Salinity Distribution Pattern Research Articles

Impacts of vegetation and tidal conditions on porewater and salt transport in coastal wetlands: Numerical simulations and field evidence

Coastal wetlands are crucial ecosystems with high fragility to environmental alterations. Despite early efforts, interactions of water and salt with vegetation in coastal wetlands have rarely been investigated especially with increasing anthropogenic disturbances. Here, field data and numerical simulations were utilized to understand the influences of vegetation, evapotranspiration (ETa), tide, and inundation events on porewater and salt transport in highly regulated tidal riparian wetlands. At the site, the presence of Phragmites australis significantly enhanced soil hydraulic conductivity (KS) and facilitated hydraulic connections between groundwater and surface soil, resulting in the rapid response of soil salinity to groundwater level fluctuations. Simulation results further demonstrated the combined effects of tides and ETa on the salinity distributions, revealing the formation of a high salinity zone in the middle region due to the inflow of water from the tides and ETa-driven upward movements of water and salt; however, as salinity levels increased within the high salinity zone, the growth of Phragmites australis was constrained, leading to reduced transpiration (Ta). Tidal parameters such as amplitudes and mean water levels could affect salt accumulation processes in soils and further the high-salinity zone. Finally, inundation events from extreme upstream discharge had a flushing and diluting effect on accumulated salts, alleviating salinity stress and promoting vegetation Ta and growth; however, further increases in ETa led to salt re-accumulation, potentially reinstating the salinity distribution pattern after inundation. These findings enhance our understanding of ecohydrological processes in coastal wetlands and have important implications for wetland management and restoration.

Identification and Spatial Analysis of Land Salinity in China's Yellow River Delta Using a Land Salinity Monitoring Index from Harmonized UAV-Landsat Imagery.

Precise identification and spatial analysis of land salinity in China's Yellow River Delta are essential for the rational utilization and sustainable development of land resources. However, the accurate retrieval model construction for monitoring land salinity remains challenging. This study constructed a land salinity retrieval framework using a harmonized UAV and Landsat-9 multi-spectral dataset. The Kenli district of the Yellow River Delta was selected as the case study area, and a land salinity monitoring index (LSMI) was proposed based on field survey data and UAV multi-spectral image and applied to the reflectance-corrected Landsat-9 OLI image. The land salinity distribution patterns were then mapped and spatially analyzed using Moran's I and Getis-Ord GI* analysis. The results demonstrated the following: (1) The LSMI-based method can accurately retrieve land salinity content with a validation determination coefficient (R2), root mean square error (RMSE), and residual predictive deviation (RPD) of 0.75, 1.89, and 2.11, respectively. (2) Land salinization affected 93.12% of the cultivated land in the study area, and the severely saline soil grade (with a salinity content of 6-8 g/kg) covered 38.41% of the total cultivated land area and was widely distributed throughout the study area. (3) Saline land exhibited a positive spatial autocorrelation with a value of 0.311 at the p = 0.000 level; high-high cluster types occurred mainly in the Kendong and Huanghekou towns (80%), while low-low cluster types were mainly located in the Dongji, Haojia, Kenli, and Shengtuo towns (88.46%). The spatial characteristics of various salinity grades exhibit significant variations, and conducting separate spatial analyses is recommended for future studies.

