Effects of Zinc in an Outdoor Freshwater Microcosm System

Abstract

A long-term exposure outdoor microcosm study was conducted to evaluate the effects of zinc (Zn) on zooplankton, phytoplankton, and periphyton in a freshwater system. Five Zn treatment concentrations (nominal: 8, 20, 40, 80, and 160 μg/L Zn) and an untreated control with 3 replicates each were used. Various physical and chemical characteristics of the microcosms and biological assessment endpoints (e.g., total abundance, group abundance, species richness, chlorophyll a, etc.) were measured to determine the effects of Zn over time. In general, physical and chemical characteristics (e.g., total dissolved solids, total suspended solids, dissolved oxygen, pH, dissolved organic carbon) of water fluctuated over time, but they were not significantly different within treatments and controls during the study. Zinc significantly affected the population dynamics and community structure of plankton. The effects occurred 7 d after initial treatment exposures began and continued to the end of the treatment phase, especially at the high treatment concentrations. Total and group abundance, species richness, the Shannon index, and chlorophyll a concentrations for high Zn treatment concentrations were significantly lower than the controls during the treatment phase. The no-observed-effect, lowest-observed-effect, and median effect concentrations were generally lower than the literature-reported results from single-species toxicity tests for fish and invertebrates, suggesting that plankton are more sensitive to Zn than planktivores. Although primary producers play an important role in the ecosystem, they have not been consistently incorporated into numerical environmental quality criteria for freshwater organisms, at least in the United States. The results of the present study are useful for development of environmental quality guidelines for freshwater ecosystems and ecological risk assessment.

Influence of water hardness on zinc toxicity in Daphnia magna

“…Spear reported the LC 50 values of 1 to 10 mg/L in soft water and 3 to 20 mg/L Zn for different fish species (Spear, 1982). Similar results were observed for phytoplankton where the no‐observed effect concentration (NOEC) values for phytoplankton kept in 22–35 mg/L calcium was 75 μg/L Zn, whereas 12–22 mg/L calcium resulted NOEC value of 21 μg/L Zn (Hoang et al, 2021; Van de Perre et al, 2016). These results demonstrated that increased hardness result in decreased acute toxicity across greatly distant species.…”

“…Twenty newly hatched daphnids were exposed to soft, medium, and hard water for 112 h. Expression levels are shown relative to 24 h in soft water. (C) jhe, (D) vtg-1, and (E) vtg-2 phytoplankton where the no-observed effect concentration (NOEC) values for phytoplankton kept in 22-35 mg/L calcium was 75 μg/L Zn, whereas 12-22 mg/L calcium resulted NOEC value of 21 μg/L Zn (Hoang et al, 2021;Van de Perre et al, 2016). These results demonstrated that increased hardness result in decreased acute toxicity across greatly distant species.…”

Diversity and Community Structure of Zooplankton in Homestead Ponds of a Tropical Coastal Area

“…Different species show various tolerances to increasing or decreasing temperature ranges, with particularly sensitive individuals being eliminated [9,10]. Low pH promotes a decreased zooplankton abundance, decreased biodiversity, and the extinction of some species, whereas alkaline conditions associated with high primary production promote zooplankton development and abundance [11][12][13][14][15]. The availability of light determines the producer's distribution, which indirectly impacts the diversity and distribution of animals.…”

“…Oxygen deficiencies can directly influence organism mortality. Heavy metals can significantly alter zooplankton's community structure and diversity [13,14] and tend to reduce community diversity and the richness of aquatic species under anthropogenic pressure [15,16]. The availability of nutrients, such as nitrates and phosphate, has a significant impact on the structure and abundance of zooplankton in an aquatic environment.…”

Seasonal dynamics of zooplankton in a eutrophic fish pond of Bangladesh in relation to environmental factors

“…While alkaline water conditions (pH>7) connected to high primary production support zooplankton development and abundance, low pH encourages decreased zooplankton abundance, reduced biodiversity, and the extinction of some species. 53,54 The present study observed alkaline pH values in pond water, which favor zooplankton abundance. In Noakhali, Bangladesh, Khan et al 17 recorded abundant zooplankton in naturally occurring ponds with an alkaline pH.…”