River flow by design: environmental flows support ecosystem services in rivers natural and novel

The October 2014 issue of ESA Frontiers spotlights river management in the Anthropocene

FOR IMMEDIATE RELEASE: Wednesday, October 8, 2014
Contact: Liza Lester, 202-833-8773 ext. 211, LLester@esa.org

The dry Colorado River delta on June 21, 2013. Credit, NASA.

Tides flow backwards up the dry channels of the Colorado River delta, as seen in an astronaut photo taken June 21, 2013. Prior to the construction of the Hoover Dam and other large water projects on the Colorado, the delta estuary supported a great diversity of species in 3,000 square miles (7,700 square kilometers) of braided channels and lagoons. Now, the riverbed often dries not far from the Arizona-Mexico border. In the spring of 2014, an experimental “pulse” of 105,000 acre-feet (130 million cubic meters) of water were released from the lowest dam on the river in an effort to recover some the lost services provided by the lower Colorado ecosystems. Credit, NASA. (Click image to enlarge it).

Last spring, the Colorado River reached its delta for the first time in 16 years, flowing into Pacific Ocean at the Gulf of California after wetting 70 miles of long-dry channels through the Sonoran Desert. The planned 8-week burst of water from Mexico’s Morelos Dam on the Arizona-Mexico border was the culmination of years of diplomatic negotiations between the United States and Mexico and campaigning from scientists and conservation organizations. Now ecologists wait to see how the short drink of water will affect the parched landscape.

This year’s spring pulse held less than 1 percent of the volume of the Colorado’s annual spring floods before the construction of ten major dams and diversions to municipalities, industry, and agriculture. A return of the lush Colorado delta of the 1920s will not be possible. But there is hope that periodic flows will bring back willow, mesquite, and cottonwood trees, revive insects and dormant crustaceans, give respite to birds migrating on the Pacific Flyway, and ease strains on fisheries in the Sea of Cortez (Gulf of California).

Environmental flows for natural, hybrid, and novel riverine ecosystems in a changing world

There are two primary ways to achieve “environmental flows” of water necessary to sustain river ecosystems, write Mike Acreman, of the UK’s Centre for Ecology & Hydrology, and colleagues in a review published this month in Frontiers in Ecology and the Environment: controlled releases like the recent experiment on the Colorado that are designed with specific objectives for ecology and ecosystem services in mind and hands-off policies that minimize or reverse alterations to the natural flow of the river.

For rivers like the Colorado, already much altered and bearing heavy demands from many different user groups, a “designer” approach is more practical than attempting to return the river closer to its natural, pre-development state, say the authors. Designers work to create a functional ecosystem or support ecosystem services under current conditions, rather than recreate a historical ecosystem.

Achieving ecological objectives requires planning beyond minimum flows and indicator species to encompass seasonal floods and slack flows and a holistic look at the plants, fish, fungi, birds and other life inhabiting the river, its banks and its marshes. Managers must plan to turn on the taps when ecosystems can capitalize on the flow, lest water releases do more harm than good. Several decades of applied research guided the planning for the engineered “spring flood” on the lower Colorado this year, which was timed for the germination of native trees.

Rebirth of the Elwha River

The Elwha River pours through the remains of the Elwha Dam in Washington State’s Olympic National Park on October 23, 2011. The river ecosystem and former reservoir beds have recovered quickly after demolition of the two dams on the river. <i>Credit Kate Benkert, <a href=“https://flic.kr/p/aMrEQD”>USFWS</a></i>.

The Elwha River pours through the remains of the Elwha Dam in Washington State’s Olympic National Park on October 23, 2011. The former reservoir beds have recovered quickly and salmon and steelhead have returned after demolition of the two dams on the river. Credit Kate Benkert, USFWS.

For rivers with fewer economic and social demands, restoration guided by historical records of the natural dynamics of the river can be an effective restoration strategy, say Acreman and colleagues. To preserve species and get the maximum value from ecosystem services, river systems need to fluctuate in natural rhythms of volume, velocity, and timing ( to put it very simplistically).

At the end of the twentieth century, Washington State decided that the water of the Elwha River would be most valuable flowing freely through Olympic National Park to the Pacific at the Strait of Juan de Fuca, supporting salmon, trout, clams, and tourism. Habitat and eroded coastline are recovering at an astonishing pace only one year after the demolition of two dams freed the river, as Noreen Parks reports for her news story “Rebirth of the Elwha River” in ESA Frontier’s October Dispatches.

Rivers of the Anthropocene?

