Reflecting on the past few months of writing this blog, I've got mixed feelings. It has reiterated to me that I'm too last-minute (don't check the dates of my posts). Truthfully, I wish I had picked a different topic as I struggled to engage with some of the content. It wasn't easy to write either. Communicating science to an audience is difficult, especially when you're not quite sure what the demographic is other than who marks the final version. It's public to anyone, so I tried to keep it scientific without being too formal. Hopefully I achieved that, and I like to think my writing skills have grown as a result.
I have learned a lot about the Amazon and am glad to have this knowledge now. There are a lot of issues, but nothing is as straightforward as I initially thought. It's not all doom and gloom, and the sheer amount of research makes me equally concerned and hopeful for the Amazon's future. It suggests that the huge amount of deforestation is causing a lot of issues, but it's also introduced me towards huge conservation efforts going on by organisations like the WWF!
So, that's me done. Remember dear reader(s), save the rainforest!
Friday 5 January 2018
Let's Get Biogeochemical
In a previous post, I spoke about nine planetary boundaries, and how four of those boundaries have already been transgressed (Rockström et al., 2009). I'll link you again to Johan Rockström's TEDTalk about it here and refresh your memory with Figure 1.
As you can see, Biogeochemical flows are one of the nine boundaries transgressed beyond the zone of uncertainty. Human industry and agriculture have altered natural nitrogen and phosphorous flows, creating more reactive nitrogen than occurs naturally and mobilised significant amounts of phosphorous. Much of this ultimately ends up in terrestrial and aquatic ecosystems, polluting waters but fertilising soils (Stockholm Resilience Centre, accessed 2018). Similar occurrences have happened with increased CO2 output from fossil-fuel emissions. Tropical forests and large bodies of water are expected to take up a lot of this excess atmospheric carbon (Mahli et al., 2000; Sabine et al., 2004), although the terrestrial tropical response is hotly debated (Hickler et al., 2008). Since these are global occurrences, the Amazon has of course been affected too, especially considering the amount of forest converted to agricultural land (Hansen et al., 2013).
Increasing severity of droughts under El Nino and deforestation-induced droughts in the Amazon are likely to affect soil emissions of N2O and CH4 in the Amazon. A study into this by Nepstad et al. (2002) reduced rain throughfall in an area of the Amazon to replicate these drought effects, finding that the resultant reduction in productivity led to an increase in N2O soil emissions and an increase in soil consumption of CH4. Although aboveground productivity was also reduced, indicating a reduction in above ground carbon storage. This suggested that carbon and nitrogen emissions in Amazon forests are sensitive to small changes in rainfall. Ultimately, this means that increased drought under anthropogenic climate change and deforestation could significantly alter carbon and nitrogen cycling in the Amazon. A loss of nitrogen from Amazonian soils is concerning considering the deteriorating soil quality in the Amazon (Martinez and Zinck, 2004).
Interestingly, Nepstad et al. suggested no decrease in leaf litter mineralisation, which is thought to be the main way nitrogen is fixed into soils in tropical forests (Körner, 2009). In contrast, Körner’s study suggested that tropical forests, including the Amazon, are likely to experience an increase in nitrogen fixation stimulated by elevated CO2 (which is set to increase in the future) and an increase in productivity and carbon storage as a result. However, the study also suggested that soil nitrogen is less of a limiting factor in growth than phosphorous is in tropical forests.
Tropical forest soil is typically of poor quality, so the previously mentioned mobilisation of phosphorous and increased nitrogen fixation (despite increased N2O emissions) seems like a good thing. More phosphorous and nitrogen would increase soil quality and mitigate the phosphorous limitation, enabling increased biomass growth and above ground carbon storage, right? Taking carbon out of the atmosphere AND encouraging forest growth – that’s two for one! Well, it’s not that simple...