Salinity distribution pattern and its induced adaptability of tomato roots

Salinity is a major abiotic stress and threat to tomato production. Roots can attenuate salt stress at a specific salinity concentration, especially with non-uniform salinity distribution conditions, and may play a role in enhancing tomato plant adaptability to salt stress. Salt stress will also have a certain impact on root growth, which in turn affects the adaptability of crops to salt stress. Under different salt gradients, if we can find a reasonable distribution strategy, we can increase the tolerance of plants to salt stress. The hydroponics method was used and the roots were split into left and right parts. We established different salinity distribution patterns: a uniform salinity distribution T1 [0, 0], T2 [0.2%, 0.2%], and T3 [0.3%, 0.3%] and a non-uniform salinity distribution T4 [0.1%, 0.3%], T5 [0.1%, 0.5%], T6 [0.2%, 0.4%]. We observed the whole growth stage, and the plant's physiological responses to salt stress were measured. The data indicated that tomato plant roots can attenuate salt stress at a salinity concentration of 0.4%. The non-uniform salinity distribution can restrict root-uptake and uptake efficiency of nutrients (Na+, K+). Fruit yield, flavor and quality were enhanced by the non-uniform salinity distribution of T4 [0.1%, 0.3%]. Increased K+ led to a decreased Na/K ratio, which could reduce the toxicity of salt ions and improve tomato growth. The antioxidant enzyme activities of both roots and leaves of tomato plants were elevated under different salt stress patterns, indicating that the subject plants have the potential to exert adversity adaptations and that the enzyme activities are responsive to the degree of salt stress. Response of tomato fruiting stage growth and development and yield quality to different salt stresses. Growth adaptation of tomato under salt stress conditions. The above issues are discussed to provide a theoretical basis for the salt tolerance mechanism of tomatoes under non-uniform salt stress and the growth status of tomatoes on saline soils.

Spatial analysis of salinity distribution patterns in upper layers of the Black Sea

Salinity is one of the most important factors that primarily determines the level of seawater’s density and, consequently, the movement of water masses in the World Ocean. Spatial distribution of the salinity in different layers of the Black Sea are associated with varying levels of water balance seasonal variability and, general circulation of Black Seas waters and in the surface layer has a seasonal structure. To study spatial distribution of salinity in upper layers of the Black Sea we’ve used data from Copernicus Marine Environment Monitoring Service, that were processed and aggregate by seasons and depth. We found that the most fluctuated layer is a top layer (up to 2.8 m) and the highest values Black Sea salinity reaches near the Bosporus Strait, where more saline water from the Sea of Marmara connected with fresher water of the Black Sea. Also we found that the impact of the river flows, mixing of the water, water regime of the sea decreasing with depth, so in the bottom of the upper layer the spatial fluctuation of the salinity is minimal and reaches about ±3‰, while in the depth of 2.8 m its reaches ±12-15‰.The lowest level of salinity through all of the upper layer (0-50 m) lays around the seashore and north-western part of the sea.

MEAN CLIMATIC PARAMETERS OF THE UPPER MIXED LAYER IN THE BERING SEA (LOWER BOUNDARY, TEMPERATURE, SALINITY) AND THEIR ANNUAL VARIABILITY

All available deep-water oceanographic data obtained in the Bering Sea in 1929–2019 are analyzed (101,425 oceanographic stations). Lower boundary of the upper mixed layer is determined from the vertical temperature profiles using the criterion of temperature deflection from SST (10 % for June-October and 0.2, 0.3, and 0.5 o С for November-May). The mixed layer is rather thin in June-September, its thickness is 10–20 m over the major part of the sea, and 30–40 m at the straits between central Aleutian Islands. In DecemberMarch, the mixed layer depth increases to 120–160 m in the northern deep-water sea and up to 180–200 m at the straits between central and eastern Aleutian Islands, though it is thinner in plumes of warm waters entering from the Pacific. At the continental shelf, the mixed layer can be traced to the depth of 20–40 m in the eastern Bering Sea and 60–80 m at Kamchatka in December-January and to 60–80 m in the eastern Bering Sea and 80–100 m at Kamchatka in February-March. The mixed layer temperature distribution is distinguished by two completely different seasonal patterns. The winter distribution pattern with the highest temperature in the areas adjacent to the Aleutian Straits is typical for November-June. The summer pattern with high temperature in the Karaginsky Bay, Bristol Bay, and Norton Sound and lower temperature near the Aleutian Straits is typical for July-October. On the contrary, the salinity distribution pattern is stable, with the highest salinity at the central and eastern Aleutian Straits and lower salinity in the coastal zone as the Anadyr Bay and Norton Sound influenced by the river runoff.

