Thursday, June 13, 2013

Sapflow and hydrochemistry

The water balance of the catchments is quantified by a member of each of the five groups working in the Tabuaco, Mesas, Presa Velha, Salta and Sao Romao catchments of the Boco River catchment. This is a jolly group that comes together occasionally to set up the meteorological tower for instance, or in this case, to install the sapflow equipment for tree transpiration measurements. Looking  for a safe site took some time and finally we decided to use the place near the saline well in Patricia's Mesas catchment.

Tree with sapflow sensor and group programming a Campbell Scientific CR1000 logger to measure transpiration.
Deciphering CRbasic program code in the field to connect the many sapflow sensor wires
Two pines and two eucalypt trees were selected for torture by drilling holes and installing the temperature and heater needles, afterward covering everything up with aluminum foil and fixing it with our famous "yellow tape".

I should say something here about this yellow tape. Michel orders this from a secret company, and it is an invaluable tool in hydrology for fixing things, and also a secret clue for finding buried piezometers back that only VU hydrology students have. The whole area is now littered with yellow tape in a functional way, as a sign to our students that "something happened" in previous years when they find yellow tape at a site.

Sharkie lost...
In the meantime, somewhere on a deserted island in the Ria de Aveiro, Valerie and Marijn were still having a go at finding fresh water. After a particularly tiring day, Valerie won a battle with a baby shark and her Dutch roots nearly forced her to eat it "herring style".

Hydrochemistry in a plantation forest

Back to the MSc students in the Boco River catchment who now have moved from installation of expensive equipment to collecting water samples.Many steps have to be taken in the right order to get a good sample. You can choose a well, but it may be dirty (dead dogs, lizards, and even a car could be inside). So better are the sometimes beautifully decorated fontes (public water holes), especially when it rains. For those who like more challenging conditions, piezometers are the real thing.

You could of course look for a piezometer installed in  earlier years, but we do hide them well and finding them back can be a challenge too, where sometimes whole stretches of forest soil are dug up. Below the joy and pride of two dedicated students and the author of this text (Waterloo) when the students found one of these lost piezometers back.

Waterloo, Joris and Robbert enjoying the view of a long lost piezometer (Thanks Anne for the photograph)
If an old piezometer has been utterly destroyed, such that you only find back some yellow tape and a damaged cap, installing a new one seems the right thing to do. The three strong guys in this group (Robbert, Corne and Joris) thought it decent to let Anne have a go at it so that they could swing her around to get the casing into the soil.

When the piezometer is finally installed, has been cleaned and otherwise approved, the teams can get water out through a simple ball-valve attached to a tube. Below you see the sampling of water at their favourite spot, the illegal garbage dump, where in addition to contaminated water, you can also find small cats to put on your balcony so that their cries can keep you up all night.

Now everything has to be meticulously clean and we are guzzling up distilled water to rinse all bottles and sampling equipment. Hydrochemistry is not a job for natural born pigs.

Vince cleaning a measuring cyclinder

Then comes the job of filtering water, sometimes done by two students and sometimes causing confusion on who should close the bottle without including an air bubble.

Rosa and Maartje, specialists at filtering and closing bottles  without air bubbles...

Joris and Corne, sometimes less adept on bottle closure decisions as they have only one hand free each
 Then comes the job of measuring pH, electrical conductivity, alkalinity, nitrate/nitrite and temperature of sometimes very smelly water.

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