Separate and combined effects of cadmium(Cd) and nonylphenol(NP) on growth and antioxidative enzymes in Hydrocharis dubia (Bl.) Backer

Cadmium (Cd) is listed as a priority pollutant, and nonylphenol(NP) is a common organic pollutant in water environment. However, the ecological risks of combined pollution of Cd and NP have not been fully elucidated. In this study, the effects of Cd (0.01, 0.1, 0.5, 1, 5 mg/L), NP (0.1, 0.5, 1, 5, 10 mg/L) and Cd-NP (0.01 + 0.1, 0.01 + 1.0, 0.5 + 0.1, 0.5 + 1.0, 5 + 0.1, 5 + 1.0 mg/L) on growth and physiology of Hydrocharis Dubia (Bl.) Backer were studied. The results showed that the toxicity of H. dubia showed a dose-dependent effect. Growth level and chlorophyll contents of H. dubia induced by NP stress alone showed a certain toxicant excitatory effect. It meant that low concentrations of toxins promote plants growth, high concentrations of toxins inhibit plants growth. The increase of H2O2 content and the decrease of soluble protein content in the plant indicated that both Cd and NP caused oxidative damage to H. dubia. Under the stress, the antioxidant defense systems were activated, the activity of superoxide dismutase (SOD) was significantly decreased. The activity of catalase (CAT) reacted negatively under stress alone, but increased significantly under combined stress. The activity of peroxidase (POD) increased, which was used to alleviate the damage caused by toxics stress. The joint toxicity evaluation showed that the joint toxicity of Cd and NP to H. dubia was antagonistic when the concentrations of Cd + NP were 0.01 + 0.1 mg/L and 0.01 + 1 mg/L. At 0.5 + 0.1 mg/L and 0.5 + 1 mg/L, Cd and NP had a strong synergistic effect on H. dubia.

Aquatic Macrophytes Determine the Spatial Distribution of Invertebrates in a Shallow Reservoir

Aquatic macrophytes determine the physical structure of many microhabitats in water and strongly influence the distribution of various aquatic animals. In this study, we analyzed the main microhabitat characteristics that affected the spatial distribution of invertebrates in shallow wetlands of South Korea (Jangcheok Reservoir). Environmental variables, macrophyte biomass, and invertebrate groups were used to analyze invertebrate distribution using a self-organizing map (SOM). Thirteen invertebrate groups were mapped onto the SOM, and each group was compared with the distribution of environmental variables and macrophyte biomass. Based on a U-matrix, five clusters were categorized according to Euclidean distance on the SOM. Invertebrate groups were closely related to macrophyte biomass. In particular, Lymnaeidae, Physidae, Viviparidae, Ecnomidae, and Hydrophilidae were abundant in quadrats with a high cover of Paspalum distichum and Nelumbo nucifera. Bithyniidae and Coenagrionidae were strongly associated with Trapa japonica and Hydrocharis dubia, whereas Planorbidae, Corduliidae, and Hydrophilidae were abundant with a high cover of Typha orientalis. Similar habitat preferences were found in a survey of gastropod distribution on the surface of each macrophyte species. The results clearly indicated that invertebrate distribution clusters were related to the spatial distribution of aquatic macrophytes in a shallow wetland.

The genus Hydrocharis L. (Hydrocharitaceae): distribution features and conservation status

The genus Hydrocharis L. includes three geographically isolated species. Analysis of the actual data (32 thousand geographical locations and 1946 herbarium sheets) covering the period 1765–2019 made it possible to clarify the nature of the distri- bution of these species and its changes. Hydrocharis morsus-ranae L. has disjunctive Eurasian – North American temperate range, with a massive North American en- clave, the formation of which began in the 1930–1940s. The range of Hydrocharis dubia (Blume) Backer is disjunctive Southeast Asian – Australian subboreal-tropical, Australia enclave began forming in the 1850–1870s. Hydrocharis chevalieri (De Wild.) Dandy is a macrothermal Central African equatorial endemic. Current threat status of all species may be estimated as Least Concern. The mean annual temperature is the most contrasting feature of the distribution areas of the species, water depth, bottom soil type and hydrochemical composition have lower impact. Prognostic models of the potential distribution of the tagged species have been made.