Water quality has recently emerged as one of the utmost severe ecological problems being faced by the developing countries all over the world, and Bangladesh is no exception. Both surface and groundwater sources contain different contaminants, which lead to numerous deaths due to water-borne diseases, particularly among children. This study presents one of the most comprehensive reviews on the current status of water quality in Bangladesh with a special emphasis on both conventional pollutants and emerging contaminants. Data show that urban rivers in Bangladesh are in a critical condition, especially Korotoa, Teesta, Rupsha, Pashur, and Padma. The Buriganga River and few locations in the Turag, Balu, Sitalakhya, and Karnaphuli rivers have dissolvable oxygen (DO) levels of almost zero. Many waterways contain traces of NO3, NO2, and PO4-3 pollutants. The majority of the rivers in Bangladesh also have Zn, Cu, Fe, Pb, Cd, Ni, Mn, As, and Cr concentrations that exceed the WHO permissible limits for safe drinking water, while their metal concentrations exceed the safety threshold for irrigation. Mercury poses the greatest hazard with 90.91% of the samples falling into the highest risk category. Mercury is followed by zinc 57.53% and copper 29.16% in terms of the dangers they pose to public health and the ecosystem. Results show that a considerable percentage of the population is at risk, being exposed to contaminated water. Despite hundreds of cryptosporidiosis cases reported, fecal contamination, i.e., Cryptosporidium, is totally ignored and need serious considerations to be regularly monitored in source water.

Sedimentary nitrogen (N) in lakes significantly influenced by eutrophication plays a detrimental role on the ecological sustainability of aquatic ecosystems. Here, we conducted a thorough analysis of the importance of N potentially released from sediments during the shift of “grass-algae” ecosystem in plateau lakes. From 1964 to 2013, the average total amount of sedimentary potential mineralizable organic nitrogen (PMON) and exchangeable N in whole Lake Dianchi were 5.50 × 10³ t and 3.44 × 10³ t, respectively. NH₄⁺-N was the main product (>90%) of sedimentary PMON mineralization. The PMON in sediments had great release potential, which tended to regulate the distribution of aquatic plants and phytoplankton in Lake Dianchi and facilitated the replacement of dominant populations. Moreover, NH₄⁺-N produced by sedimentary PMON mineralization and exchangeable NH₄⁺-N have increased the difficulty and complexity of ecological restoration in Lake Dianchi to a certain extent. This study highlights the importance of sedimentary N in lake ecosystem degradation, showing the urgent need to reduce the continuous eutrophication of lakes and restore the water ecology.

In this study, the influence of temperature and light intensity on the growth of seedlings and adults of four species of green tide algae (Ulva prolifera, Ulva compressa, Ulva flexuosa and Ulva linza) from the Yellow Sea was evaluated. The results indicated that the specific growth rate (SGR) of seedlings was much higher than that of adults for the four species. The adaptability of U. prolifera is much wider: Adult daily SGRs were the highest among the four species at 15–20°C with 10–600μmol·m−2·s−1 and 25–30°C with 200–600μmol·m−2·s−1. SGRs were 1.5–3.5 times greater than the other three species at 15–25°C with 200–600μmol·m−2·s−1. These results indicate that U. prolifera has better tolerance to high temperature and light intensity than the other three species, which may in part explain why only U. prolifera undergoes large-scale outbreaks and floats to the Qingdao coast while the other three species decline and disappear at the early stage of blooming.