Two before and after control impact experiments were carried out studying whole stream metabolism and nutrient cycling. In the first experiment, a treated effluent from a sewage treatment work (normally discharging to a wetland) was diverted to a lowland stream for two weeks. Nutrient cycling studies before the diversion indicated that the system was saturated by inorganic N and P. The treated effluent promoted heterotrophy (respiration increased by 50%), but not autotrophy (no change in gross primary production). Measurements of whole stream respiration rate appeared more relevant than BOD₅ representing only about 2% of the total oxygen demand. In the second experiment, sugar cane solution was added to an upland stream for three weeks to test whether an increase in dissolved organic carbon would alter ecosystem structure and functions. Results on whole stream metabolic activities, nutrient cycling (phosphate, nitrate, potassium) and percentage cover of primary producers will be presented. Additional hypotheses will also be presented regarding predicted changes in leaf litter decomposition, biofilm development on tiles, macroinvertebrate community structure and food web using C and N stable isotopes. Finally the outputs will be discussed within a wider context including data from published studies.