I would like to recognize my co authors on this program Irv - - PDF document

I would like to recognize my co‐authors on this program – Irv Mendelssohn, Qianxin Lin, Aixin Hou, and John Fleeger from Louisiana State University studying different aspects of this program. Stefan Bourgoin from Atkins has been my partner on the study of the macroinvertebrate communities. 1

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As a team, we are studying the plant‐microbial‐benthic ecosystem of the marsh edge and the impact of the oil spill on that system. This system is responsible for building the marsh surface elevation and controlling oil degradation, surface erosion, soil nutrient cycling, and is the base of the marsh food chain, both grazing and detrital. An oil spill can upset this balance and exacerbate wetland loss. There are several studies on the initial impacts of this and other spills on coastal wetlands; however there is little information on the long‐term impacts and recovery of these systems. We began this particular study 30 months after the Deepwater Horizon Oil Spill (November 2012). There was evidence of the spill still obvious at the heavily oiled stations with bare marsh sediment platforms and residual oil crust. The vegetation is beginning to visually recover. The overall goals of this program are to (1) document longer‐term impacts of the oil spill on the plant‐microbial‐benthic system; (2) quantify rates of, and controls on, the system recovery; and (3) evaluate the effectiveness of remediation techniques for accelerating recovery and long‐term sustainability of the system. 3

Initially, the program has included the continued sampling of 21 stations; 7 each representing various oiling levels based upon SCAT data, field observations, and initial Total Petroleum Hydrocarbon (TPH) sampling data from the sites. The sampling has occurred from November 2012 to October 2014 at intervals of 30, 36, 41, 43, 48 and 54 months after spill. Qianxin Lin and his team has been responsible for collecting TPH samples, aboveground biomass and stem density (total, live, dead) for Spartina alterniflora, and Juncus roemerianus, belowground Biomass (total at 0 – 6cm and 6 – 12cm). They are also responsible the soil parameters – soil shear strength and soil accretion. Plant Parameters Aboveground Biomass and Stem Density (Total, Live, Dead, Spartina, and Juncus) Belowground Biomass (Total, 0 – 6cm, 6 – 12cm) Soil Parameters Soil Shear Strength Soil Accretion Organisms Soil Bacteria Benthic Microalgae Benthic Meiofauna Macroinvertebrates (Uca spp. and Littoraria irrorata) Aixin Hou has been analyzing the soil bacteria. John Fleeger has been working on the benthic microalgae and benthic meiofauna. Stefan Bourgoin and I have responsible for collecting and analyzing data on the fiddler crab (Uca spp.) and periwinkle snail (Littoraria irrorata).

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The field study was carried out in coastal salt marshes in and around Bay Jimmy in northern Barataria Bay, Louisiana, one of the most severely oiled coastal marsh regions, covering a sampling area of about 8 km x 5 km. Seven field stations (replicates) were randomly selected from a larger population that received heavy, moderate and reference (non‐oiled) marshes based on SCAT data and earlier field observations, resulting in a total of 21 field stations. These stations were established in early January 2011, about 7 months after the oil spill. Surface oil samples were collected and analyzed for TPH. Plant above ground biomass (live and dead) and stem density were analyzed. Lin et al. (2012 and in press) contains early data and analysis from these stations 7, 9, 18, and 24 months after the spill. Fleeger et.al. (in press) contains early data at these stations on the benthic microalgae and benthic meiofauna 18 and 24 months after the oil spill. 5

Our sampling focused on two sentinel macroinvertebrate specie groups in the marsh – fiddler crabs, Uca spp. and the marsh periwinkle (Littoraria irrorata). Fiddler crabs are one of the most abundant and conspicuous macroinvertebrates in most salt marshes making them an appropriate organism to study relative to marsh faunal injury. They are one of the most thoroughly studied shore crab in North America. Fiddler crab literature is quite robust, examining individual species population dynamics, life history and ecology. Fiddler crabs greatly influence the marsh through burrowing and feeding activities, e.g. enhancing effects on vegetation productivity and biomass, sediment and nutrient characteristics, biogeochemical cycles, microbial processes by aerating the marsh sediment, increasing soil drainage, and facilitating nutrient

• transport. Generally, the presence of fiddler crabs has been noted as indicating greater diversity of other marsh
• rganisms and crab population densities can reflect the productivity of a wetland. Fiddler crabs have been shown to

be sensitive to oil spills making them a valuable environmental indicator. Fiddler crab burrowing can also influence oil behavior. The burrows can serve as a source of secondary porosity, allowing oil to penetrate marsh sediments, in some cases leading to longer term sediment contamination. As indicated, they can influence sediment aeration and flooding, enhancing the degradation of oil in the sediment. Oil degradation and soil stability could also be enhanced indirectly where crab burrowing increases plant productivity and above and below ground biomass. Various fiddler crab species inhabit the northern Gulf of Mexico coast. Two species, in particular, are found in the Louisiana marshes. Uca spinicarpa prefers clayey substrates in brackish marshes ranging from nearly fresh to

• hypersaline. Uca longisignalis is restricted to sediments of terrigeneous origin ((i.e. mucky soils) and found primarily

in lower salinity (upper estuaries). The two species can be found in close proximity but have preferred habitats based

• n elevation, vegetation and sediment character.

