Salt Marsh Plots Research Articles

Planting after shoreline cleanup treatment improves salt marsh vegetation recovery following the Deepwater Horizon oil spill

The Deepwater Horizon oil spill (2010) resulted in ~100 km of heavily oiled salt marsh shorelines with severe marsh vegetation impacts. Approximately 27 km of these shorelines had marsh cleanup treatments aimed at limiting oil spread and facilitating ecological recovery. Heavy oiling impacts and disturbance from intensive cleanup treatments left marsh shorelines largely bare of live vegetation. Following operational-scale shoreline cleanup and experimental planting of Spartina alterniflora, we compared oiling degree and vegetation recovery among three types of heavily oiled salt marsh plots over three years: oiled control (no cleanup treatment, no planting); mechanical cleanup treatment (unplanted); and mechanical treatment coupled with planting. Nearby reference plots were used to define recovery targets and determine recovery progress. Mechanical treatment with planting showed the most improvement in oiling conditions and was most effective in re-establishing vegetation cover and dominant plant species composition approaching reference conditions. In contrast, the oiled controls and mechanical treatment plots without planting were similar and showed much slower recovery trends. Vegetation planting should be considered as a shoreline treatment or restoration approach for heavily oiled salt marshes, especially where oil impacted areas are left largely unvegetated, natural recovery is delayed, marsh shorelines are at risk of erosion, and as a possible condition for the use of intensive cleanup treatments. Vegetation planting following oil spills could be incorporated into shoreline treatment operations during emergency response as shoreline stabilization and for oil removal via phytoremediation, or as emergency restoration under the Natural Resources Damage Assessment (NRDA) process, to limit the degree and duration of natural resource impacts.

Mangroves dramatically increase carbon storage after 3 years of encroachment

In North America, the dynamic ecotonal boundary between mangrove and salt marsh is currently fluctuating in response to freeze-free winters, which can cause rapid alterations in a number of wetland processes and attributes. Permanent plots were established in pure salt marsh habitat along the Atlantic coast of Florida in 2015, and by 2018, mangrove saplings had encroached into plots. In this study, above- and belowground biomass measurements and soil C in the top 10-cm soil profile were quantified in 2018 and compared to 2015 data to better understand the effects of mangrove encroachment on C storage in salt marsh habitat. Plant and soil fractions were tested for δ13C stable isotopic signatures to elucidate soil C sources. In 3 years, mangrove biomass increased dramatically and soil C doubled in pure salt marsh plots, consequently increasing total C in the system. Soil organic matter increased, while there was no change in soil C:N. δ13C values suggest that soil C was derived mainly from salt marsh soil organic matter, especially that of belowground, rather than aboveground biomass. These results provide real-time, quantitative data on the encroachment of mangroves into salt marshes over a relatively short period of time.

Mercury speciation and retention in a salt marsh undergoing long-term fertilization

Experimental plots in Great Sippewissett Marsh (Falmouth, MA USA) have been undergoing long-term (>48 years) fertilization through the application of commercial sewage sludge-based fertilizer. The experimental treatment focuses on the effect of added nitrogen on the salt marsh plots, but also supplies mercury (Hg) and other metals. This experiment provides a unique opportunity to test hypotheses regarding the Hg-related response of coastal marine ecosystems to eutrophication as well as assess the efficacy of salt marshes as sinks for increased loadings of Hg to the coastal zone. Hg inventories in sediments of control plots were similar to loadings from atmospheric deposition and inventories in the fertilized plots closely reflected the estimated loadings of Hg contained in the added fertilizer. In both the control and fertilized plots, distribution of Hg appeared somewhat different than the history of loadings, implying some level of Hg mobility. The relative abundance of monomethylmercury (CH3Hg+) within the plots varied with the amount of fertilizer applied with the highest percentage of Hg as CH3Hg+ found in the control plots, and the lowest percentages of CH3Hg+ and S were measured in plots fertilized at the highest dose. The results from this marsh suggest that eutrophication indirectly lowers CH3Hg+ production in this particular ecosystem, but perhaps not as a result of the sequestration of Hg(II) with S.

