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ASU researchers warn of unintended consequence of residential xeriscaping

Think you're helping environment with that xeriscape yard? Yes ... and maybe no.
High nitrate levels could lead to algae blooms that harm aquatic ecosystems.
October 28, 2016

Study says nitrogen levels in water rise as homeowners remove lawns, but there are ways to mitigate effect

About two years ago, when the full force of California’s drought came to bear, green lawns turned faces red as “drought shaming” became a social media pastime.

Shots of sprinklers spattering sidewalks, replete with full addresses. Aerial photos of celebrity homes with lush grounds (Cher, Oprah, Streisand, Kardashian — Twitter’s watching you). “The new class warfare,” one publication dubbed it.

In Tucson, a turf lawn has been seen as the green badge of ignorance for decades.

Western water woes, and accompanying municipal incentives to tear out the turf and replace it with what is being referred to as “climate-appropriate” vegetation, have given rise to a new popularity in xeriscaping. In 2015, almost 80 cities paid residents to rip out the rye. Smile. You’re doing the right thing.

A recent study by a pair of Arizona State University researchers, however, revealed that xeriscaped yards contain higher levels of nitrate than turf yards. Downstream, as irrigation transports nitrate into the soil, those levels could affect water quality, leading to algal blooms and wreaking havoc with aquatic ecosystems.

When a homeowner decides to xeriscape and rips out the lawn, either the turf is killed and removed or killed and tilled into the soil. If it’s tilled into the soil, organic material left behind decomposes and nitrates build up.

Xeriscaped yards had more nitrates than yards with lawns and increased in nitrate levels until 14 to 18 years after conversion. Older xeriscaped yards had similar nitrate levels to turf yards.

“The amounts we found are comparable to what you’d find in an agricultural landscape,” said Hannah Heavenrich, lead author of the study and a research specialist in the School of Life Sciences. “It’s sort of a big deal because in an agricultural landscape, where they’re irrigating a lot, that water is flowing off the landscape into irrigation ditches and eventually into things like canals or retention basins.”

In Arizona, this is less of a problem because natural bodies of water are few and far between.

“That doesn’t mean it’s not going to be a problem in other cities,” Heavenrich said. “Most of the large cities in California have a rebate in place for incentivizing homeowners to replace their turfgrass with some sort of xeric landscape.”

What would-be xeriscapers can do is completely remove grass with a turf cutter, reducing organic material left behind. Instead of watering and fertilizing the entire yard, add water and fertilizer only where the plant’s roots will reach. Planting mature shrubs and larger trees will increase nitrate uptake. But Heavenrich said the findings are more geared towards policy makers than homeowners.

“In a very broad sense, it’s important to look at the consequences for your actions and what are the best management practices,” she said. “It’s more geared towards managers and people who are guiding the public, rather than homeowners, because they’re going to be guided by what their city ordinances tell them to do or what they should do.”

But Heavenrich said managers should beware the best-laid plans.

“Those larger entities need to keep in mind what are those unintended consequences are,” she said. “Is there a way to create a management practice that evens the playing field, making sure you get those monetary benefits and reductions in water use, but aren’t causing some other reaction?”

The study, co-authored with associate professor Sharon Hall, was published in Environmental Research Letters.

 

Top photo by Deanna Dent/ASU Now. The School of Life Sciences is an academic unit of the College of Liberal Arts and Sciences.

Scott Seckel

Reporter , ASU Now

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Happy Halloween! These ASU researchers are scary smart.
Creepy crawlies are helping ASU scientists learn more about our world.
October 28, 2016

ASU scientists study snakes, spiders and other creatures to learn more about climate change, environment and society

Editor's note: In the spirit of Halloween, we offer a roundup of the engrossing research happening around ASU with creatures that are often relegated to spooky decorations.

Arizona State University researchers spend time in the field face-to-face with creepy, crawly organisms to better understand our environment, climate change and society.

Some research subjects bite, some sting and some are venomous, but all of them are fascinating in their own creepy ways.

Black widows

Black widow spiders on a web
A female black widow (top) and a much smaller male black widow crawl on a web at the black widow lab at ASU's West campus in Glendale. The research New College associate professor Chad Johnson and his students are conducting focuses on how spiders make a living in urban and desert environments. Photo by Deanna Dent/ASU Now

 

If you see Chad Johnson scoping out dark corners in downtown Phoenix, don’t worry — he’s just looking for black widow spiders.

“For the past 10 years I’ve focused on the black widow,” the associate professor in the School of Mathematical and Natural Sciences in ASU’s New College of Interdisciplinary Arts and Sciences said. “It’s an urban pest here in Phoenix, and in my lab we study how they deal with the environment, climate change, and their behavior, physiology and population genetics.”

Johnson is trying to understand the effects of the urban heat island on black widows and their population growth. The urban heat island is the idea that cities and urban areas are characterized by a lot of concrete, which captures heat during the day and retains it at night. In contrast, the desert soil will release heat at night, creating a cooler environment.