The marsh periwinkle is also a common and conspicuous organisms in coastal salt marshes and is also an indicator species of the health of the salt marsh habitat. The most abundant periwinkle in the salt marshes of Louisiana is Littoraria irrorata . In areas dominated by short to intermediate form Spartina alterniflora, the species has been noted to occur in densities of at least 100 individuals/m2. Periwinkles are rasping detritivore/herbivore specialists, feeding on organic matter on the marsh surface during low tide and ascending the Spartina stems to feed upon standing‐dead Spartina and its associated microbial assemblages. As a detritivore, L. irrorata influences nutrient dynamics by expediting the decomposition of Spartina alterniflora and serves as an important link between primary and secondary The presence of Spartina alterniflora is directly liked to increased abundance, growth and survival of

• L. irrorata in “natural” marshes.

Both fiddler crabs and marsh periwinkles can be severely impacted by oil spills, including direct mortality, reduced population densities, and sublethal effects. Recovery time following impacts for these organisms can vary substantially based on a variety of oiling and habitat conditions, from a year to several decades.

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We are going to look at this data more closely, but in general, we have not seen a lot of difference in the fiddler crab burrow density between the treatments over time. The fiddler crabs tend to burrow in open areas within the marsh and, once the oil crust begins to dissipate in the nearshore area, the fiddler crabs will burrow in those areas. There was a short term shift in Uca species noted by Zengel et al. (2014) with Uca spinicarpa occupying some oiled areas in his study area. When we started our studies 30 months after the spill, all species collected have been Uca longisignalis. Note that the average number of burrows per m2 is low, 10 and less. 7

This is data 6 months after the spill (October 2012) representing early impact data. Note that the crab burrow density is low (10 or so per m2). This is approximately the same level that we are seeing in our study (10 or less burrows per m2). These data were collected at 3 sites approximately 3 m from the shoreline. 8

Another set of early samples. These stations were located 1‐2 meter behind the oiled zone, so they represent areas deeper into the marsh where burrow density is typically

• higher. These were also in areas of “apparently healthy” vegetation. And a very light

substrate oiling (sheen). This study shows early impacts at minimal oiling levels. McCall and Pennings (2012) sampled a wider geographic area than Silliman (2012). This may have been part of the reason for the higher burrow density. Mouton and Felder (1996) noted the variation in density of U. longisignalis along a 15‐m transect. The burrow density was lowest near the water’s edge and highest in the middle to middle‐ upper reaches of the transect. No marked change in elevation was noted beyond about 3 m from the water’s edge. 9

This study provides data on burrow densities after the spill in a period between the Silliman et al. (2012) study and our study. This study found that there were difference in burrow density in the first year with no treatment, but no differences between the treated areas and the reference. No differences were found with any of the areas in Year

• 2. So it is not surprising that we do not find differences starting at 30 months after the
• spill. Note that these burrow density are slightly higher, but in the range of those that

we are finding at our study sites. 10

This is a continuation of the study by Zengel et al. (2013) in Area K, a marsh island located south of our study sites. Again, note that the burrow densities are variable from year‐to‐year when compared to the data from the previous slide but are similar to our study at the reference site. This study area was heavily oiled and the site of experimental marsh treatment methods. The data show the influence of oiling in the marsh, but also the benefit of planting in the recovery of the marsh fauna. 11

This graph is used to just show the differences in the average densities in Littoraria irrorata between the stations representing the oiling levels. We have found greater densities at the moderately oiled stations. The lower density at the reference stations could be due to difference in vegetation, location, setting, and possibly salinity. These confounding factors may be affecting the reference sites and making them a less than

• ptimal habitat for Littoraria . Lin et al., reporting on the vegetation in this study, found

that the live aboveground biomass and stem density of Spartina generally recovered within 9 months after the spill at the moderately oiled sites. Fleeger et al, reporting on the sediment surface microalgae and meiofauna recovery was coupled with the recovery

