Report on Harmonisation of freshwater biological methods

Number of sampling stations10080%6040201 sampling station2-10 samplingstations0AL AT BA CE EC ME NOFigure 4. Number of sampling stations for chlorophyll a in the GIGs.4. The sampling depth and volume sampled may contribute to large differences inthe determination of chlorophyll a concentrations in a lake. The most frequent methodin all the GIGs involves the collection of surface samples. In some GIGs (mostcountries in the AL, ME and NO GIGs), for a few lakes chlorophyll a is estimatedfrom integrated samples (Fig. 5). In the AL and BA GIGs the collection of more thanone discrete sample at different depths is regularly practiced.Sampling depth10080%6040200AL AT BA CE EC ME NO1 surface sample 1 integrated sample more than 1 discrete depthsFigure 5. Sampling depth for chlorophyll a in the GIGs.5. Among the most heterogeneous steps in the assessment of chlorophyll a are,however, the extraction methods (e.g. Marker, 1972; Pepe et al, 2001), which varywidely within GIGs, among GIGs and even within a single country (Table 1). Thesecan explain considerable variance in the measurement of chlorophyll a concentration.47