We left Ciudad Constitución early and made it to La Paz by 10:00am. We
stopped in to the headquarters of Baja Expeditions to talk to Tim Means
and to pick up the supplies he had purchased for us the day before. In
order to save time, we had emailed him from Los Dolores using the
satellite phone with a shopping list (food, batteries, drinks, etc.).
After packing up the trucks with crates of oranges and boxes of food,
we headed north to San Evaristo. It was a four and a half hour drive to
our new base-camp. The road showed plenty of signs of hurricane damage
with plenty of washed-out sections. When we arrived at the new
base-camp, Carolina already had the full kitchen up and running. She
was certainly happy to see all the fresh produce.
Team Mammals and Team Birds were in full swing and I should be able to
give you updates on their activities as soon as possible. In the
meantime, Dr. Mike White from the Conservation Biology Institute has
been working on the materials he collected during the first phase of
the expedition from Los Dolores. He is a limnologist, but I’ll let his
update explain the details of this field of science.
Team Limnology Update
Observations of Aquatic Systems in the Misión Dolores Region of the
Agua Verde/Cerro Mechudo Corridor
Limnology is the study of inland bodies of water, such as lakes and
rivers. Limnological investigations within the corridor are being led
by Dr. Michael White, and are focused on developing a basic
understanding of the hydrology, chemistry, and biology of the aquatic
systems present in the area. In the area around the Misión Dolores
base-camp, there are three general categories of aquatic systems:
streams, lakes, and coastal lagoons. Streams that have been explored
in the Misión Dolores region include the Arroyo Dolores (which holds
the ruins of the historic Misión Dolores), the Arroyo San Clemente (a
tributary to Arroyo Dolores), and the Arroyo La Cumbre (located in the
canyon south of the Arroyo Dolores).
These stream systems have been greatly affected by the hurricanes
(chubascos) that passed over the region in the summer. The tremendous
amount of water that they dropped in the local watersheds was apparent
from the minimal amount of vegetation remaining in the stream channels,
the large deposits of vegetation debris (often several meters up in the
remaining trees), and evidence of extensive reworking of the stream
channels, which entailed moving large volumes of boulders and cobble
stones.
The influence of the chubascos was also apparent in the amount of
freshwater present in the arroyos. Flowing water is associated with
warm mineral springs in both the Arroyo Dolores and the Arroyo La
Cumbre. The Arroyo Dolores is particularly notable for the amount of
freshwater it discharges, which is why the site proved to be suitable
for establishing the Misión Dolores. Water was brought to the mission
from a spring emerging from the canyon wall in the upper portion of the
arroyo to a cistern (pila) via an aqueduct (acequia), which are still
visible today. At the spring that supplied the old Misión and existing
rancho (and the Expedition base-camp), we recorded the water
temperature at 31ºC and conductivity of 730µS. Conductivity is a
measure of the dissolved mineral content of the water. At the large
spring in the Arroyo La Cumbre, which supplies water to about a dozen
families living in the canyon, we recorded the water temperature of
32ºC and conductivity790µS.
To look more closely at the variation in water chemistry in the Arroyo
Dolores, Dr. White and Bob Hill took measurements of temperature and
conductivity at a number of locations within the Misión Dolores.
Within this arroyo, there are sections of the stream where water was
flowing on the surface, sections where it was present in isolated
ponds, and reaches where surface water was absent but present in the
underground aquifer. The conductivity of surface water appeared to
increase as one moved higher up the arroyo. Conductivity ranged from
920µS at the bottom of the arroyo to in excess of 1990µS at the
uppermost pool we visited.
Organisms that rely on aquatic systems in arid environments such as the
Misión Dolores region, must cope with large fluctuations in many
factors such as the amount of water, velocity of flow, temperature, and
chemistry. Maggie Reinbold, Carlos Flores, and Dr. White collected
various invertebrate taxa such as mayfly larvae, beetles, dragonfly
larvae, snails, and zooplankton. The organisms will be identified to
increase our understanding of the biogeography and ecology of these
species in Baja California Sur.
One of the most interesting aquatic system explored in the first phase
of the Expedition was Laguna Kakiwi, located on a mesa south of the
Arroyo La Cumbre. Laguna Kakiwi is a very large ephemeral (temporary)
lake, which fills only with significant precipitation events such as
those associated with chubascos. Our local guide told us that Laguna
Kakiwi had not held water for 15 years, and takes 2-3 years to
completely dry.
Laguna Kakiwi had very turbid water, with extremely low transparency.
The turbidity was probably associated with clay particles suspended in
the water column by wind blowing across the lake. The conductivity of
the lake was very low (140µS). By comparison, the conductivity of
drinking water in the San Diego area is often over 500µS.
The limnology team also collected invertebrates at Laguna Kakiwi. A
very interesting find was an Anostracan crustacean (fairy shrimp) in
the genus Streptocephalus (fairy shrimp in this genus also occur in San
Diego County). These and other aquatic animals that live in ephemeral
lakes have life history strategies that allow them to survive periods
without water, which in the case of Laguna Kakiwi can be for very long
periods of time. These organisms develop resting stages (e.g., eggs
and cysts) that can remain viable in the dry sediments of the lake for
many years. When the lake fills with rain, the organisms emerge to
complete their life cyles, and produce resting stages for future dry
periods. The ephemeral Laguna Kakiwi is very unique in many respects.
For example, the botany team found a very unique plant community around
the margin of the lake that is associated with the ephemeral water
conditions.
Along the beach, adjacent to our base-camp, there are 4 coastal
lagoons. These lagoons vary in their salinity, reflecting the
influences of tidal exchange and freshwater inflows. The lagoon at the
terminus of the Arroyo Dolores is completely separated from the ocean
by a sand bar. The salinity of the lagoon is 4 parts per thousand
(ppt), reflecting the input of freshwater via groundwater. Two of the
lagoons have daily tidal exchange with the ocean, and their salinities
range from 33-36 ppt. There is also an interesting pond situated in a
topographic depression that is separated from the ocean by a sand dune. The pond is used by the people living in the area to make salt. The
deeper portions of the pond (which have been excavated for the salt
making process) exhibited an interesting vertical layering of its water
with denser brine (>100 ppt) on the bottom and less dense saline water
(21 ppt) on top.
Bradford Hollingsworth
Expedition Coordinator
and
Mike White with Limnology Update
From San Evaristo base-camp at 11:00pm |
Driving north along the road to San Evaristo.
Remnants of hurricane damage.
San Evaristo.
Dr. Mike White from the Conservation Biology Institute.
Freshwater shrimp caught at Lago Kakiwi on November 10th.
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