A better appreciation of glacial floodplain morphodynamics reveals that disturbances are not spatially homogenous: implications for biofilm development

<p>Recent decades have seen worldwide glacier retreat that has resulted in a significant increase in the spatial extent of proglacial margins. Such margins, by switching from being ice-covered to light-exposed, are open to potential colonization by new organisms. However, ecological succession in glacial forefields may be slowed or even precluded by the highly unstable nature of these environments and habitability might be highly variable both in time and in space.</p><p>Discharge-related processes are likely to dominate forefields, in particular during the melt season. Discharge defines the shear forces acting upon the streambed, and ultimately bed and suspended loads and the rate of morphodynamic change through the floodplains. Evidence suggests that during the melt season glacial streams continuously rework their accommodation spaces by erosion and deposition processes, resulting in low rates of environmental stability. This means that benthic organisms, such as biofilms, inhabiting those streams may continuously be under pressure.</p><p>Biofilms are surface-attached communities composed of microorganisms, they are at the base of instream food webs, and they are involved in multiple ecosystem processes. Nevertheless, their surface-attached nature leads them to be easily removed from their lodging substrates by hydraulic disturbances. Because disturbance-dominated regimes exist during the melt season in glacial streams, it should be expected that biofilms might not be able to develop or persist during the melt season. A core idea in glacial stream ecology is that biomass, either of biofilms but also of macrozoobenthos, increases by moving away from the glacial snout, but also that it fluctuates during the year and reaches its highest mass during windows of opportunity (i.e., spring and fall). Even though this paradigm might hold, it does not fully capture the complexity of glacial floodplain morphodynamics, and the possibility that some stable zones exist even in summer. This explains why biofilms are able to develop in summer, and why well-developed biofilms can be found even close to the glacier snouts during the melt season.</p><p>In this paper, we present the first insights about the reasons why biofilms can develop in glacial floodplains during the melt season and, in particular, how important stable zones are for biofilm development. Through classical morphological and morphodynamic analysis, we seek to demonstrate that disturbances are not spatially homogenous, and geomorphic processes can shape the environment creating hot spot for biota. In this view, we argue that floodplain terraces, either permanent or temporary, play a crucial role in defining where biofilms – and consequently organisms that feed on them – settle, develop and grow.</p>

Glacial Stream Ecology: Structural and Functional Assets

High altitude glacier-fed streams are harsh environments inhabiting specialized invertebrate communities. Most research on biotic aspects in glacier-fed streams have focused on the simple relationship between presence/absence of species and prevailing environmental conditions, whereas functional strategies and potentials of glacial stream specialists have been hardly investigated so far. Using new and recent datasets from our investigations in the European Alps, we now demonstrate distinct functional properties of invertebrates that typically dominate glacier-fed streams and show significant relationships with declining glacier cover in alpine stream catchments. In particular, we present and argue about cause-effect relationships between glacier cover in the catchment and temperature, community structure, diversity, feeding strategies, early life development, body mass, and growth of invertebrates. By concentrating on key taxa in glacial and non-glacial alpine streams, the relevance of distinct adaptations in these functional components becomes evident. This clearly demonstrates that further studies of functional characteristics are essential for the understanding of peculiar diversity patterns, successful traits and their plasticity, evolutionary triggered species adaptions, and flexibilities.

Biodiversity and Abundance of Cultured Microfungi from the Permanently Ice-Covered Lake Fryxell, Antarctica

In this work, we explore the biodiversity of culturable microfungi from the water column of a permanently ice-covered lake in Taylor Valley, Antarctica from austral field seasons in 2003, 2008 and 2010, as well as from glacial stream input (2010). The results revealed that there was a sharp decline in total culturable fungal abundance between 9 and 11 m lake depth with a concurrent shift in diversity. A total of 29 species were identified from all three water sources with near even distribution between Ascomycota and Basidomycota (15 and 14 respectively). The most abundant taxa isolated from Lake Fryxell in 2008 were Glaciozyma watsonii (59%) followed by Penicillium spp. (10%), both of which were restricted to 9 m and above. Although seven species were found below the chemocline of 11 m in 2008, their abundance comprised only 10% of the total culturable fungi. The taxa of isolates collected from glacial source input streams had little overlap with those found in Lake Fryxell. The results highlight the spatial discontinuities of fungal populations that can occur within connected oligotrophic aquatic habitats.

Response of Diamesa spp. (Diptera: Chironomidae) from Alpine streams to newly emergent contaminants and pesticides

Acute toxicity and genotoxic activity of 11 pollutants were investigated in wild populations of Diamesa cinerella and Diamesa zernyi (Diptera Chironomidae) from two alpine streams (Italian Alps). D. cinerella was collected in two sites on the non-glacial Vermigliana stream, 50 m-upstream and 5-m downstream of the Wastewater Treatment Plant (WTP) at the Tonal Pass (1799 m a.s.l.). D. zernyi was collected in the Presena glacial stream, close to the glacier snout (2685 m a.s.l.). IV-instar larvae were exposed for 24-96 h to increasing concentrations of three drugs (ibuprofen-IBU, furosemide-FUR, trimethoprim-TMP), three personal care products (triclocarban-TCC, tonalid-TON, sucralose-SUCR), and five pesticides (boscalid-BOS, captan-CAP, chlorpyrifos-CPS, metolachlor-MET, terbuthylazine-TER). The experimental concentrations were from one to several million times higher than the highest environmental concentration (EC) measured in the study sites. Two mixtures of pesticides were also prepared: MIX 1K =103 x EC of CPS, MET and TER, and MIX 10K = 104 x EC of CPS, MET and TER. Species- and site-specific responses were observed for both tests. On the basis of survival data, both species resulted very resistant to pharmaceuticals (mainly to FUR for which no effects on survival and movement or pupation were observed), and more sensitive to pesticides (mainly to CPS, MET and CAP). Genotoxicity tests (Comet assay) highlighted a WTP effect under natural conditions and a genotoxic effect for 9 of the 11 tested compounds. Overall, a clear gradient of increasing resistance in larvae from the least (PR0) to the most polluted (TP_dw) site was highlighted by both tests, ecotoxicological and of genotoxicity, as also expected according to species autecology (D. zernyi is restricted to very cold and pristine habitats). D. cinerella living downstream of the effluent accumulates a significantly higher DNA damage than the other populations, highlighting a basal physiological stress condition in nature. It is plausible that these larvae possess chemical resistance strategies to survive already under natural conditions. Diamesa spp. exhibited a higher toxic resistance than any other model species tested to date under the same pollutants, probably associable to its strong cold resistance. The results emphasised that the measured concentrations of Contaminants of Emerging Concern (CECs) and pesticides seem to be far below those required to cause acute effects. However, the effects on freshwater communities of prolonged exposure to mixture of trace CECs and pesticides remain unknown.