Geology topics

Tracy Elsey-Quirk

Publications and source records attributed to Tracy Elsey-Quirk.

4 recordsLinked to original sources

USGS2023

Elevated temperature and nutrients lead to increased N2O emissions from salt marsh soils from cold and warm climates

Salt marshes can attenuate nutrient pollution and store large amounts of ‘blue carbon’ in their soils, however, the value of sequestered carbon may be partially offset by nitrous oxide (N 2 O) emissions. Global climate and land use changes result in higher temperatures and inputs of reactive nitrogen (Nr) into coastal zones. Here, we investigated the combined effects of elevated temperature (ambient + 5℃) and Nr (double ambient concentrations) on nitrogen processing in marsh soils from two climatic regions (Quebec, Canada and Louisiana, U.S.) with two vegetation types, Sporobolus alterniflorus (= Spartina alterniflora ) and Sporobolus pumilus (= Spartina patens ), using 24-h laboratory incubation experiments. Potential N 2 O fluxes increased from minor sinks to major sources following elevated treatments across all four marsh sites. One day of potential N 2 O emissions under elevated treatments (representing either long-term sea surface warming or short-term ocean heatwaves effects on coastal marsh soil temperatures alongside pulses of N loading) offset 15–60% of the potential annual ambient N 2 O sink, depending on marsh site and vegetation type. Rates of potential denitrification were generally higher in high latitude than in low latitude marsh soils under ambient treatments, with low ratios of N 2 O:N 2 indicating complete denitrification in high latitude marsh soils. Under elevated temperature and Nr treatments, potential denitrification was lower in high latitude soil but higher in low latitude soil as compared to ambient conditions, with incomplete denitrification observed except in Louisiana S. pumilus . Overall, our findings suggest that a combined increase in temperature and Nr has the potential to reduce salt marsh greenhouse gas (GHG) sinks under future global change scenarios.

Biogeochemistry↗

USGS2022

Porewater chemistry of Louisiana marshes with contrasting salinities and its implications for coastal acidification

Dissolved inorganic carbon (DIC) and total alkalinity (TA) are fundamental components of carbonate systems that control pH and buffering capacity of the receiving water body. Three coastal marshes with contrasting salinities in Barataria Basin, Louisiana, USA, were sampled to understand seasonal changes in porewater carbonate chemistry and its impact on surrounding water bodies. Each marsh was sampled five times between December 2018 and October 2019. Porewater DIC and TA increased with depth irrespective of marsh type and ranged from 4.47 to 31.61 mmol/kg and from 1.78 to 28.56 mmol/kg, respectively. The salt marsh had higher porewater DIC and TA compared to the lower salinity intermediate and brackish marshes, probably due to sulfate reduction in the salt marsh. However, it is likely that denitrification is the dominant anaerobic process in these marshes because of low porewater TA/DIC ratios in all three marshes. Porewater TA and DIC concentrations were generally higher during warmer months than colder months. However, the marsh flooding regime had a profound influence on TA and DIC concentrations by changing the redox potential of the marsh soil. Porewater TA/DIC ratios in all three marshes were generally less than 1, while surface water TA/DIC ratios were around 1, suggesting that export of DIC and TA from coastal marshes have the potential to contribute to coastal acidification.

Louisiana↗

USGS2019

Understanding tidal marsh trajectories: Evaluation of multiple indicators of marsh persistence

Robust assessments of ecosystem stability are critical for informing conservation and management decisions. Tidal marsh ecosystems provide vital services, yet are globally threatened by anthropogenic alterations to physical and biological processes. A variety of monitoring and modeling approaches have been undertaken to determine which tidal marshes are likely to persist into the future. Here, we conduct the most robust comparison of marsh metrics to date, building on two foundational studies that had previously and independently developed metrics for marsh condition. We characterized pairs of marshes with contrasting trajectories (of marsh cover ) across six regions of the United States, using a combination of remote-sensing and field-based metrics. We also quantified decadal trends in marsh conversion to mudflat/open water at these twelve marshes. Our results suggest that metrics quantifying the distribution of vegetation across an elevational gradient represent the best indicators of marsh trajectories. The unvegetated to vegetated ratio and flood-ebb sediment differential also served as valuable indicators. No single metric universally predicted marsh trajectories, and therefore a more robust approach includes a suite of spatially integrated, landscape-scale metrics that are mostly obtainable from remote sensing. Data from surface elevation tables and marker horizons revealed that degrading marshes can have higher rates of vertical accretion and elevation gain than more intact counterparts, likely due to longer inundation times potentially combined with internal recycling of material. A high rate of elevation gain relative to local sea-level rise has been considered critical to marsh persistence, but our results suggest that it also may serve as a signature of degradation in marshes that have already begun to deteriorate. This investigation, with rigorous comparison and integration of metrics initially developed independently, tested at a broad geographic scale, provides a model for collaborative science to develop management tools for improving conservation outcomes.

Environmental Research Letters↗

USGS2019

Mississippi river sediment diversions and coastal wetland sustainability: Synthesis of responses to freshwater, sediment, and nutrient inputs

Management and restoration of coastal wetlands require insight into how inundation, salinity, and the availability of mineral sediment and nutrients interact to influence ecosystem functions that control sustainability. The Mississippi River Delta, which ranks among the world's largest and most productive coastal wetland complexes, has experienced extensive deterioration over the last century due, in large part, to enhanced vulnerability to relative sea-level rise and lateral erosion caused by a combination of natural processes and anthropogenic modifications of hydrology. This land loss crisis has prompted the State of Louisiana to develop a comprehensive restoration plan that includes constructing and implementing a series of large-scale sediment diversions that will reconnect sediment- and nutrient-rich Mississippi River water to adjacent bays, estuaries, and wetlands. Sediment loading through diversions is predicted to enhance the long-term sustainability of coastal wetlands; however, the additive effects of increased inundation, abrubt changes in the salinity regime, and high nutrient loads on wetland plant growth and organic matter (SOM) decomposition rates, which help regulate accretion and elevation change, is uncertain. Therefore, this review attempts to synthesize existing information to inform predictions of the interactive effects of diversions on these drivers of coastal wetland sustainability. The data suggest that sediment deposition within an optimal elevation range will increase the overall productivity of existing wetlands where prolonged flooding does not counter this effect by limiting plant growth. A reduction in salinity may increase plant productivity and cause vegetation shifts to less salt tolerant species, but seasonal swings in salinity may have unforeseen consequences. Nutrient-loading is predicted to lead to greater aboveground productivity, which, in turn, can facilitate additional sediment trapping; however, belowground productivity may decline, particularly in areas where sediment deposition is limited. In areas experiencing net deposition, nutrient-enrichment is predicted to enhance belowground growth into new sediment and contribute to positive effects on soil organic matter accumulation, accretion, and elevation change. Thus, we contend that sediment input is essential for limiting the negative effects of flooding and nutrient-enrichment on wetland processes. These conclusions are generally supported by the biophysical feedbacks occurring in existing prograding deltas of the Mississippi River Delta complex.

Louisiana↗