Variability in sea ice carbonate chemistry: A case study comparing the importance of ikaite precipitation, bottom ice algae, and currents across an invisible polynya

The carbonate chemistry of sea ice is known to play a role in global carbon cycles, but its importance is uncertain in part due to disparities in reported results. Variability in physical and biological drivers is usually invoked to explain differences between studies. In the Canadian Arctic Archipelago, “invisible polynyas” – areas of strong currents, thin ice, and potentially high biological productivity – are examples of extreme spatial variability. We used an invisible polynya as a natural laboratory to study the effects of inferred initial ice formation conditions, ice growth rate, and algal biomass on the distribution of carbonate species by collecting enough cores to perform a statistical comparison between sites located within, and just outside of, a polynya near Iqaluktuttiaq (Cambridge Bay, Nunavut, Canada). At both sites, the uppermost 10-cm ice horizon showed evidence of CO2 offgassing, while carbonate distributions in the middle and bottommost 10-cm horizons largely followed the salinity distribution. In the polynya, the upper-ice horizon had significantly higher bulk total inorganic carbon (TIC), total alkalinity (TA), and salinity, potentially due to freeze-up conditions that favoured frazil ice production. The middle-ice horizons were statistically indistinguishable between sites, suggesting that ice growth rate is not an important factor for the carbonate distribution under mid-winter conditions. The thicker (non-polynya) site experienced higher algal biomass, TIC, and TA in the bottom horizon. Carbonate chemistry in the bottom horizon could be explained by the salinity distribution, with the strong currents at the polynya site potentially playing a role in desalinisation; biology did not have a noticeable impact. We did see evidence of calcium carbonate precipitation, but with little impact on the TIC : TA ratio, and little difference between sites. Because differences were constrained to relatively thin layers at the top and bottom, vertically averaged values of TIC, TA, and especially the TIC : TA ratio were not meaningfully different between sites. This provides some justification for using a single bulk value for each parameter when modeling sea ice effects on ocean chemistry at coarse resolution. Exactly what value to use (particularly for the TIC : TA ratio) likely varies by region but could potentially be approximated from knowledge of the source seawater and sea ice salinity. Further insights await a rigorous intercomparison of existing data.

The three-dimensional groundwater salinity distribution and fresh groundwater volumes in the Mekong Delta, Vietnam, inferred from geostatistical analyses

Over the last decades, economic developments in the Vietnamese Mekong Delta have led to a sharp increase in groundwater pumping for domestic, agricultural and industrial use. This has resulted in alarming rates of land subsidence and groundwater salinization. Effective groundwater management, including strategies to work towards sustainable groundwater use, requires knowledge about the current groundwater salinity distribution, in particular the available volumes of fresh groundwater. At the moment, no comprehensive dataset of the spatial distribution of fresh groundwater is available. To create a 3D model of total dissolved solids (TDS), an existing geological model of the spatial distribution and thickness of the aquifers and aquitards is updated. Next, maps of drainable porosity for each aquifer are interpolated based on the sedimentological description of the borehole data. Measured TDS in groundwater, inferred TDS from resistivity measurements in boreholes and soft incomplete data (derived from measurements in boreholes and data from domestic wells) are combined in an indicator kriging routine to obtain the full probability distribution of TDS for each (x,y,z) location. This statistical distribution of TDS combined with drainable porosity yields estimates of the volume of fresh groundwater (TDS < 1 g L−1) in each aquifer. Uncertainty estimates of these volumes follow from a Monte Carlo analysis (sequential indicator simulation). Results yield an estimated fresh groundwater volume for the Mekong Delta of 867 billion cubic metres with an uncertainty range of 830–900 billion cubic metres, which is somewhat higher than previous assessments of fresh groundwater volumes. The resulting dataset can for instance be used in groundwater flow and salt transport modelling as well as aquifer storage and recovery projects to support informed groundwater management decisions, e.g. to prevent further salinization of the Mekong Delta groundwater system and land subsidence, and is available at https://doi.org/10.5281/zenodo.4441776 (Gunnink et al., 2021).