Salt Dynamics in Coastal Marshes: Formation of Hypersaline Zones

AbstractSalt is a key solute in salt marshes and under the influence of evapotranspiration can accumulate to a high concentration level in the marsh soil and precipitate in the solid form to become a significant stressor for plants, affecting marsh plant productivity and ecological zonation. Numerical simulations of coupled pore water flow and salt transport were conducted to examine how spring‐neap tides and evaporation combine to influence salt dynamics and distribution patterns in marshes. The salt pan formation was simulated with a sandy loam marsh soil subjected to a medium rate of potential evaporation. The critical condition for the salt pan formation was underpinned by hydraulic connection between the marsh surface and water table to sustain evaporation in the supratidal zone. Both low soil permeability and overly high potential evaporation were found to break the hydraulic connection. In this case, the surface soil salinity increased gradually over the intertidal zone to a maximum around the spring high tide mark followed by a rapid decrease to a lower constant level across the supratidal zone. This salinity distribution pattern has also been observed in the field. In both salt marshes with and without salt pans, excessive salt accumulated on the marsh surface due to evaporation was removed by tidally induced circulating flow and/or flow driven by density gradients associated with the accumulated salt. The salt dynamics and distribution patterns revealed here, especially the salt pan formation simulated for the first time, have important implications for studies of marsh plant growth and overall eco‐functions.

Characteristics of saltwater intrusion during high and low waters along Sungai Kilim, Langkawi Kedah

Salinity distribution is one of the physical indices that is important to determine water resources management and quality in estuaries. There are many other driven parameters in determining salt intrusion such as tides, river discharge, and river geometry. This paper studies the salinity distribution using the tide driven parameters during high and low waters. The objectives of this study are to obtain the salinity and pH values at different tidal impact of low and high waters in determining one of the physical indices along Kilim River, Langkawi. There were ten different stations with 500 m of interval along the study area starting from the Kilim River Jetty towards the river mouth. The salinity was obtained from six different depths with the reading of pH values and temperature as supporting details of the observation made along the Kilim River, Langkawi. The depth at each station varied from 0.5 to 3.0 m with 0.5 m of interval. Based on the results obtained from this study, the salinity during high water was highly stratified compared to those of low water. The salinity characteristic is important to further research on the impact of sea level rise at the estuaries. The salinity distribution pattern may contribute to the different species of vegetation along the Kilim River, Langkawi. Therefore, this study will help in contributing the mangrove migration for future research.

Spatial Patterns of Groundwater Biogeochemical Reactivity in an Intertidal Beach Aquifer

AbstractBeach aquifers host a dynamic and reactive mixing zone between fresh and saline groundwater of contrasting origin and composition. Seawater, driven up the beachface by waves and tides, infiltrates into the aquifer and meets the seaward‐discharging fresh groundwater, creating and maintaining a reactive intertidal circulation cell. Within the cell, land‐derived nutrients delivered by fresh groundwater are transformed or attenuated. We investigated this process by collecting pore water samples from multilevel wells along a shore‐perpendicular transect on a beach near Cape Henlopen, Delaware, and analyzing solute and particulate concentrations. Pore water incubation experiments were conducted to determine rates of oxygen consumption and nitrogen gas production. A numerical model was employed to support field and laboratory interpretations. Results showed that chemically sensitive parameters such as pH and ORP diverged from salinity distribution patterns, indicating biogeochemical reactivity within the circulation cell. The highest respiration rates were found in the landward freshwater‐saltwater mixing zone, supported by high dissolved inorganic carbon. Chlorophyll a, a proxy for phytoplankton, and particulate carbon did not co‐occur with the highest respiration rates but were heterogeneously distributed in deeper and hypoxic areas of the cell. The highest rates of N2 production were also found in the mixing zone coinciding with elevated O2 consumption rates but closer to the lower discharge point. Model results were consistent with these observations, showing heightened denitrification in the mixing zone. The results of this work emphasize the relationship between the physical flow processes of the circulation cell and its biogeochemical reactivity and highlight the environmental significance of sandy beaches.

