|Number of stemflow collectors:||Eight|
|Distribution of stemflow collectors on the plot:||Strictly random selection of all living stems greater than 7 cm diameter at 1.3 m height|
|Sampler description:||Helical gutters attached to the tree leading to an 80 litre bin|
|Material of the stemflow gutters:||Extruded Silicone rubber gutter. Silicone tubing leads to the collecting bin.|
|Material of the stemflow bin:||Graduated polyethylene 80 litre bin|
|Method of holding sampler:||Stemflow gutter is attached to the tree using silicon mastic and stainless steel screws at upper and lower ends.|
|Height above ground:||130 cm|
|Collection Method:||The volume of stemflow in the graduated bin is recorded on the field sheet. A sub-sample of 250 ml is taken from the 80 litre bin in a laboratory cleaned bottle. The remaining stemflow in the bin is carefully poured out around the base of the tree.|
|When the sampler overflows:||If the bin overflows, then the maximum volume of container is taken as the sample volume. Some trees consistently gave large volumes of stemflow and in this case, an overflow bin was installed.|
|Samples are rejected when:||The collector is damaged|
|There is litterfall in sample|
|There is ambiguously labelled samples, signs of human interference, recent maintenance or installation work on gutter|
|Stemflow sample transportation medium:||250 ml collection bottle with clean lid|
|Stemflow samples are transported to the laboratory by:||Courier|
|from litterfall:||Nylon Filter, 1 mm mesh, placed at the lower end of the gutter|
|from bird droppings:||The bin has a lid which keeps out contamination|
|from animals / humans:||Plot fenced|
|from algae growth:||Storage container is opaque (dark green). Preservatives are not used, weekly sampling is intended to reduce algal growth|
|Stemflow sample protection measures used, to avoid unwanted biochemical changes during storage between sampling and analysis:||Keep the sample in the dark|
|Cool the sample to < 4 degrees C when it arrives in the laboratory|
|Weekly sampling is intended to limit biochemical changes.|
Initially, the gutters, tubing and collection bins are cleaned prior to installation.
Cleaning procedure: Tap water rinse & brush; 3 distilled rinses, 3 distilled-deionised rinses; air dry.
Subsequently, the gutters and bins are not cleaned. However, after installation or maintenance, the initial four samples are discarded and not analysed.
Stemflow volume is measured for each individual sample in the field in the graduated bin.
Stemflow samples are pooled before analysis, in the laboratory in cleaned polyethylene bottles. After each collection the stemflow samples are pooled to 1 composite sample, weighted by sample volume
Contaminated samples are simply left out
Precipitation samples are chemically analysed on a weekly basis.
Pre-treatment methods: Filtering, Whatman 45 µm filter paper.
Analysis of precipitation samples comprises the following:
|pH and Conductivity||pH and Conductivity meters|
|Ammonium||Colorimetrically using the phenol-hypochlorite method (Solórzano, 1967) read on a UV at 635 nm|
|Molybdate Reactive Phosphorus||Acid-antimony-molybdate method (Murphy and Riley, 1962) read on a UV at 880 nm|
|Calcium, Magnesium, Potassium, Sodium, Manganese, total Aluminium||Inductively-coupled-plasma optical-emission spectrometry (ICP). If K <1 mg L-1, potassium was measured by atomic absorption spectrometry (AA)|
|Chloride, Nitrate, Orthophosphate, Sulphate||Ion chromatography (IC), using an anion exchange column and conductivity detection|
|Alkalinity||Gran titration (Mackereth et al., 1978)|
|Total Nitrogen||Digestion and colorimetric measurement (Koroleff, 1973)|
|Dissolved Organic Carbon||UV at 320 nm (Gorham et al., 1985), after filtration through a 0.45 µm filter and calculation by regression equation|
Repeat analysis is done on the basis of ion balances & ion ratios, comparing analysis to historical values for the same source. Critical limits are not applied. Following any repeat analysis, the less-unfamiliar-looking result is accepted. No sample is rejected on the basis of analytical results.
Last update: 20-March 2001
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