Environmental Science: Processes & Impacts

Cross-ecosystem nutrient subsidies in Arctic and alpine lakes: implications of global change for remote lakes

Journal: Environmental Science: Processes & Impacts

Manuscript ID EM-ART-11-2019-000528.R1

Article Type: Critical Review

Page 1 of 83 Environmental Science: Processes & Impacts

1 2 3 Environmental Significance Statement 4 5 6 Ecosystem nutrient subsidies are the transfer of nutrients across ecosystem boundaries. 7 Subsidies can occur between the terrestrial environment, cryosphere, atmosphere, and aquatic 8 systems. The topic of cross-ecosystem subsidies has gained increased attention over the past 9 two decades. Cross-ecosystem nutrient subsidies are important to lake ecosystems because 10 11 they influence ecological community structure and ecosystem functioning, such as the rate of 12 nutrient or carbon cycling. This review synthesizes recent freshwater ecosystem subsidy 13 research, identifies knowledge gaps, and identifies remote lakes as ideal target systems for 14 future subsidy research. Environmental changes continue to affect the amount, quality, and 15 16 timing of nutrient subsidy transfers to lakes. Thus, understanding how nutrient subsidies affect 17 ecosystems will improve our ability to predict lake ecosystem impacts. 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Environmental Science: Processes & Impacts Page 2 of 83

1 2 3 1 Cross-ecosystem nutrient subsidies in Arctic and alpine lakes: implications of global change 4 5 2 for remote lakes 1 1 6 3 Benjamin T. Burpee * and Jasmine E. Saros 7 8 4 1 Climate Change Institute and School of Biology and Ecology, University of Maine, Orono, ME 9 5 *Corresponding author: [email protected] 10 11 12 6 Abstract 13 14 15 16 7 Environmental change is continuing to affect the flow of nutrients, material and 17 18 8 organisms across ecosystem boundaries. These cross-system flows are termed ecosystem 19 20 21 9 subsidies. Here, we synthesize current knowledge of cross-ecosystem nutrient subsidies 22 23 10 between remote lakes and their surrounding terrain, cryosphere, and atmosphere. Remote 24 25 26 11 Arctic and alpine lakes are ideal systems to study the effects of cross ecosystem subsidies 27 28 12 because a.) they are positioned in locations experiencing rapid environmental changes, b.) they 29 30 31 13 are ecologically sensitive to even small subsidy changes, c.) they have easily defined ecosystem 32 33 14 boundaries, and d.) a variety of standard methods exist that allow for quantification of lake 34 35 15 subsidies and their impacts on ecological communities and ecosystem functions. We highlight 36 37 38 16 similarities and differences between Arctic and alpine systems and identify current knowledge 39 40 17 gaps to be addressed with future work. It is important to understand the dynamics of nutrient 41 42 43 18 and material flows between lakes and their environments in order to improve our ability to 44 45 19 predict ecosystem responses to continued environmental change. 46 47 48 49 20 50 Introduction 51 52 53 21 Ecosystem subsidies, defined as cross-boundary material fluxes between ecosystems1, 54 55 56 22 are important because they enrich communities with nutrients, materials, and energy that 57 58 59 1 60 Page 3 of 83 Environmental Science: Processes & Impacts

1 2 3 23 might otherwise be scarce or unavailable. Commonly discussed nutrients in freshwater ecology 4 5 6 24 research (as well as this review) include the elements nitrogen, phosphorus, silica, iron, and 7 8 25 carbon (N, P, Si, Fe, and C, respectively), their inorganic forms (such as dissolved inorganic N, or 9 10 11 26 DIN) and organic forms (such as polyunsaturated fatty acids, or PUFAs) that are present in the 12 13 27 environment as resources for organisms. In aquatic environments, nutrient subsidies can 14 15 2,3 16 28 support algal communities dominated by few high-nutrient species , change ecosystem 17 18 29 function and food web dynamics2,4-6, sustain species abundance, increase community turnover7- 19 20 30 9, and influence biological richness of animals, plants, and microbiota10,11, but effects will vary 21 22 23 31 depending on environmental nutrient limitation. In this review, we address the need for a 24 25 32 synthesis of the growing body of research investigating subsidies to freshwater ecosystems. 26 27 28 33 Due to their sensitivity and location within rapidly changing environments, we focus primarily 29 30 34 on Arctic and alpine lake ecosystems. We highlight the common themes, differences, and 31 32 33 35 emerging challenges and opportunities for subsidy research within Arctic and alpine lakes and 34 35 36 confirm these remote systems as important locales for continued subsidy research. 36 37 38 37 The study of cross-ecosystem subsidies emerged as ecologists assessed processes 39 40 38 occurring over multiple spatial and temporal scales.12 Growing from this recognition of complex 41 42 39 and multiscale ecosystem processes, the two subdisciplines of landscape ecology and meta- 43 44 45 40 ecosystems emerged. Landscape ecology recognized the importance of considering broad 46 47 41 geographic scales and heterogeneous patterning of landscapes in shaping ecosystems and 48 49 13 50 42 ecological communities. Importantly, two of its main foci include “the interactions and 51 52 43 exchanges across heterogeneous landscapes,” (172) and “the ways in which fluxes are 53 54 14 55 44 controlled within heterogeneous matrices” (331). Within the schema of landscape ecology, 56 57 58 59 2 60 Environmental Science: Processes & Impacts Page 4 of 83

1 2 3 45 ecosystem subsidies are exchanges between heterogeneous environments nested within a 4 5 6 46 broader landscape. Further, the heterogeneity of a landscape (for instance, the variable 7 8 47 vegetation cover of lake catchments moving up an elevation gradient) affects the quantity and 9 10 11 48 quality of transported materials. Thus, ecosystem subsidies are centrally important in landscape 12 13 49 ecology. 14 15 15 16 50 To explain how ecological processes operate over multiple spatial scales, Loreau et al 17 18 51 described the meta-ecosystem concept. A meta-ecosystem is a group of ecosystems that are 19 20 52 connected through fluxes of material, species, and energy. This differs from the landscape 21 22 23 53 ecology perspective in that connected ecosystems need not be spatially continuous or defined 24 25 54 at a particular spatial scale (i.e. the landscape scale). Thus, ecosystem subsidies that originate 26 27 28 55 remotely from the site where they are transported (such as agricultural fertilizers that are 29 30 56 atmospherically deposited on distant alpine ecosystems) are included within this conceptual 31 32 33 57 framework. 34 35 58 The singular topic of cross-ecosystem subsidies, which move across heterogeneous 36 37 38 59 landscapes and enrich receiving ecosystems with nutrients or energy, was explicitly addressed 39 40 60 by Polis et al.1 In particular, Polis et al reviewed the effect of ecosystem subsidies on food web 41 42 61 dynamics and described the connectedness of habitats via fluxes of material, nutrients, or 43 44 45 62 organisms. Following Polis et al1, much of ecosystem subsidy research has remained focused on 46 47 63 food web and community effects (e.g. refs. 16-26). 48 49 50 64 At present, new challenges are evident in ecosystem subsidy research. For instance, 51 52 65 over the past 20 years studies note that peak productivities and transfers between 53 54 55 66 aquatic/terrestrial habitats can be asynchronous and seasonal (e.g. refs 4,27). In other words, 56 57 58 59 3 60 Page 5 of 83 Environmental Science: Processes & Impacts

1 2 3 67 fluxes can vary temporally.28 In the past decade research has demonstrated that subsidies of 4 5 29 6 68 matter and organisms can be bidirectional, or reciprocal, across coupled ecosystems. Further, 7 8 69 ecosystems are experiencing rapid climate change, a driver that exercises both direct and 9 10 11 70 indirect effects upon the timing, direction, quality, and quantity of ecosystem subsidies. Leavitt 12 13 71 et al30 demonstrated that in lakes experiencing climate warming, lake inputs can be divided into 14 15 16 72 two categories, energy (E) and mass (M). While lakes will tend to respond coherently through 17 18 73 time to changes in E inputs (for instance, increased PAR irradiance), lake responses to M inputs 19 20 74 will likely be much more variable depending on a host of catchment and lake properties and 21 22 23 75 processes. Cross-ecosystem subsidies can be categorized as M inputs. The topic of ecosystem 24 25 76 subsidies is therefore complex: ecologists are not only concerned with structural ecosystem 26 27 28 77 responses to unidirectional subsidies (e.g. ref. 31), they are concerned with effects of climate 29 30 78 change upon the direction, timing, and magnitude of subsidies themselves. There is a hierarchy 31 32 33 79 of factors and responses involved (Figure 1), and many are interactive, making it difficult to 34 35 80 focus on any single pair of response/control variables. 36 37 38 81 In the face of this challenge, systems that exhibit naturally well-defined ecosystem 39 40 82 boundaries, measurable fluxes of material or organisms, and measurable ecosystem responses 41 42 83 to subsidies will lend themselves to ecosystem subsidy research. Lake ecosystems are therefore 43 44 45 84 exemplary for such studies. While lakes are open systems, their physical boundaries are 46 47 85 distinct, and they are relatively self-contained depending on water residency time. Following 48 49 32 50 86 Strayer et al , we consider lake ecosystem boundaries in this review in terms of our 51 52 87 investigative goals, relevant scale, and processes of interest. The ecosystem boundary of lakes 53 54 55 88 in this review are therefore delineated by the basin and body of lake water, because we are 56 57 58 59 4 60 Environmental Science: Processes & Impacts Page 6 of 83

1 2 3 89 focused on whole-lake ecological responses to ecosystem subsidies. However, we recognize 4 5 6 90 lakes are part of their larger watershed (meta-ecosystem), and the lake subsidies we consider 7 8 91 can be categorized as within-basin (e.g. benthic to pelagic transfers such as sediment P release), 9 10 11 92 within-watershed (e.g. groundwater inputs of DOM), and extra-watershed transfers (e.g. 12 13 93 atmospheric N deposition). 14 15 16 94 Fluxes into and out of lakes are measured or modeled with increasing ease and accuracy 17 18 95 (e.g., refs. 33-35). The ease with which ecological responses to cross-system transfers are 19 20 96 registered and quantified in lakes also makes them convenient for subsidy research.36-39 21 22 23 97 Because of their position at low points in the landscape, lakes behave as integrators and 24 25 98 archives of the environmental changes that occur across landscapes and catchment areas.40 The 26 27 28 99 sedimentation processes that occur within lake basins produce temporally continuous records 29 30 100 of ecosystem change. Thus, the effects of subsidies, and the environmental factors that control 31 32 9 33 101 those subsidies, can be recorded in lake sediment records via quantification of algal pigments , 34 35 102 diatoms3, and isotopes.41 36 37 38 103 Finally, lakes are highly sensitive, behaving as sentinels of ecosystem change in response 39 40 104 to environmental drivers.40 Mueller et al42 summarize why high Arctic lakes located on 41 42 105 Ellesmere Island, Canada serve as global sentinel systems of climate warming by drawing on 43 44 45 106 four decades of data collection. Ellesmere Island lake ice-out phenology and mixing regime 46 47 107 shifted abruptly in response to changes in air temperature when warming trends changed the 48 49 50 108 lakes from permanently ice-covered systems to seasonally open water. Seasonally open water 51 52 109 exposed the lake surface to wind-driven mixing, thus changing the water column structure. 53 54 42 55 110 Though biological metrics were not explicitly considered by Mueller et al , the ecological 56 57 58 59 5 60 Page 7 of 83 Environmental Science: Processes & Impacts

1 2 3 111 communities in Ellesmere Island lakes are dependent on water column mixing regime; thus, 4 5 6 112 these lakes were ecologically sensitive to climate forcing and were likely vulnerable to 7 8 113 cascading ecological regime shifts in response to the physical lake changes. As Ellesmere Island 9 10 11 114 lake changes occurred synchronously with ice shelf breakup and changes to permafrost, sea ice, 12 13 115 and glaciers, the authors demonstrate that lakes serve as robust sentinels of environmental 14 15 16 116 change beyond the regional scale. In summary, ecological sensitivity, physical boundaries, 17 18 117 location within the landscape, and a plethora of standard evaluative methods mean lakes are 19 20 118 ideal to study how rates of cross-ecosystem fluxes may shift due to anthropogenic pressures 21 22 23 119 such as land use change, nutrient delivery through atmospheric deposition or non-point 24 25 120 sources, and climate change. 26 27 28 121 Dilute, nutrient-poor and cold-water lakes with relatively simple ecological communities 29 30 122 are particularly sensitive to cross-ecosystem subsidies. This is due to watershed characteristics 31 32 33 123 of high Arctic and alpine lakes that enhance transport of nutrients to lakes (e.g. refs. 35, 43,44) 34 35 124 and because nutrient-poor lake ecosystems respond to lower thresholds of nutrient inputs (for 36 37 38 125 example, alpine lakes in western US respond to lower amounts of atmospherically deposited N 39 40 126 compared to other ecoregions).45-47 Thus, high-elevation mountain and Arctic lakes are very 41 42 127 responsive to changes in subsidy patterns.42,48 Because of Arctic and alpine lake sensitivity, 43 44 45 128 ecosystem responses observed first in these systems provides insight into changes ecologists 46 47 129 might expect to eventually observe in lakes situated in warmer climates (i.e. lower latitude and 48 49 50 130 lower elevation climates with higher annual mean air temperature compared to Arctic or high 51 52 131 elevation environments) with more complex and diverse ecological communities.40 For these 53 54 55 56 57 58 59 6 60 Environmental Science: Processes & Impacts Page 8 of 83

1 2 3 132 reasons, Arctic and alpine lakes are exceptional systems in which to conduct nutrient subsidy 4 5 6 133 research. 7 8 134 Arctic and alpine lakes have served as systems to evaluate ecosystem subsidies for 9 10 11 135 several decades. In the 1970s, nutrient fluxes were studied in Arctic ponds of Barrow, Alaska to 12 13 136 account for ecosystem nutrient budgets.49 This study provided early insights into the sources 14 15 16 137 and fates of nutrients within the tundra landscape. Lake eutrophication in the high Canadian 17 18 138 Arctic resulting from N and P associated with sewage effluent was evaluated by Schindler et 19 20 139 al.50 Ecological effects of enhanced N delivery to Lake Tahoe (located in the Sierra Nevada 21 22 23 140 Mountains of California) were evaluated by Goldman51 using a time series dating back to 1968. 24 25 141 Eutrophication from land use changes and urbanization decreased lakewater clarity and 26 27 28 142 increased lake primary productivity. 29 30 143 Arctic and alpine lakes are situated in areas that are experiencing accelerated rates of 31 32 52 33 144 climate warming. The pan-Arctic region includes large areas of North America, Europe, and 34 35 145 Asia. Major alpine lake districts are distributed globally, including the North American Rocky 36 37 38 146 Mountains, European Alps, Himalayas and Tibetan Plateau in central and western Asia, and the 39 40 147 South American Andes. Climate warming controls many environmental changes that are 41 42 148 occurring in Arctic and alpine lake catchments, including glacier recession53, catchment 43 44 45 149 “greening”54, permafrost degradation55-56, increased abundance of waterfowl57, altered 46 47 150 quantity and timing of insect emergence58, and altered hydrological connectivity.59 In turn, 48 49 50 151 many of these environmental changes control the magnitude, frequency, timing, and quality of 51 52 152 subsidies delivered to lakes from the atmosphere, cryosphere, and terrestrial catchment. 53 54 55 153 Changes of cross-ecosystem subsidies are presently not well accounted for. Large scale 56 57 58 59 7 60 Page 9 of 83 Environmental Science: Processes & Impacts

1 2 3 154 environmental drivers such as climate warming will continue to impact ecosystem subsidies 4 5 6 155 into the future, making this area of research timely and urgent. Thus, alpine and Arctic areas 7 8 156 are insightful landscapes in which numerous “natural experiments”, or comparative studies, can 9 10 11 157 be conducted to understand how cross-ecosystem subsidies affect lakes. Already, researchers 12 13 158 have compared effects of glacial meltwater60, permafrost slumping61, insect emergence62-63, 14 15 64 16 159 and dissolved organic carbon (DOC) impacts on nearby paired Arctic and alpine lake 17 18 160 ecosystems that are differentially influenced by environmental changes. Equally important are 19 20 161 the paleoecological insights that lake sediment records provide, whereby pre-Anthropocene 21 22 23 162 algae assemblages or isotope chemistries can be compared to recent ones within the same lake 24 25 163 ecosystem. 26 27 28 164 In this review we will synthesize such studies in order to outline the current state of 29 30 165 ecosystem subsidy research in Arctic and alpine lakes. Previous studies have reviewed subsidy 31 32 65-67 33 166 effects in remote lakes (Catalan et al 2006; Hobbs et al 2010; Catalan et al 2013). However, 34 35 167 these papers focused on paleolimnological records66-67 or were location-specific.65 Our review 36 37 38 168 surveys cross-ecosystem subsidies to remote lakes drawing on both contemporary ecological as 39 40 169 well as paleolimnological research. Because of its central importance to cross-ecosystem 41 42 170 subsidies, we will highlight the current and future effects of abrupt climate change. Though we 43 44 45 171 consider community and food web consequences of lake ecosystem subsidies, we emphasize 46 47 172 biological and biogeochemical responses and trends in order to situate cross-ecosystem subsidy 48 49 50 173 research as an important facet of Arctic and alpine carbon (C) and nutrient cycling and climate 51 52 174 change feedback loops. Conceptual models that illustrate current understanding of the drivers 53 54 55 175 and effects of lake subsidies explore this paradigm. Finally, we will address certain challenges 56 57 58 59 8 60 Environmental Science: Processes & Impacts Page 10 of 83

1 2 3 176 and open questions in lake ecosystem subsidy studies and call for research to address these 4 5 6 177 knowledge gaps. 7 8 9 10 178 Arctic lake subsidies 11 12 13 14 15 179 Cryosphere 16 17 18 180 Across arctic and alpine landscapes alike, perhaps the most visually obvious change is 19 20 181 the rapidly changing cryosphere involving the recession of glaciers, permafrost thawing, and 21 22 23 182 diminishing snowpack. Glaciers concentrate and store atmospheric compounds, including 24 25 183 anthropogenic pollutants. In this way, glaciers behave as “natural archives” because the 26 27 68 28 184 combined effects of emission trends and air circulation patterns is recorded within their ice. 29 30 185 Thus, glaciers are reservoirs and secondary sources of anthropogenic pollutants69, because 31 32 186 these compounds are present in glacier meltwater and are delivered to downstream 33 34 35 187 ecosystems. Climate warming increases glacial meltwater output and accelerates the release of 36 37 188 accumulated pollutants.70 While glacial pollutant storage is often associated with mountain 38 39 40 189 glaciers that are in closer proximity to source emissions, anthropogenic organic pollutants have 41 42 190 been detected in remote Arctic glacial ice and snowpack.71-73 In addition to pollutants, glacier 43 44 45 191 meltwater contains nutrient solutes as well as minerogenic particulates that are ecologically 46 47 192 important. These nutrients and minerals may be sourced from the atmosphere and 48 49 74 50 193 concentrated in glacier ice to be released upon melt , similar to anthropogenic pollutants, or 51 52 194 derived from bedrock material that gets weathered by biogeochemical and physical processes 53 54 195 and washed out via subglacial flow.75 Ice sheets and glaciers store a significant amount of labile 55 56 57 58 59 9 60 Page 11 of 83 Environmental Science: Processes & Impacts

1 2 3 196 particulate and dissolved organic matter (DOM)76,77, N60, P78-80, Si79,81, as well as many other 4 5 82 6 197 micronutrients (such as Fe) . Thus, Arctic glacier meltwaters represent an important nutrient 7 8 198 subsidy for downstream freshwater ecosystems. 9 10 82 81 11 199 In southwest Greenland, Bhatia et al and Hawkings et al demonstrated significant 12 13 200 amounts of P, N, Si, and Fe are contained in meltwater discharged from the Greenland Ice 14 15 16 201 Sheet. Ice sheet meltwater total P (TP) and DIN were important determinants of distinct algal 17 18 202 communities and higher algal biomass in Greenland glacially-fed lakes compared to nearby 19 20 203 snow and groundwater-fed lakes.80 Similarly, a lake sediment record from northeast Greenland 21 22 23 204 (Bunny Lake, fed by the Renland Ice Cap) show diatom community changes that likely coincided 24 25 205 with glacier meltwater inputs starting a thousand years ago.3 Glacially-fed lakes in Svalbard and 26 27 78 28 206 northern Sweden also exhibited elevated TP concentrations. Together, these studies show the 29 30 207 widespread potential for glacier meltwater being an important source of nutrient subsidies in 31 32 33 208 the Arctic and highlight the potential importance of glacially-fed lakes along the ice sheet 34 35 209 behaving as hotspots of C and nutrient cycling as a result of these glacial meltwater additions. 36 37 81 38 210 Fluxes of particulate and solute nutrients are greater in years of higher melt ; thus, future 39 40 211 climate warming may increase nutrient delivery to freshwater systems. These trends and 41 42 212 interactions will likely have important implications for Arctic C and nutrient cycling.83 43 44 45 213 While significant work has been completed on glacier nutrient subsidies in streams and 46 47 214 rivers (e.g. refs. 25,84,85), glacier fed Arctic lakes represent potential hotspots of nutrient 48 49 86 50 215 cycling and should be more thoroughly investigated. Compared to alpine regions, little 51 52 216 research has been conducted on Arctic lakes to understand how glacial meltwater affects their 53 54 55 217 ecology. Given that meltwater delivery to Arctic lakes will increase due to climate warming, as 56 57 58 59 10 60 Environmental Science: Processes & Impacts Page 12 of 83