Environmental conditions of a salt-marsh biodiversity experiment on the island of Spiekeroog (Germany)

Abstract. Field experiments investigating biodiversity and ecosystem functioning require the observation of abiotic parameters, especially when carried out in the intertidal zone. An experiment for biodiversity–ecosystem functioning was set up in the intertidal zone of the back-barrier salt marsh of Spiekeroog Island in the German Bight. Here, we report the accompanying instrumentation, maintenance, data acquisition, data handling and data quality control as well as monitoring results observed over a continuous period from September 2014 to April 2017. Time series of abiotic conditions were measured at several sites in the vicinity of newly built experimental salt-marsh islands on the tidal flat. Meteorological measurements were conducted from a weather station (WS, https://doi.org/10.1594/PANGAEA.870988), oceanographic conditions were sampled through a bottom-mounted recording current meter (RCM, https://doi.org/10.1594/PANGAEA.877265) and a bottom-mounted tide and wave recorder (TWR, https://doi.org/10.1594/PANGAEA.877258). Tide data are essential in calculating flooding duration and flooding frequency with respect to different salt-marsh elevation zones. Data loggers (DL) for measuring the water level (DL-W, https://doi.org/10.1594/PANGAEA.877267), temperature (DL-T, https://doi.org/10.1594/PANGAEA.877257), light intensity (DL-L, https://doi.org/10.1594/PANGAEA.877256) and conductivity (DL-C, https://doi.org/10.1594/PANGAEA.877266) were deployed at different elevational zones on the experimental islands and the investigated salt-marsh plots. A data availability of 80 % for 17 out of 23 sensors was achieved. Results showed the influence of seasonal and tidal dynamics on the experimental islands. Nearby salt-marsh plots exhibited some differences, e.g., in temperature dynamics. Thus, a consistent, multi-parameter, long-term dataset is available as a basis for further biodiversity and ecosystem functioning studies.

Influence of salt marsh canopy on black mangrove (Avicennia germinans) survival and establishment at its northern latitudinal limit

As annual minimum temperatures increase due to climate change, species once constrained by minimum temperatures are expanding poleward. Avicennia germinans (black mangrove), a freeze-intolerant tree, has been expanding northward into salt marsh-grass-dominated communities. Distribution and colonization dynamics of A. germinans are crucial for understanding changes in coastal habitats and ecosystem structure and function along the Gulf of Mexico Coast (USA). We transplanted A. germinans seedlings and propagules into salt marsh plots of S. alterniflora, half of which had the canopy removed, along a latitudinal gradient that spanned locations within and outside of A. germinans’ current range limits (29°7′20″N to 30°23′41″N). Plot microclimate and transplant survival and growth were monitored for 2 years. Canopy removal resulted in lower minimum temperatures and longer cumulative freeze duration. Seedling survival was greatest at the southernmost site; however, seedling growth was reduced in plots with the canopy intact, as hypothesized. Seedling survival at northern sites was limited to plots with the S. alterniflora canopy intact. Propagules survived and established at all sites in the second year, although there was no S. alterniflora canopy effect on propagule survival and establishment. Our results illustrate the complexity of ecological interactions between herbaceous marsh species and mangroves at the species’ range limit.

Eutrophication decreases salt marsh resilience through proliferation of algal mats

Globally, many estuaries are affected by nutrient loading from human land uses in the surrounding watersheds. One consequence of increased nutrient levels is proliferation of opportunistic macroalgae. We sought to understand spatial and temporal dynamics of ephemeral macroalgal mats and to examine their effects on salt marsh in a eutrophic estuary in central California. A time series analysis spanning 80years revealed that algal wrack has increased exponentially in frequency on the salt marsh, and was highly correlated with nutrient concentrations in the estuary, which have increased along with fertilizer use. Analysis of sediment δ15N showed a dramatic increase in nutrient loads attributable to agricultural fertilizer over the past 50years. We monitored 15 salt marsh plots along the bank edge and detected a negative relationship between algal wrack cover and salt marsh cover, flowering, and canopy height. Moreover, algal wrack led to retreat of vegetation from the bank edge, and increased bank erosion. We also experimentally added algal wrack to salt marsh edge plots. Algal addition decreased salt marsh cover, flowering, and canopy height, and increased retreat rate. By integrating time series analyses, isotope data, algal and marsh monitoring and manipulative experiments, we have identified robust linkages between increased anthropogenic nutrient loading, increased algal wrack cover, reduction in marsh resilience and conversion of marsh habitat to mudflat through bank erosion. Decreasing nutrient inputs to eutrophic estuaries is thus essential for conservation and restoration of salt marshes and enhancing their resilience in the face of sea level rise.