A first description of ciliate assemblages in a subtropical, eutrophic bay, South China Sea: species assemblage and environmental correlates

The ciliate community together with physical-chemical variables was investigated in a subtropical, eutrophic bay of the South China Sea from January 7–10 (dry season) and April 27–30 (wet season), 2012. Both temperature and salinity exhibited typical seasonality. A total of 27 species of ciliates belonging to 19 genera were identified, and the dominant species were Strombidium globosaneum in January and Codonella rapa in April. The composition and abundance exhibited spatial and temporal fluctuations, with total mean abundance of ciliates in April (1219 ± 919 ind l-1 ), was much higher than that in January (283 ± 137 ind l-1 ). Spatially, high species numbers were found mainly near the mouth of the estuary, and the abundance decreased from inside to the mouth of the bay. Statistical analysis showed that ciliate assemblages were closely related to the environmental variables. The distribution patterns of salinity and chlorophyll a concentration were similar, suggesting that, prey abundance may correlate significantly with ciliate abundance, and salinity may not be the main factor explaining the spatial variation in the ciliate community in the study area.

Estimation of soil salinity in a drip irrigation system by using joint inversion of multicoil electromagnetic induction measurements

AbstractLow frequency electromagnetic induction (EMI) is becoming a useful tool for soil characterization due to its fast measurement capability and sensitivity to soil moisture and salinity. In this research, a new EMI system (the CMD mini‐Explorer) is used for subsurface characterization of soil salinity in a drip irrigation system via a joint inversion approach of multiconfiguration EMI measurements. EMI measurements were conducted across a farm where Acacia trees are irrigated with brackish water. In situ measurements of vertical bulk electrical conductivity (σb) were recorded in different pits along one of the transects to calibrate the EMI measurements and to compare with the modeled electrical conductivity (σ) obtained by the joint inversion of multiconfiguration EMI measurements. Estimates of σ were then converted into the universal standard of soil salinity measurement (i.e., electrical conductivity of a saturated soil paste extract – ECe). Soil apparent electrical conductivity (ECa) was repeatedly measured with the CMD mini‐Explorer to investigate the temperature stability of the new system at a fixed location, where the ambient air temperature increased from 26°C to 46°C. Results indicate that the new EMI system is very stable in high temperature environments, especially above 40°C, where most other approaches give unstable measurements. In addition, the distribution pattern of soil salinity is well estimated quantitatively by the joint inversion of multicomponent EMI measurements. The approach of joint inversion of EMI measurements allows for the quantitative mapping of the soil salinity distribution pattern and can be utilized for the management of soil salinity.

