Effects Of Salinity Changes Research Articles

Salinity change evokes stress and immune responses in Atlantic salmon with microalgae showing limited potential for dietary mitigation.

Smoltification was found to impact both immune and stress responses of farmed Atlantic salmon (Salmo salar), but little is known about how salinity change affects salmon months after completed smoltification. Here, we examined (1) the effect of salinity change from brackish water to seawater on the stress and immune responses in Atlantic salmon and (2) evaluated if functional diets enriched with microalgae can mitigate stress- and immune-related changes. Groups of Atlantic salmon were fed for 8weeks with different microalgae-enriched diets in brackish water and were then transferred into seawater. Samples of the head kidney, gill, liver and plasma were taken before seawater transfer (SWT), 20h after SWT, and 2weeks after SWT for gene-expression analysis, plasma biochemistry and protein quantification. The salmon showed full osmoregulatory ability upon transfer to seawater reflected by high nkaα1b levels in the gill and tight plasma ion regulation. In the gill, one-third of 44 investigated genes were reduced at either 20h or 2weeks in seawater, including genes involved in cytokine signaling (il1b) and antiviral defense (isg15, rsad2, ifit5). In contrast, an acute response after 20h in SW was apparent in the head kidney reflected by increased plasma stress indicators and induced expression of genes involved in acute-phase response (drtp1), antimicrobial defense (camp) and stress response (hspa5). However, after 2weeks in seawater, the expression of antiviral genes (isg15, rsad2, znfx1) was reduced in the head kidney. Few genes (camp, clra, c1ql2) in the gill were downregulated by a diet with 8% inclusion of Athrospira platensis. The results of the present study indicate that salinity change months after smoltification evokes molecular stress- and immune responses in Atlantic salmon. However, microalgae-enriched functional diets seem to have only limited potential to mitigate the related changes.

Effects of salinity changes on larval survival, growth, and development of the edible sea cucumber, Holothuria leucospilota (Brandt, 1835) at two developmental stages

For large-scale artificial breeding of sea cucumber (Holothuria leucospilota), it is necessary to understand how environmental parameters affect larval rearing. In this study, the effects of salinity changes on survival, growth, and development of the mid- and late-auricularia of H. leucospilota were estimated within a 7-day culture period. Salinity shock is usually accompanied by water replacement during hatching. To replicate the occurrence of salinity changes in actual larval production, 1/2 of the larval rearing water (initial salinity ∼31.6 ppt) was replaced daily by the experimental waters at different salinity levels (18, 22, 26, 30, 34, 38, and 42 ppt). On day 7, larval survival rates varied with salinity, while the highest survival rates (44.37–46.63% for mid-auricularia; 50.71–53.98% for late-auricularia) were observed in normal salinities (30 and 34 ppt) and the lowest survival rates (15.71–23.96% for mid-auricularia; 24.11–29.57% for late-auricularia) were observed in extreme salinities (18, 22, and 42 ppt). For any sampling event, the body length of mid-auricularia in normal salinities (30 and 34 ppt) were continued to increase during the 7-day culture period. The highest length of late-auricularia was reached on day 3 (880.01 ± 84.38 and 889.06 ± 112.11 µm, respectively), then decreased to 745.31 ± 127.64 and 742.94 ± 98.43 µm on day 7 due to metamorphosis. On day 7, the proportion of mid-auricularia larvae without development potential was the lowest (36.67%) at a salinity level of 34 ppt, and the proportions were increased with both decreasing/increasing salinities. However, this proportion was much lower for the late-auricularia at the same salinity. The decrease in salinity could promote metamorphosis of the late-auricularia, and the highest proportion of doliolaria (24.32%) was observed at salinity level of 26 ppt on day 7. In extreme salinities (18, 22, and 42 ppt), the hyaline spheres (indication of larval competence) in late-auricularia were less obvious than those in other salinities. The ability in resisting salinity shock was increased with larval development, where late-auricularia had better tolerance to salinity shock than mid-auricularia, whereas larvae at both stages were more tolerant to hypertonic than hypotonic conditions. Based on our results, we propose to rear the mid- and late-auricularia at a comparatively high level of salinity (e.g., ∼31 ppt) to promote their survival and performance, while to decrease the salinity (e.g., ∼26 ppt) in the last period of late-auricularia to increase their competence to metamorphose into doliolaria.

