Presentation on theme: "Digging out the trenches, experience in Russey, August 2003, version 27.10.03 1.Delineate 3 independent contiguous trenches on a surface of 11 x 4(5) meters."— Presentation transcript:
Digging out the trenches, experience in Russey, August 2003, version 27.10.03 1.Delineate 3 independent contiguous trenches on a surface of 11 x 4(5) meters each. 2.Remove the new vegetation down to the old brown peat which was earlier exposed (if this applies). 3.Check the ground water level with piezometers: what is the lowest expected level, the highest expected level and the median level? 4.The geometry of the trenches is indicated on the figure below. It is designed so as to have a gentle slope which gives enough space to install the pots. A double line of pots needs about 3 meters along the slope (space for pots, for trampling, etc.). Depending on your ground water dynamics, you will have to adapt the trench geometry, in particular its length, to keep a gentle slope! 5.Level and indicate with sticks the desired level zero. 6.In our case, because of the observed and expected water levels, we had to refill 50 cm peat, at least on the side of the upper part of the slope (it might not be necessary on the opposite side), and therefore we had to dig out relatively few peat. 7.In order to allow for a horizontally mowing ground water level, dig out the trench to the lowest level and refill the slope with porous peat. Otherwise, if the peat in place has a low conductivity, we might end up with a water level parallel to the slope … and no hydrologic gradient! 8.Hoe and crush the peat to obtain an homogeneous and aerated surface along the slope. 9.Under summer conditions (H min), one should see the free water in the lowest part of the trench. 10.Put 2 rows of more than 3 piezometers per trench. Sometimes, the slope might not be perfectly continuous in order to reach the expected water level. 11.We decided not to cover the slope with a textile mat, in order to avoid the release of external decomposing products (later we will have to put wood boards to prevent from trampling). 12.If, because of the ground water dynamics, the trench fills up, put a lateral drain to empty (regulate) the water when the level gets to high (preferably later in order to measure the highest water level).
The trenches in Russey H = max. = old surface peat H = mediane H(water level) = min. = -33 cm Filing up 50 cm Buffer zone of 3.50 cm between trenches Low water level: upper part of the pot 30 cm above the highest H Intermediate water level High water level: upper part of the pot 10 cm above the median H Scale 100% Scale 200% 11 m Peat in place Free water If necessary, put a lateral drain to evacuate the water if the trenches fills up 50 cm 85cm cm Level zero This part has to be filled up with porous peat in order to allow for a horizontally mowing ground water level
Assignment of tubes 10 cm 30 cm 5 cm 15 cm L 1 L 2 L 3 Sp 1 Sp 2Sp 3Sp 0 L 0 Year 1Year 2 Sp 1Sp 2 Sp 3 Sp 1 Sp 2Sp 3Sp 0 Spare species; litter should not be a problem over two years chamber tube Enough space for handling the corer by two persons 1.2 m Slope Water level I Water level II Water level III Total = 15 pots x 3 water levels x 3 replicates = 135 pots, from which only 72 will be analysed! If, in some site we decide not to do the WPIII, than one could allow for 4 keystone species in WP II, which would give 3 trenches x 3 water levels x (5+5+4) = 126 pots, among them 45 to measure during the year (gaz, biometry of plants) We would decide to continue for another year looking at some plant-pots. 3 m 1 out of 3 trenches (= replicates) WP 2: Species WP3: Litter