阿拉善荒漠区灌木群落的土壤盐分特征分析

作为中国典型的荒漠生态系统，阿拉善荒漠区灌木群落不仅是中国北方重要的生态屏障，而且也是中国六大生物多样性中心之一。因此，阿拉善荒漠灌木群落的稳定对于我国生态安全与生物多样性保护具有重要意义，而土壤盐分是影响干旱区荒漠植物群落组成与结构、群落动态的决定因素之一。本文以2010~2011年阿拉善荒漠灌木资源野外调查为基础，分析了灌木群落下的土壤盐分含量、类型及分布格局等特征，得到如下结论：1) 就不同群落而言，柽柳灌丛的“盐岛”效应最明显，按总盐量排序依次为：柽柳>梭梭>白刺>霸王>沙冬青>绵刺>蒙古扁桃；2) 土壤中阴离子以 SO42- 和C1-为主，阳离子以Na+为主，土壤盐分类型以硫酸钠型和氯化钠型为主；3) 受黑河地表径流和下游强烈蒸发作用影响，土壤盐分分布格局整体表现为西北高东南低的特征，沿东南向西北呈逐级递增的趋势。 As a most typical desert ecosystem in China, Alxa desert shrub is not only a significant ecological barrier of North China, but also one of the sic biodiversity centers in China. Therefore, the stabili-zation of Alxa desert shrub community, which is observably affected by soil salinity, has important effect on ecological security and biodiversity in China. Based on the field survey of Alxa desert shrub resources in 2010-2011, the content, composition and distribution of soil salinity under the shrub community were analyzed. The following conclusions were summarized: 1) There is a salt enrichment effects under the Tamarix chinensis and the content of total salt could be arranged in the following order: Tamarix chinensis > Haloxylon ammodendron > Nitraria tangutorum > Sarco-zygium xanthoxylon >Ammopiptanthus mongolicus > Potaninia mongolica > Amygdalus mongolica; 2) The soil negative and positive ion were respectively dominated by SO42-, C1- and Na+, so that the soil salinity was sodium sulfate type and sodium chloride type; 3) The characteristics of soil salinity distribution pattern was high in northwest and low in southeast, and increased from southeast to northwest, which was mainly affected by the downstream of Heihe river runoff and intense evaporation.

Monitoring and evaluating spatial variability of soil salinity in dry and wet seasons in the Werigan–Kuqa Oasis, China, using remote sensing and electromagnetic induction instruments

In arid and semi-arid regions, soil salinization is one of the most critical environmental problems due to its severe effects on agriculture productivity and long-term sustainable development. Monitoring, evaluating and predicting soil salinization are of utmost importance in those regions. The current study proposes an evaluating and predicting approach that is based on remote sensing (e.g., Landsat TM images) and near sensing technologies (e.g., electromagnetic induction device, EM38). We investigated seasonal and spatial changes of soil salinity in a Delta Oasis between the Werigan and Kuqa River in the northern rim of Tarim Basin, Xinjiang, China. Preliminary analysis suggests that apparent soil electrical conductivity obtained from EM38 is highly correlated with soil salinity, which is obtained from post-sampling laboratory tests. The study hence uses the apparent electrical conductivity as a surrogate for soil salinity to understand the spatial pattern of the latter. To understand soil salinity distribution pattern in the study region, we integrated spectral information derived from two Landsat TM images (acquired on April 15, 2011 for the dry season and September 22, 2011 for the wet season), and applied universal kriging, spectral index regression and regression–kriging approaches to obtain the pattern. Results suggest that regression–kriging with nested spherical model produces the closest fit of the observed soil apparent electrical conductivity. Since most previous studies often employ either one or the other approaches in soil salinity monitoring and evaluation, the study suggests that combining remote and near sensing technology provides a rapid and relatively accurate assessment of soil salinity in arid and semi-arid regions, which would be essential to manage and prevent further soil salinization and re-salinization.

Movable Surface Irrigation System (MSIS) Impact on Spatial and Temporal Distribution of Soil Moisture and salinity

Movable surface irrigation system (MSIS), was carried out by modification of center pivot irrigation system and depends on replacing the sprayers by polyethylene hoses ending by nozzles. Field experiments were conducted at farm on Alex-Cairo desert road, to assess moving surface irrigation system at 2012 year. The main aims of this research are to study spatial and temporal moisture and salinity distribution patterns under (MSIS), the modification of pivot irrigation system to be more suitable to irrigate some trees, and other high crops under special conditions, to evaluate the modification system and to reduce the investment costs of the modified system. Results show that, operating the (MSIS)at low pressure head (1.5 bar), water amount was saved by (16.8%)(Abdel-Rahman, 2005), the uniformity coefficient was 90.75%, beside, the movable surface system reduced the hazard of chemigation. Finally, High efficiency of applied water distribution, reduce deep- percolation, reducing runoff and having good management without exceed water irrigation by using (MSIS).

