Belowground productivity of roots and rhizomes in a giant cordgrass marsh

Belowground production of roots and rhizomes in the top 20 cm of soil was 2.2 kg m^?2 yr^?1 based on a maximum minus minimum estimation procedure in a giant cordgrass (Spartina cynosuroides (L.) Roth) marsh in Mississippi. Approximately 1.9 kg m^?2 (86%) of this production occurred in late spring-summer and 0.3 kg m^?2 in late fall. This estimate ignores any production below 20 cm depth and is thus an underestimate. Production values increased to 4.0 kg m^?2 yr^?1 using Smalley’s technique and accounting for decomposition. Aboveground tissues (leaves and stems) were depleted in nitrogen in July which corresponded to peaks in both above- and belowground biomass. The low root/shoot ratio (2.6) on this marsh does not suggest that growth is nutrient limited. Indeed, total productivity (above- and belowground) for this marsh was high (between 4.4 and 6.2 kg m^?2 yr^?1).     

Phosphorus and nitrogen inputs to Florida Bay: The importance of the everglades watershed

A large environmental restoration project designed to improve the hydrological conditions of the Florida Everglades and increase freshwater flow to Florida Bay is underway. Here we explore how changing freshwater inflow to the southern Everglades is likely to change the input of nutrients to Florida Bay. We calculated annual inputs of water, total phosphorus (TP), total nitrogen (TN), and dissolved inorganic nitrogen (DIN) to Everglades National Park (ENP) since the early 1980s. We also examined changes in these nutrient concentrations along transects through the wetland to Florida Bay and the Gulf of Mexico. We found that the interannual variability of the water discharge into ENP greatly exceeded the interannual variability of flow-weighted mean nutrient concentrations in this water. Nutrient inputs to ENP were largely determined by discharge volume. These inputs were high in TN and low in TP; for two ENP watersheds TN averaged 1.5 mg l^?1 (0.11 mM) and 0.9 mg l^?1 (0.06 mM) and TP averaged 15 μg l^?1 (0.47 μM) and 9 μg l^?1 (0.28 μM). Both TP and DIN that flowed into ENP wetlands were rapidly removed from the water. Over a 3-km section of Taylor Slough, TP decreased from a flow-weighted mean of 11.6 μg l^?1 (0.37 μM) (0.20 μM) and DIN decreased from 240 μg l^?1 (17μM) to 36 μ l^?1 (2.6 μM). In contrast, TN, which was generally 95% organic N, changed little as it passed through the wetland. This resulted in molar TN:TP ratios exceeding 400 in the wetland. Decreases in TN concentrations only occurred in areas with relatively high P availability, such as the wetlands to the north of ENP and in the mangrove streams of western ENP. Increasing freshwater flow to Florida Bay in an effort to restore the Everglades and Florida Bay ecosystems is thus not likely to increase P inputs from the freshwater Everglades but is likely to increase TN inputs. Based on a nutrient budget of Florida Bay, both N and P inputs from the Gulf of Mexico greatly exceed inputs from the Everglades, as well as inputs from the atmosphere and the Florida Keys. We estimate that the freshwater Everglades contribute <3% of all P inputs and <12% of all N inputs to the bay. Evaluating the effect of ecosystem restoration efforts on Florida Bay requires greater understanding of the interactions of the bay with the Gulf of Mexico and adjacent mangrove ecosystems.     

Nutrient inputs from the watershed and coastal eutrophication in the Florida keys