“Urban critters, particularly male black widows, grow quickly in the warmer downtown environment,” Johnson said. “Male black widows are tiny, minute compared to the famous large females, but they can mature in a month or two after they hatch from the egg. We’re also seeing that widows adapt well to the heat, they move around quickly, and they’re able to find a lot of prey downtown. We actually have a hard time finding them in the desert when we go out looking for them.”

One of the reasons Johnson focuses on cities and urban heat islands is that as temperatures rise due to climate change, cities will be at the peak of temperature projections.

“Black widows are uniquely plastic as creatures,” he said. “They are able to adapt to different situations. Other organisms don’t have that broad spectrum.

“I’m concerned for our biodiversity, and that climate change will lead to selection for only species that can deal with its effects. In cities, that will mean pigeons, cockroaches and black widows outlast other species because they are highly tolerant, adaptable species that can handle these human changes.”

Lizards and their mites

Photographing a lizard
ASU student Lauren Jackson photographs a whiptail lizard in the field. The research studies whether the species is more susceptible to certain diseases by looking at the parasites that live on the outside of the lizard bellies. Photo courtesy of Heather Bateman

 

Heather Bateman, an associate professor in the College of Integrative Sciences and Arts, is interested in species ecology in Arizona’s floodplains and riparian areas, which are areas where land meets with rivers and streams. Bateman specifically studies amphibians and reptiles.

“I focus on these species because they’re an important part of the food chain and our ecosystem,” Bateman said. “Most lizards eat insects, and most are very good at operating with high body temperatures. They also are sensitive to changes in canopy cover and their environment.”

Whiptail lizards are one of the more peculiar lizards Bateman and her students find in the field. Most vertebrate species have a mom and a dad who reproduce to create offspring. Some whiptail lizard species are entirely female, and they reproduce parthenogenetically, or by producing eggs that are genetically identical to mom.

One student on Bateman’s team, Lauren Jackson, is studying ectoparasite loads, the number and type of parasites that live on the outside of female whiptail lizard bellies. 

“Since there’s no genetic variety in these populations, we’re looking at whether or not the species is more susceptible to certain diseases,” Bateman said. “One way to look at how well off these parthenogenic species are in terms of health and disease is to evaluate external mites.”

Lauren spent all summer finding whiptails, taking pictures of their bellies and counting mites to test a hypothesis that sexual and parthenogenic whiptails have different mite loads.

Rattlesnakes

Rattlesnake
A rattle is actually a rather polite way for a rattlesnake (such as this Western diamondback) to say back off, says ASU associate professor Dale DeNardo. This and top photo by Sandra Leander/ASU

 

Arizona’s deserts are home to a number of incredible reptilian species, including rattlesnakes. Dale DeNardo, an associate professor in the School of Life Sciences in the College of Liberal Arts and Sciences, gets up close with rattlers and other reptiles to better understand how they are handling the effects of drought and climate change.

“Rattlesnakes spend a lot of time on the desert surface, and we’re working to understand how hydration levels affect the state of the animal,” DeNardo said. “Their environment is changing quickly, and like many species dealing with the effects of climate change, they don’t have time to adapt evolutionarily; they have to cope with these changes behaviorally and physiologically.”

For many people, the sound of a rattlesnake’s warning is terrifying. But, from DeNardo’s perspective, the rattle sound actually is a generous warning.

“A bite from a rattlesnake is really a fourth line of defense,” he said. “First, they will camouflage themselves and hide while waiting for the threat — a hiker, for example — to go by. The second thing they will do is try to escape by hiding in a bush or under a rock. The third thing they’ll do is rattle. When they eat, they don’t rattle at their prey. It’s a very generous and polite warning — the snake is saying, ‘I’m tough, I can hurt you, and I want to be left alone.’ ” 

The last thing a rattlesnake wants to do is strike and waste its venom, DeNardo said. A rattlesnake’s strike pose, coiling up and facing a threat, is a means of protecting its body. Striking is a last resort for rattlesnakes because striking means having to extend their bodies, giving bigger predators an opportunity to grab and harm them.

Dracula ants

Dracula ant
An Adetomyrma venatrix, or dracula ant, specimen. Photo by April Nobile/AntWeb.org/via Wikimedia Commons

 

Many ants, maybe the kind you would see marching through your backyard or kitchen, can get nourishment from their nestmates through trophallaxis, the transfer of regurgitated food back and forth between adults or larvae.

“There is a tube-like mouthpart that allows them to pass food back and forth, and it looks a little bit like they’re licking each other,” said Ted Pavlic, associate director for research in the ASU Biomimicry Center.

Dracula ants have a darker feeding method. Instead of larvae regurgitating food to hungry adults, the adults will puncture holes in their own larvae to drink hemolymph, which is essentially insect blood.

“This doesn’t kill the larvae; the puncture sites close up and leave a visible scar,” Pavlic said. “The larvae will grow up, and queens may drink the ‘blood’ of their own offspring in the future.”

Pavlic studies natural systems, including social insect colonies, to better understand decision-making systems. He is an assistant professor jointly appointed in the School of Computing, Informatics and Decision Systems Engineering and the School of Sustainability, as well as an adjunct faculty member in the School of Life Sciences. The School of Computing, Informatics and Decision Systems Engineering is part of the Ira A. Fulton Schools of Engineering.

