Lacustrine groundwater discharge-derived carbon and nitrogen to regulate biogeochemical processes as revealed by stable isotope signals in a large shallow eutrophic lake.

Eutrophic shallow lakes are hotspots of carbon (C) and nitrogen (N) accumulation and transformation, and are increasingly recognized as important sources of greenhouse gases (GHGs: CO, CH and NO). Lacustrine groundwater discharge (LGD) is a crucial component of the water budget and terrestrial material delivery for lakes, but its interplays with intrinsic CN biogeochemical processes remain less tackled. In this study, C and N ingredients and multiple stable isotopes (δH, δO, δC, and δN) were measured seasonally in groundwater, river water and lake water of a large eutrophic shallow lake in eastern China.

Disentangling external loadings, hydrodynamics and biogeochemical controls on the fate of nitrate in a coastal embayment.

Nitrogen, as an essential nutrient, largely contributes to the coastal eutrophication. However, the accurate depiction and evaluation of how external loadings, hydrodynamics, and biogeochemical reactions mediate the occurrence, transport, and transformation of nitrate (NO) within coastal embayment still pose ongoing challenges to date. In this study, we took advantage of dual isotopes of NO to track external NO loadings, radium and dual isotopes of HO to characterize the influences of hydrodynamic on NO transport, δO-NO and δO-HO along with microbial analysis to explore major NO biogeochemical reactions in Tolo Harbour, Hong Kong.

Evolution of groundwater system in the Pearl River Delta and its adjacent shelf since the late Pleistocene.

Our extensive field studies demonstrate that saline groundwater inland and freshened groundwater offshore coexist in the same aquifer system in the Pearl River delta and its adjacent shelf. This counterintuitive phenomenon challenges the commonly held assumption that onshore groundwater is typically fresh, while offshore groundwater is saline. To address this knowledge gap, we conduct a series of sophisticated paleo-hydrogeological models to explore the formation mechanism and evolution process of the groundwater system in the inland-shelf systems.

Synergistic controls of water column stability and groundwater phosphate on coastal algal blooms.

Algal blooms have been identified as one major threat to coastal safety and marine ecosystem functioning, but the dominant mechanism regulating the formation of algal blooms remains controversial, ranging from physical control (via water column stability), the chemical control (via coastal nutrients) to joint control. Here we leveraged the unique data collected in the Hong Kong water over the annual cycle and past three decades, including direct observations of algal blooms and coastal nutrients and process model output of water column stability, and evaluated the differential competing hypotheses in regulating algal blooms. Our results demonstrate that the joint mechanism rather than the single mechanism effectively predicts all algal blooms.

The changing nature of groundwater in the global water cycle.

In recent decades, climate change and other anthropogenic activities have substantially affected groundwater systems worldwide. These impacts include changes in groundwater recharge, discharge, flow, storage, and distribution. Climate-induced shifts are evident in altered recharge rates, greater groundwater contribution to streamflow in glacierized catchments, and enhanced groundwater flow in permafrost areas.

Spatiotemporal-aware machine learning approaches for dissolved oxygen prediction in coastal waters.

Coastal waters face increasing threats from hypoxia, which can have severe consequences for marine life and fisheries. This study aims to develop a machine learning approach for hypoxia monitoring by investigating the effectiveness of four tree-based models, considering spatiotemporal effects in model prediction, and adopting the SHapley Additive exPlanations (SHAP) approach for model interpretability, using the long-term climate and marine monitoring dataset in Tolo Harbour (Zone 1) and Mirs Bay (Zone 2), Hong Kong. The LightBoost model was found to be the most effective for predicting dissolved oxygen (DO) concentrations using spatiotemporal datasets.

Uncovering the processes of microbial community assembly in the near-surface sediments of a climate-sensitive glacier-fed lake.

Glacier-fed lakes are characterized by cold temperatures, high altitudes, and nutrient-poor conditions. Despite these challenging conditions, near-surface sediments of glacier-fed lakes harbor rich microbial communities that are critical for ecosystem functioning and serve as a bridge between aquatic ecology and the deep subsurface biosphere. However, there is limited knowledge regarding the microbial communities and their assembly processes in these sediments, which are highly vulnerable to climate change.

