Summary
Lencois
Maranhenses National Park is an area of otherworldly dunes and lagoons on the northeast
coast of Brazil. The goal of the research problem in this article is to create
a digital elevation model (DEM) that can provide information on the dynamics of
dune formation in the park. The research attempts to answer how the dunes are advancing and retracting, and
whether there could be significant erosion happening.
This is an important question to answer because
coastal dunes protect against sea-level rise. Being vulnerable to natural and human
disturbances, they are also important for conservation efforts. DEMs can be helpful in identifying risk areas,
studying land use, monitoring sea-level rise, and for analyzing the dynamics of
areas under the influence of human activity.
The procedure involved three phases: data
acquisition, data processing, and DEM creation. Landsat images were retrieved from USGS to
determine ideal places for marking and surveying. Geodetic marks were placed at intervals on the
dunes where altimetric surveys would be performed to collect data. Data processing was carried out by software
that determined statistically significant changes in the dune surfaces. A DEM was generated using the triangulated
irregular network (TIN) technique in ArcGIS. A total of 1,010 and 1,700 sampling points
with irregular distribution were gathered for the data at two different dates
to monitor the changes. The use of Landsat images and
ArcGIS tools are highly reliable for the processing of spatial data because
they minimize the potential for human error.
The
researchers found that there was a decrease in sediment volume on the dunes
from 2015 to 2017, with dune migration going in the NE-SW direction. Using the
software, they found “erosion on the order of 61.43071 m³ ± 2.5 cm.” This is an alarming finding that with more
research could indicate the dunes are receding.
Review
Variables
in the article were operationally defined, and there were many cited
references. Overall, it was a comprehensive article, but there were several
shortcomings. No educational
significance of the problem was discussed, though further research was
recommended. Further education would help
more people become aware of why dune erosion and migration is important. For instance, it was unclear how the geology
of the area created these dunes in the first place, or if there was an
ecosystem being impacted. Also, previous
studies on dunes in the area were mentioned, but they were not explained. More background information like this would
help to educate people and make the issue more comprehensive for readers.
There wasn’t a specific hypothesis that the research
intended to prove or disprove. Rather,
it only sought to the answer the questions of dune erosion and migration. No expected relationship between the variables
was anticipated. The main point seemed
to be that the DEM method is better than older methods involving fieldwork.
The size of the sample population was described with only
one major characteristic: that the area chosen had the largest dunes in Lencois
Maranhenses. The reader is left to
assume this is the only reason the study area was selected. Then, the sample selection method was vaguely
described as “irregular”. The reader is
left wondering if the sample points were random or methodically irregular. Having a large sample size (over 1,000) does
provide for a strong DEM, but it would have been helpful to understand how they
were selected.
A more appropriate description of the instruments used
was needed. The researchers used the
Global Navigational Satellite System GNSS in their procedure, but it isn’t
clear how. Even the sections describing DEM
methods in ArcGIS were not descriptive enough to fully understand how the model
mapped dune migration. It seemed like
the article was only written for people with advanced knowledge of this
software.
The design seemed appropriate to answer the research
questions; DEMs are in high demand for monitoring environmental changes like
this. However, I don’t believe the
procedures were described in enough detail for the research to be replicated,
especially for someone new to the field, like a student.
Statistics were presented in the results, but without
charts or graphs, it made them hard to interpret. The only table presented showed survey
parameters- nothing about the results. No
description of probability, confidence interval, or test of significance was
described, even though it was stated earlier that the software uses statistics.
A point cloud was used to show dune
migration in one figure, while a figure for the DEM was presented to illustrate
the average changes in altitude that were calculated. The data for these figures were described well
in the text, in what I believe is the strongest part of the article.
The researchers were also strong in reporting the
results, which answered the questions they posed at the beginning. They made a strong case for future researchers
to use the DEM method instead of conventional ones involving theodolites, levels,
and stations systems. DEM is a much
cheaper and more accurate method than these older ones; plus, it saves the
researcher time but not having to go to the dunes and do a physical survey.
One weakness of the conclusion is that the results from
previous studies were not mentioned, making it impossible to compare these
results without having the reader do more research. A strength of the conclusion was that recommendations
for future research were made. To better
understand sediment dynamics and dune evolution in Lencois Marenhenses, it is
important to continue monitoring changes using DEM surveys. This is especially important since dunes,
being made of sand, can erode and migrate faster than other landforms. And while it isn’t stated in the article and may
not seem essential to conservation, preserving one of the most beautiful places
on earth should be reason enough to keep these studies going.
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