Nutrient enrichment is a significant global-scale driver of change in coastal waters, contributing to an array of problems in coastal ecosystems. The St. Lucie Estuary (SLE) in southeast Florida has received national attention as a result of its poor water quality (elevated nutrient concentrations and fecal bacteria counts), recurring toxic Microcystis aeruginosa blooms, and its proximity to the northern boundary of tropical coral species in the United States. The SLE has an artificially large watershed comprised of a network of drainage canals, one of which (C-44) is used to lower the water level in Lake Okeechobee. Public attention has primarily been directed at nutrient inputs originating from the lake, but recent concern over the importance of local watershed impacts prompted a one-year watershed study designed to investigate the interactions between on-site sewage treatment and disposal systems (OSTDS or septic systems), groundwaters, and surface waters in the SLE and nearshore reefs. Results provided multiple lines of evidence of OSTDS contamination of the SLE and its watershed: 1) dissolved nutrients in groundwaters and surface waters were most concentrated adjacent to two older (pre-1978) residential communities and the primary canals, and 2) sucralose was present in groundwater at residential sites (up to 32.0 μg/L) and adjacent surface waters (up to 5.5 μg/L), and 3) δ¹⁵N values in surface water (+7.5 ^o/_oo), macroalgae (+4.4 ^o/_oo) and phytoplankton (+5.0 ^o/_oo) were within the published range (>+3 ^o/_oo) for sewage N and similar to values in OSTDS-contaminated groundwaters. Measured δ¹⁵N values in M. aeruginosa became increasingly enriched during transport from the C-44 canal (∼5.8 ^o/_oo) into the mid-estuary (∼8.0 ^o/_oo), indicating uptake and growth on sewage N sources within the urbanized estuary. Consequently, there is a need to reduce N and P loading, as well as fecal loading, from the SLE watershed via septic-to-sewer conversion projects and to minimize the frequency and intensity of the releases from Lake Okeechobee to the SLE via additional water storage north of the lake. These enhancements would improve water quality in both the SLE and Lake Okeechobee, reduce the occurrence of toxic harmful algal blooms in the linked systems, and improve overall ecosystem health in the SLE and downstream reefs.

营养丰富是全球范围内沿海水域变化的重要驱动力，导致沿海生态系统出现一系列问题。佛罗里达州东南部的圣露西河口（SLE）由于水质差（营养物质浓度升高和粪便细菌数量增加），反复出现有毒的铜绿微囊藻而受到了全国的关注。盛开，并且靠近美国热带珊瑚物种的北部边界。SLE有一个人工大的分水岭，由排水渠网络组成，其中一条（C-44）用于降低奥基乔比湖的水位。公众的注意力主要集中在来自湖泊的营养物输入上，但是最近对局部流域影响的重要性的担忧促使进行了为期一年的流域研究，旨在研究现场污水处理与处置系统（OSTDS或化粪池系统）之间的相互作用），SLE和近岸礁石中的地下水和地表水。结果提供了多条证据表明OSTDS污染了SLE及其分水岭：污水N中地表水（+7.5 ^o / _oo），大型藻类（+4.4 ^o / _oo）和浮游植物（+5.0 ^o / _oo）中的¹⁵ N值在公布的范围（> +3 ^o / _oo）内，与OSTDS污染的地下水中的水的值。测量δ ^15个在N个值中号。假单胞菌从C-44管在运输过程中变得越来越富集的（~5.8 ^ø / _OO）插入-河口中期（〜8.0 ^ø / _oo的），表明城市化河口内污水氮源的吸收和增长。因此，有必要通过化粪池到下水道的转换项目减少SLE流域的N和P负荷以及粪便负荷，并通过额外的水使从Okeechobee湖到SLE的释放频率和强度最小化。储存在湖北。这些增强将改善SLE和奥基乔比湖的水质，减少相连系统中有毒有害藻华的发生，并改善SLE和下游礁石的整体生态系统健康。