The University of Southampton

Tag: eutrophication

Humanity must stop neglecting changes in Seagrass Meadows before disaster?

Posted on by Anonymous

Seagrass meadows are a vital habitat and food source for many endangered species but these crucial habitats are under threat from environmental change caused by human impacts climate change, coastal developments, fishing and aquaculture (Waycott etal, 2009).

Figure 1- Manatee feeding on seagrass (USGS, 2016)
Figure 1- Manatee feeding on seagrass (USGS, 2016)

Climate Change

Climate change will cause a wide variety of impacts on the oceans which will effect seagrasses increasing water temperatures will lead to increased instances of seagrass die off, ocean acidification caused damaged to the cells plants require to photosynthesize and grow (Repolho et al, 2017).

As seagrass requires shallow habitats as sea levels rise there will be a loss of seagrass in deeper areas of their range seagrasses will move shoreward this trend is similar to trends that are being seen from increased amounts of sediments within the water as they will lack the sunlight to photsynthesise (Davis et al, 2016).

Coastal Developments

The construction of ports, artificial beaches and the reclamation of land, the adding of material to the water to fill in the area, this leads to more sediments within the water. The increased amount of sediments in the water can lead to seagrass beds being completely buried by the sediment and stopping plants from photosynthesising which it needs to survive, during the construction of the Pointe-Rouge Harbour over 68ha of seagrasses were lost due to water sediment and 11ha destroyed by construction (Boudouresque et al, 2009).

Figure 2- The Light grey shows dead seagrass and the dark grey living seagrass after the laying of a cable between two islands in the South of France (Boudouresque et al, 2009)
Figure 2- The Light grey shows dead seagrass and the dark grey living seagrass after the laying of a cable between two islands in the South of France (Boudouresque et al, 2009)

 

Fishing and Aquaculture

A trawler can uproot between 99,000-363,000 shoots during a trawl and in some areas of the Mediterranean over 80% of the seagrass meadows have been destroyed due to trawling (Boudouresque et al, 2009). Aquaculture, mainly fish farms, can cause a process called eutrophication, an excessive increase in nutrients heading into a body of water leading to high algal growth, because of the nutrients from uneaten food and excretion from the fish as it is focussed in one area around the fish farm this causes the reduction in size of the plants in the area due to reduced light reaching the plants, leading to a regression of the plants in the areas around fish farms (Ruiz et al, 2001).

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Figure 3- Changes in seagrass area by coastlines and in most coastlines more studies report a decrease (Waycott et al, 2009).

Future of Endangered Species

Dugongs, sea turtles and manatees all directly depend upon seagrass in many tropical regions for food and with decreases in seagrass globally, figure 3, they is likely to be further pressure put onto these already endangered species (Waycott et al, 2009), and if humanity does not take steps to solving the problems mentioned here the future of these iconic species is in real danger.

 

 

Reference List

Boudouresque, C., Bernard, G., Pergent, G., Shili, A., Verlaque, M., (2009), Regression of Mediterranean seagrasses caused by natural processes and anthropogenic disturbances and stress: a critical review, Botanica Marina, 52, 395-418

Davis, T., Harasti, D., Smith, S., Kelaher., (2016), Using modelling to predict impacts of sea level rise and increased turbidity on seagrass distributions in estuarine embayments, Estuarine, Coastal and Shelf Science, 181, 294-301

Repolho, T., Duarte, B., Dionísio, G., Paula, J., Lopes, A., Rosa, I., Grilo, T., Caçador, I., Calado, R. and Rosa, R. (2017). Seagrass ecophysiological performance under ocean warming and acidification. Scientific Reports, 7, p.41443.

Ruiz, J., Perez, M., Romero, J., (2001), Effects of Fish Farm Loadings on Seagrass (Posidonia oceanica) Distribution, Growth and Photosynthesis, Marine pollution bulletin, 42(9), 749-760

USGS, (2016). Manatees [online] Available at: https://www.usgs.gov/centers/wetland-and-aquatic-research-center-warc/science-topics/manatees [Accessed 20 Mar. 2017].

