Improving Estuarine Water Quality in South Florida: A Quantitative Evaluation of The Efficacy of a Local Nutrient Ordinance

Degraded coastal water quality is a concern in Florida, in part due to nutrient enrichment of aquatic ecosystems causing eutrophication and excessive algal growth. In 2010, a fertilizer ordinance was enacted in Cape Coral located in Lee County Florida with the objective of reducing nutrient loads from local fertilizing practices in order to improve water quality within the city. In order to assess its efficacy, a before after control impact (BACI) design was implemented using Fort Lauderdale in Broward County Florida as a reference location. A total of twenty estuarine canal sampling locations were identified in both Lee and Broward Counties. The analysis used data spanning three years prior to (2007-2009) and post (2011-2013) the enactment of the ordinance. This study examined (1) the effect of the ordinance and seasonality on total nitrogen and total phosphorus concentrations within the estuarine canal system and (2) the relationship between post-ordinance nutrient and chlorophyll-a concentrations. The results showed mean total nitrogen concentrations declined from pre-to post-ordinance calendar years in both cities and total phosphorus concentrations were higher in summer months than winter. Furthermore, total nitrogen and total phosphorus were only correlated to chlorophyll concentrations in Broward County. The study suggests that the fertilizer ordinance may have had a positive effect on the reduction of nutrient concentrations at the estuarine canal sampling locations in Cape Coral, Florida however results raise questions about whether larger-scale factors derived from upstream source waters play a role in nutrient loading. An association was found between total nitrogen/total phosphorus and chlorophyll-a in the Fort Lauderdale estuarine canal sampling locations suggesting algae are nitrogen and phosphorus co-limited. Factors such as light attenuation, upstream loading and ocean mixing which influence water quality in the two locations differ indicating a need for different management approaches in each of the municipalities