Changes of macroinvertebrate in the glacial-fed river system Vestari-Jökulsá (Iceland) between 1996 and 2022

The ongoing retreat of glaciers driven by climate change is predicted to significantly alter the ecological dynamics of glacier-fed streams, including changes in macroinvertebrate community composition. Previous studies suggest that increased water temperatures and altered channel stability due to glacial retreat initially decrease α-diversity due to elevated runoff, followed by an eventual rise in diversity and upstream shifts of species. Additionally, β-diversity is expected to decrease along the stream as highly adapted species near the glacial snout face changing conditions. However, few studies have confirmed these predictions yet, and most focus on temperate mountainous regions rather than Arctic environments.

To improve our understanding of these processes, an ongoing long-term research project investigates macroinvertebrates along the Vestari-Jökulsá (Iceland), an Arctic glacier-fed river draining the Satújökull glacier (Hofsjökull). In 1996 and 1997, Gíslason et al. (2002) studied longitudinal changes in macroinvertebrate communities and hydro-physical and hydro-chemical parameters in this river network to detect glacial influence as a function of distance from the glacier terminus. This dataset offers a unique opportunity to detect and compare the impact of current glacier retreat on macroinvertebrate communities, as well as hydro-physical and hydro-chemical parameters in this pro-glacial ecosystem over a long time period.

Data sampling will be conducted at 12 identical or comparable sites along the Vestari-Jökulsá and reference rivers in the area. Measured parameters include conductivity, temperature, discharge, sediment load, pH, macroinvertebrate diversity and density, nutrients, dissolved ions, chlorophyll α, and dissolved organic carbon content and composition through absorbance and fluorescence analyses. Hydrometric and hydro-chemical approaches will identify water sources (e.g., glacier meltwater, snowmelt, groundwater, rainfall, and stream water) at various spatial and temporal scales.

Fauna sampling was conducted in accordance with established methods in the ongoing long-term project. Near the glacier terminus, no recent invertebrate fauna was found. Approximately 83 individuals were identified at different life stages of insects (larvae, pupae, and imago). Most individuals belonged to Chironomidae (non-biting midges), with Diamesa spp. typically present. Diamesa species are specifically adapted cold-stenothermal kryal inhabitants. We also identified individuals from Simuliidae (black flies), Phoridae (humpbacked flies), and Scathophagidae (dung flies).

In the ongoing project, investigations will continue until the end of 2025 to obtain robust data for assessing long-term changes. This research aims to explore relationships between macroinvertebrate community diversity and environmental variables, identifying key drivers of ecological change. By evaluating Arctic systems' responses to glacier retreat, the study will offer critical insights into the resilience and adaptability of macroinvertebrate communities under rapid climatic shifts.