Geology topics

J.A. Langley

Publications and source records attributed to J.A. Langley.

4 recordsLinked to original sources

USGS2014

Temperature sensitivity of organic-matter decay in tidal marshes

Approximately half of marine carbon sequestration takes place in coastal wetlands, including tidal marshes, where organic matter contributes to soil elevation and ecosystem persistence in the face of sea-level rise. The long-term viability of marshes and their carbon pools depends, in part, on how the balance between productivity and decay responds to climate change. Here, we report the sensitivity of labile soil organic-matter decay in tidal marshes to seasonal and latitudinal variations in temperature measured over a 3-year period. We find a moderate increase in decay rate at warmer temperatures (3-6% per °C, Q 10 = 1.3-1.5). Despite the profound differences between microbial metabolism in wetlands and uplands, our results indicate a strong conservation of temperature sensitivity. Moreover, simple comparisons with organic-matter production suggest that elevated atmospheric CO 2 and warmer temperatures will accelerate carbon accumulation in marsh soils, and potentially enhance their ability to survive sea-level rise.

Biogeosciences↗

USGS2013

The impact of sea-level rise on organic matter decay rates in Chesapeake Bay brackish tidal marshes

The balance between organic matter production and decay determines how fast coastal wetlands accumulate soil organic matter. Despite the importance of soil organic matter accumulation rates in influencing marsh elevation and resistance to sea-level rise, relatively little is known about how decomposition rates will respond to sea-level rise. Here, we estimate the sensitivity of decomposition to flooding by measuring rates of decay in 87 bags filled with milled sedge peat, including soil organic matter, roots and rhizomes. Experiments were located in field-based mesocosms along 3 mesohaline tributaries of the Chesapeake Bay. Mesocosm elevations were manipulated to influence the duration of tidal inundation. Although we found no significant influence of inundation on decay rate when bags from all study sites were analyzed together, decay rates at two of the sites increased with greater flooding. These findings suggest that flooding may enhance organic matter decay rates even in water-logged soils, but that the overall influence of flooding is minor. Our experiments suggest that sea-level rise will not accelerate rates of peat accumulation by slowing the rate of soil organic matter decay. Consequently, marshes will require enhanced organic matter productivity or mineral sediment deposition to survive accelerating sea-level rise.

Maryl↗

USGS2012

C 3 and C 4 biomass allocation responses to elevated CO 2 and nitrogen: contrasting resource capture strategies

Plants alter biomass allocation to optimize resource capture. Plant strategy for resource capture may have important implications in intertidal marshes, where soil nitrogen (N) levels and atmospheric carbon dioxide (CO 2 ) are changing. We conducted a factorial manipulation of atmospheric CO 2 (ambient and ambient + 340 ppm) and soil N (ambient and ambient + 25 g m -2 year -1 ) in an intertidal marsh composed of common North Atlantic C 3 and C 4 species. Estimation of C 3 stem turnover was used to adjust aboveground C 3 productivity, and fine root productivity was partitioned into C 3 -C 4 functional groups by isotopic analysis. The results suggest that the plants follow resource capture theory. The C 3 species increased aboveground productivity under the added N and elevated CO 2 treatment ( P < 0.0001), but did not under either added N or elevated CO 2 alone. C 3 fine root production decreased with added N ( P < 0.0001), but fine roots increased under elevated CO 2 ( P = 0.0481). The C 4 species increased growth under high N availability both above- and belowground, but that stimulation was diminished under elevated CO 2 . The results suggest that the marsh vegetation allocates biomass according to resource capture at the individual plant level rather than for optimal ecosystem viability in regards to biomass influence over the processes that maintain soil surface elevation in equilibrium with sea level.

Estuaries and Coasts↗

USGS2009

Elevated CO 2 stimulates marsh elevation gain, counterbalancing sea-level rise

Tidal wetlands experiencing increased rates of sea-level rise (SLR) must increase rates of soil elevation gain to avoid permanent conversion to open water. The maximal rate of SLR that these ecosystems can tolerate depends partly on mineral sediment deposition, but the accumulation of organic matter is equally important for many wetlands. Plant productivity drives organic matter dynamics and is sensitive to global change factors, such as rising atmospheric CO 2 concentration. It remains unknown how global change will influence organic mechanisms that determine future tidal wetland viability. Here, we present experimental evidence that plant response to elevated atmospheric [CO 2 ] stimulates biogenic mechanisms of elevation gain in a brackish marsh. Elevated CO 2 (ambient + 340 ppm) accelerated soil elevation gain by 3.9 mm yr −1 in this 2-year field study, an effect mediated by stimulation of below-ground plant productivity. Further, a companion greenhouse experiment revealed that the CO 2 effect was enhanced under salinity and flooding conditions likely to accompany future SLR. Our results indicate that by stimulating biogenic contributions to marsh elevation, increases in the greenhouse gas, CO 2 , may paradoxically aid some coastal wetlands in counterbalancing rising seas.

Proceedings of the National Academy of Sciences↗