Intraspecific interactions shift from competitive to facilitative across a low to high disturbance gradient in a salt marsh

Disturbances are ubiquitous among salt marshes, and disturbances such as litter removal may form stressful environmental conditions. The stress-gradient hypothesis (SGH) predicts that the relative importance of facilitation and competition between species will vary inversely to each other across abiotic stress gradients. However, how intraspecific interactions vary across disturbance levels, and whether they follow the SGH has not been investigated. To test the SGH with intraspecific interactions within Suaeda salsa individuals, we assessed individual survival in established fully mapped salt marsh plots with two treatments, disturbed, litter removal and control, undisturbed plots. Recently developed spatial statistics were applied to distinguish between random processes, intraspecific facilitation, scramble competition, and contest competition underlying the spatial patterns at different spatial scales, growth stages, and disturbance levels. We found evidence that intraspecific interactions among S. salsa individuals across disturbance levels tended to support the SGH, but this support depended on time and space. Intraspecific interactions were more likely to show positive density dependence in disturbed plots, particularly at the seedling period and when individuals were separated by < 9 cm. However, positive density dependence was not detected in undisturbed plots. The protective effects of litter on seedlings, which were lost in undisturbed sites, may have been at least partly simulated at high seedling densities. Mortality in disturbed sites was not random, and facilitation had a more important influence than competition on population dynamics in high disturbance sites. However, the influence of competition on population dynamics, specifically scramble competition was also clearly important.

The Great Sippewissett Salt Marsh Plots—Some History, Highlights, and Contrails from a Long-Term Study

The Great Sippewissett Salt Marsh Plots—Some History, Highlights, and Contrails from a Long-Term Study

Modeling soil parameters using hyperspectral image reflectance in subtropical coastal wetlands

Developing spectral models of soil properties is an important frontier in remote sensing and soil science. Several studies have focused on modeling soil properties such as total pools of soil organic matter and carbon in bare soils. We extended this effort to model soil parameters in areas densely covered with coastal vegetation. Moreover, we investigated soil properties indicative of soil functions such as nutrient and organic matter turnover and storage. These properties include the partitioning of mineral and organic soil between particulate (>53μm) and fine size classes, and the partitioning of soil carbon and nitrogen pools between stable and labile fractions. Soil samples were obtained from Avicennia germinans mangrove forest and Juncus roemerianus salt marsh plots on the west coast of central Florida. Spectra corresponding to field plot locations from Hyperion hyperspectral image were extracted and analyzed. The spectral information was regressed against the soil variables to determine the best single bands and optimal band combinations for the simple ratio (SR) and normalized difference index (NDI) indices. The regression analysis yielded levels of correlation for soil variables with R2 values ranging from 0.21 to 0.47 for best individual bands, 0.28 to 0.81 for two-band indices, and 0.53 to 0.96 for partial least-squares (PLS) regressions for the Hyperion image data. Spectral models using Hyperion data adequately (RPD>1.4) predicted particulate organic matter (POM), silt+clay, labile carbon (C), and labile nitrogen (N) (where RPD=ratio of standard deviation to root mean square error of cross-validation [RMSECV]). The SR (0.53μm, 2.11μm) model of labile N with R2=0.81, RMSECV= 0.28, and RPD=1.94 produced the best results in this study. Our results provide optimism that remote-sensing spectral models can successfully predict soil properties indicative of ecosystem nutrient and organic matter turnover and storage, and do so in areas with dense canopy cover.

Salt marsh vegetation as a carbonyl sulfide (COS) source to the atmosphere

Carbonyl sulfide (COS) is the most abundant and longest-lived reduced sulfur compound in the atmosphere; changes in its atmospheric concentration could significantly affect global climate and the biogeochemical sulfur cycle. The largest sink of COS in the troposphere is its destruction in plant leaves by the enzymes involved in photosynthesis. In this study, net fluxes of COS were measured from a coastal salt marsh on a subtropical barrier island on the Texas shore of the Gulf of Mexico. We find net emissions from sites with the common salt marsh plant Batis maritima compared to the net uptake from vegetated plots of most previously investigated biomes. The magnitude of the COS production from vegetated plots in this study was twice the emissions of soil-only salt marsh plots. This is the first time that emissions of COS have been found to be significantly enhanced by the presence of vegetation compared to soil alone. COS fluxes exceeded +110 pmol m−2 s−1 for non-inundated plots during daytime hours and were correlated with soil temperature at the depth of 5 cm. Tidal flooding inhibited soil COS exchange; however, we found continued net emissions from emergent B. maritima. This study suggests that emissions of COS resulted from interactions with the plants themselves, which would mean that B. maritima can mediate the production of atmospheric COS.