Increased salinity decreases annual gross primary productivity at a Northern California brackish tidal marsh

Tidal marshes sequester 11.4–87.0 Tg C yr−1 globally, but climate change impacts can threaten the carbon capture potential of these ecosystems. Tidal marshes occur across a wide range of salinity, with brackish marshes (0.5–18 ppt (parts per thousand)) dominating global tidal marsh extents. A diverse mix of freshwater- and saltwater-tolerant plant and microbial communities has led researchers to predict that carbon cycling in brackish wetlands may be less sensitive to changes in salinity than fresh- or saltwater wetlands. Rush Ranch, a well-monitored brackish tidal wetland of the San Francisco Bay National Estuarine Research Reserve, experiences highly variable annual salinity regimes. Within a five-year period (2014–2018), Rush Ranch experienced particularly extreme drought-induced salinization during the 2014 and 2015 growing seasons. During drought years, tidal channel salinity rose from a 15 year baseline of 4.7 ppt to growing season peaks of 10.3 ppt and 12.5 ppt. Continuous eddy covariance data from 2014 to 2018 demonstrate that during drought summers, gross primary productivity (GPP) decreased by 24%, whereas ecosystem respiration remained similar among all five years. Stepwise linear regression revealed that salinity, not air temperature or tidal height, was the dominant driver of annual GPP. A random forest model trained to predict GPP based on environmental data from low salinity years (i.e. naive to salinization) significantly over predicted GPP in drought years. When growing season salinities were doubled, annual estimates of net ecosystem exchange of CO2 decreased by up to 30%. These results provide ecosystem-scale evidence that increased salinity influences CO2 fluxes dominantly through reductions in GPP. This relationship provides a starting point for incorporating the effect of changes in salinity in wetland carbon models, which could improve wetland carbon forecasting and management for climate resilience.

Physiological basis and differentially expressed genes in the salt tolerance mechanism of Thalassia hemprichii.

Seagrass plays a vital role in the stability of marine ecology. The human development of marine resources has greatly affected the survival of seagrass. Seawater salinity is one of the important factors affecting its survival. Seagrass can survive in high saline environments for a long time and has evolved a variety of effective tolerance mechanisms. However, little is known about the molecular mechanisms underlying salinity tolerance by seagrass. Thalassia hemprichii is a seagrass species with a global distribution. It is also an ecologically important plant species in coastal waters. Nevertheless, the continuous environmental deterioration has gradually reduced the ecological niche of seagrasses. In this study, experiments were conducted to examine the effects of salinity changes on T. hemprichii. The result showed that the optimal salinity for T. hemprichii is 25 to 35 PSU. Although it can survive under high and low salinity, high mortality rates are common in such environments. Further analyses revealed that high salinity induces growth and developmental retardation in T. hemprichii and further causes yellowing. The parenchyma cells in T. hemprichii also collapse, the structure changes, soluble sugar accumulates rapidly, soluble proteins accumulate rapidly, the malondialdehyde (MDA) content reduces, and lipid peroxidation reduces in plant membranes. The molecular mechanisms of salt tolerance differ significantly between marine and terrestrial plants. We found 319 differentially expressed genes (DEGs). These genes regulate transport and metabolism, promoting environmental adaptation. The expression of these genes changed rapidly upon exposure of T. hemprichii to salinity stress for three hours. This is the first report on the physiological and biochemical changes and gene expression regulation of T. hemprichii under different salinity conditions. The findings of this study well deepen our understanding of T. hemprichii adaptations to changes in the shoal living environment.

The effects of salinity changes on anammox performance: The response rule and tolerance mechanism.

