Tuesday, June 7, 2011

Evaporation, ecohydrology and hydrochemistry

We always start our field course with a select team of students setting up a meteorological tower that will give them potential evaporation, as evaporation is always the largest component in our water balance.

Corine, Sjef, Sonia and Michel working on the meteorology

Ecohydrology is the science of water and ecosystems. Studying this can be done with computer models, which is tedious work, bad for your back and only sometimes useful. The answer on how ecosystems really behave, however, can only be found in the field. The quest here in this field course is to find out how trees behave. This means that we want to find out at what time they wake up in the morning and start consuming water and nutrients, how much water they transpire, and when they go to sleep in the evening.

We have a little trick that allows us to find this out, which is called the sapflow method. Yes, we are measuring sapflow and we do this by sticking needles in the tree, in its sapwood where the water is transported up to the leaves. This means that we have to drill small holes in the tree to stick the needles in, here gently done by Nikki. One of these needles is heated, while the other one is at normal temperature. The heated needle will lose heat depending on the velocity of the sap in the stem and by comparing this with the non-heated needle we can find out when sapflow occurs and what the velocity is. Then we wrap the stem in aluminum foil and start the power and logging system.

The sapflow team done with their business

The following days were spent on hydrochemistry, taking samples from open wells, rivers, and piezometers. As our piezometers are not installed with the purpose of having access to clean drinking water, we often have a lot of suspended matter in our water and this needs to be filtered out, with force! This is done here by the team of Lieke, Carolina and Nikki, with Carolina turning red from the effort.

Pushing muddy water through a filter

Of course there are easier ways as Anna, Rosa and Sonia are demonstrating in a very nicely restored fonte where the older Portuguese get their lunch water.

Water sampling at Fonte de Angeao

We'll ship these sample to the VU University where they will be analysed and published in the papers written by our students in July. Ate logo!!!

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