Operation

Filling the outdoor channel with sedimentClick to enlarge
Filling the outdoor channel with sediment
Source: UBA

In order to test, for example, the effect of certain substances on aquatic communities, the mesocosms has to be adequately designed and has to be rich in structure providing a wide variety of habitats for different species. In order to meet these requirements, sand and mud (soft sediment) and selected aquatic plants and organisms are introduced into the stream and pond mesocosms.

Table of Contents

 

Establishing

In order to test, for example, the effect of certain substances on aquatic communities, the mesocosms had to be adequately designed and had to be rich in structure providing a wide variety of habitats for different species. In order to meet these requirements, sand and mud (soft sediment) and selected aquatic plants and organisms were introduced into the stream and pond mesocosms.

For effect studies, the streams and ponds are filled with approx. 1,200 tons of uncontaminated sand from the Berlin/Brandenburg region which are then covered with thin layer of soft sediment from uncontaminated surface waters.

Soft sediments act as energy and nutrient stores. Furthermore, they are important for recruiting and sustaining special organisms and completing the nutrient cycles of the waterbody. Prior to use, the material is subjected to extensive eco-toxological and hygienic tests as well as to a special treatment which had already proven to be successful in the restoration of lakes to prevent the uncontrolled release of nutrients.

The test systems are then planted/inoculated with primary producers (aquatic plants and algae), consumers (zooplankton, insect larvae, fish) and destructors (decomposers, bacteria, fungi) from various lakes and rivers in and around Berlin in order to ensure a large biodiversity.

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Sampling routine

Within the scope of mesocosm studies, water, sediment and biota samples are routinely taken. Figure 1 shows the sampling procedure by means of a Ruttner water sampler, which is employed in the water column at various depths in order to obtain water for the analysis of nutrients and pollutants. Plankton is sampled with a tube (Fig. 2) in order to allow for sampling over the entire water depth and in different pond areas.

Interstitial pore water can be taken at the backside of the ponds from small tubes, which are incorporated in the sand layers of the ponds. Sediment samples as well as large (> 500 µm) bottom dwelling animals (macrozoobenthos) are obtained with a bottom grabber which function similar as an excavator shovel. Deeper sediment layers are sampled with other tools like tube corers.

Processing of water samples

For particle retention, water samples are among other things filtered prior to chemical analyses.

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Analysis

Routine parameters like oxygen, pH, conductivity or intensity of light are quickly surveyed by means of water probes. Chemical analyses are needed to monitor the actual concentration of pollutants in the test systems in order to measure its degradation and to detect fate and behaviour. This research is aligned to the chemical and physical behaviour and accordingly optimised. Nutrients are monitored, in order to check whether there are sufficient nutrients to support the growth of plants or whether there are effects of pollutants on nutrient cycles. In this context, phosphorous, nitrogen, silicate, carbon as well as alkali and alkaline earth metals, sulphate, chloride and further metallic trace elements are analysed.

The biological analysis routinely comprises the identification of selected groups of organisms, their abundance and biomass. By doing so, effects of substances like pesticides or industrial chemicals on the population dynamics can be detected and effect concentration (EC50, EC10: the concentration which causes, for example, a 50% respectively 10% reduction in the growth or the reproduction of a species) can be derived.

The groups of organisms which are routinely monitored this way include:

  • phyto- and zooplankton of the water column,
  • periphyton (Aufwuchs, biofilms),
  • macrophytes (water plants and macroalgae) and
  • macrozoobenthos.
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