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Research about Indian River Lagoon

Source-linked reports with geographic coverage including Indian River Lagoon.

9 recordsLinked to original sources
USGS2022

Evidence of a dietary shift by the Florida manatee (Trichechus manatus latirostris) in the Indian River Lagoon inferred from stomach content analyses

Investigating the long-term fluctuations of the feeding ecology of megaherbivores such as sirenians is important, as any changes could be indicative of shifts in resource availability. The Indian River Lagoon (IRL), eastern Florida, USA, is a critical habitat for the Florida manatee ( Trichechus manatus latirostris ). However, the IRL has experienced a substantial decline in seagrass due to the persistence of several harmful algal blooms. Using microhistological analysis, we examined the diet of manatees over a discontinuous sampling period spanning over 38 years using stomach contents collected from carcasses recovered in the IRL. Samples collected between 2013–2015 (post-seagrass die-off, n = 90) were compared to archived stomach samples collected between 1977–1989 (pre-seagrass die-off, n = 103). Samples analyzed from 1977–1989 contained primarily seagrasses (61.7%), followed by algae (28.4%) and vascular plants (1.7%). In contrast, stomach samples from the post-seagrass die-off primarily contained algae (49.5%), followed by seagrasses (34%) and vascular plants (2.7%). Between 1977–1989 and 2013–2015, manatees in the IRL experienced a 44.9% decline in seagrass consumption, and a 74.3% increase in algal consumption. This dietary shift was not influenced by body length, a proxy of age, or sex. Our results indicate that the dietary shift experienced by manatees is due to the decline of available seagrass forage in the IRL, and highlight the dietary plasticity of manatees in the face of changes in resource availability. However, the individual health and population-level consequences of this dietary shift are unknown. An increase in mortality due to undetermined causes in this region since 2012 can be associated with deteriorating body conditions of manatees in the IRL, possibly resulting from a lack of seagrass diet. Future research should further investigate behavioral changes affecting manatees in relation to seagrass decline in the IRL, including the energetic costs of this dietary change.

Florida↗
USGS2018

Using heat as a tracer to determine groundwater seepage in the Indian River Lagoon, Florida, April–November, 2017

The U.S. Geological Survey, in cooperation with the St. Johns River Water Management District, conducted a study to examine water fluxes in two small study areas in the Indian River Lagoon. Vertical arrays of temperature sensors were placed at multiple locations in the lagoon bed to measure temperature time series in the vertical profile. These data at one of the study areas, Eau Gallie, were used in two numerical models, 1DTempPro and VFLUX, to estimate seepage flux rates into the lagoon. 1DTempPro uses an inverse-modeling approach to calibrate groundwater flux to the measured temperature time series. VFLUX isolates the fundamental frequency signal in the temperature data and utilizes the resulting amplitude and phase differences between sensor locations to determine vertical water flux. Field measurements were made during two time periods, March 23 to April 28, 2017, and June 1 to November 3, 2017. Simulating the first, drier period at one location with 1DTempPro helped determine reasonable seepage fluctuations and provided guidelines for choosing which temperature sensor pairs used in the VFLUX simulations would produce the best results. VFLUX simulations at eight locations indicated daily average seepage flux rates of less than 20 centimeters per day (cm/d) and substantial seepage flux out to a distance of at least 110 meters from shore. The spatial variation in average seepage flux rates within 40 meters of shore seemed large, ranging from about 3 to 20 cm/d. In the VFLUX application using the June 1–November 3, 2017 data, the seepage flux has a higher magnitude and fluctuation than the first simulation period, making the isolation of the fundamental temperature frequency signal in the temperature data difficult. However, useful partial or full simulations were achieved at 6 of the 10 locations. The storm surge of Hurricane Irma on September 10, 2017, changed the depths of the sensors relative to the lagoon bed and disrupted the ability of VFLUX to compute seepage flux for the posthurricane period. The June 1 to November 3, 2017, computed seepage flux rates were higher than those for the March 24 to April 28, 2017, period and were sometimes as great as 40 cm/d, and more than 60 cm/d at one location. The seepage time-series data collected during Hurricane Irma indicates a downward seepage flux as a result of the storm surge, followed by upwelling from precipitation recharge inland. The average seepage flux rates are higher than those during the March–April period and are over 25 cm/d near the coast and about 20 cm/d 130 meters offshore.

