THE POTENTIAL OF NATURAL ECOSYSTEM SELF-PURIFYING MEASURES FOR CONTROLLING NUTRIENT INPUTS

Most ecosystems have a certain assimilative capacity regarding plant nutrient or biodegradable organic matter. Knowledge of the metabolizing processes of different ecosystems enable the use of natural systems for pollution abatement from agricultural, domestic and industrial sources. Such ecologically engineered natural systems are often very cost efficient. At the Centre for Soil and Environmental Research (JORDFORSK) studies of degradation processes and the fate of plant nutrients in small streams, ponds, wetlands, vegetative filter strips and soil are being conducted in order to gain experience with and develop self purifying methods. Preliminary results show that denitrification in streams remove only a minor part of the annual nitrogen (N) transport (1-15%), but that this process can remove a considerable part of the N transport during summer. Constructed ponds and wetlands in streams draining agricultural areas showed 10-56% retention of soil particles, 23-40% of phosphorous (P) and 5-13% of N. Narrow ponds had a higher efficiency than wide ponds per unit surface area. Short-term experiments with vegetative strips treating agricultural runoff show a sediment removal of over 95%, a P removal from 80-90% and N removal between 60 and 75%. A multistage subsurface constructed wetland treating domestic wastewater removed an average of 97% P, 91% BOD, 80% of suspended solids, 55% N and 99.9% E. coli over the first 18 months of operation. Preliminary results from a multistage plant with constructed ponds and wetlands treating landfill leachate show high treatment efficiency for the same parameters, A rapid infiltration plant in northern Norway showed an average removal of 99% P, 90% COD and 73% N after 4 years of operation. These results show that self purifying measures offer potential for design of pollution abatement systems for agricultural as well as domestic purposes in the Norwegian climate.