The influence of filter-feeding bivalves on plankton communities, nutrients, and water quality in a given aquatic ecosystem is so profound that they can be considered ecosystem engineers. In a 70-day mesocosm experiment, we tested the hypothesis that Corbicula fluminea would change plankton community structure by reducing small zooplankton and large phytoplankton and improve water quality by reducing nutrients. We monitored levels of nitrogen and phosphorus, organic suspended solids (OSS), and light at the sediment surface. Within the plankton, phytoplankton biomass (as Chl a, >0.45 μm), the biomass of microphytoplankton (>20 μm), nanophytoplankton (2–20 μm), picophytoplankton (0.2–2 μm), and zooplankton were determined. Compared with the controls, C. fluminea reduced the abundance of rotifers and the biomass of phytoplankton, and picophytoplankton, thereby modifying the plankton community structure. We did not observe reductions in TN and TP concentration, but OSS concentrations were reduced, and light intensity at the sediment surface was increased as a result of the improved water transparency. Our research shows that colonization by C. fluminea may modify plankton community structure and improve water quality of eutrophic shallow lakes, shedding further light on the ecological roles of filter-feeding bivalves in aquatic ecosystems.

Climate warming, a serious environmental problem worldwide, is considered a major threat to aquatic ecosystems. A primary feature of climate warming is elevated temperatures which in shallow aquatic ecosystems might affect competition for light and nutrient between benthic algae on the sediment surface and planktonic algae in the water. The outcomes of such competition would not only affect the distribution of primary production, but also determine the fundamental character of shallow aquatic habitats as clear water or turbid water systems. We conducted a mesocosm study to evaluate the effects of elevated temperature on competition between planktonic algae and benthic algae for light and nutrients. We found that elevated temperature increased the concentrations of total nitrogen (TN), total phosphorus (TP), and total suspended solids (TSS) in overlying water and enhanced the growth of planktonic algae (measured as chlorophylla, Chla), but decreased light intensity and benthic algal biomass (Chla). Our results indicate that elevated temperature can increase the growth of planktonic algae and enhance their competitive advantage over the benthic algae in shallow lakes, thereby contributing to eutrophication and a decline in water quality. These findings shed further light on the effects of global warming on aquatic ecosystems.

Eutrophication resulting from nutrient loading to freshwater habitats is a severe problem, leading to degradation of ecosystems, including deterioration of water quality, water clarity and loss of biodiversity. Measures enacted to restore degraded freshwater ecosystems often involve the reintroduction of submerged plants and aquatic animals with beneficial ecological functions. In a mesocosm experiment, three treatments (planting with Vallisneria natans, introduction of the snail Bellamya aeruginosa and a combined treatment with both plants and snails) were compared with controls to evaluate their effects on trophic state. The total nitrogen (TN), total phosphorus (TP) and chlorophyll a (Chl a) concentrations of planktonic and benthic algal samples were determined every two weeks, along with light intensity at the sediment surface. The plant-only treatment significantly reduced the TN levels and planktonic and benthic algal biomass and increased the light intensity at the sediment surface. The snail-only treatment reduced the concentrations of TN and reduced planktonic and benthic algal biomass. The combined treatment decreased the concentrations of TN and TP, reduced planktonic algal biomass and increased the light intensity on the sediment surface. The results indicate that while submerged plants and snails can both improve water quality, the most pronounced effect in aquatic ecosystems is achieved by their presence in combination. A combined reintroduction approach may provide enhanced benefits in restoring the eutrophic ecosystems, following the reduction of external nutrient loading. L'eutrophisation résultant de la charge nutritive dans les habitats d'eau douce est un problème grave, entraînant une dégradation des écosystèmes, y compris la détérioration de la qualité de l'eau, de la clarté de l'eau et la perte de biodiversité. Les mesures adoptées pour restaurer les écosystèmes d'eau douce dégradés impliquent souvent la réintroduction de plantes submergées et d'animaux aquatiques ayant des fonctions écologiques bénéfiques. Dans une expérience en mésocosme, trois traitements (plantation avec Vallisneria natans, introduction de l'escargot Bellamya aeruginosa et traitement combiné avec les plantes et les escargots) ont été comparés aux témoins pour évaluer leurs effets sur l'état trophique. Les concentrations d'azote total (TN), de phosphore total (TP) et de chlorophylle a (Chl a), des échantillons d'algues planctoniques et benthiques ont été déterminées toutes les deux semaines, ainsi que l'intensité de la lumière à la surface des sédiments. Le traitement aux plantes seules a réduit significativement les niveaux de TN et la biomasse d'algues planctoniques et benthiques et a augmenté l'intensité lumineuse à la surface des sédiments. Le traitement avec l'escargot seul a réduit les concentrations de TN et réduit la biomasse d'algues planctoniques et benthiques. Le traitement combiné a diminué les concentrations de TN et TP, réduit la biomasse d'algues planctoniques et augmenté l'intensité de la lumière sur la surface des sédiments. Les résultats indiquent que si les plantes submergées et les escargots peuvent améliorer la qualité de l'eau, l'effet le plus prononcé dans les écosystèmes aquatiques est obtenu par leur présence en combinaison. Une approche de réintroduction combinée peut apporter des avantages accrus dans la restauration des écosystèmes eutrophes, après réduction de la charge nutritive externe.