Irving A. Mendelssohn

Oxygen Deficiency in Spartina alterniflora Roots: Metabolic Adaptation to Anoxia

The aerenchyma (air-space) tissue in the wetland macrophyte Spartina alterniflora conveys sufficient oxygen to roots for predominately aerobic respiration in moderately, but not highly, reduced substrates. Continuously flooded plants survive by respiring anaerobically, although growth is decreased. Two metabolic adaptations to flooding are displayed in this species, depending on the degree of soil reduction.

Drought, Snails, and Large-Scale Die-Off of Southern U.S. Salt Marshes

Salt marshes in the southeastern United States have recently experienced massive die-off, one of many examples of widespread degradation in marine and coastal ecosystems. Although intense drought is thought to be the primary cause of this die-off, we found snail grazing to be a major contributing factor. Survey of marsh die-off areas in three states revealed high-density fronts of snails on die-off edges at 11 of 12 sites. Exclusion experiments demonstrated that snails actively converted marshes to exposed mudflats. Salt addition and comparative field studies suggest that drought-induced stress and grazers acted synergistically and to varying degrees to cause initial plant death. After these disturbances, snail fronts formed on die-off edges and subsequently propagated through healthy marsh, leading to cascading vegetation loss. These results, combined with model analyses, reveal strong interactions between increasing climatic stress and grazer pressure, both potentially related to human environmental impacts, which amplify the likelihood and intensity of runaway collapse in these coastal systems.

SPARTINA ALTERNIFLORA DIE-BACK IN LOUISIANA: TIME-COURSE INVESTIGATION OF SOIL WATERLOGGING EFFECTS

SUMMARY (1) Transplantation of streamside Spartina alterniflora swards into the more waterlogged and less productive inland marsh caused rapid decreases in soil redox potential and increases in interstitial water sulphide and NH4 concentrations and root alcohol dehydrogenase activity. (2) One year later, standing crops in these transplanted swards were significantly reduced compared to their streamside controls. (3) Reciprocal transplantation from inland to streamside resulted in the amelioration of the detrimental conditions associated with the waterlogged inland marsh and in an increase in standing crop to levels equivalent to streamside controls. (4) Soil salinity and pH were not significant factors in causing reduced growth of S. alterniflora. (5) Sulphide toxicity, in combination with extended periods of anaerobic metabolism in the roots, appeared to be a major factor associated with reduced growth of S. alterniflora and may be a cause of dieback in these marshes.

Response of a freshwater marsh plant community to increased salinity and increased water level

Abstract Field and greenhouse experiments in which salinity and elevation were manipulated demonstrated that the response of freshwater marshes to saltwater intrusion may be variable and dependent upon a number of factors including: species composition; level, duration, and abruptness of exposure to saline water; flooding depth; a source of propagules of more salt-tolerant species. In the field, saltwater intrusion was simulated by transplanting swards of a freshwater marsh to a higher salinity area. The three dominant species, Panicum hemitomon Schultes, Leersia oryzoides (L.) Swartz, and Sagittaria lancifolia L., succumbed to the sudden increase in salinity to 15%. However, the denuded plots were rapidly invaded by more salt-tolerant species that were present in the higher salinity marsh. Although growth was reduced, Panicum hemitomon and Leersia oryzoides were relatively tolerant of salinities up to 9.4% for at least 1 month in the greenhouse. Sagittaria lancifolia was less tolerant of salinity increases and showed symptoms of tissue damage at 4.8%. A decrease in elevation, which resulted in an increase in mean water level and a more reduced soil environment, caused a significant decrease in live above-ground biomass and stem density in the experimental field plots.

Oil Impacts on Coastal Wetlands: Implications for the Mississippi River Delta Ecosystem after the Deepwater Horizon Oil Spill

On 20 April 2010, the Deepwater Horizon explosion, which released a US government—estimated 4.9 million barrels of crude oil into the Gulf of Mexico, was responsible for the death of 11 oil workers and, possibly, for an environmental disaster unparalleled in US history. For 87 consecutive days, the Macondo well continuously released crude oil into the Gulf of Mexico. Many kilometers of shoreline in the northern Gulf of Mexico were affected, including the fragile and ecologically important wetlands of Louisianas Mississippi River Delta ecosystem. These wetlands are responsible for a third of the nations fish production and, ironically, help to protect an energy infrastructure that provides a third of the nations oil and gas supply. Here, we provide a basic overview of the chemistry and biology of oil spills in coastal wetlands and an assessment of the potential and realized effects on the ecological condition of the Mississippi River Delta and its associated flora and fauna.

The combined effects of phytoremediation and biostimulation in enhancing habitat restoration and oil degradation of petroleum contaminated wetlands

Abstract The combined effects of biostimulation and phytoremediation as a means of post-oil spill habitat restoration and enhancement of oil degradation in the soil were evaluated. Marsh sods of Spartina alterniflora and Spartina patens were dosed with 0, 4, 8, 16 and 24 l m −2 of south Louisiana crude oil in the greenhouse. Plants were killed at oil dosages of 8 l m −2 in the growing season following oil application. Two years after application of the oil, S. alterniflora and S. patens individuals were transplanted into the oiled and unoiled sods. Fertilizer was applied 1 and 7 months after transplantation. Application of the fertilizer significantly increased biomass of the transplants within 6 months and regrowth biomass of the transplants 1 year after transplantation for both plant species. The residual oil in the soil did not significantly affect the biomass of the S. patens transplants compared with that in the no oil treatment, except at the highest oil level. However, regrowth biomass of the S. alterniflora transplants treated with fertilizer was significantly higher at all oil levels up to 250 mg g −1 than in the unoiled treatment, with or without fertilizer. The oil degradation rate in the soil was significantly enhanced by the application of fertilizer in conjunction with the presence of transplants. These results suggest that vegetative transplantation, when implemented with fertilization, can simultaneously restore oil contaminated wetlands and accelerate oil degradation in the soil.

