Dissolved trace elements in Hooghly (Ganges) River Estuary, India: Risk assessment and implications for management.

Estuaries provide an ideal niche to study structure and function of bacterioplankton communities owing to the presence of a multitude of environmental stressors. Bacterioplankton community structures from nine global estuaries were compared to understand their broad-scale biogeographic patterns. Bacterioplankton community structure from four estuaries of Sundarbans, namely Mooriganga, Thakuran, Matla, and Harinbhanga, was elucidated using Illumina sequencing. Bacterioplankton communities from these estuaries were compared against available bacterioplankton sequence data from Columbia, Delaware, Jiulong, Pearl, and Hangzhou estuaries. All nine estuaries were dominated by Proteobacteria. Other abundant phyla included Bacteroidetes, Firmicutes, Acidobacteria, Actinobacteria, Cyanobacteria, Planctomycetes, and Verrucomicrobia. The abundant bacterial phyla showed a ubiquitous presence across the estuaries. At class level, the overwhelming abundance of Gammaproteobacteria in the estuaries of Sundarbans and Columbia estuary clearly stood out amidst high abundance of Alphaproteobacteria observed in the other estuaries. Abundant bacterial families including Rhodobacteriaceae, Shingomonadaceae, Acidobacteriaceae, Vibrionaceae, and Xanthomondaceae also showed ubiquitous presence in the studied estuaries. However, rare taxa including Chloroflexi, Tenericutes, Nitrospirae, and Deinococcus-Thermus showed clear site-specific distribution patterns. Such distribution patterns were also reinstated by nMDS ordination plots. Such clustering patterns could hint toward the potential role of environmental parameters and substrate specificity which could result in distinct bacterioplankton communities at specific sites. The ubiquitous presence of abundant bacterioplankton groups along with their strong correlation with surface water temperature and dissolved nutrient concentrations indicates the role of such environmental parameters in shaping bacterioplankton community structure in estuaries. Overall, studies on biogeographic patters of bacterioplankton communities can provide interesting insights into ecosystem functioning and health of global estuaries.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/mbo3.741

Exploring biogeographic patterns of bacterioplankton communities across global estuaries.

Introduction: The Rupsha-Passur River System (RS) is one of the biggest and important river systems in the Sundarbans estuarine ecosystem. It is the largest fresh water supplier into this mangrove forest. A comprehensive study was undertaken to evaluate the tidal and seasonal variations in nutrient concentrations (nitrate, phosphate, sulphate and ammonia) of the RS during October, 2010 (Post monsoon), February, 2011 (Dry winter) and August 2011 (Monsoon). In-situ measurement and laboratory analysis were conducted to measure nutrients and other physico-chemical parameters at discrete water layers of five study points under different tidal cycles. Results: Following post monsoon, NH3–N concentration showed seasonal variation with increasing trend (0.0703 to 0.0803 mg/L) in dry winter and then significant dropping (0.013 to 0.019 mg/L) in monsoon period. During field observation, no significant tidal variation in ammonia concentration was identified among the study sites. Post monsoon and winter time observation recorded lower SO4 content (7.301 to 37.508 mg/L) at all the sampling stations while in monsoon period, most of the stations showed higher concentration up to 126.92 mg/L. Contrary to post monsoon season with comparatively higher PO4–P value (0.314 to 1.347 mg/L), winter and monsoon period sampling indicated low phosphate concentrations (0.045 to 0.5 mg/L) in the Rupsha-Passur RS. Most of the study sites showed considerable tidal changes in phosphate value during post monsoon and monsoon season while only two stations went through tidal fluctuation in sulphate content during monsoon period. Concentrations of NO3–N were found to fluctuate between 0.083 and 1.233 mg/L with no distinct seasonal distribution pattern. Tidal variation of NO3–N in the experimental sites was not so prominent during post monsoon period as of winter data. Conclusion: Present study will serve as a basis for future hydrological and environmental studies in the world’s largest Sundarbans intertidal mangrove forest. Study results indicate how nutrient dynamics of such diversified estuarine system are influenced by varying weather conditions. Daily fluctuations in nutrient concentrations and other physicochemical properties due to semidiurnal tidal activity were also figured out through the study. Information generated from the research works will guide all concerned for any future conservation and management initiatives for the world heritage site.

/pdf/seasonal-nutrient-distribution-in-the-rupsha-passur-tidal-4sm2f5ewgu.pdf

Seasonal nutrient distribution in the Rupsha-Passur tidal river system of the Sundarbans mangrove forest, Bangladesh

The management of natural surface water resources needs the understanding of water quality. The present study on the physico-chemical parameters of water quality of sacred lake Nachiketa Tal of Garhwal Himalaya was undertaken. During the period from May 2015 to April 2016 at four sampling stations, seasonal variations in air temperature, water temperature, electrical conductivity, turbidity, salinity, TDS, dissolved oxygen, free CO2, hardness, alkalinity, nitrates, phosphates, chlorides, calcium and magnesium were recorded. The statistical correlation and cluster analysis between the various physico-chemical parameters of Nachiketa Tal were computed. The results of this study revealed that the concentration of the nutrients, turbidity, electrical conductivity, TDS increased with a decreasing trend of dissolved oxygen in all the sampling stations during the monsoon season. Thus, degradation in the water quality of the lake was resulted in the monsoon season.

