Catchment influence on nitrate and dissolved organic matter in Alaskan streams across a latitudinal gradient

Harms, Tamara K.; Edmonds, Jennifer W.; Genet, Hélène; Creed, Irena F.; Aldred, David; Balser, A.; Jones, Jeremy B.

doi:10.1002/2015jg003201

Cited by 52 publications

(71 citation statements)

References 108 publications

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“…Average NO x concentrations ranged from 3.1 (Tolovana River) to 20.1 μM (Chena at Two Rivers), whereas average NH 4 + concentrations were typically an order of magnitude lower (ranging between 0.3 and 1.56 μM). Annual NOx (1.7 to 7.3 kmol N year −1 km −2 ) yields were relatively low compared to lower latitude systems (Fulweiler & Nixon, ; Meybeck, ), aligning well with values from other Arctic rivers (Harms et al, ; Holmes et al, ).…”

Section: Resultssupporting

confidence: 58%

Arctic River Dissolved and Biogenic Silicon Exports—Current Conditions and Future Changes With Warming

Carey

Gewirtzman

Johnston

et al. 2020

Global Biogeochemical Cycles

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Silicon (Si) exports from terrestrial to marine systems can dictate phytoplankton species composition in Arctic coastal waters. Diatoms are often the dominant autotroph in Arctic waters, making Si an important control on Arctic marine primary productivity. Yet even as Arctic regions are among the fastest warming on Earth, we lack baseline knowledge on the magnitudes and controls of Arctic river Si exports. To address uncertainties in current and future Si behavior, we used a combination of field data and modeling to quantify daily yields of dissolved Si (DSi) and biogenic Si (BSi) from a 400 km space‐for‐time latitudinal gradient of seven basins across the boreal‐Arctic transition in Alaska (United States) over the course of 2 years (2015–2016). Mean annual DSi concentrations (33–149 μM) and yields (13–49 kmol km−2 year−1) were significantly and positively correlated with mean basin active layer depth, indicating that permafrost thaw will likely increase DSi fluxes to Arctic coastal waters. Conversely, BSi concentrations (7–16 μM) and yields (2.6–4.5 kmol km−2 year−1) were more uniform across the seven basins, indicating that warming may not substantially alter BSi loads to coastal systems in the near future. Our data also indicate that climatic warming will advance the timing of Si delivery to coastal waters in the spring, although the ratios of Si to nitrogen in Arctic river exports will likely remain steady. These results highlight the important role of basin hydrology, largely driven by permafrost extent, as a key driver of Si exchange at the land‐sea interface in the Arctic.

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Section: Resultssupporting

confidence: 58%

Arctic River Dissolved and Biogenic Silicon Exports—Current Conditions and Future Changes With Warming

Carey

Gewirtzman

Johnston

et al. 2020

Global Biogeochemical Cycles

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“…Along the same line, patterns in lake dissolved organic carbon (DOC) within an individual region are mainly related to lake area and perimeter (Frost et al, ), but at the global scale the main drivers are long‐term averages of precipitation, runoff and soil carbon content (Sobek, Tranvik, Prairie, Kortelainen, & Cole, ). Other studies have shown that carbon and nitrogen cycles in high‐latitude catchments have been linked to climate and permafrost at continental scales, but to watershed characteristics at regional scales (Harms et al, ). Together, these studies show the scale dependence of ecosystem‐level relationships in different regions of the globe, and here we have quantified this effect and explicitly demonstrated the importance of spatial structure in understanding ecosystem relationships at the macroscale.…”

Section: Discussionmentioning

confidence: 99%

Similarity in spatial structure constrains ecosystem relationships: Building a macroscale understanding of lakes

