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Florida spring complexes (springs and their associated runs) represent patches of clear, cool freshwater habitat in a landscape of tannin-stained wetlands, streams, and rivers. These spring complexes differ in morphology, water quantity and quality, and biotic characteristics as well as in their connections to other water bodies. The purpose of this study was to determine whether watershed effects or emergent physical, chemical, and biologic properties of Florida spring complexes would predict fish assemblage structure. Spring complex morphology and water quality metrics were collected from water managers or from the literature, with the exception of dissolved oxygen, which was measured in situ. Fish data were collected by video surveys using GoPro® cameras on stationary tripods at 2 to 5 locations on the banks of each spring complex. Videos were analyzed for the total number of individuals of each species/video, species richness, and diversity. The environmental characteristics of spring complexes differed between watersheds, as the St Johns River spring complexes, which are near the east coast, differed from watersheds closer to the west coast of Florida. However, specific characteristics that discriminated between springs, like low dissolved oxygen concentration or abundant macrophytes, crossed watershed boundaries. Fish assemblages also differed between the St Johns River and western watersheds, but the differences were more subtle than the differences in environmental characteristics, and the characteristics of individual spring complexes also predicted fish assemblage structure. Conductivity, dissolved oxygen concentration, and macrophyte coverage best explained the variation in the fish assemblage structure among spring complexes. The overlap in spring complex fish assemblages across watersheds may be the result of the geologic youth of the freshwater fish assemblages, the high degree of hydrologic connectivity between water bodies, and possible impairment of spring complexes in Florida. [ABSTRACT FROM AUTHOR]

Submerged aquatic vegetation (SAV) is an important structural component of many aquatic ecosystems that also affects a broad array of biogeochemical and ecological processes. In the spring-fed rivers of Florida, where SAV is the foundation of healthy community structure and function, environmental controls on SAV growth remain poorly understood. This lack of knowledge complicates the evaluation and prioritization of management and restoration activities. Our goal was to explore the relative influences of environmental drivers on annual patterns of SAV productivity in 2 spring-fed rivers (Silver River and Alexander Springs Creek) with contrasting nitrate concentrations (1.4 vs 0.05 mg N/L, respectively) but otherwise similar physical and chemical attributes. We used monthly measurements from 16 fixed plots in each river to observe spatial and temporal heterogeneity in SAV growth. Mean growth rates between the rivers were statistically indistinguishable, suggesting that SAV growth is not controlled primarily by water column N concentrations. Despite representing most of the autotroph biomass, measured SAV growth rates were only 25% of contemporaneous estimates of open-channel net primary production (i.e., gross primary production minus autotrophic respiration). This result indicates that the epiphytic assemblages that grow primarily on SAV dominate overall ecosystem metabolic activity. Pairwise associations between measured SAV growth and a suite of physical (light, redox potential, temperature, sediment texture) and chemical (porewater and water column solutes) variables revealed that no single factor can accurately predict SAV growth. Instead, 2 complementary multivariate approaches (regression trees, general linear models) yielded useful models to predict SAV growth. While we constructed models independently for each river, their best-fit model formulations were remarkably similar—light (+), sediment redox potential (−), and porewater orthophosphate (−) predicted over 50% of the variation in SAV growth. System managers could use these model results to aid in screening restoration sites for SAV suitability. Further, these results underscore the need for a broad systems approach to springs management. [ABSTRACT FROM AUTHOR]