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Imaggeo on Mondays: Coastal erosion

Imaggeo on Mondays: Coastal erosion

Coastlines take a battering from stormy seas, gales, windy conditions and every-day wave action. The combined effect of these processes shapes coastal landscapes across the globe.

In calm weather, constructive waves deposit materials eroded elsewhere and transported along the coast line via longshore-drift, onto beaches, thus building them up. Terrestrial material, brought to beaches by rivers and the wind, also contribute.  In stormy weather, waves become destructive, eroding material away from beaches and sea cliffs.

In some areas, the removal of material far exceeds the quantity of sediments being supplied to sandy stretches, leading to coastal erosion. It is a dynamic process, with the consequences depending largely on the geomorphology of the coast.

Striking images of receding coastlines, where households once far away from a cliff edge, tumble into the sea after a storm surge, are an all too familiar consequence of the power of coastal erosion.

In sandy beaches where dunes are common, coastal erosion can be managed by the addition of vegetation. In these settings, it is not only the force of the sea which drives erosion, but also wind, as the fine, loose sand grains are easily picked-up by the breeze, especially in blustery weather.

Grasses, such as the ones pictured in this week’s featured imaggeo image, work by slowing down wind speeds across the face of the dunes and trapping and stabilising wind-blown sands. The grasses don’t directly prevent erosion, but they do allow greater accumulation of sands over short periods of time, when compared to vegetation-free dunes.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Geosciences Column: The World’s soils are under threat

Geosciences Column: The World’s soils are under threat

An increasing global population means that we are more dependant than ever on soils.

Soils are crucial to securing our future supplies of water, food, as well as aiding adaptation to climate change and sustaining the planet’s biosphere; yet with the decrease in human labour dedicated to working the land, never have we been more out of touch with the vital importance of this natural resource.

Now, the first-ever comprehensive State of the World’s Soil Resources Report (SWRS), compiled by the Intergovernmental Technical Panel on Soils (ITPS), aims to shine a light on this essential non-renewable resource. The report outlines the current state of soils, globally, and what the major threats facing it are. These and other key findings of the report are summarised in a recent paper of the EGU’s open access Soil Journal.

The current outlook

Overall, the report deemed that the world’s soils are in fair to very poor condition, with regional variations.  The future doesn’t look bright: current projections indicate that the present situation will worsen unless governments, organisations and individuals come together to take concerted action.

Many of the drivers which contribute to soil changes are associated with population growth and the need to provide resources for the industrialisation and food security of growing societies. Climate change presents a significant challenge too, with factors such as increasing temperatures resulting in higher evaporation rates from soils and therefore affecting groundwater recharge rates, coming into play.

The three main threats to soils

Soil condition is threatened by a number of factors including compaction (which reduces large pore spaces between soil grains and restricts the flow of air and water into and through the soil), acidification, contamination, sealing (which results from the covering of soil through building of houses, roads and other urban development), waterlogging, salinization and losses of soil organic carbon (SOC).

Global assessment of the four main threats to soil by FAO regions. Taken from Montanarella, L., et al. 2016.

Global assessment of the four main threats to soil by FAO regions. Taken from Montanarella, L., et al. 2016.

Chief among the threats to soils is erosion, where topsoil is removed from the land surface by wind, water and tillage. Increasing rates of soil erosion affect water quality, particularly in developed regions, while crop yields suffer the most in developing regions. Estimating the rates of soil erosion is difficult (especially when it comes to wind driven erosion), but scientists do know that topsoil is being lost much faster than it is being generate. This means soil should be considered a non-renewable resource. When it comes to agricultural practices in particular, soils should be managed in such a way that soil erosion rates are reduced to near zero-values, ensuring long-term sustainability.