1 2 3 218 well as a projected increase in the abundance of glacially-fed Arctic lakes due to glacier 4 5 87 6 219 recession , the ecological responses of these systems should be a research priority. 7 8 220 Permafrost is sensitive to changes in air and ground temperatures88-90 as well as 9 10 91 11 221 rainfall. Similar to glaciers, permafrost thaw in Arctic areas is therefore predicted to 12 13 222 significantly increase in response to climate warming.55,56,92,93 Permafrost thaw is an important 14 15 16 223 source of lake nutrient subsidies. Thaw events can be episodic, representing pulse disturbances 17 18 224 to lakes, or they can be gradual and persistent, representing press disturbances.94 Moreover, 19 20 225 permafrost thaw contributes to lake nutrient subsidies directly and indirectly (Figure 2). The 21 22 23 226 active layer of soil that sits above the permafrost controls the tundra landscape’s hydrology and 24 25 227 biogeochemistry.89,95-98 As such, changes to the active layer depth affect groundwater and 26 27 89,99,100 28 228 nutrient delivery to freshwater ecosystems. However, a deepening of the active layer 29 30 229 may have variable results; DOM inputs to freshwaters may increase (e.g. refs. 101-104) or 31 32 105 106-109 33 230 decrease due to mineral sorption or groundwater flow paths becoming deeper. The 34 35 231 quality of DOM transported to lakes may change to more biolabile pools.110 Research in Alaska 36 37 38 232 and the Canadian high Arctic suggested that DIN and TP flux to freshwaters will increase with 39 40 233 continued warming.98,99,111-113 Permafrost thaw that results in altered lake catchment 41 42 234 biogeochemical and hydrological processes is an indirect control of nutrient subsidies. In 43 44 45 235 contrast to trends in current literature suggesting Arctic lakes may represent hotspots of 46 47 236 nutrient and C cycling, a recent study in Alaska revealed that the transfer and within-lake 48 49 114 50 237 respiration of terrestrial organic C was minimal. This study was located in an arid area of 51 52 238 interior Alaska that may be broadly representative of arid Arctic landscapes. Instead of 53 54 55 239 allochthonous DOC mineralization, periods of lake heterotrophy consisted of autotrophically 56 57 58 59 11 60 Page 13 of 83 Environmental Science: Processes & Impacts

1 2 3 240 produced organic C mineralization. Together, these studies suggest that permafrost thaw will 4 5 6 241 have spatially variable lake subsidy outcomes depending on thaw patterns, active layer depth, 7 8 242 soil type, biolability of C and nutrient pools, and local hydrology. 9 10 11 243 Other thermokarst processes, such as permafrost slumping, involve a direct physical 12 13 244 transfer of particulate sediments and solutes from terrestrial environments into Arctic lakes. 14 15 16 245 While thermokarst events can form lakes that occupy tundra depressions where permafrost 17 18 246 degraded, established lakes within the Arctic landscape (originated from other processes, such 19 20 247 as glacial scouring) can be influenced by thermokarst processes within their watersheds. This is 21 22 23 248 a common occurrence in the Canadian and Russian Arctic. For instance, one in ten lakes in 24 25 249 certain areas of the Canadian uplands were affected by permafrost slumping.115 In this study, 26 27 28 250 ionic concentrations were higher in lakes affected by permafrost slumping compared to 29 30 251 undisturbed lakes. Higher ionic concentrations in affected lakes were due to the exposure of 31 32 33 252 hitherto frozen watershed sediments to weathering processes, and subsequent transfer of 34 35 253 soluble materials to lakes by surface runoff. Permafrost thermokarst events in northern Alaska 36 37 38 254 increased DOC and DIN concentrations in feature outflows, with potential ecological 39 40 255 consequences for downstream freshwaters.116 In contrast, sedimentation of organic material 41 42 256 associated with slump sediments lowered lake nutrient concentrations (total dissolved N and 43 44 45 257 TP) and increased water clarity, with more recently slump-affected basins exhibiting greater 46 47 258 clarity.115,117-119 Increased water clarity following slumping may have driven increased 48 49 61 50 259 macrophyte production in affected lakes as well as diatom species turnover with increased 51 52 260 prevalence and diversity of periphytic diatoms.119 In the Canadian uplands, lakes disturbed by 53 54 120 55 261 permafrost slumping events exhibited doubled macroinvertebrate abundance. However, 56 57 58 59 12 60 Environmental Science: Processes & Impacts Page 14 of 83

1 2 3 262 increasing water clarity may expose pelagic organisms to harmful UV radiation.117 Accelerating 4 5 121,122 6 263 rates of thermokarst activity in the Arctic in response to climate warming , coupled with 7 8 264 lake responses to such disturbance events described above, suggests that permafrost slumping 9 10 11 265 will be an important modulator of lake nutrient subsidies. 12 13 266 Climate warming across the Northern Hemisphere pan-Arctic region is driving a general 14 15 16 267 reduction in snow accumulation since 1979, though there is much regional variability associated 17 18 268 with this trend.123 Snow accumulation is an important driver of ecological patterns, such as 19 20 269 plant, lichen, and moss species distributions124, plant phenology, peak plant greenness125, and 21 22 23 270 maximum plant greenness.126 As such, changing snow accumulation patterns are an important 24 25 271 impact on lake catchment processes. Accumulated snow converts to meltwater during spring 26 27 127 28 272 thaw , contributing nutrients, minerals, and particulates into lake ecosystems which may 29 30 273 increase the relative abundance of littoral epilithic algae128 or phytoplankton communities of 31 32 129 33 274 Arctic lakes. 34 35 275 Shortened lake iced-over periods and earlier spring ice-out is a general trend across the 36 37 130 38 276 Pan-Arctic in response to climate warming , and ice-out phenology has important implications 39 40 277 for Arctic lake stratification (whereby the top epilmnion and bottom hypolimnion physically 41 42 278 separate due to temperature-based water density gradients). Increased intensity and stability 43 44 45 279 of lake thermal stratification is an anticipated response to climate warming87,131,132, though this 46 47 280 may be modulated by changing ice-out phenology.133 Increased stratification is important for 48 49 50 281 within-lake benthic-to-pelagic subsidies, because hypolimnetic oxygen can become depleted 51 52 282 (anoxic) when lake thermal stratification inhibits the diffusion of oxygen from the epilimnion.134 53 54 55 283 Hypolimnetic anoxia increases the chemical reduction potential and favors the release of P 56 57 58 59 13 60 Page 15 of 83 Environmental Science: Processes & Impacts

1 2 3 284 from lake sediments that is otherwise associated with Fe and aluminum (Al) during oxygenated 4 5 135-136 6 285 conditions. In low elevation temperate lakes, sediment P release is related to algae 7 8 286 blooms.137-139 Benthic to pelagic P subsidies may be an important Arctic lake response to 9 10 11 287 climate warming, but there has been little research of anoxic sediment P release conducted in 12 13 288 Arctic lakes. Determining the mechanisms that control Arctic lake sediment P release should 14 15 16 289 therefore be a research priority, so that we may better predict Arctic lake responses to 17 18 290 increased climate warming and seasonal variability. 19 20 291 Reduced river ice jamming in the McKenzie River Delta is a cryosphere change driven by 21 22 23 292 Arctic warming trends that decreases the duration of hydrological connectivity between rivers 24 25 293 and lakes at higher elevations within the Delta (5.2 m above sea level).140 In contrast, the 26 27 28 294 duration of river-to-lake connection during peak water levels has increased in lower elevation 29 30 295 areas (2.4 m above sea level) within the Delta, due to sea level rise. It is likely that these trends 31 32 33 296 will have ecological effects because McKenzie River Delta lakes with frequent river-to-lake 34 35 297 connectivity were associated with enhanced colored DOM, P concentrations, and light 36 37 38 298 attenuation rates but lower ammonium and non-colored DOM concentrations averaged over 39 40 299 the open-water season.141 Patterns of lake nutrient and light availability were likely responsible 41 42 300 for higher abundance and production rates of bacterioplankton within less-frequently flooded 43 44 45 301 lakes. These studies demonstrate that even small environmental gradients (i.e. a change from 46 47 302 2.4 to 5.2 m elevation) can alter the directional trends in lake subsidies and the environmental 48 49 50 303 factors that influence them. 51 52 304 Many factors determine the nature, direction, and magnitude of ecological impacts in 53 54 55 305 aquatic systems from cryosphere-derived subsidies. For instance, glacier meltwater effects will 56 57 58 59 14 60 Environmental Science: Processes & Impacts Page 16 of 83

1 2 3 306 depend on magnitude of meltwater delivery, glacier bedrock material, and quality of nutrients. 4 5 6 307 Permafrost effects will depend on soil quality, depth and biogeochemical activity of the active 7 8 308 layer, water flow paths, and slumping events. Lastly, recent snow pack trends are highly 9 10 11 309 variable throughout the Arctic, which will affect photosynthetically active radiation (PAR) and 12 13 310 spring snowmelt nutrient additions. Parsing out this variability will be critical to understand why 14 15 16 311 certain trends are occurring in some areas of the Arctic but not others, or why opposite 17 18 312 responses follow seemingly identical disturbance events in different areas (e.g. DOC 19 20 313 concentrations following permafrost degradation, or nutrient concentrations following 21 22 23 314 slumping events). 24 25 26 315 Atmospheric deposition 27 28 29 316 N deposition is considered to be more important to lakes in mid-latitude areas that have 30 31 32 317 experienced higher anthropogenic development, compared to high-latitude Arctic areas which 33 34 318 are more remote and typically have lower rates of N deposition (Figure 3a; refs. 66, 142). For 35 36 66 37 319 example, Hobbs et al suggested that changes observed in diatom beta diversity over the 20th 38 39 320 century in the Greenland Arctic are driven by rapid climate warming, versus that observed in 40 41 321 western US alpine lakes, driven by high rates of atmospheric reactive N (N ) deposition. 42 r 43 44 322 However, Holmgren et al143 observed that recent changes in preserved Arctic lake sediment 45 46 323 diatom assemblages on Svalbard are coincident with enhanced sediment N derived from 47 48 49 324 anthropogenic sources, suggesting a causal link between lake ecological change and N 50 51 325 deposition. Diatom sediment records demonstrated that anthropogenic N deposition in the 52 53 54 326 Canadian Arctic, along with climate warming, had driven lake conditions and diatom 55 56 327 communities to no-analogue states in two nearby lakes.144 Community changes include 57 58 59 15 60 Page 17 of 83 Environmental Science: Processes & Impacts

1 2 3 328 increased abundances of Aulacoseira distans, Brachysira vitrea, Fragilaria spp., Cyclotella rossii, 4 5 143 6 329 and Discostella stelligera, which indicated nutrient enrichment. Similarly, Holmgren et al 7 8 330 demonstrated that four Svalbard lakes exhibited diatom community changes over the past 30 9 10 11 331 years coherent with increased rates of N deposition. A study conducted in sub-Arctic Sweden 12 13 332 demonstrated that lakes shifted from N to P limitation as a result of N deposition.145 As the 14 15 16 333 study lakes were remote, high latitude, dilute and unproductive, they serve as good analogues 17 18 334 for Arctic systems. Climate warming cannot be ruled out as a synergistic driver of these 19 20 335 ecological changes because of the coherence of warming, N deposition, and diatom 21 22 23 336 responses.144,146 Taken together, however, these studies suggest a causal link between sensitive 24 25 337 Arctic lake ecosystem change and high latitude N deposition. 26 27 28 338 Though Greenland is remote, it is downwind of North American industrial emission 29 30 339 sources and is thus vulnerable to modifications of the Northern Hemisphere atmosphere.147 31 32 - 147-149 33 340 Several ice cores demonstrated recent increases in NO3 concentrations in Greenland, 34 35 341 Svalbard150,151 and the Canadian Arctic.152,153 Averaged across sites, these records showed a 36 37 - -2 -1 154 38 342 30% increase of NO3 flux since preindustrial times (from 2.5 to 3.2 μg cm yr ), with more 39 40 343 than a doubling in some locations such as Greenland.147 N isotope analysis (δ15N) indicated that 41 42 344 NO - in Greenland ice is derived from increasing anthropogenic N emissions since 1850.155 43 3 44 45 345 Matching these cryosphere records, the presence of anthropogenic N deposition has coherently 46 47 346 increased in lake sediment cores across high latitudes of the Northern Hemisphere since the 48 49 156 50 347 beginning of the 20th century. An outstanding question, however, is whether N deposition 51 52 348 rates in the Arctic are high enough to be ecologically important. 53 54 55 56 57 58 59 16 60 Environmental Science: Processes & Impacts Page 18 of 83

1 2 3 349 N deposition in the Arctic is typically low (0.2 - 0.5 kg NO - ha-1 yr-1)144 but Arctic 4 3 5 6 350 freshwaters are sensitive to small inputs of nutrients. Though rates of N deposition have not 7 8 351 been as high in Arctic areas compared to mid-latitude ones, there is a clearly increasing trend 9 10 41 11 352 that could be ecologically important. Anderson et al used lake sediment cores to demonstrate 12 13 353 that coastal Greenland lakes have received increased amounts of anthropogenically sourced Nr 14 15 -1 -1 16 354 since 1860, despite relatively low deposition rates in this area (0.4 kg ha yr ). This trend was 17 18 355 not recorded in inland lakes possibly because lower deposition rates (0.2 kg ha-1 yr-1), and 19 20 356 higher in-lake TN pools and microbial cycling rates could further confound the signal of external 21 22 23 357 anthropogenic inputs. Arens et al157 demonstrated by nutrient addition experiments that small 24 25 358 amounts of N deposition (0.5 g m-1 yr-1) have nonlinear impacts on terrestrial Arctic ecosystem 26 27 28 359 structure and function, increasing vegetation cover, photosynthesis, and CO2 exchange. 29 30 360 Similarly, Gordon et al158 observed that their lowest N addition treatment (10 kg ha-1 yr-1) 31 32 33 361 increased physiologically active bryophyte shoots in Arctic heath, indicating the minimum 34 35 362 ecologically important rate of atmospheric N deposition is likely below this value. These results 36 37 38 363 suggest even small increases in rates of atmospheric deposition will be ecologically important. 39 40 364 The vulnerability of Arctic lakes to environmental change is due to spatially variable acid 41 42 365 neutralizing capacity (ANC),144,159,160 sparse catchment vegetation, short growing seasons, 43 44 45 366 shallow active soil layers,161 and low in-lake nutrient concentrations and productivity. Evidence 46 47 367 for Arctic freshwater sensitivity comes from ecological and paleoecological studies. For 48 49 162 50 368 instance, Benstead et al enriched a small Arctic stream on Alaska’s north slope with NH4-N 51 52 369 and soluble reactive P (SRP) to 6.4 μM and 0.45 μM, respectively. This addition increased algal 53 54 55 370 biomass (measured as Chlorophyll a; Chl a), fungal biomass, rates of litter breakdown, and 56 57 58 59 17 60 Page 19 of 83 Environmental Science: Processes & Impacts

1 2 3 371 macroinvertebrate abundance and biomass.162 In a long-term, whole-lake manipulation 4 5 -2 -1 6 372 experiment in Arctic northern Alaska, half of Lake N-2 was subsidized with 131 mmol N m yr 7 8 373 and 10.4 mmol P m-2 yr-1, approximately five times the normal loading rates of nearby Toolik 9 10 163 11 374 Lake, while the other half was partitioned off as a control. Ecological responses included 12 13 375 increased phytoplankton biomass and productivity, lower water clarity, and eventual 14 15 16 376 hypolimnetic anoxia coupled with sediment P release. 17 18 377 Wind can distribute fine particulate matter, including pollen, bacteria, diatoms, and 19 20 378 dust, long distances to Arctic and alpine areas.39,164-168 Dust production, emission, and 21 22 23 379 deposition rates can be high in glacierized Arctic landscapes, such as Canada, Alaska, 24 25 380 Greenland, and Iceland (see Bullard et al169), comparable to rates of lower latitude regions such 26 27 170 171 28 381 as New South Wales, Australia or Nevada and California, USA. Glacier dust production 29 30 382 occurs when glacial flour (fine mineral particulates resulting from subglacial bedrock erosion) is 31 32 33 383 transported to floodplains by subglacial meltwater. Winds then deflate the glacier flour, and 34 35 384 can transport it across tundra, lakes, rivers, and ocean. Key controls of dust production include 36 37 38 385 subglacial substrate erodibility, drainage system size and structure, ice mass size, and 39 40 386 meltwater runoff rates.169 The amount of high-latitude dust contributions to the earth’s dust 41 42 387 budget is currently estimated to be ~5% and is expected to increase with climate warming.172 43 44 45 388 The magnitude of dust events in southwestern Greenland, for example, has increased since the 46 47 389 1990s (calculated using the Dust Storm Index).173 Most of the dust produced in high latitude 48 49 50 390 areas remains in these regions. In western Greenland for example, dust transport from the Ice 51 52 391 Sheet margin was mostly confined to the local landscape, with a small percentage reaching the 53 54 173 55 392 North Atlantic Ocean, and very little being transported back onto the ice sheet itself. This was 56 57 58 59 18 60 Environmental Science: Processes & Impacts Page 20 of 83

1 2 3 393 due to the consistent direction of the katabatic winds blowing west from the ice sheet,174 as 4 5 6 394 well as a lack of thermal uplift in the Arctic that is required for long-distance transport of dust- 7 8 395 containing stable air parcels.175,176 Conversely, dust plumes derived from glaciofluvial deposits 9 10 11 396 along the Gulf of Alaska (GoA) coastal region can be deposited into the ocean several hundred 12 13 397 kilometers beyond the continental shelf, serving as an Fe subsidy for Fe-limited marine 14 15 177 16 398 systems. It is unknown to what extent glaciofluvial-derived dust is deposited into lake 17 18 399 ecosystems in this region, but glacially-sourced dust accumulates in nearby terrestrial 19 20 400 systems.178 A sediment core from an interior western Alaska lake isolated from glacial processes 21 22 23 401 suggested dust deposition is related to aridity, lack of catchment vegetation, and windiness as 24 25 402 opposed to glacial processes.179 26 27 173 28 403 The ecological effects of dust deposition on Arctic lakes are not well understood. 29 30 404 Because dust production and deflation in Greenland occurs throughout the entire year 31 32 173 33 405 including the winter months, accumulated dust on and within lake ice and snow can cause a 34 35 406 pulse disturbance to lake ecosystems during snowmelt and ice off periods in spring, in contrast 36 37 38 407 to a more consistent press disturbance of dust addition to lakes throughout the summer 39 40 408 months.180 Glacier flour in southwest Greenland is P and Fe-rich,79,82 properties which carry 41 42 409 over into deflated dust from this area,181 and coastal Alaska.177,178 Fowler et al181 proposed 43 44 45 410 DOM adsorption to Fe-rich dust as a mechanism for recent decadal DOC concentration declines 46 47 411 observed in a number of Greenland lakes, though microcosm incubation experiments did not 48 49 50 412 support this hypothesis. To the extent that the P content of glacially derived dust is 51 52 413 bioavailable,80 dust addition to lakes could stimulate lake bacterial production and 53 54 182,183 55 414 metabolism, or in-lake sediment P cycling. 56 57 58 59 19 60 Page 21 of 83 Environmental Science: Processes & Impacts

1 2 3 415 More evidence is needed to assess the ecological effects of atmospheric N and P 4 5 6 416 deposition in Arctic lakes. This mode of ecosystem subsidization has not been paid due 7 8 417 attention in the Arctic, likely because of the relatively low absolute values of N deposition rates 9 10 11 418 compared to low elevation temperate regions. However, studies which attribute recent 12 13 419 changes of algal communities in Arctic lake sediment records to climate warming alone184 may 14 15 16 420 be missing the important contributions of anthropogenically sourced atmospheric deposition. 17 18 421 High latitude dust production was only recently assessed as a significant contributor to the 19 20 422 global dust budget (see Bullard et al169), positioning Arctic dust deposition as an intriguing topic 21 22 23 423 of research for terrestrial and aquatic ecologists and biogeochemists. Further, climate warming 24 25 - 424 will likely influence Nr and dust deposition alike. Greenland ice core NO3 , a proxy for 26 27 28 425 atmospheric Nr deposition, was correlated with the North Atlantic Oscillation, suggesting 29 30 154 426 greater deposition of anthropogenic Nr occurs when the NAO is in its positive phase. A 31 32 33 427 climate change impact model on atmospheric N deposition suggested that increased 34 35 428 precipitation will enhance N deposition rates in northern Europe.185 Though changes in N 36 37 38 429 deposition will be gradual in most areas, certain areas, including western Norway, may 39 40 430 experience a 40% increase in N deposition by 2100 due to projected increases in precipitation. 41 42 431 Warming could also release previously deposited and accumulated N from perennial snow 43 r 44 45 432 packs and glaciers in the form of meltwater. Lastly, warming will likely increase dust production 46 47 433 in high latitude areas because increased meltwater will deposit greater amounts of glacier flour 48 49 169 50 434 into floodplain areas. 51 52 53 54 55 56 57 58 59 20 60 Environmental Science: Processes & Impacts Page 22 of 83

