Burning our bridges? Network analysis reveals trends in freshwater expertise

By Lauren Kuehne

January 8, 2020

As scientists, when we think about conservation problems, it’s often in terms of missing information – “knowledge gaps”, anyone? But the role of expertise – implying not only growth but also continuity in development and application of knowledge – is invariably less emphasized. This may be in part simply due to the tradition of science where knowledge and concepts are built incrementally – think Thomas Kuhn’s notion of normal science. However, it also can stem from more prosaic problems of maintaining research focus in the overburdened, underfunded world of environmental science.

In a new paper just out in BioScience, the Freshwater Ecology Conservation Lab examined expertise in a conservation area close to our hearts, which is assessment of freshwater ecosystems. This new paper follows up on a review published in 2016, in which we examined the way that ecological integrity of freshwater ecosystems have been assessed since passage of the 1972 Clean Water Act. In that review, we found that although methods have been becoming more standardized, there was a disheartening disconnect between assessment and management or policy-making.

Network graphs - then and now
Computational power to analyze networks has changed since the first “sociograms” were developed by psychiatrist J. L. Moreno in 1934 (right), to creating partial maps of the internet circa 2005 (left), but the basic concept of evaluating the strength and direction of relationships between individuals or organizations remains the same.

This finding spurred us to follow up by examining the position and role of expertise in freshwater assessment through time. We sought to answer the question: Which entities and individuals contribute most to this body of knowledge, and how are they collaborating with each other across organizational and ecosystem boundaries? Our goal was to assess the state of expertise – or “human capital” – related to freshwater assessment, expertise that is needed for everything from development of methods to participation in legislative and administrative reforms related to the Clean Water Act.

We used network analysis – a technique first formalized in the 1930s and used frequently in the social sciences – to analyze relationships between authors of grey and peer-reviewed publications related to freshwater assessment. Authors were categorized by their organizational affiliations – i.e., academic, federal government, NGO, etc – allowing us to analyze the frequency of collaborations both within and between organizational types. In network analysis, these are known as bonding (within) and bridging (between) ties, and are good indicators of strong relationships, regular paths of communication, and ability/propensity to collaborate. We also looked at cross-ecosystem exchange by examining ties between research groups working in different types of freshwater systems.

What we found was surprising. By the numbers, academic authors outweigh other groups, but when we looked at centralities – meaning the frequency that authors were connected to and formed a bridge between others – it was authors affiliated with federal agencies that were involved in the largest number of bonding and bridging ties. Authors affiliated with state government, NGOs, and consulting companies also held comparable importance in the network, depending on the type of centrality; for example, despite relatively low numbers, state agency affiliated authors were as prominent in the core network as those associated with universities. And although agencies like the US EPA might be expected in the core network, agencies that were less expected to be playing a role in such assessments, such as the National Park Service and Bureau of Land Management, were also well represented.

Network Graph - freshwater assessment
Network graph of individuals with expertise in assessment of fresh waters since passage of the 1972 Clean Water Act. The network is diverse, but highly fragmented, and with little evidence of increasing connectivity over time, making it vulnerable to loss of key individuals or organizations.

Diversity of the entities contributing to and sustaining expertise and knowledge exchange should be celebrated, but it must also be considered in light of the fact the network as a whole was highly fragmented, with little evidence of becoming less fragmented over time. This means that the network is only tenuously connected, and therefore highly vulnerable to loss of key individuals or groups, which can easily occur due to extended losses in funding or government shutdowns.

Given the war on science and scientists associated with the federal government during the last three years, it seems like a bad punchline to publish research that says those same scientists are the current mainstay of freshwater assessment knowledge and expertise. And although our analysis focused on freshwater assessment, research in other areas of ecology and conservation supports a similarly central role of government agencies in sustaining and building collaboration networks. Conservation science needs information, but we also need expertise and continuity; our goal with this paper was to establish where this expertise currently resides, and where it may need to be fostered and protected in the future. We hope that this study will spur important conversations about the value of knowledge networks in the years to come.

This article was originally published by the Freshwater Ecology Conservation Lab. 


What Drives Resource Integration in Lakes?