Widespread use of septic tanks in the Florida Keys increase the nutrient concentrations of limestone groundwaters that discharge into shallow nearshore waters, resulting in coastal eutrophication. This study characterizes watershed nutrient inputs, transformations, and effects along a land-sea gradient stratified into four ecosystems that occur with increasing distance from land: manmade canal systems (receiving waters of nutrient inputs), seagrass meadows, patch reefs, and offshore bank reefs. Soluble reactive phosphorus (SRP), the primary limiting nutrient, was significantly elevated in canal systems compared to the other ecosystems, while dissolved inorganic nitrogen (DIN; NH₄ ⁺ and NO₃ ^?) a secondary limiting nutrient, was elevated both in canal systems and seagrass meadows. SRP and NH₄ ⁺ concentrations decreased to low concentrations within approximately 1 km and 3 km from land, respectively. DIN and SRP accounted for their greatest contribution (up to 30%) of total N and P pools in canals, compared to dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) that dominated (up to 68%) the total N and P pools at the offshore bank reefs. Particulate N and P fractions were also elevated (up to 48%) in canals and nearshore seagrass meadows, indicating rapid biological uptake of DIN and SRP into organic particles. Chlorophylla and turbidity were also elevated in canal systems and seagrass meadows; chlorophylla was maximal during summer when maximum watershed nutrient input occurs, whereas turbidity was maximal during winter due to seasonally maximum wind conditions and sediment resuspension. DO was negatively correlated with NH₄ ⁺ and SRP; hypoxia (DO<2.5 mg l^?1) frequently occurred in nutrient-enriched canal systems and seagrass meadows, especially during the warm summer months. These findings correlate with recent (<5 years) observations of increasing algal blooms, seagrass epiphytization and die-off, and loss of coral cover on patch and bank reef ecosystems, suggesting that nearshore waters of the Florida Keys have entered a stage of critical eutrophication.     

Controls on herbaceous litter decomposition in the estuarine ecotones of the Florida Everglades

The effects of nutrient availability and litter quality on litter decomposition were measured in two oligotrophic phosphorus (P)-limited Florida Everglades esturies, United States. The two estuaries differ, in that one (Shark River estuary) is directly connected to the Gulf of Mexico and receives marine P, while the other (Taylor Slough estuary) does not receive marine P because Florida Bay separates it from the Gulf of Mexico. Decomposition of three macrophytes.Cladium jamaicense, Eleochaaris spp., andJuncus roemerianus, was studied using a litter bag technique over 18 mo. Litter was exposed to three treatments: soil surface+macroinvertebrates (=macro), soil surface without macroinvertebrates (=wet), and above the soil and water (=aerial). The third treatment replicated the decomposition of standing dead leaves. Decomposition rates showed that litter exposed to the wet and macro treatments decomposed significantly faster than the aerial treatment, where atmospheric deposition was the only source of nutrients. Macroinvertebrates had no influence on litter decompostion rates.C. jamaicense decomposed faster at sites, with higher P, andEleocharis spp. decomposed significantly faster at sites with higher nitrogen (N). Initial tissue C:N and C:P molar ratios revealed that the nutrient quality of litter of bothEleocharis spp. andJ. roemerianus was higher thanC. jamaicense, but onlyEleocharis spp. decomposed faster thanC. jamaicense. C. jamaicense litter tended to immobilize P, whileEleocharis spp. litter showed net remineralization of N and P. A comparison with other estuarine and wetland systems revealed the dependence of litter decomposition on nutrient availability and litter quality. The results from this experiment suggest that Everglades restoration may have an important effect on key ecosystem processes in the estuarine ecotone of this landscape.     

Patterns of mangrove forest structure and soil nutrient dynamics along the Shark River estuary, Florida

