How clams help determine at-risk ecosystems

Findings from a new study published in the journal Environmental Pollution show that clams can act as a litmus test for ecological risks of plastic pollution.

Researchers in China discovered microplastics in Asian clams in the Yangtze River to be representative of microplastic pollution in the river’s ecosystems.

“The levels of microplastics in the Asian clam can serve to track the amount of microplastics that may be available to marine animals of a similar size,” say the authors. “From an ecological perspective, Asian clams can provide a snapshot of what can be ingested across a large area.”

Microplastics are tiny plastic particles that are smaller than 5mm—or about the width of a pencil.

These small particles were detected at high levels in 96% of Asian clams sampled. At these levels, researchers say, habitat contamination and transfer to other organisms is likely.

Clams were chosen as “indicators” of microplastic pollution because they are filter feeders—essentially acting as a strainer trapping food and other small particles in water.

Along with clams, sediment and water were collected for microplastic analysis at 21 sites along the Yangtze river. Within those study areas, three different ecosystems were selected: lakes, rivers, and estuaries—transition zones where saltwater meets freshwater.

To isolate microplastics, the researchers used a series of elaborate filters, nets, and vacuums.

Levels of microplastics varied greatly across the three ecosystems. Rivers contained higher levels, which could be attributed to lower water volume, or even proximity to industrial plants.

“Some of the rivers are located in urban areas and receive more wastewater than lakes,” the authors say. “Sediments in river drainage areas are also likely hotspots for microplastics.”

Microplastics are ubiquitous in marine environments. These particles have pervaded every marine ecosystem in the world. Plastic pollution found in marine animals has ran the gamut from sea birds, sea snakes, and sea turtles to penguins, seals, and sea lions.

The extent of microplastic pollution in freshwater systems—like lakes and rivers—is less clear. However, recent studies are beginning to paint a bigger picture.

A few months ago, scientists in Germany discovered that rivers are responsible for a considerable amount of marine plastic pollution—with rivers in Asia being a heavy contributor.

Although this pollution can seem distant to humans, we are not isolated from it. Shellfish, such as the Asian clam, are a source of nutrition for billions of people, and are widely consumed throughout China. People typically eat clams without removing the digestive tract. As a result, the contents of a clam’s stomach—and plastics within it—become the contents of the consumer’s stomach. Ingestion of these microplastics is a possible health risk and has been shown to cause inflammatory reactions.

“Few studies have determined the level of microplastics exposure from freshwater shellfish consumption,” say the researchers of the current study. “So, it will be valuable to set the baseline for microplastic consumption by humans. Potential human health risks should not be ignored.”

Climate change threatens future stability of rice ecosystems

New research claims climate and land-use change will greatly lower rice yields by the end of the century.

Rice yields in the Philippines and Vietnam could decline 30% by the year 2100.

“Because of a temperature increase in the Philippines and Vietnam of up to 4°C, rice yields can be kept steady only at the expense of natural vegetation, which would likely reduce native habitat and biodiversity,” say the authors of the new study published in the journal Environmental Research Letters.

The researchers created simulation models (from 2000-2099) comprising seven study areas to arrive at these conclusions. For climate change, two future scenarios were considered: a 1.5°C-2°C trajectory and a 3°C-4°C trajectory. For land use change, three future scenarios were chosen: low rice conversion, high rice conversion, and one based on global economic trends. The scientists then determined how these models affected ecosystem services—benefits humans gain from the environment—provided by rice ecosystems.

Along with rice yields, the study predicted a climate-induced decline in two other ecosystem services: carbon storage and carbon sequestration.

Carbon storage, a plant’s ability to store carbon long-term, is estimated to decrease 15% by the end of the century. This loss of storage capacity is caused by less photosynthesis (absorbing carbon) and more respiration (releasing carbon). Just like the proteins in our bodies, proteins driving photosynthesis slow down at high temperatures.

Land-use change also worsened carbon storage. As land is converted to rice fields, forests are decimated and the stored carbon is released

The outcome of climate and land-use change on carbon sequestration is more nuanced, though. Sequestration can be thought of as a carbon scale: photosynthesis as a weight on one side and respiration as a weight on the other side. Overall, by the end of the century, respiration outweighed photosynthesis—carbon sequestration declined by 12%.

However, when land-use change was added in high amounts, carbon sequestration shot up. To rapidly grow, crop plants—like rice—imbibe large amounts of carbon, while releasing little. This is in contrast to older forests, which absorb less carbon as their growth slows.

Another ecosystem service, irrigation water, was projected to increase by 10%-20%. Despite this, rice yields still markedly decreased. Although more land-use somewhat offsets the effects of climate change on yields in the early 21st century, those offsets are later negated in the latter half of the century by rising temperatures.

As rice is a staple food for 3.5 billion people—nearly half of the world’s population—declining yields could have prodigious consequences. Rice cultivation is the main source of income for over 100 million households across the world.

Cultural identity is at stake, too. These ecosystems shape farmers’ values, spiritual experiences, and connection to the natural environment.

“Locally specific land use policies and development plans have to consider more than the availability of rice,” the researchers say. “Cultural services to maintain future human wellbeing must be included.”

A 1.5°C cap to global warming could greatly benefit Europe

New research shows that limiting warming to 1.5°C would reduce the frequency of extreme heat and rainfall across Europe.

This is compared to a previously sought 2°C limit to global warming. Many scientists now say a 2°C cap is not enough, and would place extreme stress on many of the world’s most sensitive ecosystems. A 0.5°C difference may seem insignificant, but it could make all the difference in avoiding record-breaking heat waves.

Researchers at the University of Melbourne and the University of Oxford used simulations—called coupled climate models—to show that 1.5°C of global warming would make extreme heat waves in Europe less likely to occur.

“For example, we found that events similar to the European heat wave of 2003, which caused tens of thousands of deaths, would be 24% less frequent in a world at 1.5°C global warming compared to 2°C global warming,” say the researchers.

Changes in rainfall were also included in the climate models. Although the changes are less pronounced compared to warming, they could still have major consequences for European countries.

“There is an increase in the frequency of very wet days like those seen during May–July 2007 over the UK and Ireland. In a 2°C world, such extreme rainfall events are at least 17% more likely than in a 1.5°C world.”

In England alone, the economic cost of damage to property from the Summer 2007 floods was estimated at $4 billion. If a 2°C threshold is reached, Europe could expect flooding damage like this once every 10 years.

The Paris Agreement—an international effort to keep global warming below 2°C and to attempt to cap the warming further to 1.5°C—has recently sparked a wave of studies examining what’s needed to achieve this cap. Many of these studies now suggest that negative emissions, removing carbon dioxide from the atmosphere, are needed to keep global warming below 2°C, which is becoming increasingly unlikely.

This failure to limit global warming could have considerable consequences for Europe.

“In future scenarios of 1.5°C and 2°C warming, heat extremes become considerably more frequent,” the authors of the current study say. “Even at only 1.5°C of warming we estimate that hot years across Europe, like 2016, the hottest year on record, would happen roughly one-in-every-two years.”