Evaluating efficiency

Aquatic ecosystems need nutrients to survive, but excess nutrients can be a big problem – they can lead to blooms of algae in lakes, ponds, and bays (I’ve written about algal blooms before, here and here). Algal blooms are a natural phenomenon often exacerbated and made more frequent by human activities, primarily through the addition of nutrients to a watershed – a glut of nutrients adds fuel to the fire of a bloom.

Wastewater is one of the many sources of human-added nutrients in aquatic systems. Treatment plants collect wastewater from households (and sometimes industrial customers), process the water in some way, and release the treated water, or effluent, back into the local watershed. Depending on the type of facility, there may still be large amounts of nitrogen and phosphorous – the main nutrients in aquatic ecosystems – present in the effluent. Those nutrients will be washed downstream, where they can harm humans and natural systems by, among other things, contributing to algal blooms.

As older wastewater treatment plants are replaced by more efficient facilities, they need to be evaluated. The first step is deciding which metrics to use – what do you measure to see if an ecosystem is responding to a reduction in nutrients?

A research team working in France recently had the opportunity to answer that question when the city of Nîmes, in southwestern France, updated their wastewater treatment plant. The scientists measured a suite of metrics to assess water quality, before and after the new wastewater treatment plant opened; the results of their study were reported recently in the journal Freshwater Science.

Macroinvertebrate activity – the way aquatic insects are behaving – as well as their numbers and diversity can be a kind of barometer of stream health. In this study, the researchers found that the way the macroinvertebrates were functioning in the stream (the way they behaved) told a different story than the way they were structured in the stream (the number of different species, and the number of individuals of each species).

By the numbers, the sites below the wastewater treatment plant had begun to recover – they began to resemble a reference site above the treatment plant outfall, and sites in other, more pristine streams – within three months of the improved system coming online. The functional metrics, however, suggested that the health of the stream still had room to improve – by the end of the study, three years after the new treatment plant was built, the sites below the treatment plant still had not recovered according to many of those measures.

“Taxonomy-based metrics detected the first signs of river reach recovery rapidly,” the scientists write, “but combinations of trait-based metrics and taxonomic abundance-based metrics are more likely to identify functional recovery” of macroinvertebrate communities following nutrient reductions. In other words, in order to figure out if we’re cleaning up our act as much as we think we are when we make improvements to our wastewater treatment plants, we probably need to measure several different metrics of ecosystem response.

Even small towns often have wastewater treatment plants; this one serves a rural community of less than 1,000 people.

(Image by Emily Benson)

Shetland's wind

The first thing I noticed about Shetland – a series of islands off the northern coast of mainland Scotland – was the lack of trees. The second thing was the water. Exquisite, turquoise seawater lapping at craggy cliffs, or, in some places, white sand beaches that looked like they’d been lifted straight from the latest ad campaign for some tropical resort, the only thing marring the picture the layers polar fleece and wool piled on the people there. In June.

A sandy shoreline on the coast of Shetland.

(Image by Emily Benson)

At roughly the same latitude as Anchorage, Alaska, mid-summer weather in Lerwick, the capital of Shetland, can be pretty chilly – typical temperatures barely hit 60°F on the hottest days of the year.

There are some trees in gardens and yards in and around Lerwick, but outside the town, the landscape is dominated by grass-covered hills. Trees once grew throughout the islands, but most were long ago cut down for firewood, and the ubiquitous presence of grazing sheep has kept the forests from growing back. I visited Shetland for three weeks in June almost 10 years ago (I was working on a project that had to do with modern interpretations of traditional folk art). If the wind came up when I was out walking in the hills, surrounded by nothing but open space, it felt as if the whole world was blowing by.

Rocky coastline in northern Shetland.

(Image by Emily Benson)

Recent research conducted by a team of scientists at the Scottish Marine Institute suggests that the same winds that I found overpowering on land might be changing the dynamics of algae blooms at sea. Seafood production, including catching or farming fish and shellfish, is a major component of Shetland’s economy; over the past few decades, blooms of Dinophysis, a dinoflagellate that produces toxins responsible for diarrhetic shellfish poisoning, have periodically threatened shellfish production and led to closures of shellfish harvesting areas. In order to predict when and where Dinophysis population booms might occur, these researchers turned to wind records.