Eutrophication in lake Slotsø, Kolding, Denmark. Credit: Alevtina Evgrafova (distributed via imaggeo.egu.eu)

Eutrophication in lake Slotsø, Kolding, Denmark. Credit: Alevtina Evgrafova (distributed via imaggeo.egu.eu)

Soils contain nutrients, such as nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulphur (S), crucial for growing crops and pastures for raising cattle. While nutrient balance in soils has a natural variability, farming practices accelerate changes in soil nutrient content. Over-use of soils rapidly depletes the land-cover of nutrients and result in lower food production yields. This imbalance is often remedied by the addition of nutrients; in particular N and P. Excessive use of these practices, however, can lead to negative environmental effects, such as eutrophication (which increases the frequency and severity of algal blooms) and contamination of water resources. The findings of the report advocate for the overall reduction of use of fertilisers, with the exception of tropical and semi-tropical soils in regions where food security is a problem.

Carbon (C) is a fundamental building block of life on Earth and the carbon cycle balances the amount of C which ultimately enters the atmosphere, helping to stabilise the planets temperature. Soils play a significant role in helping to preserve this balance. Soil organic carbon (SOC) acts as a sink for atmospheric C, but converting forest land to crop land saw a decrease of 25-30% in SOC stocks for temperate regions, with higher losses recorded for the tropics. Future climate change will further affect SOC stocks through increased temperatures and fluctuating rainfall, ultimately contributing to risks of soil erosion and desertification and reducing their ability to regulate carbon dioxide emissions. It is vitally important that governments work towards stabilising, or better still, improving existing SOC stocks as a means of combating global warming.

Preserving a valuable resource

The case is clear: soils are a vital part of life on Earth. It is estimated that worsening soil condition will affect those already most vulnerable, in areas affected by water scarcity, civil strife and food insecurity.

Bed planting in northern Ethiopia. Credit: Elise Monsieurs (distributed via imaggeo.egu.eu)

Bed planting in northern Ethiopia. Credit: Elise Monsieurs (distributed via imaggeo.egu.eu)

Initiatives such as the 2015 International Year of Soil and the production of the SWRS report are fundamental to raise awareness of the challenges facing soil resources, but more needs to be done:

      1. Sustainable soil management practices, which minimise soil degradation and replenish soil productivity in regions where it has been lost, must be adopted to ensure a healthy, global, supply of food.
      2. Individual nations should make a dedicated effort to establish appropriate SOC-improving strategies, thus aiding adaptation to climate change.
      3. Manging the use of fertilisers, in particular N and P, should be improved.
      4. There is a dearth of current data, with many of the studies referenced in the SWRS report dating from the 1980s and 1990s. For accurate future projections and the development and evaluation of tools to tackle the major threats facing soils, more up-to-date knowledge about the state of soil condition is required.

Soils, globally, are under threat and their future is uncertain. The authors of report argue that “the global community is presently ill-prepared and ill-equipped to mount an appropriate response” to the problem. However, adoption and implementation of the report findings might (by policy-makers and individuals alike) just turn the tide and ensure soils remain “humanity’s silent ally”.

By Laura Roberts Artal, EGU Communications Officer

References

Montanarella, L., Pennock, D. J., McKenzie, N., Badraoui, M., Chude, V., Baptista, I., Mamo, T., Yemefack, M., Singh Aulakh, M., Yagi, K., Young Hong, S., Vijarnsorn, P., Zhang, G.-L., Arrouays, D., Black, H., Krasilnikov, P., Sobocká, J., Alegre, J., Henriquez, C. R., de Lourdes Mendonça-Santos, M., Taboada, M., Espinosa-Victoria, D., AlShankiti, A., AlaviPanah, S. K., Elsheikh, E. A. E. M., Hempel, J., Camps Arbestain, M., Nachtergaele, F., and Vargas, R.: World’s soils are under threat, SOIL, 2, 79-82, doi:10.5194/soil-2-79-2016, 2016.

Status of the World’s Soil Resources, 2015, Food and Agricultire Organization (FAO) of the United Nations.

Soils are endangered, but degradation can be rolled back, 2015, FAO News Article.

Imaggeo on Mondays: Why is groundwater so important?

Imaggeo on Mondays: Why is groundwater so important?

