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“Most of the research on rivers in Brazil relates to large rivers, so we know much less about how human activities affect small rivers and streams, especially in the most biodiverse expanse of tropical forest on Earth, the Amazonian rainforest ” says Cecilia Gontijo Leal, who won the Brazilian Zoological Society’s 2015 prize for the best PhD thesis in Biological Conservation.

“My idea was to investigate how agriculture, deforestation and other human activities impact the water quality and structure of small watercourses, and the fish species within them.”

Cecilia defined small watercourses as streams and rivers you can wade through. Her results show that they are a very important, if neglected, habitat for wildlife, and that they are being adversely affected by human activities, often in unexpected ways.

The Sustainable Amazon Network

Cecilia was one of the first researchers to take advantage of a dual PhD scheme run by Lancaster University and the Federal University of Lavras in Brazil, giving her the chance to spend a year in the UK, analysing her data at the Lancaster Environment Centre.

She is also a member of the Sustainable Amazon Network, a group of more than 100 researchers and graduate students from 30 institutions that aims to assess the sustainability of land-use systems that characterise tropical forests.

“I had a lot of help from people who have a vast experience of working in the Amazon. In the field, we worked together as a big group – at least six PhD students and several field assistants - each person doing a different aspect and sharing information. I was responsible for fish sampling, others looked at aquatic macro-invertebrates, dragonflies and water quality.”

Great biodiversity in small streams

“There is a great variety of fish species in these rivers and streams, even though they are in an area that has been used for agriculture, road and pasture for the past 50 years. And many streams are unique in terms of species composition. So they are still very important for biodiversity.”

However it became clear that fish and water quality were being affected by human activity, often in unexpected ways.

“For instance we found that the dirt roads that spread across the landscape have a significant impact on water quality and fish species and on other ecosystem services such as preventing floods and regulating the flow.” 

“This is because people don’t usually build appropriate bridges when dirt roads cross small rivers and streams but create small dams that fragment the flow and can cause erosion and sedimentation. There are thousands of these roads so the cumulative impact is huge.”

Implications for conservation

Cecilia, who was funded by the Brazilian Government’s Science without Borders programme, also found that the rivers were affected by changes in the catchment, such as deforestation, far away from the watercourses themselves.

“These impacts are still not catastrophic, and there is a lot of room for conservation and management to make a positive impact, but we need to act now and start paying attention to the effects of catchment-level deforestation and road crossings for instance.

“You might think that if you protect the riparian forest it would be enough and rivers would be protected but this is not true.

“This has implications for legislation. We believe there should be planned management of agricultural lands on a catchment scale.”

Joint supervision

Cecilia’s prize winning thesis, ‘Multiscale anthropogenic impacts on stream condition and fish assemblages in Amazonian landscapes’, was supervised jointly by Dr Paulo Pompeu, from the Federal University of Lavras, Professor Jos Barlow, from Lancaster Environment Centre, and Dr Toby Gardner from the Stockholm Environment Institute.

“Having these different supervisors and discussions within the Sustainable Amazon Network really opened my mind to different aspects of tropical ecology, including the importance of social and economic aspects and of historical context.”

“This prize is a very important achievement for Cecilia, and it recognises the incredible effort she put into her research,” said Jos. “It also helps draw attention to the importance of tropical streams, and highlights their remarkable diversity.”

Cecilia is continuing her research as a post-doctoral researcher. “I am now expanding the approach used in my thesis to data we collected on other aquatic organisms, for example macro-invertebrates and dragonflies, in order to improve our understanding of land-use impacts on Amazonian stream systems across multiple groups of organisms.

“I will use this information to evaluate current Brazilian environmental legislation, and to develop effective management and conservation actions for Amazonian streams in human impacted landscapes.”

Learn more about doing a PhD at Lancaster Environment Centre