I’ve written before about predicting algae blooms based on temperature; the blooms off the coast of Shetland appear to be increasing faster than Dinophysis can grow, suggesting that seawater containing Dinophysis cells is being blown in from other locations and that wind, rather than temperature, might be a good bloom predictor in this system.

The largest Dinophysis blooms the scientists studied occurred during the summers of 2006 and 2013; during those years, the prevailing summer winds were more westerly than in other years, when they tended to come from the south. The researchers suspect that the westerly winds blew in water full of Dinophysis, a supposition supported by their observation that water samples from sites on the eastern side of Shetland, protected from the westerly winds, contained fewer Dinophysis cells than samples from the western side of the islands.

“As the frequency of harmful algal blooms around the globe is perceived to be on the increase,” the scientists write, “and as the levels of investment in aquaculture rise, an understanding of their underlying causes . . . is more important than ever.”

When I recall standing on the stark cliffs and beaches of Shetland’s landscape, bundled in sweaters and a hat in June, it’s not hard to believe that wind may be exacerbating harmful algae blooms – in Shetland, wind seemed to be a driving force behind many things.

A storm blowing in on a windy day.

(Image by Emily Benson)

Lab work, field work

Sometimes scientists work in a lab, under carefully coordinated conditions finely tuned to elicit certain reactions from whatever they’re studying. Sometimes, they work in the field, under whatever circumstances nature serves up when they happen to be outside, observing, measuring, recording, and sweating or shivering, depending on the day.

Ecologists are interested in how the natural world works – lab experiments can fill in the details, but they (by definition) don’t include all of the variables that are actually at play in the real world. Field observations can flesh out the big picture, but without control over environmental dynamics, researchers often can’t be sure which factors are responsible for observed changes.

One way to balance the strengths and weaknesses of these two approaches is to move the lab outside – which is just what two researchers from the Netherlands Institute of Ecology did when they wanted to investigate the way nutrients and plant-eating ducks affect aquatic vegetation, as reported recently in the journal Oecologia.

The scientists combined the benefits of a controlled setting – they used 20 man-made ponds in their experiment, all the same size, shape, and depth – with the advantages of working in a natural system: they filled the ponds with lake water and exposed them to the daily rhythms of weather and sunlight by working outside.

The researchers fertilized half of the experimental ponds with extra nutrients, and introduced ducks – which eat mainly plants, though they also consume insects – to half of each type of pond (fertilized and unfertilized). By the end of the experiment, the fertilized ponds with ducks had 50% less plant material than the fertilized ponds without ducks, but in the unfertilized ponds, the ducks didn’t appear to have eaten any of the aquatic plants. The scientists suspect that this may have been due to plant nutrient levels – the plants in the fertilized ponds contained more nutrients than the ones in the unfertilized ponds, which could have made them more appetizing to the ducks. The fertilized ponds also developed a different plant community than the unfertilized ponds – perhaps the most prevalent plant in the fertilized ponds simply tasted better, from the ducks’ perspective, than the plant that came to dominate the unfertilized ponds.

“In our study,” the scientists write, “the effect of plant species and pond nutrient status cannot by fully separated and the relative importance of plant species and plant nutrient concentrations in determining grazing pressure thus remains to be investigated in more detail.” Therein lies the challenge of experiments conducted in natural settings – when all factors cannot be controlled, it’s difficult to tease apart which ones are most important.

Field and lab studies both have advantages and drawbacks, but, luckily for science, not the same ones – fieldwork and lab work are two sides of the same coin, complementary tools that scientists can use to puzzle out the mysteries of the natural world.

Mallard ducks can live in almost any kind of slow-moving aquatic habitat, including ponds, marshes, floodplains, and many other places. 

(Image by Carsten Niehaus via Wikimedia Commons)

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)