Determining tolerance limits for restoration and phytoremediation with Spartina patens in crude oil-contaminated sediment in greenhouse

Oil spills may detrimentally damage sensitive coastal habitats, such as coastal wetlands. Successful restoration of oiled habitats primarily depends on the tolerance of vegetation transplants to oil. In this study, tolerance limits of the dominant coastal brackish marsh plant Spartina patens to South Louisiana crude (SLC) oil and its phytoremediation effectiveness on petroleum hydrocarbons in wetland sediments were investigated in the greenhouse environment. Spartina patens was transplanted into brackish marsh sediments contaminated with SLC oil at concentrations of 0, 40, 80, 160, 320, 640 and 800 mg SLC oil g^?1 dry sediment. High oil concentrations adversely affected plant stem density, aboveground biomass and belowground biomass even one year after transplantation. At the 320 mg g^?1 oil dosage, plant belowground biomass was significantly lower than the control although aboveground variables were not significantly different from the control. All plant parameters mentioned above at the 640 mg g^?1 oil dosage were less than 50% of the control. Spartina patens did not survive the 800 mg g^?1 oil dosage. The tolerance limit of S. patens to SLC was estimated about 320 mg oil g^?1 dry sediment. In addition, S. patens transplants enhanced oil degradation in the sediment; concentrations of residual total petroleum hydrocarbons (TPH) in the sediments vegetated by S. patens were significantly lower than those of un-vegetated sediments for both the surface and subsurface sediment at the 40 and 160 mg g^?1 SLC oil dosages. Decreases in the concentrations of polycyclic aromatic hydrocarbons (PAHs) further demonstrated the capacity of S. patens to phytoremediate residual oil; residual total targeted PAHs in the phytoremediation treatment were less than 20% of the un-vegetated treatment at the 40 mg g^?1 oil dosage. These results demonstrated the potential of phytoremediation with S. patens to simultaneously restore and remediate petroleum-contaminated coastal marsh habitats.     

Effects of tidal inundation and predation on Avicennia germinans seedling establishment and survival in a sub-tropical mangal/salt marsh community

The black mangrove, Avicennia germinans, occurs sympatric withSpartina alterniflora in coastal Louisiana. Zonation exists alongan elevational gradient with A. germinans dominant at higherelevation creekbanks and S. alterniflora at interior, lowerelevation sites with greater depth and duration of flooding.Establishment of A. germinans seedlings was examined in cagesthat excluded predators and limited horizontal, but not vertical,movement of propagules by the tides and showed that blackmangrove could readily establish in the Spartina zone. Survivalof A. germinans seedlings after one year in cages was notsignificantly different between the two zones, and seedlings weresignificantly taller in the Spartina zone. Thus, neitherinundation per se nor other abiotic factors alone could accountfor the absence of A. germinans in the interior marsh. Althoughpropagules were dispersed into both zones, a net removal ofuncaged propagules from plots in the Spartina zone (–1.3 ± 0.6m^-2 d^-1) compared to a net addition to plots in the Avicennia zone (+0.5 ± 0.4 m^-2d^-1) indicated that retention of propagulesdiffered between zones. Causes of mortality were decay (Spartina> Avicennia zone), desiccation (Avicennia > Spartina zone), andpredation (Spartina > Avicennia zone). Although few propaguleswere completely consumed by predators (snails and crabs), damageto the cotyledons promoted decay. The results suggest that tidalaction limits retention and settlement of A. germinans propagulesin the Spartina zone, and a combination of predator damage andfrequent flooding leads to rapid decay of propagules that strandthere.     

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.     

Mass mortality of birds of prey caused by Azodrin,an organophosphorus insecticide

Mass increases of the levant vole (Microtus guentheri) are common in alfalfa fields in Israel. Deep ploughing, which is the main factor controlling vole numbers in other agricultural areas, is not possible in alfalfa. As alfalfa is a preferred food, voles in these fields are not attracted to poison baits and cannot be controlled by this means.A particularly striking increase of voles developed during the winter of 1975–1976 on 8 km² of alfalfa fields in the northern Huleh Valley in Israel. This mass increase attracted large numbers of raptors and owls, mainly those wintering and on migration, but also resident species.Because the voles, which reached densities of 2400/ha, caused considerable damage to the alfalfa crop, destroying it completely in some places, the farmers sprayed the fields with Azodrin (Monocrotophos). This persistent insecticide is recommended in Israel only for the control of pests on cotton and in orchards. The dangers to wildlife described on the original label do not appear in the Hebrew translation.Due to secondary poisoning with Azodrin there was a mass mortality of raptors and owls that had fed on poisoned voles and birds on these 8 km². 116 raptors and 29 owls were found dead during December 1975 through February 1976; 53 raptors and 16 owls were found poisoned but still alive, and were saved and later released. According to repeated counts of the black kite (Milvus migrans) population in the area it was estimated that about twice as many birds as those found were affected. Since it is probable that no poisoned birds could recover in the field, about 400 birds of prey had been destroyed on 8 km² within three months.     

Mid-latitude wind stress: the energy source for climatic shifts in the North Pacific Ocean

Analyses of atmospheric observations in the North Pacific demonstrate extensive decadal-scale variations in the mid-latitude winter surface wind stress. In the decade after 1976 winter, eastward wind stress doubled over a broad area in the central North Pacific and the winter zero wind stress curl line was displaced about 6° southward. This resulted in increased southward Ekman transport, increased oceanic upwelling, and increased turbulent mixing as well as a southward expansion of the area of surface divergence. All these factors contributed to a decadal winter cold anomaly along the subtropical side of the North Pacific Current. In summer the cold anomaly extended eastward, almost reaching the coast of Oregon. The increased gradient in wind stress curl and southward displacement of the zero curl line also resulted in an increase in total North Pacific Current transport, primarily on the Equator side of this Current. Thus, surface water entering the California Current was of more subtropical origin in the post-1976 decade. Southward (upwelling favourable) wind stress and sea surface temperature (SST) in the area off San Francisco exhibit at least three different types of decadal departures from mean conditions. In association with the 1976 climatic shift, marine fishery production in the Oyashio, California and Alaska Currents altered dramatically, suggesting that these natural environmental variations significantly alter the long-term yields of major North Pacific fisheries.     

The whooping crane (Grus americana) population of North America

A model of the whooping crane population of North America shows that its rate of increase has been the result of a stabilized death rate, in spite of an overall decrease in the birth rate and no significant increase in the breeding population. Projections—based on current trends—predict a total population of about 76 individuals in 10 years and 114 in 20 years, with a doubling time of approximately 18 years, but these projections will have to be revised downward if the birth rate continues to decline, or if the carrying capacity of the wintering grounds becomes limiting.     

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.