1 2 3 4 435 Animal vectors 5 6 7 436 Animals are important vectors for nutrient transfer between ecosystem types, and this 8 9 10 437 mode of transfer between aquatic and terrestrial systems has received increased attention over 11 12 438 the past decade. Unlike other transfers that have been discussed thus far, animals represent a 13 14 439 bi-directional flow of energy and nutrients, whereby inputs of terrestrial C and nutrients to 15 16 17 440 lakes are cycled back to terrestrial environments by boundary-crossing organisms.24 The C that 18 19 441 is delivered to terrestrial systems from emerging mosquitos, for instance, is a mix of terrestrial 20 21 22 442 and aquatic material, and the terrestrial:aquatic C ratio depends on the magnitude of terrestrial 23 24 443 inputs into the aquatic ecosystem, as well as light intensity.186 Vander Zanden and Gratton187 25 26 27 444 highlighted that insect emergence and subsidies to terrestrial systems increased as a function 28 29 445 of lake size, while rates of terrestrial inputs of particulate organic C to lakes decreased as a 30 31 32 446 function of their size. Thus, reciprocal transfers between lakes and terrestrial habitats are 33 34 447 modified by environmental variables. A detailed understanding of variables that influence 35 36 448 reciprocal transfers between lakes and watersheds is an important research priority, because it 37 38 39 449 will allow for better assessment of how reciprocal subsidies will be affected by different 40 41 450 environmental changes. 42 43 44 451 In the Arctic, aquatic-terrestrial transfers often take place as abrupt seasonal pulses, and 45 46 452 can be limited by distance from the lake, with an exponential decrease of insect infall with 47 48 188,189 49 453 distance from lake. However, observed transfer distance was greater from lakes (150 m) 50 51 454 than from streams (50 m).190,191 For instance, midges (Diptera: Chironomidae) are an important 52 53 54 455 nutrient subsidy from lakes to terrestrial systems. In Iceland, annual midge inputs from lakes 55 56 456 were as high as 1200-2500 kg ha-1 yr-1, though these inputs decreased logarithmically from 57 58 59 21 60 Page 23 of 83 Environmental Science: Processes & Impacts

1 2 3 457 shore.188 Peak rates of midge infall occured in August and can reach rates over 1500 kg ha-1 d-1 4 5 -1 -1 192 6 458 at a distance of 5 m from shore (median rate 290 kg ha d ). Midge N content is 9.2%, and so 7 8 459 this seasonal transfer was nutrient-rich, as high as 230 kg N ha-1 yr-1.188 δ13C and δ15N isotope 9 10 11 460 analysis demonstrated this subsidy is important for terrestrial arthropods (e.g. spiders), which 12 13 461 consume midges directly or indirectly as a food source. Aquatic insects are a high-quality food 14 15 193 16 462 source, in part because of their polyunsaturated fatty acid content. Martin-Creuzburg et al 17 18 463 demonstrated that the terrestrial subsidies of polyunsaturated fatty acids from aquatic insect 19 20 464 emergence was significant (mean rate was 150 mg m-2 yr-1 within 100 m of shore). Thus, in 21 22 23 465 areas with high midge emergence rates, midges maintain higher abundances of terrestrial 24 25 466 arthropods compared to areas with low midge emergence rates. In Iceland and northern 26 27 28 467 Sweden, subsidized terrestrial arthropods include detritivore and herbivore species as well as 29 30 468 predators.62,194-196 An Icelandic study demonstrated that willow (Salix phylicifolia) located at 31 32 33 469 high-midge emergence lakes contained 8-11% higher N content than those located at low- 34 35 470 midge emergence lakes, and herbivorous caterpillars (Hydriomena furcata) were 72% heavier at 36 37 63 38 471 the high-midge emergence sites. 39 40 472 Arctic Chironomid midge emergence is synchronous, with the bulk of the community 41 42 473 emerging from a single pond within 4 weeks, and a single species emerging within one week.197 43 44 45 474 In response to climate warming, Alaskan midge emergence has advanced by one week since the 46 47 475 1970s.198 As midge adults only live for a few days, such shifts in aquatic insect phenology may 48 49 50 476 have repercussions for Arctic predators, such as avian consumers. For example, in UK lakes in 51 52 477 the South Pennines, climate warming shifted the dates of egg laying by an Arctic wader species 53 54 55 478 (golden plover, Pluvialis apricaria) and tipulid (cranefly) emergence earlier, but at different 56 57 58 59 22 60 Environmental Science: Processes & Impacts Page 24 of 83

1 2 3 479 rates.199 Thus, climate predictions for 2070-2090 suggest that first-laying dates for golden 4 5 6 480 plover will advance 25 days, but tipulid emergence only 12 days. As emerging tipulids are an 7 8 481 important prey resource for golden plover chicks, this phenological mismatch may reduce 9 10 11 482 breeding success of this species at this location by 11%. Because Arctic lake midge emergence is 12 13 483 synchronous, short in duration, and is an important resource for Arctic terrestrial and avian 14 15 16 484 predators, phenology of Arctic lake midges and their predators require more investigation in 17 18 485 order to determine if temporal mismatches will occur, and what ecological impact they will 19 20 486 have. 21 22 23 487 With climate warming and other anthropogenic environmental changes, waterfowl 24 25 488 habitat range and population sizes are increasing. Global goose population, for example, nearly 26 27 200 201 28 489 doubled from 1996 (12.5 million) to 2006 (21.4 million). Dense nesting colonies of 29 30 490 waterfowl have the potential to transfer significant amounts of terrestrially derived nutrients (N 31 32 202,203 33 491 and P) into Arctic lake ecosystems in the form of feces. In Svalbard, goose guano has 34 35 492 caused lake and pond eutrophication, increasing P concentrations four-fold since the 1960s.204 36 37 38 493 A small-scale incubation experiment demonstrated that algal biomass increases from goose 39 40 494 guano-derived nutrients.205 Sediment cores from Canadian Arctic ponds demonstrated strong 41 42 495 relationships between algal biomass and chironomid heads in response to N derived from 43 44 45 496 seabird guano.206,207 Paleolimnological records demonstrated an increasing colony population 46 47 497 enriches lake sediment δ15N, indicating a marine to lake linkage. Thus, coastal Arctic lake 48 49 50 498 ecosystems may experience subsidies from different sources compared to inland lakes. 51 52 499 Particular areas of the Arctic, such as Iceland, have received attention regarding lake-to- 53 54 55 500 land transfers of nutrients in the form of emerging aquatic insects, but there is a lack of 56 57 58 59 23 60 Page 25 of 83 Environmental Science: Processes & Impacts

1 2 3 501 research in other Arctic areas where lake-to-land nutrient transfers would be seemingly 4 5 6 502 important. For instance, some Greenland lakes experience high densities of emerging 7 8 503 chironomid adults during peak summer, which have not been characterized in terms of nutrient 9 10 11 504 quality and quantity. Further, with high rates of climate warming in western Greenland, 12 13 505 outbreaks of moth larvae (Eurois occulta and Gynaephora groenlandica) have become more 14 15 208 16 506 common. These larvae commonly fall into lakes and streams (personal observation). Though 17 18 507 larval outbreaks in western Greenland have been linked to terrestrial defoliation209 and changes 19 20 508 in C-burial rates,208 the effect on aquatic ecosystems is unknown. 21 22 23 24 25 509 Alpine lake subsidies 26 27 28 29 510 Cryosphere 30 31 32 511 Alpine areas in North America have numerous glaciers and rock glaciers. 1500 glacier 33 34 210 35 512 and 10000 rock glacier features have been identified in the western US alone. Because of 36 37 513 their abundance and location within the continental US and Europe, studies published to date 38 39 40 514 that investigate the effects of nutrient-rich glacial meltwater on lake ecological structure and 41 42 515 function have largely focused on alpine rather than Arctic lakes (e.g., refs. 2, 60, 210, 211). 43 44 45 516 Climate warming has increased glacier melt to mountain surface waters in the Pacific 46 47 517 Northwest region of the US over the past 70 years.212 Enhanced glacial melting has also 48 49 518 increased glacial lake abundance and area across the Central and Patagonian Andes.213 Glacier 50 51 52 519 recession is widespread and accelerating throughout the Tibetan Plateau214,215, and is cited as 53 54 520 one of the factors leading to increased lake levels across the region.216-218 In addition to 55 56 57 58 59 24 60 Environmental Science: Processes & Impacts Page 26 of 83

1 2 3 521 warming trends, climate-mediated dust deposition can alter glacier snow and ice albedo 4 5 6 522 leading to greater glaciofluvial transport of glacier meltwater to high elevation lakes in 7 8 523 southwestern Tibet.219 Glacier meltwater subsidizes systems with essential elements such as 9 10 11 524 Ca, K, Mg, nutrients such as Si, Fe, N and DOM, and organisms such as microbes, though the 12 13 525 characteristics of these subsidies differ among mountain ranges and between glacier types 14 15 161,219 16 526 (rock glaciers vs glaciers). In contrast to Arctic glacier meltwater, which typically has high P 17 - 18 527 but low to medium N content, alpine glacier meltwater can have elevated NO3 , with subsidized 19 20 528 lakes containing concentrations as high as 236 µg NO -1-N L-1.60 Thus, NO --N enriched glacially- 21 3 3 22 23 529 fed lakes in the Beartooth Mountains of Wyoming and Montana exhibit lower diatom species 24 25 530 richness60 and higher phytoplankton primary productivity rates and biomass compared to 26 27 2 28 531 nearby snow and groundwater-fed lakes. Although glacially-fed lakes in both Arctic and alpine 29 30 532 areas are often turbid with suspended glacial flour, the target glacially-fed lakes from the 31 32 33 533 Beartooth Mountains in these studies were clear due to either minimal subglacial weathering 34 35 534 or upstream entrapment.60 These studies are useful because the clarity of the glacially-fed lakes 36 37 38 535 makes them similar to snow and groundwater-fed lakes. Thus, the ecological effects of these 39 40 536 particular glacially-sourced N subsidies could provide insights into remote cold, oligotrophic 41 42 537 lakes receiving other types of N subsidies (such as atmospheric deposition, or increased goose 43 44 45 538 guano). 46 47 539 As in Arctic lakes80, glacial transport of suspended mineral particulates that constitute 48 49 50 540 milky-colored glacial flour can alter the transparency and light penetration of alpine lakes, 51 52 541 giving them a characteristic grey to turquoise hue.220 Turbidity can reach high levels in alpine 53 54 221 220 55 542 lakes (644 NTU recorded in the Swiss Alps; unit conversion by Sommaruga and Kandolf ). 56 57 58 59 25 60 Page 27 of 83 Environmental Science: Processes & Impacts

1 2 3 543 Sediment transport is increased during glacial recession as a function of meltwater flux and is 4 5 222,223 224 6 544 therefore affected by climate warming. Because of their small size (<32 μm) and sharp 7 8 545 edges, glacial flour particulates can have direct negative impacts on interception- or filter- 9 10 11 546 feeding aquatic organisms (such as Daphnia, and heterotrophic nanoflagellates), that may 12 13 547 ingest them.220,225 Other physical consequences of suspended glacial flour in alpine lakes 14 15 226 16 548 includes density underflows (also a function of cold meltwater temperature), a reduced 17 18 549 euphotic zone and high UV light attenuation, both of which have consequences for ecosystem 19 20 550 primary production rates,227 phytoplankton and zooplankton stoichiometry,228,229 and plankton 21 22 23 551 survival.227 Further, surface temperature of glacially-fed alpine lakes can be surprisingly warm 24 25 552 (late August mean surface temperature from 3 glacially fed lakes was 16.0 °C, calculated from 26 27 230 28 553 Peter and Sommaruga ), similar to that of a nearby snow and groundwater-fed, clear lake 29 30 554 (15.3 °C).230 Though mean lake water temperatures can be cooler in glacially-fed lakes 31 32 33 555 compared to snow and groundwater-fed ones (a 1.1 °C difference was demonstrated in Alaska, 34 35 556 for example; Koenings et al225), the warming of the surface by attenuated solar radiation leads 36 37 38 557 to discontinuous polymictic thermal stratification, a situation where thermal stratification of 39 40 558 these lakes can undergo fast and abrupt mixing throughout the summer, caused by cold night- 41 42 559 time temperatures or precipitation events.230 43 44 45 560 While Arctic glacier meltwater contains P that is associated with weathered minerogenic 46 47 80 - 561 subglacial flour the source of NO3 that is concentrated in alpine glacier meltwater is 48 49 211 - 50 562 unclear. Determining the extent to which meltwater NO3 is derived from anthropogenic 51 52 563 sources, minerogenic material, or subglacial microbial processing of organic material may 53 54 55 564 inform conservation or management decisions. Further, alpine glaciers are projected to 56 57 58 59 26 60 Environmental Science: Processes & Impacts Page 28 of 83

1 2 3 565 disappear in the American Rocky Mountains by 2030,231 and certain areas of the European Alps 4 5 232 6 566 by 2050. It is currently an outstanding question what the ecological effects of glacier 7 8 567 disappearance will be on glacially-fed lakes, and whether legacy effects of previously glaciated 9 10 11 568 catchments will persist following deglaciation. For instance, given the abundance of glaciers in 12 13 569 the western United States,210 it will be important to determine how C and nutrient cycling may 14 15 16 570 change as a lake goes from turbid and glacially-fed to clear and fed by groundwater sources. 17 18 19 571 Atmospheric deposition 20 21 22 572 Like Arctic lakes, alpine lakes are ecologically sensitive to atmospheric deposition due to 23 24 573 their slow weathering bedrock and spatially variable ANC, absent or poorly developed 25 26 27 574 catchment soils, sparse catchment vegetation cover, and low nutrient water chemistry.44,233-234 28 29 575 In contrast to Arctic lakes, high elevation exposes alpine lakes to greater rates of atmospheric 30 31 235 32 576 deposition. In mountain regions of the US, enhanced N deposition results from fossil fuel and 33 34 577 agricultural emissions.142,236,237 35 36 37 578 Atmospheric N deposition can change the nutrient limitation status of lake ecosystems. 38 39 579 Many North American alpine lakes were historically N-limited.60,238-240 However, in both North 40 41 580 America and Europe, atmospheric N deposition has shifted lake nutrient limitation patterns 42 43 44 581 from N-limitation to N and P co-limitation or P-limitation.241,242 Ecological responses to N 45 46 582 deposition can be rapid, because primary producers with high reproductive rates, such as 47 48 49 583 phytoplankton, are sensitive to nutrient changes.46,243 Such responses include increased 50 51 584 primary productivity,5,244,245 increased phytoplankton biomass5,246 decreased lake clarity,244,245 52 53 54 585 and directional algal community changes caused by increased dominance by opportunistic 55 56 57 58 59 27 60 Page 29 of 83 Environmental Science: Processes & Impacts

1 2 3 586 diatom species such as Fragilaria crotonensis, Asterionella formosa, and Discostella 4 5 7,8,211,244,245,247,248 60,249-251 6 587 stelligera, that respond rapidly to nutrient enrichment. 7 8 588 In addition to N deposition, alpine lakes are ecologically sensitive to P deposition. In 9 10 11 589 mountain areas, N deposition is associated with both wet deposition (DIN associated with 12 13 590 precipitation or fog droplets252,253) and dry deposition (consisting of nitric acid and particulate 14 15 254 16 591 ammonium and nitrate ). P deposition is associated with dry deposition (associated with 17 18 592 particulate matter, or dust).255 Dust is sourced from anthropogenic activities and biomass 19 20 593 burning,256 and dust deposition can be related to climate. For instance, dust storms and strong 21 22 23 594 winds have increased in frequency in the Tibetan plateau over the past 44 years, observable via 24 25 595 grain-size analysis in a high-elevation lake sediment record (Lake Sugan, 3,000 m above sea 26 27 34 28 596 level). A longer lake sediment record spanning 1,600 years from Kusai Lake in the central 29 30 597 Tibetan Plateau suggests that dust deposition is positively related to summer temperature.257 31 32 33 598 The link between dust and climate was also demonstrated in the southwest Tibetan Plateau by 34 35 599 Conroy et al219 by comparing western Tibet temperature258 and Dasuopu Ice Core259 dust 36 37 38 600 deposition records over the past 1000 years. Dust deposition has increased 400% in some areas 39 40 601 of the western US over the past twenty years, with mountainous areas being particularly 41 42 602 impacted.260 Brahney et al261 compared paleoecological records from two Wind River Range 43 44 45 603 lakes in Wyoming, North and Lonesome, which were compared as dust-affected and control 46 47 604 sites, respectively. The authors demonstrated a tripling in sediment P content, a tenfold 48 49 50 605 increase in diatom production, increasing cyanobacteria, and diatom community changes in 51 52 606 North Lake. These changes correspond to increasing dust flux starting around 1940. Brahney et 53 54 262 55 607 al demonstrated that lakes of the Wind River Range were subsidized by dust deposition rates 56 57 58 59 28 60 Environmental Science: Processes & Impacts Page 30 of 83

1 2 3 608 as high as 276 μg P m2 day-1. The source of this dust was from a local valley, and lakes closer to 4 5 6 609 the source were more affected by P subsidies. Lake ecological effects included enhanced water 7 8 610 and sediment P concentrations, greater phytoplankton and zooplankton biomass, and 9 10 11 611 dominance of diatom communities by high-nutrient species, such as Asterionella formosa. 12 13 612 Dust may also originate from distant sources. In the Mediterranean region of Europe, 14 15 16 613 for example, dust deposition was dominated by material from the Sahara-Sahel desert region in 17 18 614 northern Africa, with maximum inputs occurring during spring and summer.263 SRP contained in 19 20 615 this dust and deposited in the SW Mediterranean stimulated bacterial abundance and 21 22 23 616 decreased phytoplankton species diversity in an alpine lake in the Spanish Sierra Nevada 24 25 617 Mountains.264 Reche et al265 observed positive effects of dust inputs on bacterial abundance in 26 27 28 618 two alpine lakes of the Sierra Nevada, Spain, though no effect on bacterial community 29 30 619 composition was observed. In addition to P, Saharan dust can deliver chromophoric, aromatic, 31 32 266 33 620 and fluorescent DOM to European alpine lakes. Saharan dust input could therefore be 34 35 621 partially responsible for the relatively higher concentrations of DOC and CDOM in lakes of Sierra 36 37 267 38 622 Nevada versus those of the Pyrenees and Alps that do not receive this input. Saharan dust 39 40 623 also transfered viable bacteria (Gammaproteobacteria) that were deposited and grew in alpine 41 42 624 lake water in the Austrian Alps.268 Similarly, Reche et al265 observed growth of 43 44 45 625 Gammaproteobacteria in dust-inoculated water of the oligotrophic Quéntar Reservoir in Spain. 46 47 626 Together, these studies suggest that atmospheric dust deposition can indirectly affect lake 48 49 50 627 microbial community assemblages by influencing environmental selection pressures (such as P 51 52 628 availability or DOM quality) or microbial assemblages can be directly affected by the 53 54 55 629 introduction of exogenous species. 56 57 58 59 29 60 Page 31 of 83 Environmental Science: Processes & Impacts

1 2 3 630 Determining what factors determine lake ecological sensitivity will be a critical research 4 5 6 631 priority that will be able to inform lake management schemes. For instance, critical loads of N 7 8 632 deposition (thresholds below which effects of deposition cannot be detected)269 are typically 9 10 -1 -1 11 633 low (1.0-1.5 kg N ha yr ) for high elevation lake systems in the Sierras and Rocky Mountains of 12 13 634 western United States.45,46 However, nutrient deposition rates alone are not a good predictor of 14 15 16 635 lake ecological sensitivity and response to enrichment. For instance, elevation (positive 17 18 636 association), talus cover (positive association), unvegetated catchment area (positive 19 20 637 association), alluvium (negative association), and riparian areas (negative association) were 21 22 23 638 important factors in determining surface water susceptibility (measured from stream and lake 24 25 639 outlets) to nutrient enrichment following atmospheric N deposition in Yosemite National Park, 26 27 44 28 640 USA. There are other factors, such as lake depth, clarity, and nutrient limitation that may be 29 30 641 important in determining lake sensitivity. Analyses that include these factors across multiple 31 32 33 642 spatial scales will be important in explaining the local and regional variation that we observe in 34 35 643 lake responses to atmospheric deposition. 36 37 38 644 Animal vectors 39 40 41 645 Like Arctic lakes, high-elevation lakes are connected to their terrestrial environments via 42 43 44 646 reciprocal flows of material. While inputs to alpine lake ecosystems are often passive 45 46 647 hydrological or atmospheric processes determined by slope gradient and gravity, lake-to- 47 48 49 648 terrestrial solid and liquid subsidies rely on animal vectors. For alpine lake ecosystems, the 50 51 649 relative importance of aquatic- or terrestrial-derived subsidies to its neighboring environment 52 53 54 650 can depend on lake elevation. For instance, based on research in the Sierra Nevada and 55 56 651 Klamath mountain ranges of the western United States, Piovia-Scott et al6 hypothesized that 57 58 59 30 60 Environmental Science: Processes & Impacts Page 32 of 83