Nitrogen interception and export by experimental salt marsh plots exposed to chronic nutrient addition

Mass balance studies conducted in the 1970s in Great Sippewissett Salt Marsh, New England, showed that fertilized plots intercepted 60 to 80% of the nitrogen (N) applied at several treatment levels every year from April to October, where interception mechanisms include plant uptake, denitrification and burial. These results pointed out that salt marshes are able to intercept land-derived N that could otherwise cause eutrophication in coastal waters. To determine the long-term N interception capacity of salt marshes and to assess the effect of different levels of N input, we measured nitrogenous materials in tidal water entering and leaving Great Sippewissett experimental plots in the 2007 growing season. Our results, from sampling over both full tidal cycles and more inten- sively sampled ebb tides, indicate high interception of externally added N. Tidal export of dissolved inorganic N (DIN) was small, although it increased with tide height and at high N input rates. NH4 + export was gen- erally 2 to 3 times NO3 - export, except at the highest N addition, where DIN export was evenly partitioned between NO3 - and NH4 + . Exports of dissolved organic N were not enhanced by N addition. Overall, export of added N was very small, <7% for all treatments, which is less than earlier estimates. Apparent enhanced tidal export of N from N-amended plots ceased when N additions ended in the fall. Nitrogen cycling within the vegetated marsh appears to limit N export, such that interception of added N remains high even after over 3 decades of external N inputs.

Distribution of phosphatase activity in marsh sediments along an estuarine salinity gradient

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 292:75-83 (2005) - doi:10.3354/meps292075 Distribution of phosphatase activity in marsh sediments along an estuarine salinity gradient Xiaoqing Huang1,2,*, James T. Morris1 1Department of Biological Sciences, University of South Carolina, 700 Sumter Street, Columbia, South Carolina 29208, USA2Present address: Earth Sciences and Resources Institute, University of South Carolina, 901 Sumter Street, Columbia, South Carolina 29208, USA *Email: huang@esri.sc.edu ABSTRACT: Acid phosphatase activity (APA) was measured in intertidal marsh sediments located along the Cooper River estuary, South Carolina, at North Inlet, SC, and in a marsh on the Rowley River, MA. We found that APA increased from 4.3 ± 2.3 to 29.3 ± 18.8 µmol p-nitrophenol released g–1 h–1 with decreasing sediment salinity from 22 g l–1 to 0.1 g l–1. A study of APA kinetics revealed that the maximum specific activity (Vmax) followed the same trend as in situ phosphatase activity. Sediment salinity (p < 0.05; R2 = 0.43) and pH (p < 0.01; R2 = 0.56) were negatively correlated with APA, while soil organic matter (SOM) content (p < 0.01; R2 = 0.57), clay content (p < 0.05; R2 = 0.37) and sediment organic P (SOP) (p < 0.01; R2 = 0.50) were positively correlated. Collectively, these variables accounted for 78% of the variation in APA (p < 0.05). APA was not significantly correlated with sulfide, NH4+, soluble reactive phosphorus (SRP), sediment total P, the N:P ratio, aboveground biomass, or macro-organic matter content. In salt marsh plots at North Inlet that were experimentally fertilized with N and P, we found that fertilization with only P had no effect on APA, while N-only or N + P fertilization significantly increased APA to 6.4 µmol p-nitrophenol released g–1 h–1 from 1.5 µmol p-nitrophenol released g–1 h–1 in control plots. However, even in the fertilized salt marsh plots, APA was still significantly lower than in freshwater, oligohaline and mesohaline marshes. KEY WORDS: Acid phosphatase activity · Marsh sediment · Salinity gradient · Estuary Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 292. Online publication date: May 12, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Gladstone, Australia Field Studies: Weathering and Degradation of Hydrocarbons in Oiled Mangrove and Salt Marsh Sediments With and Without the Application of an Experimental Bioremediation Protocol

