Functional trait responses of emergent and free-floating Alternanthera philoxeroides to increasing salinity with sea level rise: stress tolerance, avoidance, and escape strategies

ABSTRACTGlobal climate change has resulted in a gradual sea-level rise. Sea-level rise can cause saline water to migrate upstream in estuaries and rivers, thereby threatening freshwater habitat and drinking water supplies. On the other hand, sea-level rise, resulting from thermal expansion of ocean waters and increased melting of glaciers and ice caps, is one of the most apparent and widespread consequences of climate change. This phenomenon has been taken into account in all the Assessment Reports published by the Intergovernmental Panel on Climate Change (IPCC). In this paper, salinity intrusion and intrusion length due to possible sea-level rise in the Sebou estuary (Morocco) was investigated. A one-dimensional hydrodynamic-salinity transport model was used for the simulation of the salinity intrusion and associated water quality, with observed field data being used for model calibration and validation. Additionally, the model validation process showed that the model results fit the observed data fairly well. A coupled gas-cycle/climate model was used to generate the climate change scenarios in the studied area that showed sea-level rises varying from 0.3 to 0.9 m for 2100. The models were then combined to assess the impact of future sea-level rise on the salinity distribution and intrusion length in the Sebou estuary. The response of salt intrusion length to changes in important dimensional parameters are presented, showing that the salinity intrusion length is inversely correlated with the river discharge, i.e., a high river discharge results in a reduced salt intrusion and vice versa, and directly with the sea-level rise. Additionally, the magnitude and frequency of the salinity standard violations at the two pump stations were predicted for 2100, showing that the salinity violations under climate change effects can increase to ∼45–48% of the times at these locations. Finally, the main objective of this simulation method is to accelerate and facilitate of systems' behavior learning in the current and future situation.

Estuarine systems are very sensitive environments to sea level rise as a consequence of climate changes, which can enhance seawater intrusion and affect multiple water uses. The seawater intrusion under sea level scenarios in an estuarine river by applying the one-dimensional hydrodynamic and water quality model HEC-RAS 5.0.5 was studied. The study was carried out at the estuarine reach of Cubatao River, in Sao Paulo, Brazil. Considering sea level rise scenarios of ΔH = 0.25 m, 0.50 m, and 1.0 m combined with constant freshwater discharge conditions for Cubatao River (16 m3/s, mean annual discharge and 8 m3/s, dry season discharge), the model results showed that seawater intrusion moves significantly upstream the river in all cases and the maximum seawater intrusion length may reach 10 km in the worst scenario (ΔH = 1.0 m and 8 m3/s freshwater discharge), 70% higher than the current sea level and the mean discharge. At the local water abstraction point for urban supply, salinity concentration may reach 12 g/kg, making conventional water treatment unfeasible. Sea level rise may threaten water supply facilities and require water resource management solutions, such as water abstraction restricted times when salinity concentration is low; higher freshwater reservation; new water abstraction locations, farther the present ones; or higher water discharges in Cubatao River from a local hydroelectric power plant, which can cause water resource management conflicts.

An integrated framework to model salinity intrusion in coastal unconfined aquifers considering intrinsic vulnerability factors, driving forces, and land subsidence

Salinity intrusion in the Vietnamese Mekong Delta (VMD) has been exacerbated significantly in recent years by the changing upstream inflows, sea level rise resulting from climate change, and socioeconomic development activities. Despite significant damage to agricultural production and freshwater supplies, quantitative assessments of future flows and salinization remain limited due to lack of observation data and modelling tools to represent a highly complex hydraulic network. In this study, we combine 1D-MIKE 11 and 2D-MIKE 21 hydrodynamic models to simulate future flows, water level and salinity intrusion in the Hau River—one main river branch in the Mekong Delta. Future hydrological changes are simulated under multiple scenarios of upstream inflow changes, climate change and sea level rise for the 2036–2065 period. We first use the 1D-MIKE 11 to simulate the flow regime throughout the whole VMD using upstream discharges, outlet water levels and rainfall data as boundary conditions. Output from this step is then used to force the 2D-MIKE 21 model to estimate flow velocity, water level and salinity concentration in the Hau River, focusing on the salinization-prone section between Can Tho, Dinh An, and Tran De estuaries. Simulation results show that salinization will increase substantially, characterized by (1) higher salinity intrusion length under spring tide from 6.78% to 7.97%, and 8.62% to 10.89% under neap tide; and (2) progression of the salinity isohalines towards the upper Mekong Delta, from 3.29 km to 3.92 km for 1 practical salinity unit (PSU) under spring tide, and 4.36 km to 4.65 km for 1 PSU concentration under neap tide. Additionally, we found that salinity intrusion will make it more difficult to re-establish the freshwater condition in the estuary in the future. In particular, the flushing time required to replace saltwater with freshwater at the estuaries tends to increase to between 7.27 h for maximum discharge of 4500 m3/s and 58.95 h for discharge of 400 m3/s under the most extreme scenario. Increasing salinization along the Hau River will have important consequences for crop production, freshwater supplies and freshwater ecosystems, therefore requiring timely adaptation responses.

