Reclamation-induced tidal restriction increases dissolved carbon and greenhouse gases diffusive fluxes in salt marsh creeks

Accelerated stochastic processes of plankton community assembly due to tidal restriction by seawall construction in the Yangtze River Estuary

Seawall construction has complex ecological impacts. However, the ecological mechanisms within plankton communities under tidal restriction resulting from seawall construction remain unexplored. Using environmental DNA (eDNA) metabarcoding, this study examined the impact of seawall construction on the assembly process of planktonic eukaryote and bacteria communities from the unrestricted area and the tide-restricted area in the Chongming Dongtan Nature Reserve of Yangtze River Estuary. While environmental heterogeneity did not exert a significant influence on alpha diversity of plankton, it had a significant impact on community structure. Variation partitioning analysis (VPA) and neutral community model indicated that neither environmental nor spatial factors were predominant drivers of plankton community composition and structure, instead, they were influenced by stochastic processes. Moreover, it was observed that the relative significance of stochastic processes in the tide-restricted area exceeded that in the unrestricted area. High habitat uniformity and water connectivity resulting from seawall construction may facilitate homogenization and spread among high-abundance groups. The results have significant implications for understanding the mechanisms underlying succession and composition, and for improving ecological assessment and remediation efforts in areas impacted by tidal restriction.

Photovoltaic Power Station Impacts on the Benthic Ecosystem and Sediment Carbon Storage in Tidal Flats in China

Photovoltaic power is a rapidly growing component of the renewable energy sector. Photovoltaic power stations (PVPSs) on coastal tidal flats offer benefits, but the lack of information on the effects of PVPSs on benthic ecosystems and sediment carbon storage can hamper the development of eco-friendly renewable energy. We sampled the macrobenthos and sediment cores at a PVPS on a coastal tidal flat in eastern China. The biodiversity indicators and benthic ecological quality based on macrobenthos were mostly higher under the photovoltaic panels than elsewhere. These variations were primarily driven by pH, sediment grain size, and chlorophyll-a content. However, the PVPS had exerted a considerable influence on the macrobenthic community structure. Furthermore, the carbon stocks in the sediment cores from under the photovoltaic panels were similar to those in the reference sites. These results suggest that this PVPS has not had discernible short-term adverse effects on the benthic ecosystems or sediment carbon storage of the tidal flat. Nevertheless, the potentially long-term and cascading risks throughout the ecosystem warrant caution. Therefore, we recommend that policymakers adopt a cautious development strategy and implement long-term, high-frequency monitoring to ensure the sustainability of renewable energy production on coastal tidal flats.

Assessing the ecological response plant and soil to the seawalls in the Laizhou bay coastal wetland, China

Coastal wetlands are extremely vulnerable to both marine damage and human activities. In order to protect these wetlands, many artificial seawalls have been constructed. However, studies are required to understand how coastal wetlands will evolve under the influence of artificial seawalls. Therefore, to understand this succession process of plants and their adaptation to habitats divided by seawalls, two different habitats inside and outside the seawalls were selected in Laizhou Bay, China. The results showed that there were 5 plant species outside the seawalls that were lower than the 13 species inside. Additionally, the dominant plant species were varied between the two habitats, with mostly annual herbs observed outside the seawalls and perennial shrubs inside. Soil salinity was higher outside the seawalls, which was the key impact factor of soil nutrient differences. The distribution of annual and perennial species may be constrained by spatial differences in soil stoichiometry. Therefore, the plants in coastal wetlands vary significantly at a small scale in response to the disturbance of artificial seawalls. The differences in soil and plants between the two habitats divided by the artificial seawalls provide a new insight for evaluating the artificial coastal projects. The only way to reduce the effects of seawalls on natural coastal wetland vegetation and ecosystem functions is to restore connectivity of tidal flow inside and outside the seawalls.

Current research hotspots and frontier trends on carbon budget of coastal wetlands: A bibliometric analysis

Coastal wetlands are the main distribution of blue carbon in coastal zones and well known for their high carbon sequestration capacity. Investigating the variation of carbon budget is crucial for understanding the functionality of coastal wetlands and effectively addressing climate change. In this study, a bibliometric analysis of 4,509 articles was conducted to reveal research progress, hot issues, and emerging trends in the coastal wetland carbon budget field. The number of publications and citations in this field increased exponentially from 1991 to 2022. The leading subject category was Environmental Sciences with 1,844 articles (40.9%). At present, studies have been focused on blue carbon, the effects of climate change and man-made disturbances on carbon cycle, and the restoration of coastal wetlands. Based on the hotspots and trends in this field, the future researches should include (1) exploring the functional mechanisms of various factors affecting carbon cycle and establishing a methodological system for the estimation of blue carbon in coastal wetlands; (2) researching restoration techniques of coastal wetland and constructing wetland restoration evaluation index system; and (3) formulating enforceable carbon trading policy and strengthening international cooperation.