Some wastewaters contain high concentrations of ammonia coexisting with large amounts of salt, which might negatively affect the anaerobic ammonium oxidation (anammox) process. In this study, the performance of the anammox process under different saline conditions was investigated using an upflow anaerobic sludge bed-anammox system. After long-term operating for 275 days, the results indicated that the nitrogen removal efficiency remained high under the 0-40 g NaCl/L, and low salinity (15 g NaCl/L) substantially promoted specific anammox activity. Affected by the saline environment, the appearance, color, and shape of sludge notably changed, and the amount of extracellular polymeric substances gradually increased with increasing salinity, which might be one of the reasons for the strong salt tolerance of the system. Chloroflexi and Planctomycetes were the dominant strains under long-term salinity, and Brocadiaceae_g_ unclassified exhibited halophilic characteristics. The redundancy analysis results showed that the concentration of influent NH4 + -N and salinity were the main environmental factors affecting the microbial community of the system. PRACTITIONER POINTS: Provides data to support the maximum value for salinity wastewater treatment with anammox processes' tolerance of 40 g NaCl/L. EPS changes may be responsible for the response to salinity challenges and provide direction for high salinity wastewater treatment. Brocadiaceae_g_ unclassified exhibited a halophilic quality. And it can be focused on to improve treatment efficiency.

Electrochemical Evaluation of the Effect of Different NaCl Concentrations on Low Alloy- and Stainless Steels under Corrosion and Erosion-Corrosion Conditions

The main objective of this study was to assess the influence of salt concentration on the corrosion behaviour, including the role of hydrodynamic conditions, of two broad classes of ferrous engineering materials. These are comprised of alloys, typified by a low-alloy steel (UNS G43400) that corrodes actively in aqueous conditions and a range of passive-film-forming stainless steels (UNS S31600, UNS S15500 and UNS S32760). Corrosion monitoring employed electrochemical (potentiodynamic polarisation) techniques. Three concentrations of aerated sodium chloride were utilised: 0.05 wt% NaCl, 3.5 wt% NaCl and 10 wt% NaCl. In quiescent, liquid impingement and solid/liquid impingement conditions, the corrosion rate of the low-alloy steel was observed to peak at 3.5 wt% NaCl, followed by a reduction in 10 wt% NaCl solution. These findings expand the range of previously reported trends, focused on static conditions. Such corrosion rate/salinity trends were observed to be dictated by the progress of the anodic reaction rather than influence on the cathodic reaction. Detailed studies were undertaken using segmented specimens to facilitate comparisons of the influence of hydrodynamic variations on corrosion behavior; these revealed that such variations influence the corrosion rates of low-alloy steel to a much lesser extent than the effect of changes in salinity. For the stainless steels, in quiescent and flowing conditions, when surface passive films are stable, there was a constant increase in corrosion rate with salinity. In solid-liquid conditions, however, the periodic film-destruction/repassivation events resulted in a similar corrosion rate/salinity trend to that displayed by the low-alloy steel, but with a much larger effect of hydrodynamic conditions. Additonally, the study revealed an underlying influence of stainless steel composition that mirrored, to an extent, the corrosion behaviour in pitting/re-passivation situations

Effects of salinity changes on the osmoregulatory and stress responses in the bay scallop Argopecten irradians

Effects of salinity changes on the osmoregulatory and stress responses in the bay scallop Argopecten irradians

The effect of salinity change on the burrowing behavior of an adult brackish water bivalve Corbicula japonica

The effect of salinity change on the burrowing behavior of an adult brackish water bivalve Corbicula japonica

Impact of Salinity Changes in Shatt Al-Arab Estuary on Biodiversity of Marine Mammals of the Arabian Gulf: A Review

Salinity changes in the Shatt Al-Arab Estuary and North-West Arabian Gulf were monitored and reviewed in terms of the shortage of freshwater inflows to the Shatt Al-Arab Estuary. Data from previous and current surveys on marine mammals in the area have also been checked and compared to study the biodiversity under newly-developed circumstances. The Eco-physiological investigation was performed to assess the salinity tolerance limits of whales, dolphins and dugong. One-third of the world’s 81 species of whales and dolphins, collectively called cetaceans, are thought to occur off the shores in the area. The new checklist is prepared according to recent surveys in the neighbouring Arab Gulf countries and the known checklist of mammals in Iraqi waters. Spatial variation of the marine mammals of the southern part was governed by the occurrence of feeding habitats rather than a direct response to salinity variations. Alteration of seaweed’s habitats in response to water pollution is reported to have a direct effect on the biodiversity of mammals in the gulf. The results of this review were discussed in terms of salinity tolerance, hazardous ecological factors and spatial variation. No obvious effect of salinity changes imposed by the shortage of freshwater inflow on the distribution or loss of marine mammals neither on their habitat in the Arabian Gulf.

