Ocean dead zones, the case of the Gulf of Mexico

In focus today…. The Gulf of Mexico Dead Zone.

In continuation to my post on eutrophication and dead zones, I will investigate how livestock farming has caused major impacts on marine environments by taking a closer look at the Gulf of Mexico (GoM) dead zone. I thought focusing on a case study would be a better way to illustrate and understand an issue that is happening today in the United States.

The Gulf of Mexico Dead Zone is a temporal dead zone characterized by seasonal periods of hypoxia due to rich nutrient discharges arriving from the Atchfalaya and Mississippi River that cross Louisiana State in the United States. Levels of hypoxia decrease in October and continue to do so throughout most of the winter until the warmer season where hypoxic regions expand over most of the summer (NOAA, 2015).

 Figure 1: 2015 map area of Gulf of Mexico Dead Zone - NOAA 2015

Recently, in August 2015, the National Oceanic and AtmosphericAdministration (NOAA, 2015) reported the dead zone to be ‘above average size’ due to high precipitation in June 2015 and increasing nutrient presence in Louisiana Rivers.  Trends have shown that the GoM hypoxic zones have slowly been increasing over the past 180 years covering most northern waters of the Gulf (Osterman et al, 2005). Through four sediment cores extracted from Louisiana shelf, Osterman et al (2005), recorded increasingly lower oxygen levels over a time span of 180 years.  Indeed, hypoxic periods were measured according to the abundance of three benthic foraminifers species, here called PEB (Pseudomonion atlanticum, Epistominella vitrea and Buliminella morgana), that live in nutrient rich habitats with low oxygen levels such as dead zones. According to the plots, PEB percentages start increasing in the 1950s and peak at the beginning of the 21^st century. 

Figure 2: Plots of PEB percentage and trends over the course of 180 years - (Osterman et al, 2005)

Turner et al (2003) attributes these changes in PEB numbers partially to natural factors but essentially to human induced factors such as land clearing for agriculture.

Indeed, The National Science and Council Committee on Environmentand Natural Resources 2000 assessment on hypoxia in the Northern Gulf of Mexico reported that landscape alteration for agriculture, manifested through deforestation were causing greater numbers of nutrients from entering aquatic environments. Harmful nutrients are no longer filtered by soil due to the lack of plant coverage and soil destruction caused by deforestation (NSCCENR, 2000). The report places agricultural fertilisers and particularly nitrogen (fertilisers composed mainly of nitrogen)  as the main factor contributing to the eutrophication of GoM waters. Both the Mississippi and Atchfalaya Rivers, collect runoff from Midwestern farmer’s fertilizing practices, that end up in the GoM and heavily impacts unique species in the region (NSCCENR, 2000). Some species are more affected than others. For instance, in extreme hypoxia cases, longer living species died with low levels of oxygen and shorter living species tend to survive and adapt to conditions (NSCCENR, 2000). The Gulf of Mexico has experienced biodiversity imbalances with increased numbers of more resilient species such as jellyfish (OECD, 2010). Furthermore, Eby et al (2004) explain that some surviving species try to find refuge in more highy oxygenated areas by traveling out of the hypoxia zones but often leads to overcrowding and density dependent grow reductions.  

Part 2: From land to sea, though not forgetting freshwater, river and streams

Key terms here: fertilisers, eutrophication or hypertrophication, hypoxia, deadzones.

Although fertilisers have revolutionized agriculture since the 19^th century, its use for animal agriculture and growing feed has major implication on our environment, today.  Fertilisers, both chemical or natural, are rich in nutrient, and particularly high in nitrogen and phosporus, that help increase crop yields. However, plants only intake less than 20% of nitrogen and phosphorus (Dybas 2005), the rest is washed away by rain and ends up directly in freshwater and groundwater ecosystems, riparian environments and oceans (See table). Nutrient encourage the growth of aquatic plants such as phytoplankton, just as they do on land. The lake is thus exposed to a process of eutrophication (excessive numbers of nutrient in an aquatic environment) and causes oxygen depletion a.k.a. hypoxia in which aquatic organisms are unable to survive due to the low oxygen concentrations. The remaining bodies of water are called dead zone.

