Physicochemical degradation of Avicennia marina mangrove soils in the Red Sea: implications for coastal ecosystem services

ABSTRACTThis study was conducted at eight different sites of the mangrove ecosystem in Kaozhou Yang, Huidong District, Huizhou Guangdong, South China Sea. The concentration of nutrients (NH4+, NO2−, NO3−, PO43− and SiO32−) was determined (both water and soil samples). Based on the nutrient concentration, the comparison of mangrove biomass production, total organic matter and bacterial count were also investigated. The level of nutrient values and biomass production of mangrove and bacterial count in both water and soil samples followed the same trend. The results showed that the highest concentration of NH4+ (0.457 ± 0.051 mg/L), NO2− (0.223 ± 0.018 mg/L), NO3− (0.521 ± 0.038 mg/L), PO43− = P (0.242 ± 0.049 mg/L) and SiO32− = Si (4.094 ± 0. 095 mg/L) were found in the water samples from station S‐1, while the lowest values of NH4+ (0.063 ± 0.007 mg/L), NO2− (0.0124 ± 0.001 mg/L), NO3− (0.053 ± 0.003 mg/L), PO43− = P (0.012 ± 0.002 mg/L) and SiO32− (0.713 ± 0.009 mg/L) were recorded in station S‐8. The order of nutrient values and bacterial count in the water and soil samples was same: S‐1 > S‐5 > S‐3 > S‐6 > S‐4 > S‐2 > S‐7 > S‐8. Avicennia marina was the only species found in all stations therefore; this species was considered for the assessment of the biomass of above‐ and belowground parts. The highest biomass (aboveground parts; 131.23 ± 2.09 Mg/ha, belowground parts; 139.86 ± 2.57 Mg/ha) was recorded at station S‐1. The lowest biomass (aboveground parts; 119.72 ± 1.99 Mg/ha, belowground parts; 127.13 ± 2.01 Mg/ha) was found at station S‐8. The analysis of organic matter (both water and soil samples) also showed the same trend. It was concluded that that mangrove biomass was nutrient‐dependent, confirming our hypothesis that “mangrove biomass could depend on the availability of nutrients.” Mangrove ecosystem plays an important role in coastal and marine food webs and is closely connected to the well‐being of coastal communities. Therefore, the mangrove ecosystem is mainly included in the United Nations Sustainable Development Goals (SDGs) and the Paris Agreement (climate change mitigation) in this decade. This study is in line with SDGs 12 (Responsible consumption and production of food), 13 (Climate action), 14 (Life below water) and 17 (Partnerships with the goals). The mangrove plants convert carbon dioxide (toxic form of carbon) in its useful form (biomass), and in addition, the mangrove ecosystem serves as a food and nursery area for fish and shellfish fisheries. Therefore, this research promotes the role of the mangrove ecosystem to benefit the blue economy and mitigate climate change. It was concluded that the abundance of bacteria and the biomass of mangroves depend on the availability of nutrients. Therefore, the results of this study strengthen our hypothesis. In the future, this study could serve as a reference study for blue carbon sequestration in the mangrove ecosystem.

