Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Human Impact Felt on Black Sea Long Before Industrial Era

05.09.2012
When WHOI geologist Liviu Giosan first reconstructed the history of how the Danube River built its delta, he was presented with a puzzle.
In the delta’s early stages of development, the river deposited its sediment within a protected bay. As the delta expanded onto the Black Sea shelf in the late Holocene and was exposed to greater waves and currents, rather than seeing the decline in sediment storage that he expected, Giosan found the opposite. The delta continued to grow. In fact, it has tripled its storage rate.

If an increase in river runoff was responsible for the unusual rapid build up of sediment in the delta, says Giosan, the question is, “Was this extraordinary event in the Danube delta felt in the entire Black Sea basin? And if so, what caused it?”

In answering those questions, Giosan and an international team of collaborators including environmental engineers, modelers, paleogeographers, and paleobiologists pieced together a unique history of the region that ultimately provides evidence for a transformative impact of humans on the Black Sea over hundreds, if not thousands of years. The study was published on August 30 in Scientific Reports, a new online journal of the Nature Publishing Group.

The largest and longest river in the European Union, the Danube is the source of over 60 percent of the freshwater running into the Black Sea, and therefore is a dominant factor in the biogeochemistry of this basin. Because the Black Sea is nearly enclosed, changes in its hinterland provoked by climate or people should be readily reflected there.

The research team reconstructed a 9000-year record of the delta’s growth, and through various scientific techniques, developed and mapped against it a record of changes in the Black Sea’s salinity, nutrients, and relative abundance of its ecosystem's major phytoplankton groups. Finally, they also examined the history of land use in the greater Danube watershed.

To reconstruct the salinity, the WHOI team analyzed sediments containing highly resistant organic compounds called alkenones, which are uniquely produced by Emiliania huxleyi – the same photosynthetic organism oceanographers study to determine past sea surface temperatures. By examining the ratio of two hydrogen isotopes in the alkenones, they were able to map the salinity trend in the Black Sea over the last 6,500 years.

“One of the isotopes, deuterium, is not very common in nature,” explains WHOI marine paleoecologist Marco Coolen, “and it doesn't evaporate as easily as other isotopes. Higher ratios of deuterium are indicative of higher salinity.”

Salinity began to rise in the Black Sea about 9000 years ago, when the ocean invaded the previously freshwater lake through the Straits of Bosporus, and continued to increase until approximately 3000 years ago, when the levels approached normal ocean values.

“But the trend since then is counter-intuitive,” says Giosan. “The entire basin freshened, especially in the last 1,500 years.” The likely explanation points to a increase in the river input combined with a reduced evaporation as the climate cooled at the time, he adds.

Such an influx of nutrient-rich river water would affect the composition of the ecosystem, and would be reflected by the ecological history of major phytoplankton groups in the Black Sea, such as diatoms and dinoflagellates.

Researchers traditionally conduct paleo studies of phytoplankton by using a microscope to count the fossil skeletons found in sediment cores. But, this method is limited because some phytoplankton leave no fossils, so, instead, Coolen looked for sedimentary genetic remains of the past inhabitants of the Black Sea water column.

“DNA offers the best opportunity to learn the past ecology of the Black Sea,” says Coolen. “Calcareous and organic-walled dinocysts are frequently used to reconstruct past environmental conditions, but 90 percent of the dinoflagellate species do not produce such diagnostic resting stages, yet their DNA remains in the fossil record.”

His analysis found that major phytoplankton groups in the Black Sea changed drastically over the last millennium. Beginning about 500 years ago, a rise in diatoms suggests there was more silicate available in the Black Sea. The team at WHOI also found an increase in the abundance of dinoflagellate DNA beginning about 650 years ago. Both of these changes are consistent with increased nutrient availability that would occur as a result of human activity – the clearing of forests and increased agriculture. Interestingly, a significant drop in diatom DNA occurred in recent times when more recent human activity – the damming of the rivers – entered the scene.

The final piece of the picture comes from a model developed by Jed Kaplan, a scientist at Ecole Polytechnique Federale de Lausanne in Switzerland. Kaplan looked at the expansion of lands cleared for agriculture in the Danube watershed as population grew and farming technology became more advanced over the last 7000 years ago. His findings agree very well with recently published studies of the relative abundance of grass pollen over tree pollen and the appearance of charcoal in the sediment record from clearing large swaths of trees by burning. All of these land signals point to human deforestation and increased agriculture.

The model suggests that deforestation of the lower basin of the Danube rapidly accelerated over the last millennium and especially in the last 500 years. In contrast in the western sector of the watershed, farther from the Black Sea, deforestation was already substantial as the Roman Empire expanded there.

“This story started by looking at how Danube River built its delta in the Black Sea,” says Giosan. “But together these indicators tell a story of changing land use that ultimately changed the ecosystem of an entire sea.”

The ability to define baselines and separate natural variability from human-induced changes is essential for understanding biogeochemical cycles and managing marine ecosystems, which ultimately depends on the detection and attribution of long term environmental trends, the authors write. “Our ancestors changed that baseline a long time ago in the Black Sea” says Giosan. “And they probably fertilized other coastal seas with nutrients inadvertently stripped from soils much earlier than we think.”

Meanwhile, the Danube delta remains an extraordinarily lush, vibrant habitat, home to hundreds of species of birds and fish. “This is a unique piece of land – the Danube delta – blessed, productive, and important for countless forms of life,” adds Giosan. “What is amazing to me is that we owe much of this biodiversity to our own history of changing Nature.”

A map of the Black Sea's drainage basin. The Danube's watershed is delimited by a continuous white line, its course is highlighted in blue, and the Danube delta is shown in green. The Danube drains most of the Central and Eastern Europe to dominate the freshwater and sediment budget of the Black Sea. A sediment core shown by a white circle was used to reconstruct the salinity and ecosystem composition in the Black Sea over the last 7000 years. (Figure courtesy Liviu Giosan, Woods Hole Oceanographic Institution; Stefan Constantinescu, University of Bucharest)

The Woods Hole Oceanographic Institution is a private, non-profit organization on Cape Cod, Mass., dedicated to marine research, engineering, and higher education. Established in 1930 on a recommendation from the National Academy of Sciences, its primary mission is to understand the oceans and their interaction with the Earth as a whole, and to communicate a basic understanding of the oceans' role in the changing global environment.

Originally published: September 4, 2012

WHOI Media Relations | EurekAlert!
Further information:
http://www.whoi.edu
http://www.whoi.edu/main/news-releases?tid=3622&cid=148569

More articles from Ecology, The Environment and Conservation:

nachricht Successful calculation of human and natural influence on cloud formation
04.11.2016 | Goethe-Universität Frankfurt am Main

nachricht Invasive Insects Cost the World Billions Per Year
04.10.2016 | University of Adelaide

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

Plasma-zapping process could yield trans fat-free soybean oil product

02.12.2016 | Agricultural and Forestry Science

What do Netflix, Google and planetary systems have in common?

02.12.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>