The basal area and productivity of managrove wetlands are described in relation to selected soil properties to understand the general pattern of optimum forest stature at the mouth of estuaries in the Everglades, such as the Shark River Slough, Florida (U.S.). The basal area of mangroves decreases from 40.4 m² ha⁻¹ and 39.7 m² ha⁻¹ at two stations 1.8 km and 4.1 km from the estuary mouth to 20.7 m² ha⁻¹ and 19.6 m² ha⁻¹ at two sites 9.9 km and 18.2 km from the mouth, respectively. The gradient in basal area at these four sites is mostly the result of approximately 34 yr of growth since Hurricane Donna. Wood productivity is higher in the lower estuary (10.7 Mg ha⁻¹ yr⁻¹ and 12.0 Mg ha⁻¹ yr⁻¹) than in the upper estuary (3.2 Mg ha⁻¹ yr⁻¹ and 4.2 Mg ha⁻¹ yr⁻¹). Porewater salinity among these four mangrove sites during seasonal sampling in 1994 and 1995 ranged from 1.6 g kg⁻¹ to 33.5 g kg⁻¹, while sulfide was generally<0.15 mM at all sites. These soil values indicate that abiotic stress cannot explain the decrease in forest structure along this estuarine gradient. Concentrations of nitrogen (N) and phosphorus (P) are more closely related to patterns of forest development, with higher soil fertility at the mouth of the estuary as indicated by higher concentrations of extractable ammonium, total soil P, and available P, along with higher ammonium production rates. The more fertile sites of the lower estuary are dominated by Laguncularia racemosa, whereas the less fertile sites in the intermediate and upper estuary are dominated by Rhizophora mangle. Relative N mineralization per unit of total N is higher in the lower estuary and is related positively to concentrations of available P, indicating the importance of turnover rates and nutrient interactions to soil fertility. Concentrations of Ca-bound P per volume soil in the lower estuary is 40-fold higher than in the upper estuary, and along with an increase in residual P in the upper estuary, indicate a shift from mineral to organic P along the estuarine gradient. Mineral inputs to the mouth of Shark River estuary from the Gulf of Mexico (rather than upland inputs) apparently control the patterns of mangrove structure and productivity.     

Late Quaternary coastal and inner shelf stratigraphy, Apalachicola Delta region, Florida

Since the beginning of the Tertiary the sedimentology of the Gulf of Mexico Basin has been dominated by the depositional activity of the Mississippi River. The sedimentologic influence of the Mississippi diminishes with distance east or west of the Louisiana shelf, however. The Texas and northwest Florida shelf margins, for example, are characterized by a series of smaller deltas. In the inner and mid-shelf areas of these regions the near-surface sedimentary units include infilled stream channels and small deltas. Such features are commonly observed in sub-bottom seismic records from the middle and inner shelf of the northeastern Gulf, along the Apalachicola River coast of northwest Florida.

The Apalachicola River is the principal source of clastic sediment to the northeastern Gulf of Mexico. During the late Holocene virtually all of the river's sediment load has been deposited in the modern Apalachicola Delta and in the river's estuary, Apalachicola Bay, which has been filling rapidly. During late Quaternary lowstands, prior to the development of the modern estuary, the river traversed the present-day inner and mid-shelf, incising a network of channels. Based on seismic records, many of these buried shelf channels were considerably larger than their modern counterparts.

During lowstands the Apalachicola River also deposited coarse sediment on the shelf as deltaic and associated river-mouth sediments. These deposits comprise the modern near-surface sediments of the inner and middle shelf. An investigation of subsurface sedimentary features observed in seismic profiles provides details on the late Quaternary development of the northeastern Gulf of Mexico shelf. Seismic reflection profiles obtained on the inner and mid-shelf regions of northwest Florida reveal an approximately 50 m thickness of late Quaternary sediments, comprised of two and sometimes three discrete clastic sequences. Two lower fluvial sequences total as much as 40–50 m in thickness. A transgressive marine sand deposit overlies the older features in some places, varying in thickness from 0 to 5 m. Identification of seismic facies, combined with stratigraphic data from a suite of coastal boreholes, enables correlation of offshore seismic stratigraphic units with late Tertiary and Quaternary coastal stratigraphy.     

Differences in the crab fauna of mangrove areas at a southwest Florida and a northeast Australia location: Implications for leaf litter processing

Existing paradigms suggest that mangrove leaf litter is processed primarily via the detrital pathway in forests in the Caribbean biogeographic realm whereas herbivorous crabs are relatively more important litter processors in the Indo-West Pacific. To test this hypothesis, we used pitfall traps to collect intertidal crabs to characterize the crab fauna in a mangrove estuary in southwest Florida. We also tethered mangrove leaves to determine if herbivorous crabs are major leaf consumers there. We compared the results with previously published data collected in an analogous manner from forests in northeastern Australia. The crab fauna in Rookery Bay, Florida, is dominated by carnivorous xanthid and deposit-feeding ocypodid crabs whereas that of the Murray River in northeastern Australia is dominated by herbivorous grapsid crabs. No leaves tethered at five sites in the forests in Southwest Florida were taken by crabs. This contrasts greatly with reported values of leaf removal by crabs in Australian forests of 28–79% of the leaves reaching the forest floor. These differences in the faunal assemblages and in the fate of marked or tethered leaves provide preliminary support for the hypothesis that leaf litter is in fact processed in fundamentally different ways in the two biogeographic realms.     

