The 2012 ASHS Annual Conference

The need to protect our water resources and increasing public awareness of the importance of cleaner water for ecological and health purposes have driving creation of regulations limiting nutrient release from traditionally exempt, nonpoint source agricultural contributors.  Growers all over the United States will likely need to modify irrigation and fertilization practices to reduce impacts on our current resources. Modification of production practices alone may not be adequate to meet regulated nutrient criterion limits for runoff, whether from irrigation or stormwater source, entering surface waters.  Two wetland technologies, one in common use for over forty years and the other an emerging application, are ideally suited to help agricultural producers meet these regulations.  Constructed wetlands (either free water surface or subsurface flow) have been used to treat a variety of wastewaters and over the past ten years have been implemented by nursery growers to remediate irrigation runoff.  We have monitored two free water surface constructed wetlands since 2003 and results demonstrate that nitrogen is consistently removed, though removal efficacy varies with season.  Spring and summer nitrogen removal efficacy averaged 94.1% while winter nitrogen removal efficacy averaged 70.7%.  Free water surface constructed wetlands do not consistently remediate phosphorus.  Floating treatment wetlands effectively remediate both nitrogen and phosphorus, this unique technology utilizes buoyancy and floating mats to maintain plant crowns above the water surface while permitting plant root systems to serve as filters and to provide surface area for microbial colonization in the water column.  Our research has shown that floating treatment wetlands effectively remediate nitrogen with effluent concentrations leaving medium and small-scale systems averaged 0.12 ± 0.02 and 0.03 ± 0.01 mg•L^-1 nitrogen, respectively.  Total phosphorus concentrations in effluent leaving the medium and small scale systems averaged 0.03 ± 0.01 and 0.02 ± 0.01 mg•L^-1, respectively.  Both wetland technologies have benefits and limitations.  The choice of treatment technology applied by growers should be based upon site-specific considerations and the endpoint under consideration.