Pola Sebaran Salinitas dengan Model Numerik Dua Dimensi di Muara Sungai Musi

The aim of this research is to describe the spread salinity with two dimensions numerical model at the Musi River’s estuary, and also to determined relationship of spread salinity with hydrodynamic unsure in water. The research has been done at Juli – Agustus 2011 at Musi River’s estuary, South Sumatra. Determination of sampling points is done by using purposive sampling method. The sample is measured by in-situ method and the data is proceed using Surface Water Modelling System (SMS 8.1) software, then verified with field measurement. The result of this research indicated that when the condition of sea-water tidal waters not too far into the river, the concentration of salinity in the surface layer (0.2 D) ranged between 6 - 28o/oo, in the water column (0.5 D) between 6 - 27o/oo, and in the deep waters (0.8 D) between 5 - 27o/oo. In other hand, at low tide condition, the influence of river moved farther out to the sea, with the concentration of salinity in the surface layer (0.2 D) ranged between 5 - 26o/oo, the salinity in the water column (0.5 D) and in the deep waters (0.8 D) between 4 - 27 o/oo. The result of spread salinity of the model simulation shows that the salinity distribution patterns follow the formed of the flow so that it can be said that the flow will affect the distribution of salinity in the waters. Based on the results of the flow simulation and salinity with or without the effects of wind’s flow and salinity patterns are the same, in the range 0.9 to 23.9o/oo. The verified average error result of measurement and simulation the model (MRE) with or without wind is 3,163 E-11%. So, factor of the wind did not significantly affect the movement of flow on the research.

Spatial and temporal mapping of groundwater salinity using ordinary kriging and indicator kriging: The case of Bafra Plain, Turkey

Groundwater salinity contributes significantly to soil salinization in irrigated areas. In this study, spatial and temporal analyses of groundwater salinity were performed based on data from 97 wells monitored over a 7-year period. ArcGIS Geostatistical Analyst was used in exploratory data analysis, semivariogram model selection, cross-validation and development of a groundwater salinity distribution pattern. Groundwater salinity semivariogram models varied by year and included exponential (2004, 2009), spherical (2005), J-Bessel (2006) and rational (2007, 2008, 2010) models. Ordinary Kriging (OK) was used to analyze spatial variability of groundwater salinity, whereas Indicator Kriging (IK) was used to analyze groundwater salinity in relation to pollution threshold values.Spatial variability maps show a decrease in groundwater salinity from 2004 to 2010, with salinity levels in 31% of the study area exceeding 5.0dSm−1 in 2004, compared to 9% of the study area in 2010. Moreover, probability maps show that 13.60% of the total area had the highest probability (0.8–1.0) of exceeding the threshold in 2004, compared to 0% in 2010.

Assessment of spatial variability in some soil properties as related to soil salinity and alkalinity in Bafra plain in northern Turkey

The objectives of this study were to assess the variability in soil properties affecting salinity and alkalinity, and to analyze spatial distribution patterns of salinity (EC) and alkalinity (ESP) in the plain, which was used irrigation agriculture with low quality waters. Soil samples were collected from 0-30 cm, 30-60 cm, 60-90 cm and 90-120 cm soil depths at 60 sampling sites. Soil pH had the minimum variability, and hydraulic conductivity (Ks) had the maximum variability at all depths. The mean values of pH, EC, ESP and Ks increased while the mean values of CEC decreased with soil depth. Values pH, EC and ESP were generally high in the east and northeastern sides. Soil properties indicated moderate to strong spatial dependence. ESP and pH were moderately spatially dependent for three of the four depths, EC exhibited moderate spatial dependence for one of the four depths, CEC had a moderate spatial dependence at all depths, and Ks exhibited a strong spatial dependence. EC, CEC, and ESP were considerably variable in small distances. The spatial variability in small distances of EC, CEC, pH and ESP generally increased with depth. All geostatistical range values were greater than 1230 m. It was inferred that the strong spatial dependency of soil properties would be resulted in extrinsic factors such as ground water level, drainage, irrigation systems and microtopography.