Mangrove ecosystems are known to act as filters for contaminants between land and sea. In New Caledonia, urbanization has increased along the coastline during the last decades. However, the impact of urbanization on contaminant cycling in mangrove forests has remained unexplored. In this study, we investigated trace metals (TM) dynamics in an urban mangrove soil and their transfer to mangrove tissues for the two dominant mangrove species in New Caledonia: Avicennia marina and Rhizophora stylosa. The results suggest that decades of urban rainwater runoff from an upper neighborhood induced large variations of mangrove soil physico-chemical properties compared to a control mangrove site sharing the same geological watershed. The urban mangrove site had a neutral pH and low salinity in the upper soil, while the control mangrove site presented acidic pH and a salinity ranging from 24 to 62 g L−1. Most TM were significantly less concentrated in the urban mangrove soil varying from 1.3 ± 0.3 μg g−1 at the urban site and 1.9 ± 0.5 μg g−1 at the control site for Cd, to 30 ± 8 mg g−1 and 49 ± 11 mg g−1 for Fe at the urban and control site, respectively. However, higher root bioconcentration factors were measured for As, Cd, Co, Cr, Fe, Mn, Ni, and Pb in the urban mangrove soil (1.7 ± 0.9, 0.14 ± 0.06, 0.23 ± 0.13, 0.042 ± 0.026, 0.088 ± 0.057, 0.47 ± 0.39, 0.21 ± 0.12, and 0.25 ± 0.09, respectively) compared to the control mangrove soil (0.11 ± 0.03, 0.041 ± 0.016, 0.045 ± 0.021, 0.010 ± 0.004, 0.013 ± 0.007, 0.094 ± 0.030, 0.022 ± 0.011, and 0.12 ± 0.03, respectively). The bioavailability of TM in the urban mangrove soil may be favored by suboxic conditions associated to less Cl-TM complexes and pyrite-TM complexes in the soil. Only Cu, Pb, Ti, and Zn, usually associated with urbanization, were more concentrated in the urban mangrove soil with mean concentrations of 27 ± 4, 17 ± 2, 4,571 ± 492, and 62 ± 12 μg g−1 at the urban site, respectively, and 21 ± 4, 10 ± 3, 2,834 ± 541, and 57 ± 12 μg g−1 at the control site, respectively. No significant difference in translocation factors was measured between the two sites, evidencing a regulation of TM translocation to the upper tissues by mangrove trees.

A study was conducted in the coastal blue carbon habitats of Bangladesh regarding soil organic carbon (SOC) stocks. Fifty soil samples covering 10 soil profiles at five different depths level up to 1 m was considered to complete the above research. In the salt marsh sites, SOC ranged from 13.1 to 45.7 g/kg with a mean value of 27.5 g/kg. In the mangrove sites, SOC varied from 14.1 to 46.3 g/kg with a mean value 26.4 g/kg. In Mangrove ecosystem soils, clay contents showed a very strong positive correlation with SOC (r = 0.901 and p < 0.01) whereas silt showed a significant positive correlation with the SOC (r = 0.691 and p< 0.05) in the salt marsh sites. As the mangrove ecosystem holds more clay than the salt marsh ecosystem so it may be said that mangrove soils are more potential for carbon storage than salt marsh soils. The study revealed that both of these ecosystems hold more carbon than the threshold level (20.0 g/kg). It is suggested to protect and regenerate the blue carbon habitats in the coastal ecosystem considering the present findings to tackle climate change and other sudden disasters. Dhaka Univ. J. Biol. Sci. 32(2): 179-188, 2023 (July)

Forested coastal wetlands are globally important systems sequestering carbon and intercepting nitrogen pollution from nutrient-rich river systems. Coastal wetlands that have suffered extensive disturbance are the target of comprehensive restoration efforts. Accurate assessment of restoration success requires detailed mechanistic understanding of wetland soil biogeochemical functioning across restoration chrono-sequences, which remains poorly understood for these sparsely investigated systems. This study investigated denitrification and greenhouse gas fluxes in mangrove and Melaleuca forest soils of Vietnam, using the 15N-Gas flux method. Denitrification-derived N2O was significantly higher from Melaleuca than mangrove forest soils, despite higher potential rates of total denitrification in the mangrove forest soils (8.1 ng N g-1 h-1) than the Melaleuca soils (6.8 ng N g-1 h-1). Potential N2O and CO2 emissions were significantly higher from the Melaleuca soils than from the mangrove soils. Disturbance and subsequent recovery had no significant effect on N biogeochemistry except with respect to the denitrification product ratio in the mangrove sites, which was highest from the youngest mangrove site. Potential CO2 and CH4 fluxes were significantly affected by restoration in the mangrove soils. The lowest potential CO2 emissions were observed in the mid-age plantation and potential CH4 fluxes decreased in the older forests. The mangrove system, therefore, may remove excess N and improve water quality with low greenhouse gas emissions, whereas in Melaleucas, increased N2O and CO2 emissions also occur. These emissions are likely balanced by higher carbon stocks observed in the Melaleuca soils. These mechanistic insights highlight the importance of ecosystem restoration for pollution attenuation and reduction of greenhouse gas emissions from coastal wetlands. Restoration efforts should continue to focus on increasing wetland area and function, which will benefit local communities with improved water quality and potential for income generation under future carbon trading.

