Wastewater treatment at the Houghton Lake wetland: Hydrology and water quality

Lagoon-treated wastewater was discharged to a natural peatland to remove nutrients. For thirty consecutive years, an average of 600,000 m3 of treated water was discharged to the Porter Ranch peatland near the community of Houghton Lake, Michigan. This discharge was seasonal, commencing no sooner than May 1 and ending no later than October 31. During the winter half-year, treated wastewater was stored at the lagoon site. This water contained 3.5 mg/L of total phosphorus, and 7 mg/L of dissolved inorganic nitrogen. Other wastewater quality parameters were CBOD5 = 15 mg/L, TSS = 34 mg/L, and fecal coliforms at 66 cfu/100 ml. The peatland was large, about 700 ha, but the zone that provided wastewater polishing was approximately 100 ha. Outflows from the larger peatland showed no effects of the discharge, and maintained concentrations of 40 μg/L of phosphorus, and 85 μg/L of ammonia nitrogen. Nutrients were stored in the 100-ha irrigation area, which removed 94% of the phosphorus (53 metric tons) and 95% of the dissolved inorganic nitrogen. All other constituents were also removed in the irrigation area, except for pass-through substances such as chloride. Phosphorus was stored in new biomass, increased soil sorption, and accretion of new soils and sediments, the last being dominant. A simple growth and uptake model described the removal of phosphorus, with an uptake rate coefficient that did not change over time. Thus, rates in this system were stable over time, and the P-removal capacity did not diminish. The irrigation area underwent large changes in ecosystem structure. There was an initial fertilizer response, characterized by much larger standing crops of vegetation. There was also a plant community shift, from the initial sedge-willow cover type to a cattail-dominant cover type. This new cattail patch became a floating mat.