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In laboratory studies, the short-term response of Phragmites australis and Spartina alterniflora to root immersion in solutions of different salinity and sulfide concentration was measured as the rate of ammonium depletion (a proxy for root uptake) from an initial concentration of 20 μM. From 0 to 20 ppt in the absence of sulfide, ammonium uptake as a function of dry root weight decreased for both Phragmites (from 29.7 ± 3.5 s.e. to 8.2 ± 1.5 μmol N g −1 h −1 ) and Spartina (from 25.5 ± 3.5 to 9.0 ± 1.5 μmol N g −1 h −1 ). With an average sulfide concentration of 582 μM at 20 ppt, the rate of ammonium uptake for Spartina (10.9 ± 2.2 μmol N g −1 h −1 ) was not significantly different from the rate in the absence of sulfide. In contrast, the rate of ammonium uptake was significantly lower for Phragmites when the average sulfide concentration was increased from 0 to 375 μM (1.7 ± 1.6 μmol N g −1 h −1 ). In a tidal saltmarsh, the average porewater sulfide concentration in Phragmites australis stands (124 ± 206 μM) was almost an order of magnitude lower than that measured in stands of Spartina alterniflora (989 ± 166 μM). These field and laboratory results support the notion that increased sulfide in the rhizosphere reduces the ability of Phragmites to take up nutrients relative to species such as Spartina that are better-adapted to sulfidic soil conditions, thus restricting the distribution of Phragmites in tidal saltmarshes.

Porewater chemistry and plant height were examined along 5 short transects extending from sections of tidal marsh dominated by the common reedPhragmites australis to those dominated bySpartina alterniflora. Phragmites was found at relatively higher tidal elevations along 4 of 5 transects; along all transects,Phragmites was growing and flowering throughout a porewater salinity range from 12 to 30 ppt. Dissolved inorganic phosphorus concentrations varied from 0 to >35 μM in bothSpartina andPhragmites sections of marsh, but ammonium concentrations averaged >40 μM in zones dominated bySpartina and 400 μM, perhaps due to sulfide inhibition of nitrogen uptake for growth. The persistence ofPhragmites at field conditions of high salinity and elevated sulfide concentrations suggests that hydrologic management may be insufficient to eradicatePhragmites in tidal wetlands.

The distribution of phosphorus among six sequentially extracted fractions was determined in suspended load and bottom sediments from Lagunitas Creek and Tomales Bay, California. The sequential extraction scheme was a modification of the sedex scheme of Ruttenberg (1992), using the surfactant sodium dodecyl sulfate (SDS) to extract organic phosphorus. SDS effectively removed organic phosphorus from sediments with little interference from inorganic phosphorus containing phases. The distribution of phosphorus in the sequentially extracted fractions was similar in suspended load and bottom sediments collected from Lagunitas Creek and the bay. The concentration of phosphorus in CDB-extractable iron oxide phases was below detection in all samples. Most of the phosphorus (70–80%) contained in these sediments was found in the organic and residual phases. Porewaters from sediment cores were analyzed for dissolved inorganic carbon, ammonium, phosphate, sulfate, iron, calcium and fluoride. Within bay sediments, porewaters were depleted in phosphate relative to dissolved inorganic carbon and ammonium, suggesting that phosphate released from organic matter decomposition is being removed from the porewaters. Sequential extraction results suggest that approximately 15% of the phosphate released from organic matter decomposition could be removed from the porewaters by adsorption into the exchangeable phosphorus fraction and an additional 3% may be precipitated as authigenic phosphate minerals. The remaining phosphate (82%) released from organic matter decomposition must be either taken up within the sediment mixed layer (0–40 cm) or escapes to the overlying water column.

Tomales Bay and its adjacent watershed are the location of integrated research on the CNPSi biogeochemical coupling between the land and coastal ocean and cycling of these materials within the bay. In the present paper, budgets have been constructed to describe the rainfall delivery of dissolved nutrients to the watershed and export of dissolved and particulate nutrients from the watershed, mostly in runoff. The quantity of dissolved materials, especially dissolved organic materials, delivered to the watershed by rainfall is about the same as the export. Suspended load transport represents the major net removal of C, N, and P from the watershed, and this flux shows large interannual variation. Runoff adjusted particle flux from the watershed is small at present in comparison with estimates based on sedimentation rate in the bay over the past 130 years. This difference apparently cannot be explained by natural or managed interannual variation in runoff or by other obvious aspects of water management. We believe that changes in agricultural land use have led to recent decreases in erosion and removal of particulate materials from the watershed. Even though the watershed has been disturbed by agricultural practices over the past 130 years, the system as a whole appears largely to have recovered to steady-state conditions.

