While research was proceeding apace with assembled systems such as the Metcalf 

 farm pond and the TMC, significant strides were being made with excised systems for 

 ecological effects. As noted above, these have been confined largely to inorganics 

 rather than toxic organics, and studies have focused on decomposition, respiration, 

 nutrient cycling, primary productivity, and, to a lesser degree, community structure 

 and spatial composition. Both aquatic and terrestrial microcosms have been 

 developed. 



The simplest excised terrestrial system is the soil core microcosms (SCM) which 

 may have a variety of configurations (Figure 4(a)). A core is plugged from the soil, 

 with or without removing surface vegetation, and immediately attached to a funnel 

 and support to collect leachate. The leachate contains nutrients and trace minerals 

 and reflects the status of the soil community. Excessive loss of nutrients such as 

 calcium, phosphate, and nitrite/ nitrate upon exposure to a toxicant would indicate 

 loss of community integrity and is frequently seen in the margins of ecosystems 

 severely damaged by mining, smelting, etc. 



Van Voris and co-workers at the Oak Ridge National Laboratory'^ performed 

 very significant experiments with cores (Figure 4(b)) from a fescue meadow. 

 Encasing the top with a plastic chamber, they recorded carbon dioxide concen- 



(a) 



PVC Casing ^[, 



Soil Core 

 (intact) 



Glass Funnel 



Rubber Stopper-^ 

 (2 hole) 



Removable 

 Glass Cover 



COzTrap 



Silicon 

 Rubber Seal 



Perforated 



Polyethylene 



Disc 



Leachate 



Collection 



Flask 



High Density 

 Polyethylene 



Tilled Soil 



Intact 



Undisturbed 



Soi 



l^^ ^ Glass Wool 



Buchner 

 Funnel 



Figure 4. Excised soil core microcosms (SCM )'° have been prepared that are (a) 5 cm 

 (d) X 10 cm (I), and (b) 15 cm x 30 cm."'^ These may contain indigenous 

 flora and fauna or be prepared from bare soil. Total CO2 evolved or COz 

 concentration is used to follow respiration while the nutrient loss is meas- 

 ured in leachate. 



159 



