Submerged plants reduce greenhouse gas emissions from shallow lakes and ditches

Shallow lakes and ditches emit less greenhouse gases if rooted submerged plants are predominant instead of free-floating plants or algae. There are several reasons why Dutch water managers should encourage more submerged plants in Dutch waterways, researchers argue. But these plants will have a better chance of survival if fewer fertilizers are leached into Dutch waters. The researchers recently published their findings in the journal Water Research.

Lakes and ditches cause a large share of the total emissions of methane, a greenhouse gas, in the Netherlands (estimated to be around 16%). Unfortunately, climate change amplifies this problem, because emissions of methane increase rapidly as water warms up. This happens especially in nutrient-rich water, where a lot of organic matter is present on the bottom that microorganisms convert into methane via the process of decay.

Free-floating aquatic plants (such as duckweed) and algae benefit the most from climate change, because they grow near the surface and so are the first to take advantage of the higher temperatures and higher CO2 concentrations in the air. Meanwhile, the increasingly heavy rainfall is causing even more fertilizer to leach from farmland into the surface water.

More oxygen

However, in water where submerged plants predominate rather than free-floating plants, emissions increase much more slowly as the water warms up, researchers from Radboud University, the Netherlands Institute of Ecology (NIOO-KNAW), Wageningen University and IGB Berlin have revealed. They made their discovery by simulating Dutch waters in large tanks containing either mainly algae, free-floating plants or submerged plants. Half of the tanks were warmed by 4 °C, anticipating the expected degree of climate warming by the end of this century.

“We think submerged plants cause this effect because they leak oxygen into the soil, enabling the microorganisms there to consume more methane,” explains first author Ralf Aben of Radboud University. “There is a caveat though: we used the common plant watermilfoil. It is not clear whether all submerged plants have the same effect. That will require further research.”

Win-win situation

The discovery is good news for Dutch water managers, says final author Sarian Kosten of Radboud University. They are already investing in increasing the coverage of submerged plants in Dutch lakes and ditches, mainly to improve the water quality and biodiversity. “But this research shows that it is also good for reducing greenhouse gas emissions from bodies of water. So it’s a win-win,” continues Kosten.

“Unfortunately, too much fertilizer is still leaching into our surface water in everyday practice. This is due to the gigantic network of ditches we have in the Netherlands,” Kosten explains. “As a result, free-floating plants, which grow well in such waters, remain dominant. So, if we can reduce the amount of fertilizer, this will not only reduce nitrogen emissions, but it will also reduce greenhouse gas emissions from lakes and ditches.”


Crayfish and carp among the invasive species pushing lakes towards ecosystem collapse

Certain invasive, non-native species can disrupt lakes to the point of rapid ecosystem collapse, contaminating water for drinking, aquaculture and recreation, a new study has found.

Human activity and climate change are causing invasive non-native species to spread rapidly across the globe. Researchers have found that certain invasive species can push lake ecosystems beyond a critical ‘tipping point’, causing a sudden shift from healthy to degraded conditions that is difficult to reverse.

Invasive fish such as Asian silver carp Hypophthalmichthys molitrix, and crustaceans such as American signal crayfish Pacifastacus leniusculus, were found to significantly reduce the abundance of other important organisms in lakes and degrade water quality. The findings, published today in the journal Global Change Biology, also provide guidance on the best ways to manage waterbodies.

Shallow lakes naturally exist in one of two alternative stable states: either healthy—with clear water with an abundance of vegetation, or degraded—with cloudy water dominated by algae. When a lake is in the latter state, algae use up all the nutrients in the water and block sunlight, preventing the growth of aquatic vegetation that would aid ecosystem recovery.

Deteriorated, algae-dominated freshwater ecosystems also threaten the health and water security of human populations. Blooms of cyanobacteria, known as ‘blue-green algae‘ can produce toxins that contaminate food webs and poison water supplies.

“Algal blooms represent one of the most significant threats to the security of the Earth’s surface freshwaters. Simply undoing the circumstances that triggered a tipping point will not restore the ecosystem—the road to recovery is slow and steep,” said Dr. Sam Reynolds in the University of Cambridge’s Department of Zoology, first author of the report.

However, although invasive species are recognized as a significant threat to global biodiversity, their impacts on ecosystem services may not be uniformly negative. Invasive molluscs, including the zebra mussel Dreissena polymorpha, were found to engineer the opposite biological and environmental response: they delay ecosystem collapse and potentially aid the recovery of degraded lake ecosystems. 