Eco-Physiological Controls on the Productivity of Spartina Alterniflora Loisel

The intertidal salt marshes of the Atlantic and Gulf coasts of the United States are dominated by the perennial grass, Spartina alterniflora Loisel. The ecology of salt marshes in which this species dominates has been extensively investigated because of the documented biogeochemical functions that these ecosystems perform and the resulting societal values they provide. Since many of the salt marsh-derived values originate, either directly or indirectly, from the presence of a vegetated marsh and its primary productivity, it has long been a major goal of salt marsh ecology to elucidate the determinants of the growth of Spartina. This paper reviews the interaction of the abiotic environment with key eco-physiological processes controlling the growth of this important plant species. The productivity of Spartina can vary on both spatial and temporal scales. Spatial differences in productivity on a local scale are primarily determined by abiotic factors, particularly the interaction of soil anoxia, soluble sulfide, and salinity, with plant nitrogen uptake and assimilation. Also, Spartina can induce a positive feedback on productivity by enhancing substrate aeration. The growth enhancing effects of marsh infauna, e.g., fiddler crabs, are mediated through these interacting abiotic variables. Productivity differences on regional scales are largely dependent on geographical differences in climate, tidal amplitude, and soil parent material. Temporal variation results from seasonal and annual variation in climatic and tidal controls that may influence marsh salinity and/or inundation. The concerted research of a large number of scientists has provided one of the most comprehensive and ecologically-relevant analyses of determinants of the primary productivity of any nonagricultural plant species.

Factors controlling the formation of oxidized root channels: A review

Although root plaques and associated oxidized root channels are used for wetland identification as field indicators of wetland, hydrology, little information is available concerning their reliability as related to the environmental and biotic factors controlling their formation. Therefore, this review describes and evaluates the current state of knowledge of the factors controlling the formation of iron plaques and recommends research to address information gaps.Both abiotic and biotic factors control the presence and degree of iron plaque formation. The most important abiotic factor is the availability of soil iron. However, the effect of site variation in soil physico-chemical characteristics (e.g., texture, organic matter, pH, Eh, and soil fertility), on iron availability and microbial activity can influence the formation and persistence of root plaques and oxidized root channels. Although the oxidizing capacity of the plant root is the most important biotic factor controlling plaque formation, only a limited number of wetland species have been evaluated for this ability, so species-specific differences are generally unknown.Unlike some of the other hydrologic indicators used in wetland delineation (e.g., water marks on trees or sediment deposits) root plaques and oxidized root channels indicate soil saturation for a sufficient period to produce anaerobic soil conditions. Additionally, when found in conjunction with a living root, oxidized root channels indicate that the anaerobic conditions occurred within the life span of the plant root. Therefore, the presence of oxidized root channels and iron plaque surrounding living roots is a relatively good indicator of current wetland hydrologic conditions. However, research is needed to elucidate the relative abilities of different plant species to produce oxidized root channels, the temporal persistence of the root iron plaque and the role that soil physico-chemical condition plays in controlling plaque formation. Without a better understanding of the controls on iron plaque formation and disappearance, the absence of oxidized root channels, in itself, should not be used to indicate the absence of a wetland.

NITROGEN METABOLISM IN THE HEIGHT FORMS OF SPARTINA ALTERNIFLORA IN NORTH CAROLINA

Selected aspects of the nitrogen nutrition of salt marsh cordgrass, Spartina alterni- flora, were investigated in Oak Island Marsh, North Carolina, USA. Nitrate was of minor importance as a nitrogen source for Spartina in this marsh as indicated by low soil interstitial water nitrate concentrations and low plant tissue nitrate concentrations and nitrate reductase activities. However, Spartina did have the capability of assimilating nitrate nitrogen when available. Interstitial water and plant tissue ammonium concentrations were 1-2 orders of magnitude > that for nitrate which strongly indicated that ammonium was the dominant inorganic nitrogen source. Leaf and root nitrogen con- stituents (total nitrogen, soluble nitrogen, ammonium, and nitrate) and nitrogen metabolism measured via glutamate dehydrogenase activity indicated that the nitrogen status of the short height form of Spartina was deficient relative to that of the tall form.

Impacts and Recovery of the Deepwater Horizon Oil Spill on Vegetation Structure and Function of Coastal Salt Marshes in the Northern Gulf of Mexico

We investigated the impacts of the Deepwater Horizon (DWH) oil spill on two dominant coastal saltmarsh plants, Spartina alterniflora and Juncus roemerianus, in the northern Gulf of Mexico and the processes controlling differential species-effects and recovery. Seven months after the Macondo MC 252 oil made landfall along the shoreline salt marshes of northern Barataria Bay, Louisiana, concentrations of total petroleum hydrocarbons in the surface 2 cm of heavily oiled marsh soils were as high as 510 mg g(-1). Heavy oiling caused almost complete mortality of both species. However, moderate oiling impacted Spartina less severely than Juncus and, relative to the reference marshes, had no significant effect on Spartina while significantly lowering live aboveground biomass and stem density of Juncus. A greenhouse mesocosm study supported field results and indicated that S. alterniflora was much more tolerant to shoot oil coverage than J. roemerianus. Spartina recovered from as much as 100% oil coverage of shoots in 7 months; however, Juncus recovered to a much lesser extent. Soil-oiling significantly affected both species. Severe impacts of the Macondo oil to coastal marsh vegetation most likely resulted from oil exposure of the shoots and oil contact on/in the marsh soil, as well as repeated oiling events.