Tidal wetland restoration typically has as one of its primary goals the reestablishment of ecosystem-level functions and services to marsh habitats degraded by reductions in tidal flow. On a fundamental level, reduction or restriction of tidal flooding alters the wetland environment so dramatically that soils, hydrology, and vegetation are all impacted, so that wetland function de facto is changed. Luckily, restoration of tidal flows in many wetlands can reverse some of the functional changes caused by tidal restriction.

Juvenile growth rate and adult body size are important components of life-history strategies because of their direct impact on fitness. The diamondback terrapin (Malaclemys terrapin) is a sexually dimorphic, long-lived turtle inhabiting brackish waters throughout the Atlantic and Gulf coasts of the United States. In parts of its range, terrapins face anthropogenically imposed mortality: juveniles of both sexes inadvertently enter commercial crab traps and drown. For adult females, the carapace eventually grows large enough that they cannot enter traps, whereas males almost never reach that critical size. We compared age structure, carapace dimensions, growth curves, and indices of sexual dimorphism for a Chesapeake Bay population of terrapins (where mortality of turtles is high due to crab traps) with contemporary terrapins from Long Island Sound and museum specimens from Chesapeake Bay (neither group subject to commercial crab traps). We also calculated the allochronic and synchronic rates of evolutionary change (haldanes) for males and females to measure the rate of trait change in a population or between populations, respectively. We found a dramatic shift to a younger male age structure, a decrease in the length of time to terminal female carapace size, a 15% increase in female carapace width, and an increase in sexual dimorphism in Chesapeake Bay. In a new twist, our results implicate a fishery in the selective increase in size of a reptilian bycatch species. These sex-specific changes in life history and demography have implications for population viability that need to be considered when addressing conservation of this threatened turtle.

Various nutrient incorporation and plant production parameters were measured to assess their relative usefulness in determining possible nutrient limitation of the wetland plant Peltandra virginica (L.) Kunth. From four stations located along a transect in a tidal freshwater marsh, we documented spatial differences in peak standing biomass of plants. Plant biomass was positively correlated with porewater concentrations of both ammonium and phosphate, but not with sediment concentrations of total nitrogen and phosphorus. Tissue nitrogen and phosphorus concentrations decreased significantly over the growing season, but there were no differences among plants from the four stations, and correlations between plant biomass and ratios of carbon to nitrogen and carbon to phosphorus were weak. Because in situ fertilization of plants had no effect on either peak biomass or tissue concentrations of nitrogen and phosphorus, growth of Peltandra was probably not nutrient limited. Other criteria did predict nitrogen or nitrogen and phosphorus limitation, however, demonstrating that application of parameters used by ecologists to support contentions of nutrient limitation can yield conflicting results. Assessment of nutrient limitation of primary producers may be an ambiguous and unnecessary task in some environments where these criteria are utilized.

In the United States, Phragmites australis is often viewed as a pest species because it forms monocultures that dominate a site for longer time scales than other wetland plants and because it decreases biodiversity. While research has shown that Phragmites is successful in tidal marshes where it tolerates the effects of prolonged flooding and salinity, to date there is little evidence of its influence on ecosystem-level processes. We review the literature and suggest future areas of research by regarding the specific question of whether Phragmites can dominate a site through its ability to control the cycling of limiting nutrients. Phragmites sequesters nutrients in standing live and dead biomass that either accumulates in the soil or is removed from the system by tidal flushing. Phragmites reduces light and temperature under its dense growth that decreases decomposition rates and immobilizes nutrients in long-term storage pools. Phragmites outcompetes other species for increased nutrient inputs from various anthropogenic sources. We focus in particular on two possible mechanisms which may be related to Phragmites success: Phragmites immobilizes nitrogen into forms (e.g., DON) which cannot be utilized by other species; and/or Phragmites accumulates Si and/or Al which immobilize P making it unavailable to other plants. Identifying the relative importance of these mechanisms to Phragmites expansion could assist the development of successful wetland restoration and management plans.