While this does happen, we’re offsetting it with our physical destruction of the rainforest, by reducing Amazon forest extent and reducing biodiversity, which I’ve talked about in my previous posts. That hinders growth immensely. What’s more is the potential for Phosphorous- and Nitrogen-containing fertiliser used in agriculture to run off into the Amazon River and cause algal blooms that reduce light penetration and cause oxygen-starvation to Amazon River plumes as bacteria consume these algae (Lock et al., 2015; Stockholm Resilience Centre, accessed 2018). The fish can’t breathe! Let’s consider also that my previous post determined that dam building is already reducing fish diversity in the Amazon river basin! Concerning, I know.
The issue of biogeochemical cycling is a little less cut-and-dry than some of the other issues I’ve discussed in the Amazon. There appear to be benefits to the Amazonian terrestrial ecosystems; potential increases in productivity and soil fertility, but definite negatives to our effects on biogeochemical cycling, particularly in Amazonia’s aquatic ecosystems. At least we can be sure in the knowledge that we’re effecting change again. We do a lot of that, unfortunately.
See you next time, for the final, reflective post of the blog!
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| Figure 1: The nine defined planetary boundaries. Biogeochemical flows is currently beyond the zone of uncertainty, indicating that it is at high risk. (Source: Stockholm Resilience Centre, accessed 2018) |
As you can see, Biogeochemical flows are one of the nine boundaries transgressed beyond the zone of uncertainty. Human industry and agriculture have altered natural nitrogen and phosphorous flows, creating more reactive nitrogen than occurs naturally and mobilised significant amounts of phosphorous. Much of this ultimately ends up in terrestrial and aquatic ecosystems, polluting waters but fertilising soils (Stockholm Resilience Centre, accessed 2018). Similar occurrences have happened with increased CO2 output from fossil-fuel emissions. Tropical forests and large bodies of water are expected to take up a lot of this excess atmospheric carbon (Mahli et al., 2000; Sabine et al., 2004), although the terrestrial tropical response is hotly debated (Hickler et al., 2008). Since these are global occurrences, the Amazon has of course been affected too, especially considering the amount of forest converted to agricultural land (Hansen et al., 2013).
Increasing severity of droughts under El Nino and deforestation-induced droughts in the Amazon are likely to affect soil emissions of N2O and CH4 in the Amazon. A study into this by Nepstad et al. (2002) reduced rain throughfall in an area of the Amazon to replicate these drought effects, finding that the resultant reduction in productivity led to an increase in N2O soil emissions and an increase in soil consumption of CH4. Although aboveground productivity was also reduced, indicating a reduction in above ground carbon storage. This suggested that carbon and nitrogen emissions in Amazon forests are sensitive to small changes in rainfall. Ultimately, this means that increased drought under anthropogenic climate change and deforestation could significantly alter carbon and nitrogen cycling in the Amazon. A loss of nitrogen from Amazonian soils is concerning considering the deteriorating soil quality in the Amazon (Martinez and Zinck, 2004).
Interestingly, Nepstad et al. suggested no decrease in leaf litter mineralisation, which is thought to be the main way nitrogen is fixed into soils in tropical forests (Körner, 2009). In contrast, Körner’s study suggested that tropical forests, including the Amazon, are likely to experience an increase in nitrogen fixation stimulated by elevated CO2 (which is set to increase in the future) and an increase in productivity and carbon storage as a result. However, the study also suggested that soil nitrogen is less of a limiting factor in growth than phosphorous is in tropical forests.
Tropical forest soil is typically of poor quality, so the previously mentioned mobilisation of phosphorous and increased nitrogen fixation (despite increased N2O emissions) seems like a good thing. More phosphorous and nitrogen would increase soil quality and mitigate the phosphorous limitation, enabling increased biomass growth and above ground carbon storage, right? Taking carbon out of the atmosphere AND encouraging forest growth – that’s two for one! Well, it’s not that simple...