“Managers of drinking water reservoirs, for example, may be able to avoid the cost of dealing with blooms of harmful algae, by removing invasive crayfish but allowing established non-native zebra mussels to remain and act as biological filters,” said Professor David Aldridge, senior author of the report.

He added: “Early detection and rapid response plans should always be our first line of attack. But in situations where invaders have already established and can no longer be eradicated, it may be appropriate to embrace their positive effects.”

The researchers focused on shallow lake ecosystems, but say that their framework could be applied to other critical ecosystems that experience catastrophic tipping points—such as coral reefs, kelp forests and desert shrublands.


Deepwater renewal in Lake Geneva in light of climate change

EPFL scientists have studied two mechanisms that can help bring oxygen to the depths of a lake—essential for preserving the lake’s ecosystem. The classical deepwater renewal caused by surface cooling during winter is becoming less efficient due to climate change, especially in deep lakes.

Lakes need to contain a certain level of dissolved oxygen to maintain water qualityand preserve their ecosystems. While the upper layers of a lakeare typically rich in oxygen, that’s not the case for deeper layers; in most lakes, oxygenation of these layers occurs primarily through a process called convective cooling that takes place during the cooler autumn and winter periods. For deep lakes in temperate climates, like Lake Geneva, winters are often not cold enough for this process to occur on an adequate scale, meaning the very deep waters are not affected. The last full-depth convective cooling in Lake Geneva took place in 2012 during a severe cold spell (CIPEL).

Understanding other deepwater renewal mechanisms

“With climate change, there are more and more winters when the conditions needed for this process are not met,” says Rafael Reiss, a recent Ph.D. graduate at EPFL’s Ecological Engineering Laboratory (ECOL). “So we need to understand other mechanisms that could enable the oxygenation of a lake’s deeper layers.” He studied two alternative deepwater renewal mechanisms as part of his Ph.D. thesis, both of which are induced by wind: interbasin exchange, where water is exchanged between the shallow Petit Lac and the deeper Grand Lac basin, and coastal upwelling. “Unlike convective cooling that’s triggered by cold air temperatures, the mechanisms we studied are less sensitive to climate change because they are wind-driven. They occur in Lake Geneva several times each winter and could therefore play an increasingly important role in renewing and aerating the deeper layers,” says Reiss.

Water in these deep layers is usually cold, oxygen-poor and nutrient-rich. The upper layers, on the other hand, are warmer with higher concentrations of oxygen and lower concentrations of nutrients. The two layers barely mix for most of the year due to their different densities—warm water is less dense than cold water, leading to a so-called stable stratification. But once the air temperature drops during autumn and winter, the surface waters cool and the stable stratification is gradually eroded from the top downwards. If the winter is cold enough, the waters near the surface reach the same temperature, and consequently the same density, as the deeper waters. The result is a complete overturning of the water column, whereby oxygen from the upper layers is brought to the bottom and nutrients from the lower layers rise to the surface.

Deepwater renewal several times a winter

Reiss’ study showed that, under the effect of the earth’s rotation, the strong winter winds that frequently blow across Lake Geneva from the southwest push coastal waters at the northern shore of the Grand Lac towards the center of the lake, with these waters being replaced by the rising of deeper waters. The same winds push the surface waters of the Petit Lac towards the Grand Lac, causing deeper waters from the Grand Lac to take their place. These two complex exchange mechanisms cause the oxygen-poor, nutrient-rich lower layers to rise upwards, sometimes from depths of over 200 meters (Lake Geneva has a maximum depth of 309 meters). These upwelled, deep waters can remain close to the surface for several days (or even reach the surface) before descending back to great depths, allowing them to be enriched with oxygen through exchange with the upper layers and the atmosphere.

To carry out this study, Reiss and his team first spent two winters collecting data in the field, measuring current velocities and water temperatures. They then employed a 3D hydrodynamic model and combined it with a modeling technique called particle tracking in order to analyze the pathways of the upwelling waters in great detail. “Our findings show just how complex these mechanisms are,” says Reiss. “They take place in 3D, meaning they can’t be described using the one-dimensional models that are frequently used to predict the impact of climate change on lakes. These mechanisms deserve further attention when assessing deepwater renewal in large, deep lakes.”


Crews clean 250,000 pounds of oil debris from Orange County shores as beaches reopen

In a sign of progress in the Orange County oil spill, Huntington Beach city and state beaches reopened Monday morning as cleanup crews continued their work combing the shores for vestiges of oil and tar.

As of Sunday, officials said 5,400 gallons of oil have been collected from vessels and 250,000 pounds of oil debris have been cleaned from beaches and other areas.

The reopening comes after water-quality test results showed nondetectable amounts of oil toxins in the water, city officialssaid.

