Arctic Station Dirigibile Italia

Effects of warming and eutrophication on the structure and functioning of Arctic lake food webs: implications for carbon sink and nutrient export to marine coastal waters (MILESTONE)

IADC_id: 840

active Call year: 2026

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Motivation and relevance of the proposed research :
Arctic lake ecosystems serve as crucial carbon sinks, support both endemic and non-endemic biodiversity, including species of conservation or hunting interest, and regulate nutrient inputs into rivers and marine waters, thereby influencing coastal eutrophication (Vincent et al. 2013). The internal circulation of nutrients, their recycling into the atmosphere, or export downstream depends on the structure and functioning of lake food webs, including the microbial component, which will be significantly impacted by climate change. Indeed, rising temperatures will decrease the duration of ice cover in lakes (Woelders et al. 2018), potentially affecting primary productivity and the composition, biomass and activity of microorganisms and macroinvertebrates. Additionally, increasing nutrient inputs due to the growing abundance of bird fauna can impact the quantity and quality of food supporting lake food webs, alleviate nutrient limitations to organic matter degradation, and alter the feeding choices of aquatic consumers, ultimately influencing nutrient transfer along detritus and herbivore food chains (Calizza et al. 2022). Hence, predicting how climate change will affect the composition and complexity of lake food webs, the accumulation of nutrients in the living biomass, their long-term storage in sediment or their release from lake. ecosystems is challenging. To answer this question, a deep understanding of the architecture of food webs, their relationship with nutrient cycling in lakes, and their vulnerability to future environmental changes is necessary.
Nevertheless, there is currently a lack of quantitative food web studies to establish the relationship between the structure and functioning of high Arctic lake ecosystems, particularly across gradients of lakes at varying distances from the sea or glaciers. This knowledge gap impedes a mechanistic understanding of the ecological consequences of climate change in the Arctic. Therefore, it is imperative to comprehend how the increase of temperature and nutrient inputs in the Arctic region will affect food webs, both as individual drivers and in combination, their seasonal dynamics, and the dependent nutrient output to the atmosphere or coastal waters. Such understanding is key for predicting the changes that these ecosystems will undergo over time, including the biodiversity they host and the services they provide. We hypothesis an increase in food web complexity and productivity with increasing temperature and external nutrient inputs. We also hypothesis an increase in C and N gas emission from lakes due to augmented microbial activity. No a priori hypotheses are formulated regarding dissolved nutrient export through lake effluents. Indeed, we expect that the accumulation in plant and animal biomass or export downstream will depend on the distribution of living biomass among food wed compartments, the relative importance of nutrient transfer along food chains vs. microbial degradation of organic matter, and the turnover rate of lake waters. With reference to lake water turnover, we hypothesis that a faster turnover will be associated to a relatively lower retention of nutrients within food webs and a relatively higher export downstream (with respect to nutrient inputs in each lake).

Objectives and impacts:
The aim of the project is to provide a mechanistic understanding of the structure and functioning of Arctic lake food webs and their vulnerability to warming and eutrophication, with a focus on their relationship with carbon sink and nutrient export from lakes. The study considers lake ecosystems along a gradient of distance from the coast and glaciers (Fig. 1 and 2). It focuses both on the entire food web and key components: the microbial community, a dominant macroinverterbate species Lepidurus arcticus, and a dominant vertebrate species, the goose Branta leucopsis.
Using field measurements, laboratory experiments, 3D mapping of lakes and data modeling, the project explores the impacts of temperature and organic N inputs on:
i. Food web structure, including biodiversity and stability;
ii. The microbial community's composition and function;
iii. C and N in sediment, their transfer along food chains and recycling into the atmosphere;
iv. Quantity and quality of nutrient export from lakes to downstream waters.
The first two years will be dedicated to field measurements at the start and the end of each summer season, followed by a third-year lab experiment in Svalbard. This will allow us to disentangle natural seasonal variations from temperature and nutrient-related differences among lakes.
The project will develop a new interdisciplinary approach applicable across the whole Arctic. Quantitative description of food webs coupled with measure of nutrient transfer among environmental compartments will inform on the vulnerability of lake biodiversity and nutrient cycling to environmental changes.