/pdf/seasonal-physico-chemical-characterization-of-water-of-4pgr1r05jx.pdf

Seasonal physico-chemical characterization of water of sacred lake Nachiketa Tal, Garhwal Himalaya

Tropical primary forests have been disappearing quickly to make use of the land for commercial purposes. Land-use change has an impact on downstream aquatic processes, but those impacts have mainly been studied in temperate climate regions. The present article reviews the impacts of various tropical land-use changes caused by human activities on downstream riverine and estuarine water properties and biogeochemical cycles, focusing especially on the behaviors of nitrogen (N) and phosphorus (P). Logging of tropical primary forests, subsequent establishment of pasture lands, and occasional wildfire or intentional burning have decreased terrestrial N fixation and increased the discharge of P combined with soils, which has lowered the N:P ratio of dissolved inorganic nutrients in the adjacent stream waters and downstream rivers. Agricultural fertilizers and aquacultural practices basically cause nutrient enrichment in downstream riverine and estuarine waters, changing the N:P ratio depending on the source. Finally, urbanization causes eutrophication in many tropical estuaries, where a halocline forms easily because of a warm temperature throughout the year and the water at the bottom of the estuary tends to become hypoxic or anoxic. Overall, the impact of land-use change on aquatic processes may be more serious in tropical regions than in temperate or cold climate regions because of (1) a higher biomass and nutrient stock in original tropical forests; (2) higher precipitation, more frequent episodic flooding, and warmer temperatures in tropical regions; and (3) certain practices that are rapidly expanding in tropical regions such as land-based aquaculture. Various land-use changes are causing downstream nutrient enrichment or disturbance of the nutrient balance at tropical land-sea interfaces, and the overall N:P ratios in the aquatic ecosystem seem to be declining. Nonetheless, if proper management is conducted and the discharge of nutrients and soils ceases, tropical aquatic systems may have the potential to recover faster than those in other climate regions because of their abundant precipitation and warm temperature. Long-term monitoring and more attention to elemental stoichiometry are important areas for future research.

/pdf/the-impact-of-tropical-land-use-change-on-downstream-7yjgw1jna2.pdf

The impact of tropical land-use change on downstream riverine and estuarine water properties and biogeochemical cycles: a review

Seasonal and tidal variations in nutrient concentration and water quality were investigated in the western Sundarbans of Bangladesh during the post-monsoon, winter and monsoon seasons during 2010–2011. Water collected from the surface, middle and bottom layers at six locations of the Kholpetua-Arpangashia river system during high and low tides was analyzed for temperature, salinity, pH, dissolved oxygen (DO), total dissolved solids (TDS), electrical conductivity (EC) and dissolved nutrients (NO3–N, PO4–P, SO4 and NH3–N). The study revealed that nutrient concentrations were influenced by seasonal changes. Mean nutrient levels during post-monsoon, winter and monsoon seasons, respectively, were in the following ranges: nitrate (0.06–0.40, 0.06–0.46 and 0.08–0.46 mg/L); phosphate (0.09–0.18, 0.05–0.42 and 0.10–0.16 mg/L); sulphate (58.71–86.14, 68.68–119.01 and 78.15–136.47 mg/L) and ammonia (0.02–0.08, 0.02–0.04 and 0.26–0.38 mg/L). Increased levels of PO4–P, SO4 and NH3–N and lower DO and salinity were recorded during the monsoon period. Most of the experimental sites showed higher NO3–N content during monsoon, whereas few elevated concentrations were observed during post-monsoon and winter periods. High and low tidal waters contained mean nutrient levels in the following ranges: nitrate (0.05–0.46 and 0.04–0.40 mg/L); phosphate (0.05–0.42 and 0.07–0.18 mg/L); sulphate (63.63–125.36 and 58.71–136.47 mg/L) and ammonia (0.02–0.38 and 0.02–0.37 mg/L) without following any distinct fluctuation patterns. The western part of the Sundarbans receives less freshwater input during the monsoon season than other areas of the ecosystem, which reduces the variability of nutrient levels and water quality components. This study provides considerable advances in understanding the seasonality of nutrient distribution with possible tidal influence. The data generated from this study will guide continuing efforts to support a sound management for coastal mangrove ecosystems.

/pdf/nutrient-dynamics-in-the-sundarbans-mangrove-estuarine-2sfbznpb2f.pdf

SM Shahjahan Siraj

Papers

Nutrient dynamics in the Sundarbans mangrove estuarine system of Bangladesh under different weather and tidal cycles