Inhibition of the decomposition ofZostera capricornii litter by macrobenthos and meiobenthos in a brackish coastal lake system

As part of the development of rapid assays to measure ecological processes, rates of decomposition of eelgrass,Zostera capricornii, were measured using litter bags placed at different distances from the sea in a coastal lake system. Average loss of dry mass over 28 d in bags with coarse mesh, which excluded animals >1.5 mm, varied from 364 to 448 mg in late winter to between 644 and 868 mg in autumn, depending on locality. Rates of loss were significantly greater in bags with small mesh (0.063 mm), from which all macrofauna were excluded, varying from 420 to 532 mg and from 868 to 924 mg in winter and autumn, respectively. There were consistent negative correlations between loss of litter and numbers of macrofauna and meiofauna in the bags. Rates of decrease in the organic fraction of the litter were positively correlated with numbers of animals. The results imply that the fauna inhibited decomposition, possibly by reducing microbial populations through grazing.     

Distribution of Hg in mangrove trees and its implication for Hg enrichment in the mangrove ecosystem

The aim of this study was to evaluate Hg distribution in mangrove plants and changes of Hg content during leaf aging; the contribution of litterfall to Hg enrichment in mangrove ecosystems is also discussed. Contents of total Hg (THg) and methylmercury (MeHg) in mangrove plants and sediments were determined. Contents of THg and MeHg in the sediments were 225 ± 157 ng/g and 0.800 ± 0.600 ng/g. Concentrations of THg and MeHg in the mangrove plants were 1760 ± 1885 ng/g and 0.721 ± 0.470 ng/g (dry weight), respectively, which were much higher than those in terrestrial plants. Enrichment of THg in mangrove plants was different, following the order Rhizophra apiculata > Rhizophora stylosa > Kandelia candel > Aegiceras corniculatum > Avicennia marina; while MeHg contents in mangrove plants decreased in the order of R. stylosa > K. candel > A. corniculatum > R. apiculata > A. marina. There were obvious interspecies differences, regional differences, individual differences and tissue differences between THg and MeHg contents of mangrove plants, all of which were closely related to the environmental and the physiological characteristics of mangrove plants. In juvenile leaves, mature leaves and leaf litter, THg contents ranged 55.3-1760 ng/g, 204-1800 ng/g, and 385-2130 ng/g (dry weight), respectively; MeHg contents ranged 0.17-2.39 ng/g, 0.01-1.28 ng/g, and 0.13-1.47 ng/g (dry weight), respectively. Except for A. corniculatum and Bruguier gymnorrhiza, THg content of mature leaves was always higher than that in juvenile leaves, but MeHg showed a contrasting trend. THg content of litter leaves was between that of juvenile leaves and mature leaves, while MeHg content was generally lower than that of juvenile leaves and mature leaves. In the mangrove ecosystem, Hg enrichment contributed by the litterfall decreased in the order of K. candel > A. corniculatum > A. marina.     

Developing oxygen isotope proxies from archaeological sources for the study of Late Holocene human–climate interactions in coastal southwest Florida

