Effects of common carp (Cyprinus carpio) on water quality in aquatic ecosystems dominated by submerged plants: a mesocosm study

Common carp (Cyprinus carpio) have been introduced into aquatic systems across the world, where their benthivorous feeding behavior has resulted in serious water quality problems. A 12-week mesocosm experiment was set up to test the hypotheses that common carp increase water column nutrient levels and decrease water clarity in aquatic ecosystems dominated by submerged plants. Further, we tested whether the effect of common carp on macrophytes depended on the species of plants. Relative to the controls, the presence of carp decreased water clarity by increasing total suspended solids (TSS) and light attenuation. However, levels of total nitrogen (TN) and total phosphorus (TP) in the water column were reduced. No significant change in phytoplankton biomass (measured as chlorophyll a) and the biomass of Hydrilla verticillata was observed between common carp treatment mesocosms and controls, but the common carp did reduce the biomass of the submerged macrophyte Vallisneria denseserrulata. We conclude that removal of common carp is likely to improve water clarity in aquatic ecosystems dominated by submerged plants primarily by decreasing TSS and that the effect of common carp on macrophytes is stronger for the meadow forming Vallisneria than for the canopy forming Hydrilla

Effects of Short-Term Hydrological Processes on Benthic Macroinvertebrates in Salt Marshes: a Case Study in Yangtze Estuary, China

Understanding the effects of hydrological processes on the benthic macroinvertebrates in salt marshes can provide theoretical basis for species diversity restoration, coastal environment protection, and comprehensive exploitation and utilization of salt marsh ecosystems. In this study, 4 fixed-point sampling sites were set up in the salt marsh of the East Nanhui tidal flat in the Yangtze Estuary for benthic macroinvertebrate survey, hydrological monitoring and sedimentary parameter collection over two short-time scales (semidiurnal and fortnightly cycles). Based on the results of these surveys, we analyzed the effects of hydrological processes on the benthic macroinvertebrates over different timescales. The results showed that benthic macroinvertebrates assemblages varied significantly over the semidiurnal and fortnightly tide periods but not between sites. The number of species and the abundance of the benthic macroinvertebrates during spring tide period were significantly lower than that during neap tide period, although the biomass during both tidal periods were not significantly different. There was no significant variation in the number of species, abundance, and biomass of benthic macroinvertebrates over the semidiurnal tidal scale in general with few exceptions. However, there were significant differences in most of the hydrological and sedimentary parameters between the spring and neap tide periods, as well as between semidiurnal tides in these two periods. Two principal components, the intensity of hydrological processes (PC1) and the physicochemical properties of water and sediment (PC2), were derived from principal component analysis on hydrological factors and sedimentary physicochemical parameters. The results show that PC1 had a significant effect on abundance of benthic macroinvertebrate community; while PC2 had a significant effect on biomass. The best combined environmental factors, which exhibited significant correlations with the characteristics of the benthic macroinvertebrates and also their taxonomic classes, varied across the sampling periods. This study indicates that short-term hydrological processes can not only directly affect the benthic macroinvertebrates, but also indirectly affect the communities by altering sedimentary physicochemical factors. There were significant differences in the effects of the hydrological processes on the benthic macroinvertebrate community over the semidiurnal and fortnightly tidal scales, and it could be inferred that the scale effect still exists in the short-time scale

Effects of common carp (

Common carp (Cyprinus carpio) have been introduced into aquatic systems across the world, where their benthivorous feeding behavior has resulted in serious water quality problems. A 12-week mesocosm experiment was set up to test the hypotheses that common carp increase water column nutrient levels and decrease water clarity in aquatic ecosystems dominated by submerged plants. Further, we tested whether the effect of common carp on macrophytes depended on the species of plants. Relative to the controls, the presence of carp decreased water clarity by increasing total suspended solids (TSS) and light attenuation. However, levels of total nitrogen (TN) and total phosphorus (TP) in the water column were reduced. No significant change in phytoplankton biomass (measured as chlorophyll a) and the biomass of Hydrilla verticillata was observed between common carp treatment mesocosms and controls, but the common carp did reduce the biomass of the submerged macrophyte Vallisneria denseserrulata. We conclude that removal of common carp is likely to improve water clarity in aquatic ecosystems dominated by submerged plants primarily by decreasing TSS and that the effect of common carp on macrophytes is stronger for the meadow forming Vallisneria than for the canopy forming Hydrilla

Effects of Nile Tilapia (

Nile tilapia is a highly invasive fish species, deliberately introduced into many lakes and reservoirs worldwide, sometimes resulting in significant ecosystem alterations. A short-term mesocosm experiment with and without Nile tilapia (Oreochromis niloticus) was designed to test the hypotheses that the presence of tilapia may affect phytoplankton community structure, increase nutrients availability in water column and deteriorate water quality. Nutrients, total suspended solids (TSS) and biomass of phytoplankton in different size classes (as Chl a) were measured. We found that tilapia increased the total nitrogen (TN), total dissolved nitrogen (TDN), NH4 + and TSS concentrations, deteriorating the water quality. In addition, under tilapia presence, the biomass of phytoplankton, as well as that of micro- and nano-phytoplankton, increased leading to a change in the structure of the phytoplankton assemblage. Moreover, a reduction in the biomass of periphyton was observed. Omnivorous tilapia is often dominant in tropical and subtropical waters, and removal of this fish may represent an effective management tool to improve the water quality

Effects of Sulfamethazine on Denitrification and the Associated N₂O Release in Estuarine and Coastal Sediments

Denitrification is an important pathway of nitrogen removal and nitrous oxide (N₂O) production in estuarine and coastal ecosystems, and plays a significant role in counteracting aquatic eutrophication induced by excessive nitrogen loads. Estuarine and coastal environments also suffer from increasing antibiotic contamination because of the growing production and usage of antibiotics. In this study, sediment slurry incubation experiments were conducted to determine the influence of sulfamethazine (SMT, a sulphonamide antibiotic) on denitrification and the associated N₂O production. Genes important for denitrification and antibiotic resistance were quantified to investigate the microbial physiological mechanisms underlying SMT’s effects on denitrification. SMT was observed to significantly inhibit denitrification rates, but increasing concentrations of SMT enhanced N₂O release rates. The negative exponential relationships between denitrifying gene abundances and SMT concentrations showed that SMT reduced denitrification rates by restricting the growth of denitrifying bacteria, although the presence of the antibiotic resistance gene was detected during the incubation period. These results imply that the wide occurrence of residual antibiotics in estuarine and coastal ecosystems may influence eutrophication control, greenhouse effects, and atmospheric ozone depletion by inhibiting denitrification and stimulating the release of N₂O