1 2 3 652 terrestrial C inputs were important controls for in-lake processes at lower elevations, and in 4 5 6 653 contrast, in-lake processes were relatively more important for terrestrial consumers at higher 7 8 654 elevation. Though lower-elevation lakes had higher absolute rates of lake-to-land C transfer 9 10 11 655 than high-elevation lakes in the form of emergent insects and amphibians, the difference 12 13 656 between lake C output vs. lake C input was smaller in low elevation lakes. This is due to the fact 14 15 16 657 that high elevation catchments deliver significantly less terrestrial C to lake ecosystems. 17 18 658 Further, because relatively little C was terrestrially derived in high elevation lakes, their 19 20 659 ecosystems were dependent on inorganic C fixation, making them net C sinks. Lower elevation 21 22 23 660 lake ecosystems, with greater amounts of terrestrial organic C, were instead CO2 sources. 24 25 661 Although on average lake-to-land animal C transfer decreased with lake elevation across the 26 27 28 662 Klamath mountain landscape, the density of terrestrial insect infall was higher in high-elevation 29 30 663 lakes close to shore compared to lower elevation lakes, creating a hotspot of C and nutrient 31 32 6 33 664 deposition. 34 35 665 Many species of trout have been introduced into naturally fishless alpine lakes for sport 36 37 270-273 38 666 fishing. The presence of predatory fish can significantly reduce the quantity of lake-to-land 39 40 667 animal C and nutrient transfer due to predation on insect and amphibian larvae.6 For instance, 41 42 668 trout have reduced insect emergence in the Sierra Nevada (U.S.), such that fishless lakes can 43 44 45 669 have 20 times more emergent insect biomass.274 Introduced trout have reduced amphibian 46 47 670 abundance in mountain lakes by predation,275-277 as has the fungal pathogen Batrachochytrium 48 49 278 58 50 671 dendrobatidis. Greig et al demonstrated that predatory fish reduce not only insect 51 52 672 emergence directly by predation, but also reduce decomposition of terrestrial organic detritus 53 54 55 673 indirectly, where increased phytoplankton blooms influenced by pelagic trophic cascades 56 57 58 59 31 60 Page 33 of 83 Environmental Science: Processes & Impacts

1 2 3 674 increase sedimentation rates and establish anoxic benthic conditions. Thus, in addition to 4 5 6 675 reducing lake-to-land subsidies, predatory fish may also modulate land-to-lake C transfer by 7 8 676 reducing the amount of terrestrial C that is incorporated into aquatic consumer pathways. Such 9 10 11 677 food web interactions that decouple cross-system subsidies can have important effects on 12 13 678 reciprocal communities; in Sierra Nevada (U.S.) lakes, introduced trout outcompete Rosey- 14 15 16 679 finches (Leucosticte tephrocotis dawsoni) for mayfly larvae, so that Rosey-finches are 6 times 17 18 680 more abundant at fishless lakes.279 Introduced trout also outcompete and consume native frog 19 20 681 species (Rana muscosa) such that these frog species are 10 times more abundant in fishless 21 22 23 682 lakes of the Sierra Nevada (U.S.).274 24 25 683 Quality of a subsidy and its relative availability in the receiving environment is also an 26 27 21,23,280 28 684 important factor when considering lake-to-land nutrient subsidies. For instance, long- 29 30 685 chain polyunsaturated fatty acids (LC-PUFAs) are critical nutrients for organismal cell 31 32 281-283 33 686 membranes, structure, development, function, and signaling. LC-PUFAs occur 34 35 687 disproportionally in aquatic environments because they are synthesized by algae, but not by 36 37 281,284,285 38 688 terrestrial plants, and they bioaccumulate rapidly (twice the rate of bulk C) in higher 39 40 689 trophic levels because of their nutritional status.286 Thus, mobile or metamorphic organisms 41 42 690 such as frogs, salamanders, aquatic insects, and birds280,286-290 represent an important 43 44 45 691 terrestrial nutrient subsidy (LC-PUFA) that is disproportionate to the mass bulk of the 46 47 692 transferred material. 48 49 50 693 The ecological effects of climate warming on lake-to-land transfers in alpine areas 51 52 694 requires more attention. For instance, it is unknown what effects climate warming will have on 53 54 55 695 the timing, magnitude, species composition, and nutrient quality of lake-to-land transfers 56 57 58 59 32 60 Environmental Science: Processes & Impacts Page 34 of 83

1 2 3 696 across Northern hemisphere alpine areas. Further, the environmental factors that determine 4 5 6 6 697 average lake respiration vs primary production along an elevation gradient may become less 7 8 698 distinct, so that high elevation lakes may become net heterotrophic, and lake-to-land nutrient 9 10 11 699 contributions become relatively less important. 12 13 14 15 700 Conclusions and synthesis 16 17 18 19 701 The environmental forces acting upon Arctic and alpine lakes are similar: warming rates 20 21 702 in the Arctic are greater than the Northern Hemisphere average,291 and many alpine regions 22 23 292 24 703 exhibit accelerated warming as well. Atmospheric deposition is subsidizing both areas with N 25 26 704 and P,156,169,241,242,260 though deposition rates and sources of deposition differ between Arctic 27 28 29 705 and alpine areas. Despite high spatial variability, annual precipitation is on average declining in 30 31 706 Arctic areas,123 resulting in reduced annual snowpack and contributing to glacier shrinkage. 32 33 707 Though these environmental factors are changing Arctic and alpine lakes nutrient subsidies 34 35 36 708 (both in terms of material inputs and outputs), these changes are not entirely parallel (Figure 37 38 709 4). For instance, both Arctic and alpine landscapes contain an abundance of glacially-fed lakes, 39 40 41 710 but nutrient subsidies delivered into lake ecosystems via glacier meltwater vary regionally 42 43 711 depending on bedrock and atmospheric deposition patterns (e.g. refs. 60 and 80). 44 45 46 712 Ecosystem subsidies across Arctic and alpine landscapes will lead to changes in lake 47 48 713 ecosystem C and nutrient cycling depending on a suite of lake, landscape, and climatological 49 50 51 714 variables. For instance, DOC groundwater exports are variable in Arctic landscapes depending 52 53 715 on soil and groundwater flow path properties.106,107 Due to expected trajectories of 54 55 716 climatological and environmental changes, Arctic lakes may become greater sources of CO and 56 2 57 58 59 33 60 Page 35 of 83 Environmental Science: Processes & Impacts

1 2 3 717 CH as respiration and methanogenesis increase from enhanced nutrient and C availability and 4 4 5 6 718 stronger thermal stratification. Lower-latitude Arctic lakes generally have more vegetated 7 8 719 watersheds and developed soils than alpine lakes, thus DOC will likely be important in Arctic 9 10 11 720 lakes compared to alpine ones. DOC is an important factor in determining thermal stratification 12 13 721 of Arctic lakes to the extent that it contributes to PAR absorption.293 Thus, lakes experiencing 14 15 16 722 greater DOC subsidies from their surrounding catchments may exhibit enhanced thermal 17 18 723 stratification129 (Figure 3). In turn, stronger thermal stratification could contribute to 19 20 724 hypolimnetic anoxia resulting in greater in-lake P cycling as it is released from the sediments.294 21 22 23 725 Further, larger DOC contributions could increase lake respiration, anoxic hypolimnetic 24 25 726 methanogenesis, and denitrification rates.295-298 In contrast, alpine lakes can be expected to 26 27 28 727 increase rates of primary production and C fixation, because declining seasonal snowpack 29 30 728 coupled with steep alpine catchments with sparse vegetation means that little DOC is 31 32 6 33 729 transferred into alpine lake ecosystems. With relatively scarce organic C, increased nutrient 34 35 730 loading from glaciers, snowmelt, and atmospheric deposition will likely increase rates of 36 37 6 38 731 primary production in alpine lakes, establishing them as C sinks. 39 40 732 In the Arctic, increased waterfowl abundance enhances the transfer of terrestrial- and 41 42 733 marine-derived nutrients to lakes and ponds, 202,203,206,207 with the potential to cause 43 44 45 734 eutrophication of these remote ecosystems. Lake-to-land transfer of C and nutrients is 46 47 735 dominated by insect emergence in both alpine and Arctic lake ecosystems. Increased insect 48 49 50 736 emergence that tracks warming and nutrient availability could lead to altered nutrient cycling in 51 52 737 lake catchments. For instance, in lake catchments with high rates of emergent insect infall, 53 54 63 55 738 nutrient content of plants and size and abundance of herbivorous caterpillars increased. 56 57 58 59 34 60 Environmental Science: Processes & Impacts Page 36 of 83

1 2 3 739 Similarly, herbivorous, detritivorous, and predatory arthropod abundance increases.62 Climate 4 5 6 740 warming and increased nutrient loading to Arctic and alpine lakes can be expected to change 7 8 741 the timing, magnitude, and species composition of emergence.6,58 Phenological mismatches 9 10 11 742 may occur in both Arctic and alpine landscapes between emergent insects and their terrestrial 12 13 743 and avian predators but more Arctic- and alpine-specific research is needed to confirm and 14 15 16 744 characterize these mismatches, as remote lakes are presently underrepresented in this 17 18 745 relatively new research area. 19 20 746 Cross-ecosystem subsidies are mass (M) inputs, and as Leavitt et al30 describe, lake 21 22 23 747 ecosystem responses to M inputs are variable. This variability comes from differences in lake 24 25 748 catchments, ecological communities, physical structure, and water and sediment chemistry that 26 27 28 749 interact with M inputs. Additionally, differences in lake energy budgets between Arctic and 29 30 750 alpine areas will likely interact with subsidies in different ways. Many alpine lakes are located at 31 32 33 751 low latitudes with greater annual solar irradiance than those at high latitudes. For instance, 34 35 752 among 59 lakes surveyed across the Tibetan Plateau, latitude was positively related to ice cover 36 37 299 38 753 duration, reflecting lower temperatures and decreased irradiance toward the north. Thus, 39 40 754 researchers can expect variation in responses between Arctic and alpine lakes to similar drivers, 41 42 755 as well as variation of responses amongst lake groups in either region. From a lake 43 44 45 756 management and conservation standpoint, an important outstanding research priority involves 46 47 757 accounting for this variation by assessing what factors determine lake sensitivity and responses 48 49 50 758 to large-scale drivers, such as warming, permafrost thaw, or atmospheric deposition. 51 52 759 In closing, we have summarized cross-ecosystem subsidies to Arctic and alpine lake 53 54 55 760 ecosystems from three major sources: the cryosphere, atmosphere, and animals. Though 56 57 58 59 35 60 Page 37 of 83 Environmental Science: Processes & Impacts

1 2 3 761 aquatic-terrestrial links were not addressed with their own explicit category, terrestrial-aquatic 4 5 6 762 interactions were considered across all three types of nutrient subsidy classification. It is clear 7 8 763 from this review that there are many questions to be addressed before we have an in-depth 9 10 11 764 understanding of how nutrient subsidies are controlled by environmental factors, and how they 12 13 765 in turn control the ecological behavior of cold, dilute, oligotrophic lakes. Research that assesses 14 15 16 766 these factors will be crucial not only for Arctic and alpine ecologists and biogeochemists, but 17 18 767 the broader ecological community. This is because ecosystem subsidies provide an important 19 20 768 framework to understand and assess the types of environmental and ecosystem changes that 21 22 23 769 will continue to occur in the 21st century. Our goal in this review has been not only to 24 25 770 summarize recent ecosystem subsidy research in Arctic and alpine areas, but to promote 26 27 28 771 remote lakes as exemplary systems with much to contribute to ecosystem subsidy research. 29 30 772 Remote lakes in rapidly changing areas have much insight to provide concerning the 31 32 33 773 mechanisms, processes, and ecological impacts of cross-ecosystem nutrient subsidies that 34 35 774 occur in other ecosystems, such as low-elevation temperate lakes and streams. 36 37 38 39 775 Conflicts of interest 40 41 42 43 776 There are no conflicts to declare. 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 36 60 Environmental Science: Processes & Impacts Page 38 of 83

1 2 3 4 777 Acknowledgements 5 6 7 8 778 We would like to thank Kevin Simon, Amanda Klemmer, Mark Skidmore, and Brian McGill for 9 10 779 their preliminary review and comments. The funding for this article was provided by NSF 11 12 13 780 (award no. 1144423). 14 15 781 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 37 60 Page 39 of 83 Environmental Science: Processes & Impacts

1 2 3 4 782 Notes and references 5 6 7 8 783 1. Polis GA, Anderson WB, Holt RD. Toward an integration of landscape and food web 9 10 784 ecology: the dynamics of spatially subsidized food webs. Annual review of ecology and 11 12 13 785 systematics. 1997 Nov;28(1):289-316. 14 15 786 2. Slemmons KE, Saros JE. Implications of nitrogen-rich glacial meltwater for 16 17 18 787 phytoplankton diversity and productivity in alpine lakes. Limnology and Oceanography. 19 20 788 2012 Nov;57(6):1651-63. 21 22 23 789 3. Slemmons KE, Medford A, Hall BL, Stone JR, McGowan S, Lowell T, Kelly M, Saros JE. 24 25 790 Changes in glacial meltwater alter algal communities in lakes of Scoresby Sund, Renland, 26 27 28 791 East Greenland throughout the Holocene: Abrupt reorganizations began 1000 years 29 30 792 before present. The Holocene. 2017 Jul;27(7):929-40. 31 32 793 4. Nakano S, Murakami M. Reciprocal subsidies: dynamic interdependence between 33 34 35 794 terrestrial and aquatic food webs. Proceedings of the National Academy of Sciences. 36 37 795 2001 Jan 2;98(1):166-70. 38 39 40 796 5. Nydick KR, Lafrancois BM, Baron JS, Johnson BM. Nitrogen regulation of algal biomass, 41 42 797 productivity, and composition in shallow mountain lakes, Snowy Range, Wyoming, USA. 43 44 45 798 Canadian Journal of Fisheries and Aquatic Sciences. 2004 Jul 1;61(7):1256-68. 46 47 799 6. Piovia-Scott J, Sadro S, Knapp RA, Sickman J, Pope KL, Chandra S. Variation in reciprocal 48 49 50 800 subsidies between lakes and land: perspectives from the mountains of California. 51 52 801 Canadian Journal of Fisheries and Aquatic Sciences. 2016 May 31;73(11):1691-701. 53 54 55 56 57 58 59 38 60 Environmental Science: Processes & Impacts Page 40 of 83

1 2 3 802 7. Wolfe AP, Baron JS, Cornett RJ. Anthropogenic nitrogen deposition induces rapid 4 5 6 803 ecological changes in alpine lakes of the Colorado Front Range (USA). Journal of 7 8 804 Paleolimnology. 2001 Jan 1;25(1):1-7. 9 10 11 805 8. Wolfe AP, Van Gorp AC, Baron JS. Recent ecological and biogeochemical changes in 12 13 806 alpine lakes of Rocky Mountain National Park (Colorado, USA): a response to 14 15 16 807 anthropogenic nitrogen deposition. Geobiology. 2003 Oct;1(2):153-68. 17 18 808 9. Slemmons KE, Saros JE, Stone JR, McGowan S, Hess CT, Cahl D. Effects of glacier 19 20 809 meltwater on the algal sedimentary record of an alpine lake in the central US Rocky 21 22 23 810 Mountains throughout the late Holocene. Journal of paleolimnology. 2015 Apr 24 25 811 1;53(4):385-99. 26 27 28 812 10. Xiankai L, Jiangming M, Shaofeng D. Effects of nitrogen deposition on forest biodiversity. 29 30 813 Acta Ecologica Sinica. 2008 Nov 1;28(11):5532-48. 31 32 33 814 11. Bobbink R, Hicks K, Galloway J, Spranger T, Alkemade R, Ashmore M, Bustamante M, 34 35 815 Cinderby S, Davidson E, Dentener F, Emmett B. Global assessment of nitrogen 36 37 38 816 deposition effects on terrestrial plant diversity: a synthesis. Ecological applications. 2010 39 40 817 Jan 1;20(1):30-59. 41 42 818 12. Levin SA. The problem of pattern and scale in ecology: the Robert H. MacArthur award 43 44 45 819 lecture. Ecology. 1992 Dec;73(6):1943-67. 46 47 820 13. Turner MG. Landscape ecology: the effect of pattern on process. Annual review of 48 49 50 821 ecology and systematics. 1989 Nov;20(1):171-97. 51 52 822 14. Pickett ST, Cadenasso ML. Landscape ecology: spatial heterogeneity in ecological 53 54 55 823 systems. Science. 1995 Jul 21;269(5222):331-4. 56 57 58 59 39 60 Page 41 of 83 Environmental Science: Processes & Impacts

1 2 3 824 15. Loreau M, Mouquet N, Holt RD. Meta-ecosystems: a theoretical framework for a spatial 4 5 6 825 ecosystem ecology. Ecology Letters. 2003 Aug;6(8):673-9. 7 8 826 16. Nakano S, Miyasaka H, Kuhara N. Terrestrial–aquatic linkages: riparian arthropod inputs 9 10 11 827 alter trophic cascades in a stream food web. Ecology. 1999 Oct;80(7):2435-41. 12 13 828 17. Holt RD. Food webs in space: on the interplay of dynamic instability and spatial 14 15 16 829 processes. Ecological Research. 2002 Mar 1;17(2):261-73. 17 18 830 18. Huxel GR, McCann K, Polis GA. Effects of partitioning allochthonous and autochthonous 19 20 831 resources on food web stability. Ecological Research. 2002 Jul 1;17(4):419-32. 21 22 23 832 19. Sears AL, Holt RD, Polis GA. Feast and famine in food webs: the effects of pulsed 24 25 833 productivity. Food webs at the landscape level. University of Chicago Press, Chicago, 26 27 28 834 Illinois, USA. 2004 Feb 22:359-86. 29 30 835 20. Barrett K, Anderson WB, Wait DA, Grismer LL, Polis GA, Rose MD. Marine subsidies alter 31 32 33 836 the diet and abundance of insular and coastal lizard populations. Oikos. 2005 34 35 837 Apr;109(1):145-53. 36 37 38 838 21. Marczak LB, Thompson RM, Richardson JS. Meta-analysis: trophic level, habitat, and 39 40 839 productivity shape the food web effects of resource subsidies. Ecology. 2007 41 42 840 Jan;88(1):140-8. 43 44 45 841 22. Leroux SJ, Loreau M. Subsidy hypothesis and strength of trophic cascades across 46 47 842 ecosystems. Ecology letters. 2008 Nov;11(11):1147-56. 48 49 50 843 23. Marcarelli AM, Baxter CV, Mineau MM, Hall Jr RO. Quantity and quality: unifying food 51 52 844 web and ecosystem perspectives on the role of resource subsidies in freshwaters. 53 54 55 845 Ecology. 2011 Jun;92(6):1215-25. 56 57 58 59 40 60 Environmental Science: Processes & Impacts Page 42 of 83

1 2 3 846 24. Scharnweber K, Vanni MJ, Hilt S, Syväranta J, Mehner T. Boomerang ecosystem fluxes: 4 5 6 847 organic carbon inputs from land to lakes are returned to terrestrial food webs via 7 8 848 aquatic insects. Oikos. 2014 Dec;123(12):1439-48. 9 10 11 849 25. Fellman JB, Hood E, Raymond PA, Hudson J, Bozeman M, Arimitsu M. Evidence for the 12 13 850 assimilation of ancient glacier organic carbon in a proglacial stream food web. Limnology 14 15 16 851 and Oceanography. 2015 Jul;60(4):1118-28. 17 18 852 26. Creed IF, Bergström AK, Trick CG, Grimm NB, Hessen DO, Karlsson J, Kidd KA, Kritzberg E, 19 20 853 McKnight DM, Freeman EC, Senar OE. Global change-driven effects on dissolved organic 21 22 23 854 matter composition: Implications for food webs of northern lakes. Global change 24 25 855 biology. 2018 Aug;24(8):3692-714. 26 27 28 856 27. Takimoto G, Iwata T, Murakami M. Seasonal subsidy stabilizes food web dynamics: 29 30 857 balance in a heterogeneous landscape. Ecological Research. 2002 Jul 1;17(4):433-9. 31 32 33 858 28. Yang LH, Bastow JL, Spence KO, Wright AN. What can we learn from resource pulses? 34 35 859 Ecology. 2008 Mar;89(3):621-34. 36 37 38 860 29. Soininen J, Bartels PI, Heino J, Luoto M, Hillebrand H. Toward more integrated 39 40 861 ecosystem research in aquatic and terrestrial environments. BioScience. 2015 Jan 41 42 862 24;65(2):174-82. 43 44 45 863 30. Leavitt PR, Fritz SC, Anderson NJ, Baker PA, Blenckner T, Bunting L, Catalan J, Conley DJ, 46 47 864 Hobbs WO, Jeppesen E, Korhola A. Paleolimnological evidence of the effects on lakes of 48 49 50 865 energy and mass transfer from climate and humans. Limnology and Oceanography. 51 52 866 2009 Nov;54(6part2):2330-48. 53 54 55 56 57 58 59 41 60 Page 43 of 83 Environmental Science: Processes & Impacts