Desiccation of the Aral Sea left a vast area of unstable, saline, and barren seafloor. In response, afforestation using indigenous trees, mainly Haloxylon species, has been performed to ameliorate the soil. This study examined 1) changes in topsoil chemical properties after vegetation establishment based on 30-year chronosequence of afforested sites and 2) dynamics in the topsoil properties in two cases of naturally vegetated versus afforested areas. In August 2019, soils were sampled from the northeastern Aral Sea bed, Kazakhstan, where the shoreline retreated during the 1970s. We selected a non-saline area without any vegetation, a visibly salinized area without any natural vegetation, and 12 paired sites with predominantly sandy soil texture that were naturally vegetated or afforested during 1990, 2000, 2005, 2008, 2013, and 2017. In the 0‒10 cm soil layer, 3 points were sampled in each site and we analyzed soil pH, electrical conductivity (EC), total dissolved solids (TDS), exchangeable sodium percentage (ESP), total nitrogen (TN) and carbon (TC), total organic carbon (TOC), available phosphorus concentration (P2O5), exchangeable cation concentrations (K+, Mg2+, Ca2+, and Na+), and cation exchange capacity (CEC). The soil samples in chronosequence sites showed a wide range of EC, without any significant temporal trend. The pH ranged between 8.5 and 10.0, characterized soil as alkaline. CEC ranged from 9 to 45 cmolc kg-1. Soil pH, EC, and TDS variations among the chronosequence sites (natural or afforested) were not statistically significant. In contrast, we observed marginal increases in K+ and P2O5 after the vegetation establishment. Also, TN and TOC concentrations increased over time, significantly faster in afforested than in naturally vegetated sites. However, TC contents showed a sudden decrease in the oldest natural vegetation. This result may be partly attributed to the spatial variability in sampling locations used for the chronosequence analysis. Lastly, there were strong positive correlations among TOC, TN, K+, and P2O5; which imply an increase in soil organic materials’ contribution to nutrient accumulation and overall soil quality. In conclusion, afforestation contributed to soil amelioration but this effect was also observed in naturally vegetated sites.

Mangroves are highly productive wetland ecosystems strategically located at the interface between land and sea. They play an important role in the biogeochemical cycles of the coastal environment, acting as sources of nutrients to adjacent marine and terrestrial ecosystems through active and passive transport. We examined the nutrient contents in mangrove and nonmangrove soils in and around the Bhitarkanika National Park, India and assessed whether the local agricultural producers were aware of and placed a value on this contribution of mangrove forests in enhancing agroecosystem productivity. Soil samples from both mangrove and nonmangrove areas were analysed and quantity of organic carbon, total nitrogen, available phosphorus and potassium were derived. The replacement cost method was used to derive the value of nutrients in mangrove soils. We estimated that each hectare of mangrove contains additional nutrients worth US$232.49 in comparison to nonmangrove areas. The difference in nutrient content in mangrove versus nonmangrove areas gave the value of US$3.37 million for the nutrients in 145 km2 of mangrove forests. The agricultural producers were aware that mangrove forests act as a source of nutrients and were willing to pay a higher price for the land adjoining mangrove forests. Around 92% of the producers ranked nutrient retention as a secondary function of mangrove forests. Despite crop depredation from wild ungulates and conflict with salt water crocodiles the agriculturist finds the benefit to cost ratio of mangrove forests high and more than 76% were in favour of mangrove restoration. This study provides an opportunity to highlight the importance of mangrove ecosystems to the livelihoods of the local people and the urgent need to sustain these through proper policy and market interventions.

