Chemical oxygen demand (COD) is measured by colonmetric determination 

 following digestion. Ammonium is measured in all samples colorimetrically, and 

 total Kjeldahl nitrogen TKN is determined whenever a control parameter is 

 varied. From April 5 to August 16, 1996, approximate average influent 

 concentrations were 200, 80, 8, and 8 mg/L for COD, NH 4 , P0 4 -P, and S0 4 -S, 

 respectively. From August 17, 1996 through October 19, 1997 all concentrations 

 were halved. Virtually all influent nitrogen was in ammonia form. Since October 

 20, 1997 approximate influent concentrations have been 450, 25, 45, 8, 8 mg/L 

 for COD, NFU, TKN, PO4-P, and SO4-S, respectively At all times appropriately 

 scaled smaller concentrations of micro-nutrients have been maintained. Details 

 can be found in Stein et al., 1998. 



Results and Discussion 



After construction of the wetland cells, but prior to planting, the baseline 

 hydrodynamics of all cells were analyzed using a conservative tracer (KBr with 

 bromide measured colorimetrically). The system demonstrates less than ideal 

 plug-flow as bromide appeared in the effluent before one tH, and remained for at 

 least 4 tn- Repetition of tracer tests at 18 months after planting showed little 

 change in hydrodynamics for all cells (Stein et al., 1998). 



Significant evapo-transpiration (ET) loss has been observed during summer 

 months from all treatments. Using a crude technique, initial estimates of July ET 

 are Cattail = 15.1 ml/min, Bulrush = 7.1 ml/min, Control = 3.9 ml/min. The 

 significance of these initial ET estimates demonstrated the need for continuous 

 monitoring of effluent rate. A system designed to meet this objective has recently 

 been implemented and should greatly enhance our understanding of wetland 

 evapo-transpiration and its influence on water quality. 



Approximately 1550 water quality samples have been drawn and analyzed 

 since project initiation. Mean values for measured concentrations of COD, 

 ionized ammonia (NFL;), phosphate, and sulfate from each plant treatment type 

 are shown in a time series format in Figs. 1-4, respectively. 



Chemical Oxygen Demand (COD) concentration data are presented as a five 

 point moving average in Fig. 1. Note the correlation between influent and 

 effluent concentration variation offset by approximately one residence time and 

 the increase in variance at the higher influent concentration. Differences in 

 effluent concentration between treatments are confounded by different effluent 

 flow rates. During periods of active plant growth, and therefore significant ET, 

 effluent concentration is greatest for cattail, followed by control and bulrush. 

 During relative plant dormancy, control treatments had the greatest COD effluent 

 concentration but the differences are very small. 



Ammonium concentration data are shown as a five point moving average in 

 Fig. 2. Nitrate and nitrite have not been detected in either influent or effluent. 

 Occasional measurement of total nitrogen using TKN analysis showed that 

 ammonium constitutes more than 95% of the total nitrogen load through the 



Stein et al 