Waycott, M., Duarte, C., Carruthers, T., Orth, R., Dennison, W., Olyarnik, S., Calladine, A., Fourqurean, J., Heck, K., Hughes, A., Kendrick, G., Kenworthy, W., Short, F. and Williams, S., (2009). Accelerating loss of sea grass across the globe threatens coastal ecosystems,. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 106(30), 12377-12381

 

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Eutrophication: A powerful poison to aquatic life

Posted on by Xi Lan

 

3Such tragic pictures were taken in China telling stories of the low-income people who live on fisheries lost their fishes due to the algae bloom. However, this problem does not only present in China: according to reports, during 1972 to 1999 US commercial fisheries lost over 18 million dollars every year due to the poor water quality (National Science Foundation, 2000).

 

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How is it developed?

Under warm and excessive nutrient conditions (e.g., introduction of nitrogen and phosphorus), algae in the lake starts to grow rapidly. In most healthy lakes, all depths are well oxygenated and the species in lakes are diverse. The excessive nutrient loads leads to the dominance of algae to the lakes, in other word, algae bloom. Massive algae bloom in the surface results in water turbidity increasing therefore the sunlight is blocked from underwater plants. Additionally, algae in the lakes has a short lifespan and depletes the oxygen in water causing a death zone along the water column (hypoxia); some algae can release toxins which are deadly to fish (Hallegraeff, 1993). In this stage the amount of fishes along with aquatic plants decreases rapidly. The healthy, well-oxygenated and clear lake becomes turbid, unsightly with few species alive and a disgusting smell.

 

What happens to ecosystem within the lake?
1The submerged aquatic plants which are adapted themselves to original lake conditions (e.g. high concentration of chlorophyll) are almost wiped out from the lakebed during the algae bloom (Jupp and Spence, 1977). In the case of Taihu lake in China, the area covered by submerged aquatic plants was over 530 km2 which reduced to around 300 km2   in 2009 (Qin et al., 2012).

The decreasing amount aquatic plants would have an impact to the zooplanktons. Less coverage of submerged aquatic plants on lakebed means less refuge capacity provided for zooplanktons (SCHRIVER et al., 1995). Therefore, besides the pressure of hypoxia, zooplanktons are struggling to survive at high predation risk.

One pronounced impact of lake eutrophication is the decreasing trend of overall fish population along with rising algal population as oxygen depleted environment is no longer able to hold big fish population as a healthy lake. Aparting from decreasing quantity of fish community, the fish community quality is also under threat. Generally, highly eutrophic lakes often are dominated by ferocious fish species such as carp (Lee and Jones, 1991). They are more adapted to the poorly oxygenated environment and they are voracious predator of zooplanktons that eat algae, which is an enhancing factor of lake eutrophication (Reinertsen et al., 1990). Decreasing fish community diversity could also happen when low oxygen condition driving deep-water living fish coming to open water under oxygen pressure which result in hybrid with open water fish.

 

Human interference to the ecosystem

Under such environmental pressure, countries like China decides to apply biotic approach to solve the algae bloom causing by eutrophication. Deploying algae-munching fish is well-known as approach to regulate algae population (Andersson et al., 1978). However, massive releasing algae-munching fish would dramatically changing the composition of current aquatic community leading unpredictable problems in future.

 

 

 

References

Andersson, G., Berggren, H., Cronberg, G. and Gelin, C. (1978). Effects of planktivorous and benthivorous fish on organisms and water chemistry in eutrophic lakes. Hydrobiologia, 59(1), pp.9-15.

Hallegraeff, G. (1993). A review of harmful algal blooms and their apparent global increase*. Phycologia, 32(2), pp.79-99.

Jupp, B. and Spence, D. (1977). Limitations on Macrophytes in a Eutrophic Lake, Loch Leven: I. Effects of Phytoplankton. The Journal of Ecology, 65(1), p.175.

Lee, G. and Jones, A. (1991). Effects of Eutrophication on Fisheries. Reviews in Aquatic Science, [online] 5(3). Available at: http://www.gfredlee.com/Nutrients/Effects_Eutroph_Fisheries.pdf             [Accessed 22 Mar. 2017].

McKinnon, J. and Taylor, E. (2012). Biodiversity: Species choked and blended. Nature, 482(7385), pp.313-314.

National Science Foundation, (2000). Estimated Annual Economic Impacts from Harmful Algal Blooms (HABs) in the United States. [online] National Science Foundation. Available at:                       http://www.whoi.edu/cms/files/Economics_report_18564_23050.pdf [Accessed 22 Mar. 2017].