Strain-specific morphological response of the dominant calcifying phytoplankton species Emiliania huxleyi to salinity change.

The future physiology of marine phytoplankton will be impacted by a range of changes in global ocean conditions, including salinity regimes that vary spatially and on a range of short- to geological timescales. Coccolithophores have global ecological and biogeochemical significance as the most important calcifying marine phytoplankton group. Previous research has shown that the morphology of their exoskeletal calcified plates (coccoliths) responds to changing salinity in the most abundant coccolithophore species, Emiliania huxleyi. However, the extent to which these responses may be strain-specific is not well established. Here we investigated the growth response of six strains of E. huxleyi under low (ca. 25) and high (ca. 45) salinity batch culture conditions and found substantial variability in the magnitude and direction of response to salinity change across strains. Growth rates declined under low and high salinity conditions in four of the six strains but increased under both low and high salinity in strain RCC1232 and were higher under low salinity and lower under high salinity in strain PLYB11. When detailed changes in coccolith and coccosphere size were quantified in two of these strains that were isolated from contrasting salinity regimes (coastal Norwegian low salinity of ca. 30 and Mediterranean high salinity of ca. 37), the Norwegian strain showed an average 26% larger mean coccolith size at high salinities compared to low salinities. In contrast, coccolith size in the Mediterranean strain showed a smaller size trend (11% increase) but severely impeded coccolith formation in the low salinity treatment. Coccosphere size similarly increased with salinity in the Norwegian strain but this trend was not observed in the Mediterranean strain. Coccolith size changes with salinity compiled for other strains also show variability, strongly suggesting that the effect of salinity change on coccolithophore morphology is likely to be strain specific. We propose that physiological adaptation to local conditions, in particular strategies for plasticity under stress, has an important role in determining ecotype responses to salinity.

Scale sensitivity of environmental effects on the temporal beta diversity of fishes in tropical coastal lagoons

Disentangling multilevel sources of variation is critical for understanding of diversity patterns in high-variability environments. We investigated the scale sensitivity of short-term environmental effects on the temporal beta diversity of fishes in 3 tropical coastal lagoons in Southeastern Brazil. Environmental effects were investigated at 3 hierarchical levels (local, zone, and lagoon). An AICc-based model selection was applied to generalized linear mixed models relating abundance-based beta diversity (Bray-Curtis dissimilarity; βBC) to environmental distances and random effects for other sources of variability. Abundance gradients (βBC-GRA) contributed more for βBC at all hierarchical levels, most likely due to random changes in the abundances of numerous rare marine-origin species. The temporal and spatial marine influences favored the balanced variation in the abundance of different species (βBC-BAL), probably by allowing for marine species with different environmental tolerances and requirements. The freshwater vs. marine influences were primarily represented by short-term effects of salinity changes at the local and zone levels and tide height and accumulated rainfall at the lagoon level. Other environmental effects (e.g. pH and transparency) were representative of that balance depending on the βBC component and hierarchical level. Random effects for morphometric features (local level, width of the connections between zones; lagoon level, distance from the ocean) and climate-related factors (local and zone levels, wind intensity and accumulated rainfall; lagoon level, changing seasons) were also relevant for the relationships between environmental variability and βBC. This study evidenced major scale-related mechanisms driving the temporal beta diversity of fishes in tropical coastal lagoons.

