Impact of Storm Water Treatment Area Discharge On P Concentrations of L40 Canal Using Generalized Linear Mixed Model Approach.

The L40 canal is a perimeter canal surrounding the Arthur R. Marshall Loxahatchee National Wildlife Refuge (Refuge) that typically receives low P discharges at various flows from the stormwater treatment area, STA-1E. In the present study, the generalized linear mixed model, GLIMMIX, approach was used to evaluate total-P (TP) concentrations of L40 canal.We also quantified the overall effects of drainage, distance, water-year (WY), and season on TP concentrations with  sampling locations  incorporated in the model to quantify the effects of repeated measures across the  canal. Twelve sampling locations including four locations north and eight locations south of  STA-1E discharge structure S-362 were sampled monthly for three WY from 2007 to 2009. Predicted TPconcentrations correlated positively (r²=0.93) with the observed concentrations values.  In addition, STA 1E released significantly higher TPconcentrations and loads in the months of July-September, concurrent with the wet season. The mean TP concentrations of canal water during WY2007 were significantly higher (p<0.01) than in WY2008 and WY 2009. Significant interactions (p<0.01) were found between distance from the discharge structure and drainage, season and drainage, distance and WY, drainage and WY, indicating that the TP concentrations varied with the quality of treated water being discharged into the L40 canal. The use of GLIMMIX provided further insight into the effects of STA-1E discharge on P concentrations and seasonal water quality in the L40 canal.