Berlin Environmental Atlas

02.01 Quality of Surface Waters (Edition 1993)

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Chlorophyll a

Chlorophyll a amounts in waters are also presented separately. This depiction is in keeping with the Environmental Atlas standard because one of the main problems in Berlin waters is high nutrient impacts.

Chlorophyll a is the blue-green portion of chlorophyll (leaf-green). The determination of chlorophyll a levels in waters gives an indication of algae density. Chlorophyll a levels are not valid as an absolute measure for phytoplankton biomass, but indeed this pigment amount, in common with other biomass and bioactivity parameters, gives information about amounts present and the potential metabolic capabilities of phytoplankton in waters.

The pigment exploitation of the diatomic algae, which appear in spring and late autumn, is somewhat higher by the same wavelength in tests than that of blue-green algae, which form primarily in summer. The comparison of chlorophyll a values with counts determined by census of algae biomasses is thus recommended at special measuring points.

The development of phytoplankton composition varies according to the time of year and depends on various factors, including temperature, light penetration, zooplankton development, and level and type of nutrients. While diatomic algae (Bacillariophyceae) develop primarily in spring, blue-green algae (Cyanophyceae) dominate the phytoplankton make-up in high-summer (cf. Fig. 3). Precisely the higher temperatures and intense light penetration in high-summer facilitate algae growth. If excess loads of nutrients are present at the same time, massive algae bloom can occur.

Figure 3
Fig. 3: Phytoplankton Development in Müggelsee (lake middle) 1991

The phytoplankton minimum principally occurs in May and June and depends on many factors, such as weather, composition of algae types, and especially zooplankton structures. If the spring algae community is dominated by edible types (diatomic algae), then a mass development of zooplankton can occur which are capable of filtering great amounts of algae biomass. A high water transparency can be reached (cf. Fig. 4). This "clear water stage" is observed more frequently in the Spree, the Upper Havel and somewhat in the Lower Havel, but not in the Dahme, where thready, hardly edible blue-green algae appear as early as spring.

Figure 4
Fig. 4: Chlorophyll a Amounts and Water Transparency in Grosser Müggelsee (lake middle) 1991

The measured values for April to September 1991 are represented in the maps. The maximum and minimum values of this period for single water sections are displayed beside the mean values. The strips depicting the average value of the months April to June and July to September reflect the development of phytoplankton in spring and high-summer. Algae development also influences the turbidity of water, so the 6th strip depicts the water transparency with the average value of the summer half-year, April to September.

Measurement values are ordered in a 7-stage evaluation scale. The value of 30 g chlorophyll a per liter is considered as the restoration goal for Berlin waters. This value is used as the upper value of quality class 1 and 2. Quality classes 1 to 3 follow a linear graduation of measurement values. The linear graduation in quality classes 3 and 4 was not used because of a greater imprecision of measurement process at higher measuring values.

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