Florida↗
USGS2013

Variations of iron flux and organic carbon remineralization in a subterranean estuary caused by interannual variations in recharge

We determine the inter-annual variations in diagenetic reaction rates of sedimentary iron (Fe ) in an east Florida subterranean estuary and evaluate the connection between metal fluxes and recharge to the coastal aquifer. Over the three-year study period (from 2004 to 2007), the amount of Fe-oxides reduced at the study site decreased from 192 g/yr to 153 g/yr and associated organic carbon (OC) remineralization decreased from 48 g/yr to 38 g/yr. These reductions occurred although the Fe-oxide reduction rates remained constant around 1 mg/cm 2 /yr. These results suggest that changes in flow rates of submarine groundwater discharge (SGD) related to changes in precipitation may be important to fluxes of the diagenetic reaction products. Rainfall at a weather station approximately 5 km from the field area decreased from 12.6 cm/month to 8.4 cm/month from 2004 to 2007. Monthly potential evapotranspiration (PET) calculated from Thornthwaite’s method indicated potential evapotranspiration cycled from about 3 cm/month in the winter to about 15 cm/month in the summer so that net annual recharge to the aquifer decreased from 40 cm in 2004 to -10 cm in 2007. Simultaneously, with the decrease in recharge of groundwater, freshwater SGD decreased by around 20% and caused the originally 25 m wide freshwater seepage face to decrease in width by about 5 m. The smaller seepage face reduced the area under which Fe-oxides were undergoing reductive dissolution. Consequently, the observed decrease in Fe flux is controlled by hydrology of the subterranean estuary. These results point out the need to better understand linkages between temporal variations in diagenetic reactions and changes in flow within subterranean estuaries in order to accurately constrain their contribution to oceanic fluxes of solutes from subterranean estuaries.

Florida↗
USGS2011

Reactive-transport modeling of iron diagenesis and associated organic carbon remineralization in a Florida (USA) subterranean estuary

Iron oxides are important terminal electron acceptors for organic carbon (OC) remineralization in subterranean estuaries, particularly where oxygen and nitrate concentrations are low. In Indian River Lagoon, Florida, USA, terrestrial Fe-oxides dissolve at the seaward edge of the seepage face and flow upward into overlying marine sediments where they precipitate as Fe-sulfides. The dissolved Fe concentrations vary by over three orders of magnitude, but Fe-oxide dissolution rates are similar across the 25-m wide seepage face, averaging around 0.21 mg/cm 2 /yr. The constant dissolution rate, but differing concentrations, indicate Fe dissolution is controlled by a combination of increasing lability of dissolved organic carbon (DOC) and slower porewater flow velocities with distance offshore. In contrast, the average rate constants of Fe-sulfide precipitation decrease from 21.9 × 10 − 8 s − 1 to 0.64 × 10 − 8 s − 1 from the shoreline to the seaward edge of the seepage face as more oxygenated surface water circulates through the sediment. The amount of OC remineralized by Fe-oxides varies little across the seepage face, averaging 5.34 × 10 − 2 mg/cm 2 /yr. These rates suggest about 3.4 kg of marine DOC was remineralized in a 1-m wide, shore-perpendicular strip of the seepage face as the terrestrial sediments were transgressed over the past 280 years. During this time, about 10 times more marine solid organic carbon (SOC) accumulated in marine sediments than were removed from the underlying terrestrial sediments. Indian River Lagoon thus appears to be a net sink for marine OC.