Termites

Termites in a mound
Termites are social insects. They have large colonies with a king and queen, and workers that will take care of eggs. Photo by Gavinevans via Wikimedia Commons

 

Not all termites eat wood, but it is a favorite source of tasty cellulose for lower termites. When lower termites move into your house, they can cause large amounts of damage for their size. In order for them to digest piles of cellulose, termites get help from protozoa that live in their hind gut compartments.

“The protozoa are packed in, and they writhe around in there and help termites digest,” said Gillian Gile, an assistant professor in ASU’s School of Life Sciences. Gile is an evolutionary microbiologist who studies symbiosis, or the relationship between distinct organisms, such as termites and their protozoa, maintained over an evolutionary time.

Each termite can have between 1,000 and 1,000,000 protozoa. For a 4-foot, 9-inch human weighing 100 pounds, this would be like carrying 40 pounds of snails, slugs and worms in their lower intestine.

The world has about 1,000 lower termite species, and each has its own set of protozoa. Arizona is home to 16 species, and the most commonly found is Heterotermes aureus. Termites also are social insects. They have large colonies with a king and queen, and workers that will take care of eggs.

Bees

The Southwest is home to a number of bee species, including one that is responsible for pollinating a single type of flower that blooms for just a few weeks each year: cactus flowers on saguaro, prickly pear and other cactus species.

A man wears a beard made of bees
ASU professor Brian Smith says his bee beard "actually tickled." Photo courtesy of Smith

For Brian Smith, a professor in the School of Life Sciences, bees are fascinating. So much so that he once wore a bee beard made of 10,000 living bees crawling on his face.

“I didn’t get stung,” he said. “All the little bee feet actually tickled.”

Smith studies how animals learn about odors in order to predict important events, such as an encounter with food, a mate or a predator. He also is interested in how animals learn and their memory processes.

“Bees are excellent learners — they are brilliant,” he said. “Bees can learn things, skills and processes, that are good to know now but may not be useful for tomorrow when they need to learn something else. Their world, the insect world, changes fast, and they are eager to learn and be flexible.”

In 2016, bees were added to the U.S. endangered species list for the first time. To help bee populations, Smith encourages people to speak with experts at their local nurseries about types of flowering plants that are good for bees. He also encourages people to not spray their yards and flowers with pesticides.

Bats

Little brown bat
The little brown bat has been nearly wiped out by white-nose syndrome, a fungal pathogen that happens to grow best and affect bats most often during hibernation conditions. Photo by U.S. Fish and Wildlife Service Headquarters via Wikimedia Commons

 

Many bats in northern Arizona head into caves to hibernate during the winter months. During hibernation, their bodies drop to ambient temperatures, often just above freezing. Their hearts beat as few as 10 times per minute. Their circulation is reduced, they don’t eat and they are dependent on fats stored prior to hibernation.

That’s where Marianne Moore, assistant professor in the College of Integrative Sciences and Arts, comes in. Moore’s research focuses on white-nose syndrome, a fungal pathogen that happens to grow best and affect bats most often during hibernation conditions. The syndrome was first observed in 2006 and has nearly wiped out some species of bats, including the Myotis lucifugus, or little brown bat. The little brown bat was once the most common bat in North America, but today only 4 percent of that 2006 population remains at heavily impacted sites.

“The syndrome attacks them through their skin and causes them to come in and out of hibernation more often than normal,” Moore said. “Every time bats go through this process they expend a lot of energy, and many that we find dead due to the syndrome are emaciated. We know it’s due to the pathogen, and we’re trying to understand the mechanisms that result in the death of bats. Now, while this is very scary and horrible, there is some hope.”

Moore does find survivors near areas where the syndrome hits hard. Those survivors are banded, so her team will know how long they’ve been around.

“We don’t know why yet, but some bats appear to be completely resistant,” she said.

Bats are voracious consumers of agricultural pests and nocturnal insects, including mosquitoes. The loss of bats means the loss of control over the insects they consume. What can people do to help?

“The most important thing is for people to be aware of this and to know that it likely was caused by humans,” she said. “If people are recreational or avid cavers, there are ways for them to decontaminate their clothes and equipment so they don’t spread the syndrome when they explore different caves.”

ASU’s Hasbrouck Insect Collection

Insect collection
The ASU Hasbrouck Insect Collection is open to the public, by reservation.

 

Want to explore some creepy critters yourself? A few miles south of the Tempe campus is a 24,000-square-foot collections research facility with nearly 2 million insects, reptiles, fish, birds and mammals arranged on shelves, set on pins and lined up in glass drawers.

The ASU Hasbrouck Insect Collection is open to the public, and visitors should call ahead or email to arrange a tour. Visitors who stop in will be greeted by 5-foot-tall models of a Mormon cricket, a robber fly and a spider.

“We have a large collection of Arizona spiders and scorpions,” said Nico Franz, curator of the collection. “We operate very much like a museum, but when visitors come here they get to interact directly with researchers who can answer questions about different species.”

Get more information about the collection online.

Leslie Minton

Media Relations Manager , Media Relations and Strategic Communications

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