Christopher D. Reich

Seepage meters and Bernoulli's revenge

Evaluation of seepage data from a network of 50 permanently deployed submarine seepage meters, specially construc ted from fiberglass, indicates that the devices artificially advect (Bernoulli effect) shallow ground water. Reverse flow into the rock was not observed even when adjacent piezometers installed 2-m to 20-m below the rock-water interface in dicated negative groundwater heads. Quantitative testing of five different designs, including conventional end-of-oildrum designs, indicates that meters presenting positive relief on the sea floor are subject to the Bernoulli effect when placed in areas where there are waves and/or currents. Advection does not appear to be caused by flexing of the collection bags.

Distribution of Heavy Metals and Foraminiferal Assemblages in Sediments of Biscayne Bay, Florida, USA

Abstract Heavy-metal pollution is an issue of concern in estuaries influenced by agriculture, urban, and harbor activities. Foraminiferal assemblages have been shown to be effective indicators of pollution. Sediment samples (n = 110) from Biscayne Bay were analyzed for heavy metals, foraminiferal assemblages, and grain-size distribution. Highest Cu, Zn, Cr, Hg, Pb, and Ni concentrations were found closest to Miami and near the mouths of several canals along the western margin of the bay. Few samples exceeded limits of possible biological effects as defined by previous studies. Ammonia and Cribroelphidium, two known stress-tolerant genera, correlated positively with Cu, Zn, Hg, and Ni (r ≥ 0.43). Symbiont-bearing foraminifers, Archaias, Laevipeneroplis, and Androsina, correlated negatively with Cu, Zn, Hg, and Ni (r ≤ −0.26).

Foraminiferal assemblages in Biscayne Bay, Florida, USA: responses to urban and agricultural influence in a subtropical estuary.

This study assessed foraminiferal assemblages in Biscayne Bay, Florida, a heavily utilized estuary, interpreting changes over the past 65 years and providing a baseline for future comparisons. Analyses of foraminiferal data at the genus level revealed three distinct biotopes. The assemblage from the northern bay was characterized by stress-tolerant taxa, especially Ammonia, present in low abundances ( approximately 2.0 x 10(3) foraminifers/gram) though relatively high diversity ( approximately 19 genera/sample). The southwestern margin of the bay was dominated by Ammonia and Quinqueloculina, an assemblage characterized by the lowest diversities ( approximately 12 genera/sample) and highest abundances ( approximately 1.1 x 10(4) foraminifers/gram), influenced by both reduced salinity and elevated organic-carbon concentrations. A diverse assemblage of smaller miliolids and rotaliids ( approximately 26 genera/sample) characterized the open-bay assemblage, which also had a significant component ( approximately 10%) of taxa that host algal endosymbionts. In the past 65 years, populations of symbiont-bearing taxa, which are indicators of normal-marine conditions, have decreased while stress-tolerant taxa, especially Ammonia spp., have increased in predominance.

New Maps, New Information: Coral Reefs of the Florida Keys

Abstract A highly detailed digitized map depicts 22 benthic habitats in 3140.5 km2 of the Florida Keys National Marine Sanctuary. Dominant are a seagrass/lime-mud zone (map area 27.5%) throughout Hawk Channel and seagrass/carbonate-sand (18.7%) and bare carbonate-sand (17.3%) zones on the outer shelf and in The Quicksands. A lime-mud/seagrass–covered muddy carbonate-sand zone (9.6%) abuts the keys. Hardbottom communities (13.2%) consist of bare Pleistocene coralline and oolitic limestone, coral rubble, and senile coral reefs. Smaller terrestrial (4.0%) and marine habitats, including those of live coral (patch reefs, 0.7%), account for the rest (13.7%) of the area. Derived from aerial photomosaics, the seabed dataset fits precisely when transposed onto a newly developed National Geophysical Data Center hydrographic-bathymetry map. Combined, the maps point to new information on unstudied seabed morphologies, among them an erosional nearshore rock ledge bordering the seaward side of the Florida Keys and thousands of patch-reef clusters aligned in mid–Hawk Channel. Preliminary indications are that the ledge may represent the seaward extent of the 125-ka Key Largo and Miami Limestone that form the keys, and the patch reefs colonized landward edges of two noncoralline, non-dune-ridge topographic troughs. The troughs, their substrate, and inner-shelf location along the seaward side of the Hawk Channel bedrock depression are the first of that type of nuclei to be recognized in the Florida reef record. Together, the map datasets establish the efficacy and accuracy of using aerial photographs to define in extraordinary detail the seabed features and habitats in a shallow-reef setting.

