Date of Award

Summer 8-16-2024

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Ecology and Environmental Sciences

Advisor

Jasmine Saros

Second Committee Member

Jacob Yde

Third Committee Member

Kristin Schild

Abstract

The fate of heavy metals and nutrients melting out of the cryosphere into aquatic systems is not well understood. In chapter 2 of this thesis, we addressed this knowledge gap by measuring heavy metals and nutrients in the water and sediment of four glacially-fed (GF) and four snow and groundwater-fed (SF) lakes near Kangerlussuaq, West Greenland during the summer of 2023. GF lakes had 86% higher water concentrations of nutrients -- total phosphorus (TP), NO3-, and NH4+ -- and 137% higher concentrations of some metals -- Cd, Pb, Cr, Co, Ni, Al, Fe, Cu, Zn -- compared to nearby SF lakes. This pattern was reflected in the sediment, where metal concentrations were generally higher in GF lakes compared to SF lakes. However, a few metals, including Hg, As, Cu, and Pb, were higher in SF compared to GF sediment. Our results suggest metals may be increasing over the past few years to decades in GF lakes, and certain metals have increased in SF lakes, notably Hg has substantially increased (298%) in SF lakes over the past century. We observed diatom deformities in both GF and SF lake surface sediments, potentially due to the heavy metals, particularly the high concentrations of Ni, Cr, and Cu observed in the lake sediments. In one GF lake, we quantified inputs and outputs of metals and nutrients, and we found that loads declined by an average of 71% for metals and 68% for nutrients from the lake inlet to outlet, suggesting the lake is a sink for these materials. SF lakes also appear to be reservoirs of some metals, specifically atmospherically deposited metals (Hg, Pb, As, and Cu). Our results highlight that GF lakes in our study region are elevated in nutrients and metals compared to nearby SF lakes, indicating that the source of these materials is likely meltwater from the glacial system. We found that GF lakes can sequester a high percentage of the nutrients and metals flowing into them; however, as meltwater fluxes increase due to climate change, the ability of these lakes to remain sinks is an open question.

Chapter 3 of this thesis focused on the Jostedalsbreen Ice Cap in Western Norway, which is the largest Ice Cap in mainland Europe and has experienced an overall decline in mass balance over the past 60 years (Andreassen et al., 2020). To better understand the biogeochemistry of glacial lakes fed by the Jostedalsbreen Ice Cap and how increasing melt might affect these lakes and downstream areas, we measured heavy metals and nutrients in the water of four glacially-fed (GF) and three snow and groundwater-fed (SF) lakes near the Jostedalsbreen Ice Cap during September of 2023. We also measured heavy metals in two GF lake sediment cores. Nutrients - total phosphorus (TP) and NO3- - and most heavy metals (Pb, Cr, Zn, Al, Fe, Co) were higher (107% and 158%, respectively) in GF lakes compared to SF lakes. In contrast, the metals As and Cd were higher (70%) in SF compared to GF lakes, which could be due to geological or residence time differences between the GF and SF lakes. We also investigated the geochemical effects of an extreme flood event in one of the GF lakes, Nigardsbrevatnet. We found that all metals, two major ions (K and Mg), TP, total suspended solids (TSS), and turbidity were all higher 1-day post flood compared to 24-days post flood. We suggest that the intense amount of precipitation, combined with the steep topography surrounding Nigardsbrevatnet, caused metals and other elements to be washed off the landscape into the lake. Our results show that GF lakes have a distinct geochemistry compared to nearby SF lakes, and increasing inputs of glacial meltwater could potentially increase heavy metal and nutrient concentrations in GF lakes. Additionally, extreme precipitation events, which are expected to increase in Europe in the future (Hosseinzadehtalaei et al., 2020), can contribute large amounts of metals and other materials to aquatic systems, potentially affecting the biota in these environments.

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