Distribution and Diversity of Macrobenthos in Sangu River, Bangladesh

This study was conducted to understand the macrobenthos distribution and abundance in Sangu River to monitor the aquatic pollution level. Both surface and sub-surface water and benthic sediments were collected from three stations of the Sangu River. A few indices viz. Shannon-wiener, Simpson, Margalef’s and Evenness were used to estimate the macrobenthic assemblages. In this study, a total of 11 major taxa comprising total 870 macobenthic species were identified. Shannon-wiener index was maximum (1.58) at lower part (LP) which indicated moderate to heavily pollute aquatic environment of the Sangu River. The average diversity values of Shannon, Evenness, Simpson and Margalef’s indices were 0.97, 0.43, 0.39 and 1.54 respectively. The concentration of dissolved oxygen was the lowest (4.90 mg/L) at LP and the highest (5.08 mg/L) at upper part (UP). This study showed that macrobenthos abundances was influenced by higher temperature, salinity, and pH. The percentage of organic carbon content was maximum (98.18%) at LP where the macrobenthic abundance was 330 individuals/m2, whereas it was minimum (80.77%) at UP where macrobenthic abundance was 248 individuals/m2 that indicated carbon content also influence the assemblages of the macrobenthos in the Sangu River. A clear gradient of physico-chemical and benthic soil parameters fluctuation was also found to be responsible for the variations of macrobenthos assemblage in the Sangu River. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 9(2), 2020, P 27-34

Microbial community assembly in a multi-layer dendritic metacommunity

ABSTRACTA major goal of metacommunity ecology is to infer the local- and regional-scale processes that underlie community assembly. In dendritic ecological networks (e.g., stream metacommunities), branching and directional dispersal connectivity can alter the balance between local and regional factors during assembly. However, the implications of vertical habitat structure (e.g., planktonic versus benthic sediments) in dendritic metacommunities remain unclear. In this study, we analyzed the bacterial metacommunity of a fifth-order mountain stream network to assess habitat differences in the (1) dominant community assembly processes, (2) spatial scaling of community assembly processes, and (3) longitudinal variation in community assembly. Using taxonomic and phylogenetic null modeling approaches, we found habitat-specific spatial patterns of community assembly across the dendritic network. Compositional differences between planktonic and benthic communities were maintained by divergent species sorting, but stochasticity influenced assembly at local scales. Planktonic communities showed scale-dependent assembly, transitioning from convergent sorting at local scales to divergent sorting at regional scales, while sediment community assembly was less scale dependent (convergent sorting remained important across all scales). While divergent sorting structured headwaters in both habitat types, sediment communities converged in structure downstream. Taken together, our results show that vertical habitat structure regulates the scale-dependent processes of community assembly across the dendritic metacommunity.

Spatial Variation of Metallic Contamination and Its Ecological Risk in Sediment and Freshwater Mollusk: Melanoides tuberculata (Müller, 1774) (Gastropoda: Thiaridae)

Heavy metal pollution has been on the rise with serious implications for the wellbeing of aquatic ecosystems. Benthic sediments and freshwater mollusk (snail): Mellanoides tuberculata were sampled from five stations for determination of heavy metals concentrations and measurement of antioxidant enzyme activities. The spatial variation was studied using an enrichment factor, potential ecological risk index, and mean probable effect limit quotient (mPELq). From the results, Cu, Zn, Cd, Cr, Pb, Ni, and Co contamination levels were high at stations S3, S4, and S5 with an mPEL quotient of 94.40%. The variation of metal concentration and Enrichment factor were in the order S5 > S3 > S4 > S2 > S1, which was attributed to anthropogenic influences at the catchment due to industrial activities and atmospheric deposition of metals. Station five in this study is downstream and requires the most monitoring and management to prevent several ecological risks of metal pollutants in River Kaduna.

Examining the correlation between quantifiable SVOCs and organic carbon content or particulate size in benthic sediments as a function of ocean stratum

Stratum-directed correlation between DDT, PAH or PCB levels and TOC or % fines.

Phosphorus attenuation in streams by water-column geochemistry and benthic sediment reactive iron

Streams can attenuate inputs of phosphorus (P) and, therefore the likelihood of ecosystem eutrophication. This attenuation is, however, poorly understood, particularly in reference to the geochemical mechanisms involved. In our study, we measured P attenuation mechanisms in the form of (1) mineral (co-)precipitation from the water-column and (2) P sorption with benthic sediments. We hypothesized that both mechanisms would vary with catchment geology and, further, that P sorption would depend on reactive Fe content in sediments. We sampled 31 streams at baseflow conditions, covering a gradient of P inputs (via land use), hydrological characteristics, and catchment geologies. Geochemical equilibria in the water-column were measured and benthic sediments ( 90 %) and varied with parent geology. Similarly, most sediment Fe was in a recalcitrant form (generally > 90–95 %). However, despite its small contribution to total sediment Fe, the pool of surface-reactive Fe was a strong predictor for sediment P sorption potential. Our results suggest that, in these streams, it is the combination of biogeochemical Fe and P cycles and the exchange with the hyporheic zone that attenuates DRP in baseflow. Such combinations are likely to vary spatiotemporally within a catchment and must be considered alongside inputs of P and sediment if the P concentrations at baseflow – and eutrophication risk – are to be well managed.

Infection with behaviour-manipulating parasites enhances bioturbation by key aquatic detritivores

The ecological ubiquity of parasites and their potential impacts on host behaviour have led to the suggestion that parasites can act as ecosystem engineers, structuring their environment and physical habitats. Potential modification of the relationship between parasites and their hosts by climate change has important implications for how hosts interact with both their biotic and abiotic environment. Here, we show that warming and parasitic infection independently increase rates of bioturbation by a key detritivore in aquatic ecosystems (Gammarus). These findings have important implications for ecosystem structure and functioning in a warming world, as alterations to rates of bioturbation could significantly modify oxygenation penetration and nutrient cycling in benthic sediments of rivers and lakes. Our results demonstrate a need for future ecosystem management strategies to account for parasitic infection when predicting the impacts of a warming climate.