Studies on soil quality of mangrove forests would be of immense use in minimizing soil degradation and in adopting strategies for soil management at degraded sites. Among the various parameters of soil quality, biological and biochemical soil properties are very sensitive to environmental stress and provide rapid and accurate estimates on changes in quality of soils subjected to degradation. In this study, we determined the general and specific biochemical characteristics of soils (0-30 cm) of inter-tidal areas of 10 undisturbed mangrove forest sites of S. Andaman, India. In order to determine the effects of disturbance, soils from the inter-tidal areas of 10 disturbed mangrove forest sites were also included in the study. The general biochemical properties included all the variables directly related to microbial activity and the specific biochemical parameters included the activities of extracellular hydrolytic enzymes that are involved in the carbon, nitrogen, sulfur and phosphorus cycles in soil. The pH, clay, cation exchange capacity, Al2O3 and Fe2O3 levels exhibited minimum variation between the disturbed and undisturbed sites. In contrast, organic C, total N, Bray P and K levels exhibited marked variation between the sites and were considerably lower at the disturbed sites. The study also revealed marked reductions in microbial biomass and activity at the disturbed sites. In comparison to the undisturbed sites, the levels of all the general biochemical parameters viz., microbial biomass C, microbial biomass N, N flush, basal respiration, metabolic quotient (qCO2), ATP, N mineralization rates and the activities of dehydrogenase and catalase were considerably lower at the disturbed sites. Similarly, drastic reductions in the activities of phosphomonoesterase, phosphodiesterase, s-g1ucosidase, urease, BAA-protease, casein-protease, arylsulfatase, invertase and carboxymethylcellulase occurred at the disturbed sites due mainly to significant reductions in organic matter/substrate levels. The data on CO2 evolution, qCO2 and ATP indicated the dominance of active individuals in the microbial communities of undisturbed soils and the ratios of biomass C:N, ATP:biomass C and ergosterol:biomass C ratios indicated low N availability and the possibility of fungi dominating over bacteria at both the mangrove sites. Significant and positive correlations between soil variables and biochemical properties suggested that the number and activity of soil microorganisms depend mainly on the quantity of mineralizable substrate and the availability of nutrients in these mangrove soils.

Mangrove soils have been recognized as sources of greenhouse gases, but the atmospheric fluxes are poorly characterized, and their adverse warming effect has rarely been considered with respect to the potential contribution of mangrove wetlands to climate change mitigation. The current study balanced the warming effect of soil greenhouse gas emissions with the plant carbon dioxide (CO2) sequestration rate derived from the plants’ net primary production in a productive mangrove wetland in South China to assess the role of mangrove wetlands in reducing the atmospheric warming effect. Soil characteristics were also studied in the summer to examine their relationships with gas fluxes. The soil to atmosphere fluxes of nitrous oxide (N2O), methane (CH4) and CO2 ranged from −1.6 to 50.0 μg m−2 h−1, from −1.4 to 5360.1 μg m−2 h−1 and from −31 to 512 mg m−2 h−1, respectively, which indicated that the mangrove soils act as sources of greenhouse gases in this area. The gas fluxes were higher in summer than in the cold seasons and were variable across mangrove sites. Gas fluxes in summer were positively correlated with the soil organic carbon, total nitrogen, and ammonia contents. The mangrove plants sequestered a considerable amount of atmospheric CO2 at rates varying from 3652 to 7420 g CO2 m−2 yr−1. The ecosystem acted as a source of CH4 and N2O gases but was a more intense CO2 sink. However, the warming effect of soil gas emissions accounted for 9.3–32.7% of the plant CO2 sequestration rate, partially reducing the benefit of mangrove plants, and the two trace gases comprised 9.7–33.2% of the total warming effect. We therefore propose that an assessment of the reduction of atmospheric warming effects by a mangrove ecosystem should consider both soil greenhouse gas emissions and plant CO2 sequestration.

This study assessed heavy metal concentrations and physicochemical properties in soil and water samples from mechanic workshops in Apir and North Bank, Makurdi, Nigeria. sixteen soils, sixteen water samples were collected using a systematic random sampling design, along with control samples from uncontaminated sites. Soil samples were collected from depth of 15 cm using a hand auger and stored in labeled polyethylene bags, while water samples were collected in clean plastic bottles and taken to the laboratory. The physicochemical properties analyzed included pH, moisture content, cation exchange capacity (CEC), electrical conductivity (EC), and total dissolved solids (TDS), measured using standard laboratory procedures. Heavy metal concentrations of manganese (Mn), lead (Pb), iron (Fe), and chromium (Cr) were determined using atomic absorption spectrophotometry (AAS) after acid digestion. The results showed that North Bank soils had higher manganese levels (1.24 mg/kg) compared to Apir (0.28 mg/kg), while Apir exhibited elevated concentrations of lead (3.14 mg/kg) and chromium (1.04 mg/kg) compared to North Bank (Pb: 2.78 mg/kg, Cr: 0.57 mg/kg). However, all heavy metal concentrations were below the NESREA (National Environmental Standards and Regulations Enforcement Agency) permissible limits. Soil pH values were 7.2 for North Bank and 6.9 for Apir, both within the acceptable NESREA range (6.5–8.5). Moisture content and CEC were higher in North Bank and Apir, respectively. Water samples contained no detectable levels of manganese, lead, or chromium, and their physicochemical properties, including pH, EC, and TDS, were within safe limits. The findings suggest that soil contamination remains within regulatory thresholds, necessitating continuous monitoring and improved waste management practices.