“We understand the significance our beaches have on tourism, our economy and our overall livelihood here in Huntington Beach,” Mayor Kim Carr said in a statement. “It is important that our decision to reopen our shoreline and water be based on data and that we continue to monitor the water quality going forward.”

In the first few days after the spill, officials warned that up to 144,000 gallons of crude may have seeped out of the pipeline, which runs from a processing and production platform called Elly off the shore in Huntington Beach to the Port of Long Beach.

But later in the week, a U.S. Coast Guard official said the spill was probably smaller than initially projected, downgrading the leak to between 24,696 gallons and 131,000 gallons.

Authorities believe that a ship’s anchor scraped the pipeline and dragged it across the ocean floor.

The Coast Guard said Friday that the anchor strike probably occurred months ago, and possibly as long as a year ago. A slight crack in the pipeline may have grown worse over time, or may have survived the first strike intact but suffered damage in another incident, officials said.


Growing dominance of diatom algae in the Pearl River estuary

It is a common perception that waters close to population would be more polluted than those offshore or at higher latitudes.  However, researchers from The Hong Kong University of Science and Technology (HKUST) found that the ratio between two common microalgae diatom and dinoflagellate (dino) – a common benchmark of water quality, has been nearly doubled in the Pearl River Estuary (PRE), one of the world’s most urbanized subtropical coastal waters, over the past two decades. 

Usually, the higher the Diatom/Dino ratio is, the healthier the water quality is supposed to be.  However, according to Prof. Liu Hongbin, Associate Head and Chair Professor of HKUST’s Department of Ocean Science who led the research, it is not conclusive whether this finding indicates an improved water quality at PRE, as the team discovered that temperature as well as the level of nutrient concentration in the ocean also took a toll to the algae population. 

Algae, or phytoplankton, is important to the marine ecosystem as they not only help covert carbon dioxide into organic matter and oxygen, but is also a key food source to a wide array of sea creatures.  In Hong Kong waters, diatom and dino are the two main types of algae which together made up about 80 per cent of the entire algae population.  While diatom has long been considered the ‘good algae’ as they usually grow in less polluted water, dino is the evil brother as its toxicity can kill fish and cause hypoxia in coastal waters.  The Diatom/ Dino ratio has long been used as a benchmark to indicate the optimal level of a marine ecosystem. Theoretically, the more the proportion of diatom, the better the water quality. 

Now, a research team led by Prof Liu, which analyzed a plethora of data ranging from temperature, nutrient concentration to oxygen levels of the PRE during the 18 years to 2017, has observed a growing diatom dominance, or an increase in the Diatom/Dino ratio since 2000.  

However, using a combination of multiple data-driven statistical models, the team found that the abundance of diatom may not be a result of water quality improvement, but a change of nutrient composition in the PRE—in particular a rapid increase of nitrate against a relatively constant level of ammonium and phosphate arising from the increasing anthropogenic input.  Moreover, the team also found that the abundances of both diatom and dino were positively correlated with temperature, they predicted that for every rise of 1 to 4°C in temperature, the Diatom/Dino ratio could surge by up to 12% under the same nutrient content.  

While there had been many studies on the phytoplankton abundance in higher latitudes or offshore waters, few research were done on highly urbanized subtropical or tropical coastal waters like those of the PRE.  

Prof. Liu said, “Algae bloom is a major environmental problem, our model sheds light on prediction and even prevention of future blooms.  Meanwhile, some studies suggest that not all diatoms species are angels, some from the Pseudo-nitzschia genus—for example, may produce an acid that is detrimental to the neural system of marine mammal and birds.  Going forward, we will also study the ecological sequences of diatom blooms, as well as the abundance and physiology of those toxic diatoms.” 

The findings were recently published in the scientific journal Global Change Biology.


Satellite images show positive impact of conservation efforts for China’s coastal wetlands

Coastal wetlands support diverse and vital ecosystems central to coastal areas’ biodiversity and economic vitality. However, coastal wetlands are threatened by sea level rise that can lead to flooding and land use changes that alter the way people can live or work in these areas. These impacts are large. Approximately 600 million people live less than 10 meters, approximately 33 feet, above sea level, while 2.4 billion people live within 100 km, or around 60 miles, of the coast.

An international, interdisciplinary research team led by University of Oklahoma professor Xiangming Xiao is using satellite imagesto measure the changes of coastal wetlands in China from the early 1980s to the present. The research team is also assessing the effects of conservation efforts on preserving and recovering these important ecosystems. Their findings on China’s coastal wetlands are now published in the journal, Nature Sustainability.

