Carbon cycle (Biogeochemistry)

Coastal nutrient loading is a growing concern in urbanized communities and has led to alterations in above- and belowground processes throughout estuarine systems. Mangrove forests are highly productive coastal habitats that exhibit large carbon stocks contained mostly to the deep soils. Since nutrient enrichment has been found to increase mangrove aboveground growth, it’s presumed that nutrient enrichment will also increase belowground respiration rates. Disturbances in soil nutrient content may alter the mangrove carbon cycle by increasing the amount of CO2 lost to the atmosphere from enhanced microbial and root respiration. In this study, soil respiration responded greatest to nitrogen enrichment, but pneumatophore root respiration responded greatest to phosphorus enrichment. Nutrient limitation can shift between different ecological processes and responses to nutrient enrichment tend to be system specific in tidally influenced ecosystems. Understanding the implications of coastal nutrient loading will improve ecosystem models of carbon exchange and belowground processes.

Storing almost a third of the global soil carbon pool, wetlands are an essential component of the carbon cycle, and carbon-rich peat soil accumulates when carbon input through primary productivity exceeds output through decomposition. However, woody shrub encroachment in herbaceous wetlands can alter soil carbon processes, potentially diminishing stored carbon. To examine the effects of shrub encroachment on soil carbon, I compared soil carbon input through litterfall and fine root production, output through decomposition, and below-canopy microclimate conditions between Carolina willow shrub (Salix caroliniana) and herbaceous sawgrass (Cladium jamaicense) in the Blue Cypress Marsh Conservation Area (BCMCA), FL. To assess the level of production and its response to water level, I compared aboveground green biomass by measuring normalized difference vegetation index (NDVI) and photosynthetic stress by measuring photochemical reflectance index (PRI) between sawgrass and willow. I collected willow litterfall using litter traps and measured sawgrass and willow fine root production with fine root ingrowth bags. Litter decomposition was measured with decomposition bags deployed using a reciprocal litter placement design at BCMCA and incubated in a greenhouse to examine the effects of char and water level on decomposition. Above and belowground microclimate conditions were measured using sensors installed within sawgrass and willow canopies. Despite experiencing more photosynthetic stress, willow produced more green biomass than sawgrass. However, willow produced fewer fine roots than sawgrass and these roots were deeper within the soil. Willow litter decomposed faster even though sawgrass decomposition increased under drier conditions. Compared to the sawgrass canopy, the willow canopy had greater light availability, lower evaporative demand plus warmer and drier soils; however, litter decomposition did not differ between the canopies. These results suggest that willow encroachment can reduce the amount and alter the distribution of carbon within an herbaceous wetland, likely resulting in a net loss of soil carbon. Although willow encroachment may increase aboveground biomass carbon stocks, these stocks will likely be offset by a loss of soil carbon due to reduced fine root production and increased decomposition. Therefore, the transition from herbaceous wetland to shrub wetland will likely result in a loss of stored soil carbon.

Peat soils are known to be a significant emitter of atmospheric greenhouse gasses.
However, the spatial and temporal variability in production and release of greenhouse
gases (such as methane) in peat soils remains uncertain, particularly for low-latitude
peatlands like the Florida Everglades, as the majority of studies on gas dynamics in
peatlands focus on northern peatlands. The purpose of the work outlined here is focused
on understanding the spatial and temporal variability in biogenic gas dynamics (i.e.
production and release of methane and carbon dioxide) by implementing various
experiments in the Florida Everglades at different scales of measurement, using noninvasive
hydrogeophysical methods. Non-invasive methods include ground-penetrating
radar (GPR), gas traps, time-lapse cameras, and hydrostatic pressure head measurements,
that were constrained with direct measurements on soil cores like porosity, and gas
composition using gas chromatography. By utilizing the measurements of in-situ gas
volumes, we are able to estimate gas production using a mass balance approach, explore
spatial and temporal variabilities of gas dynamics, and better constrain gas ebullition models. A better understanding of the spatial and temporal variability in gas production
and release in peat soils from the Everglades has implications regarding the role of
subtropical wetlands in the global carbon cycle, and can help providing better production
and flux estimates to help global climate researchers improve their predictions and
models for climate change.

While ocean acidification (OA) is predicted to inhibit calcification in marine
macroalgae, species whose photosynthesis is limited by current dissolved inorganic
carbon (DIC) levels may benefit. Furthermore, variations in macroalgal morphology will
likely give rise to a range of OA tolerance in calcifying macroalgae. One genus of
calcifying macroalgae that has shown varying species’ tolerance to OA is Halimeda, a
major carbonate sediment producer on tropical reefs. Species within this genus occupy a
range of habitats within tropical environments (reefs and lagoons), illustrating their
ability to adapt to diverse environmental conditions (e.g. carbonate chemistry,
irradiance). To date it is not clear if morphological and photophysiological diversity in
Halimeda will translate to different tolerances to OA conditions (elevated pCO2 and
lower pH).