1 2 3 867 31. Caraco N, Cole J. When terrestrial organic matter is sent down the river: the importance 4 5 6 868 of allochthonous carbon inputs to the metabolism of lakes and rivers. Food webs at the 7 8 869 landscape level. 2004 Feb 22:301-16. 9 10 11 870 32. Strayer DL, Power ME, Fagan WF, Pickett ST, Belnap J. A classification of ecological 12 13 871 boundaries. BioScience. 2003 Aug 1;53(8):723-9. 14 15 16 872 33. Coppin P, Lambin E, Jonckheere I, Muys B. Digital change detection methods in natural 17 18 873 ecosystem monitoring: A review. InAnalysis of multi-temporal remote sensing images 19 20 874 2002 (pp. 3-36). 21 22 23 875 34. Qiang M, Chen F, Zhang J, Zu R, Jin M, Zhou A, Xiao S. Grain size in sediments from Lake 24 25 876 Sugan: a possible linkage to dust storm events at the northern margin of the Qinghai– 26 27 28 877 Tibetan Plateau. Environmental Geology. 2007 Feb 1;51(7):1229-38. 29 30 878 35. Nanus L, Clow DW, Saros JE, Stephens VC, Campbell DH. Mapping critical loads of 31 32 33 879 nitrogen deposition for aquatic ecosystems in the Rocky Mountains, USA. Environmental 34 35 880 Pollution. 2012 Jul 1;166:125-35. 36 37 38 881 36. Battarbee RW, Jones VJ, Flower RJ, Cameron NG, Bennion H, Carvalho L, Juggins S. 39 40 882 Diatoms. In Tracking environmental change using lake sediments 2002 (pp. 155-202). 41 42 883 Springer, Dordrecht. 43 44 45 884 37. Leavitt PR, Hodgson DA. Sedimentary pigments. In Tracking environmental change using 46 47 885 lake sediments 2002 (pp. 295-325). Springer, Dordrecht. 48 49 50 886 38. Smol JP, Birks HJ, Last WM. Using biology to study long-term environmental change. In 51 52 887 Tracking environmental change using lake sediments 2002 (pp. 1-3). Springer, 53 54 55 888 Dordrecht. 56 57 58 59 42 60 Environmental Science: Processes & Impacts Page 44 of 83

1 2 3 889 39. Harper MA. 22 Diatoms as markers of atmospheric transport. In The diatoms: 4 5 6 890 applications for the environmental and earth sciences. 2001 Jul 19:429. 7 8 891 40. Williamson CE, Saros JE, Vincent WF, Smol JP. Lakes and reservoirs as sentinels, 9 10 11 892 integrators, and regulators of climate change. Limnology and Oceanography. 2009 12 13 893 Nov;54(6 part 2):2273-82. 14 15 16 894 41. Anderson NJ, Curtis CJ, Whiteford EJ, Jones VJ, McGowan S, Simpson GL, Kaiser J. 17 18 895 Regional variability in the atmospheric nitrogen deposition signal and its transfer to the 19 20 896 sediment record in Greenland lakes. Limnology and Oceanography. 2018 21 22 23 897 Sep;63(5):2250-65. 24 25 898 42. Mueller DR, Van Hove P, Antoniades D, Jeffries MO, Vincent WF. High Arctic lakes as 26 27 28 899 sentinel ecosystems: Cascading regime shifts in climate, ice cover, and mixing. 29 30 900 Limnology and Oceanography. 2009 Nov;54(6 part 2):2371-85. 31 32 33 901 43. Sickman JO, Melack JM, Stoddard JL. Regional analysis of inorganic nitrogen yield and 34 35 902 retention in high-elevation ecosystems of the Sierra Nevada and Rocky Mountains. In 36 37 38 903 The Nitrogen Cycle at Regional to Global Scales 2002 (pp. 341-374). Springer, Dordrecht. 39 40 904 44. Clow DW, Nanus L, Huggett B. Use of regression-based models to map sensitivity of 41 42 905 aquatic resources to atmospheric deposition in Yosemite National Park, USA. Water 43 44 45 906 Resources Research. 2010 Sep;46(9), DOI: 10.1029/2009WR008316. 46 47 907 45. Saros JE, Clow DW, Blett T, Wolfe AP. Critical nitrogen deposition loads in high-elevation 48 49 50 908 lakes of the western US inferred from paleolimnological records. Water, Air, & Soil 51 52 909 Pollution. 2011 Mar 1;216(1-4):193-202. 53 54 55 56 57 58 59 43 60 Page 45 of 83 Environmental Science: Processes & Impacts

1 2 3 910 46. Baron JS, Driscoll CT, Stoddard JL, Richer EE. Empirical critical loads of atmospheric 4 5 6 911 nitrogen deposition for nutrient enrichment and acidification of sensitive US lakes. 7 8 912 Bioscience. 2011 Aug 1;61(8):602-13. 9 10 11 913 47. Pardo LH, Fenn ME, Goodale CL, Geiser LH, Driscoll CT, Allen EB, Baron JS, Bobbink R, 12 13 914 Bowman WD, Clark CM, Emmett B. Effects of nitrogen deposition and empirical nitrogen 14 15 16 915 critical loads for ecoregions of the United States. Ecological Applications. 2011 17 18 916 Dec;21(8):3049-82. 19 20 917 48. Adrian R, O'Reilly CM, Zagarese H, Baines SB, Hessen DO, Keller W, Livingstone DM, 21 22 23 918 Sommaruga R, Straile D, Van Donk E, Weyhenmeyer GA. Lakes as sentinels of climate 24 25 919 change. Limnology and oceanography. 2009 Nov;54(6 part 2):2283-97. 26 27 28 920 49. Hobbie JE. Limnology of tundra ponds, Barrow, Alaska. 1980. Dowden, Hutchinson & 29 30 921 Ross, Stroudsburg, PA. 31 32 33 922 50. Schindler DW, Kalff J, Welch HE, Brunskill GJ, Kling H, Kritsch N. Eutrophication in the 34 35 923 High Arctic—Meretta Lake, Cornwallis Island (75 N Lat.). Journal of the Fisheries Board 36 37 38 924 of Canada. 1974 May 1;31(5):647-62. 39 40 925 51. Goldman CR. Primary productivity, nutrients, and transparency during the early onset of 41 42 926 eutrophication in ultra-oligotrophic Lake Tahoe, Califomia-Nevada 1. Limnology and 43 44 45 927 oceanography. 1988 Nov;33(6):1321-33. 46 47 928 52. Hassan R, Scholes R, Ash N. Ecosystems and human well-being: current state and trends. 48 49 50 929 Volume 1. Washington, DC: Island Press; 2005. 51 52 930 53. Meier MF, Dyurgerov MB, McCabe GJ. The health of glaciers: Recent changes in glacier 53 54 55 931 regime. Climatic change. 2003 Jul 1;59(1-2):123-35. 56 57 58 59 44 60 Environmental Science: Processes & Impacts Page 46 of 83

1 2 3 932 54. Guay KC, Beck PS, Berner LT, Goetz SJ, Baccini A, Buermann W. Vegetation productivity 4 5 6 933 patterns at high northern latitudes: a multi-sensor satellite data assessment. Global 7 8 934 Change Biology. 2014 Oct;20(10):3147-58. 9 10 11 935 55. Jorgenson MT, Racine CH, Walters JC, Osterkamp TE. Permafrost degradation and 12 13 936 ecological changes associated with a warming climate in central Alaska. Climatic change. 14 15 16 937 2001 Mar 1;48(4):551-79. 17 18 938 56. Jorgenson MT, Shur YL, Pullman ER. Abrupt increase in permafrost degradation in Arctic 19 20 939 Alaska. Geophysical Research Letters. 2006 Jan;33(2), DOI: 10.1029/2005GL024960. 21 22 23 940 57. Fox AD, Madsen J, Boyd H, Kuijken E, Norriss DW, Tombre IM, Stroud DA. Effects of 24 25 941 agricultural change on abundance, fitness components and distribution of two 26 27 28 942 arctic-nesting goose populations. Global Change Biology. 2005 Jun;11(6):881-93. 29 30 943 58. Greig HS, Kratina P, Thompson PL, Palen WJ, Richardson JS, Shurin JB. Warming, 31 32 33 944 eutrophication, and predator loss amplify subsidies between aquatic and terrestrial 34 35 945 ecosystems. Global Change Biology. 2012 Feb;18(2):504-14. 36 37 38 946 59. Lane SN, Bakker M, Gabbud C, Micheletti N, Saugy JN. Sediment export, transient 39 40 947 landscape response and catchment-scale connectivity following rapid climate warming 41 42 948 and Alpine glacier recession. Geomorphology. 2017 Jan 15;277:210-27. 43 44 45 949 60. Saros JE, Rose KC, Clow DW, Stephens VC, Nurse AB, Arnett HA, Stone JR, Williamson CE, 46 47 950 Wolfe AP. Melting alpine glaciers enrich high-elevation lakes with reactive nitrogen. 48 49 50 951 Environmental science & technology. 2010 Jun 7;44(13):4891-6. 51 52 53 54 55 56 57 58 59 45 60 Page 47 of 83 Environmental Science: Processes & Impacts

1 2 3 952 61. Mesquita PS, Wrona FJ, Prowse TD. Effects of retrogressive permafrost thaw slumping 4 5 6 953 on sediment chemistry and submerged macrophytes in Arctic tundra lakes. Freshwater 7 8 954 Biology. 2010 Nov;55(11):2347-58. 9 10 11 955 62. Dreyer J, Hoekman D, Gratton C. Lake-derived midges increase abundance of shoreline 12 13 956 terrestrial arthropods via multiple trophic pathways. Oikos. 2012 Feb;121(2):252-8. 14 15 16 957 63. Bultman H, Hoekman D, Dreyer J, Gratton C. Terrestrial deposition of aquatic insects 17 18 958 increases plant quality for insect herbivores and herbivore density. Ecological 19 20 959 entomology. 2014;39(4):419-26. 21 22 23 960 64. Mariash HL, Cazzanelli M, Rautio M, Hamerlik L, Wooller MJ, Christoffersen KS. Changes 24 25 961 in food web dynamics of low Arctic ponds with varying content of dissolved organic 26 27 28 962 carbon. Arctic, Antarctic, and Alpine Research. 2018 Jan 1;50(1), DOI: 29 30 963 10.1080/15230430.2017.1414472. 31 32 33 964 65. Catalan J, Camarero L, Felip M, Pla S, Ventura M, Buchaca T, Bartumeus F, Mendoza GD, 34 35 965 Miró A, Casamayor EO, Medina-Sánchez JM. High mountain lakes: extreme habitats and 36 37 38 966 witnesses of environmental changes. limnetica. 2006;25(1-2):551-84. 39 40 967 66. Hobbs WO, Telford RJ, Birks HJ, Saros JE, Hazewinkel RR, Perren BB, Saulnier-Talbot É, 41 42 968 Wolfe AP. Quantifying recent ecological changes in remote lakes of North America and 43 44 45 969 Greenland using sediment diatom assemblages. PloS one. 2010 Apr 2;5(4), DOI: 46 47 970 10.1371/journal.pone.0010026. 48 49 50 971 67. Catalan J, Pla-Rabés S, Wolfe AP, Smol JP, Rühland KM, Anderson NJ, Kopáček J, Stuchlík 51 52 972 E, Schmidt R, Koinig KA, Camarero L. Global change revealed by palaeolimnological 53 54 55 56 57 58 59 46 60 Environmental Science: Processes & Impacts Page 48 of 83

1 2 3 973 records from remote lakes: a review. Journal of Paleolimnology. 2013 Mar 1;49(3):513- 4 5 6 974 35. 7 8 975 68. Wang X, Gong P, Zhang Q, Yao T. Impact of climate fluctuations on deposition of DDT 9 10 11 976 and hexachlorocyclohexane in mountain glaciers: Evidence from ice core records. 12 13 977 Environmental pollution. 2010 Feb 1;158(2):375-80. 14 15 16 978 69. Schmid P, Bogdal C, Blüthgen N, Anselmetti FS, Zwyssig A, Hungerbühler K. The missing 17 18 979 piece: sediment records in remote mountain lakes confirm glaciers being secondary 19 20 980 sources of persistent organic pollutants. Environmental science & technology. 2011 Jan 21 22 23 981 1;45(1):203-8. 24 25 982 70. Bogdal C, Nikolic D, Lüthi MP, Schenker U, Scheringer M, Hungerbühler K. Release of 26 27 28 983 legacy pollutants from melting glaciers: model evidence and conceptual understanding. 29 30 984 Environmental science & technology. 2010 Jun 1;44(11):4063-9. 31 32 33 985 71. Wania F, Mackay D. Global fractionation and cold condensation of low volatility 34 35 986 organochlorine compounds in polar regions. Ambio. 1993 Feb 1:10-8. 36 37 38 987 72. Kawamura K, Suzuki I, Fuji Y, Watanabe O. Ice core record of polycyclic aromatic 39 40 988 hydrocarbons over the past 400 years. Naturwissenschaften. 1994 Nov 1;81(11):502-5. 41 42 989 73. AMAP. AMAP Assessment 2002: Persistent organic pollutants. Arctic monitoring and 43 44 45 990 assessment programme (AMAP). Oslo, Norway. 46 47 991 74. Daly GL, Wania F. Organic contaminants in mountains. Environmental science & 48 49 50 992 technology. 2005 Jan 15;39(2):385-98. 51 52 993 75. Williams MW, Knauf M, Cory R, Caine N, Liu F. Nitrate content and potential microbial 53 54 55 994 signature of rock glacier outflow, Colorado Front Range. Earth Surface Processes and 56 57 58 59 47 60 Page 49 of 83 Environmental Science: Processes & Impacts

1 2 3 995 Landforms: The Journal of the British Geomorphological Research Group. 2007 4 5 6 996 Jun;32(7):1032-47. 7 8 997 76. Hood E, Fellman J, Spencer RG, Hernes PJ, Edwards R, D’Amore D, Scott D. Glaciers as a 9 10 11 998 source of ancient and labile organic matter to the marine environment. Nature. 2009 12 13 999 Dec;462(7276):1044. 14 15 16 1000 77. Hood E, Battin TJ, Fellman J, O'neel S, Spencer RG. Storage and release of organic carbon 17 18 1001 from glaciers and ice sheets. Nature geoscience. 2015 Feb;8(2):91. 19 20 1002 78. Hodson A, Mumford P, Lister D. Suspended sediment and phosphorus in proglacial 21 22 23 1003 rivers: bioavailability and potential impacts upon the P status of ice-marginal receiving 24 25 1004 waters. Hydrological processes. 2004 Sep;18(13):2409-22. 26 27 28 1005 79. Hawkings J, Wadham J, Tranter M, Telling J, Bagshaw E, Beaton A, Simmons SL, Chandler 29 30 1006 D, Tedstone A, Nienow P. The Greenland Ice Sheet as a hot spot of phosphorus 31 32 33 1007 weathering and export in the Arctic. Global Biogeochemical Cycles. 2016 Feb 34 35 1008 1;30(2):191-210. 36 37 38 1009 80. Burpee BT, Anderson D, Saros JE. Assessing ecological effects of glacial meltwater on 39 40 1010 lakes fed by the Greenland Ice Sheet: The role of nutrient subsidies and turbidity. Arctic, 41 42 1011 Antarctic, and Alpine Research. 2018 Jan 1;50(1), DOI: 43 44 45 1012 10.1080/15230430.2017.1420953. 46 47 1013 81. Hawkings JR, Wadham JL, Tranter M, Lawson E, Sole A, Cowton T, Tedstone AJ, 48 49 50 1014 Bartholomew I, Nienow P, Chandler D, Telling J. The effect of warming climate on 51 52 1015 nutrient and solute export from the Greenland Ice Sheet. Geochem. Perspect. Lett. 2015 53 54 55 1016 Jan 1;1:94-104. 56 57 58 59 48 60 Environmental Science: Processes & Impacts Page 50 of 83

1 2 3 1017 82. Bhatia MP, Kujawinski EB, Das SB, Breier CF, Henderson PB, Charette MA. Greenland 4 5 6 1018 meltwater as a significant and potentially bioavailable source of iron to the ocean. 7 8 1019 Nature Geoscience. 2013 Apr;6(4):274. 9 10 11 1020 83. Lyons W, Finlay J. Biogeochemical processes in high-latitude lakes and rivers. Oxford 12 13 1021 University Press, Oxford; 2008 Sep 11. 14 15 16 1022 84. Brittain JE, Milner AM. Ecology of glacier-fed rivers: current status and concepts. 17 18 1023 Freshwater Biology. 2001 Dec;46(12):1571-8. 19 20 1024 85. Scott D, Hood E, Nassry M. In-stream uptake and retention of C, N and P in a supraglacial 21 22 23 1025 stream. Annals of Glaciology. 2010;51(56):80-6. 24 25 1026 86. McClain ME, Boyer EW, Dent CL, Gergel SE, Grimm NB, Groffman PM, Hart SC, Harvey 26 27 28 1027 JW, Johnston CA, Mayorga E, McDowell WH. Biogeochemical hot spots and hot 29 30 1028 moments at the interface of terrestrial and aquatic ecosystems. Ecosystems. 2003 Jun 31 32 33 1029 21;6(4):301-12. 34 35 1030 87. Anderson NJ, Saros JE, Bullard JE, Cahoon SM, McGowan S, Bagshaw EA, Barry CD, 36 37 38 1031 Bindler R, Burpee BT, Carrivick JL, Fowler RA. The Arctic in the twenty-first century: 39 40 1032 Changing biogeochemical linkages across a paraglacial landscape of Greenland. 41 42 1033 BioScience. 2017 Feb 1;67(2):118-33. 43 44 45 1034 88. Hinkel KM, Nelson FE. Spatial and temporal patterns of active layer thickness at 46 47 1035 Circumpolar Active Layer Monitoring (CALM) sites in northern Alaska, 1995–2000. 48 49 50 1036 Journal of Geophysical Research: Atmospheres. 2003 Jan 27;108(D2), DOI: 51 52 1037 10.1029/2001JD000927. 53 54 55 56 57 58 59 49 60 Page 51 of 83 Environmental Science: Processes & Impacts

1 2 3 1038 89. Zhang Y, Chen W, Smith SL, Riseborough DW, Cihlar J. Soil temperature in Canada during 4 5 6 1039 the twentieth century: Complex responses to atmospheric climate change. Journal of 7 8 1040 Geophysical Research: Atmospheres. 2005 Feb 16;110(D3), DOI: 9 10 11 1041 10.1029/2004JD004910. 12 13 1042 90. Romanovsky VE, Sazonova TS, Balobaev VT, Shender NI, Sergueev DO. Past and recent 14 15 16 1043 changes in air and permafrost temperatures in eastern Siberia. Global and Planetary 17 18 1044 Change. 2007 Apr 1;56(3-4):399-413. 19 20 1045 91. Kokelj SV, Tunnicliffe J, Lacelle D, Lantz TC, Chin KS, Fraser R. Increased precipitation 21 22 23 1046 drives mega slump development and destabilization of ice-rich permafrost terrain, 24 25 1047 northwestern Canada. Global and Planetary Change. 2015 Jun 1;129:56-68. 26 27 28 1048 92. Lawrence DM, Slater AG. A projection of severe near-surface permafrost degradation 29 30 1049 during the 21st century. Geophysical Research Letters. 2005 Dec 1;32(24), DOI: 31 32 33 1050 10.1029/2005GL025080. 34 35 1051 93. Anisimov O, Reneva S. Permafrost and changing climate: the Russian perspective. 36 37 38 1052 AMBIO: A Journal of the Human Environment. 2006 Jun;35(4):169-76. 39 40 1053 94. Vonk JE, Tank SE, Bowden WB, Laurion I, Vincent WF, Alekseychik P, Amyot M, Billet MF, 41 42 1054 Canario J, Cory RM, Deshpande BN. Reviews and syntheses: Effects of permafrost thaw 43 44 45 1055 on Arctic aquatic ecosystems. Biogeosciences. 2015;12(23):7129-67. 46 47 1056 95. Hinzman LD, Kane DL, Gieck RE, Everett KR. Hydrologic and thermal properties of the 48 49 50 1057 active layer in the Alaskan Arctic. Cold Regions Science and Technology. 1991 May 51 52 1058 1;19(2):95-110. 53 54 55 56 57 58 59 50 60 Environmental Science: Processes & Impacts Page 52 of 83

