A review of: Baker, D. M., Jorda’n-Dahlgren, E., Maldonado, M. A. and Harvell, C. D. 2010. Sea fan corals provide a stable isotope baseline for assessing sewage pollution in the Mexican Caribbean. Limnology and oceanography, 55(5), 2139-2149.
As populations continue to rise, especially on the coastlines, sewage pollution is becoming a greater threat to coastal marine systems. The input of contaminants, especially nutrients such as nitrogen and phosphate can greatly disturb the environment. Increases in primary productivity can smother critical species such as sea grasses and reef building corals, pathogens can cause disease especially in corals and there is a generally common result of lowered biodiversity. While monitoring of this kind of activity is important everywhere, it is especially important that it is studied and controlled in developing regions which are often dependent on their ecosystem’s health and wellbeing.
This study hypothesised that sewage-derived nitrogen inputs are detectable and more severe in developed areas along the Mesoamerican barrier reef of Mexico. To test their hypothesis in this area they compared the stable nitrogen isotope (δ15N) values from the common Caribbean sea fan, Gorgonia ventalina, collected from a developed and undeveloped are of the coastline. Akumal coast was selected as the developed site as there are a great number of residents and a huge influx of tourists. The shoreline of Mahahual was selected to be the undeveloped site since there were few residents and tourists and a sewage treatment infrastructure.
The isotopic ratio of 15N:14N is regarded as an effective and direct indicator of human nitrogen pollution. Enriched isotope values arise from the accumulation and degradation of human and animal wastes and are easily distinguishable from other sources. Perpendicular to the shore samples of sea fans were taken 1km from the shore. 2cm-squared fragments were cut that are
likely to represent the previous year of growth. Stable isotope analysis was performed on the samples. The prevalence of Enterococcus was sampled at sites adjacent to where the sea fans were sampled. Enterococcus assays were used to determine if the nitrogen isotope analysis values were correlated with sewage pollution. Positive results for this test would rule out the possibility of enrichment due to denitrification. Statistical analysis was then performed.
Results found that samples from the developed site sea fans were enriched in δ15N (as high as 7.7‰ near shore) and were ≈3.5‰ greater than sea fan samples from the undeveloped site. The δ15N values were also positively correlated with faecal Enterococcus counts from the seawater. This confirms that the enrichments are associated with sewage and not denitrification. This study suggests that data collected from the undeveloped site which is relatively pristine could now be used as an isotopic baseline for monitoring the Mesoamerican barrier reef at sites where increased development is planned or underway. Another interesting find of this study was that the highest Enterococci counts were found to be from a lagoon popular with bathing tourists. The counts were approximately 59CFU per 100mL. The presence of faecal Enterococci is well above US Environmental Protection Agency standards for recreational waters which is 35CPU per 100mL.
This method of stable isotope analysis in sea fans could be a promising tool for monitoring changes in the contribution of human nitrogen sources to nearby ecosystems, especially in developing regions where water quality monitoring programs are not established.
As populations continue to rise, especially on the coastlines, sewage pollution is becoming a greater threat to coastal marine systems. The input of contaminants, especially nutrients such as nitrogen and phosphate can greatly disturb the environment. Increases in primary productivity can smother critical species such as sea grasses and reef building corals, pathogens can cause disease especially in corals and there is a generally common result of lowered biodiversity. While monitoring of this kind of activity is important everywhere, it is especially important that it is studied and controlled in developing regions which are often dependent on their ecosystem’s health and wellbeing.
This study hypothesised that sewage-derived nitrogen inputs are detectable and more severe in developed areas along the Mesoamerican barrier reef of Mexico. To test their hypothesis in this area they compared the stable nitrogen isotope (δ15N) values from the common Caribbean sea fan, Gorgonia ventalina, collected from a developed and undeveloped are of the coastline. Akumal coast was selected as the developed site as there are a great number of residents and a huge influx of tourists. The shoreline of Mahahual was selected to be the undeveloped site since there were few residents and tourists and a sewage treatment infrastructure.
The isotopic ratio of 15N:14N is regarded as an effective and direct indicator of human nitrogen pollution. Enriched isotope values arise from the accumulation and degradation of human and animal wastes and are easily distinguishable from other sources. Perpendicular to the shore samples of sea fans were taken 1km from the shore. 2cm-squared fragments were cut that are
likely to represent the previous year of growth. Stable isotope analysis was performed on the samples. The prevalence of Enterococcus was sampled at sites adjacent to where the sea fans were sampled. Enterococcus assays were used to determine if the nitrogen isotope analysis values were correlated with sewage pollution. Positive results for this test would rule out the possibility of enrichment due to denitrification. Statistical analysis was then performed.
Results found that samples from the developed site sea fans were enriched in δ15N (as high as 7.7‰ near shore) and were ≈3.5‰ greater than sea fan samples from the undeveloped site. The δ15N values were also positively correlated with faecal Enterococcus counts from the seawater. This confirms that the enrichments are associated with sewage and not denitrification. This study suggests that data collected from the undeveloped site which is relatively pristine could now be used as an isotopic baseline for monitoring the Mesoamerican barrier reef at sites where increased development is planned or underway. Another interesting find of this study was that the highest Enterococci counts were found to be from a lagoon popular with bathing tourists. The counts were approximately 59CFU per 100mL. The presence of faecal Enterococci is well above US Environmental Protection Agency standards for recreational waters which is 35CPU per 100mL.
This method of stable isotope analysis in sea fans could be a promising tool for monitoring changes in the contribution of human nitrogen sources to nearby ecosystems, especially in developing regions where water quality monitoring programs are not established.
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