Contribution of microalgae to carbon sequestration in a natural karst wetland aquatic ecosystem: An in-situ mesocosm study

This study was undertaken to investigate the physicochemical characteristics of Ambo District soils collected from four Kebeles (Awaro Qora, Gosu Qora, Qibafkube and Elamu Goromti), Ethiopia. The soil was analyzed for the parameters like soil pH, electrical conductivity, (EC), moisture content (MC), total dissolved solid (TDS), cation exchange capacity (CEC), organic carbon (OC), organic matter (OM), available nitrogen, available phosphorous, and available potassium. K and CEC values were analyzed using flame photometer, available phosphorous was analyzed using ultraviolet-visible spectrophotometer while conventional analytical methods were employed for the determination of the rest of the physicochemical parameters. During the course of study fluctuation in the various parameters were recorded. The results obtained revealed that the concentrations of physicochemical parameters in the soil samples were: MC (19.31–28.25%), pH (5.68–7.63), EC(0.11–0.27 mS/cm), TDS (72.7–172 mg/L), OC (1.61–2.84%), OM (2.78–4.89%), CEC (36.28–65.73 cmol(+)/kg), available N (0.012–0.020%), available P (14.01–26.14 kg/ha), and available K (116.59–345.19 kg/ha). Statistical test of significance using ANOVA revealed that there were significant differences (p < 0.05) between the values of moisture content, TDS, CEC and available nutrients (N, P and K) in the soil samples obtained from all the sampling sites. This variation of values observed in the different parameters is due to the soil quality in different places. The soil studied can be considered as good sources of available nutrients and this information will help farmers to solve the problems related to soil nutrients, the type and amount of fertilizers to be used to increase the yield of crops.

Despite few studies of forest health and environmental conditions of mangrove forest in Sarawak, the data was not sufficient to facilitate baseline data and direct comparison of mangrove forest health obtained for mangrove forest in Awat-Awat, Lawas, Sarawak. The objectives of the study were to determine the total N and available P concentration in the mangrove forest soil along with the effect of the soil depth on nutrient concentration. Mangrove soil samples were taken from Lawas Division of Sarawak at 0-15 cm and 15-30 cm depths. Selected soil chemical properties as N, P, pH and Soil Cation Exchange Capacity (CEC) were determined using standard methods. As a result, means of selected chemical properties are as follow, 0-30 cm N% (0.196), P (15.59 ppm), pH in water solution (5.83), pH in 1M KCl (5.32) and CEC (27.53 cmol) while at 30-50 cm, Total N% (0.403), P (6.45 ppm), pH in water (5.59), pH in 1 M KCl (4.99) and CEC (29.57 cmol). Conclusion of this study, soil depth has given significant effects on the soil acidity, total N, available P and CEC with the difference depth. Where top soil contains less nutrient concentration than the bottom soil. The data statistical analysis has shown there are significantly different between the depths of the mangrove soil. Obtained data can be useful for further study of nutrient content and for the rehabilitation of the mangrove forest in another area.

Assessing the influence of land use on soil physic chemical properties is crucial for developing sustainable land management strategies. This study was conducted to evaluate the effect of different land uses and soil depth on selected soil properties in three randomly selected sites of Sidama regional state. 54 composite soil samples were collected from three land uses (cultivated land, enset and forest) at two soil depths (0-20cm and 20-40cm). In addition, undisturbed soil samples were collected using a core sampler to assess the bulk density. Laboratory analyses were conducted for selected soil properties following standard procedures. The results of the study revealed that land use and soil depth significantly influenced soil properties. Except particle size distribution, all measured soil properties were significantly influenced by land use types. Bulk density, total nitrogen and available phosphorus were found to be influenced by soil depth. Enset had the highest mean values for available phosphorus, total nitrogen, cation exchange capacity, while cultivated land had the lowest value for all soil properties excluding bulk density. The highest value of all soil properties under enset land use might be attributed to farmer’s practice of frequent application of manure and household refuses. Bulk density and clay content were increased with soil depth while sand, silt, pH, Av.P, total nitrogen was decreased with soil depth. The highest value of bulk density and lowest value of other measured soil parameters were might be attributed to frequent tillage without organic input application. This study indicated that the cultivation of land continuously without proper management leads to the deterioration of soil properties. From this study, it can be concluded that conversion of forest land to cultivated land can lead to soil fertility degradation. Therefore, continuous cultivation needs the application of organic amendments in combination with inorganic fertilizer for sustainable soil management.