1 2 3 1059 96. Waelbroeck C, Monfray P, Oechel WC, Hastings S, Vourlitis G. The impact of permafrost 4 5 6 1060 thawing on the carbon dynamics of tundra. Geophysical Research Letters. 1997 Feb 7 8 1061 1;24(3):229-32. 9 10 11 1062 97. Schuur EA, Bockheim J, Canadell JG, Euskirchen E, Field CB, Goryachkin SV, Hagemann S, 12 13 1063 Kuhry P, Lafleur PM, Lee H, Mazhitova G. Vulnerability of permafrost carbon to climate 14 15 16 1064 change: Implications for the global carbon cycle. BioScience. 2008 Sep 1;58(8):701-14. 17 18 1065 98. Frey KE, McClelland JW. Impacts of permafrost degradation on arctic river 19 20 1066 biogeochemistry. Hydrological Processes: An International Journal. 2009 Jan 21 22 23 1067 1;23(1):169-82. 24 25 1068 99. Hobbie JE, Peterson BJ, Bettez N, Deegan L, O'Brien WJ, Kling GW, Kipphut GW, Bowden 26 27 28 1069 WB, Hershey AE. Impact of global change on the biogeochemistry and ecology of an 29 30 1070 Arctic freshwater system. Polar Research. 1999 Jan 12;18(2):207-14. 31 32 33 1071 100. White D, Hinzman L, Alessa L, Cassano J, Chambers M, Falkner K, Francis J, Gutowski WJ, 34 35 1072 Holland M, Holmes RM, Huntington H. The arctic freshwater system: Changes and 36 37 38 1073 impacts. Journal of geophysical research: Biogeosciences. 2007 Dec 1;112(G4), DOI: 39 40 1074 10.1029/2006JG000353. 41 42 1075 101. Carey SK. Dissolved organic carbon fluxes in a discontinuous permafrost subarctic alpine 43 44 45 1076 catchment. Permafrost and Periglacial Processes. 2003 Apr;14(2):161-71. 46 47 1077 102. Frey KE, Smith LC. Amplified carbon release from vast West Siberian peatlands by 2100. 48 49 50 1078 Geophysical Research Letters. 2005 May;32(9), DOI: 10.1029/2004GL022025. 51 52 53 54 55 56 57 58 59 51 60 Page 53 of 83 Environmental Science: Processes & Impacts

1 2 3 1079 103. Holmes RM, McClelland JW, Raymond PA, Frazer BB, Peterson BJ, Stieglitz M. Lability of 4 5 6 1080 DOC transported by Alaskan rivers to the Arctic Ocean. Geophysical Research Letters. 7 8 1081 2008 Feb;35(3), DOI: 10.1029/2007GL032837. 9 10 11 1082 104. Spencer RG, Mann PJ, Dittmar T, Eglinton TI, McIntyre C, Holmes RM, Zimov N, Stubbins 12 13 1083 A. Detecting the signature of permafrost thaw in Arctic rivers. Geophysical Research 14 15 16 1084 Letters. 2015 Apr 28;42(8):2830-5. 17 18 1085 105. Kawahigashi M, Kaiser K, Kalbitz K, Rodionov A, Guggenberger G. Dissolved organic 19 20 1086 matter in small streams along a gradient from discontinuous to continuous permafrost. 21 22 23 1087 Global Change Biology. 2004 Sep;10(9):1576-86. 24 25 1088 106. Striegl RG, Aiken GR, Dornblaser MM, Raymond PA, Wickland KP. A decrease in 26 27 28 1089 discharge-normalized DOC export by the Yukon River during summer through autumn. 29 30 1090 Geophysical Research Letters. 2005 Nov;32(21), DOI: 10.1029/2005GL024413. 31 32 33 1091 107. Walvoord MA, Striegl RG. Increased groundwater to stream discharge from permafrost 34 35 1092 thawing in the Yukon River basin: Potential impacts on lateral export of carbon and 36 37 38 1093 nitrogen. Geophysical Research Letters. 2007 Jun;34(12), DOI: 10.1029/2007GL030216. 39 40 1094 108. Harms TK, Jones Jr JB. Thaw depth determines reaction and transport of inorganic 41 42 1095 nitrogen in valley bottom permafrost soils: Nitrogen cycling in permafrost soils. Global 43 44 45 1096 Change Biology. 2012 Sep;18(9):2958-68. 46 47 1097 109. Harms TK, Edmonds JW, Genet H, Creed IF, Aldred D, Balser A, Jones JB. Catchment 48 49 50 1098 influence on nitrate and dissolved organic matter in Alaskan streams across a latitudinal 51 52 1099 gradient. Journal of Geophysical Research: Biogeosciences. 2016 Feb;121(2):350-69. 53 54 55 56 57 58 59 52 60 Environmental Science: Processes & Impacts Page 54 of 83

1 2 3 1100 110. Abbott BW, Larouche JR, Jones Jr JB, Bowden WB, Balser AW. Elevated dissolved organic 4 5 6 1101 carbon biodegradability from thawing and collapsing permafrost. Journal of Geophysical 7 8 1102 Research: Biogeosciences. 2014 Oct;119(10):2049-63. 9 10 11 1103 111. McClelland JW, Stieglitz M, Pan F, Holmes RM, Peterson BJ. Recent changes in nitrate 12 13 1104 and dissolved organic carbon export from the upper Kuparuk River, North Slope, Alaska. 14 15 16 1105 Journal of Geophysical Research: Biogeosciences. 2007 Dec;112(G4), DOI: 17 18 1106 10.1029/2006JG000371. 19 20 1107 112. Dugan HA, Lamoureux SF, Lewis T, Lafrenière MJ. The impact of permafrost disturbances 21 22 23 1108 and sediment loading on the limnological characteristics of two high Arctic lakes. 24 25 1109 Permafrost and Periglacial Processes. 2012 Apr;23(2):119-26. 26 27 28 1110 113. Khosh MS, McClelland JW, Jacobson AD, Douglas TA, Barker AJ, Lehn GO. Seasonality of 29 30 1111 dissolved nitrogen from spring melt to fall freezeup in Alaskan Arctic tundra and 31 32 33 1112 mountain streams. Journal of Geophysical Research: Biogeosciences. 2017 Jul 34 35 1113 1;122(7):1718-37. 36 37 38 1114 114. Bogard MJ, Kuhn CD, Johnston SE, Striegl RG, Holtgrieve GW, Dornblaser MM, Spencer 39 40 1115 RG, Wickland KP, Butman DE. Negligible cycling of terrestrial carbon in many lakes of the 41 42 1116 arid circumpolar landscape. Nature Geoscience. 2019 Mar;12(3):180. 43 44 45 1117 115. Kokelj SV, Zajdlik B, Thompson MS. The impacts of thawing permafrost on the chemistry 46 47 1118 of lakes across the subarctic boreal-tundra transition, Mackenzie Delta region, Canada. 48 49 50 1119 Permafrost and Periglacial Processes. 2009 Apr;20(2):185-99. 51 52 53 54 55 56 57 58 59 53 60 Page 55 of 83 Environmental Science: Processes & Impacts

1 2 3 1120 116. Abbott BW, Jones JB, Godsey SE, Larouche JR, Bowden WB. Patterns and persistence of 4 5 6 1121 hydrologic carbon and nutrient export from collapsing upland permafrost. 7 8 1122 Biogeosciences. 2015 Jun 17;12(12):3725-40. 9 10 11 1123 117. Thompson MS, Kokelj SV, Prowse TD, Wrona FJ. The impact of sediments derived from 12 13 1124 thawing permafrost on tundra lake water chemistry: an experimental approach. In 14 15 16 1125 Proceedings of the 9th International Conference on Permafrost, edited by: Kane, DL and 17 18 1126 Hinkel, KM 2008 Jun (Vol. 2, pp. 1763-1768). 19 20 1127 118. Thompson MS, Wrona FJ, Prowse TD. Shifts in plankton, nutrient and light relationships 21 22 23 1128 in small tundra lakes caused by localized permafrost thaw. Arctic. 2012 Dec 1:367-76. 24 25 1129 119. Thienpont JR, Ruehland KM, Pisaric MF, Kokelj SV, Kimpe LE, Blais JM, Smol JP. Biological 26 27 28 1130 responses to permafrost thaw slumping in Canadian Arctic lakes. Freshwater Biology. 29 30 1131 2013 Feb;58(2):337-53. 31 32 33 1132 120. Moquin PA, Mesquita PS, Wrona FJ, Prowse TD. Responses of benthic invertebrate 34 35 1133 communities to shoreline retrogressive thaw slumps in Arctic upland lakes. Freshwater 36 37 38 1134 Science. 2014 Sep 29;33(4):1108-18. 39 40 1135 121. Lantz TC, Kokelj SV. Increasing rates of retrogressive thaw slump activity in the 41 42 1136 Mackenzie Delta region, NWT, Canada. Geophysical Research Letters. 2008 Mar;35(6), 43 44 45 1137 DOI: 10.1029/2007GL032433. 46 47 1138 122. Segal RA, Lantz TC, Kokelj SV. Acceleration of thaw slump activity in glaciated landscapes 48 49 50 1139 of the Western Canadian Arctic. Environmental Research Letters. 2016 Mar 17;11(3), 51 52 1140 DOI: 10.1088/1748-9326/11/3/034025. 53 54 55 56 57 58 59 54 60 Environmental Science: Processes & Impacts Page 56 of 83

1 2 3 1141 123. Liston GE, Hiemstra CA. The changing cryosphere: Pan-Arctic snow trends (1979–2009). 4 5 6 1142 Journal of Climate. 2011 Nov;24(21):5691-712. 7 8 1143 124. Niittynen P, Luoto M. The importance of snow in species distribution models of arctic 9 10 11 1144 vegetation. Ecography. 2018 Jun;41(6):1024-37. 12 13 1145 125. Zeng H, Jia G, Forbes BC. Shifts in Arctic phenology in response to climate and 14 15 16 1146 anthropogenic factors as detected from multiple satellite time series. Environmental 17 18 1147 Research Letters. 2013 Sep 4;8(3), DOI: 10.1088/1748-9326/8/3/035036. 19 20 1148 126. Pedersen SH, Liston GE, Tamstorf MP, Abermann J, Lund M, Schmidt NM. Quantifying 21 22 23 1149 snow controls on vegetation greenness. Ecosphere. 2018 Jun;9(6), DOI: 24 25 1150 10.1002/ecs2.2309. 26 27 28 1151 127. Jones HG. The ecology of snow-covered systems: a brief overview of nutrient cycling and 29 30 1152 life in the cold. Hydrological processes. 1999 Oct;13(14-15):2135-47. 31 32 33 1153 128. McGowan S, Gunn HV, Whiteford EJ, Anderson NJ, Jones VJ, Law AC. Functional 34 35 1154 attributes of epilithic diatoms for palaeoenvironmental interpretations in South-West 36 37 38 1155 Greenland lakes. Journal of paleolimnology. 2018 Aug 1;60(2):273-98. 39 40 1156 129. Rosén P, Cunningham L, Vonk J, Karlssona J. Effects of climate on organic carbon and the 41 42 1157 ratio of planktonic to benthic primary producers in a subarctic lake during the past 45 43 44 45 1158 years. Limnology and Oceanography. 2009 Sep;54(5):1723-32. 46 47 1159 130. Šmejkalová T, Edwards ME, Dash J. Arctic lakes show strong decadal trend in earlier 48 49 50 1160 spring ice-out. Scientific reports. 2016 Dec 7;6:38449. 51 52 1161 131. Winder M, Sommer U. Phytoplankton response to a changing climate. Hydrobiologia. 53 54 55 1162 2012 Nov 1;698(1):5-16. 56 57 58 59 55 60 Page 57 of 83 Environmental Science: Processes & Impacts

1 2 3 1163 132. Vincent WF, Laurion I, Pienitz R, Walter Anthony KM. Climate impacts on Arctic lake 4 5 6 1164 ecosystems. Climatic change and global warming of inland waters: Impacts and 7 8 1165 mitigation for ecosystems and societies. 2013:27-42. 9 10 11 1166 133. Warner KA, Fowler RA, Northington RM, Malik HI, McCue J, Saros JE. How does changing 12 13 1167 ice-out affect arctic versus boreal lakes? A comparison using two years with ice-out that 14 15 16 1168 differed by more than three weeks. Water. 2018 Jan;10(1):78. 17 18 1169 134. Jankowski T, Livingstone DM, Bührer H, Forster R, Niederhauser P. Consequences of the 19 20 1170 2003 European heat wave for lake temperature profiles, thermal stability, and 21 22 23 1171 hypolimnetic oxygen depletion: Implications for a warmer world. Limnology and 24 25 1172 Oceanography. 2006 Mar;51(2):815-9. 26 27 28 1173 135. Marsden MW. Lake restoration by reducing external phosphorus loading: the influence 29 30 1174 of sediment phosphorus release. Freshwater Biology. 1989 Apr;21(2):139-62. 31 32 33 1175 136. Søndergaard M, Jensen JP, Jeppesen E. Role of sediment and internal loading of 34 35 1176 phosphorus in shallow lakes. Hydrobiologia. 2003 Nov 1;506(1-3):135-45. 36 37 38 1177 137. Sommer U. Seasonal succession of phytoplankton in Lake Constance. Bioscience. 1985 39 40 1178 Jun 1;35(6):351-7. 41 42 1179 138. French TD, Petticrew EL. Chlorophyll a seasonality in four shallow eutrophic lakes 43 44 45 1180 (northern British Columbia, Canada) and the critical roles of internal phosphorus loading 46 47 1181 and temperature. Hydrobiologia. 2007 Jan 1;575(1):285-99. 48 49 50 1182 139. Wilhelm S, Adrian R. Impact of summer warming on the thermal characteristics of a 51 52 1183 polymictic lake and consequences for oxygen, nutrients and phytoplankton. Freshwater 53 54 55 1184 Biology. 2008 Feb;53(2):226-37. 56 57 58 59 56 60 Environmental Science: Processes & Impacts Page 58 of 83

1 2 3 1185 140. Lesack LF, Marsh P. Lengthening plus shortening of river-to-lake connection times in the 4 5 6 1186 Mackenzie River Delta respectively via two global change mechanisms along the arctic 7 8 1187 coast. Geophysical Research Letters. 2007 Dec 16;34(23). 9 10 11 1188 141. Spears BM, Lesack LF. Bacterioplankton production, abundance, and nutrient limitation 12 13 1189 among lakes of the Mackenzie Delta (western Canadian arctic). Canadian Journal of 14 15 16 1190 Fisheries and Aquatic Sciences. 2006 Apr 1;63(4):845-57. 17 18 1191 142. Galloway JN, Dentener FJ, Capone DG, Boyer EW, Howarth RW, Seitzinger SP, Asner GP, 19 20 1192 Cleveland CC, Green PA, Holland EA, Karl DM. Nitrogen cycles: past, present, and future. 21 22 23 1193 Biogeochemistry. 2004 Sep 1;70(2):153-226. 24 25 1194 143. Holmgren SU, Bigler C, Ingólfsson O, Wolfe AP. The Holocene–Anthropocene transition 26 27 28 1195 in lakes of western Spitsbergen, Svalbard (Norwegian High Arctic): climate change and 29 30 1196 nitrogen deposition. Journal of Paleolimnology. 2010 Feb 1;43(2):393-412. 31 32 33 1197 144. Wolfe AP, Cooke CA, Hobbs WO. Are current rates of atmospheric nitrogen deposition 34 35 1198 influencing lakes in the eastern Canadian Arctic? Arctic, Antarctic, and Alpine Research. 36 37 38 1199 2006 Aug 1;38(3):465-76. 39 40 1200 145. Bergström AK, Jonsson A, Jansson M. Phytoplankton responses to nitrogen and 41 42 1201 phosphorus enrichment in unproductive Swedish lakes along a gradient of atmospheric 43 44 45 1202 nitrogen deposition. Aquatic Biology. 2008 Nov 4;4(1):55-64. 46 47 1203 146. Wolfe AP, Hobbs WO, Birks HH, Briner JP, Holmgren SU, Ingólfsson Ó, Kaushal SS, Miller 48 49 50 1204 GH, Pagani M, Saros JE, Vinebrooke RD. Stratigraphic expressions of the Holocene– 51 52 1205 Anthropocene transition revealed in sediments from remote lakes. Earth-Science 53 54 55 1206 Reviews. 2013 Jan 1;116:17-34. 56 57 58 59 57 60 Page 59 of 83 Environmental Science: Processes & Impacts

1 2 3 1207 147. Laj P, Palais JM, Sigurdsson H. Changing sources of impurities to the Greenland ice sheet 4 5 6 1208 over the last 250 years. Atmospheric Environment. Part A. General Topics. 1992 Oct 7 8 1209 1;26(14):2627-40. 9 10 11 1210 148. Mayewski PA, Lyons WB, Spencer MJ, Twickler MS, Buck CF, Whitlow S. An ice-core 12 13 1211 record of atmospheric response to anthropogenic sulphate and nitrate. Nature. 1990 14 15 16 1212 Aug;346(6284):554. 17 18 1213 149. Fischer H, Wagenbach D, Kipfstuhl J. Sulfate and nitrate firn concentrations on the 19 20 1214 Greenland ice sheet: 1. Large-scale geographical deposition changes. Journal of 21 22 23 1215 Geophysical Research: Atmospheres. 1998 Sep 20;103(D17):21927-34. 24 25 1216 150. Simões JC, Zagorodnov VS. The record of anthropogenic pollution in snow and ice in 26 27 28 1217 Svalbard, Norway. Atmospheric Environment. 2001 Jan 1;35(2):403-13. 29 30 1218 151. Isaksson E, Hermanson M, Hicks S, Igarashi M, Kamiyama K, Moore J, Motoyama H, Muir 31 32 33 1219 D, Pohjola V, Vaikmäe R, van de Wal RS. Ice cores from Svalbard––useful archives of past 34 35 1220 climate and pollution history. Physics and Chemistry of the Earth, Parts A/B/C. 2003 Jan 36 37 38 1221 1;28(28-32):1217-28. 39 40 1222 152. Goto-Azuma K, Koerner RM. Ice core studies of anthropogenic sulfate and nitrate trends 41 42 1223 in the Arctic. Journal of Geophysical Research: Atmospheres. 2001 Mar 43 44 45 1224 16;106(D5):4959-69. 46 47 1225 153. Yalcin K, Wake CP. Anthropogenic signals recorded in an ice core from Eclipse Icefield, 48 49 50 1226 Yukon Territory, Canada. Geophysical Research Letters. 2001 Dec 1;28(23):4487-90. 51 52 1227 154. Burkhart JF, Bales RC, McConnell JR, Hutterli MA. Influence of North Atlantic Oscillation 53 54 55 1228 on anthropogenic transport recorded in northwest Greenland ice cores. Journal of 56 57 58 59 58 60 Environmental Science: Processes & Impacts Page 60 of 83

1 2 3 1229 Geophysical Research: Atmospheres. 2006 Nov 27;111(D22), DOI: 4 5 6 1230 10.1029/2005JD006771. 7 8 1231 155. Hastings MG, Jarvis JC, Steig EJ. Anthropogenic impacts on nitrogen isotopes of ice-core 9 10 11 1232 nitrate. Science. 2009 Jun 5;324(5932):1288. 12 13 1233 156. Holtgrieve GW, Schindler DE, Hobbs WO, Leavitt PR, Ward EJ, Bunting L, Chen G, Finney 14 15 16 1234 BP, Gregory-Eaves I, Holmgren S, Lisac MJ. A coherent signature of anthropogenic 17 18 1235 nitrogen deposition to remote watersheds of the northern hemisphere. Science. 2011 19 20 1236 Dec 16;334(6062):1545-8. 21 22 23 1237 157. Arens SJ, Sullivan PF, Welker JM. Nonlinear responses to nitrogen and strong 24 25 1238 interactions with nitrogen and phosphorus additions drastically alter the structure and 26 27 28 1239 function of a high arctic ecosystem. Journal of Geophysical Research: Biogeosciences. 29 30 1240 2008 Sep 1;113(G3), doi:10.1029/2007JG000508. 31 32 33 1241 158. Gordon CW, Wynn JM, Woodin SJ. Impacts of increased nitrogen supply on high Arctic 34 35 1242 heath: the importance of bryophytes and phosphorus availability. New Phytologist. 2001 36 37 38 1243 Mar;149(3):461-71. 39 40 1244 159. Betts-Piper AM, Zeeb BA, Smol JP. Distribution and autecology of chrysophyte cysts 41 42 1245 from high Arctic Svalbard lakes: preliminary evidence of recent environmental change. 43 44 45 1246 Journal of Paleolimnology. 2004 May 1;31(4):467-81. 46 47 1247 160. Lepori F, Keck F. Effects of atmospheric nitrogen deposition on remote freshwater 48 49 50 1248 ecosystems. Ambio. 2012 May 1;41(3):235-46. 51 52 53 54 55 56 57 58 59 59 60 Page 61 of 83 Environmental Science: Processes & Impacts