Offshore freshened groundwater in the Pearl River estuary and shelf as a significant water resource.

Large-river deltaic estuaries and adjacent continental shelves have experienced multiple phases of transgressions and regressions to form interlayered aquifer-aquitard systems and are expected to host vast paleo-terrestrial groundwater hundreds of kilometres offshore. Here, we used offshore hydrogeology, marine geophysical reflections, porewater geochemistry, and paleo-hydrogeological models, and identified a previously unknown offshore freshened groundwater body with a static volume up to 575.6 ± 44.

Storm accelerated subsurface Escherichia coli growth and exports to coastal waters.

Storm significantly deteriorates coastal water fecal pollution now and beyond. Questions relating to storm exerting on coastal water safety are often intertwined with both surface water and subsurface processes. Stormwater runoff is a vital metric for coastal water fecal pollution under current cognition, while the controls of subsurface system remain unclear.

Effective coastal Escherichia coli monitoring by unmanned aerial vehicles (UAV) thermal infrared images.

Coastal Escherichia coli (E. coli) significantly influence ocean safety and public health, thus requiring an effective E. coli pollution monitoring.

Microbial community assembly and co-occurrence relationship in sediments of the river-dominated estuary and the adjacent shelf in the wet season.

In the estuarine ecosystem, microbial community plays a vital role in controlling biogeochemical processes. However, there is currently limited comprehensive study on the deterministic and stochastic processes that drive the microbial community assembly in the estuaries and adjacent shelves. In this study, we systematically investigated the co-occurrence relationship and microbial community assembly in the sediments along a large river-dominated estuary to shelf in the northern South China Sea during the wet season.

Dominance of evaporation on lacustrine groundwater discharge to regulate lake nutrient state and algal blooms.

As global threats to freshwater lakes, eutrophication and harmful algal blooms (HABs) are governed by various biogeochemical, climatological and anthropogenic processes. Groundwater is key to join these processes in regulating HABs, but the underlying mechanisms remain unclear. Here, we leveraged basin-wide field data of Lake Taihu (China's largest eutrophic lake) and global archives, and demonstrate the dominance of evaporation on lacustrine groundwater discharge (LGD) in shallow lakes.

Delineating E. coli occurrence and transport in the sandy beach groundwater system by radon-222.

Fecal pollution poses a global threat to environmental safety and ecosystem, but the mechanism of microbial transport and occurrence in the beach groundwater system is still poorly explored. Here, we leveraged one-year field data of Escherichia coli (E. coli) and radon-222 (Rn) and found that E.

Subglacial Meltwater Recharge in the Dongkemadi River Basin, Yangtze River Source Region.

Glaciers on the Tibetan Plateau play an important role in the local hydrological cycle. However, there are only few studies on groundwater in the alpine basins in the Tibetan Plateau which considered the effects of glaciers. Glaciers are extensively distributed in the Dongkemadi River Basin, which is a representative alpine basin in the Yangtze River source region.

Two-decade variations of fresh submarine groundwater discharge to Tolo Harbour and their ecological significance by coupled remote sensing and radon-222 model.

Although submarine groundwater discharge (SGD) comprises an insignificant proportion of the global hydrologic cycle, it contributes significantly to chemical fluxes into the coastal waters due to concentrated constituents in coastal groundwater. Large nutrient loadings derived from SGD can lead to a series of environmental and ecological problems such as algal blooms, resulting in water discoloration, severe dissolved oxygen depletion, and eventually beach closures and massive fish kills. Previous studies have demonstrated the relationship between algal blooms and SGD obtained from direct measurement with seepage meters or from geo-tracer (i.

The dynamics of dissolved inorganic nitrogen species mediated by fresh submarine groundwater discharge and their impact on phytoplankton community structure.