Xiao is a George Lynn Cross Research Professor in the Department of Microbiology and Plant Biology, Dodge Family College of Arts and Sciences, and the director of the Center for Earth Observation and Modeling at OU. Xinxing Wang, a graduate student at Fudan University in China, is the first author of the paper.

Since the 1980s, the coastal zone of China has experienced increased urbanization, industrialization and population growth, combined with increased sea level rise, that has led to significant decreases of wetland areas.

“Because coastal wetlands provide diverse important ecosystem goods and services, their loss has reduced biodiversity, affecting water quality, carbon storage and coastal protection from storm events and increased regional vulnerability to sea level rise which, together, pose threats to human health and coastal sustainability,” Xiao explained.”We wanted to know how these coastal zones have changed over recent decades, which had been very difficult to do,” he said. “However, in the past 10 years or so, cloud computing facilities like Google Earth Engine have become available, and a lot of satellite imagery has become freely available, so the technology has come to the point where we can track, at a high spatial resolution, coastal zone changes over time and space.”

The researchers analyzed more than 62,000 satellite images of coastal wetlands in China taken between 1984 to 2018. They generated two three-year maps (1985-88 and 1988-91) and 29 annual maps of coastal wetlands for the period 1990 to 2018, for a total of 31 maps. They also identified and mapped three types of coastal wetland areas, tidal flats, saltmarshes and mangroves.

They were interested in seeing whether these images could show the impact of China’s development and enforcement of environmental laws and regulations on mitigating the loss of wetland areas. They found that wetland areas significantly decreased during 1984 through 2011. However, following increased conservation and restoration efforts under China’s drive for sustainable development and ecological civilization, the outlook improves.

“We found a substantial increase in saltmarsh area and a stable trend of tidal flat areas after 2012, driven by decreased anthropogenic activities (pollution) and increased conservation and restoration efforts,” said Xiao.

“To achieve the sustainability of coastal wetlands, China must continue to give top priority to conservation and the restoration of coastal wetlands and their ecosystem services,” he added. “Our satellite-based mapping tools and resultant maps of coastal wetlands at high spatial resolution (30-m) are important in assessing, monitoring, reporting and verifying future changes in the coastal wetlands of China and the world.”


Predicting water quality via biogeochemical modeling

A new modeling capability developed at Oak Ridge National Laboratory incorporates important biogeochemical processes happening in river corridors for a clearer understanding of how water quality will be impacted by climate change, land use and population growth.

Researchers used high-performance computing and the award-winning Amanzi-ATS software to include biogeochemical reactions in microbially active zones near streams in models that track the movement of dissolved chemicals in river networks. These reactions have a major influence on the cycling of carbon, nutrients and contaminants at basin scales. The new multiscale model better tracks water quality indicators such as nitrogen and mercury levels. 

“To build a next-generation modeling capability to address water quality issues, we needed a new multiscale framework that allows us to incorporate fundamental understanding of key processes and how those fine-scale processes manifest at much larger scales,” ORNL’s Scott Painter said.

The research team validated and demonstrated the model on several watersheds.


Hungry caterpillars an underappreciated river of carbon emissions

A study led by the University of Cambridge has found that periodic mass outbreaks of leaf-munching caterpillars can improve the water quality of nearby lakes—but may also increase the lakes’ carbon dioxide emissions.

Outbreaks of caterpillars of invasive gypsy moths, Lymantria dispar dispar, and forest tent caterpillar moths, Malacasoma disstriaoccur at least every five years in temperate forests. The insects munch through so many leaves that the resulting decrease in leaf-fall and increase in insect excrement has been found to alter the cycling of nutrients, particularly carbon and nitrogen, between land and nearby lakes on a huge scale.

Nitrogen-rich insect excrement, called frass, can wash into lakewater and act as fertilizer for microbes, which then release carbon dioxide into the atmosphere as they metabolize. The researchers suggest that in outbreak years the large quantities of frass will favor the growth of greenhouse gas-producing bacteria in lakes at the expense of algae that remove CO2 from the atmosphere.

“These insects are basically little machines that convert carbon-rich leaves into nitrogen-rich poo. The poo drops into lakes instead of the leaves, and this significantly changes the water chemistry—we think it will increase the extent to which lakes are sources of greenhouse gases,” said Professor Andrew Tanentzap in the University of Cambridge’s Department of Plant Sciences, senior author of the paper.

Northwards range expansion and increased insect population growth is anticipated as the climate changes. This puts northern forests at increased risk of defoliator outbreaks in the future, potentially causing greater quantities of CO2 to be released from nearby lakes.