Qin, B., Gao, G., Zhu, G., Zhang, Y., Song, Y., Tang, X., Xu, H. and Deng, J. (2012). Lake eutrophication and its ecosystem response. Chinese Science Bulletin, 58(9), pp.961-970.

Reinertsen, H., Jensen, A., Koksvik, J., Langeland, A. and Olsen, Y. (1990). Effects of Fish Removal on the Limnetic Ecosystem of a Eutrophic Lake. Canadian Journal of Fisheries and Aquatic             Sciences, 47(1), pp.166-173.

SCHRIVER, P., BOGESTRAND, J., JEPPESEN, E. and SoNDERGAARD, M. (1995). Impact of submerged macrophytes on fish-zooplanl phytoplankton interactions: large-scale enclosure                         experiments in a shallow eutrophic lake. Freshwater Biology, 33(2), pp.255-270.

 

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Denial isn’t just a river in Egypt

Posted on by Sarah Hill
bog-river
Stream in the Redwood National Park

Humans (Homo sapiens) have been on this planet for at least 200,000 years (Hopkin, 2005) and throughout this time we have caused large changes to the river network. These modifications have occurred for many reasons;

  • Flood defence
  • Irrigation
  • Transport of goods
  • Drinking water
  • Power
  • Sanitation

But any changes made to a system has knock on effects to the organisms living there through changes in their biotic, living, and abiotic, non-living, environment. Human mediated change is no exception.

 

Pollution

As a result of human infrastructure and urbanisation rivers have become polluted with PAHs and heavy metals that have been washed off hard surfaces, such as roads. Industrialisation releases sulphur dioxide and nitrous oxide into the atmosphere which enters the rivers through acid rain. Sewage is also discharged into rivers in some areas, such as from houseboats and canal boats, which reduces the amount of oxygen available in the water for the organisms. Agriculture uses fertilisers and chemicals which, through the process of leaching and run-off, can end up in the river system. Pesticides and herbicides will kill insects and plants in the river system. Other chemicals are toxic to organism, as ammonia is to fish (Ip et al, 2001). Increasing nutrients in the rivers can result in eutrophication:

 

Flow modification

Some river channels have been deepened and widened to prevent flooding, resulting in their flow becoming faster. Flow has also been slowed in some rivers through the addition of dams, which have been built to supply drinking water and power to the public. Altering the flow of a river has wide spread effects on the ecosystem as it changes the abiotic and biotic composition. A slow flow results in higher temperatures (Dickson et al, 2012) and more sediment deposition (Christiansen et al, 2000) than a fast flow. Dams not only restrict the movement of the water but also organisms, which is a massive problem for migrating species such as eels and salmon. Irrigation results in a reduced water level which can be adverse for larger fish species and also alters the velocity of the flow.

blog-irrigation
Typical structure of surface irrigation

 

Introduced species

Introductions to rivers can be both intentional, eg for fishing, or unintentional, eg from the underside of boats. Only 1% of introduced species become invasive, affecting native species (Jeschke and Strayer, 2005), by competing for resources, preying on native species or introducing harmful diseases and parasites. This is a major problem in river systems due to their connectivity which mitigates the migration of these species to other reaches of the river making control and eradication difficult.

 

Harvesting

Excessive commercial harvesting of fish and shellfish in rivers can drastically reduce their numbers and the number of species. Eel and white bait numbers have declined significantly in the Waikato River, New Zealand, since the 1970s for this precise reason (Chapman, 1996). Reducing the population size of a particular species effects those that feed on them, such as other fish, birds, mammals and even reptiles.

blog-bird-and-snake
Snake eating a fish in the water and puffin with fish in its beak

 

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References

Chapman M.A. 1996. Human impacts on the Waikato River system, New Zealand. GeoJournal. 40, 85-99.

Christiansen T., Wiberg P.L. and Milligan T.G. 2000 Flow and sediment transport on a tidal salt marsh surface. Estuarine, coastal and shelf science. 50, 315-331.

Dickson N.E., Carrivick J.L. and Brown L.E. 2012. Flow regulation alters alpine river thermal regimes. Journal of hydrology. 464, 505-516.

Hopkin M. 2005. Ethiopia is top choice for cradle of Homo sapiens. Nature news. doi:10.1038/news050214-10.

