Ecological investigation of zooplankton abundance in the river Haraz, northeast Iran: Impact of environmental variables

A Geostatistical Framework Predicting Zooplankton Abundance in a Large River: Management Implications towards Potamoplankton Sustainability

The zooplankton community is a widely used bioindicator for the biological assessment of riverine aquatic ecosystems. Phyto-zooplankton interaction and spatially varying river environment parameters perceivably govern their spatial distribution in a large river. This invites the challenge of predicting zooplankton abundance along the river channel. The present article has proposed a geostatistical framework to predict zooplankton abundance along the river course while decoupling phyto-zooplankton relationship from spatial dependency. The strength of secondary data on the river Narmada-a large tropical river in India-has been utilised to accomplish the goal. The nonlinear logistic regression kriging has been found to be the most effective framework. The phyto-zooplankton relationship captured 66% of zooplankton variability, having moderate (37%) residual spatial dependence. The results have shown longitudinally fluctuating spatial variability, which supports the river serial discontinuity concept. The proposed framework has generated smooth zooplankton abundance and sustainability predictive maps that have allowed detection of the change point locations of zooplankton abundance. The map has precisely identified the most productive zone of zooplankton sustainability. The study also has appraised obtaining approximate data in the areas where sampling is infeasible, which will be helpful for location-specific management strategies on a lower spatial scale.

Effect of Gated Weir Opening on the Topography and Zooplankton Community of Geum River, South Korea

Hydrological changes affect not only the physicochemical factors and habitat structure of river ecosystems, but also the structure of biological communities sensitive to environmental changes, such as zooplankton. In this study, we investigate the effects of weir opening on environmental variables and topographic structures at Sejong Weir in South Korea and monitor the resulting changes in the structure and distribution of the zooplankton community. Weir opening led to increased dissolved oxygen and decreased conductivity, turbidity, chlorophyll a, total phosphorus, and total nitrogen and increased the diversity of topographic structures (reduced pool area and increase riffle and grassland/bare land areas) in the section downstream of Sejong Weir. Prior to weir opening (2015–2016), the cladoceran community was dominated by Chydrous spaeericus and Moina microcopa. After opening (2018–2019), the abundance of other cladoceran communities such as Bosmina groups (Bosmina longiseta, Bosmina fatalis, and Bosminopsis deitersi), Ceriodaphnia sp., and Daphnia obtusa increased. In contrast, the copepod species (Cyclops vicinus and Mesocyclops leukarti) were abundant before weir opening. We conclude that artificial weir opening helped maintain the unique environmental characteristics of the river ecosystem in terms of river continuity and led to a different zooplankton community composition in the new river environment.

How Do Specific Environmental Conditions in Canals Affect the Structure and Variability of the Zooplankton Community?

The present study investigates the responses of zooplankton (including changes in their structure and diversity) to physicochemical and biological parameters in two artificial waterways. Water samples were collected monthly from the Bydgoszcz Canal, the Noteć Canal, and the Brda River during the growing season of April–October 2019. We analyzed how selected parameters (including water temperature, Secchi disk visibility, oxygen concentration, conductivity, and pH, as well as nitrate, phosphate, and chl-a concentrations) affected seasonal variations in zooplankton diversity (T) and density (N). In total, we recorded 98 species, and average zooplankton density was 320 ind/L. At all sites, the same zooplankton species were dominant: Keratella cochlearis among rotifers and the Cladocera Bosmina longirostris among crustaceans. Rotifers dominated qualitatively and quantitatively over crustaceans. Zooplankton density and biomass, as well as the number of zooplankton species, were higher in the Bydgoszcz Canal than in the Brda River or the Noteć Canal. This may be connected to the locks on the Bydgoszcz Canal slowing down water flow, thereby increasing macrophyte vegetation, which creates ecological niches supporting zooplankton development.

Synergy between glyphosate and cypermethrin formulations on zooplankton: evidences from a single-specie test and a community mesocosm experiment

Agrochemicals can reach freshwater bodies by drift, leaching, or runoff, where they constitute complex mixtures. Given that glyphosate and cypermethrin are within the most worldwide used pesticides, they are likely to co-occur in freshwater bodies. The aim of this study was to analyze the interaction between glyphosate and cypermethrin formulations on the cladoceran Ceriodaphnia dubia (Richard 1894) through an acute toxicity test and on a zooplankton assemblage through a mesocosm (30 L) experiment. The 24-h LC50 of both isolated pesticides and their equitoxic mixture was obtained for C. dubia. The mesocosm was performed by exposing a zooplankton assemblage to both pesticides isolated and in combination. The acute toxicity of the equitoxic mixture in C. dubia was 3 and 4 times higher than the isolated toxicity of glyphosate and cypermethrin, respectively. The total toxic units of the mixture were 0.53, indicating a synergistic interaction. In the mesocosm experiment, both pesticides also interacted causing a synergistic negative effect in Cladocera and Copepoda abundances. No interactions between pesticides were found for Rotifera; therefore, the mixture effect was considered additive. It is suggested to continue analyzing pesticide mixture effects on the basis of complementary scales of analysis to reach more environmentally relevant information.