Sea-level rise from a warming climate threatens to inundate coastlines around the world.1 But some of the world’s most vulnerable coasts—those fringing flat delta plains, mainly in Southeast Asia—face the far more immediate threat of sinking land.2 Induced mainly by human activities on a local rather than global scale, this phenomenon, known as land subsidence, can outpace sea-level rise substantially. Indonesia’s biggest city, Jakarta, is sinking at an average rate of 5–10 cm per year,3 much faster than the global rate of sea-level rise, which clocks in at 3.2 mm per year, according to the recent estimates.1 Should subsidence in Jakarta continue unabated, the city could sink up to 6 m by the end of the century, according to JanJaap Brinkman, a water management specialist with Deltares Research Institute in Delft, the Netherlands.

In the context of global warming, rising sea levels are intensifying seawater intrusion in coastal areas. Due to the complex hydrodynamic conditions and increasing groundwater over-extraction in these regions, understanding the patterns of seawater intrusion is crucial for effective prevention and control. This study employed a sandbox model to investigate both vertical and horizontal seawater intrusion into a coastal unconfined aquifer with an impermeable dam under varying conditions of sea level rise, coastal slope, and groundwater pumping rate. Additionally, a two-dimensional SEAWAT model was developed to simulate seawater intrusion under these experimental conditions. The results indicate that sea level rise significantly increases the extent and intensity of seawater intrusion. When sea level rises by 3.5 cm, 4.5 cm, and 5.5 cm, the areas of the saline wedge reached 362 cm2, 852 cm2, and 1240 cm2, respectively, with both horizontal and vertical intrusion ranges expanding considerably. When groundwater extraction is superimposed, vertical seawater intrusion is notably intensified. At an extraction rate of 225 cm3/min, the vertical intrusion areas corresponding to sea level rises of 3.5 cm, 4.5 cm, and 5.5 cm were 495 cm2, 1035 cm2, and 1748 cm2, respectively, showing significant expansion, and this expansion becomes more pronounced as sea levels rise. In contrast, slope variations had a significant impact only on vertical seawater intrusion. As the slope decreased from tanα = 1/5 to tanα = 1/9, the upper saline wedge area expanded from 525 cm2 to 846 cm2, considerably increasing the vertical intrusion range. Finally, the combined effects of groundwater extraction and sea level rise exacerbate seawater intrusion more severely than either factor alone, presenting greater challenges for coastal water resource management.

Coastal wetlands protect coastlines through efficient storage of organic carbon (OC) that decreases wetland vulnerability to sea level rise (SLR). Accelerated SLR is driving saltwater intrusion and altering vegetation communities and biogeochemical conditions in coastal wetlands with uncertain implications. We quantified changes in OC stocks and fluxes driven by 1) saltwater and phosphorous intrusion on freshwater and brackish marshes, 2) vegetation along an experimental saltmarsh to mangrove gradient, 3) saltwater intrusion and vegetation change across a marsh to mangrove ecotone, and 4) vegetation change and mangrove forest development along a marsh to mangrove ecotone. Increasing salinity in freshwater marshes decreased root biomass and soil elevation within one year. In brackish marshes, increased salinity decreased root productivity and biomass and increased root breakdown rate (k), while added salinity did not increase elevation loss. In our experimental marsh-mangrove ecotone, mangrove vegetation promoted higher organic carbon (OC) storage by increasing above and belowground biomass and reducing organic matter k. However, mangroves also increased belowground k, and decreased allochthonous marine subsidies, indicating the potential for OC storage trade-offs. In the Southeast Everglades, we identified strong interior-coastal gradients in soil stoichiometry and mangrove cover. Interior freshwater soil conditions increased k, while total soil OC stocks decreased toward the coast indicating that saltwater intrusion is driving large scale soil OC loss. In the southeast Everglades, mangrove expansion increased root biomass and root productivity, but did not mitigate the overall loss of OC stocks toward the coast. Similarly, in the southwest Everglades, saltwater intrusion drove a decrease in soil OC. However, mangrove encroachment drove a rapid recovery and increased OC stocks. Mangrove encroachment doubled aboveground biomass within the last ten years, increased it 30 times in the last 30 years, and doubled belowground biomass after 20 years. Our research shows that 1) moderate saltwater intrusion without mangrove encroachment will lead to a loss in OC stocks and potentially lead to wetland elevation loss and submergence, 2) in the absence of a change in saltwater intrusion, mangrove expansion can enhance OC storage 3) mangrove expansion can mitigate OC loss during saltwater intrusion, but this pattern depends on mangrove recruitment and ecosystem productivity.