Effects of salinity changes on hatching, hatching-gene expression, and hatching-enzyme expression in anchoveta Engraulis ringens eggs

The Peruvian anchoveta Engraulis ringens is one of the most important commercial fishes along the Humboldt Current. Previous studies have shown that egg quality (volume, protein and lipid content) and hatching rates decrease during the spawning season, from the rainy winter to late spring. In this study, we assessed whether changes in atmospheric condition that led to an intense drought over a decade modified the freshwater river fluxes and seawater salinity at an E. ringens coastal spawning zone off central Chile (36° 30’ S), and determined if changes in salinity affect the hatching-gene expression, hatching-enzyme expression, and hatching success in eggs incubated at a range of salinities (27-35 psu) normally occurring during the reproductive season. Results showed that hatching-enzyme expression increased as the embryo developed. The highest expression of the hatching-enzyme gene and of the enzyme itself, along with hatching success were obtained at the lowest incubating salinity (27 psu). In the field, hatching success decreased from late winter to late spring, the start of the upwelling period at the end of the reproductive season. Thus, variations in salinity of the seawater during the spawning period are coincident with changes in gene expression of the hatching enzyme, the hatching enzyme expression, and hatching success. Spawning late in winter when rainfall is higher and seawater salinity in the coastal area is lower may increase hatching success, a reproductive strategy that might be affected by the observed climate changes and severe drought in central Chile.

Influence of salinity on population growth, oxidative stress and antioxidant defense system in the marine monogonont rotifer Brachionus plicatilis.

Salinity stress influences energy balance, induction of stress proteins, and reproductive success, which are important to life parameters of aquatic organisms. However, physiological and molecular responses of salinity stress have not been studied in the rotifer. To understand the effects of salinity changes on the rotifer, we examined the marine monogonont rotifer Brachionus plicatilis (B. plicatilis) for salinity stress-induced changes in population growth, reactive oxygen species (ROS) levels, and antioxidant enzymatic activities (e.g., glutathione S-transferase [GST], superoxide dismutase [SOD] and catalase [CAT]). In addition, antioxidant-related transcripts (GSTs [GSTs-1-1 and GSTs-1-2], MnSOD1 and CAT2) were investigated in different salinity-exposed rotifers. A significant decrease (P<0.05) in population growth was observed in response to high salinity (35psu) in B. plicatilis. Moreover, the rotifers exposed to high salinity (35psu) exhibited increased ROS levels with enhanced SOD and CAT enzymatic activities, compared to those in controls (15psu). Additionally, significant change (P<0.05) of antioxidant-related genes (GSTs [GSTs-1-1 and GSTs-1-2], MnSOD1 and CAT2) was observed in response to different salinities. Overall, these findings indicate that high salinity induce ROS-mediated oxidative stress, leading to growth retardation and modulation of the antioxidant defense system in B. plicatilis. These findings provide a better understanding on the adverse effects of salinity changes on lifecycle parameters and oxidative stress defense mechanism in rotifers.

Total and Methylmercury of Suaeda heteroptera Wetland Soil Response to a Salinity Gradient Under Wetting and Drying Conditions.

Mercury (Hg) methylation could occur in freshwater ecosystems with low or high salinity. However, few studies are available about the effects of salinity change on mercury(Hg) release and methylation. In-situ experiments using Suaeda heteroptera wetland soil column from the Liaohe estuary were performed to decipher how total mercury (THg) and methylmercury (MeHg) contents change under fluctuant salinity and wet and dry soil conditions. Salinity gradients were set to 0.50% (S1), 1.00% (S2), 1.50% (S3) and 1.80% (S4), and pure deionized water was used as a blank control (CK). Wet and dry soil conditions were set to full inundation condition (WD1) and naturally dried treatment (WD2). Results indicated that the highest THg and MeHg contents were found in surface and bottom soil when water salinity treatment was CK under WD1. THg and MeHg decreased with salinity under WD1. THg contents in overlying water varied from 0.854 to 1.243µg L-1 under WD1 treatments and increased with salinity change. When under WD2 treatment, THg contents in both soil layers gradually decreased with rising salinity. Meanwhile, MeHg contents in both soil layers reached the lowest level at CK (1.666μg kg-1and 2.520μg kg-1) and increased gradually with the rising salinity. By comparison, THg content of the soil was much lower in WD1 than that in WD2. Under the WD1 condition, the MeHg contents and %MeHg decreased with rising salinity and showed significantly different in different salinity treatment, however, its showed an opposite trend with rising salinity under the WD2 condition.