While this does happen, we’re offsetting it with our physical destruction of the rainforest, by reducing Amazon forest extent and reducing biodiversity, which I’ve talked about in my previous posts. That hinders growth immensely. What’s more is the potential for Phosphorous- and Nitrogen-containing fertiliser used in agriculture to run off into the Amazon River and cause algal blooms that reduce light penetration and cause oxygen-starvation to Amazon River plumes as bacteria consume these algae (Lock et al., 2015; Stockholm Resilience Centre, accessed 2018). The fish can’t breathe! Let’s consider also that my previous post determined that dam building is already reducing fish diversity in the Amazon river basin! Concerning, I know.
The issue of biogeochemical cycling is a little less cut-and-dry than some of the other issues I’ve discussed in the Amazon. There appear to be benefits to the Amazonian terrestrial ecosystems; potential increases in productivity and soil fertility, but definite negatives to our effects on biogeochemical cycling, particularly in Amazonia’s aquatic ecosystems. At least we can be sure in the knowledge that we’re effecting change again. We do a lot of that, unfortunately.
See you next time, for the final, reflective post of the blog!
-
Thursday 4 January 2018
Can't Mistake My Biodiversity
I thought of a title pun this time! Congrats if you got it. Anyway, leading on from my previous post...
The Amazon Rainforest showcases tremendously high genetic diversity and species richness per unit area (Phillips et al., 1994), one of the highest worldwide. It's a global biodiversity hot-spot and is extremely important to preserve! Although the research into this may not be what you expect. The Amazon is actually classified as a zone of low vulnerability as far as biodiversity conservation efforts go. Despite this, it's also a zone of high irreplaceability due to its sheer amount of biodiversity being so ecologically important (Brooks et al., 2006). It's important to consider this when discussing the Amazon Rainforest, even though it may seem contrary to the narrative I've laid out so far. It's not quite as doom and gloom as it seems, but that doesn't mean there isn't a problem!
A recent study explored the effect of building dams for hydropower in the Amazon, Congo, and Mekong river basins and found a worrying correlation between fish diversity and the location of dams (Winemiller et al., 2016) (Figure 1). These basins contain approximately one-third of the world's freshwater fish species (2320 in the Amazon, 1488 of which are endemic), all of which are at risk of population decline. Figure 1 shows just how impactful dam constructions are on fish diversity, and the density of proposed dams in already-impacted areas is concerning. One bit of hope that Winemiller et al. point to, however, is that actual fish diversity is underestimated since multiple new fish species are discovered annually.
In terrestrial fauna, models suggest that significant land-use change in the central Amazon results in biodiversity loss by causing forest fragmentation (Dale et al., 1994). As forest is cleared for anthropogenic use, parts of the forest become isolated from each other, so the total available habitat area for species becomes smaller, particularly for relatively immobile species incapable of crossing these gaps. Ultimately, with a smaller living space, biodiversity rates decrease. Any guesses at what organisms have little to no gap-crossing ability whatsoever? That's right, plants!
The floral side of Amazonian biodiversity is a bit less clear though. According to Hopkins (2007), our knowledge of floral biodiversity in the Amazon is limited by a lack of data, since very few regions of the rainforest are well-documented. This suggests that what knowledge we have is very biased to these few regions and we have little understanding of how floral diversity is distributed across the Amazon. Hopkins' study actually indicated that four major regions of the Amazon basin are poorly understood and likely contain a significant number of plant species. This is particularly problematic given the fragmented nature of the Amazon under current forestry regimes and their propensity to house endemic species as a result (Dale et al., 1994). It's entirely possible that the biases towards certain regions and forest fragmentation mean that our estimates of total floral biodiversity are under or overestimated. Bloody forest clearing. We're compounding our own problems!
Land use change isn't the only thing likely to affect Amazon biodiversity in the future though. Climate Change is a pesky old thing! Increasing temperatures under climate changes and increased frequency of extreme weather events (that can often lead to fires) are predicted to cause habitat destruction and fragmentation, and subsequent species extinctions (Brodie et al., 2012). Though this is acknowledged to be under circumstances in which such changes result in organisms needing to change their habitat distributions in order to avoid rising temperatures under climate change. Unfortunately, Brodie et al. suggest that these extinctions would be the most severe in low lying tropical rainforest drainages, where organisms try to reach higher elevations where temperatures are cooler. Yep, that includes the Amazon.
