditions are good, where they are poor, and then deciding what to tackle, in particular to find out which sections are the most critical ones,” added Rojo. “River ecosystems are fundamental in carbon cycles, nutrient cycles, and on the planet. And they are often the great forgotten,” concluded Professor Boyero.

Additional information

This study is part of the PhD thesis being written up by Diana Rojo; her supervisor is Dr Luz Boyero, Ikerbasque Research Professor in the EHU’s Department of Plant Biology and Ecology, who leads the international GLoBE network, whose main aim is to study the patterns and factors that drive the functioning of river ecosystems on a global scale.

Technical staff of the Green Belt area of Vitoria-Gasteiz (Vitoria-Gasteiz City Council) collaborated in the study.

Bibliographic reference

Diana Rojo, Alberto Alonso, Javier Pérez, Agustí Agut, Brais Hermosilla, Scott D. Tiegs, Luz Boyero

Decomposition of different organic matter substrates and algal biomass accrual as early warning indicators of human impacts on stream ecosystems

Ecological Indicators

DOI: 10.1016/j.ecolind.2025.113998