• f Spartina. Both of these studies report recovery at the moderately oiled sites within 2

years after the spill. Our study of the Littoraria population began 30 months (2+ years) after the spill. Certainly, we are capturing the moderately oiled stations on the path to recovery. Stagg and Mendelssohn (2012) in a study of marshes restored using sediment from dredging operations found that Littoraria growth, survival, and productivity were positively correlated to increasing Spartina canopy cover. Restoration of Spartina productivity is “imperative” for the successful restoration of Littoraria individual and population health. As the aboveground biomass and stem density of Spartina increases, the Littoraria population will increase. 12

This graphic leads into the discussion on the population dynamics of Littoraria and how it was affected by oiling levels. Using all of the data, the heavily oiled sites have a smaller shell length compared to the reference and the moderately oiled sites. This indicates that the Littoraria population at the heavily oiled sites was affected by the spill by the removal of a portion of that population and has been in a re‐growth stage. That is, as the Spartina returns to the heavily oiled stations, juvenile snails can begin to repopulate. 13

The numbers of snails at the heavily oiled stations are in less numbers and smaller through the study. Even at 41 month after sampling, the heavily oiled stations have a very small adult population and are just showing a subadult group entering the population (in the sampling periods before this time, the numbers in all sizes was small and the patterns erratic). At 43 months, the heavily oiled stations are beginning to show a small adult population. Note that through these periods the reference and moderately

• iled stations have populations with typical seasonal bimodal subadult and adult
• patterns. The difference being that the reference station has a smaller number of

individuals. 14

As we move into the sampling from last year at 48 and 54 months after the spill. The patterns are more similar, but the heavily oiled stations still have slightly smaller individuals when compared to the reference and moderately oiled stations. The reference and heavily oiled stations have less individuals than the moderately oiled stations. 15

This is data 6 months after the spill (October 2012) representing early impact data. This represents some of the first data collected after the spill, nearest to the oil coming onto the shoreline. A definite impact with 0 snails per m2 vs. 50 per m2. These data were collected at 3 sites approximately 3 m from the shoreline. 16

It is not surprising that McCall and Pennings (2012) did not find a difference in Littoraria density between oiled and control sites. These stations were located 1‐2 meter behind the oiled zone in areas of “apparently healthy” vegetation and a very light substrate

• iling (sheen).

This study shows early impacts at minimal oiling levels. 17

This study provides data on burrow densities after the spill in a period between the Silliman et al. (2012) study and our study. Obvious density impacts in 2011 and 2012 and it could be argued that there was lower density even at the reference stations. The shell length frequency data from 2012 shows very good recruitment at the reference stations and little to no recovery at the treatment stations. 18

This study on Are K south of our study sites shows continuing impacts and lack of recovery 3+ years after the spill. In this study, the vegetation has not recovered in either the oiled control sites or the mechanical treatment without planting. Again, the recovery of the Littoraria population is defined by the vegetation cover and species composition (especially Spartina) . Planting has begun the recovery process. At this sampling period, the planted sites had similar Spartina cover as the reference sites. There is a positive influence of planting, but there is a lag‐time for the recovery of the Littoraria population. The planted stations are similar in population pattern to the heavily oiled stations in our study. 19

This is the Littoraria total abundance data from the study periods. The study periods varied in difference with the heavily oiled stations with definite difference from the reference and moderately oiled stations at 36 months. At 40 months, the moderately

• iled population begins to become significantly greater than the reference or the heavily
• iled sites. That pattern is resumed at 48 months and is generally occurring at 54

months. 20

This figure better illustrates the trends in the data with the moderately oiled stations showing a growing population with seasonal trends. At 36 months (Spring 2013), the population begins a growth pattern that reduces slightly in the winter months (40 and 42 months after the spill) and continues growth again the next spring at 48 months (April 2014). The slightly lower population numbers in the winter (54 months) is expected. Recovery is anticipated when the population generally levels off into a spring (rise) to fall (lower) pattern. The reference stations are still somewhat depressed in population in year 3 (36 months) and seem to be continuing to grow at 54 months. The heavily oiled stations had low population numbers through 40 months after the spill and have begun to grow after that. All of these stations could have (and most probably were) affected by oil in the water during egg release and larval return for at least one year (while oil was on the water) and more probably two years. 21

I have the total petroleum hydrocarbon data through 42 months. There was still some petroleum on the moderately oiled station at 36 months possibly affecting the snail population. 22

Total live aboveground biomass remains significantly lower than the reference or heavily

• iled stations through 48 months, generally reflecting the Littoraria total abundance at

hose oiling levels. 23

The same is true for the total dead aboveground biomass data. 24

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