Remember the anthropogenic fires I talked about in a previous post? Remember how our forest clearing is increasing the possibility of these? Well, yeah, we're ruining things again. If Amazonian ecosystems are unable to adapt or cope with increased fire frequency, then habitat destruction is going to increase as a result, and put a greater number of species at risk of extinction. Worst case scenario; some models have predicted that this deadly combination of climate change and land use change (I told you everything was interlinked!) will cause large scale drying in the Amazon and large enough increases in fire frequency to reach a tipping point in some parts of the Amazon by 2030, causing a shift to drier, savanna-like ecosystems (Nepstad et al., 2008). Figure 2 depicts exactly where this has been predicted.
The profound negative impacts this would have on indigenous peoples is bad enough (Finner et al., 2008), let alone the decrease in biodiversity this would lead to. Tropical Savannah and dry ecosystems typically exhibit lower rates of biodiversity than tropical rainforests (WWF, 2006). Although Savannah ecosystems are still quite diverse, they do not make suitable habitats for most rainforest species that exist within relatively narrow climate envelopes. One thing to note though, is that this shift is projected by a model. It's not a given, so interpret this with a critical lens.
There's a lot science is unsure of or can't decide on, such as Amazonian floral biodiversity, or just how vulnerable the Amazon actually is. What we are quite confident about, however, is that this biodiversity hot spot isn't doing as well as it could be. A lot of species in the Amazon are at risk currently; we're just not sure how much risk. While significant Amazonian extinction may not occur within our lifetimes, we must be careful not to breach a tipping point in the Amazon to cause mass extinction in the future. We certainly don't want the Amazon to follow the same trend as the global genetic diversity planetary boundary.
And on that depressing note, I'm out. See you next time!
The Amazon Rainforest showcases tremendously high genetic diversity and species richness per unit area (Phillips et al., 1994), one of the highest worldwide. It's a global biodiversity hot-spot and is extremely important to preserve! Although the research into this may not be what you expect. The Amazon is actually classified as a zone of low vulnerability as far as biodiversity conservation efforts go. Despite this, it's also a zone of high irreplaceability due to its sheer amount of biodiversity being so ecologically important (Brooks et al., 2006). It's important to consider this when discussing the Amazon Rainforest, even though it may seem contrary to the narrative I've laid out so far. It's not quite as doom and gloom as it seems, but that doesn't mean there isn't a problem!
A recent study explored the effect of building dams for hydropower in the Amazon, Congo, and Mekong river basins and found a worrying correlation between fish diversity and the location of dams (Winemiller et al., 2016) (Figure 1). These basins contain approximately one-third of the world's freshwater fish species (2320 in the Amazon, 1488 of which are endemic), all of which are at risk of population decline. Figure 1 shows just how impactful dam constructions are on fish diversity, and the density of proposed dams in already-impacted areas is concerning. One bit of hope that Winemiller et al. point to, however, is that actual fish diversity is underestimated since multiple new fish species are discovered annually.
 |
| Figure 1: The distribution of existing and planned dams in the Amazon river basin and the species richness distribution. Areas of high dam density appear to coincide with areas of lower species richness. (Source: Winemiller et al., 2016) |
In terrestrial fauna, models suggest that significant land-use change in the central Amazon results in biodiversity loss by causing forest fragmentation (Dale et al., 1994). As forest is cleared for anthropogenic use, parts of the forest become isolated from each other, so the total available habitat area for species becomes smaller, particularly for relatively immobile species incapable of crossing these gaps. Ultimately, with a smaller living space, biodiversity rates decrease. Any guesses at what organisms have little to no gap-crossing ability whatsoever? That's right, plants!