This northwards shift is also concerning because there are more freshwater lakes further north. And climate change is also expected to favor broadleaved deciduous trees around the lakes, which will amplify the effect of the insects.

The study found that in years with insect outbreaks, the leaf area of forests was reduced by an average of 22%. At the same time, nearby lakes contained 112% more dissolved nitrogen and 27% less dissolved carbon compared to non-outbreak years. The effects were greatest when lake catchments contained higher proportions of deciduous broadleaved trees, such as oaks and maples, which the caterpillars favor over coniferous trees like pines.To get their results, researchers combined 32 years of government data from insect outbreak surveys and lake water chemistry in 12 lake catchments across Ontario, Canada, and satellite remote sensing data on forest type and monthly leaf area cover. The results are published today in the journal Nature Communications.


Toxic foam covers India’s sacred Yamuna river

One of India’s holiest rivers was coated with toxic foam on Monday, adding to the woes of New Delhi residents already enduring a blanket of thick smog over the capital.

The Yamuna is already one of the most polluted waterways in the country but parts of the river, which courses through the centre of Delhi, were coated in mounds of white foam resembling snowfall.

The city government blamed the blight on “heavy sewage and industrial waste” discharged into the river from further upstream last week.

It did not deter several Hindu worshippers from taking a dip in the river to mark Chhath Puja, a four-day festival to offer prayers to the sun. 

But the pollution did disrupt water supply to part of the city, according to local officials, who did not say how many households had been affected.

“I would like to thank the affected residents for their cooperation,” Raghav Chadha, vice-chair of the city’s water authority, said in a Sunday statement.

“Our team of officers and engineers are working day and night to ensure Delhi residents’ water woes stay at a minimum.”

Indian officials have long pledged to clean the Yamuna but without success, and the blooms of toxic foam have become an annual occurrence. 

A 2020 government report found water quality in the river had become “critically worse” over the last five years.

Delhi and its surrounds have also been engulfed in thick and hazardous smog since last week. 

The haze has been compounded by agricultural fires in nearby farming communities and a barrage of fireworks set off by the capital’s residents to mark Diwali, despite a ban on their sale. 

Levels of harmful PM 2.5 particles have topped 400 in several areas, which is 16 times higher than the daily safe limit set by the World Health Organization.


Florida surpasses a grim milestone: One thousand dead manatees

Since July, every weekly update from state wildlife officials has set a new record for the most manatee deaths counted in a single year. On Wednesday, Florida crossed an especially tragic threshold: More than 1,000 manatees dead.

The exact count, through Nov. 12, was 1,003 manatees, according to the Florida Fish and Wildlife Conservation Commission.

That is up from 637 all of last year and far above the previous record, 830, in 2013. Florida passed the previous high halfway through 2021. Manatee death reports are filed each Friday and published by the state the following Wednesday.

“It makes me sad and angry,” said Patrick Rose, executive director of Save the Manatee Club, a conservation nonprofit.

The bad year got off to a quick start. Manatees took shelter from cold water by warm discharges from a power plant in the Indian River Lagoon off Brevard County, scientists say. The area is a typical wintering spot, but years of algal blooms there have killed tens of thousands of acres of seagrass. That destruction left manatees without enough food. Many starved.

“It could’ve been prevented,” Rose said. The algal blooms that have decimated the lagoon are fueled by human pollution, like septic and sewer overflows and fertilizer runoff during rainstorms.

Starvation is not the only culprit for manatee deaths, though. Nearly 100 have been killed in collisions with boats or other watercraft, according to Conservation Commission data. Red Tide has also contributed. The Tampa Bay and Pinellas shorelines were hit hard by a toxic bloom this summer.

The die-off in 2021 has left some with fears for the long-term health of one of Florida’s most beloved and iconic species. Manatees are listed as a threatened animal, after federal wildlife regulators improved their status from endangered in 2017. The Conservation Commission in recent years estimated at least 7,520 were alive.

U.S. Rep. Vern Buchanan, R-Fla., introduced a bill in August to return manatees to an endangered status. If passed, HR 4946 could draw more funding and attention, Buchanan said, which he hopes would help protect the creatures.

“I represent Manatee County. Manatees are so beloved there, but also across Florida,” Buchanan said. “People are very passionate about it.”

Manatees aren’t only cute, Rose said. Their health is a signal for the well-being of the overall ecosystem. Many fish and turtles also eat or live in seagrass, and poor water qualityaffects human health.

The damage that caused the die-off last winter is not easily repaired. State scientists and conservationists fear a repeat if manatees around Brevard County again struggle to find food this winter.