Salt variation induces oxidative stress response in aquatic macrophytes: The case of the Eurasian water-milfoil Myriophyllum spicatum L. (Saxifragales: Haloragaceae)

Wetlands are very fragile systems and susceptible to being affected by human activity. S'Albufera de Mallorca Natural Park is the main wetland in Mallorca Island (Spain), and undergoes a salinization process derived from the overexploitation of adjacent aquifers, which favors marine intrusion. The objective was to evaluate the effects of salinity changes in a channel in s'Albufera de Mallorca through the analysis of biomarkers of oxidative stress in the submerged macrophyte Myriophyllum spicatum. Six different points were analysed along a channel characterized by different salinity values, ranging from ~2 to ~11. The % of macrophyte coverage in the studied stations followed an inverse salinity pattern with greater coverage in areas of low salinity and minimal coverage in those with higher saline concentration. The photosynthetic pigments index (D430/D665), determined in M. spicatum leaves, was significantly higher at the stations most affected by salinity. All antioxidant enzyme activities – catalase, superoxide dismutase, glutathione peroxidase and glutathione reductase – followed a similar pattern of response with an increase in activity as salinity increases. Similarly, the levels of malondialdehyde, as marker of lipid peroxidation, were also increased the stations with the highest salinity. In conclusion, marine water intrusion causes an increase in the salinity of inland waters in s’Albufera de Mallorca, which is evidenced by the increase in the antioxidant enzyme activities and oxidative damage.

Long-term exposure to salinity variations induces protein carbonylation in the copepod Acartia tonsa

Salinity is a key variable influencing the life history of aquatic organisms. Environmental variability in salinity has been associated with increases in the formation of reactive species, ending up in a state of oxidative stress. In copepods, information about effects of salinity variations mostly includes data from short-term experiments where the effects of salinity changes are evaluated in terms of survival and vital rates, and data involving oxidative stress biomarkers are limited. Here, we experimentally evaluate the effects of long-term salinity variations in the estuarine copepod Acartia tonsa through the analysis of protein carbonylation, vital rates (egg production, EPR; ingestion, IR) and gross growth efficiency (GGE). Cultured copepods were subjected to alternate salinity increases and decreases between S = 10 and 20, in steps of 5 units every 12 h, during 15 days (Sv treatment). A control group (no salinity change) was subjected to the same manipulation but in a constant salinity condition (S = 15). Protein carbonylation was higher in females under the Sv treatment compared to control, whereas in males this was not observed. However, males presented significantly higher levels of protein carbonylation than females, irrespective of experimental condition. EPR was higher in control while IR was higher in Sv treatment, but differences were not significant. Instead, GGE showed clear cut and significant differences between Sv and control. While decreased GGE was indicative of significantly increased metabolic expenditures under variable salinity condition, higher oxidative damage was likely a side effect of increased metabolic demands and production of reactive oxygen species.

Combined effects of salinity changes and salicylic acid exposure in Mytilus galloprovincialis.

Pharmaceuticals and Personal care products (PPCPs) are frequently released into several marine matrices, representing significant environmental and ecotoxicological risks. Among the widest spread PPCPs in aquatic systems is Salicylic acid (SA), with known negative effects on marine and freshwater species. Nevertheless, the toxicity resulting from these emerging pollutants, including SA, together with climate change has still received little attention up to date. Among climate change related factors salinity is one that most affects aquatic organisms. To better understand the combined impacts of SA and salinity, the present study evaluated the biochemical alterations induced in Mytilus galloprovincialis mussels exposed to SA and different salinity levels, acting individually and in combination. The effects observed clearly highlighted that cellular damages were mainly observed at higher salinity (35), with no additive or synergistic effects derived from the combined presence of SA. Higher antioxidant capacity of mussels in the presence of SA may prevent increased LPO levels in comparison to uncontaminated mussels. Nevertheless, in the presence of SA mussels revealed loss of redox balance, regardless of the salinity level. Furthermore, mussels exposed to SA at control salinity showed increased metabolic capacity which decreased when exposed to salinities 25 and 35. These findings may indicate the protective capacity of mussels towards higher stressful conditions, with lower energy reserves expenditure when in the presence of SA and salinities out of their optimal range. Although limited cellular damages were observed, changes on mussel's redox balance, antioxidant mechanisms and metabolism derived from the combined exposure to SA and salinity changes may compromise mussel's growth and reproduction. Overall, the present study highlights the need to investigate the impacts induced by pollutants under present and future climate change scenarios, towards a more realistic environmental risk assessment.