Mangrove ecosystems are threatened worldwide by a wide range of factors including climate change, coastal development, and pollution. The effects of these factors on soil bacterial communities of Neotropical mangroves and their temporal dynamics is largely undocumented. Here we compared the diversity and taxonomic composition of bacterial communities in the soil of two mangrove forest sites of the Panama Bay: Juan Diaz (JD), an urban mangrove forest in Panama City surrounded by urban development, with occurrence of five mangrove species, and polluted with solid waste and sewage; and Bayano (B), a rural mangrove forest without urban development, without solid waste pollution, and with the presence of two mangrove species. Massive amplicon sequencing of the V4 region of the 16S rRNA gene and community analyses were implemented. In total, 20,691 bacterial amplicon sequence variants were identified, and the bacterial community was more diverse in the rural mangrove forest based on Faith's phylogenetic diversity index. The three dominant phyla of bacteria found and shared between the two sites were Proteobacteria, Desulfobacterota, and Chloroflexi. The ammonia oxidizing archaea class Nitrosphaeria was found among the top 10 most abundant. Dominant genera of bacteria that occurred in the two mangrove sites were: BD2-11_terrestrial_group (Gemmatimonadota), EPR3968-O8a-Bc78 (Gammaproteobacteria), Salinimicrobium (Bacteroidetes), Sulfurovum (Campylobacteria), and Woeseia (Gammaproteobacteria) of which the first three and Methyloceanibacter had increased in relative abundance in the transition from rainy to dry to rainy season in the urban mangrove forest. Altogether, our study suggests that factors such as urban development, vegetation composition, pollution, and seasonal changes may cause shifts in bacterial diversity and relative abundance of specific taxa in mangrove soils. In particular, taxa with roles in biogeochemical cycles of carbon, nitrogen, sulfur, and phosphorus, and on rhizosphere taxa, could be important for mangrove plant resilience to environmental stress.

The lack of site specific fertilizer recommendation to replenish declining soil fertility has been the major challenge to boost crop production in Ethiopia. Therefore, an investigation was conducted on soil macronutrient status of Kedida Gamela, Kechabra and Damboya worded as of Ethiopia. Four hundred sixty three geo-referenced soil samples were collected by using grid survey method. phosphorus (P), potassium (K), sulphur (S), calcium (Ca) and magnesium (Mg) were extracted by using Mehlich-III extraction method. Soil reaction was determined by pH meter. Total nitrogen (TN), Organic carbon and cation exchange capacity were predicted from Mid Infrared Spectra. The fertility maps and predication were prepared by ordinary kriging. Calcium showed strong spatial dependence but the spatial dependence of pH, OM, TN and K was moderate whereas the spatial dependence of P, S and Mg was weak. The pH of the soil samples ranged from 4.5 to 8.6 and about 83.5% of all agricultural soils were acidic in reaction. The measured EC values ranged from 0.02 to 0.81 dSm-1. Available P ranged from 0 to 267 ppm. Available S ranged between 3 and 63ppm and nearly 98% of the agricultural soils of the study areas had below optimum sulphur values. The TN content ranged between 0.0003% and 0.51% and about 61% of analyzed soil samples were below optimum level in TN status. The soil OM ranged from 0.0003 to 7.35%. The exchangeable K, Ca and Mg values ranged from 0.39 to 4.24, 4.9 to 19.5 and 0.68 to 6.09 cmolc kg-1, respectively. The proper rate of limes for acidic soil of the study area and P, N and S fertilizers should be applied to boost the agricultural productivity. Further correlation and calibration of soil test data with plant response is reconsidered.