Groundwater is an often underestimated natural resource, but it is vital to the functioning of both natural and urban environments. Indeed, it is a large source of drinking water for communities world-wide, as well as being heavily used for irrigation of crops and crucial for many industrial processes. The water locked in the pores and cracks within the Earth’s soils and rocks, also plays an important role in the recharge of water in lakes, rivers and wetlands, as Anna Menció explains in today’s Imaggeo On Monday’s post.

The Pletera salt marsh area (NE Spain) is located in the north of the mouth of the Ter River, in a region mainly dominated by agriculture and tourism activities. Some of the coastal lagoons and wetlands in this area have been affected by the incomplete construction of an urban development. These wetlands and lagoons are the focus of a Life+ project, which aims to restore this protected area, and to recover its ecological functionality.

The Pletera coastal lagoons are periodically flooded by both, freshwater from streams and seawater, during storm events. However, the surface water inputs alone are insufficient to maintain them as permanent lagoons.

This picture is of Fra Ramon lagoon, one of the natural lagoons in the area. The preliminary results of a recent study showed that the recharge of Fra Ramon is dependent on groundwater inputs. In most of the sampling campaigns, freshwater from the aquifer may account for >50% of the lagoon water.

The ecological quality of these lagoons is also affected by nitrogen inputs, mainly produced during flooding events. Although in this area nitrate pollution is also detected in groundwater, with concentrations up to 100 mg NO3/L, natural attenuation processes in the aquifer occur. Effects of these processes are particularly detected close to the lagoons area, where low nitrate concentrations in groundwater are observed, with values below the detection limit. Considering that groundwater may present lower nitrogen concentrations than surface inputs observed during flooding events, these results reinforce the importance of groundwater dynamics in these systems, not only to maintain the permanent lagoons during dry periods, but also to preserve their quality.

By Anna Menció, researcher at the Department of Environmental Sciences of the University of Girona.

Acknowledgments: the study of the Pletera coastal lagoons is founded by LIFE 13 NAT/ES/001001, MINECO CGL-2014-57215-C4-2R, and UdG MPCUdG2016/061 projects.

 

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Geosciences Column: Pollen tells a 7300 year old story of Malta’s climate and vegetation

Geosciences Column: Pollen tells a 7300 year old story of Malta’s climate and vegetation

Figuring out what the climate was like, and how it changed, throughout Earth’s history is like trying to complete a 1000 piece puzzle. Except that scientists usually don’t have all the nuggets and building a comprehensive picture relies on a multidisciplinary approach in order to fill in the blanks.

This is particularly true during the Holocene, which spans the last 11,700 years of the Earth’s history, and began at the end of the last ice age. It marks a time of significant climate change across the planet, coupled with changing vegetation dynamics and the emergence of humans, who even at that early time, started leaving their mark on Earth. Bringing together all the evidence to build a complete picture of what the environment looked like is no easy task.

The Mediterranean, in particular, is considered a hot-spot for changing climate and biodiversity in the Holocene. The start of the epoch, in southern Europe, was characterised by a wet climate. The late Holocene, dominated by the presence of humans, is thought to have been warmer and drier. But disentangling the signature of naturally induced change vs. anthropogenically induced change continues to be difficult.

Queue the Maltese archipelago.

A small archipelago in the middle of the Mediterranean Sea

Located in the centre of the Mediterranean basin, approximately 96 km south of Sicily, Malta and a cluster of low-lying islands, including Gozo and Comino, are the focus of a recently published study in the open access journal Climate of the Past.

Study area. (a) Mediterranean region highlighting the Maltese Islands. Selected regional sites mentioned in text: 1: Lago Preola, 2: Gorgo Basso, 3: Biviere di Gela, 4: Lago Pergusa, 5: Lago Trifoglietti, 6: Lago Accesa, 7: Lago Ledro, 8: Tenaghi P., 9: SL152, 10: MNB-3, 11: NS14, 12: HCM2-22, 13: Soreq Cave; base map source: Arizona Geographic Alliance; (b) Maltese Islands: key sites mentioned in text; (c) average annual temperature and rainfall, based on Galdies (2011) data for the 30-year climatic period 1961–1990; (d) the topography and catchment area (blue) of Burmarrad.

