Few estuaries remain unaffected by water management and altered freshwater deliveries. The Caloosahatchee River Estuary is a perfect case study for assessing the impact of altered hydrology on natural oyster reef (Crassostrea virginica) populations. The watershed has been highly modified and greatly enlarged by an artificial connection to Lake Okeechobee. Accordingly, to generate data to support water management recommendations, this study monitored various oyster biometrics over 15 years along the primary salinity gradient. Oyster reef densities were significantly affected by both prolonged high volume freshwater releases creating hyposaline conditions at upstream sites and by a lack of freshwater input creating hypersaline conditions at downstream sites. Low freshwater input led to an increase in disease caused by Perkinsus marinus and predation. Moderate (< 2000 cfs) and properly timed (winter/spring) freshets benefited oysters with increased gametogenesis, good larval mixing, and a reprieve from disease. If high volume freshets occurred in the late summer, extensive mortality occurred at the upstream site due to low salinity. These findings suggest freshwater releases in the late summer, when reproductive stress is at its peak and pelagic larvae are most vulnerable, should be limited to < 2000 cfs, but that longer freshets (1-3 weeks) in the winter and early spring (e.g., December-April) benefit oysters by reducing salinity and lessening disease intensity. Similar strategies can be employed in other managed systems, and patterns regarding the timing of high volume flows are applicable to all estuaries where the management of healthy oyster reefs is a priority.

The linearity of the BZI (biomass, photic depth and irradiance) regression model for the estimate of depth-integrated primary productivity in the water column is evaluated. It is shown that the linear model can be derived from traditional production-irradiance (P-I) curves by assuming a linear production-irradiance relationship. A correction tem is obtained for water depth shallower than the photic depth. The analysis revealed that the slope of the linear BZI model is determined by the slope of the P-I curve. Following similar steps and assumptions, some of the well-known nonlinear light functions such as Steele's function, Smith's function and the Monod function were analytically integrated yielding nonlinear BZI models which go through the origin naturally allowing zero productivity at zero light. The nonlinear model integrated from Steele's function was successfully applied to three subtropical estuaries in Florida: the St. Lucie Estuary on the east coast, the Caloosahatchee River and Estuary and the Escambia Bay on the west coast. Despite being more faithful to theory (zero intercept), the non-linear version yielded only slightly better results than the linear model.

Links between hydrologic modifications, flow and salinity regimes, and submerged aquatic vegetation (SAV) species composition and abundance were assessed with an empirical analysis of 33 years of monitoring data collected at nine sites in Florida’s Caloosahatchee River Estuary (CRE). Freshwater inflows to the estuary (30-day means) were often outside the previously recommended envelope of 12.74 to 79.29 m 3 s −1 . Discharges from Lake Okeechobee through a synthetic hydrologic link were responsible for 43% of the above-envelope flows, but reduced the incidence of below-envelope flows by 30%. A salinity model and salinity stress indices developed for each SAV species indicated that the observed flows generated variable salinity conditions likely to harm both seagrasses and freshwater SAV in the estuary. Regression modeling of SAV abundance generally confirmed the flow and salinity responses expected for each species: Halodule wrightii and Thalassia testudinum in the lower estuary were both harmed by high-flow, low-salinity conditions, while Vallisneria americana in the upper estuary was decimated by low-flow, high-salinity conditions. There was a species-specific effect of the seasonal timing of high flows— T. testudinum was more negatively correlated with high flows in the dry season; H. wrightii in the wet season . The regression analyses also highlighted strong, year-to-year autocorrelations in SAV abundance, indicating reduced resilience after severe losses, particularly for V. americana . Large residual variation in some regression models suggested that factors other than salinity (e.g., optical water quality or grazing impacts) may also influence the system dynamics and should be incorporated in continuing research. This analysis suggests that use of artificial water management infrastructure to reduce extreme high and low flows to the Caloosahatchee and other estuaries could help maintain SAV health in light of intensifying climate variability and degraded watershed flow regulation capacity.