By Beka Stiling, MS Candidate, School of Aquatic & Fishery Sciences, University of Washington

Graph depicting the reliance on littoral-benthic resources by rainbow trout. Small populations of trout will use the all of the littoral-benthic habitat. Large populations use more littoral-benthic resources as more habitat is available.
Variability in reliance on littoral-benthic derived resources by rainbow trout may be partially explained by an interaction between rainbow trout population density and littoral zone extent.

Evidence suggests that the integration of energetic pathways via the transfer of resources across habitat boundaries can influence community structure, maintain species biomass, and promote food web stability. Despite our ability to measure resource integration, we do not have a strong understanding of the factors that determine the varying degrees of resource integration that we observe in fish.

In lakes, the carbon that serves as the energetic base of the food web originates in three distinct habitats: pelagic (open water), littoral-benthic (submerged, illuminated edge), and terrestrial (land surrounding the lake). Fish, as mobile consumers, can use resources derived from different habitats, thereby integrating resources from multiple energetic pathways. Floating algae, or phytoplankton, has long been recognized as an important base of aquatic food webs, but increasing evidence points to attached littoral-benthic algae as a substantial contributor of energy to lake food webs as well. Discussions are ongoing about the role of terrestrial carbon, exported from the surrounding watershed into the lake, as a basal resource for aquatic communities.

Attached algae, scrubbed from a rock, is collected on a filter.

My study aims to identify factors that might drive resource integration by rainbow trout in order to better anticipate how alterations to lake littoral habitat from human use and climate change may impact lake ecosystem function in the future. I am testing two potential factors. The first is resource availability. Do fish integrate resource pathways in ratios that reflect the relative extent of the habitats providing carbon to the ecosystem? The second factor is population structure. Does the density of the rainbow trout population influence how fish might rely on different energetic pathways?

To address the challenge of focusing on just two of the many interacting factors that may influence resource integration, I selected study lakes that were similar with respect to climate, geology, human impacts, and species composition, but differed in terms of littoral habitat availability and rainbow trout population structure. From these 17 lakes I collected rainbow trout and samples of primary producers from the pelagic, littoral-benthic, and terrestrial habitats. In the lab I am conducting analyses that leverage naturally occurring differences in molecules formed in these three habitats to elucidate rainbow trout reliance on energy that originated in each habitat.

Map depicting location of the lakes from Stiling's study
The study lakes, located on the western side of the Cascade crest, are naturally fishless mountain lakes stocked with rainbow trout at varying numbers and frequencies, resulting in a gradient of fish population densities.

After I analyzed a subset of my samples, preliminary findings revealed an interaction between habitat availability and rainbow trout density, where at low densities rainbow trout are more reliant on littoral-benthic derived resources regardless of littoral habitat availability, but, as population density increases, reliance on littoral-benthic resources decreases with reduced littoral availability. This interaction between factors suggests that for rainbow trout the utilization of multiple pathways may be a solution to competitive pressure on a preferred resource pathway — an example of how resource integration can contribute to the stability of a top predator population.

Stiling weighs out samples on a microbalance in preparation for stable isotope analysis.

My next steps are to wrap up my lab-based processing and begin to analyze the full complement of my data. I am excited to uncover the full story and see if the trends I found with a subset of my samples persist! I am thankful to the Washington State Lake Protection Association for the Dave Lamb Memorial Scholarship funding that supports this project. The scholarship funding jump-started my field data collection and provides critical assistance for lab-based sample processing.

Beka Stiling is an MS Student in the School of Aquatic and Fishery Sciences at the University of Washington, advised by Julian Olden and Gordon Holtgrieve.

Email: stilir@uw.edu

Twitter: @rebekahstiling

This article was originally published by the Washington State Lake Protection Association (WALPA) in the September 2019 Waterline newsletter.


Prepare River Ecosystems for an Uncertain Future

As the climate warms, we can’t restore waterways to pristine condition, but models can predict potential changes, write UW SAFS professor Julian Olden and colleagues in Nature Magazine.

Dead fish on the banks of the Guadiaro River in southern Spain during severe drought
Dead fish on the banks of the Guadiaro River in southern Spain during severe drought. (Jose Luis Roca / AFP / Getty)

June 18, 2019

Jonathan D. Tonkin, N. LeRoy Poff, Nick R. Bond, Avril Horne, David. M. Merritt, Lindsay V. Reynolds, Julian D. Olden, Albert Ruhi & David A. Lytle

In January, millions of fish died in Australia’s Murray–Darling Basin as the region experienced some of its driest and hottest weather on record. The heat also caused severe water shortages for people living there. Such harsh conditions will become more common as the world warms. Iconic and valuable species such as the Murray cod (Maccullochella peelii peelii) — Australia’s largest freshwater fish — could vanish, threatening biodiversity and livelihoods.