This field study was a combined chemical and biological investigation of the relative rates of weathering and biodegradation of oil spilled in sediments and testing the influence of a bioremediation protocol. The aim of the chemistry work presented here was to determine whether the bioremediation protocol affected the rate of penetration, dissipation or long-term retention of a medium range crude oil (Gippsland) and a Bunker C oil stranded in tropical Rhizophora sp. mangrove and Halosarcia sp. salt marsh environments. Permission for the planned oil spills was granted in the Port Authority area of Gladstone, Queensland (Australia). Sediment cores from three replicate plots of each treatment for mangroves and four replicate plots for the salt marsh (oil only and oil plus bioremediation) were analysed for total hydrocarbons (THC) and for individual alkane markers using gas chromatography with flame ionization detection (GC–FID). Sediments were collected at day 2, then 1, 2, 5 or 6 and 12 or 13 months post-spill for mangroves and day 2, 1, 3 and 9 months post-spill for salt marshes. Over this time, hydrocarbons in all of the oil treated plots decreased exponentially. There was no statistical difference in initial oil concentrations, penetration of oil to depth, or in the rates of oil dissipation between untreated oil and bioremediated oil in the mangrove plots. The salt marsh plots treated with the waxy Gippsland oil showed a faster rate of biodegradation of the oil in the bioremediated plots. In this case only, the degradation rate significantly impacted the mass balance of remaining oil. The Bunker C oil contained only minor amounts of highly degradable n-alkanes and bioremediation did not significantly impact its rate of loss in the salt marsh sediments. At the end of each experiment, there were still n-alkanes visible in the gas chromatograms of residual oils. Thus it was concluded that there was unlikely to be any change in the stable internal biomarkers of the oils over this time period. The predominant removal processes in both habitats were evaporation and dissolution, with a lag-phase of 1–2 months before the start of microbial degradation.

The Density of Redshank Tringa totanus Breeding on the Salt-Marshes of the Wash in Relation to Habitat and Its Grazing Management

Coastal salt-marshes in Great Britain are of both national and international significance for their breeding redshank Tringa totanus populations. These habitats are currently under threat, as a result of habitat loss due to erosion and changes in the use of salt-marshes for grazing livestock. The application of 'soft engineering' methods to coast protection and sea defence work, and the development of management plans for estuaries, offer mechanisms to create and manage salt-marsh habitats suitable for breeding redshank. However, there is a need for more information on the importance of different salt-marsh habitats and their grazing management, which could be used to ensure that these various mechanisms benefit the conservation of redshank in Britain. The primary aim of our study was to describe, in detail, the relationship between the density of breeding redshank, the extent of different salt-marsh habitats and their grazing management. Our approach consisted of undertaking a survey of redshank breeding on a sample of 50 salt-marsh plots from 19 sites located in the Wash in eastern England. We used standard survey methods during which we also collected detailed data on salt-marsh habitats, vegetation structure and the intensity of grazing from survey sites. Multiple regression modelling revealed that redshank densities were positively correlated with the extent of the sea-couch grass community on survey plots, but the form of this relationship varied in relation to grazing intensity. On heavily grazed plots, breeding density increased significantly more rapidly as the extent of the sea-couch grass community increased, compared with ungrazed plots. The rate of increase on moderately grazed plots was intermediate. Breeding densities were also negatively correlated with the extent of the glasswort and annual sea-blite community, although the form of this relationship appeared unaffected by the intensity of grazing. Redshank densities also varied significantly between sites, in addition to any variation attributable to habitat or grazing. Our analyses suggested that the relationship between the extent of the sea-couch grass community and redshank density, under different grazing intensities, could be explained by variation in vegetation structure. Heavily grazed plots, dominated by the sea-couch grass community, supported the most structurally diverse vegetation, and the highest breeding densities. In contrast, ungrazed plots of similar habitat contained tall, uniform vegetation and supported significantly lower breeding densities. Our analyses indicate that grazing salt-marsh sites dominated by sea-couch grass on the Wash is beneficial to breeding redshank. This means that current grazing practices should be maintained at such sites and grazing re-introduced to sites which were formerly grazed. The density of cattle on the Wash is 1 cow per hectare of grazed salt-marsh, suggesting that this level of grazing pressure would be most appropriate. Caution is required, however, if sites dominated by lower salt-marsh habitats are grazed, because any slight increase in breeding density resulting from grazing might be offset by an increased risk of nest loss due to trampling. In this case, cattle should, if possible, be put on to the marsh towards the end of the redshank nesting season (i.e. late May/early June) to minimize this trampling risk.