In situ production of chromophoric dissolved organic matter in coastal environments

The horizontal and vertical distribution of marine humic‐like fluorophore, namely, chromophoric dissolved organic matter (CDOM) fluorescence, was surveyed in Ise Bay, Japan. The distribution patterns of salinity and marine humic‐like fluorescence intensity suggested that riverine humic‐like fluorophore conservatively distributed along with fresh‐sea water mixing in surface water at Ise Bay. However, analysis of mixing behavior of riverine CDOM implied that the 25.1 ± 10.6% in average of bulk marine humic‐like fluorescence intensity of Ise Bay surface waters was derived not from a terrestrial origin but an in situ production. A degradation experiment using natural plankton demonstrated the rapid production of marine humic‐like fluorophore within a day. The results consistently suggested that in situ production of marine humic‐like fluorophore plays an important role in the dynamics of CDOM in coastal environments.

Dissolved Inorganic Nutrient Fluxes from Two Seasonal Rivers into Gazi Bay, Kenya

The riverine contribution to the dissolved inorganic nutrient budget of Gazi Bay, a little-studied pristine system, has been investigated. River Mkurumuji had estimated nutrient discharge rates equivalent to 12·21±9·98kgNday−1in the form of NH4+, 37·45±30·59kgNday−1in the form of NO3−+NO2−and 31·66±25·86kgPday−1in the form of PO43−during the wet months of the study period. During the dry months, the corresponding values were 0·28±0·17, 0·27±0·16 and 0·93±0·57, respectively. River Kidogoweni discharged nutrients at rates equivalent to 5·37±4·69kgNday−1in the form of NH4+, 9·83±8·59kgNday−1as NO3−+NO2−and 9·00±7·87kgPday−1in the form of PO43−during the wet months. Corresponding mean discharge rates during dry months were 0·013±0·009, 0·0057±0·0038 and 0·035±0·023, respectively.From the salinity distribution patterns, it is evident that during wet seasons, River Mkurumuji influences the nutrient distribution patterns of coral reef and seagrass zones, while River Kidogoweni influences the nutrient distribution pattern of the mangrove zone of the Bay. There seems to be minimal riverine influence during thedry seasons. The mean gross primary productivity of the Bay during the two seasons is a manifestation of thisobservation. Mean values for the mangrove, seagrass and coral reef biotopes, respectively, were: 540·41±222·63, 552·22±291·36, 388·88±247·12mgCm−3day−1(wet seasons); and 377·67±159·7, 230·84±84·75, 240·27±115·29mgCm−3day−1(dry seasons).The levels of dissolved inorganic nutrient concentrations between the waters of both rivers are not significantly different (P=0·35), but are higher than for the Bay waters, which are characteristically oceanic. Gazi Bay nutrient levels are lower than those reported elsewhere within the region, therefore suggesting that the Bay is a relatively pristine environment.

Processes and History of Terminos Lagoon, Mexico

There is a net flow of Gulf of Mexico high salinity water into Terminos Lagoon through the eastern inlet, mixing with runoff from three large rivers, and a net flow of low-salinity lagoon water out through the western inlet. The average circulation is reflected in distribution patterns of salinity, sediment size distributions, forams, percent of calcium carbonate in the sediments, and water turbidity. Relatively high organic productivity is indicated by numerous large standing stocks of forams. The lagoon is on the boundary between biogenic carbonate sediments on the east and detrital river-borne sediments on the west. The modern lagoon barrier began during the Holocene on a foundation of calcilutite when sea level was at about -- 10 m. When it reached about its present level the inlets were east of the present ones. Predominant flow of lagoon water out through the western inlet as at present is indicated by river-borne detritus under a surface cap of biogenic carbonate on the western end of the barrier. The seaward side of the barrier is being eroded, except on the western end, where there is deposition. The lagoon is essentially filled with sediment, and most detritus being delivered by rivers is bypassing the lagoon. It is suggested that deposits similar to those in Terminos Lagoon can be identified in ancient sediments.