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A B C

D E F

G H I
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Figure 2. Common Cuban landscapes and example sample sites. (A) Sugarcane and dirt roads are common on the island. (B) Cattle grazing on cleared fields.
(C) Citrus groves on slopes in southern field area. (D) Horses were frequently in rivers, CU-132. (E) Plane-bed sand and gravel channel with cows in the river,
CU-101. (F) Large point bar flooded during Hurricane Alberto showing dynamic range of river flows over time, CU-114. (G) Boulder/bedrock channel during con-
ductivity measurement, CU-115. (H) Bedrock channel, CU-114. (I) Low flow sample site in incised channel, CU-122. Locations identified by letter in Figure 3N.

orite deposits including those that contain Cuba exceeds that on other, e.g., volcanic, with tectonically induced rock fracturing, is
nitrite (Figs. 3, 4, and 5). Caribbean islands (Fig. 6A), chemical denu- likely responsible for the continued supply
The relationship between water chemis- dation rates estimated from central Cuban of fresh, easily weatherable rock, and thus
try and bedrock type in central Cuba sug- river water samples are similar to other high chemical weathering rates.
gests the presence of fresh, weatherable Caribbean islands (Fig. 6B) because mean
mineral surfaces along flow paths carrying annual precipitation and thus runoff in Human Activities and Water Quality
subsurface flow to Cuban rivers. This infer- Cuba is lower. All Caribbean chemical High TDS in central Cuban river water as
ence is supported by comparison of Cuban denudation rates are high when compared a result of bedrock chemical weathering is
river water chemistry with that from to global data (Larsen et al., 2014). not hazardous but could limit some uses.
Martinique, Guadeloupe, and Dominica Field observations of incised, bedrock- About 20% of samples we collected have
(Rad et al., 2013). The latter three islands floored river channels and the chemical TDS and Na levels above the taste threshold.
are underlain primarily by andesite, and data that mandate extensive water/rock High TDS samples may cause CaCO scal-
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their surface water contains more Si and K interaction similar to that on tectonically ing on pipes, household cooking imple-
and less Ca and Mg than Cuban rivers (Fig. active, volcanic Caribbean islands suggest ments, and industrial equipment; scaling
6A). The higher concentration of most other ongoing bedrock uplift in central Cuba could be a health benefit if lead remains in
anions and cations in Cuban waters as com- rather than tectonic stability and the devel- the water distribution system. High levels
pared to waters from volcanic Caribbean opment of a deep tropical weathering man- of DOC (up to 9 mg/L) in central Cuban
islands reflects the influence of readily sol- tle. Raised marine terraces along southern river water suggest a potential risk of triha-
uble carbonate and evaporite rocks in Cuba. and eastern Cuba (Muhs et al., 2017) are lomethane formation during chlorination
Although average TDS for waters from consistent with such uplift, which, along (Engelage et al., 2009), which is the most

6 GSA Today | March-April 2020