Is host-plant quality responsible for the populational pulses of salt-marsh planthoppers (Homoptera: Delphacidae) in northwestern Florida?

Abstract. 1 Rare populational pulses of the sibling species of plant-hoppers Prokelisia dolus Wilson and P.marginata (Van Duzee) occur along the Gulf Coast of Florida. Densities at least three standard deviations ahove the average number of adult planthoppers per stem host plant are exhibited during these pulses. 2 This context of rare local irruptions provides a basis for testing a component of T. C. R. White's hypothesis, which states that the trigger for insect outbreaks is an increase in the nutritional quality, in terms of available nitrogen, of host-plant tissue. 3 In the field, over approximately five generations of these hoppers (9 months), we elevated foliar nitrogen in host plants substantially by fertilizing, six times, salt-marsh plots of 10 m2 with ammonium nitrate. No densities approaching a populational pulse occurred in either fertilized or unfertilized plots during the course of this study or in the year following. Fertilization did increase adult densities in the spring but this increase deteriorated over the summer months and was lost in the autumn. Host plants in fertilized plots retained high levels of nitrogen for at least the second year. 4 Several very dense pulses, of more than thirty adult hoppers per stem, occurred at other sites during the course of this study. Host-plant nitrogen in a pulse site did not differ from that found in host plants immediately adjacent to the pulse. We conclude that increased foliar nitrogen is not the proximate cause of the populational pulse behaviour exhibited by these planthoppers. 5 We speculate that these pulses result from behavioural aggregation of adult hoppers.

Evaluation of alternative oil spill cleanup techniques in a Spartina alterniflora salt marsh

Three oil spill situations which cause long-term impact were simulated in 1 m 2 salt marsh plots to evaluate the effectiveness of alternative cleanup techniques at removing oil and reducing damage to Spartina alterniflora. Cleanup techniques, implemented 18–24 h after oiling, were not effective at removing oil after sediment penetration. When oil remained on the sediment surface, flushing techniques were most effective at removal, reducing levels of added oil by 73% to 83%. The addition of dispersant to the flushing stream only slightly enhanced oil removal. Clipping of vegetation followed by sorbent pad application to sediment was moderately effective, reducing added oil by 36% to 44%. In contrast to flushing and clipping, burning increased the amount of oil in sediment by 27% to 72%. Although flushing and clipping were effective at oil removal, neither technique reduced initial damage to plants or enhanced long-term recovery. While flushed plots sustained no additional plant damage due to cleanup, clipped and burned plots sustained additional initial plant damage. Based on these results, first considerations should be given to natural tidal flushing as the means to remove oil, especially in salt marshes subject to ample tidal inundation. Although our results do not support cleanup in salt marshes with ample tidal inundation, low pressure flushing may be warranted when fuel oils or large quantities of crude oil impact salt marshes subject to reduced tidal flushing. Flushing, when warranted, should be initiated prior to oil penetration into the substrate. Clipping may be considered as a cleanup response only when heavy oil cannot be effectively removed from vegetation by flushing. Burning is not recommended because it enhances oil penetration into sediment and causes substantial initial plant damage.

THE ROLE OF JUNCUS ROEMERIANUS IN CLEANUP OF OIL-POLLUTED SEDIMENTS

ABSTRACT Several locations in the Mississippi Sound of the Central Gulf of Mexico have been sites of accidental and simulated oil spills over the past decade, providing excellent testing grounds for detecting interactions of indigenous marsh vegetation with petroleum pollutants. Spartina alterniflora and Juncus roemerianus, dominant marsh plants of this region, show resilience in the face of acute oil spills, with J. roemerianus decidedly more resilient in chronic exposures. More important, J. roemerianus can remove large amounts of petroleum hydrocarbons from the underlying sediments and from the water column. Collections of Juncus and underlying sediment from five estuarine environments showed levels and distributions of petroleum hydrocarbons in the aerial leaf portions that mirrored those found in the sediment substrate. Up to 9,000 ppm total hydrocarbons were found in J. roemerianus growing in oil-contaminated sediments. In two different studies, salt marsh plots of Juncus roemerianus and Spartina alterniflora were exposed to sediments inoculated with three different crude oils, an alkene, chrysene, and naphthalene, and uptake was monitored with time. Juncus was able to take up hydrocarbons unaltered within 10 days. Spartina showed no evidence of uptake, though it did show relative increases in lipid fractions.

