Replenishing California's aquifers

Water is a perennial topic in California. How much rain is falling, and where? How can we get cities and farmers to use less? How fast are we sucking it from underground aquifers? And, of course, how can we get more?

UC Santa Cruz professor Andy Fisher and his graduate student Sarah Beganskas are working on that last question. They’re building percolation ponds in the Pajaro Valley, on the central coast of California. Their goal is to replenish groundwater, which we’re using faster than nature alone can replace. The idea is to capture excess storm water before it gushes out to sea. (Recently, I wrote about their work for the San Jose Mercury News.) 

One problem with collecting storm water is that it can pick up fertilizers and pesticides as it cascades across the landscape. The UCSC scientists are trying to figure out how to deal with that issue; one idea is to enlist the help of bacteria. Adding a layer of microbe-harboring wood chips to infiltration basins might reduce pollutants before water soaks into the aquifer below. Early results from tests Beganskas and Fisher are running at Watsonville's Harkins Slough suggest that wood chips alone may not be enough, though. The microbes need time to work, so the researchers will experiment with slower infiltration rates in future trials.

When it rains, water collects in this infiltration basin at Harkins Slough, then percolates through the soil to recharge the groundwater below. (Image by USDA/Lance Cheung)

Scoops of seawater

The Great Barrier Reef World Heritage Area, off the northeast coast of Australia, is “one of the richest and most diverse natural ecosystems on Earth.” Thousands of species of mollusks, more than 1,500 species of fish, and 400 species of coral live within its waters.

There’s something else there, too – herbicides, washed into the ocean via rivers draining agricultural areas.

Herbicides can breakdown in nature (UV rays can degrade the molecules, or microbes can consume them), but it’s unclear how long that process might take under the conditions that occur around the Great Barrier Reef – many of the studies conducted in the past included unrealistic conditions, like unusually low temperatures or levels of herbicides 500 times higher than what researchers typically find there. A group of scientists working in Queensland, Australia, sought to detail the timing of herbicide persistence in seawater from the Great Barrier Reef lagoon kept under more natural conditions; they recently published the results of their study in the journal PLoS ONE.

Working with samples of water scooped up from off the coast of Queensland, the researchers added several different herbicides, then stored the flasks under different combinations of conditions: some in the dark, some under partially lit conditions, some at 77 degrees Fahrenheit (the average temperature of seawater around the Great Barrier Reef over the course of a year), and some at 88 degrees Fahrenheit (the summertime high temperature of seawater near the shore in part of the Great Barrier Reef lagoon). They took samples from the flasks every few weeks for a year to measure the herbicide concentrations, allowing them to estimate how quickly the herbicides broke down.

The estimated half-life of each herbicide – the time it takes for half of the initial amount of the chemical to degrade – ranged from about 150 days to more than 5,000 days. The light and temperature conditions the flasks were stored under didn’t lead to consistent patterns in how the herbicides broke down.

The scientists also added a chemical that stops microbial activity to some of the flasks, and no herbicide degradation occurred under those conditions, suggesting that it was the microbial community present in the seawater collected from the Great Barrier Reef lagoon that broke down the herbicides.

“Chronic exposure of [the Great Barrier Reef] and catchment biota to . . . herbicides (from microbial communities to macrophytes) remains largely unstudied,” the researchers note, “and should be a future focus for research and risk assessment.”

Australia's Great Barrier Reef World Heritage Area stretches over 1,000 miles along the coast of Queensland. 

(Image by Tchami via Flickr: Creative Commons license)

Microbial mats

The thermometer in the hottest pool read 108°F. I inched down the astroturfed steps, gripping the wooden railing and grimacing at the way the heat stung my toes, a faint tinge of sulfur swirling up to my nostrils. At the bottom of the steps, I sat on a bench built into the timber beams lining the sides of the pool, the wood slippery under my skin. I made it barely five minutes before I retreated to the biggest pool at the hot springs, perhaps 10°F chillier than the little hot pot, the cooler water still warm enough to be a welcome respite from the autumn air as a few pellets of early snow dropped down from the clouds.

I couldn’t stay in the hottest pool for very long, but some organisms live their whole lives in water that hot – the wooden walls of each of the pools at the springs were coated with green mats of microbes, apparently thriving in the thermal pools.

An underwater view of microbes blanketing a wooden beam supporting the side of the larger, cooler thermal pool.

(Image by Emily Benson)

Hot springs have long been known to harbor some interesting bacteria – in fact, the modern method for analyzing DNA was revolutionized in the mid-1980s by the isolation of Taq polymerase, an enzyme derived from the heat-loving bacteria Thermus aquaticus. Because Thermus aquaticus lives at 176°F, the enzymes it produces are able to function at high temperatures – making them extremely useful for industrial processes, including replicating and analyzing DNA (pdf). Thermus aquaticus was discovered in 1966 by Thomas Brock, a biology professor, in a hot spring pool in Yellowstone National Park. Brock’s discovery ushered in a new era of “bioprospecting” in the park – researchers and entrepreneurs began searching for microbes that produce heat-stable proteins and enzymes that might prove useful in high-temperature industrial processes (pdf).

Thermal springs continue to yield previously undiscovered microorganisms, as reported recently in the journal Geobiology. A team of researchers collected microbial samples from 28 springs located throughout the southwestern United States. They focused on springs that are mesothermal – in other words, “cool but above ambient temperature,” the sort of springs that humans like to slip into for a dip (many natural hot springs, including most of the Yellowstone hot springs, are too hot for swimming).

Genetic analysis of the samples revealed that the springs contained a wide variety of organisms, and that the mix of microbes – the community composition – in each spring was distinctive. The microbes that the researchers couldn’t match to known samples – the ones that may be novel – were primarily found in just four of the springs they sampled, suggesting that some springs have more potential for harboring new microbes than others.

I didn’t take any samples from the hot springs I visited, but the microbial community appeared to be doing quite well. Perhaps there was an unidentified microbe right under my fingertips when I ran my hands down the slick wooden walls of the pools, just waiting to be discovered.

A swimmer's view of the changing rooms at the hot springs. 

(Image by Emily Benson)