Seagrass meadows in Florida Bay and Shark Bay contain substantial stores of both organic carbon and nutrients. Soils from both systems are predominantly calcium carbonate, with an average of 82.1% CaCO3 in Florida Bay compared with 71.3% in Shark Bay. Soils from Shark Bay had, on average, 21% higher organic carbon content and 35% higher phosphorus content than Florida Bay. Further, soils from Shark Bay had lower mean dry bulk density (0.78 ± 0.01 g mL–1) than those from Florida Bay (0.84 ± 0.02 mg mL–1). The most hypersaline regions of both bays had higher organic carbon content in surficial soils. Profiles of organic carbon and phosphorus from Florida Bay indicate that this system has experienced an increase in P delivery and primary productivity over the last century; in contrast, decreasing organic carbon and phosphorus with depth in the soil profiles in Shark Bay point to a decrease in phosphorus delivery and primary productivity over the last 1000 y. The total ecosystem stocks of stored organic C in Florida Bay averages 163.5 MgCorg ha–1, lower than the average of 243.0 MgCorg ha–1 for Shark Bay; but these values place Shark and Florida Bays among the global hotspots for organic C storage in coastal ecosystems.

Sulfate reduction rates (SRR) in subtidal sediments of Tomales Bay, California, were variable by sediment type, season and depth. Higher rates were measured in near-surface muds during summer (up to 45 nmol cm-3 h-1), with lower rates in sandy sediments, in winter and deeper in the sediment. Calculations of annual, average SRR throughout the upper 20 cm of muddy subtidal sediments (about 30 mmol S m-2 d-1) were much larger than previously reported net estimates of SRR derived from both benthic alkalinity flux measurements and bay wide, budget stoichiometry (3.5 and 2.6 mmol m-2 d-1, respectively), indicating that most reduced sulfur in these upper, well-mixed sediments is re-oxidized. A portion of the net alkalinity flux across the sediment surface may be derived from sulfate reduction in deeper sediments, estimated from sulfate depletion profiles at 1.5 mmol m-2 d-1. A small net flux of CO2 measured in benthic chambers despite a large SRR suggests that sediment sinks for CO2 must also exist (e.g., benthic microalgae).

The process of dissolved phosphate removal from aqueous solution, which occurs during oxidation of soluble ferrous compounds to insoluble ferric forms, was examined in soils of two tidal freshwater marshes. Sites of amorphous iron deposition and sorption or co-precipitation of phosphate were found to be in surface soils and along creekbanks, where both ion diffusion and porewater advection move dissolved iron and phosphate from reduced to oxidized regions. Profiles of extractable iron and total phosphorus from creekbank and interior soils were consistent with hypothesized differences between a high and a low marsh. Porewater concentrations of dissolved phosphate were higher in creekbank soils of the high marsh, compared with water actually discharging from the creekbank during tidal exposure. We propose that an iron curtain of ferric hydroxides functions as a barrier to diffusive and advective movement of dissolved phosphate along surfaces of tidal freshwater marshes, and has important implications for the distribution and availability of phosphorus in other types of wetlands and aqueous systems.

Analysis of 3-m sediment cores revealed that profiles of carbon (C), sulfur (S), and iron (Fe) varied with relative distance from marine and terrestrial sediment sources in Tomales Bay California. Despite relatively high sedimentation rates throughout the bay (historically 3–30 mm yr−1), sulfate reduction of deposited organic matter led to free-sulfide accumulation in sediments only at the location farthest from terrestrial runoff, the source of reactive iron. Acid-volatile sulfide concentrations in all sediments (

We investigated the size and structure of a population of diamondback terrapins (Malaclemys terrapin) inhabiting Piermont Marsh on the lower Hudson River, New York. From 6 June through 24 August 1997, 39 trapping periods were completed using trammel nets set in and around the marsh complex. Only eight terrapins were captured six males and two females indicative of a small or broadly-dispersed population. Terrapins were trapped near a sandbar area outside of the marsh but never seen or trapped in two marsh creeks, suggesting the creeks were not used by terrapins during the time of the study. Instead, terrapins were observed basking and swimming around the rocky piers and breakwaters in the Hudson River. Recent development, soil subsidence, and Phragmites australis growth may have deteriorated traditional terrapin nesting sites in the region.

Sediment macropores (with effective diameters larger than 100 μm) comprise 11% of the bulk sediment volume in a tidal freshwater wetland vegetated withPeltandra virginica. In order to determine effects of macroporous sediment structure on solute transport, we conducted a solute tracer experiment in the sediment. The effective transport volume (θeff, the volume of sediment through which solute was transported normalized to sediment bulk volume) was 0.15 cm3 cm−3, which is considerably smaller than the total pore space that is potentially available for transport (porosity of sediment is 0.63 cm3 cm−3). A mean transport time of 13 d was required to flush preferential flow paths inPeltandra hummocks; hydrologic turnover of the volumetrically dominant matrix pores (0.53 cm3 cm−3) was apparently much slower. Based on porewater sampler design and hydrological principles, we suggest that N2-purged tension solution samplers and diffusion equilibrators preferentially sample porewater from macropore and matrix domains, respectively. Dissolved ammonium and orthophosphate concentrations were three-fold higher in matrix pores compared to macropores, which is consistent with our finding that more rapid hydrological flushing occurred in macropores compared to matrix pores. Further evaluation of porewater sampler designs in macroporous sediment is needed to improve studies of hydrologic transport and biogeochemical cycling in wetlands.

