Hello all!
It’s Monica and Emily, and we are excited to update you all on the latest presentation of data from our lab’s work in Cuba. After visiting Western Cuba to collect more new samples, we were thrilled to double back to share some of what we’re learned from our first set of samples, and what we’re eager to learn about our newest set that we’ve collected.
Above: Map of our August 2018 and July 2019 sample watersheds
To give you a refresher: After Cuba transitioned to organic agriculture from sugarcane monoculture after the collapse of the Soviet Union, as a country it presents a unique multi-decadal opportunity to assess the impacts that sustainable agricultural techniques have on erosion. A major part of our process has been collaborating internationally across multiple institutions to get a full picture of Cuba’s rivers including water quality and cosmogenic erosion rate sampling, and this data only represents the first of three field seasons in the project.
With our main question being what the effect of transitioning to organic agriculture had on Cuba, we sampled large (250-850 micron) and small grained (<63 micron) samples from 26 different catchments. With our central question focusing on land use, the variety of land uses depicted in A-I in this second figure show the intense variety in land use type. Another complication was the persistence of sugarcane-based monoculture in certain areas, which adds complexity to our results.
Above: Sites labeled A-I show different sites in the 26 catchments that were sampled
Below: Spatial Distribution of isotopic results for both fine and coarse-grained fractions
Our results show some very interesting trends. When showing things from a spatial perspective above, we notice that there were diverse spatial patterns for each isotope. 7Be was higher in fine grained samples, but had no overall detectable spatial pattern, with few samples having detectable 7Be. 137Cs was detectable in about half of samples, coarse and fine grained activities were uncorrelated, and there were no spatial patterns. 210Pbex was detectable in about 60% of samples, with no spatial patterns or correlation between coarse and fine grained activity and the fine grained activity was higher.
We considered instead that the relationship might be better understood through environmental factors, but ran into the issue that these factors often covary (ex: slope and % agricultural land use), so it was difficult to parse out correlation and causation.
Below: Activity by different types of environmental factors
Some of our findings from the above analysis were that elevation, slope, area, and agriculture may be directly related to 210Pbex activity, but as mentioned above covariance complicates the analysis. Additionally, coarse-grained samples may provide more insight into causality due to higher variability in activity. Among the factors, we noticed that sites with 7Be, 137Cs, 210Pbex have more agricultural land, lower slopes, sites with isotopes below detectable levels tend to have more rain, and sites with only 210Pbex have higher slopes and less agriculture than sites with 137Cs and 210Pbex.
To continue with our work, we are excited to have not only rerun some of our samples that were below detectable levels, but also to have now run all the samples from our 2nd field season! As our third and final field season is in planning, we are excited to get moving on some data analysis to hopefully continue to draw more informed conclusions about erosional patterns in Cuba!
Until next time,
Emily and Monica
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