Geology topics

Xin-Fu Zhao

Publications and source records attributed to Xin-Fu Zhao.

4 recordsLinked to original sources

USGS2022

Are existing modeling tools useful to evaluate outcomes in mangrove restoration and rehabilitation projects? A minireview

Ecosystem modeling is a critical process for understanding complex systems at spatiotemporal scales needed to conserve, manage, and restore ecosystem services (ESs). Although mangrove wetlands are sources of ESs worth billions of dollars, there is a lack of modeling tools. This is reflected in our lack of understanding of mangroves’ functional and structural attributes. Here, we discuss the “state of the art” of mangrove models used in the planning and monitoring of R/R projects during the last 30 years. The main objectives were to characterize the most frequent modeling approach, their spatiotemporal resolution, and their current utility/application in management decisions. We identified 281 studies in six broad model categories: conceptual, agent-based (ABM), process-based (PBM), spatial, statistical, and socioeconomic/management (ScoEco). The most widely used models are spatial and statistical, followed by PBM, ScoEco, and conceptual categories, while the ABMs were the least frequently used. Yet, the application of mangrove models in R/R projects since the early 1990s has been extremely limited, especially in the mechanistic model category. We discuss several approaches to help advance model development and applications, including the targeted allocation of potential revenue from global carbon markets to R/R projects using a multi-model and integrated approach.

Forests↗

USGS2021

Calcite U-Pb dating unravels the age and hydrothermal history of the giant Shuiyindong Carlin-type gold deposit in the Golden Triangle, south China

The ages of Carlin-type gold deposits in the Golden Triangle of South China have long been questioned due to the general lack of minerals unequivocally linked to gold deposition that can be precisely dated using conventional radiogenic isotope techniques. Recent advances in U-Pb methods show that calcite can be used to constrain the ages of hydrothermal processes, but few studies have been applied to ore deposits. Herein, we show that this approach can be used to constrain the timing of hydrothermal activity that generated and overprinted the giant Shuiyindong Carlin-type gold deposit in the Golden Triangle. Three stages of calcite (Cal-1, Cal-2, and Cal-3) have been recognized in this deposit based on crosscutting relationships, cathodoluminescence colors, and chemical (U, Pb, and rare earth element [REE]) and isotope (C, O, Sr) compositions. Cal-1 is texturally associated with ore-stage jasperoid and disseminated Au-bearing arsenian pyrite in hydrothermally altered carbonate rocks, which suggests it is synmineralization. Cal-2 fills open spaces and has a distinct orange cathodoluminescence, suggesting that it precipitated during a second fluid pulse. Cal-1 and Cal-2 have similar carbonate rock-buffered chemical and isotopic compositions. Cal-3 occurs in veins that often contain realgar and/or orpiment and are chemically (low U, Pb, and REE) and isotopically (higher δ 13 C, lower δ 18 O and Sr i values) distinct from Cal-1 and Cal-2, suggesting that it formed from a third fluid. U-Pb isotope analyses, by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) for U-rich Cal-1 and Cal-2 and by LA-multicollector (MC)-ICP-MS for U-poor Cal-3, yield well-defined age constraints of 204.3 to 202.6, 191.9, and 139.3 to 137.1 Ma for Cal-1, Cal-2, and Cal-3, respectively. These new ages suggest that the Shuiyindong gold deposit formed in the late Triassic and was overprinted by hydrothermal events in the early Jurassic and early Cretaceous. Given the association of Cal-3 with orpiment and realgar, and previous geochronologic studies of several other major gold deposits in the Golden Triangle, we infer that the latest stage of calcite may be associated with an early Cretaceous regional gold metallogenic event. Combined with existing isotopic ages in the region, these new ages lead us to propose that Carlin-type gold deposits in the Golden Triangle formed during two metallogenic episodes in extensional settings, associated with the late Triassic Indochina orogeny and early Cretaceous paleo-Pacific plate subduction. This study shows that the calcite U-Pb method can be used to constrain the timing of Carlin-type gold deposits and successive hydrothermal events.

Golden Triangle, south China↗

USGS2020

Modeling soil porewater salinity in mangrove forests (Everglades, Florida, USA) impacted by hydrological restoration and a warming climate

Hydrology is a critical driver controlling mangrove wetlands structural and functional attributes at different spatial and temporal scales. Yet, human activities have negatively affected hydrology, causing mangrove diebacks and coverage loss worldwide. In fact, the assessment of mangrove water budgets, impacted by natural and human disturbances, is limited due to a lack of long-term data and information that hinders our understanding of how changes in hydroperiod and salinity control mangrove productivity and spatial distribution. In this study, we implemented a mass balance-based hydrological model (RHYMAN) that explicitly considers groundwater discharge in the Shark River estuary (SRE, southwestern Everglades) located in a karstic geomorphic setting and influenced by regional hydrological restoration. We used long-term hydroperiod and porewater salinity (PWS) datasets obtained from 2004 to 2016 for model calibration and validation and to determine spatiotemporal variability in water levels and PWS at three riverine mangrove sites (downstream, SRS-6; midstream, SRS-5; upstream, SRS-4) along SRE. Model results agree with a distinct PWS pattern along the estuarine salinity gradient where the highest PWS occurs at SRS-6 (mean: 25, range: 22–30 ppt), followed by SRS-5 (17, 14–25 ppt) and SRS-4 (5, 3–13 ppt). A commensurate increase in PWS over a thirteen-year period indicates a long-term reduction in freshwater inflow coupled with sea-level rise (SLR). Increasing freshwater scenario simulation results show a significant reduction (17–27%) in PWS along the estuary in contrast with a high SLR scenario when salinity increases up to 1.1 to 2.5 times that of control values. Model results show that freshwater inflow and SLR are key drivers controlling mangrove wetlands PWS in this karstic coastal region. Given its relatively simple structure, this mass balance-based hydrological model could be used in other environmental settings to evaluate potential habitat and regime shifts due to changes in hydrology and PWS under regional hydrological restoration management.

Florida↗

USGS2019

Wetland biomass and productivity in Coastal Louisiana: Base line data (1976-2015) and knowledge gaps for the development of spatially explicit models for ecosystem restoration and rehabilitation initiatives

Coastal Louisiana host 37% of the coastal wetland area in the conterminous US, including one of the deltaic coastal regions more susceptible to the synergy of human and natural impacts causing wetland loss. As a result of the construction of flood protection infrastructure, dredging of channels across wetlands for oil/gas exploration and maritime transport activities, coastal Coastal Louisiana hosts 37% of the coastal wetland area in the conterminous US, including one of the deltaic coastal regions more susceptible to the synergy of human and natural impacts causing wetland loss. As a result of the construction of flood protection infrastructure, dredging of channels across wetlands for oil/gas exploration and maritime transport activities, coastal Louisiana has lost approximately 4900 km2 of wetland area since the early 1930s. Despite the economic relevance of both wetland biomass and net primary productivity (NPP) as ecosystem services, there is a lack of vegetation simulation models to forecast the trends of those functional attributes at the landscape level as hydrological restoration projects are implemented. Here, we review the availability of peer-reviewed biomass and NPP wetland data (below and aboveground) published during the period 1976–2015 for use in the development, calibration and validation of high spatial resolution (<200 m × 200 m) vegetation process-based ecological models. We discuss and list the knowledge gaps for those species that represent vegetation community associations of ecological importance, including the long-term research issues associated to limited number of paired belowground biomass and productivity studies across hydrological basins currently undergoing different freshwater diversions management regimes and hydrological restoration priorities.

Louisiana↗