The floral side of Amazonian biodiversity is a bit less clear though. According to Hopkins (2007), our knowledge of floral biodiversity in the Amazon is limited by a lack of data, since very few regions of the rainforest are well-documented. This suggests that what knowledge we have is very biased to these few regions and we have little understanding of how floral diversity is distributed across the Amazon. Hopkins' study actually indicated that four major regions of the Amazon basin are poorly understood and likely contain a significant number of plant species. This is particularly problematic given the fragmented nature of the Amazon under current forestry regimes and their propensity to house endemic species as a result (Dale et al., 1994). It's entirely possible that the biases towards certain regions and forest fragmentation mean that our estimates of total floral biodiversity are under or overestimated. Bloody forest clearing. We're compounding our own problems!
Land use change isn't the only thing likely to affect Amazon biodiversity in the future though. Climate Change is a pesky old thing! Increasing temperatures under climate changes and increased frequency of extreme weather events (that can often lead to fires) are predicted to cause habitat destruction and fragmentation, and subsequent species extinctions (Brodie et al., 2012). Though this is acknowledged to be under circumstances in which such changes result in organisms needing to change their habitat distributions in order to avoid rising temperatures under climate change. Unfortunately, Brodie et al. suggest that these extinctions would be the most severe in low lying tropical rainforest drainages, where organisms try to reach higher elevations where temperatures are cooler. Yep, that includes the Amazon.
Remember the anthropogenic fires I talked about in a previous post? Remember how our forest clearing is increasing the possibility of these? Well, yeah, we're ruining things again. If Amazonian ecosystems are unable to adapt or cope with increased fire frequency, then habitat destruction is going to increase as a result, and put a greater number of species at risk of extinction. Worst case scenario; some models have predicted that this deadly combination of climate change and land use change (I told you everything was interlinked!) will cause large scale drying in the Amazon and large enough increases in fire frequency to reach a tipping point in some parts of the Amazon by 2030, causing a shift to drier, savanna-like ecosystems (Nepstad et al., 2008). Figure 2 depicts exactly where this has been predicted.
 |
| Figure 2: The extent of predicted dry forest covering the Amazon by 2030 as a result of large scale drying under climate change. (Source: Nepstad et al., 2008) |
The profound negative impacts this would have on indigenous peoples is bad enough (Finner et al., 2008), let alone the decrease in biodiversity this would lead to. Tropical Savannah and dry ecosystems typically exhibit lower rates of biodiversity than tropical rainforests (WWF, 2006). Although Savannah ecosystems are still quite diverse, they do not make suitable habitats for most rainforest species that exist within relatively narrow climate envelopes. One thing to note though, is that this shift is projected by a model. It's not a given, so interpret this with a critical lens.
There's a lot science is unsure of or can't decide on, such as Amazonian floral biodiversity, or just how vulnerable the Amazon actually is. What we are quite confident about, however, is that this biodiversity hot spot isn't doing as well as it could be. A lot of species in the Amazon are at risk currently; we're just not sure how much risk. While significant Amazonian extinction may not occur within our lifetimes, we must be careful not to breach a tipping point in the Amazon to cause mass extinction in the future. We certainly don't want the Amazon to follow the same trend as the global genetic diversity planetary boundary.
And on that depressing note, I'm out. See you next time!
Biodiversity (I can't think of a clever title for this one)
The Importance of Biodiversity and Global Trends
Ever wondered what's happening to all those animals, plants, and creepy crawlies living in the Amazon? Not to be all doom and gloom, but our 'burn everything!' approach to land clearing is kind of screwing them over... just a little bit. I've made no secret of this and have explicitly stated in previous posts that many species native to the Amazon Rainforest are under threat. "But, what's really happening?", I pretended to hear you ask! Well, that's what I'm here to tell you; whether you asked for it or not. Be educated, my reader(s)!