Pollution abatement reducing the river N2O emissions although it is partially offset by a warming climate: Insights from an urbanized watershed study

Global nitrogen (N) pollution has resulted in increased river nitrous oxide (N₂O) emissions, which contribute to climate change. However, little is known about how pollution abatement conversely reduces river N₂O production in a warming climate. Here, field observations and microcosmic experiments were conducted in a coastal urbanized watershed (S.E. China) to explore the interactive effect of changing nitrate and temperature on river sediment denitrification (DNF) and N₂O production. The results showed that urban river reaches (UR) with higher organic carbon content and denitrifying gene abundance in sediments have a greater DNF rate, nitrate removal efficiency (NRE), and N₂O concentration than agricultural river reaches (AR). Microcosmic incubation suggested that the DNF rate and associated N₂O production decreased under low nitrate addition, wherein the NRE increased. The scenario simulation illustrated a nonlinear response of N₂O production to nitrate removal (i.e., ΔN₂O/ΔNO₃-N) from both UR and AR sediments at a given temperature, and the DNF rate and N₂O production increased with increasing temperature. An increase in temperature by 1 degree Celsius would offset 18.75% of the N₂O reduction by nitrate removal via DNF. These findings implied that watershed pollution abatement undoubtedly contributes to the reduction in global river N₂O emissions although it is partially offset by extra N₂O production caused by global warming.

Greenhouse gas emissions and environmental drivers in different natural wetland regions of China

Wetlands sequestrate carbon at the highest rate than any other ecosystems on Earth. However, the spatial and temporal dynamics of GHGs emissions from the wetland ecosystems in China are still elusive. We synthesized 166 publications that contain 462 in situ measurements of GHGs emissions from the natural wetlands in China, and further analyzed the variability and the drivers of GHGs emissions in eight subdivisions of China's wetlands. The results show that the current studies are mainly concentrated in the estuaries, Sanjiang Plain, and Zoige wetlands. The average CO₂ emissions, CH₄ fluxes and N₂O fluxes from Chinese wetlands were 218.84 mg·m^-2·h^-1, 1.95 mg·m^-2·h^-1 and 5.8 × 10^-2 mg·m^-2·h^-1, respectively. The global warming potential (GWP) of China's wetlands was estimated to be 1881.36 TgCO₂-eq·yr^-1, with CO₂ emissions contributing more than 65% to the GWP value. The combined GWP values of Qinghai-Tibet Plateau wetlands, coastal wetlands and northeastern wetlands account for 84.8% of GWP of China's wetlands. Correlation analysis showed that CO₂ emissions increased with the increasing mean annual temperature, elevation, annual rainfall, and wetland water level, but decreased with soil pH. CH₄ fluxes increased with the mean annual temperature and soil water content but decreased with the redox potential. This study analyzed the drivers of GHGs emissions from wetland ecosystems at the national scale, and GWP values of eight wetland subregions of China were comprehensively assessed. Our results are potentially useful for the global GHGs inventory, and can help assess the response of GHGs emissions of wetland ecosystem to environmental and climate change.

Temporal dynamics of lateral carbon export from an onshore aquaculture farm

Many coastal areas are hotspots of aquaculture expansion, where the overuse of artificial feeds results in the accumulation of organic carbon in nearshore aquaculture ponds. In rural areas, wastewater from the aquaculture ponds is discharged to the nearshore waters through artificial ditches causing lateral carbon export from the land to the ocean. Such flux may be meaningful in coastal carbon budgets since aquaculture is the hotspot of carbon sequestration and storage. To quantify the magnitude and temporal dynamics of lateral carbon export from aquaculture ponds, we used high-frequency in-situ monitoring of turbidity, fluorescent dissolved organic matter, etc. across different temporal scales. We measured water levels and velocity profiles in a ditch cross-section to obtain year-round water exchange. Carbon export was integrated from water fluxes and organic carbon concentrations. Our results suggested that aquaculture ponds were a source of particular organic carbon (POC) and dissolved organic carbon (DOC). The net lateral flux of POC and DOC was 148 ± 38 kg yr^-1 and 296 ± 18 kg yr^-1. Temporally, the export of POC and DOC is influenced by both tides and wastewater discharge. Under the disturbance with aquaculture wastewater discharge, the mean DOC export in the ditch increased by 497 kg, which was 1.5 times that of the undisturbed; the mean POC export increased by 190 kg, which was 1.8 times that of the undisturbed. Thus, aquaculture activities can considerably disturb the coastal carbon balance by facilitating carbon-rich fluid exchange from onshore farms to nearshore estuaries. As aquaculture expands across Asia and the globe, this study provides important insights into the impacts of aquaculture on coastal carbon budgets.