Author: Sean Allen Ravenberg

Microbial diversity and community respiration in freshwater sediments influenced by artificial light at night

Posted on by Sean Allen Ravenberg

Background: The purpose of this study was an analysis of the impacts of light pollution on benthic microbial populations. The researchers state how these kinds of microbial populations are populous all over the planet and are highly diverse. They hypothesized that artificial light pollution will affect the composition and behavior of these populations and therefore will change ecosystem dynamics, affecting the global carbon cycle. The study was designed to take two similar benthic microbial populations and expose one to artificial light at night for six months and have the other in natural conditions to see whether this was true, and what effects this artificial light would have on the communities and their processes. 

Methods: The study was conducted by identifying two sites of benthic microbial organisms, two agricultural drainage ditches. The team verified that moisture levels were near identical for both sites, and also established that the species and populations were biologically similar enough for their study. They did this through DNA metabarcoding and included these results in the study to verify that their two populations were suitable for experimentation. These sites were located in a verified Dark Sky zone to confirm that the control would not experience any artificial light at night. One site was therefore chosen as a control and would receive no treatment, and the other site had artificial lamps installed over it. The lumens of the treatment for this site were also measured and controlled to be similar to the average lumens experienced in other urban settings that experienced artificial light at night. This data was also included in the study to verify that treatment levels were significantly similar to actual experienced light levels. Then, the light was maintained over the treatment site for six months. At the end of this time period, biological information about population composition, cellular respiration, and carbon sinking were recorded. 

Results: The study returned results that photosynthetic autotrophic organisms saw statistically significant population growth and comprised a larger percentage of the benthic ecosystem in the site that received treatment than in the one that didn’t. They also detected that cellular respiration levels had decreased. Overall this indicates a decrease in species diversity as the benthic communities were made to shift towards auto phototrophic majority populations, however they did anticipate that this could eventually lead to net positive NEP in these kinds of communities as light levels at night increase over time. This answers one major question of the experiment, which was whether or not light levels at night, significantly lower in intensity than sunlight, would be enough to stimulate photosynthesis for these benthic autotrophic organisms. 

Criticisms: I think that this experiment was set up very well. They accounted for many factors that could affect the results of their work and took data measurements to ensure that these factors were mitigated as much as they could be to establish reliable results. The difference in species between locations were accounted for by the DNA metabarcoding to ensure a similarity of species richness. The moisture levels were accounted for by testing to ensure similarity, and the lumen levels of the control site were measured to ensure they met natural dark sky levels to establish significant differences if they appeared. I think that all these precautions show a lot of forethought in the experiment and help to establish credibility of the results. I do think that perhaps they are extrapolating a bit much about the results in the discussion portion. They claim that the results of their experiments are proof that increasing light levels at night in the world will turn benthic organisms into ecosystems of net positive production at night year round, and that this will affect carbon sinking on a global scale. All this experiment really proved is that a long term presence of artificial light at night increased photosynthetic production in this one treatment group. I think these claims they make in their discussion are reasonable hypotheses and absolutely excellent grounds for future experimentation, but not truly establishable from this experiment alone. 

https://royalsocietypublishing.org/doi/full/10.1098/rstb.2014.0130

Direct and indirect effects of noise pollution alter biological communities in and near noise-exposed environments

Posted on by Sean Allen Ravenberg

Background: The point of this study was to measure the effect that noise pollution, primarily automobile generated, affected wildlife populations close to the sources of noise. While there is much documentation about direct effects of noise pollution on wildlife species that have auditory senses, especially birds and mammals, this study was designed to look at the cascading effects of noise pollution on ecosystems and food webs as a whole. Additionally, the study wanted to see if the effects of noise pollution would reach communities in quiet ecosystems separated from the noise pollution that were adjacent to the area with the exposure. The hypothesis was that noise pollution has greater systematic and cascading effects on wildlife than previously widely known.

Methods: The study measured both forest and grassland ecosystems. Six treatment sites were chosen for each ecosystem, along with six control sites for each ecosystem. All of these sites were roadless, wild sites in their respective ecosystem that had negligible noise pollution. In treatment sites, artificial recorded traffic noises were played from stationary points, and the treatment zones were split into near and far groups at the 150 meter mark from the noise source. This point was chosen because that is the distance at which the decibels of the traffic noise were registered as the same as the constant decibels of the noiseless control sites. The decibels were also measured and that data provided to confirm the treatment zones were appropriate. After a period of time, species richness and abundance data was collected in each zone for birds, grasshoppers, which represented insects capable of hearing, and odonates, which cannot hear. 

Results: The results show that a statistically significant lower amount of bird richness and abundance was recorded at the sites close to the noise, but only in forest sites. Grasshoppers and odonates showed statistically significant lower amounts of richness and abundance at the sites farther away from the noise source. The study believes that this is proof of the cascading effect of noise pollution, and claims that the results support their hypothesis. The study claims the change in bird population is responsible for the change in insect populations, and therefore the claim of cascading effects of noise pollution is proven. 

Criticisms: The study looked at result categories in a very general sense. The results contained species richness and abundance for “songbirds” as a category. I think it may be more informative to, if possible, collect more specific species data to get a sense on if these noise conditions affect all songbirds equally. While the study is focused on communities as a whole and the cascading interactions between niches, I still think more specified species information could provide a clearer picture. It’s also not clear if species abundance and richness was measured in each site beforehand, or if only theorized. If it was measured, a figure with that data does not appear to be included. I would have liked to see this experiment done with a focus on change in richness and abundance before and after treatment, rather than raw numbers on richness and abundance, as that would more clearly indicated if the treatment had an effect on the animals, rather than some other effect, or preexisting conditions of the site. I also do not know if this study is truly enough to prove that noise pollution has cascading effects. Proof of changing results for insect populations can certainly be correlated with changing results for bird populations, but I don’t know if causality can be proven. How do we know the noise itself isn’t also responsible for insect population changes?

Citation: Sensaki, Mazayuki., Kadoya, Taku., and Francis, Clinton. Direct and indirect effects of noise pollution alter biological communities in and near noise-exposed environments. NIH National Library of Medicine. 2020 Mar 25. https://pubmed.ncbi.nlm.nih.gov/32183626/