The Influence of Sodium Chloride on the Performance of Gammarus Amphipods and the Community Composition of Microbes Associated with Leaf Detritus

Abstract

Leaf litter decomposition is a fundamental part of the carbon cycle and helps support aquatic food webs along with being an important assessment of the health of rivers and streams. Disruptions in this organic matter breakdown can signal problems in other parts of ecosystems. One disruption is rising chloride concentrations.

Chloride concentrations are increasing in many rivers worldwide due to anthropogenic sources that can harm biota and affect ecosystem processes. Elevated chloride concentrations can lead to lethal or sublethal impacts. While many studies have shown that excessive chloride uptake impacts health (e.g. lowered respiration and growth rates) in a wide variety of aquatic organisms including microbes and benthic invertebrates). The impacts of high chloride concentrations on decomposers are less well understood.

My research objective was to assess how increasing chloride concentrations affect the performance and diversity of decomposer organisms in freshwater systems. I experimentally manipulated chloride concentrations in microcosms containing leaves colonized by microbes or containing leaves, microbes and amphipods. Respiration rate, decomposition, and community composition of the microbes were measured along with the amphipod growth rate, egestion rate, and mortality.

Elevated chloride concentration did not impact microbial respiration rates or leaf decomposition, but had large impacts on bacteria community composition. It did cause a decrease in instantaneous growth rate, and 100% mortality in the highest amphipod chloride treatment, but amphipod egestion rate was not significantly affected. The results of my research suggest that the widespread increases in chloride concentrations in rivers will have an impact on decomposer communities in these systems.