Geology topics

Lian Xu

Publications and source records attributed to Lian Xu.

4 recordsLinked to original sources

USGS2025

Rising sea level reduces carbon sequestration and CO2 and N2O fluxes while promoting CH4 flux from mangroves

Sea-level rise (SLR) may reduce mangrove carbon sequestration by increasing greenhouse gas (GHG) emissions—a key factor in forecasting the trajectory of blue carbon reserves. Nonetheless, predictions of future GHG fluxes under SLR remain uncertain. Unlike prior studies limited to controlled or single-site settings, we deploy cross-latitude “marsh-organ” designs in China to access GHG fluxes in mangroves and neighboring mudflats. Our findings show that SLR-stimulated CH 4 emissions in mangroves could increase by 10% under RCP 4.5 and by 22% under RCP 8.5, relative to current sea level by 2100. Conversely, SLR decreases ecosystem respiration and N 2 O emissions by 35%–51% and 28%–36%, respectively, while net ecosystem productivity decreases by 12%–28% as SLR increases. Overall, our results forecast a 17%–30% decline in mangroves’ climate mitigation efficiency. We recommend focusing on non-CO 2 GHG emissions from mangroves, as they may significantly offset climate mitigation capacity under climate change.

Cell Reports Sustainability↗

USGS2019

Leakage and increasing fluid pressure detected in Oklahoma's wastewater disposal reservoir

The Arbuckle Group is the principal reservoir used for wastewater disposal in Oklahoma. In Osage County—a seismically quiet part of the state—continuous measurements of fluid pressure reveal that pressure in the reservoir is increasing by at least 5 kPa annually and sometimes at a much higher rate. Tidal analysis reveals that fluid level changes lead the local strain tides, with no apparent influence from transient permeability changes; this indicates a response that is inconsistent with flow in a radially extensive, confined reservoir. We investigate whether this is due to vertical flow to the water table, vertical flow within the Arbuckle, or local distortions from fractures. While none of these alternative models can fully explain both the observed tidal phases and amplitude ratios, the observed response to teleseismic waves supports a mechanism related to leakage rather than fracture effects. At this location fluid influx associated with wastewater disposal is offset by migration into surrounding layers, which include the Precambrian basement below. Thus, our findings suggest the need to monitor for changes in the induced seismicity hazard, while pore pressures increase in a leaky disposal reservoir.

Oklahoma↗

USGS2018

Tidal response of groundwater in a leaky aquifer—Application to Oklahoma

Quantitative interpretation of the tidal response of water levels measured in wells has long been made either with a model for perfectly confined aquifers or with a model for purely unconfined aquifers. However, many aquifers may be neither totally confined nor purely unconfined at the frequencies of tidal loading but behave somewhere between the two end‐members. Here we present a more general model for the tidal response of groundwater in aquifers with both horizontal flow and vertical leakage. The model has three independent parameters: the transmissivity ( T ) and storativity ( S ) of the aquifer and the specific leakage ( K′/b′ ) of the leaking aquitard, where K′ and b′ are the hydraulic conductivity and the thickness of the aquitard, respectively. If T and S are known independently, this model may be used to estimate aquitard leakage from the phase shift and amplitude ratio of water level in wells obtained from tidal analysis. We apply the model to interpret the tidal response of water level in a US Geological Survey (USGS) deep monitoring well installed in the Arbuckle aquifer in Oklahoma, into which massive amount of wastewater coproduced from hydrocarbon exploration has been injected. The analysis shows that the Arbuckle aquifer is leaking significantly at this site. We suggest that the present method may be effective and economical for monitoring leakage in groundwater systems, which bears on the safety of water resources, the security of underground waste repositories, and the outflow of wastewater during deep injection and hydrocarbon extraction.

Oklahoma↗

USGS2018

Kinematics of the 2015 San Ramon, California earthquake swarm: Implications for fault zone structure and driving mechanisms

Earthquake swarms represent a sudden increase in seismicity that may indicate a heterogeneous fault-zone, the involvement of crustal fluids and/or slow fault slip. Swarms sometimes precede major earthquake ruptures. An earthquake swarm occurred in October 2015 near San Ramon, California in an extensional right step-over region between the northern Calaveras Fault and the Concord–Mt. Diablo fault zone, which has hosted ten major swarms since 1970. The 2015 San Ramon swarm is examined here from 11 October through 18 November using template matching analysis. The relocated seismicity catalog contains ∼4000 events with magnitudes between − 0.2 < M d < 3.6 "> −0.2< M d <3.6 . The swarm illuminated three sub-parallel, southwest striking and northwest dipping fault segments of km-scale dimension and thickness of up to 200 m. The segments contain coexisting populations of different focal-mechanisms, suggesting a complex fault zone structure with several sets of en échelon fault orientations. The migration of events along the three planar structures indicates a complex fluid and faulting interaction processes. We searched for correlations between seismic activity and tidal stresses and found some suggestive features, but nothing that we can be confident is statistically significant.

California↗