A brief note before we begin; I will be splitting the biodiversity post into two since it would otherwise be too lengthy. This post will cover global biodiversity trends and the importance of biodiversity as a concept. The next post will focus specifically on biodiversity in the Amazon in regards to these ideas.
Ecosystem biodiversity, which is sometimes referred to as genetic diversity, is analogous to the species richness of an ecosystem. That is, the number of different species co-existing and living per unit area (Encyclopaedia Britannica, accessed 2018). Basically, it's just how many different kinds of organisms there are. Although simple, it's an important concept and is important in maintaining ecosystem functioning, which provides goods and services to human society, such as freshwater filtration and raw materials. Yep, biodiversity is economically valuable as well - remember this! High biodiversity rates have been shown to increase ecosystem productivity and nutrient retention rates, make ecosystems less susceptible to invasion by foreign species, and somewhat mitigate the negative impacts of environmental disturbances (Hooper et al., 2005).
Experimental work by Balvanera et al. (2006) spanning 50 years has shown increased biodiversity to have a net positive effect, although this is stronger on the community-level, where populations are smaller, than at the ecosystem level. Balvanera et al.'s study also indicated that biodiversity has a greater positive relationship with ecosystem productivity than ecosystem stability.
Figure 1 from Gamfeldt et al. (2008) below conceptualises this relationship well, where species richness is biodiversity. The black and grey lines show the result of changes in species richness with ecosystem functioning for high and low redundancy ecosystems. In high redundancy ecosystems, there are a number of species capable of filling a specific ecological niche that results in a specific ecosystem function. The high redundancy scenario in this case shows the maximum loss in functioning where the species lost are those most efficient at filling their ecological niche. With high redundancy, you would expect functioning to remain higher than with low redundancy, since multiple species are able to fill the same niche in the former, despite the most efficient species being lost. The general trend, however, is that ecosystem functioning remains higher under higher species richness across both redundancy levels. Ultimately, high levels of biodiversity prevent ecosystems from tipping into unenviable states.
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| Figure 1: The relationship between biodiversity (species richness) and ecosystem functioning is neatly conceptualised, distinguishing between the degree of relationship in high and low redundancy ecosystems. (Source: Gamfeldt et al., 2008) |
Knowing that biodiversity is important, it's been monitored and studied extensively on a global scale. A landmark study by Rockström et al. (2009) defined nine planetary boundaries that humanity can safely operate in. Johan Rockström himself did a TED Talk on the topic, which you can find here, in case you're interested! It is suggested by Rockström et al. that transgressing these boundaries could bring about abrupt and potentially irreversible environmental shifts. Biosphere integrity, aka biodiversity, is one of these, and has already been exceeded on a global scale. Figure 2 illustrates this, where the threshold for biodiversity is shown as extinctions per million species-years (E/MSY). It's not surprising that this planetary boundary has been breached, considering that ongoing patterns of biodiversity loss have contributed to the first anthropogenically-driven major extinction event ever seen on Earth - and only the sixth ever event (Chapin et al., 2000).
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| Figure 2: The nine planetary boundaries as defined by Rockstrom et al. (2009). Four of these, including biodiversity (shown here as genetic diversity), have already transgressed into the 'zones of uncertainty', where there is a high risk of potentially irreversible and abrupt environmental shifts to undesirable states. (Source: Stockholm Resilience Centre, accessed 2018) |
So, it looks like loss of biodiversity is currently, and will continue to be, a major problem and we have a good idea about how this might affect ecosystems globally. We know it's not going to be good. But the studies I've presented so far have alluded to an economic impact as well, since ecosystems provide us with a number of goods and services (Gamfeldt et al., 2008). Anyone know of a tropical forest that's being carelessly exploited for economic gains?
Oh, that's right... The Amazon Rainforest! Of course, the Amazon is not exempt from this issue. Nothing is ever so easy! But I'll be ending this post here and continuing on with the Amazon in the next one, as promised at the start of this post. See you soon, dear reader(s)!
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