Florida↗
USGS2009

Vegetation effects on fish distribution in impounded salt marshes

We compared the density and biomass of resident fish in vegetated and unvegetated flooded habitats of impounded salt marshes in the northern Indian River Lagoon (IRL) Estuary of east-central Florida. A 1 -m 2 throw trap was used to sample fish in randomly located, paired sample plots ( n = 198 pairs) over 5 seasons in 7 impoundments. We collected a total of 15 fish taxa, and 88% of the fishes we identified from the samples belonged to three species: Cyprinodon variegatus (Sheepshead Minnow), Gambusia holbrooki (Eastern Mosquitofish), and Poecilia latipinna (Sailfin Molly). Vegetated habitat usually had higher density and biomass of fish. Mean fish density (and 95% confidence interval) for vegetated and unvegetated sites were 8.2 (6.7–9.9) and 2.0 (1.6–2.4) individuals m -2 , respectively; mean biomass (and 95%) confidence interval) for vegetated and unvegetated sites were 3.0 (2.5–3.7) and 1.1 (0.9–1.4) g m -2 , respectively. We confirmed previous findings that impounded salt marshes of the northern IRL Estuary produce a high standing stock of resident fishes. Seasonal patterns of abundance were consistent with fish moving between vegetated and unvegetated habitat as water levels changed in the estuary. Differences in density, mean size, and species composition of resident fishes between vegetated and unvegetated habitats have important implications for movement of biomass and nutrients out of salt marsh by piscivores (e.g., wading birds and fishes) via a trophic relay.

Florida↗
USGS2006

Advection within shallow pore waters of a coastal lagoon, Florida

Ground water sources can be a significant portion of a local water budget in estuarine environments, particularly in areas with high recharge rates, transmissive aquifers, and permeable marine sediments. However, field measurements of ground water discharge are often incongruent with ground water flow modeling results, leaving many scientists unsure which estimates are accurate. In this study, we find that both measurements and model results are reasonable. The difference between estimates apparently results from the sources of water being measured and not the techniques themselves. In two locations in the Indian River Lagoon estuarine system, we found seepage meter rates similar to rates calculated from the geochemical tracers 222 Rn and 226 Ra. Ground water discharge rates ranged from 4 to 9 cm/d using seepage meters and 3 to 20 cm/d using 222 Rn and 226 Ra. In contrast, in comparisons to other studies where finite element ground water flow modeling was used, much lower ground water discharge rates of ∼0.05 to 0.15 cm/d were estimated. These low rates probably represent discharge of meteoric ground water from land-recharged aquifers, while the much higher rates measured with seepage meters, 222 Rn, and 226 Ra likely include an additional source of surface waters that regularly flush shallow (< 1 m depth) sediments. This resultant total flow of mixed land-recharged water and recirculated surface waters contributes to the total biogeochemical loading in this shallow estuarine environment.

Florida↗
USGS2005

Evaporation, precipitation, and associated salinity changes at a humid, subtropical estuary

The distilling effect of evaporation and the diluting effect of precipitation on salinity at two estuarine sites in the humid subtropical setting of the Indian River Lagoon, Florida, were evaluated based on daily evaporation computed with an energy-budget method and measured precipitation. Despite the larger magnitude of evaporation (about 1,58 mm yr −1 ) compared to precipitation (about 1,180 mm yr −1 ) between February 2002 and January 2004, the variability of monthly precipitation induced salinity changes was more than twice the variability of evaporation induced changes. Use of a constant, mean value of evaporation, along with measured values of daily precipitation, were sufficient to produce simulated salinity changes that contained little monthly (root-mean-square error = 0.33‰ mo −1 and 0.52‰ mo −1 at the two sites) or cumulative error (<1‰ yr −1 ) compared to simulations that used computed daily values of evaporation. This result indicates that measuring the temporal variability in evaporation may not be critical to simulation of salinity within the lagoon. Comparison of evaporation and precipitation induced salinity changes with measured salinity changes indicates that evaporation and precipitation explained only 4% of the changes in salinity within a flow-through area of the lagoon; surface water and ocean inflows probably accounted for most of the variability in salinity at this site. Evaporation and precipitation induced salinity changes explained 61% of the variability in salinity at a flow-restricted part of the lagoon.

Florida↗