Climate change, rising sea levels, over pumping and seawater intrusion (SWI) pose major challenges to water resource management in coastal areas. Over pumping is considered a major cause of SWI into coastal aquifers and rising sea levels accelerate the intrusion. The combined effects of over pumping and rising sea levels make the problem worse and require more attention. Therefore, SWI due to over pumping and rising sea levels should be predicted and controlled to protect groundwater. In this study a coupled transient density-dependent finite element model is developed to investigate the effects of over pumping and rising sea levels on SWI in Gaza aquifer. Three scenarios are considered: over pumping, rising sea levels due to climate change and combination of the two. The results show that rising sea level has a significant effect on the intrusion of saline water. However, the combination of sea level rise and over pumping results in more intrusion and large amounts of freshwater in the Gaza aquifer could be polluted. To manage SWI into Gaza aquifer, three scenarios have been presented including decreasing abstraction from the aquifer and using other sources of water such as desalination, increasing recharge to the aquifer using tertiary treated wastewater and combination of the two. The results revealed that using tertiary treated wastewater to increase the recharge to Gaza aquifer combined with decreasing the abstraction from the aquifer could help in protecting the aquifer from deterioration.

De-submergence responses of antioxidative defense systems in two wetland plants having escape and quiescence strategies

Seawater intrusion is considered as one of the main processes that degrade water quality by raising salinity to levels exceeding acceptable drinking water standards. Over-abstraction is the main cause of seawater intrusion. Moreover, climate change and sea level rise speed up seawater intrusion. This paper presents the development of a coupled transient finite element model for simulation of fluid flow and solute transport in soils and its application to study seawater intrusion in Gaza aquifer. The effects of likely sea level rise due to climate change and over-pumping on seawater intrusion in Gaza aquifer are studied using three scenarios: rise in sea level due to climate change; decrease in piezometric head on the land side due to over-pumping; and a combination of sea level rise and over-pumping. The results show that a rise of 1 m in sea level has a significant effect on the position of the transition zone and can result in a further 0.5 km seawater intrusion in Gaza aquifer. However, the combination of sea level rise and over-pumping results in movement of the transition zone further inland (nearly 1.0 km). The results show that Gaza aquifer is subjected to severe seawater intrusion from the Mediterranean Sea and there is an urgent need to protect the aquifer from seawater intrusion.

Estuary bays are vulnerable to salinization effects due to relative sea level rise and modification in upland hydrology owing to a variety of factors. Much research has evaluated the one‐sided effect of runoff discharge or sea level on the water exchange and saltwater intrusion for an estuary, while their combined effects have not been evaluated, especially for an estuary bay with narrow river mouth. Taking the Wanquan Estuary Bay (WEB), China, as study case, this paper has revealed the long‐term significant increasing trend of freshwater runoff in non‐flood season during years 1956–2017 using the Man‐Kendall trend analysis, robust principle component regression and Theil–Sen's estimator. A 3‐D hydrodynamic‐salinity‐tracer numerical model is built and calibrated based on the finite‐volume community ocean model, and the effects of runoff increase and sea level rise on the water exchange and saltwater intrusion are investigated. This paper shows the following: (1) The freshwater runoff during non‐flood season in WEB shows significant long‐term increasing trend, and the mean changing magnitude is 0.4546 m3/s/a. (2) The increased runoff accelerates the water exchange, and reduces the turn‐over time and saltwater intrusion in the WEB. The sea level rise reduces the water exchange and increase the saltwater intrusion. (3) For the estuary bay with narrow river mouth, the salinity distributions show more vertical stratification characteristics. The freshwater runoff has power relationships with the average turnover time and salinity, and the sea level has linear relationships. (4) The water exchange and salinity of an estuary bay is more vulnerable to the changed runoff than the sea level rise, while the impacts of sea level rise would increase for estuaries with wide river mouth. This paper provides support for the freshwater exploitation and utilization in estuary bay under the background of climate change and sea level rise.

Influence of aquifer heterogeneity on sea level rise-induced seawater intrusion: A probabilistic approach

Is it worth it? Land-fallowing and saltwater intrusion control under uncertainty.

Trends of sea-level rise effects on estuaries and estimates of future saline intrusion

Saltwater intrusion is a major hazard to coastal communities as it causes degradation of fresh water resources. The impact of rising sea level on the saltwater intrusion into coastal aquifers has been studied for decades, but how human activities affect the extent of saltwater intrusion is poorly understood. Human activities are known to influence groundwater availability indirectly by affecting precipitation patterns and directly by extracting groundwater and reducing recharge. In this paper the authors investigated the integrated impacts of human activities and rising sea level on aquifer recharge in Quintana Roo, Mexico, by incorporating anthropogenic impacts on groundwater recharge into an analytical saltwater intrusion model. The impact of human activities on groundwater extraction was firstly calculated; then, the resulting groundwater recharge was used in a Ghyben–Herzberg analytical model to determine the inland distance of saltwater intrusion. The analytical model tested six scenarios stemming from different combinations of human development patterns, hydrological settings, hydraulic conditions and rising sea level to obtain the range of possible inland movement of saltwater intrusion. Our results indicate that the groundwater recharge will decrease to 32.6 mm year−1 if human activities increase by 50 % more. With 1-m sea level rise, inland saltwater intrusion distance is estimated to be up to 150 and 1 km under head-controlled and flux-controlled scenarios, respectively. A sensitivity analysis of the model reveals that the large hydraulic conductivity of the Quintana Roo aquifer (0.26–68.8 m s−1) is the most important factor in determining saltwater intrusion distance. Therefore, in this aquifer, the response to human activities is greatly exceeded by natural hydrogeological conditions.