Rivers around the world are struggling to cope with changing weather patterns. In Germany and Switzerland, a heatwave last year killed thousands of fish and blocked shipping on the River Rhine. California is emerging from a six-year drought1 that restricted water supplies and devastated trees, fish and other aquatic life. Across the US southwest, extended dry spells are destroying many more forests and wetlands.

What should river managers do? They cannot look to tools of old: conventional management techniques that aim to restore ecosystems to their original state. Ongoing human development and climate change mean that this is no longer possible. And models based on past correlations do a poor job of predicting how species might respond to unprecedented changes in future (see ‘Ecosystem change’). A different approach is called for.

A graph projecting cottonwood and sagebrush occupation of floodplains with increasing drought over the next 200 years. A new model that includes biological processes shows a sharp downturn in plant

To maintain water supplies and avoid devastating population crashes, rivers must be managed adaptively, enhancing their resilience and limiting risk. Researchers must also develop better forecasting tools that can project how key species, life stages and ecosystems might respond to environmental changes. This will mean moving beyond simply monitoring the state of ecosystems to modeling the biological mechanisms that underpin their survival.

Model process

Today, river managers track properties such as species diversity and population abundance, and compare them with historical averages. If they spot troubling declines, they might intervene by, for instance, altering the amount of water released from dams. But by the time trends are detected, they can be impossible to arrest.

Understanding how sensitive ecosystems might change is crucial to managing them in the future. For example, in the American west, native cottonwoods (Populus spp.) are valuable, long-lived trees that anchor river banks and offer habitats for many species. They are finely tuned to seasonal flood patterns, releasing their seeds in early summer when river flows peak. The seeds take root in moist ground after the flood recedes2. But if the flood is delayed, even by a few days, many seeds fall on dry ground and die. Drought-tolerant species, such as salt cedar (Tamarix ramosissima), that disperse seeds over a longer period will move in and dramatically alter conditions for native flora and fauna.

Models based on biological processes or mechanisms — that is, how rates of survival, reproduction and dispersal vary with environmental conditions — can follow and predict such shifts. For example, by modelling the impacts of changes in flood timing on aquatic invertebrates, it is possible to predict how the numbers of dragonflies and mayflies in a dryland river will vary with different patterns of dam releases3.

Process-based models can be tailored to particular life stages of a species, or sequences of events4. They can identify tipping points and bottlenecks. For example, they have revealed that the early juvenile stage of coho salmon (Oncorhynchus kisutch) in the northwestern United States is most sensitive to summer droughts. The salmon spawn in streams that flow into coastal rivers, and might spend a couple of years in fresh water before moving to the sea. Juveniles might not survive, or might find it hard to travel downstream, when the river levels are low5.

Such models can also track how interactions among species in communities vary under changing conditions6. For example, the loss of riparian specialists in dryland river ecosystems and invasion by both non-native and upland species in a drier future could create a vicious cycle6. River ecosystems could become more vulnerable to climate change and to alien species.

Trees grow along the banks of the Dolores River in Utah
Native cottonwoods are being displaced by non-native salt cedar in the Dolores River, Utah, owing to flow alteration by damming. (Mark Uliasz / Alamy)

Armed with all this information, managers can intervene before a problem arises. For example, in wet years, conservationists in the Pacific Northwest could find and support habitats that are crucial to juvenile salmon. They could manage water flows in dry years to enable the salmon to migrate. Similarly, in the US southwest, river flows could be increased strategically from reservoirs to protect important species, such as cottonwoods. And in Australia, letting more water pass through dams in spring could stop rivers drying up while the eggs of Murray cod mature7.

Rivers must also be managed for people. Allocating scarce water resources is contentious. Policymakers, water-resource engineers, conservationists and ecologists must work together to decide how much water should be diverted to people, agriculture and industry, and how much is needed to protect ecosystems during drought.