Effect of salinity change and exposure time on the egg stages of two abalone species Haliotis discus discus and H. gigantea

The embryonic developmental response of two abalone species (disk abalone Haliotis discus discus, giant abalone Haliotis gigantea) to a drop in salinity with different exposure times was investigated to gain a better understanding of the reasons for the decrease in natural stock populations. Two experimental designs—first, combinations of two salinities (34 and 17 psu) and four exposure times (0, 1, 2 and 4 h), and second, combinations of three salinities (34, 24 and 14 psu) and four exposure times (0, 1, 3 and 6 h)—were tested on disk and giant abalone eggs to determine the effects on hatching onset time, hatching success, percentage of abnormality and survival rate. Hatching onset time increased significantly for both species as salinity dropped and exposure time increased. Both species followed a decreasing trend in terms of hatching success as exposure time increased at low salinity levels. As for abnormality, both species showed a significant negative effect of low salinity and long exposure times. Giant abalone showed better adaptability to long exposure time at low salinity levels, and hence a higher survival rate, than disk abalone.

Experimental study on the effect of salinity change on Fe and Cr removal from estuary water

Freshwater mental contaminants which in the estuary tend to precipitate into intertidal surface sediments during freshwater-seawater mixing because of heavy water chemical reaction. The impacts of ferric hydroxide on the removal rate of Cr with increasing pH and salinity were conducted by laboratory simulation experiment. The removal rate of Cr by ferric hydroxide decreased with increasing pH from river water to seawater in the estuary; this is because pH changed the Zeta potential of ferric hydroxide. And with increasing salinity, the removal rate of Cr by ferric hydroxide firstly decreased and then increased. On the hand, Na+ entering the sliding surface, which could improve Zeta potential and stability of ferric hydroxide colloid, which leads to the amount of Cr removal by colloid aggregation decreased. On the other hand, there was competitive adsorption between Cland CrO42-/HCrO4-. In this study, Fe was the key factor of heavy metal Cr distribution with pH change.

Effects of abrupt salinity increase on nitrification processes in a freshwater moving bed biofilter

The nitrification process is a widely used biological approach responsible for ammonia and nitrite removal in recirculating aquaculture system (RAS) biofilters. Given this pivotal role, the influence of different water quality parameter on nitrification efficiency is important information for RAS operations. One influencing parameter is salinity, and salinity fluctuations in freshwater RAS biofilters are reported to affect the nitrifying bacteria. This study investigated the effects of abrupt increase in salinity in freshwater RAS on substrate-dependent (1’-order) as well as substrate independent (0’-order) nitrification rates. A 100% inhibition was found for surface specific removal (STR) of total ammonia nitrogen (TAN) and surface specific nitrite removal (SNR) when salinity was abruptly increased to 25‰ and above. A fast turnover (i.e. steep decline in [NH4-N+] and [NO2-N−]) were observed at lower salinities (≤10‰), while limited/no degradation of either ammonia or nitrite was seen at salinities above 25‰. At low substrate loading (1’-order process), removal rate constants (k1a) of 0.22 and 0.23 m d-1 were observed for ammonia and nitrite degradation, respectively, declining to 0.01 m d-1when adding marine RAS water increasing the salinity to 15‰. Similar observations followed at high nutrient loadings (0’-order process) with STR and SNR of 0.10 and 0.12 g N m-2 d-1, respectively, declining to 0.01 g N m-2 d-1 at 15‰. When salinities of 25‰ and 35‰ were applied, neither TAN nor nitrite degradation was seen. The results thus demonstrate a pronounced effect of salinity changes when freshwater RAS biofilters are subjected to fast/abrupt changes in salinity. RAS facility operators should be aware of such potential effects and take relevant precautions.