Conventional methods of measuring total suspended sediments (TSS) and total particulate phosphorus (TPP) are typically low-resolution and miss critical processes that impact their exports in aquatic environments. To create high-resolution TSS and TPP estimates, echo intensity (EI), a biproduct of velocity measurements from acoustic devices, was utilized. An acoustic Doppler velocimeter (ADV) and an acoustic Doppler current profiler (ADCP) were deployed in three locations in the L-29 Canal in South Florida, USA, to obtain estimates near the canal bed and in the water column, respectively. Corrections for transmission losses from the ADCP proved unnecessary due to the low vertical variability in the measured EI. EI calibrations were performed using artificially created TSS obtained from bed sediments (ADV) and gravimetrically measured TSS from water samples that matched the depths and times of the ADCP deployments. The measured TSS values were then analyzed for total phosphorus and converted to TPP estimates. The results showed that high TSS and TPP were caused by the rapid discharge releases typical of managed canals. This work demonstrates that high-resolution estimates are imperative for assessing the effects of such swift hydrologic changes on the potential export of sediments and nutrients to delicate ecosystems downstream.

Understanding and predicting water exchange between the ocean and estuaries are critical for effective water quality management. Linkages between these two end members can best be assessed using salt as a conservative tracer and by examining salinity flux near the mouth of an estuary. In this study, salt flux in the Peace River Estuary (PRE), Florida, USA, was decomposed into three mechanisms: riverine transport, estuarine circulation, and tidal dispersion. Most previous investigations of salt flux have focused on estuaries dominated by semi-diurnal tides. In contrast, the PRE experiences mixed tides, which alter the conventional dynamics of estuarine exchange. Whereas most estuaries exhibit greater stratification and stronger estuarine exchange during neap tides with smaller tidal ranges, the timing of maximum stratification and exchange in mixed-tide estuaries depends on both the phase of the K1-O1 tidal beat and the phase lag between the co-oscillating M2-S2 and K1–O1 tidal beats. These dynamics were investigated using a 70-day deployment of an acoustic Doppler current profiler (ADCP) and a vertical array of salinity and temperature sensors in the PRE. Results show that total salt flux in the PRE is dominated by estuarine circulation. Seasonal variations associated with tidal phase lag were simulated over a one-year period using the General Ocean Turbulence Model (GOTM), and the simulations accurately reproduced the field observations. In estuaries with mixed tides, estuarine circulation is strongest during equatorial tides when tropic and spring tides coincide, and strongest during tropic tides when tropic and neap tides coincide. These periods correspond to enhanced water exchange between the ocean and estuary and may represent times of increased vulnerability to the import of harmful algal blooms (HABs), such as Karenia brevis , or other offshore contaminants.

Oysters are important estuarine species, providing numerous ecosystem services, including habitat and filtration. However, natural oyster reefs are declining, largely due to increased coastal development, habitat loss, and water-quality degradation. Despite these declines, little attention is given to understanding the natural stressors experienced by oysters. In Southwest Florida, reefs are predominantly intertidal, exposing oysters to a suite of stressors that may interact to decrease fitness. Yet, spatial and temporal variation in these natural environments is largely understudied. To fill this gap, we monitored five oyster reefs (Crassostrea virginica) across Estero Bay, FL, over two years, measuring oyster performance alongside numerous environmental factors. Oyster condition varied within reefs, among neighboring reefs, and across the estuary, but no single environmental variable consistently explained these patterns. Neighboring reefs separated by only hundreds of meters differed in oyster condition and live cover despite similar water-quality conditions, corresponding instead with fine-scale differences in reef elevation. Across the estuary, the influence of reef elevation was context dependent: greater exposure was associated with favorable oyster condition at one site but increased thermal exposure and reduced live cover at another. Oysters exposed to chronic low salinity also maintained condition and growth comparable to reefs experiencing more moderate salinity regimes, suggesting an important role of environmental history. Collectively, these findings demonstrate that oyster performance emerges from interacting physical and environmental processes operating across multiple scales. Reef-scale morphology, hydrodynamics, and biologically relevant measures of environmental variability may therefore provide more informative indicators of reef condition than broad environmental averages alone.