Study area. (a) Mediterranean region highlighting the Maltese Islands. (Selected regional sites mentioned in text of the paper, but not mentioned in this blog post). (b) Maltese Islands. (Key sites mentioned in text of the paper, but not mentioned in this blog post). (c) average annual temperature and rainfall, based on Galdies (2011) data for the 30-year climatic period 1961–1990; (d) the topography and catchment area (blue) of Burmarrad. From B. Gambin et al. (2016). Click to enlarge.

It is their central Mediterranean location that makes the collection of isles so attractive, as they provide a good representation of the overall Mediterranean climate and can help decipher some of the questions regarding southern European climate during the Holocene.

The first human occupants sailed the short distance from Sicily, to settle in the region some 7200 years ago, introducing with them vegetation changes to the area. This well-defined date can be used as a possible marker to distinguish between naturally induced vegetation changes, brought about by climate variations, versus those triggered by the presence of humans.

In the paper, the researchers, led by B. Gambin, also present the first palaeoclimatic reconstruction for the Maltese islands and an updated palaeovegetation reconstruction.

But as encouraging as it sounds, using the Maltese archipelago as a study site for palaeoclimatic reconstructions has one, rather large, limitation. It has no peat bogs or lake deposits, which are the most suitable sites for the collection of data on old vegetation.

Using pollen to reconstruct the story of past climate

The spring and summer months are synonym of the onset of hay fever season for many. But the allergy triggering grains also play a surprisingly important role when it comes to reconstructing past climates, especially when there are no lakes or peat bogs around!

Palynology, the study of pollen grains, has been an important element in piecing together the history of our planet’s past climates since the early 20th Century.

Ancient pollen grains, extracted from sedimentary cores, can contribute to identifying changes in vegetation over time for a given region. If an area’s plant life changes to include more drought resistant varieties, it can point towards a warming climate in that region, whereas propagation of water-loving species might indicate wetter climes. Similarly, a sudden increase (or change) in the presence of pollen from cultivated taxa, like wheat, barely, olives, grapes, etc… highlights the presence of human (anthropogenic) influences in the region.

It is the pollen record, extracted from a core drilled in the region of Burmarrad in Northwest Malta, that the team of scientists used to compile their Maltese palaeoclimatic reconstruction.

Mediterranean climate and key events throughout the late Holocene

BM2 sedimentary profile and age–depth model interpo- lated curve. Dates on the core obtained via radiocarbon dating (for method and age detials, please see the paper). From B. Gambin et al. (2016).

BM2 sedimentary profile and age–depth model interpolated curve. Dates on the core obtained via radiocarbon dating (for method and age detials, please see the paper). From B. Gambin et al. (2016). Click to enlarge.

The 10m long BM2 drill core, extracted using a percussion corer, contained information on the climate, vegetation and precipitation history of the Maltese islands from the early Neolithic period (7280 before present,(BP)) through to the Roman age (1730 BP).

The early Neolothic

Pollen samples collected from the oldest section of the core indicate that from 7280 BP through to 6700 BP the Burmarrad region surrounded an ancient bay (in contrast to the present day agricultural plain setting) with the local vegetation affirming this. The researchers found pollen from non-arboreal (such as herbs and shrubs) taxa, as well as pollen from aquatic and marine species, such as Botryococcus, a common green algae species.

Drill core analysis also highlighted that average temperatures during this period were mild, stable and comparable to present-day values; while winter and summer precipitation levels were relatively high.

The early Neolithic period on the island coincided with the arrival of permanent settlers. But many of the pollen species which usually indicate the onset of anthropogenic influences are also native to Malta making it difficult for the scientists to draw conclusions as to whether the vegetation records show the arrival of the first human inhabitants.