Oxygen isotopes (δ¹⁸O) derived from archaeological Mercenaria campechiensis shells and Ariopsis felis otoliths potentially provide low-latitude paleoclimate data for studying Late Holocene human–climate interactions in coastal southwest Florida. Specimens analyzed come from the Pineland site complex. Deposits record abrupt and subtle environmental changes appearing to have been climate-related and to have impacted the sedentary human residents. One archaeological shell-otolith set dates to 2nd/3rd century A.D. within the Roman Optimum (RO) climatic episode. A second set dates to 13th/14th century A.D. within the Little Ice Age (LIA). A modern shell-otolith set was analyzed for comparison. δ¹⁸O_ARAGONITE of modern and LIA shells suggest similar seasonal conditions. RO shell is 1‰ more positive during summer, suggesting higher estuarine salinity than in modern and LIA times. Modern and LIA otoliths also have similar δ¹⁸O_ARAGONITE. Estimated Winter temperatures are within measured instrument records. Summer temperatures are overestimated reflecting Summer migration into less-saline water. Estimated Summer temperatures for RO otolith are similar to today's, suggesting elevated estuarine salinity and diminished rainy season, consistent with similar aged zooarchaeological assemblages. Comparisons of two taxa aid in interpreting archaeological δ¹⁸O data; however, early results are mixed with expected profiles for RO specimens and unexpected profiles for LIA specimens.     

Comparative study of dissolved organic matter from groundwater and surface water in the Florida coastal Everglades using multi-dimensional spectrofluorometry combined with multivariate statistics

Dissolved organic matter (DOM) in groundwater and surface water samples from the Florida coastal Everglades were studied using excitation–emission matrix fluorescence modeled through parallel factor analysis (EEM-PARAFAC). DOM in both surface and groundwater from the eastern Everglades S332 basin reflected a terrestrial-derived fingerprint through dominantly higher abundances of humic-like PARAFAC components. In contrast, surface water DOM from northeastern Florida Bay featured a microbial-derived DOM signature based on the higher abundance of microbial humic-like and protein-like components consistent with its marine source. Surprisingly, groundwater DOM from northeastern Florida Bay reflected a terrestrial-derived source except for samples from central Florida Bay well, which mirrored a combination of terrestrial and marine end-member origin. Furthermore, surface water and groundwater displayed effects of different degradation pathways such as photodegradation and biodegradation as exemplified by two PARAFAC components seemingly indicative of such degradation processes. Finally, Principal Component Analysis of the EEM-PARAFAC data was able to distinguish and classify most of the samples according to DOM origins and degradation processes experienced, except for a small overlap of S332 surface water and groundwater, implying rather active surface-to-ground water interaction in some sites particularly during the rainy season. This study highlights that EEM-PARAFAC could be used successfully to trace and differentiate DOM from diverse sources across both horizontal and vertical flow profiles, and as such could be a convenient and useful tool for the better understanding of hydrological interactions and carbon biogeochemical cycling.     

Pyritization of trace metals in mangrove sediments

The present study investigates the levels of Mn, Zn, Ni, and Co pyritization in mangrove sediments along distinct sedimentary zones in Enseada das Gra?as, a lagoon-type estuary located on the southeastern coast of Brazil. The coastal geology is characterized by intense interactions of trace metals, forming pyrite minerals. Specific orders of DOP (degree of pyritization) and DTMP (degree of trace-metal pyritization) are shown: supratidal flat?<?mangrove forest?<?mud flat. Distinct changes in content along the sediment profiles are noted, where a supratidal flat presented low levels of DOP and DTMP with little variance along the sedimentary depths. The mangrove forest showed relatively high values of DOP and DTMP in the lower depths, while the mud flat showed the highest levels of DOP and DTMP.     

Characterization of a Malaysian mangrove estuary

The Sungai Merbok estuary, in wet tropical Peninsular Malaysia, borders the Straits of Malacca. Tide, current, and salinity data are used to describe the salient hydrographic features of the mangrove-fringed system. The Sungai Merbok estuary is characterized by a 1.7 m semidiurnal tide with a 0.16 form number, peak currents of 1.3 m s^?1, and mean freshwater discharge of 20 m³ s^?1. The system is classified as 2a/2b estuary (Hansen and Rattray 1966) or 1a/1b during periods of low runoff. Gravitational circulation is highly variable (but coincides with the neap stratification) and vertical stratification varies from 10^?2 to 1. The estuary displays a pronounced fortnightly neap-spring stratification-destratification cycle. The effective longitudinal dispersion coefficient is approximately 100 m² s^?1.     