Cattle manure is rich in nitrogen, phosphorus and potassium, which represent the major causes of eutrophication. One peer-reviewed study argued that Industrialised Animal Production were major sources of nutrients and therefore were contributing to the eutrophication of some environments in the United States (Mallin et al, 2003). Focusing on Concentrated Animal Feeding Operations (CAFOs), which represent big companies for intensive meat production, Mallin et al (2013) argue that the high concentration of CAFOs puts pressure on regional environment due to major imbalance in waste production and the capacity to effectively manage this waste. This ‘mismanaged’ waste is left to spread on fields and enters our environment through a process groundwater infiltration and overland flow (Edwards et al, 1992). In consequence, some of North Carolina’s major lakes have experienced large microbial contaminations and the presence of algal bloom that have caused major fish kills. These surface runoff not only affect large lakes and rivers but also heavily impact smaller temporal water bodies such as vernal pools, that are particularly important for containing endemic plant species but are often used for cattle grazing due it promoting the growth of native plant species (Brudvig et al, 2007). A recent 2011 study (Croel et al, 2011) showed that, though cattle grazing nearby vernal pools might increase some plant diversity on land, cattle manure was influencing vernal pool water quality. The presence of nutrient rich materials in pools, have caused increasing growth of algal blooms which have been detrimental for the already endangered plant communities that live amongst vernal environments (Croel et al, 2011).

 This post explained and presented how the livestock industries are indirectly affecting freshwater environments such as wetlands, lakes , rivers and streams

George Monbiot at University College London

Hi everyone!

UCL’s Geographical Society invited as their guest lecturer the famous journalist and blogger: George Monbiot. The topic of the talk was ‘Rewilding: the mass restoration of Britain’s ecosystem’ which I found particularly interesting and knowledge enriching in regards to Britain ecosystems.

I thought this would be a great occasion to ask him about what have been writing about for the past few weeks: the desertification debate!

However I did not get the chance to do so as he was only given four questions to answer and as I raised my hand to ask a question, his ‘question time was already’ up.  LLL

After having listened to the talk, I decided to read a bit more on his most recent post and find out if he discussed livestock farming in any of his posts.

I came across an interesting post on animal and dairy production, more precisely on how cow manure was impacting some rivers and streams in Britain. I chose to talk about this today as it will be a topic of discussion my next upcoming posts.

In his talk, Monbiot talked about his passion for hiking and walking amongst Britain nature reserves; However, he noted that the last few months he has experience many expales of a degrading nature. One of them, that is also discussed in his blog, was the increasing pollution of water bodies caused by agriculture and presence of cattle to nearby streams. Some of these impacts are captured in the photos below.

Here, we see the physical and visual impacts of a British dairy farm on different types of water bodies.

In July 2015, the British Environmental Agency published a report (E.A., 2015) on water pollution incidents and showed that the only sector where pollution incident are increasing rather than decreasing like the rest of the trend, is the farming sector. (See figure 1)

Furthermore, in figure 2, we see that the dairy industry has had the most water pollution incidents for three years now, 2012, 2013, 2014.

--> We must not forget that livestock production also includes its bioproducts such as eggs and dairy and have as much as an impact on our environment than beef, poultry farming.

Part 1: From land to sea, though not forgetting freshwater, rivers and streams.

Water Usage and consumption

The more direct and obvious effect of animal agriculture on our environments is the physical use and consumption of water use and comsuption of water essentially used to

Water is needed for the livestock to survive and grow but water is also used to grow feed for these animals. This explains the rather striking statistics on global water consumption where an average of 55 trillion gallons of water are used annualy  for animal agriculture ( an average of it ranging from 34 to 76 trillion gallions). Similarly, to produce one pound of beef, equivalent to your weekly cheese burger, an average of 2500 gallons fo water are needed.

Considering how these statistics only touch on the direct consumption of water that impacts our environment, what other more indirect effects does livestock farming have on our aquatic environments and habitats?

This post represents the first of my ‘water blogpost series’ where I move away from land environments to investigate freshwater and ocean environments in greater detail.

For the first post of this series, I felt it would be particularly interesting to look at how the physical presence of cattle near a water stream can impact water quality. A recent 2014 peer reviewed article (Benskin et al , 2014) examines how cattle in-steam presence has potential impact on Suspended Solid Concentrations (small particles often found in suspension in water bodies due to the movement and flows of water)  which are used as indicators of good water quality. Presence and movements of cattle in streams moved streamed storage around and re-suspend previously deposited sediment loads within the stream thus changing its water quality. In this study, the use of a high resolution water quality data collection showed that 58% of SSC events, where an increase in sediment load was recorded, were accounted for by cattle in-stream presence. Thus it underlined how cattle grazing near a stream and their presence had a considerable impact on water pollution, through changes in nutrients within the water.