Allochthonous inputs of suspended particulate matter from freshwater environments to estuaries influence nutrient cycling and ecosystem metabolism. Contributions of different biogeochemical reactions to phosphorus dynamics in Tomales Bay, California, were determined by measuring dissolved inorganic phosphorus exchange between water and suspended particulate matter in response to changes in salinity, pH, and sediment redox. In serum bottle incubations of suspended particulate matter collected from the major tributary to the bay, dissolved inorganic phosphorus release increased with salinity during the initial 8 h; between 1–3 d, however, rates of release were similar among treatments of 0 psu, 16 psu, 24 psu, and 32 psu. Release was variable over the pH range 4–8.5, but dissolved inorganic phosphorus releases from sediments incubated for 24 h at the pH of fresh water (7.3) and seawater (8.1) were similarly small. Under oxidizing conditions, dissolved inorganic phosphorus release was small or dissolved inorganic phosphorus was taken up by particulate matter with total P content 50 μmoles P g−1. In contrast, under reducing conditions maintained by addition of free sulfide (HS−), dissolved inorganic phosphorus was released from particles at all concentrations of total phosphorus in suspended particulate matter, presumably from the reduction of iron oxides. Since extrapolated dissolved inorganic phosphorus release from this abiotic source can account for only 12.5% of the total dissolved inorganic phosphorus flux from Tomales Bay sediments, we conclude most release from particles is due to organic matter oxidation that occurs after estuarine deposition. The abiotic, sedimentary flux of dissolved inorganic phosphorus, however, could contribute up to 30% of the observed net export of dissolved inorganic phosphorus from the entire estuary.

Experimental chambers were used in a Virginia salt marsh to partition the tidal flux of dissolved nutrients occurring at the marsh surface and in the water column. On five dates from June to October 1989, six replicate chambers in the short Spartina alterniflora zone were monitored over complete tidal cycles. When reservoir water, used to simulate tidal flooding in the chambers, was initially low in dissolved nutrients, the marsh surface was a source of both ammonium and phosphate to the water column. Calculations of the physical processes of diffusion and advection could not account for total nutrient release from the marsh surface. We hypothesize the primary source of nutrients was organic matter mineralization in surface sediments, which released nutrients into the flooding water column. Assimilation (uptake) of phosphate measured in water-column incubation experiments was nearly equal to phosphate released from the marsh surface. Surface release of ammonium, however, was somewhat greater than water-column uptake. In this salt marsh, benthic production and release of ammonium and phosphate is comparable in magnitude to pelagic consumption, thereby yielding only a small “net” transfer of these nutrients to the estuary.

An experimental chamber is described which is closed to the water column but encompasses a selected section of the marsh surface. The microcosm is connected to a subsurface collapsible reservoir which functions as a flood water source. Head differences due to tidal fluctuations force reservoir water into and out of the microcosm, so that over complete tidal cycles the net exchanges of materials can be quantified. For this study, seasonal patterns of ammonium and phosphate dynamics in a tidal freshwater marsh were determined using four experimental chambers. On average, phosphate was removed from the water column during the spring, and released to the water column during summer and early fall. Seasonal patterns of ammonium dynamics were less clear, but the marsh removed ammonium from the water column on two of three summer sampling dates. Ammonium and phosphate removal from replicated chambers in vegetated sections of the marsh complex was greater than from unvegetated sections, indicating spatial heterogeneity of nutrient processing. The use of chambers in tidal marshes creates the opportunity to run controlled experiments in situ without imposing artificial hydrologic regimes.

The assumption that potassium bromide is a conservative tracer for soil-water studies was tested in a series of batch sorption experiments. Sorption experiments were conducted on soil samples collected from the O, E, and A horizons of the Albemarle soil series near Charlottesville, VA. The experiments were conducted under conditions of differing bromide concentration and filter treatments. Bromide concentrations in soil-solution mixtures were measured through time using an Orion bromide-specific electrode. An analysis of variance of results showed no significant sorption of bromide through time under any concentration level or filter treatment (α = 0·01). No sorption of bromide between different soil horizons could be determined. This work clearly indicates that bromide is conservative under the conditions examined.