1 2 3 1249 161. Birks HJ, Jones VJ, Rose NL. Recent environmental change and atmospheric 4 5 6 1250 contamination on Svalbard as recorded in lake sediments–an introduction. Journal of 7 8 1251 Paleolimnology. 2004 May 1;31(4):403-10. 9 10 11 1252 162. Benstead JP, Deegan LA, Peterson BJ, Huryn AD, Bowden WB, Suberkropp K, Buzby KM, 12 13 1253 Green AC, Vacca JA. Responses of a beaded Arctic stream to short-term N and P 14 15 16 1254 fertilisation. Freshwater Biology. 2005 Feb;50(2):277-90. 17 18 1255 163. O'Brien WJ, Barfield M, Bettez N, Hershey AE, Hobbie JE, Kipphut G, Kling G, Miller MC. 19 20 1256 Long-term response and recovery to nutrient addition of a partitioned arctic lake. 21 22 23 1257 Freshwater Biology. 2005 May;50(5):731-41. 24 25 1258 164. Burckle LH, Gayley RI, Ram M, Petit JR. Diatoms in Antarctic ice cores: some implications 26 27 28 1259 for the glacial history of Antarctica. Geology. 1988 Apr 1;16(4):326-9. 29 30 1260 165. Gayley RI, Ram M, Stoermer EF. Seasonal variations in diatom abundance and 31 32 33 1261 provenance in Greenland ice. Journal of Glaciology. 1989;35(120):290-2. 34 35 1262 166. Donarummo Jr J, Ram M, Stoermer EF. Possible deposit of soil dust from the 1930's US 36 37 38 1263 dust bowl identified in Greenland ice. Geophysical Research Letters. 2003 Mar;30(6). 39 40 1264 167. Rousseau DD, Schevin P, Ferrier J, Jolly D, Andreasen T, Ascanius SE, Hendriksen SE, 41 42 1265 Poulsen U. Long-distance pollen transport from North America to Greenland in spring. 43 44 45 1266 Journal of Geophysical Research: Biogeosciences. 2008 Jun;113(G2). 46 47 1267 168. Weide DM, Fritz SC, Brinson BE, Thompson LG, Billups WE. Freshwater diatoms in the 48 49 50 1268 Sajama, Quelccaya, and Coropuna glaciers of the South American Andes. Diatom 51 52 1269 Research. 2017 Apr 3;32(2):153-62. 53 54 55 56 57 58 59 60 60 Environmental Science: Processes & Impacts Page 62 of 83

1 2 3 1270 169. Bullard JE. Contemporary glacigenic inputs to the dust cycle. Earth Surface Processes 4 5 6 1271 and Landforms. 2013 Jan;38(1):71-89. 7 8 1272 170. McTainsh GH, Lynch AW. Quantitative estimates of the effect of climate change on dust 9 10 11 1273 storm activity in Australia during the Last Glacial Maximum. Geomorphology. 1996 Sep 12 13 1274 1;17(1-3):263-71. 14 15 16 1275 171. Reheis MC, Kihl R. Dust deposition in southern Nevada and California, 1984–1989: 17 18 1276 Relations to climate, source area, and source lithology. Journal of Geophysical Research: 19 20 1277 Atmospheres. 1995 May 20;100(D5):8893-918. 21 22 23 1278 172. Bullard JE, Baddock M, Bradwell T, Crusius J, Darlington E, Gaiero D, Gasso S, Gisladottir 24 25 1279 G, Hodgkins R, McCulloch R, McKenna-Neuman C. High-latitude dust in the Earth 26 27 28 1280 system. Reviews of Geophysics. 2016 Jun;54(2):447-85. 29 30 1281 173. Bullard JE, Mockford T. Seasonal and decadal variability of dust observations in the 31 32 33 1282 Kangerlussuaq area, west Greenland. Arctic, Antarctic, and Alpine Research. 2018 Jan 34 35 1283 1;50(1), DOI: 10.1080/15230430.2017.1415854. 36 37 38 1284 174. van den Broeke MR, Duynkerke PG, Oerlemans J. The observed katabatic flow at the 39 40 1285 edge of the Greenland ice sheet during GIMEX-91. Global and Planetary Change. 1994 41 42 1286 Jan 1;9(1-2):3-15. 43 44 45 1287 175. Arnalds O, Dagsson-Waldhauserova P, Olafsson H. The Icelandic volcanic aeolian 46 47 1288 environment: Processes and impacts—A review. Aeolian Research. 2016 Mar 1;20:176- 48 49 50 1289 95. 51 52 53 54 55 56 57 58 59 61 60 Page 63 of 83 Environmental Science: Processes & Impacts

1 2 3 1290 176. Zwaaftink CG, Grythe H, Skov H, Stohl A. Substantial contribution of northern 4 5 6 1291 high-latitude sources to mineral dust in the Arctic. Journal of Geophysical Research: 7 8 1292 Atmospheres. 2016 Nov 27;121(22):13-678. 9 10 11 1293 177. Crusius J, Schroth AW, Gasso S, Moy CM, Levy RC, Gatica M. Glacial flour dust storms in 12 13 1294 the Gulf of Alaska: Hydrologic and meteorological controls and their importance as a 14 15 16 1295 source of bioavailable iron. Geophysical Research Letters. 2011 Mar 1;38(6). 17 18 1296 178. Muhs DR, Budahn JR, McGeehin JP, Bettis III EA, Skipp G, Paces JB, Wheeler EA. Loess 19 20 1297 origin, transport, and deposition over the past 10,000 years, Wrangell-St. Elias National 21 22 23 1298 Park, Alaska. Aeolian Research. 2013 Dec 1;11:85-99. 24 25 1299 179. Dorfman JM, Stoner JS, Finkenbinder MS, Abbott MB, Xuan C, St-Onge G. A 37,000-year 26 27 28 1300 environmental magnetic record of aeolian dust deposition from Burial Lake, Arctic 29 30 1301 Alaska. Quaternary Science Reviews. 2015 Nov 15;128:81-97. 31 32 33 1302 180. Bullard JE. The distribution and biogeochemical importance of high-latitude dust in the 34 35 1303 Arctic and Southern Ocean-Antarctic regions. Journal of Geophysical Research: 36 37 38 1304 Atmospheres. 2017 Mar 16;122(5):3098-103. 39 40 1305 181. Fowler RA, Saros JE, Osburn CL. Shifting DOC concentration and quality in the freshwater 41 42 1306 lakes of the Kangerlussuaq region: An experimental assessment of possible mechanisms. 43 44 45 1307 Arctic, Antarctic, and Alpine Research. 2018 Jan 1;50(1), DOI: 46 47 1308 10.1080/15230430.2018.1436815. 48 49 50 1309 182. Carlsson P, Caron DA. Seasonal variation of phosphorus limitation of bacterial growth in 51 52 1310 a small lake. Limnology and Oceanography. 2001 Jan;46(1):108-20. 53 54 55 56 57 58 59 62 60 Environmental Science: Processes & Impacts Page 64 of 83

1 2 3 1311 183. del Giorgio PA, Newell RE. Phosphorus and DOC availability influence the partitioning 4 5 6 1312 between bacterioplankton production and respiration in tidal marsh ecosystems. 7 8 1313 Environmental microbiology. 2012 May;14(5):1296-307. 9 10 11 1314 184. Smol JP, Wolfe AP, Birks HJ, Douglas MS, Jones VJ, Korhola A, Pienitz R, Rühland K, 12 13 1315 Sorvari S, Antoniades D, Brooks SJ. Climate-driven regime shifts in the biological 14 15 16 1316 communities of arctic lakes. Proceedings of the National Academy of Sciences. 2005 Mar 17 18 1317 22;102(12):4397-402. 19 20 1318 185. Hole L, Engardt M. Climate change impact on atmospheric nitrogen deposition in 21 22 23 1319 northwestern Europe: a model study. AMBIO: A Journal of the Human Environment. 24 25 1320 2008 Feb;37(1):9-18. 26 27 28 1321 186. Kraus JM, Vonesh JR. Fluxes of terrestrial and aquatic carbon by emergent mosquitoes: a 29 30 1322 test of controls and implications for cross-ecosystem linkages. Oecologia. 2012 Dec 31 32 33 1323 1;170(4):1111-22. 34 35 1324 187. Vander Zanden MJ, Gratton C. Blowin’in the wind: reciprocal airborne carbon fluxes 36 37 38 1325 between lakes and land. Canadian Journal of Fisheries and Aquatic Sciences. 2011 Jan 39 40 1326 7;68(1):170-82. 41 42 1327 188. Gratton C, Donaldson J, Vander Zanden MJ. Ecosystem linkages between lakes and the 43 44 45 1328 surrounding terrestrial landscape in northeast Iceland. Ecosystems. 2008 Aug 46 47 1329 1;11(5):764-74. 48 49 50 1330 189. Gratton C, Zanden MJ. Flux of aquatic insect productivity to land: comparison of lentic 51 52 1331 and lotic ecosystems. Ecology. 2009 Oct;90(10):2689-99. 53 54 55 56 57 58 59 63 60 Page 65 of 83 Environmental Science: Processes & Impacts

1 2 3 1332 190. Petersen I, Winterbottom JH, Orton S, Friberg N, Hildrew AG, Spiers DC, Gurney WS. 4 5 6 1333 Emergence and lateral dispersal of adult Plecoptera and Trichoptera from Broadstone 7 8 1334 Stream, UK. Freshwater Biology. 1999 Nov;42(3):401-16. 9 10 11 1335 191. Power ME, Rainey WE, Parker MS, Sabo JL, Smyth A, Khandwala S, Finlay JC, McNeely 12 13 1336 FC, Marsee K, Anderson C. River-to-watershed subsidies in an old-growth conifer forest. 14 15 16 1337 Food webs at the landscape level. 2004 Feb 22:217-40. 17 18 1338 192. Gardarsson A, Einarsson A, Jonsson E, Gislason GM, Olafsson JS, Hrafnsdottir T, Ingvason 19 20 1339 HR. Population indices of Chironomidae at Myvatn over 20 years, 1977–1996. Myvatn, 21 22 23 1340 Iceland: Myvatn Research Station. 2000. 24 25 1341 193. Martin-Creuzburg D, Kowarik C, Straile D. Cross-ecosystem fluxes: Export of 26 27 28 1342 polyunsaturated fatty acids from aquatic to terrestrial ecosystems via emerging insects. 29 30 1343 Science of the Total Environment. 2017 Jan 15;577:174-82. 31 32 33 1344 194. Jonsson M, Wardle DA. The influence of freshwater-lake subsidies on invertebrates 34 35 1345 occupying terrestrial vegetation. Acta Oecologica. 2009 Sep 1;35(5):698-704. 36 37 38 1346 195. Hoekman D, Dreyer J, Jackson RD, Townsend PA, Gratton C. Lake to land subsidies: 39 40 1347 experimental addition of aquatic insects increases terrestrial arthropod densities. 41 42 1348 Ecology. 2011 Nov 1;92(11):2063-72. 43 44 45 1349 196. Hoekman D, Bartrons M, Gratton C. Ecosystem linkages revealed by experimental lake- 46 47 1350 derived isotope signal in heathland food webs. Oecologia. 2012 Nov 1;170(3):735-43. 48 49 50 1351 197. Butler MG. Emergence phenologies of some arctic Alaskan Chironomidae. In 51 52 1352 Chironomidae 1980 Jan 1 (pp. 307-314). Pergamon. 53 54 55 56 57 58 59 64 60 Environmental Science: Processes & Impacts Page 66 of 83

1 2 3 1353 198. Braegelman SD. Seasonality of some Arctic Alaskan chironomids (Doctoral dissertation, 4 5 6 1354 North Dakota State University). 7 8 1355 199. Pearce-Higgins JW, Yalden DW, Whittingham MJ. Warmer springs advance the breeding 9 10 11 1356 phenology of golden plovers Pluvialis apricaria and their prey (Tipulidae). Oecologia. 12 13 1357 2005 Apr 1;143(3):470-6. 14 15 16 1358 200. Madsen J, Reed A, Andreev A. Status and trends of geese (Anser sp., Branta sp.) in the 17 18 1359 world: a review, updating and evaluation. Gibier Faune Sauvage. 1996;13(2):337-53. 19 20 1360 201. Wetlands International. Waterbird population estimates, 4th ed. Wageningen, The 21 22 23 1361 Netherlands: Wetlands International. 2006. 24 25 1362 202. Hahn S, Bauer S, Klaassen M. Estimating the contribution of carnivorous waterbirds to 26 27 28 1363 nutrient loading in freshwater habitats. Freshwater Biology. 2007 Dec;52(12):2421-33. 29 30 1364 203. Côté G, Pienitz R, Velle G, Wang X. Impact of geese on the limnology of lakes and ponds 31 32 33 1365 from Bylot Island (Nunavut, Canada). International Review of Hydrobiology. 2010 34 35 1366 May;95(2):105-29. 36 37 38 1367 204. Hessen DO, Tombre IM, van Geest G, Alfsnes K. Global change and ecosystem 39 40 1368 connectivity: How geese link fields of central Europe to eutrophication of Arctic 41 42 1369 freshwaters. Ambio. 2017 Feb 1;46(1):40-7. 43 44 45 1370 205. Tugend, C.A., III, and Saros, Jasmine E. Effects of Geese and Caribou on Nutrient and 46 47 1371 Carbon Cycling in Southwest Greenland. Thesis for the completion of a Master of 48 49 50 1372 Science degree, University of Maine. 2017. 51 52 1373 206. Michelutti N, Liu H, Smol JP, Kimpe LE, Keatley BE, Mallory M, Macdonald RW, Douglas 53 54 55 1374 MS, Blais JM. Accelerated delivery of polychlorinated biphenyls (PCBs) in recent 56 57 58 59 65 60 Page 67 of 83 Environmental Science: Processes & Impacts

1 2 3 1375 sediments near a large seabird colony in Arctic Canada. Environmental pollution. 2009 4 5 6 1376 Oct 1;157(10):2769-75. 7 8 1377 207. Griffiths K, Michelutti N, Blais JM, Kimpe LE, Smol JP. Comparing nitrogen isotopic 9 10 11 1378 signals between bulk sediments and invertebrate remains in High Arctic seabird- 12 13 1379 influenced ponds. Journal of Paleolimnology. 2010 Aug 1;44(2):405-12. 14 15 16 1380 208. Lund M, Raundrup K, Westergaard-Nielsen A, López-Blanco E, Nymand J, Aastrup P. 17 18 1381 Larval outbreaks in West Greenland: instant and subsequent effects on tundra 19 20 1382 ecosystem productivity and CO exchange. Ambio. 2017 Feb 1;46(1):26-38. 21 2 22 23 1383 209. Post E, Pedersen C. Opposing plant community responses to warming with and without 24 25 1384 herbivores. Proceedings of the National Academy of Sciences. 2008 Aug 26 27 28 1385 26;105(34):12353-8. 29 30 1386 210. Fegel TS, Baron JS, Fountain AG, Johnson GF, Hall EK. The differing biogeochemical and 31 32 33 1387 microbial signatures of glaciers and rock glaciers. Journal of Geophysical Research: 34 35 1388 Biogeosciences. 2016 Mar 1;121(3):919-32. 36 37 38 1389 211. Williams JJ, Nurse A, Saros JE, Riedel J, Beutel M. Effects of glaciers on nutrient 39 40 1390 concentrations and phytoplankton in lakes within the Northern Cascades Mountains 41 42 1391 (USA). Biogeochemistry. 2016 Dec 1;131(3):373-85. 43 44 45 1392 212. Granshaw FD, Fountain AG. Glacier change (1958–1998) in the north Cascades national 46 47 1393 park complex, Washington, USA. Journal of Glaciology. 2006;52(177):251-6. 48 49 50 1394 213. Wilson R, Glasser NF, Reynolds JM, Harrison S, Anacona PI, Schaefer M, Shannon S. 51 52 1395 Glacial lakes of the Central and Patagonian Andes. Global and Planetary Change. 2018 53 54 55 1396 Mar 1;162:275-91. 56 57 58 59 66 60 Environmental Science: Processes & Impacts Page 68 of 83

1 2 3 1397 214. Yao T, Pu J, Lu A, Wang Y, Yu W. Recent glacial retreat and its impact on hydrological 4 5 6 1398 processes on the Tibetan Plateau, China, and surrounding regions. Arctic, Antarctic, and 7 8 1399 Alpine Research. 2007 Nov 1;39(4):642-50. 9 10 11 1400 215. Kehrwald NM, Thompson LG, Tandong Y, Mosley-Thompson E, Schotterer U, Alfimov V, 12 13 1401 Beer J, Eikenberg J, Davis ME. Mass loss on Himalayan glacier endangers water 14 15 16 1402 resources. Geophysical Research Letters. 2008 Nov;35(22). 17 18 1403 216. Zhang G, Xie H, Kang S, Yi D, Ackley SF. Monitoring lake level changes on the Tibetan 19 20 1404 Plateau using ICESat altimetry data (2003–2009). Remote Sensing of Environment. 2011 21 22 23 1405 Jul 15;115(7):1733-42. 24 25 1406 217. Liu J, Wang S, Yu S, Yang D, Zhang L. Climate warming and growth of high-elevation 26 27 28 1407 inland lakes on the Tibetan Plateau. Global and Planetary Change. 2009 Jun 1;67(3- 29 30 1408 4):209-17. 31 32 33 1409 218. Zhang G, Yao T, Xie H, Kang S, Lei Y. Increased mass over the Tibetan Plateau: From lakes 34 35 1410 or glaciers? Geophysical Research Letters. 2013 May 28;40(10):2125-30. 36 37 38 1411 219. Conroy JL, Overpeck JT, Cole JE, Liu KB, Wang L, Ducea MN. Dust and temperature 39 40 1412 influences on glaciofluvial sediment deposition in southwestern Tibet during the last 41 42 1413 millennium. Global and planetary change. 2013 Aug 1;107:132-44. 43 44 45 1414 220. Sommaruga R, Kandolf G. Negative consequences of glacial turbidity for the survival of 46 47 1415 freshwater planktonic heterotrophic flagellates. Scientific reports. 2014 Feb 17;4:4113. 48 49 50 1416 221. Bonalumi M, Anselmetti FS, Kaegi R, Wüest A. Particle dynamics in high-Alpine proglacial 51 52 1417 reservoirs modified by pumped-storage operation. Water Resources Research. 2011 53 54 55 1418 Sep;47(9), DOI: 10.1029/2010WR010262. 56 57 58 59 67 60 Page 69 of 83 Environmental Science: Processes & Impacts

1 2 3 1419 222. Leonard EM, Reasoner MA. A continuous Holocene glacial record inferred from 4 5 6 1420 proglacial lake sediments in Banff National Park, Alberta, Canada. Quaternary Research. 7 8 1421 1999 Jan;51(1):1-13. 9 10 11 1422 223. Vinebrooke RD, Thompson PL, Hobbs W, Luckman BH, Graham MD, Wolfe AP. Glacially 12 13 1423 mediated impacts of climate warming on alpine lakes of the Canadian Rocky Mountains. 14 15 16 1424 Internationale Vereinigung für theoretische und angewandte Limnologie: 17 18 1425 Verhandlungen. 2010 Jan 1;30(9):1449-52. 19 20 1426 224. Brown GH, Tranter M, Sharp MJ. Experimental investigations of the weathering of 21 22 23 1427 suspended sediment by alpine glacial meltwater. Hydrological Processes. 1996 24 25 1428 Apr;10(4):579-97. 26 27 28 1429 225. Koenings JP, Burkett RD, Edmundson JM. The exclusion of limnetic Cladocera from 29 30 1430 turbid glacier-meltwater lakes. Ecology. 1990 Feb;71(1):57-67. 31 32 33 1431 226. Gilbert R, Crookshanks S. Sediment waves in a modern high-energy glacilacustrine 34 35 1432 environment. Sedimentology. 2009 Apr;56(3):645-59. 36 37 38 1433 227. Sommaruga R. When glaciers and ice sheets melt: consequences for planktonic 39 40 1434 organisms. Journal of plankton research. 2015 Apr 29;37(3):509-18. 41 42 1435 228. Sterner RW, Elser JJ, Fee EJ, Guildford SJ, Chrzanowski TH. The light: nutrient ratio in 43 44 45 1436 lakes: the balance of energy and materials affects ecosystem structure and process. The 46 47 1437 American Naturalist. 1997 Dec;150(6):663-84. 48 49 50 1438 229. Laspoumaderes C, Modenutti B, Souza MS, Bastidas Navarro M, Cuassolo F, Balseiro E. 51 52 1439 Glacier melting and stoichiometric implications for lake community structure: 53 54 55 56 57 58 59 68 60 Environmental Science: Processes & Impacts Page 70 of 83

1 2 3 1440 zooplankton species distributions across a natural light gradient. Global change biology. 4 5 6 1441 2013 Jan;19(1):316-26. 7 8 1442 230. Peter H, Sommaruga R. Alpine glacier-fed turbid lakes are discontinuous cold polymictic 9 10 11 1443 rather than dimictic. Inland Waters. 2017 Jan 2;7(1):45-54. 12 13 1444 231. Hall MH, Fagre DB. Modeled climate-induced glacier change in Glacier National Park, 14 15 16 1445 1850–2100. BioScience. 2003 Feb 1;53(2):131-40. 17 18 1446 232. Paul F, Kääb A, Maisch M, Kellenberger T, Haeberli W. Rapid disintegration of Alpine 19 20 1447 glaciers observed with satellite data. Geophysical research letters. 2004 Nov;31(21), 21 22 23 1448 DOI: 10.1029/2004GL020816. 24 25 1449 233. Psenner R. Living in a dusty world: airborne dust as a key factor for alpine lakes. Water, 26 27 28 1450 Air, and Soil Pollution. 1999 Jun 1;112(3-4):217-27. 29 30 1451 234. Nanus L, Campbell DH, Williams MW. Sensitivity of alpine and subalpine lakes to 31 32 33 1452 acidification from atmospheric deposition in Grand Teton National Park and Yellowstone 34 35 1453 National Park, Wyoming. Denver, Colorado: US Geological Survey; 2005. 36 37 38 1454 235. Williams MW, Tonnessen KA. Critical loads for inorganic nitrogen deposition in the 39 40 1455 Colorado Front Range, USA. Ecological Applications. 2000 Dec;10(6):1648-65. 41 42 1456 236. Howarth RW, Boyer EW, Pabich WJ, Galloway JN. Nitrogen use in the United States from 43 44 45 1457 1961–2000 and potential future trends. AMBIO: A Journal of the Human Environment. 46 47 1458 2002 Mar;31(2):88-97. 48 49 50 1459 237. Hundey EJ, Moser KA, Longstaffe FJ, Michelutti N, Hladyniuk R. Recent changes in 51 52 1460 production in oligotrophic Uinta Mountain lakes, Utah, identified using paleolimnology. 53 54 55 1461 Limnology and Oceanography. 2014 Nov;59(6):1987-2001. 56 57 58 59 69 60 Page 71 of 83 Environmental Science: Processes & Impacts