Outside protected wilderness, the Elwha’s story may be more of an anomaly than a blueprint for future river restoration projects. As non-native species, land development, and climate change remodel river ecosystems, it is no longer easy to define what is “natural” for river systems. But heavily used, regulated, and altered rivers have ecological value.

“The future of freshwater biodiversity is inextricably linked to land and water infrastructure management,” writes N LeRoy Poff of Colorado State University in his guest editorial for ESA Frontiers, in which he contemplates whether rivers have changed so much that we need to rethink some of our conceptions about restoration.

“We are rapidly entering an era where restoration interventions will be guided less by statistical deviations from historical reference conditions and more by “process-based” understanding of organism–environment relationships,” he writes.



Mike Acreman, Angela H Arthington, Matthew J Colloff, Carol Couch, Neville D Crossman, Fiona Dyer, Ian Overton, Carmel A Pollino, Michael J Stewardson, and William Young (2014). Environmental flows for natural, hybrid, and novel riverine ecosystems in a changing world. Frontiers in Ecology and the Environment 12: 466–473. http://dx.doi.org/10.1890/130134

Noreen Parks (2014). “Rebirth of the Elwha River.” Dispatches. Frontiers in Ecology and the Environment 12: 428–432. http://dx.doi.org/10.1890/1540-9295-12.8.428

N LeRoy Poff (2014). Rivers of the AnthropoceneFrontiers in Ecology and the Environment 12: 427–427.http://dx.doi.org/10.1890/1540-9295-12.8.427


ESA is the world’s largest community of professional ecologists and a trusted source of ecological knowledge, committed to advancing the understanding of life on Earth.  The 10,000 member Society publishes six journals and broadly shares ecological information through policy and media outreach and education initiatives. The Society’s Annual Meeting attracts over 3,000 attendees and features the most recent advances in ecological science. Visit the ESA website at http://www.esa.org.


This month in ecology: oysters, big rivers, biofuels

April highlights from Ecological Society of America journals


Media Advisory

For immediate release: 20 July 2012

Contact: Liza Lester (202) 833-8773 x 211; llester@esa.org


Ecological dimensions of biofuels: state of the science

Mississippi Basin - Pracheil et al. fig. 3

Mississippi River Basin. Green tributaries have sufficient flow for large-river specialist fishes, and long stretches unobstructed by obstacles of civilization. Blue tributaries fall below a critical flow threshold. Yellow tributaries discharge enough water, but are blocked by dams. From Figure 3 of Pracheil et al. Contact ESA for reuse.

Are biofuels a renewable, environmentally friendly energy source? The Ecological Society of America reviews bioethanol and biodiesel in conventional production as well as feedstocks still in development. Biofuels in commercial scale production are made from the sugars and oils of food crops, and share the ecological impacts of high intensity agriculture. Corn, the primary biofuel source in the United States, demands a lot of fuel to produce fuel. It needs nitrogen fertilizer, fixed using energy-intensive industrial processes. Much of that nitrogen ends up in waterways, where it causes problems for fish and fisheries. In some of the drier western states, farmers are drawing down groundwater resources to irrigate corn for biofuel. Cornfields are usually tilled, which releases greenhouse gasses stored in soil, loses topsoil to erosion, and loses water to evaporation.

Much hope has been placed in the “cellulosic” biofuels for their superior environmental benefits. Made from grasses, woody crops like poplar, crop silage and other plant wastes, cellulosic ethanol does not compete with the food supply for feedstocks, which consume fewer resources, and are potentially more compatible with wildlife. Mixes of perennial native grasses, for example, offer better habitat than monocultures and don’t need intensive fertilizer, pesticide, and water inputs. But cellulosic ethanol contributes only 0.5% of current biofuel production, and still faces major implementation challenges to become commercially viable. Algal biofuels remain in development. The authors conclude the report with recommendations to get the most out of biofuels going forward, improving ecosystem services, reducing greenhouse gases, and providing new income for rural communities.


  • Net greenhouse gas emissions: vary greatly by feedstock. Conversion of fallow, range, or wild lands to biofuel production releases greenhouse gases stored in soil. Tilling existing croplands also contributes greenhouse gasses. High intensity agriculture uses fuel for irrigating, fertilizing, sowing, harvesting, and transporting biofuel crops.
  • Water: biofuel processing plants do not use much water, but some of the biofuel crops do. Perennial crops such as switchgrass and mixed prairie grasses do not demand the irrigation, nitrogen fertilizer and yearly soil tilling typical of high intensity corn production.
  • Land use and wildlife diversity: biofuel crops compete with food crops. Demand for biofuels drives conversion of prime agricultural land, expansion into marginal agricultural lands and reopening of reserves. To meet current US energy demand through biofuels alone would require conversion of 41% of US land to corn, 56% to switchgrass, or 66% to rapeseed, but potentially only 3-13% to algae. Drought tolerance, fast growth and pest resistance, traits that make plants fine candidates for biofuel feedstocks, also make them fine candidates for becoming invasive. Some, such as the old world grass miscanthus, are already invasive in North America.