Sebaran Salinitas secara Horisontal di Muara Sungai Bondet, Cirebon, Jawa Barat

Fluktuasi salinitas merupakan kondisi yang umum terjadi di daerah muara yang merupakan tempat bercampurnya massa air laut dengan air tawar. Salah satunya adalah muara Sungai Bondet yang terletak di Desa Mertasinga, Kabupaten Cirebon, Jawa Barat. Masuknya air laut ke sungai menyebabkan menurunnya fungsi penting sungai sebagai penunjang kehidupan masyarakat sehari-hari, pertambakan, dan sarana transportasi nelayan. Berdasarkan hal tersebut, maka penelitian ini dilakukan dengan tujuan untuk mengetahui distribusi salinitas di muara Sungai Bondet ke arah hulu sungai. Pengambilan data dilakukan di 10 stasiun pengamatan dari tanggal 19 Agustus sampai 21 Agustus 2020, secara horisontal dan vertikal. Pengolahan data menggunakan software ODV (Ocean Data View) 4.0, Surfer 9 dan ArcGis 10.3. Hasil penelitian menunjukkan bahwa distribusi salinitas secara horisontal dari 10 stasiun pengamatan berkisar dari 0 sampai >30 ppt, dan masuknya air asin mencapai 1,2 km dari muara ke sungai. Salinity fluctuations are a common condition in estuary where seawater and fresh water mix. One of the estuary is the Bondet River which is located in Mertasinga Village, Cirebon Regency, West Java. Saltwater intrusion causes the important function of the river as a support for daily household activities, aquaculture, and also transportation for fishing boats become decrease. Therefore, this research was conducted to knowing the salinity distribution at the estuary of the Bondet River to the upstream. Data collection was carried out at 10 observation stations from August, 19 to August, 21 2020, horizontally and vertically. Data processing using ODV (Ocean Data View) 4.0, Surfer 9 and ArcGis 10.3 software. The results showed that the horizontal distribution of salinity from 10 observation station ranged from 0 to > 30 ppt, and the intake of saltwater reached 1,2 km from the estuary to the river.

Application of Electromagnetic Sensing and Infiltration Measurements to Evaluate Salinity Reclamation and Turfgrass Management Options for Improved Leaching

Scarce freshwater resources in arid and semiarid regions means that recreational landscapes should use recycled or low quality waters for irrigation, increasing the risk of salinity and infiltration problems. We map salinity distribution within turf fields using electromagnetic sensing, evaluate need for leaching and evaluate post leaching results for subsequent management decisions. Electromagnetic measurements were made with two EM38 instruments positioned vertically and horizontally in order to determine salinity distribution. Sensor readings were coupled to GPS data to create spatial salinity maps. Next, optimal calibration point coordinates were determined via ESAP software. Soil samples were taken from 0-60 cm at 5 depths for each calibration point. Laboratory soil saturation percentage, moisture content, ECe and pHe of saturation extracts were determined for calibration to convert resistivity measurements to ECe. Next, ECe maps were created using ESAP software. Leaching for reclamation was performed by means of sprinkling. Treated municipal wastewater was utilized both for irrigation and for reclamation leaching. Low water content and high spatial variability of soil texture adversely affected the accuracy of the readings. Pre and post leaching surveys indicate that there was only a 30% decrease in salinity, very low relative to expected results considering the amount of water applied. This relatively low reduction in salinity and the lack of runoff during irrigation combined with infiltration measurements suggests that aeration techniques for healthier grasses led to water bypassing small pores thus limiting leaching efficiency. In this instance practices to improve infiltration lead paradoxically to less salinity reclamation than expected.

