Impact of increased instream heterogeneity by deflectors on the removal of hydrogen sulfide of regulated urban waterways-A laboratory study

Laboratory experiments were conducted to test the hypothesis that increase in physical heterogeneity by deflectors would improve the water quality of urban regulated (straight and prismatic) waterways. Deflectors changed the near-uniform flow to a rapidly varied flow, as such the depth, velocity, and Froude number (Fr) variations were four, 10, and 14 times more than the without deflector scenario, respectively. Removal of hydrogen sulfide (H₂ S), the main focus of the study, was significantly high when deflectors were placed in the laboratory urban waterway. Introduction of a sediment bed further improved H₂ S removal; however, in this case turbidity and color were significantly high too. These observations endorse the fact that attenuation induced by deflectors and assimilation promoted by the sediment bed aids the H₂ S removal. These facts were further strengthened by the significant strong negative correlations H₂ S made with DO and pH for all experiments. Further studies are recommended for different deflector orientations and modified sediment beds (e.g., mixture of sediment and gravel), identification of localized water quality hot spots to capture spatial variation of water quality, and impact of increased heterogeneity on flood safety. PRACTITIONER POINTS: Increase in physical heterogeneity (by deflectors) on water quality improvement was studied in a laboratory set up. Deflectors changed the near-uniform flow to rapidly varied flow with several mesoscale physical habitats. Hydrogen sulfide (H₂ S) removal was greatest with deflectors and the sediment bed, but was characterized by high turbidity. H₂ S removal showed strong negative correlations with dissolved oxygen and pH.

Seasonal Changes in the Content of Photosynthetic Pigments of Dominant Macrophytes in the Bardača Fishpond Area

In this paper, changes in the content of photosynthetic pigments during the vegetation season in the leaves of Phragmites communis Trin., Salvinia natans (L.) All., Trapa natans L. and Utricularia vulgaris L. in the area of Bardača fishpond (Sinjak pond) were monitored. Physical and chemical characteristics of water are defined in order to determine their association with the content of photosynthetic pigments. The obtained results indicate the specificity in the content of photosynthetic pigments between aquatic macrophytes and significant variations during the vegetation season. The maximum content of pigments was determined in the leaves of the emerged species, while the minimum content was measured in the submerged and floating leaves. The investigated macrophytic species showed a similar trend in the total chlorophyll content during the vegetation period; with two maximums recorded – May and September, while the minimum values were recorded with the senescence process (October). Total chlorophyll and carotenoids were in a negative correlation with temperature, pH, saturation, water transparency and orthophosphate content in water. On the other hand, they were in a positive correlation with the content of nitrates in water. The correlation analysis of the physical and chemical parameters of water quality and the concentration of macrophytes photosynthetic pigments showed a significant influence of certain abiotic factors on the photosynthetic pigments’ content in the leaves of Phragmites communis Trin., Salvinia natans (L.) All., Trapa natans L. and Utricularia vulgaris L.

Macrophytes in the littoral of Lake Arakhley in different states of water regime

The study of aquatic vegetation in the littoral of the dimictic water bodies of taiga is of particular interest in case of long-term observations carried out under conditions of climate fluctuations. During the low-water period, drying of the littoral with a decrease in the water level leads to the changes in phytomass of macrophytes, as well as in the composition of species and their distribution by depth. The area of littoral covered with ice in winter is also large in the low-water period; it affects the growth of perennial plants. When the water level decreases, the sand beach replaces the sand and pebble beach; it leads to the disappearance of epilithon and the predominance of rooting plants. The features of vegetation were determined for each period of water content. The low-water period is characterised mostly by grass-type vegetation; the high-water period is characterised by vegetation of mixed type.