Quantitative relationships between biological resources and hydrological variables are often needed to fulfill legislative requirements for management of estuaries and coastal waters. We used a 28-year record of blue crab landings to support development of a minimum flow (defined in Florida Statutes as the point at which further withdrawals of freshwater will cause "significant harm" to the resources or ecology) for the Caloosahatchee Estuary in Florida, USA. Annual catch per unit effort (CPUE) was computed from monthly landings of crabs and measures of fishing effort. Both unadjusted and de-trended annual CPUE were significantly correlated with rainfall, freshwater inflow and the Multivariate ENSO Index during the previous year's dry season. Increases in CPUE from 1 year to the next were positively related to dry season rainfall in the first of the 2 years. The Minimum Flow was intended to protect the resources from an impact taking 2 or more years to recover. Geometric mean functional regressions and Monte Carlo simulations were used to identify the dry season rainfall associated with this level of impact. Both a spectral analysis and the Monte Carlo simulations indicated that this level of rainfall occurred about once every 6 years. The corresponding Minimum Flow ranged from 8.6 to 12.3 m(3)/s (averaged over the dry season and measured at the headwater control structure of the estuary). This study demonstrated the relationship between hydrologic variables (rainfall, freshwater inflow) and blue crab landings and the usefulness of fisheries catch data in providing the technical basis for developing environmental flow targets.

Coastal water bodies are impacted by watershed alterations, increased population density, modifications to inlets and shorelines, climatic periodicity, and increases in external material loads. Estuaries such as Lake Worth Lagoon (LWL) in south Florida possess all these attributes. The LWL watershed extends from the southeastern portion of Lake Okeechobee through Palm Beach County, where it meets the lagoon. Palm Beach County Department of Environmental Resources Management recognizes the social and ecological importance of the similar to 36 km lagoon and aims to maintain suitable water and habitat quality for all stakeholders. Recent declines and shifts of seagrass distribution along the lagoon prompted a step toward better understanding the water quality patterns of the system. In support of these efforts, this study assessed bathymetry, inflow, flushing, and water quality attributes (chlorophyll a, salinity, total nitrogen, total phosphorus, total suspended solids, turbidity) using data collected along a series of 14 midlagoon stations from 2007 to 2015. Salinity in the North Segment was higher and less variable because of proximity to Palm Beach Inlet. Although concentrations of chlorophyll a, total nitrogen, and total phosphorus correlated with freshwater inflow, turbidity and total suspended solids were not. Fast flushing of the lagoon on a scale of days likely precludes water quality issues common to many estuaries with higher resident times. However, the combination of landscape-scale water management, a shoreline that is almost 70% modified by hard structures, and changes in essential nearshore habitats, introduces new levels of uncertainty to both the understanding and management of LWL. From this study, increased knowledge of relationships among water quality parameters and their spatial and temporal variability in LWL provides points of reference from which targeted studies can be developed to explore links between environmental parameters and responses of key organisms in this unique system.

Understanding anthropogenic and hydro-climatic influences on nutrient concentrations and export from highly managed catchments often necessitates trend detection using long-term monitoring data. This study analyzed the temporal trend (1979–2014) of total nitrogen (TN) and total phosphorus (TP) concentrations and export from four adjacent coastal basins in south Florida where land and water resources are highly managed through an intricate canal network. The method of integrated seasonal-trend decomposition using LOESS (LOcally weighted regrESSion) was employed for trend detection. The results indicated that long-term trends in TN and TP concentrations (increasing/decreasing) varied with basins and nutrient species, reflecting the influence of basin specific land and water management practices. These long-term trends were intervened by short-term highs driven by high rainfall and discharges and lows associated with regional droughts. Seasonal variations in TP were more apparent than for TN. Nutrient export exhibited a chemostatic behavior for TN from all the basins, largely due to the biogenic nature of organic N associated with the ubiquity of organic materials in the managed canal network. Varying degrees of chemodynamic export was present for TP, reflecting complex biogeochemical responses to the legacy of long-term fertilization, low soil P holding capacity, and intensive stormwater management. The anthropogenic and hydro-climatic influences on nutrient concentration and export behavior had great implications in nutrient loading abatement strategies for aquatic ecosystem restoration of the downstream receiving waterbody.