Ip Y.K., Chew S.F. and Randall D.J. 2001. Ammonia toxicity, tolerance, and excretion. Fish physiology. 20, 109-148.

Jeschke J.M. and Strayer D.L. 2005. Invasion success of vertebrates in Europe and North America. PNAS. 102, 7198-7202.



Combatting the change: we must not forget the global change indicators under our feet and above our heads

Posted on by Ellen Williams

The world as we know it, and the species within it, are experiencing rapid changes (MEA, 2005). Us humans are the monsters, with our activity having a huge global impact. This human-induced activity can take many forms, including land-use change, increased CO2 and nitrogen concentration. Many complex interactions exist in the natural world, involving predation and competition, but recent human-induced changes have added great pressure, termed global change (Vitousek, 1994), to these intermingled global connections:

“It would not be surprising to see entire patterns of community organisation jumbled as a result of global change.” (Kareiva et al. 1993).

How can this happen?

Synthetic fertiliser production and industrial processes using fossil fuels over the past 50 years have led to an increase in nitrogen deposition (Suddick et al. 2013). This can consequently result in eutrophication: a literal example of ‘too much of a good thing’, which is explained here:

Nitrogen eutrophication can lead to a great decline in species richness (Börgstrom et al., 2017) but it affects interactions between these species, some which we can and some which we cannot see: An individual species is always part of a bigger story, with the effects of nitrogen eutrophication cascading through many chapters. It is hard to study these hidden interactions, for obvious reasons! But it provides a complete view of what is going on in an ecosystem. It is important to note that drivers of global change do not work in isolation: for example, increasing temperatures only aggravate the effects of nitrogen deposition.

But, how does this work?

For example, insect herbivores above- and below-ground will interact differently in response to nitrogen eutrophication. This has a knock-on effect on the composition of the plant community; affecting worms in the soil, and land mammals which graze on the plants (Börgstrom et al., 2017). Plants gain positively from nitrogen deposition by improved nectar quality and abundance of flowers, yet the negative effects of increased competition outweigh these positives, resulting in a net reduction in pollination. Which again, may have a knock-on effect on seed dispersal by a fruit-eating animal, for example. It can also result in increased plant fungal diseases! (Parmesan, 2006)

Nitrogen deposition favours those plant species which are better adapted to a higher nitrogen concentration, which increases competition between species.

What about on a larger scale?

Migratory birds could potentially connect different ecosystems (Hessen et al. 2017). Eutrophication strongly impacts Arctic freshwater ecosystems, due to increasing geese populations in temperate regions, and improved breeding success in the Arctic. The faeces from the geese provide the environment with increased nutrients (who knew this could be beneficial?!), which can affect the composition of the plant community.

Migrating geese. From: www.planet-science.com.

But, how does this affect us?

Understanding how communities and entire ecosystems respond to nitrogen deposition is important, as our well-being depends on the services they provide, such as wood production and food. Given that effects of global change are widespread (thanks, geese!), an international management of ecosystems will prove useful in the future.

References

Börgstrom, P et al. (2017). Above- and belowground insect herbivory modifies the response of a grassland plant community to nitrogen eutrophication. Ecology. 98:545- 554.

Hessen DO et al. (2017) Global change and ecosystem connectivity: How geese link fields of central Europe to eutrophication of Arctic freshwaters. Ambio. 46:40-47.

Kareiva, PM et al. (1993). Introduction. In: Biotic Interactions and Global Change (eds Kareiva, P.M., King- solver, J.G. & Huey, R.B.). Sinauer Associates Inc., Sunderland, MA, pp. 1–6.

Millennium Ecosystem Assessment (MEA) (2005). Ecosystems and Human Well-Being: Scenarios. Island Press, Washington, DC.

Parmesan, C. (2006). Ecological and evolutionary responses to recent climate change. Annu. Rev. Ecol. Evol. Syst., 37, 637–669.

Suddick EC et al. (2013) The role of nitrogen in climate change and the impacts of nitrogen-climate interactions in the United States: foreword to thematic issue. Biogeochemistry. 114(1):1-10.

Vitousek PM (1994) BEYOND GLOBAL WARMING: ECOLOGY AND GLOBAL CHANGE. Ecology. 75(7):1861-1876.

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