Geology topics

Brian C. Perez

Publications and source records attributed to Brian C. Perez.

5 recordsLinked to original sources

USGS2016

Component greenhouse gas fluxes and radiative balance from two deltaic marshes in Louisiana: Pairing chamber techniques and eddy covariance

Coastal marshes take up atmospheric CO 2 while emitting CO 2 , CH 4 , and N 2 O. This ability to sequester carbon (C) is much greater for wetlands on a per-area basis than from most ecosystems, facilitating scientific, political, and economic interest in their value as greenhouse gas sinks. However, the greenhouse gas balance of Gulf of Mexico wetlands is particularly understudied. We describe the net ecosystem exchange (NEE c ) of CO 2 and CH 4 using eddy covariance (EC) in comparison with fluxes of CO 2 , CH 4 , and N 2 O using chambers from brackish and freshwater marshes in Louisiana, USA. From EC, we found that 182 g C m -2 y -1 was lost through NEE c from the brackish marsh. Of this, 11 g C m -2 y -1 resulted from net CH 4 emissions and the remaining 171 g C m -2 y -1 resulted from net CO 2 emissions. In contrast, -290 g C m 2 y -1 was taken up through NEE c by the freshwater marsh, with 47 g C m -2 y -1 emitted as CH 4 and -337 g C m -2 y -1 taken up as CO 2 . From chambers, we discovered that neither site had large fluxes of N 2 O. Sustained-flux greenhouse gas accounting metrics indicated that both marshes had a positive (warming) radiative balance, with the brackish marsh having a substantially greater warming effect than the freshwater marsh. That net respiratory emissions of CO 2 and CH 4 as estimated through chamber techniques were 2-4 times different from emissions estimated through EC requires additional understanding of the artifacts created by different spatial and temporal sampling footprints between techniques.

Journal of Geophysical Research: Biogeosciences↗

USGS2016

Ecosystem level methane fluxes from tidal freshwater and brackish marshes of the Mississippi River Delta: Implications for coastal wetland carbon projects

Sulfate from seawater inhibits methane production in tidal wetlands, and by extension, salinity has been used as a general predictor of methane emissions. With the need to reduce methane flux uncertainties from tidal wetlands, eddy covariance (EC) techniques provide an integrated methane budget. The goals of this study were to: 1) establish methane emissions from natural, freshwater and brackish wetlands in Louisiana based on EC; and 2) determine if EC estimates conform to a methane-salinity relationship derived from temperate tidal wetlands with chamber sampling. Annual estimates of methane emissions from this study were 62.3 g CH 4 /m 2 /yr and 13.8 g CH 4 /m 2 /yr for the freshwater and brackish (8–10 psu) sites, respectively. If it is assumed that long-term, annual soil carbon sequestration rates of natural marshes are ~200 g C/m 2 /yr (7.3 tCO 2 e/ha/yr), healthy brackish marshes could be expected to act as a net radiative sink, equivalent to less than one-half the soil carbon accumulation rate after subtracting methane emissions (4.1 tCO 2 e/ha/yr). Carbon sequestration rates would need case-by-case assessment, but the EC methane emissions estimates in this study conformed well to an existing salinity-methane model that should serve as a basis for establishing emission factors for wetland carbon offset projects.

Louisiana↗

USGS2011

Elevation trends and shrink-swell response of wetland soils to flooding and drying

Given the potential for a projected acceleration in sea-level rise to impact wetland sustainability over the next century, a better understanding is needed of climate-related drivers that influence the processes controlling wetland elevation. Changes in local hydrology and groundwater conditions can cause short-term perturbations to marsh elevation trends through shrink–swell of marsh soils. To better understand the magnitude of these perturbations and their impacts on marsh elevation trends, we measured vertical accretion and elevation dynamics in microtidal marshes in Texas and Louisiana during and after the extreme drought conditions that existed there from 1998 to 2000. In a Louisiana marsh, elevation was controlled by subsurface hydrologic fluxes occurring below the root zone but above the 4 m depth (i.e., the base of the surface elevation table benchmark) that were related to regional drought and local meteorological conditions, with marsh elevation tracking water level variations closely. In Texas, a rapid decline in marsh elevation was related to severe drought conditions, which lowered local groundwater levels. Unfragmented marshes experienced smaller water level drawdowns and more rapid marsh elevation recovery than fragmented marshes. It appears that extended drawdowns lead to increased substrate consolidation making it less resilient to respond to future favorable conditions. Overall, changes in water storage lead to rapid and large short-term impacts on marsh elevation that are as much as five times greater than the long-term elevation trend, indicating the importance of long-term, high-resolution elevation data sets to understand the prolonged effects of water deficits on marsh elevation change.

Louisiana, Texas↗

USGS2007

Potential consequences of saltwater intrusion associated with Hurricanes Katrina and Rita

Hurricanes Katrina and Rita pushed salt water from the Gulf of Mexico well inland into freshwater marsh communities in coastal Louisiana. This paper describes the spatial extent of saltwater intrusion and provides an initial assessment of impacts (salt stress) to coastal marsh vegetation communities.

Louisiana↗

USGS2007

Environmental impact of Hurricane Katrina on Lake Pontchartrain

Hurricane Katrina slammed the Louisiana-Mississippi Gulf Coast with 135-mi/hour (217-km/hour) winds and up to a 30-ft (9-m) storm surge. Lake Pontchartrain was further subjected to environmental threat by way of the millions of gallons of contaminated flood water that were pumped daily from the city of New Orleans into the lake.

Louisiana↗