The American Crocodile in Florida Bay

The American crocodile was declared endangered in the United States in 1975. At that time 75% of the remaining crocodile nests were in Everglades National Park, in Florida Bay. In 1980, the National Park Service established a crocodile sanctuary in northeastern Florida Bay to protect nesting and nursery habitat. In 1985, a monitoring program, focused on nesting, growth, and survival, was established to evaluate the effects of modified water deliveries on crocodiles in Florida Bay. The number and range of crocodile nests increased between 1970 and 1995, but nesting success decreased slightly. Nests on artificial substrates in the Greater Flamingo-Cape Sable area accounted for most of the increase in nests. Nests on artificial substrates were more prone to predation by raccoons. At least 1.5% of marked hatchlings survived for more than 12 mo, and growth rates were variable. Detailed information on growth and survival of crocodiles is still lacking. It is no longer a question of whether crocodiles with survive in Florida Bay, but how ecosystem restoration and management can be applied to improve conditions for crocodiles.     

Quaternary cave levels in peninsular Florida

The hypothesis that caves in the Florida Peninsula are tied to Quaternary sea levels was proposed by hydrogeologists, without data, some 40 years ago. The hypothesis is a version of glacial control of cave levels, which is the logical combination of the water-table theory of speleogenesis and the concept that base level positions the water table. At the USA type example of glacial control of cave levels—Mammoth Cave in the Paleozoic rocks of Kentucky—the intermediary is base level determined by rivers. By hypothesis, the intermediary for Florida is glacioeustatic sea level. This paper presents elevation data that supports this hypothesis.Recent cave surveys in the air-filled caves and spot elevations from archived maps reveal prominent levels of passages centered at 5, 12, 21, and 30 m above sea level over broad areas. They do not follow the large-scale structure of the Floridan aquifer. Instead, they align with nearby, coastal marine terraces identified as modal peaks on frequency plots from various topographic data bases. Levels matching with the three highest terraces—Wicomico, Penholoway, and Talbott—are particularly clear. Lower levels, if they accord with sea-level stands, are likely composites.Data from cavities encountered in drilled wells (e.g., bit drops) and spot elevations from archived underwater cave maps demonstrate passage levels at depths of 15, 30, 70, and 90–120 m below the modern water table. The depths below water table are similar to the depths below sea level of distant submerged terraces and paleoshoreline features identified using multibeam bathymetric data in the Gulf of Mexico.The cave, bit-drop, and terrace data are all consistent with the concept that Quaternary sea level is the fundamental control on the cave-scale porosity within the Floridan aquifer. This conclusion does not rule out the possibility that lithologically favored positions, paleokarst features and confining units, and mixing zones are also involved in the location of caves levels in this near-coastal environment.     

Recent increased aridity in peninsular Florida

Precipitation and river-flow data from peninsular Florida show a trend toward increased aridity beginning about 1960. The trend follows by 10–20 yr the onset of Northern Hemispheric cooling and indicates a possible present-day link between this cooling and the recent decrease in precipitation in peninsular Florida. This phenomenon tends to support the hypothesis of a return to cooler and drier conditions, perhaps, similar to those prevailing during the Little Ice Age.     

Nitrate depuration of secondary sewage effluents in mangrove sediments

The sewage treatment plant (STP) at La Parguera, on the southwest coast of Puerto Rico, discharges an average of 228,000 dm³ of secondary sewage effluents per day into percolation ponds located at the landward margin of the coastal mangrove fringe. Effluents flowing from the STP percolation ponds to the adjacent mangrove fringe typically exhibited nitrate levels between 0.2 mM and 1.0 mM. Experimental determination of actual and potential denitrification using acetylene block and substrate disappearance techniques indicate that mangrove sediment microbial communities are capable of depurating 10 to 15 times the nitrate added in the STP effluent. Plots of porewater salinities vs nitrate concentrations show exponential decay of nitrate concentration. Our observations confirm the potential of mangrove sediment-microbial communities for nitrate depuration of secondary sewage effluents.