Some river basins are beginning to be managed adaptively — agencies are trying different management practices, learning from them and updating them as needed. For example, in Australia, state and federal agencies periodically reassess and rebalance water allocations, as climate trends, information and assessment tools develop. Similarly, the Bay–Delta Plan in California proposes to revisit relationships between target species, water flows and water quality in San Francisco Bay and the Sacramento–San Joaquin River Delta every five years.

But adaptive management alone might miss conservation targets. Unexpected consequences could emerge over the long term as impacts mount. Process-based models can look further ahead and save time, money and disruption by limiting the number of interventions as well as avoiding adverse impacts. They would help stakeholders and managers to choose which features of ecosystems to maintain, to justify costly interventions such as major engineering works and to weigh trade-offs to build resilience under increasing climatic uncertainty8.

Obstacles to implementation

Process-based models are already used in fisheries and conservation. For example, they have shown conservationists that it is more effective to protect juvenile loggerhead sea turtles from being caught in fishing nets than to safeguard their eggs on beaches9. And such models help to guide the management of wetland habitats in the United States for the endangered Everglades snail kite (Rostrhamus sociabilis), the fledglings of which are susceptible to droughts10.

But they are rarely used in river management, mainly because data on the basic biology of local species are lacking. Such data are costly for scientists and agencies to collect. Measuring fecundity or survival, for example, takes years and thus requires long-term funding and commitment. Such campaigns are usually reserved for endangered or commercially valuable species.

Simplifying models might help to bridge the data gaps in the interim. Species with similar life histories or characteristics might respond similarly to changing river conditions. Studies of one could inform models and management of similar species in other places. For instance, plains cottonwood (Populus deltoides) in North America, river red gum (Eucalyptus camaldulensis) in Australia, and Euphrates poplar (Populus euphratica) in North Africa and Eurasia are all riparian trees that have similar hydrological requirements and drought tolerances. They share characteristics such as shallow roots and furrowed bark that resists flood scour, and can resprout after being buried by sediment. Analytical methods could also be developed to extrapolate across gaps in data sets.

Four steps

River scientists and managers should take the following steps.

Collect data on mechanisms. We call for a fresh global campaign to gather natural-history data on the responses of biodiversity to changes in river flow. Estimates of fecundity and survival at various life stages will require monitoring in the field. Other information, such as flood-induced mortality rates, could be gathered through field and laboratory experiments. Data from different sources can also be combined, including species traits, population abundances across life stages and remote-sensing data about the states of ecosystems on wider scales4.

We urge local, state and federal agencies, as well as researchers, non-governmental organizations and other bodies, to make existing data available. Facilities for hosting these already exist, such as the COMPADRE and COMADRE global databases, which hold population models for hundreds of plant and animal species, respectively. Organizations such as the Alliance for Freshwater Life, the wildlife charity WWF and the Group on Earth Observations Biodiversity Observation Network should lobby global funding bodies to support data collection.

Describe key processes in models. Scientists need to better articulate the relationships between population dynamics and water-flow patterns in process-based models. For example, the models need to describe how well different life stages of plants reproduce or survive under flood or drought conditions, the flow conditions and timing that are required for fish to reproduce or the growth rates of insect populations after floods of different sizes35,7. Outputs need to be expressed clearly so that river managers and decision makers can understand and use them.

Focus management on bottlenecks. Targeted interventions to avoid populations collapsing during extreme flows will be a cornerstone of managing rivers for resilience in future. Accordingly, dam managers should focus on the most vulnerable or responsive life stages, not just population abundance. Sadly, as flow extremes become more common, scientists and managers will be able to observe die-offs and calibrate the models.

Pinpoint uncertainty. The level of confidence that managers have in the results of models will influence how willing they will be to deal with varying levels of risk. Predictions should thus quantify the level of trust that can be placed in them. Scientists must present uncertainties in forecasts clearly. Models should be tested by hindcasting (predicting past or present population size, for example), and uncertainty in model inputs should be traced through to the outputs. The knowledge gaps that most compromise accuracy should be identified. The models should be regularly updated, tested and improved as new data arrive.

Freshwater biodiversity is disappearing on our watch. As the crisis deepens, we must model and manage rivers to safeguard the services they provide.

This article was originally published in Nature magazine.