Regional quaternary submarine geomorphology in the Florida Keys

High-quality seismic reflection profiles fill a major gap in geophysical data along the south Florida shelf, allowing updated interpretations of the history of the Quaternary coral reef system. Incorporation of the new and existing data sets provides the basis for detailed color maps of the Pleistocene surface and thickness of overlying Holocene accretions. The maps cover the Florida Keys to a margin-wide upper-slope terrace (30 to 40 m deep) and extend from The Elbow Reef (north Key Largo) to Rebecca Shoal (Gulf of Mexico). The data indicate that Pleistocene bedrock is several meters deeper to the southwest than to the north east, yet in general, Holocene sediments are ∼3 to 4 m thick shelf-wide. The Pleistocene map demonstrates the significance of a westward-dipping bedrock surface to Holocene flooding history and coral reef evolution. Seismic facies show evidence for two possible Holocene stillstands. Aerial photographs provide information on the seabed surface, much of which is below seismic resolution. The photographs define a prominent, regional nearshore rock ledge that extends ∼2.5 km seaward from the keys9 shoreline. They show that bands of rock ridges exist along the outer shelf and on the upper-slope terrace. The photographs also reveal four tracts of outlier reefs on the terrace, one more than had been documented seismically. Seismic and photographic data indicate the tracts are >200 km long, nearly four times longer than previously thought. New interpretations provide insights into a youngest possible terrace age (ca. 175 ka?) and the likelihood that precise ages of oxygen isotope substage 5e ooid tidal-bar and coral reef components may differ. The tidal-bar/reef complex forms the Florida Keys.

The role of vermetid gastropods in the development of the Florida Middle Ground, northeast Gulf of Mexico

ABSTRACT Reich, C.D.; Poore, R.Z., and Hickey, T.D., 2013. The role of vermetid gastropods in the development of the Florida Middle Ground, northeast Gulf of Mexico. In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 46–57, Coconut Creek (Florida), ISSN 0749-0208. The Florida Middle Ground is a complex of north to northwest trending ridges that lie approximately 180 km northwest of Tampa Bay, Florida. The irregular ridges appear on the otherwise gently sloping West Florida shelf and exhibit between 10–15 m of relief. Modern studies interpret the ridges as remnants of a Holocene coral-reef buildup that today provide a hard substrate for growth of a variety of benthic organisms including hydrocorals, scleractinians, alcyonarians, and algae. Recent rotary coring reveals that the core of the eastern ridge of the Florida Middle Ground complex consists of unconsolidated marine calcareous muddy sand that is capped by a boundstone composed primarily of the sessile vermetid gastropod Petaloconchus sp., and overlays a weathered, fossiliferous limestone. Accelerator Mass Spectrometry radiocarbon ages (uncalibrated) on the 3.6-m thick vermetid worm rock indicate that it developed during a sea-level stillstand in the early Holocene (8,225 ±30–8,910 ± 25 yr B.P.). Our observations suggest that the Florida Middle Ground is a remnant of a series of shore parallel bars that formed in the early Holocene and were capped by a 3.6-m thick unit of vermetid gastropods. During a rapid sea-level rise that began ∼8,000 yr B.P. the vermetids growth ceased and the worm rock preserved the ridges structure. Diver observations document that the edges of the ridges are currently being eroded and undermined by biological activity and current action, leading to calving of large capstone blocks.

Reply to comments by Corbett and Cable on our paper, "Seepage meters and Bernoulli's revenge

We thank Corbett and Cable (2003) for questioning our results and for pointing out the great number of studies that have employed various forms of seepage meters. It was the ever-increasing use of seepage meters and the spurious results we obtained that led us to warn the seepage meter community of possible defects in the method. Apparently our choice of an eye-catching title served its purpose. It was never our intent to perform the kind of engineering style quantitative tests that we hope this exchange will stimulate. We purposely used larger collection bags, because preliminary experiments with smaller bags showed they filled to capacity in less than 24 hr. For reasons of efficiency and the large spatial nature of our meter distribution, it was not practical to sample on hourly or multi-hour schedules. Our purpose therefore was to obtain 24-hr measurements that would average about four tidal intervals. Because our monitoring wells vividly showed tidal pumping and water transport are limited to the porous and permeable Pleistocene limestone, we chose to permanently seal our meters directly to the rock. Lee-type meters, on the other hand, must be placed in the sedimentary veneer that caps about 25% of the limestone in eastern Florida Bay (Prager and Halley 1999). Unlike most other areas where meters have been used, ground water entering the Lee-type meters in the Florida Keys ultimately comes from and is driven by tidal pumping and leakage from the underlying limestone. We are nevertheless surprised and pleased that the Lee-type meters of Corbett and Cable produced seepage rates paralleling those we obtained directly from the rock. Clearly, their meters were placed either in permeable shelly or marine grass-covered shell and lime mud sediments where permeabilities are greater than on bare lime mud substrates. Such areas are riddled with