Ecological Dimensions of Biofuels. Cifford S. Duke, Richard Pouyat, Philip Robertson, and William J. Parton. Issues in Ecology No. 17, Spring 2013.

Looking to large tributaries for conservation gain

On big rivers like the Mississippi, the infrastructure of modern civilization – dams, locks, dikes, power plants, cities – has made life easier for people, but harder for fish and other denizens of the river. Restoration is a tricky problem. Economic reliance on these big rivers makes fundamental reversals like dam removals unlikely. Conservation laws and projects tend to be local, on the city or state level, and the river crosses many borders, complicating the restoration picture.

Brenda Pracheil and colleagues at the University of Wisconsin, Madison, say tributaries have under-appreciated potential to compensate for habitat loss on the major concourses of the Mississippi Basin. The Platte, for example, has 577 kilometers of free-flowing, relatively intact habitat. It feeds into the heavily altered Missouri, a large mainstem river in the Mississippi Basin, and harbors many of the same fishes.

Pracheil found a correspondence between the volume rate of water flow and the presence of 68 large-river fishes, including paddlefish, blue catfish, and silver chub, most of which are threatened. A steep threshold separates tributaries with large-river fish from those without; 166 cubic meters per second is big enough for roughly 80% of large river specialist species. Below the threshold, almost none of these species are around. Pracheil says this threshold could be used to target tributaries for conservation attention. Existing regulatory structures don’t allow improvements on tributaries to count toward mainstem restoration mandates. The UW scientists argue that more flexibility could, in some cases, provide a better return on investment of conservation dollars, complementing efforts on the larger rivers downstream.

Enhancing conservation of large-river biodiversity by accounting for tributaries (2013) Brenda M Pracheil, Peter B McIntyre, and John D Lyons. Frontiers in Ecology and the Environment 11(3): 124-128

Oyster reefs buffer acidic inputs to Chesapeake Bay

When European settlers arrived on Chesapeake Bay, it was encrusted with a treasure trove of oysters and other bivalves. The living oyster reef and its stockpile of empty shells was voluminous enough to influence the water chemistry of the bay, says marine ecologist George Waldbusser and colleagues. Based on harvest records from the 17th century, he estimates that the oyster-impoverished bay of 2013 is running “at least 100 million bushels behind where it was before we started harvesting, in terms of shell budget.”

Oysters eat microscopic phytoplankton, including algae, which the bay generally has overabundance of thanks to excess fertilizer runoff. Oysters are not just a tasty economic resource – they make Chesapeake Bay cleaner. The missing shells are a direct loss to oyster restoration, because oyster larvae are choosy about where they glue themselves down and start building their shells. They prefer other oyster shells as anchorage.

But in addition to providing habitat for future generations, oyster reefs appear to alter their local water chemistry. Like slow dissolving Tums in the belly of the estuary, disintegrating oyster shells are slow release capsules of calcium carbonate, an alkaline salt and a buffer against acidity. Seawater mixing in on the tide has a relatively high capacity to absorb acid inputs without a large change in pH. Fresh water flowing out to sea generally has a low buffering capacity, and is sensitive to acid sources, whether from human made point sources like coal plants or natural processes like the oysters’ own respiration. Coastal estuaries, where the waters meet, are also where oysters tend to cluster.

Ecosystem effects of shell aggregations and cycling in coastal waters: An example of Chesapeake Bay oyster reefs. (2013) George G. Waldbusser, Eric N. Powell, and Roger Mann. Ecology 94(4): 895-903 (Currently in authors’ preprint; contact Liza Lester for a type-set copy).

Journalists and public information officers can gain access to full texts of all ESA publications by contacting the public affairs office. Email Liza Lester, llester@esa.org.


The Ecological Society of America is the world’s largest community of professional ecologists and a trusted source of ecological knowledge. ESA is committed to advancing the understanding of life on Earth. The 10,000 member Society publishes five journals, convenes an annual scientific conference, and broadly shares ecological information through policy and media outreach and education initiatives. Visit the ESA website at http://www.esa.org.

To subscribe to ESA press releases, contact Liza Lester at llester@esa.org