Methodology:
The project will focus on the Brøgger peninsula, Spitzbergen, Svalbard. The area represents a natural laboratory for studying ecological effects of climate change in the Arctic. It hosts numerous fishless shallow lakes that differ for the abundance of barnacle geese and their mean summer temperature, which is associated with the distance from the coast and glaciers and produce differences in the length of the ice cover. From the coastline to the interior, marked differences in these parameters can be observed over a few kilometers (Fig. 2). In parallel, lake watersheds at a similar distance from the coast differ in geese abundance (Calizza et al. 2022). This generates a natural experiment to test the effect of temperature and nutrient inputs from geese on i) the composition and complexity of food webs, ii) the microbial diversity and metabolic activity, iii) the amount of bioavailable, refractory and inorganic carbon in sediment, iv) the rate of C and N gaseous emissions from lakes or their export downstream.
Four groups of three lakes each will be studied both at the beginning and the end of the summer season (Fig. 1). Each group will include lakes characterized by relatively high, intermediate or low temperature. The four lake groups will differ for the high, intermediate, low or null presence of geese. Lake watersheds will be selected through remote sensing (Sentinel 2) and webcam image analysis of ice cover, previous measurements of temperature (PRA-EcoClimate), and previous knowledge of geese abundance owned by the Partners.
C and N elemental and stable isotope analyses ( ?13C and  ?15N) in all food web components will be performed through elemental analysis coupled with mass spectrometry.  ?13C informs on the terrestrial vs. aquatic origin of C;  ?15N informs on the organic vs. inorganic origin of N (Rundel et al. 2012). Baysian mixing models will be applied to isotopic data to assign trophic links among species (Careddu et al. 2015). Water volume will be estimated through 3D bathymetry mapping with an hydrographic drone, while in situ measurements will provide quantity of water inflow and outflow. Terrestrial runoff patterns will be reconstructed through 3D Digital Elevation Models of watersheds (Calizza et al., 2016). An automatic system based on high resolution cameras and the ethovision system to quantify the number of geese in watersheds will be developed. Physicochemical data and nutrient concentrations will be measured at the inflow, center and outflow of lakes. In parallel, microbial abundance and diversity, degradative metabolic rates and functionality will be quantified, and gaseous emissions at the water-air interface will be in situ recorded through floating chambers connected to a LI-COR infrared gas analyser. Laboratory experiments to test effects of temperature and nutrient concentration on microbial communities and the hatching and feeding activity of L. arcticus will be performed at the King’s Bay Marine Lab in Ny-Alesund.

Expected Results:
The study will quantify impacts of warming and eutrophication on lake food webs, including their microbial components, C and N transfer along food chains, their release or downstream export. We will evaluate food web complexity, inherent biodiversity and stability across temperature and nutrient gradients, and our data will support models for nutrient load, microbial activity, and food web structure in relation to goose population trends and IPCC scenarios.
As temperature and nutrient inputs increase, we anticipate heightened microbial activity, primary and secondary production. This could lead to increased C and N gas emissions from lakes. However, variations in nutrients accumulated in sediment or exported downstream are not obvious. Indeed, their retention within food webs will depend on biomass distribution and nutrient transfer across trophic levels. Accordingly, the project will clarify the role of food webs in nutrient input and output dynamics in Arctic lakes. Lepidurus arcticus will serve as model species to investigate how climate change might disrupt trophic interactions due to changes in phenological rhythms and predatory activity. We'll determine the relative significance of innate timing versus environmental stimulation in egg hatching, shedding light on the role of temperature sensitivity in emergence dates. Additionally, we'll measure adult feeding rates and biomass accrual at various temperatures to understand the impact of warming on nutrient uptake and transfer along food chains.
Lakes will be characterised by examining their thermal regimes, nutrient and chlorophyll concentrations under different environmental conditions (ice-free season length and bird fauna presence). Variations in trophic conditions and temperature can influence microbial biodiversity and enzymatic profiles, which are expected to vary between lakes. The project will provide a comprehensive understanding of the evolution of microbial communities and their role in organic matter remineralization and enzymatic hydrolysis, and will contribute to our knowledge of C, N and P cycles in lakes, their dependence on temperature and nutrient inputs, and potential future variations in line with IPCC scenarios.
Detailed descriptions of lake geometry, volume, and water circulation will be provided. Geostatistical maps showing water temperature, chlorophyll, turbidity, nutrient concentrations and their seasonal variations, along with nutrient anomalies and plumes, will be generated. These maps will reveal fine-scale dependencies of nutrient concentration on eco-hydro-morphological features. Predicted variations in hydrologic regimes will be linked to external nutrient inputs, internal budgets, and lake exports, enabling us to model impacts of climate change on nutrient cycling. Additionally, we will identify trends, including potential ecological regime shifts resulting from the combined effects of expected warming and increased organic inputs from migratory birds.

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Project information

Effects of warming and eutrophication on the structure and functioning of Arctic lake food webs: implications for carbon sink and nutrient export to marine coastal waters (MILESTONE)