Submarine groundwater discharge (SGD)-driven nutrient inputs have long been speculated to sustain the high frequency of red tide occurrence in Tolo Harbour, Hong Kong, for its larger flux and higher nutrient loadings than river discharge. Based on analysis of high resolution time series biogeochemical and climatological data from 2000 to 2015, fresh SGD-derived dissolved inorganic nitrogen (DIN) is found to be a significant regulator of the annual cycle of phytoplankton community structure in the harbour. In the wet season, fresh SGD supplies nutrients with NH:NO ratio < 1 to the seawater, meanwhile creates an intensive vertical stratification environment.

Nutrients and heavy metals mediate the distribution of microbial community in the marine sediments of the Bohai Sea, China.

The Bohai Sea, one of the largest marginal seas in China, is extensively influenced by human and industrial activities. The pollutant loads from anthropogenic activities have induced severe ecological problems. The study investigates the physicochemical characteristics of seawater and sediments in Bohai Bay and Laizhou Bay of the Bohai Sea.

Sensitivity Analysis of Leakage Correction of GRACE Data in Southwest China Using A-Priori Model Simulations: Inter-Comparison of Spherical Harmonics, Mass Concentration and In Situ Observations.

The Gravity Recovery and Climate Experiment (GRACE) level-2 spherical harmonic (SH) solutions are noisy and thus require filtering. Filtering reduces noise but affects signal quality via signal leakage. Generally, a leakage correction is required for GRACE applications to remove leakage signal and recover the true signal.

Tidal induced dynamics and geochemical reactions of trace metals (Fe, Mn, and Sr) in the salinity transition zone of an intertidal aquifer.

Biogeochemical reactions in an intertidal aquifer influences the submarine groundwater discharge (SGD) associated trace metal flux to the ocean. Tidal fluctuation greatly affects the physical mixing, and biogeochemical transformation of trace metals in the intertidal aquifer. This study presents the dynamics of trace metals (Fe, Mn, and Sr) and the production of Fe in the salinity transition zone is discovered.

Significant chemical fluxes from natural terrestrial groundwater rival anthropogenic and fluvial input in a large-river deltaic estuary.

The shores of the Pearl River estuary are home to 35 million people. Their wastes are discharged into the large river delta-front estuary (LDE), one of the most highly polluted systems in the world. Here we construct a radium reactive transport model to estimate the terrestrial groundwater discharge (TGD) into the highly urbanized Pearl River LDE.

Nitrogen fate in a subtropical mangrove swamp: Potential association with seawater-groundwater exchange.

Coastal mangrove swamps play an important role in nutrient cycling at the land-ocean boundary. However, little is known about the role of periodic seawater-groundwater exchange in the nitrogen cycling processes. Seawater-groundwater exchange rates and inorganic nitrogen concentrations were investigated along a shore-perpendicular intertidal transect in Daya Bay, China.

Abundance and Diversity of Aerobic/Anaerobic Ammonia/Ammonium-Oxidizing Microorganisms in an Ammonium-Rich Aquitard in the Pearl River Delta of South China.

Natural occurring groundwater with abnormally high ammonium concentrations was discovered in the aquifer-aquitard system in the Pearl River Delta, South China. The community composition and abundance of aerobic/anaerobic ammonia/ammonium-oxidizing microorganisms (AOM) in the aquitard were investigated in this study. The alpha subunit of ammonia monooxygenase gene (amoA) was used as the biomarker for the detection of aerobic ammonia-oxidizing archaea (AOA) and bacteria (AOB), and also partial 16S rRNA gene for Plantomycetes and anaerobic ammonium-oxidizing (anammox) bacteria.

Submarine groundwater discharge and nutrient loadings in Tolo Harbor, Hong Kong using multiple geotracer-based models, and their implications of red tide outbreaks.

Multiple tracers, including radium quartet, (222)Rn and silica are used to quantify submarine groundwater discharge (SGD) into Tolo Harbor, Hong Kong in 2005 and 2011. Five geotracer models based on the end member model of (228)Ra and salinity and mass balance models of (226)Ra, (228)Ra, (222)Rn, and silica were established and all the models lead to an estimate of the SGD rate of the same order of magnitude. In 2005 and 2011, respectively, the averaged SGD based on these models is estimated to be ≈ 5.