Lapierre

Collins

Seekell

et al. 2018

Global Ecol Biogeogr

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Aim We aimed to measure the dominant spatial patterns in ecosystem properties (such as nutrients and measures of primary production) and the multi‐scaled geographical driver variables of these properties and to quantify how the spatial structure of pattern in all of these variables influences the strength of relationships among them. Location and time period We studied > 8,500 lakes in a 1.8 million km2 area of Northeast U.S.A. Data comprised 10‐year medians (2002–2011) for measured ecosystem properties, long‐term climate averages and recent land use/land cover variables. Major taxa studied We focused on ecosystem properties at the base of aquatic food webs, including concentrations of nutrients and algal pigments that are proxies of primary productivity. Methods We quantified spatial structure in ecosystem properties and their geographical driver variables using distance‐based Moran eigenvector maps (dbMEMs). We then compared the similarity in spatial structure for all pairs of variables with the correlation between variables to illustrate how spatial structure constrains relationships among ecosystem properties. Results The strength of spatial structure decreased in order for climate, land cover/use, lake ecosystem properties and lake and landscape morphometry. Having a comparable spatial structure is a necessary condition to observe a strong relationship between a pair of variables, but not a sufficient one; variables with very different spatial structure are never strongly correlated. Lake ecosystem properties tended to have an intermediary spatial structure compared with that of their main drivers, probably because climate and landscape variables with known ecological links induce spatial patterns. Main conclusion Our empirical results describe inherent spatial constraints that dictate the expected relationships between ecosystem properties and their geographical drivers at macroscales. Our results also suggest that understanding the spatial scales at which ecological processes operate is necessary to predict the effects of multi‐scaled environmental changes on ecosystem properties.

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“…Mineralized N is frequently a limiting nutrient in Arctic ecosystems (Dormann and Woodin ), the fate of which is key to understanding changes in the availability of nutrients to catchment vegetation and lake biota. Where the permafrost underlying tundra has started to thaw (e.g., North Slope of Alaska) (McClelland et al ; Harms and Ludwig ; Harms et al ), there have been dramatic changes in nutrient soil water interactions. Deepening of the active layer leads to enhanced soil organic matter decomposition rates and consequently to greater N mineralization.…”

Section: Discussionmentioning

confidence: 99%

Regional variability in the atmospheric nitrogen deposition signal and its transfer to the sediment record in Greenland lakes

Anderson

Curtis

Whiteford

et al. 2018

Limnology & Oceanography

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Disruption of the nitrogen cycle is a major component of global environmental change. δ15N in lake sediments is increasingly used as a measure of reactive nitrogen input but problematically, the characteristic depleted δ15N signal is not recorded at all sites. We used a regionally replicated sampling strategy along a precipitation and N‐deposition gradient in SW Greenland to assess the factors determining the strength of δ15N signal in lake sediment cores. Analyses of snowpack N and δ15N‐NO3 and water chemistry were coupled with bulk sediment δ15N. Study sites cover a gradient of snowpack δ15N (ice sheet: −6‰; coast −10‰), atmospheric N deposition (ice sheet margin: ∼ 0.2 kg ha−1 yr−1; coast: 0.4 kg ha−1 yr−1) and limnology. Three 210Pb‐dated sediment cores from coastal lakes showed a decline in δ15N of ca. −1‰ from ∼ 1860, reflecting the strongly depleted δ15N of snowpack N, lower in‐lake total N (TN) concentration (∼ 300 μg N L−1) and a higher TN‐load. Coastal lakes have 3.7–7.1× more snowpack input of nitrate than inland sites, while for total deposition the values are 1.7–3.6× greater for lake and whole catchment deposition. At inland sites and lakes close to the ice‐sheet margin, a lower atmospheric N deposition rate and larger in‐lake TN pool resulted in greater reliance on N‐fixation and recycling (mean sediment δ15N is 0.5–2.5‰ in most inland lakes; n = 6). The primary control of the transfer of the atmospheric δ15N deposition signal to lake sediments is the magnitude of external N inputs relative to the in‐lake N‐pool.

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Catchment influence on nitrate and dissolved organic matter in Alaskan streams across a latitudinal gradient

Cited by 52 publications

References 108 publications

Arctic River Dissolved and Biogenic Silicon Exports—Current Conditions and Future Changes With Warming

Arctic River Dissolved and Biogenic Silicon Exports—Current Conditions and Future Changes With Warming

Similarity in spatial structure constrains ecosystem relationships: Building a macroscale understanding of lakes

Regional variability in the atmospheric nitrogen deposition signal and its transfer to the sediment record in Greenland lakes

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