In our new post, Natalie Rideout from the Canadian River Institute at the University of New Brunswick, presents her MsC research in the paper ‘Environmental filtering of macroinvertebrate traits influences ecosystem functioning in a large river floodplain’. She highlights the importance of floodplains for ecological research, emphasises the need for teamwork to answer research questions, and shares her passion for the natural world.

About the paper

The first time I saw the spring freshet of the Wolastoq | Saint John River, driven by a huge ice jam upstream of my city of Fredericton, Canada—I had just started my MSc. I was immediately forced to rework my mental maps of this new-to-me city as water overflowed the banks of the river and turned city streets into a kayaker’s delight. This moment highlighted two things at the forefront of the research I was about to start on the downstream wetlands of this mighty river: 1. I was lucky to be conducting research on one of the last intact large river floodplains on the eastern coast of North America—many of the world’s great rivers have been altered to the point of functional extinction through flow regulation, water extraction and channelization; and 2. My beautiful river was not immune to encroaching and increasing human development. The upstream dams have altered the likelihood and location of ice jams (one of the rivers’ primary flood mechanisms), urbanization has allowed for development along high flood risk areas, and climate change has influenced the timing and magnitude of floods. Despite this, while water overflowed the streets of the city, the downstream wetlands in the Portobello Creek and Grand Lake Meadows wetland complex were receiving sediment, water, and biological propagules that helps keep floodplains one of the most productive ecosystems in the world.

            My fellow Canadian Rivers Institute colleagues and I teamed up with the Hajibabaei lab from the University of Guelph Centre for Biodiversity Genomics—together we set out to research the Biodiversity Ecosystem Function hypothesis in these floodplain wetlands. We knew that floodplains are not only highly productive, but that many of the functions they perform underpin ecosystem services that society relies on. We also knew that the temporal and spatial dynamics of flooding and sediment deposition creates highly heterogeneous, mosaicked landscapes, making this diverse habitat a fantastic place to use trait-based ecology to tease apart ecosystem linkages. Taking a whole ecosystem approach, and employing high resolution DNA metabarcoding techniques on aquatic macroinvertebrate communities—a common biomonitoring group—we asked how functional diversity differs across the floodplain and if it mediates ecosystem functioning. We also wanted to know the environmental drivers or filters of these processes, and if human development over the past 70 years has played a role shaping current ecosystems.

We found that this relationship was complex and that it challenged some of our initial hypotheses. In lotic systems, the autumn’s falling leaf litter represents an important food source, creating a competitive environment and resulting in high shredder diversity. In fact, the insects that make up this functional feeding group are responsible for over half of decomposition in these ecosystems and higher diversity results in higher rates of function. In floodplain wetlands, contrastingly, leaf litter often comes through in flood pulses, and then settles and builds up in the sheltered coves, where it has been recorded to stay for up to seven years. These elevated carbon levels—along with relatively low rates of disturbance—encourage diverse underwater plant communities, complete with seemingly never-ending microhabitats. Rather than compete for a pulsed resource, aquatic macroinvertebrates fill a variety of niches, becoming both more functionally rich and even, and, in turn, allowing for high rates of primary production. Interestingly, these sheltered coves were also more likely to have experienced shoreline changes from alteration in the flood pulse, as their slopes allowed for easy inundation and shifting of boundaries from wet to dry. Hyper-diverse and productive habitats also tended to be in areas of higher governmental protection, but this finding is nuanced; while there are more restrictions with higher protection, ease of access is an important underlying factor that is often ignored.

About the research

In answering our broad question about biodiversity and ecosystem function, we unveiled other important questions—arguably, this is how science operates and continues its cycle. How does the role of aquatic insects in ecosystem functioning differ from running water habitats, like cobble bottom streams, to floodplain wetlands? Does the number and evenness of traits or niches help us understand the ecosystem more than just the number of species? If biodiversity and ecosystem functioning are linked (one of the tenets of ecological theory), do we need to broaden our scope of study taxa? For example, if we looked at fungal communities, would these patterns remain the same? Does protection actually help conserve biodiversity, or is it (as so often is the case) enacted in places where access is more limited anyway?

Science rarely happens alone, and, like many other projects, this research would not have happened without a lot of teamwork and support. From digitizing old aerial photographs, to conducting vegetation surveys in highly diverse macrophyte beds, being chest-deep in water and knee-deep in sediment, to lab work drying and weighing leaf packs and sequencing benthic samples, we were supported by a team of staff, interns and students. The transition from thesis to publication was also a road with twists and offshoots. While the work ultimately is stronger for it—often the argument for continuing the cycle— the scientific process can be a particular mental slog for graduate students. In the end, we thank the dozens of people who helped bring this research to light so that we can highlight the amazing diversity and resilience of these threatened ecosystems.

About the author

Growing up surrounded by trees—on a free-flowing river and marsh—I have long borne witness to the value of the environment and of protecting nature for its own intrinsic rights. I believe that the first step to learning how to preserve and conserve the environment is to understand how our actions as humans have impacted and degraded it. From there, we can work to remove anthropogenic influences, learning to live in harmony with the earth so that our ecosystems can continue to function and provide the vital ecosystem services on which we rely.

I completed the research for this paper as part of my MSc in Donald Baird’s lab at the University of New Brunswick with the Canadian Rivers Institute, where I am lucky to be once again on the banks of a free flowing river watching the power of the spring freshet bring fresh life into the surrounding environment. When I’m not in the field or office pursuing my PhD, my passion for the natural world continues in the form of hiking, bird watching, climbing, and painting. I live by a belief that work-life balance, and particularly enjoying our natural world as curious, creative individuals, makes us better ecologists and advocates for a better world.

Enjoyed the blogpost? Read the research here!