One-Third of the World’s Longest Rivers Remain Free-Flowing, New Analysis Finds

Grand Coulee Dam
The Grand Coulee Dam on the Columbia River in Washington. (WSDOT)

Michelle Ma, UW News

May 8, 2019

Just over one-third of the world’s 246 longest rivers remain free-flowing, according to a new study published May 8 in Nature. Dams and reservoirs are drastically reducing the diverse benefits that healthy rivers provide to people and nature across the globe.

Laird River
The Laird River in Canada is among the 10 longest free-flowing rivers in the country.

A team of 34 international researchers from McGill University, World Wildlife Fund, the University of Washington and other institutions assessed the connectivity status of 12 million kilometers of rivers worldwide, providing the first-ever global assessment of the location and extent of the planet’s remaining free-flowing rivers.

Among other findings, the researchers determined that only 21 of the world’s 91 rivers longer than 1,000 kilometers (621 miles) that originally flowed to the ocean still retain a direct connection from source to sea. The planet’s remaining free-flowing rivers are largely restricted to remote regions of the Arctic, the Amazon Basin and the Congo Basin.

“The world’s rivers form an intricate network with vital links to land, groundwater, and the atmosphere,’’ said lead author Günther Grill of McGill’s Department of Geography. “Free-flowing rivers are important for humans and the environment alike, yet economic development around the world is making them increasingly rare. Using satellite imagery and other data, our study examines the extent of these rivers in more detail than ever before.”

Dams and reservoirs are the leading contributors to connectivity loss in global rivers. The study estimates there are around 60,000 large dams worldwide, and more than 3,700 hydropower dams are currently planned or under construction. They are often planned and built at the individual project level, making it difficult to assess their real impacts across an entire basin or region.

Republic of Congo hydropower dam
The town of Sembé in the Republic of the Congo will receive power from this newly constructed hydropower dam. (Jaap van der Waarde / WWF-Netherlands)

“Our findings are quite sobering — ongoing dam construction will continue to dwindle the number of remaining free-flowing rivers,” said co-author Julian Olden, a professor at the UW School of Aquatic and Fishery Sciences. “But, optimistically, the removal of aging and obsolete dams can help reverse this course.”

Healthy rivers support freshwater fish stocks that improve food security for hundreds of millions of people, deliver sediment that keeps deltas above rising seas, mitigate the impact of extreme floods and droughts, prevent loss of infrastructure and fields to erosion and support a wealth of biodiversity. Disrupting rivers’ connectivity often diminishes or even eliminates these critical ecosystem services.

“Science clearly points to the importance of habitat connectivity to support healthy populations of Pacific salmon,” Olden said. “The findings of our study put the challenges facing the Columbia River Basin and many Puget Sound rivers into a global context.”

Protecting remaining free-flowing rivers is also crucial to saving biodiversity in freshwater systems. Recent analysis of 16,704 populations of wildlife globally showed that populations of freshwater species experienced the most pronounced decline of all vertebrates over the past half century, falling on average 83 percent since 1970.

Mekong River, Laos
Life along the banks of the Mekong River in Laos. (Nicolas Axelrod / Ruom / WWF-Greater Mekong)

The study also notes that climate change will further threaten the health of rivers worldwide. Rising temperatures are already impacting flow patterns, water quality and biodiversity. Meanwhile, as countries around the world shift to low-carbon economies, hydropower planning and development is accelerating, adding urgency to the need to develop energy systems that minimize overall environmental and social impact.

“While hydropower inevitably has a role to play in the renewable energy landscape, countries should also consider other renewable options,” said Michele Thieme, lead freshwater scientist at World Wildlife Fund. “Well-planned wind and solar energy can have less detrimental impacts on rivers and the communities, cities, and biodiversity that rely on them.”

The international community is committed to protect and restore rivers under Agenda 2030 for Sustainable Development, which requires countries to track the extent and condition of water-related ecosystems. This study delivers methods and data necessary for countries )to maintain and restore free-flowing rivers around the world.

See the paper for a full list of co-authors and institutions.

This study was funded by World Wildlife Fund, the Natural Sciences and Engineering Research Council of Canada and McGill University.

For more information, contact Olden at olden@uw.edu. To reach authors at McGill University or World Wildlife Fund, contact Brooke Hirsheimer at brooke.hirsheimer@wwfus.org or (202) 495-4759.

This has been adapted from a World Wildlife Fund news release.