Effects of autumn application of oil on Spartina alterniflora in a Texas salt marsh

Arabian crude oil, Libyan crude oils, No. 6 fuel oil and No. 2 fuel oil were applied, in November 1981, to 1 m 2 salt marsh plots in Galveston Bay, Texas. Oil treatments were: no oil, 1 litre on sediment, 1·5 litres on sediment and lower 30 cm of Spartina alterniflora and 2 litres on sediment and entire S. alterniflora surfaces. All oils caused death of above-ground parts of plants within 3 weeks when applied to entire plant surfaces. Partial coverage was harmful only with No. 2 fuel oil, while sediment application had no effect. By 5 months, new growth had occurred from roots and rhizomes in Arabian crude oil, Libyan crude oil and No. 6 fuel oil plots and live biomass was near that of controls. By 1 year recovery was complete. For No. 2 fuel oil plots, which sustained the greatest mortality, growth was significantly below control levels at 5 months and 1 year, but recovery was complete within 2 years. Slow recovery in No. 2 fuel oil plots appeared to be due to the initial mortality of below-ground, as well as above-ground, plant parts. Toxicity of residual oil in the sediment did not appear to be a factor in slow recovery since seedling establishment had occurred within 5 months and little residue of No. 2 fuel oil was present in the sediments after 1 year. Also, this residue did not contain alkyl-substituted naphthalenes, toxic components present in the original oil. Considerable residues of all oils except No. 2 fuel oil were present in the sediment after 1 year. Pristance/ nC 17 and phytane/ nC 18 ratios indicated that removal of some oil components had occurred through biodegradation.

Response of a salt marsh microbial community to inputs of heavy metals: Aerobic heterotrophic metabolism

The addition of a sterilized, sludge-based fertilizer to experimental salt marsh plots increased both the nitrogen and the heavy metal content of the surface sediment. Aerobic heterotrophic microorganisms collected from these plots differed from microbes collected from control plots in their oxygen uptake rates on a uniform sediment medium both in the presence and absence of metals. When metals were not present, microbes from fertilized plots took up significantly less oxygen that did microbes from control plots. In the presence of metals, oxygen uptake by microbes from both plots was depressed; however, activity of microbes from the fertilized plots was significantly less inhibited than was that of microbes from the control plots, indicating a greater degree of metal tolerance in the former. To assess the effect of a metal on the microbial community in the absence of nutrient enrichment, chromium solutions were applied to several 1-m2 marsh plots. Microbes from these plots developed a tolerance to both copper and chromium within 1 month. The oxygen uptake on sediment media in the absence of metals did not differ from that demonstrated by nonmetal-tolerant microbes.

EFFECTS OF OIL ON GROWTH AND DECOMPOSITION OF SPARTINA ALTERNIFLORA

ABSTRACT Four oils (Arabian crude oil, Libyan crude oil, No. 6 fuel oil, and No. 2 fuel oil) were applied to one-square-meter salt marsh plots in Galveston Bay, Texas. Oils were applied at four levels: no oil, 1 liter on sediment, 1.5 liters on sediment and lower portions of Spartina alterniflora, and 2 liters on sediment and entire S. alterniflora surfaces. Within one week of oil application, nylon bags containing cut stems of S. alterniflora were staked in the center of all unoiled and 1.5 liter oil plots. Oil caused mortality of S. alterniflora within three weeks; the degree of mortality varied with oil type and the extent of plant coverage. Plant mortality was highest in plots with No. 2 fuel oil and those where oil was applied to entire plant surfaces. After five months, growth of plants in No. 2 fuel oil plots still was significantly below control levels. However, initial recovery was apparent in No. 2 fuel oil plots receiving 2 liters. Live biomass in Arabian crude oil, Libyan crude oil, and No. 6 fuel oil plots after five months was comparable to that of controls. Plots clipped three weeks after oil application were recolonized after five months by growth of new stems and seedlings. However, Arabian crude oil and No. 2 fuel oil significantly reduced the emergence of new stems while increasing the germination of seedlings. The decomposition of S. alterniflora was not affected significantly through the first eight months after oil application.