Nitrogen deposition to lakes in national parks of the western Great Lakes region: Isotopic signatures, watershed retention, and algal shifts

Abstract

Atmospheric deposition is a primary source of reactive nitrogen (Nr) to undisturbed watersheds of the Great Lakes region of the U.S., raising concerns over whether enhanced delivery over recent decades has affected lake ecosystems. The National Atmospheric Deposition Program (NADP) has been measuring Nr deposition in this region for over 35 years. Here we explore the relationships among NADP-measured Nr deposition, nitrogen stable isotopes (δ 15 N) in lake sediments, and the response of algal communities in 28 lakes situated in national parks of the western Great Lakes region of the U.S. We find that 36% of the lakes preserve a sediment δ 15 N record that is statistically correlated with some form of Nr deposition (total dissolved inorganic N, nitrate, or ammonium). Furthermore, measured long-term (since 1982) nitrogen biogeochemistry and inferred critical nitrogen loads suggest that watershed nitrogen retention and climate strongly affect whether sediment δ 15 N is related to Nr deposition in lake sediment records. Measurements of algal change over the last~150 years suggest that Nr deposition, in-lake nutrient cycling, and watershed inputs are important factors affecting diatom community composition, in addition to direct climatic effects on lake physical limnology. The findings suggest that bulk sediment δ 15 N does reflect Nr deposition in some instances. In addition, this study highlights the interactive effects of Nr deposition and climate variability.

Effects of Climate Change on Lake Thermal Structure and Biotic Response in Northern Wilderness Lakes

“…The larger and deeper lakes of ISRO, Siskiwit and Richie, had turnovers of 0.46 and 1.14 SD units (Figures 14 and 15). Lake Richie in particular had the highest community turnover rates among the eight lakes ( Figure 14); this wilderness lake has been noted to have periodic cyanobacteria blooms since 2007 [3].…”

“…For the first time in park history, the lake experienced its first recorded noxious cyanobacterial bloom that required park managers to post warning for wilderness campers. This wilderness lake may be experiencing a threshold ecological response [71] as diatom, cyanobacterial, and fish (loss of coregonids) communities are all undergoing dramatic restructuring [3,13,72].…”

“…Significant ecological changes are occurring in remote northern lakes [1][2][3]. These changes do not fit the traditional paradigm of nutrient loading and eutrophication due to obvious land use and may be the result of recent climate warming.…”

“…Recent studies have documented a series of possible climate-induced changes in boreal-region lakes, including a longer ice-free season [4][5][6][7], stronger or weaker thermal stratification [8,9], increased inputs of dissolved organic carbon and increased carbon burial [2,10], shifts in algal communities [1], and an increased frequency of cyanobacterial blooms [3]. These changes have been noted in remote lakes far removed from direct human disturbance, with the strongest evidence coming from the …”

Stimulation of long-term ammonium nitrogen deposition on methanogenesis by Methanocellaceae in a coastal wetland

“…Impacts by nitrogen deposition occur on a global scale, especially in terrestrial ecosystems (Asner et al, 2001;Matson et al, 2002). Meanwhile, nitrogen deposition affects various ecological types, such as marine (Zhang et al, 2010), forest (Zhang et al, 2016), grassland (Gomez-Casanovas et al, 2016), lake (Hobbs et al, 2016), and coastal (Pakeman et al, 2016) systems. Understanding of how nitrogen deposition affects coastal wetlands is limited, although this type of ecosystem is vulnerable to environmental change (Wolters et al, 2016).…”