Gravitational circulation in straits and estuaries

A coupled set of partial differential equations and associated boundary conditions is written to describe circulation and salt-flux processes for estuaries in which turbulent mixing results primarily from tidal currents. Similarity solutions, motivated by characteristic salinity distributions observed in estuaries, are obtained for this set of equations and are compared with observational data. The circulation is separated into modes analogous to the barotropic, baroclinic, and Ekman modes of oceanic circulation. The salinity distribution, although coupled to the velocity distribution, is found to vary independently of it as well. The theoretical results are discussed in regard to: (i) correlation between the vertical variations of mean velocity and salinity, (ii) the role of this correlation in maintaining the steady-state salinity distribution in estuaries, and (iii) some implications for computations of flushing and dispersion of contaminants.

Effects of sea level rise on salinity and tidal flooding patterns in the Guadiana Estuary

Sea level rise is a worldwide concern as a high percentage of the population accommodates coastal areas. The focus of this study is the impact of sea level rise in the Guadiana Estuary, an estuary in the Iberian Peninsula formed at the interface of the Guadiana River and the Gulf of Cadiz. Estuaries will be impacted by sea level rise as these transitional environments host highly diverse and complex marine ecosystems. The major consequences of sea level rise are the intrusion of salt from the sea into fresh water and an increase in flooding area. As the physical, chemical, and biological components of estuaries are sensitive to changes in salinity, the purpose of this study is to further evaluate salt intrusion in the Guadiana Estuary caused by sea level rise. Hydrodynamics of the Guadiana Estuary were simulated in a two-dimensional numerical model with the MOHID water modeling system. A previously developed hydrodynamic model was implemented to further examine changes in salinity distribution in the estuary in response to sea level rise. Varying tidal amplitudes, freshwater discharge from the Guadiana River and bathymetries of the estuary were incorporated in the model to fully evaluate the impacts of sea level rise on salinity distribution and flooding areas of the estuary. Results show an overall increase in salinity and land inundation in the estuary in response to sea level rise.

Assessment of river water–groundwater–seawater interactions in the coastal delta of Bangladesh based on hydrochemistry and salinity distribution

A synchronization study among hydrochemistry, hydrochemical facies evaluation, EC observation, salinity distribution and groundwater flow direction has been addressed to assess river water–groundwater–seawater interactions in the coastal delta of southern Bangladesh. The findings show that river water, shallow groundwater and deep groundwater interact with seawater at various intensities within the complex dynamics of hydrochemical facies evaluation. Deep groundwater is intensively influenced by seawater, where shallow groundwater is moderately affected and river water is very negligibly affected. Major cation and anion have been plotted in the Piper diagrams and hydrochemical facies diagrams (HFE-D) to clarify the result. More than 60% of the water samples of the river lie on the Ca-HCO3 (or Mg-HCO3) facies quadrant, and more than 70% of the shallow groundwater samples and more than 95% of the deep groundwater samples lie on the Na-Cl facies quadrant of the HFE-D diagram. River water types are dissimilar, and approximately 82% of facies are characterized by freshening phases and 18% by intrusion phases. Mixed water types with predominate of Na-Cl were observed in shallow groundwater where the hydrochemical facies are characterized by 53 percent freshening phases and 47 percent intrusion phases. Deep groundwater hydrochemistry clearly indicates the dominant Na-Cl type of water in the study area where only four hydrochemical facies are observed and 78 percent correspond to the intrusion phases and 22 percent to the freshening phases. Both direct and reverse cation exchange reactions take place in shallow groundwater, where deep groundwater is predominantly characterized by reverse cation exchange reactions. Two end members: seawater of Bay of Bengal and freshwater, contribute to the exchange reactions in the coastal aquifer of the study area. In terms of nitrate contamination, river waters are affected by negligible to low concentrations, shallow groundwater is affected by moderate to high concentrations and deep groundwater is affected by moderate to very high nitrate concentrations. Dissimilarity in electrical conductivity (EC) values, variation of salinity distribution maps and groundwater flow direction suggest the possible interconnections among river water, groundwater and aquifer sediments. Significant concentrations of Na+ and Cl− ions lead to seawater contamination in groundwater, and HCO3− along with Na+, Ca2+, Mg2+ in river water suggests mixing of freshwater and seawater, which could have adverse effects both in coastal delta aquatic life and in agriculture.