A moister climate from 6700 BP resulted in the spread of Pistacia, a leafy green shrub, across the ancient bay. The damper conditions prevailed across the southern Mediterranean, with increased Pistacia populations found in Sicily and Spain too. The geographically wide-spread nature of the vegetation change indicates it was likely climate driven.

Templar period

By 6050 BP, human settlers started to make their presence felt on the tiny island. Communities started building free-standing stone temples, used for ritual purposes, which are unique to Malta. This settling period is accompanied by the rise in pollen from Olea plants – otherwise known as olive trees – herbaceous taxa such as Brassicaceae (which include mustard plants, radishes and cabbages), and fungus spores which occur in the dung of domestic livestock as well as wild herbivores.

Ggantija Temples of Malta. Image by Daniel Hausner. Attribution to Norum [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons

Ggantija Temples of Malta. Image by Daniel Hausner. Attribution to Norum [GFDL or CC-BY-SA-3.0], via Wikimedia Commons.

While individually these plants do not directly indicate vegetation change brought about by humans, when found together they do suggest human activity in the region, particularly the onset of grazing livestock.

The Bronze Age

The onset of the Bronze Age (4900 to 2650 BP) was marked by a drier climate where winter precipitation decreased and annual temperatures fluctuated between lows of 7°C and highs of 14°C. This coincides with the decrease in abundance of tree pollen found in the BM2 core and an increase in herbaceous taxa (plants which don’t have permanent woody stems).

Microcharcoal horizons become more prevalent in the core too, indicating an increase in fire activity. The drier climate and subsequent vegetation change might be a contributing factor to the increased burning in the region, but it is also likely that slash-and-burn farming was taking hold at this time. Further human activity is indicated by the rise in pollen from plants associated with pastoral activity and the increase in fungus spores commonly found in the dung of livestock.

The strain put on the environment of the Burmarrad Bay at this time is evident by the rise of algal spores and the Glomus fungus, typically associated with increased soil erosion rates. It is further supported by a reduction in overall pollen count in the core, indicating the land could support less plant-life.

The increased erosion rates had a significant impact on the landscape, with the marine lagoon slowly infilling with sediment and eventually becoming landlocked throughout the Bronze Age.

Roman occupation period

By 1972 BP the area became a well-developed fertile deltaic plain, so it’s not surprising that an increase in pollen concentrations from cultivated crop taxa, pointing towards a rise in agricultural activity, were found in the core. The area also benefited from a long period of stable climate with limited temperature and precipitation changes.

During this time, Malta became an important producer and exporter of olive oil, as evidenced by the extensive port-like remains, of this age, found across the island. This is supported by the Olea pollen count in the core, which is high too.

Synthesis of cultural phases, LPAZs (local pollen assemblage zones), sediment, vegetation dynamics, and climatic reconstruction: BM2 core, Malta. From B. Gambin et al. (2016).

Synthesis of cultural phases, LPAZs (local pollen assemblage zones), sediment, vegetation dynamics, and climatic reconstruction: BM2 core, Malta. From B. Gambin et al. (2016). Click to enlarge.

Climate- vs. human –driven environmental change in the Holocene

The research shows just how powerful palynology is as a tool for reconstructing past climates. The study of the BM2 core allowed scientists to put together a 7300 year history of climatic, vegetation and anthropogenic change in Malta.

At the same time it highlights the ongoing challenge of unravelling the signature of climate- vs. human –driven environmental change in the Holocene.

Taken as a whole, the researchers hope that the findings can be a starting point for further research into this subject, with hopes to gain better understanding of the factors and processes affecting past, present and future Mediterranean landscapes.

By Laura Roberts Artal, EGU Communications Officer

Reference

Gambin, B., Andrieu-Ponel, V., Médail, F., Marriner, N., Peyron, O., Montade, V., Gambin, T., Morhange, C., Belkacem, D., and Djamali, M.: 7300 years of vegetation history and climate for NW Malta: a Holocene perspective, Clim. Past, 12, 273-297, doi:10.5194/cp-12-273-2016, 2016.

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