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A B frequently used water treatment technique
in Cuba (Cueto and De Leon, 2010).
Bacterial contamination of river water in
Field conductivity [µS] 1000 Cl and SO 4 [mg/L] 100 ubiquitous presence of livestock on the
150

central Cuba is consistent with the nearly

landscape, perhaps because animals have in
part replaced fossil-fuel–powered transpor-

tation and farm equipment (Fig. 3). We do
500
however, the ungulate match in one of two

50 Cl not know the source of the detected E. coli;

samples we tested is consistent with numer-

2
R = 0.95 0 SO 4 ous cows we observed walking in and
200 400 600 800 0 50 100 around rivers as well as extensive pastures
Total dissolved solids [mg/L] 800 D Na [mg/L] islands, including Martinique, Trinidad, and
near and upstream of many sampling sites.
High levels of E. coli are found in rivers
C
Conductivity
TDS [mg/L] and Conductivity [µS] 1000 Total dissolved solids [mg/L] 600 Puerto Rico, show similarly high E. coli lev-

around the world. Data from other Caribbean
TDS
els in river, spring, and coastal waters
(Bachoon et al., 2010; Pommepuy et al.,
2000; Wampler and Sisson, 2011). E. coli lev-
400

els above health advisory levels are routinely
500
measured in Vermont river water, a similarly
agricultural state with more than a quarter
200

million cows, only half the stocking density

per area of Cuba (Riera, 1994). Although
25
0
100
50
75
pigs and chickens were common in central
Agricultural land use [%] ContinentalMafic Marine Cuba, we did not see them near rivers, which
Dominant rock type
may explain why tests for fecal matter from
Figure 4. Rock type influences river water chemistry. Red symbols indicate basins with distinct water these animals were negative as were those
chemistry highlighted in Figures 3 and 5. (A) Total dissolved solids (TDS) and field conductivity are well
correlated. (B) Positive correlation of Na with SO and Cl suggests evaporite source of these solutes. for human fecal bacteria.
4
(C) No correlation between percent basin area used for agriculture and total dissolved solids or con- Central Cuban river waters provide evi-
ductivity. (D) Basins underlain by marine and mafic rocks have higher river water TDS.
dence that agriculture need not overload riv-
ers, and thus reservoirs and coastal zones,
with nutrients. N and P are present in Cuban
river waters, but at lower concentrations than
Dominant Rock in the United States, where agriculture is
80 Ultramafic intensive and fertilizer use is heavy (Fig. 6).
80
pE marine strata
Total dissolved nitrogen in central Cuban river
SO + Cl 4 40 60 60 Ca + Mg uC marine strata water is <50% of the Mississippi River aver-

Metamorphic
age and <25% of peak Mississippi River con-
40
Amphibolites

120 Plutonic centrations (Fig. 6C). Cuban waters have only
slightly more TDN than less agricultural
20
20
121 Undivided Caribbean volcanic islands (Rad et al., 2013).
Volcanic

122 The history of fertilizer use over time is

telling (Fig. 6D). Cuban fertilizer use peaked
132 in 1978 and then declined, whereas fertilizer
use in the United States rose after 1961 and
80 20 80 has remained high, more than twice the area-
normalized value as Cuba. Sustainable agri-
Mg 60 40 Na + K Alkalinity as HCO 3 20 60 SO 4 cultural initiatives, implemented in Cuba
40

40 60 60 40 after the end of Soviet assistance, have
122 121 resulted in less fertilizer use and better river

20 120 132 80 80 132 120 20 water quality (Fig. 6). The result is far less

121 122 downstream transport and loading of nutri-

ents into coastal waters, nutrients that can

20 40 60 80
20
40
80
60
Ca Cl have a profound and negative effect, includ-
Figure 5. Piper diagram of all data color-coded by mapped lithology (Fig. 3) (French and Schenk, 2004). ing the presence of anoxic, marine dead
Numbered samples are those with distinct water chemistry influenced by evaporite rocks. zones (Obenour et al., 2013).
8 GSA Today | March-April 2020