1 2 3 1462 238. Elser JJ, Marzolf ER, Goldman CR. Phosphorus and nitrogen limitation of phytoplankton 4 5 6 1463 growth in the freshwaters of North America: a review and critique of experimental 7 8 1464 enrichments. Canadian Journal of fisheries and aquatic sciences. 1990 Jul 1;47(7):1468- 9 10 11 1465 77. 12 13 1466 239. Nydick KR, Lafrancois BM, Baron JS, Johnson BM. Lake-specific responses to elevated 14 15 16 1467 atmospheric nitrogen deposition in the Colorado Rocky Mountains, USA. Hydrobiologia. 17 18 1468 2003 Dec 1;510(1-3):103-14. 19 20 1469 240. Fenn ME, Baron JS, Allen EB, Rueth HM, Nydick KR, Geiser L, Bowman WD, Sickman JO, 21 22 23 1470 Meixner T, Johnson DW, Neitlich P. Ecological effects of nitrogen deposition in the 24 25 1471 western United States. BioScience. 2003 Apr 1;53(4):404-20. 26 27 28 1472 241. Bergström AK, Jansson M. Atmospheric nitrogen deposition has caused nitrogen 29 30 1473 enrichment and eutrophication of lakes in the northern hemisphere. Global Change 31 32 33 1474 Biology. 2006 Apr;12(4):635-43. 34 35 1475 242. Elser JJ, Andersen T, Baron JS, Bergström AK, Jansson M, Kyle M, Nydick KR, Steger L, 36 37 38 1476 Hessen DO. Shifts in lake N:P stoichiometry and nutrient limitation driven by 39 40 1477 atmospheric nitrogen deposition. Science. 2009 Nov 6;326(5954):835-7. 41 42 1478 243. Pardo LH, Fenn ME, Goodale CL, Geiser LH, Driscoll CT, Allen EB, Baron JS, Bobbink R, 43 44 45 1479 Bowman WD, Clark CM, Emmett B. Effects of nitrogen deposition and empirical nitrogen 46 47 1480 critical loads for ecoregions of the United States. Ecological Applications. 2011 48 49 50 1481 Dec;21(8):3049-82. 51 52 53 54 55 56 57 58 59 70 60 Environmental Science: Processes & Impacts Page 72 of 83

1 2 3 1482 244. Goldman CR. Primary productivity, nutrients, and transparency during the early onset of 4 5 6 1483 eutrophication in ultra-oligotrophic Lake Tahoe, California-Nevada. Limnology and 7 8 1484 Oceanography. 1988 Nov;33(6):1321-33. 9 10 11 1485 245. Jassby AD, Reuter JE, Axler RP, Goldman CR, Hackley SH. Atmospheric deposition of 12 13 1486 nitrogen and phosphorus in the annual nutrient load of Lake Tahoe (California-Nevada). 14 15 16 1487 Water Resources Research. 1994 Jul;30(7):2207-16. 17 18 1488 246. Sickman JO, Melack JM, Clow DW. Evidence for nutrient enrichment of high-elevation 19 20 1489 lakes in the Sierra Nevada, California. Limnology and Oceanography. 2003 21 22 23 1490 Sep;48(5):1885-92. 24 25 1491 247. Baron J, Norton SA, Beeson DR, Herrmann R. Sediment diatom and metal stratigraphy 26 27 28 1492 from Rocky Mountain lakes with special reference to atmospheric deposition. Canadian 29 30 1493 Journal of Fisheries and Aquatic Sciences. 1986 Jul 1;43(7):1350-62. 31 32 33 1494 248. Spaulding SA, Otu MK, Wolfe AP, Baron JS. Paleolimnological records of nitrogen 34 35 1495 deposition in shallow, high-elevation lakes of Grand Teton National Park, Wyoming, 36 37 38 1496 USA. Arctic, Antarctic, and Alpine Research. 2015 Nov 1;47(4):703-17. 39 40 1497 249. Saros JE, Michel TJ, Interlandi SJ, Wolfe AP. Resource requirements of Asterionella 41 42 1498 formosa and Fragilaria crotonensis in oligotrophic alpine lakes: implications for recent 43 44 45 1499 phytoplankton community reorganizations. Canadian Journal of Fisheries and Aquatic 46 47 1500 Sciences. 2005 Jul 1;62(7):1681-9. 48 49 50 1501 250. Köster D, Pienitz R. Seasonal diatom variability and paleolimnological inferences–a case 51 52 1502 study. Journal of Paleolimnology. 2006 Feb 1;35(2):395-416. 53 54 55 56 57 58 59 71 60 Page 73 of 83 Environmental Science: Processes & Impacts

1 2 3 1503 251. Saros JE, Stone JR, Pederson GT, Slemmons KE, Spanbauer T, Schliep A, Cahl D, 4 5 6 1504 Williamson CE, Engstrom DR. Climate-induced changes in lake ecosystem structure 7 8 1505 inferred from coupled neo-and paleoecological approaches. Ecology. 2012 9 10 11 1506 Oct;93(10):2155-64. 12 13 1507 252. Zannetti P. Dry and Wet Deposition. In Air Pollution Modeling 1990 (pp. 249-262). 14 15 16 1508 Springer, Boston, MA. 17 18 1509 253. Burns DA. Atmospheric nitrogen deposition in the Rocky Mountains of Colorado and 19 20 1510 southern Wyoming—a review and new analysis of past study results. Atmospheric 21 22 23 1511 Environment. 2003 Mar 1;37(7):921-32. 24 25 1512 254. Butler TJ, Likens GE, Vermeylen FM, Stunder BJ. The impact of changing nitrogen oxide 26 27 28 1513 emissions on wet and dry nitrogen deposition in the northeastern USA. Atmospheric 29 30 1514 Environment. 2005 Sep 1;39(27):4851-62. 31 32 33 1515 255. Morales-Baquero R, Pulido-Villena E, Reche I. Atmospheric inputs of phosphorus and 34 35 1516 nitrogen to the southwest Mediterranean region: Biogeochemical responses of high 36 37 38 1517 mountain lakes. Limnology and Oceanography. 2006 Mar;51(2):830-7. 39 40 1518 256. Mahowald N, Jickells TD, Baker AR, Artaxo P, Benitez-Nelson CR, Bergametti G, Bond TC, 41 42 1519 Chen Y, Cohen DD, Herut B, Kubilay N. Global distribution of atmospheric phosphorus 43 44 45 1520 sources, concentrations and deposition rates, and anthropogenic impacts. Global 46 47 1521 biogeochemical cycles. 2008 Dec;22(4), DOI: 10.1029/2008GB003240. 48 49 50 1522 257. Liu X, Yu Z, Dong H, Chen HF. A less or more dusty future in the Northern Qinghai- 51 52 1523 Tibetan Plateau? Scientific reports. 2014 Oct 22;4:6672. 53 54 55 56 57 58 59 72 60 Environmental Science: Processes & Impacts Page 74 of 83

1 2 3 1524 258. Bao Y, Bräuning A, Yafeng S. Late Holocene temperature fluctuations on the Tibetan 4 5 6 1525 Plateau. Quaternary Science Reviews. 2003 Nov 1;22(21-22):2335-44. 7 8 1526 259. Thompson LG, Yao T, Mosley-Thompson E, Davis ME, Henderson KA, Lin PN. A high- 9 10 11 1527 resolution millennial record of the South Asian monsoon from Himalayan ice cores. 12 13 1528 Science. 2000 Sep 15;289(5486):1916-9. 14 15 2+ 16 1529 260. Brahney J, Ballantyne AP, Sievers C, Neff JC. Increasing Ca deposition in the western 17 18 1530 US: The role of mineral aerosols. Aeolian Research. 2013 Sep 1;10:77-87. 19 20 1531 261. Brahney J, Mahowald N, Ward DS, Ballantyne AP, Neff JC. Is atmospheric phosphorus 21 22 23 1532 pollution altering global alpine Lake stoichiometry? Global Biogeochemical Cycles. 2015 24 25 1533 Sep;29(9):1369-83. 26 27 28 1534 262. Brahney J, Ballantyne AP, Kociolek P, Spaulding S, Otu M, Porwoll T, Neff JC. Dust 29 30 1535 mediated transfer of phosphorus to alpine lake ecosystems of the Wind River Range, 31 32 33 1536 Wyoming, USA. Biogeochemistry. 2014 Aug 1;120(1-3):259-78. 34 35 1537 263. Moulin C, Lambert CE, Dulac F, Dayan U. Control of atmospheric export of dust from 36 37 38 1538 North Africa by the North Atlantic Oscillation. Nature. 1997 Jun;387(6634):691. 39 40 1539 264. Pulido-Villena E, Reche I, Morales-Baquero R. Evidence of an atmospheric forcing on 41 42 1540 bacterioplankton and phytoplankton dynamics in a high mountain lake. Aquatic 43 44 45 1541 sciences. 2008 Apr 1;70(1):1-9. 46 47 1542 265. Reche I, Ortega-Retuerta E, Romera O, Villena EP, Baquero RM, Casamayor EO. Effect of 48 49 50 1543 Saharan dust inputs on bacterial activity and community composition in Mediterranean 51 52 1544 lakes and reservoirs. Limnology and Oceanography. 2009 May;54(3):869-79. 53 54 55 56 57 58 59 73 60 Page 75 of 83 Environmental Science: Processes & Impacts

1 2 3 1545 266. Mladenov N, Lípez-Ramos J, McKnight DM, Rechea I. Alpine lake optical properties as 4 5 6 1546 sentinels of dust deposition and global change. Limnology and oceanography. 2009 7 8 1547 Nov;54(6part2):2386-400. 9 10 11 1548 267. Mladenov N, Pulido-Villena E, Morales-Baquero R, Ortega-Retuerta E, Sommaruga R, 12 13 1549 Reche I. Spatiotemporal drivers of dissolved organic matter in high alpine lakes: Role of 14 15 16 1550 Saharan dust inputs and bacterial activity. Journal of Geophysical Research: 17 18 1551 Biogeosciences. 2008 Jun 1;113(G2), DOI: 10.1029/2008JG000699. 19 20 1552 268. Peter H, Hörtnagl P, Reche I, Sommaruga R. Bacterial diversity and composition during 21 22 23 1553 rain events with and without Saharan dust influence reaching a high mountain lake in 24 25 1554 the Alps. Environmental microbiology reports. 2014 Dec;6(6):618-24. 26 27 28 1555 269. Burns DA, Blett T, Haeuber R, Pardo LH. Critical loads as a policy tool for protecting 29 30 1556 ecosystems from the effects of air pollutants. Frontiers in Ecology and the Environment. 31 32 33 1557 2008 Apr;6(3):156-9. 34 35 1558 270. Nelson JS, Paetz MJ. The fishes of Alberta. University of Alberta; 1992. 36 37 38 1559 271. Knapp RA. Non-native trout in natural lakes of the Sierra Nevada: an analysis of their 39 40 1560 distribution and impacts on native aquatic biota. In Sierra Nevada ecosystem project: 41 42 1561 final report to Congress 1996 (Vol. 3, pp. 363-407). 43 44 45 1562 272. Miró A, Ventura M. Historical use, fishing management and lake characteristics explain 46 47 1563 the presence of non-native trout in Pyrenean lakes: Implications for conservation. 48 49 50 1564 Biological Conservation. 2013 Nov 1;167:17-24. 51 52 53 54 55 56 57 58 59 74 60 Environmental Science: Processes & Impacts Page 76 of 83

1 2 3 1565 273. Tiberti R, Nelli L, Brighenti S, Iacobuzio R, Rolla M. Spatial distribution of introduced 4 5 6 1566 brook trout Salvelinus fontinalis (Salmonidae) within alpine lakes: evidences from a fish 7 8 1567 eradication campaign. The European Zoological Journal. 2017 Jan 1;84(1):73-88. 9 10 11 1568 274. Finlay JC, Vredenburg VT. Introduced trout sever trophic connections in watersheds: 12 13 1569 consequences for a declining amphibian. Ecology. 2007 Sep;88(9):2187-98. 14 15 16 1570 275. Knapp RA. Effects of nonnative fish and habitat characteristics on lentic herpetofauna in 17 18 1571 Yosemite National Park, USA. Biological Conservation. 2005 Jan 1;121(2):265-79. 19 20 1572 276. Matthews KR, Pope KL, Preisler HK, Knapp RA. Effects of nonnative trout on Pacific 21 22 23 1573 treefrogs (Hyla regilla) in the Sierra Nevada. Copeia. 2001 Dec;2001(4):1130-7. 24 25 1574 277. Welsh Jr HH, Pope KL, Boiano D. Sub-alpine amphibian distributions related to species 26 27 28 1575 palatability to non-native salmonids in the Klamath mountains of northern California. 29 30 1576 Diversity and Distributions. 2006 May;12(3):298-309. 31 32 33 1577 278. Rachowicz LJ, Knapp RA, Morgan JA, Stice MJ, Vredenburg VT, Parker JM, Briggs CJ. 34 35 1578 Emerging infectious disease as a proximate cause of amphibian mass mortality. Ecology. 36 37 38 1579 2006 Jul;87(7):1671-83. 39 40 1580 279. Epanchin PN, Knapp RA, Lawler SP. Nonnative trout impact an alpine-nesting bird by 41 42 1581 altering aquatic-insect subsidies. Ecology. 2010 Aug;91(8):2406-15. 43 44 45 1582 280. Fritz KA, Whiles MR, Trushenski JT. Subsidies of long-chain polyunsaturated fatty acids 46 47 1583 from aquatic to terrestrial environments via amphibian emergence. Freshwater Biology. 48 49 50 1584 2019 May;64(5):832-42. 51 52 1585 281. Brett MT, Müller-Navarra DC. The role of highly unsaturated fatty acids in aquatic 53 54 55 1586 foodweb processes. Freshwater Biology. 1997 Dec;38(3):483-99. 56 57 58 59 75 60 Page 77 of 83 Environmental Science: Processes & Impacts

1 2 3 1587 282. Arts MT, Kohler CC. Health and condition in fish: the influence of lipids on membrane 4 5 6 1588 competency and immune response. In Lipids in Aquatic Ecosystems 2009 (pp. 237-256). 7 8 1589 Springer, New York, NY. 9 10 11 1590 283. Parrish CC. Essential fatty acids in aquatic food webs. In Lipids in Aquatic Ecosystems 12 13 1591 2009 (pp. 309-326). Springer, New York, NY. 14 15 16 1592 284. Gladyshev MI, Sushchik NN, Makhutova ON. Production of EPA and DHA in aquatic 17 18 1593 ecosystems and their transfer to the land. Prostaglandins & Other Lipid Mediators. 2013 19 20 1594 Dec 1;107:117-26. 21 22 23 1595 285. Hixson SM, Sharma B, Kainz MJ, Wacker A, Arts MT. Production, distribution, and 24 25 1596 abundance of long-chain omega-3 polyunsaturated fatty acids: a fundamental 26 27 28 1597 dichotomy between freshwater and terrestrial ecosystems. Environmental Reviews. 29 30 1598 2015 Aug 25;23(4):414-24. 31 32 33 1599 286. Gladyshev MI, Sushchik NN, Anishchenko OV, Makhutova ON, Kolmakov VI, Kalachova 34 35 1600 GS, Kolmakova AA, Dubovskaya OP. Efficiency of transfer of essential polyunsaturated 36 37 38 1601 fatty acids versus organic carbon from producers to consumers in a eutrophic reservoir. 39 40 1602 Oecologia. 2011 Feb 1;165(2):521-31. 41 42 1603 287. Gladyshev MI, Arts MT, Sushchik NI. Preliminary estimates of the export of omega-3 43 44 45 1604 highly unsaturated fatty acids (EPA+ DHA) from aquatic to terrestrial ecosystems. In 46 47 1605 Lipids in Aquatic Ecosystems 2009 (pp. 179-210). Springer, New York, NY. 48 49 50 1606 288. Gladyshev MI, Krylov AV, Sushchik NN, Malin MI, Makhutova ON, Chalova IV, Kalacheva 51 52 1607 GS. Transfer of essential polyunsaturated fatty acids from an aquatic to terrestrial 53 54 55 56 57 58 59 76 60 Environmental Science: Processes & Impacts Page 78 of 83

1 2 3 1608 ecosystem through the fish-bird trophic pair. In Doklady Biological Sciences 2010 Apr 1 4 5 6 1609 (Vol. 431, No. 1, p. 121). Springer Science & Business Media. 7 8 1610 289. Gladyshev MI, Kharitonov AY, Popova ON, Sushchik NN, Makhutova ON, Kalacheva GS. 9 10 11 1611 Quantitative estimation of dragonfly role in transfer of essential polyunsaturated fatty 12 13 1612 acids from aquatic to terrestrial ecosystems. In Doklady Biochemistry and Biophysics 14 15 16 1613 2011 Jun 1 (Vol. 438, No. 1, pp. 141-143). MAIK Nauka/Interperiodica. 17 18 1614 290. Yermokhin MV, Sushchik NN, Tabachishin VG, Kalacheva GS, Kolmakova AA, Gladyshev 19 20 1615 MI. Amphibia as a Vector of Transfer of Long-Chain Polyunsaturated Omega-3 Fatty 21 22 23 1616 Acids from Aquatic to Terrestrial Ecosystems. In Doklady Biochemistry and Biophysics 24 25 1617 2018 Jul 1 (Vol. 481, No. 1, pp. 195-197). Pleiades Publishing. 26 27 28 1618 291. Serreze MC, Barrett AP, Stroeve JC, Kindig DN, Holland MM. The emergence of surface- 29 30 1619 based Arctic amplification. The Cryosphere. 2009 Feb 4;3(1):11-9. 31 32 33 1620 292. Pepin N, Bradley RS, Diaz HF, Baraër M, Caceres EB, Forsythe N, Fowler H, Greenwood G, 34 35 1621 Hashmi MZ, Liu XD, Miller JR. Elevation-dependent warming in mountain regions of the 36 37 38 1622 world. Nature Climate Change. 2015 May;5(5):424. 39 40 1623 293. Saros JE, Northington RM, Osburn CL, Burpee BT, John Anderson N. Thermal 41 42 1624 stratification in small arctic lakes of southwest Greenland affected by water 43 44 45 1625 transparency and epilimnetic temperatures. Limnology and Oceanography. 2016 46 47 1626 Jul;61(4):1530-42. 48 49 50 1627 294. Nürnberg GK. The prediction of internal phosphorus load in lakes with anoxic 51 52 1628 hypolimnia. Limnology and oceanography. 1984 Jan;29(1):111-24. 53 54 55 56 57 58 59 77 60 Page 79 of 83 Environmental Science: Processes & Impacts

1 2 3 1629 295. Kling GW, Kipphut GW, Miller MC. Arctic lakes and streams as gas conduits to the 4 5 6 1630 atmosphere: implications for tundra carbon budgets. Science. 1991 Jan 7 8 1631 18;251(4991):298-301. 9 10 11 1632 296. Tranvik LJ, Downing JA, Cotner JB, Loiselle SA, Striegl RG, Ballatore TJ, Dillon P, Finlay K, 12 13 1633 Fortino K, Knoll LB, Kortelainen PL. Lakes and reservoirs as regulators of carbon cycling 14 15 16 1634 and climate. Limnology and oceanography. 2009 Nov;54(6part2):2298-314. 17 18 1635 297. Northington RM, Saros JE. Factors controlling methane in arctic lakes of southwest 19 20 1636 Greenland. PloS one. 2016 Jul 25;11(7), DOI: 10.1371/journal.pone.0159642. 21 22 23 1637 298. Molot LA, Dillon PJ. Nitrogen mass balances and denitrification rates in central Ontario 24 25 1638 lakes. Biogeochemistry. 1993 Sep 1;20(3):195-212. 26 27 28 1639 299. Kropáček J, Maussion F, Chen F, Hoerz S, Hochschild V. Analysis of ice phenology of lakes 29 30 1640 on the Tibetan Plateau from MODIS data. The Cryosphere. 2013;7(1):287. 31 32 33 1641 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 78 60 Environmental Science: Processes & Impacts Page 80 of 83

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 81 of 83 Environmental Science: Processes & Impacts

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Environmental Science: Processes & Impacts Page 82 of 83

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 83 of 83 Environmental Science: Processes & Impacts

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60