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1. Species Abundance Counts of Benthic Diatoms in the Upper Kuparuk River, Alaska, 1997-2022

   https://doi.org/10.18739/A2KW57K95  

   Sahlmann, Lindsey (January 2024, NSF Arctic Data Center)

   This dataset contains species abundance data of epilithic diatoms collected from the Upper Kuparuk River, Alaska (USA), spanning from 1997 to 2022. The dataset is part of a long-term study aimed at understanding the ecological impacts of phosphorus enrichment in Arctic freshwater ecosystems. Samples were collected annually from the river to examine if physical, chemical, biological, weather, and climate variables influence diatom community composition over time. The dataset includes detailed records of diatom species identified and their relative abundances ins the reference reach only. Analyses of this dataset using permutational multivariate analysis of variance (PERMANOVA), canonical correspondence analysis (CCA), and partial canonical correspondence analysis (pCCA) . Analyses reveal significant shifts in diatom community composition over time, closely linked to changes in alkalinity, nitrate + nitrite, total dissolved phosphorus, dissolved organic carbon, and wind speed. We identify specific diatom taxa as bioindicators, highlighting their sensitivity to shifts in alkalinity, nitrate + nitrite, and wind speed. This dataset provides valuable insights on how climate change is reshaping the structure and function of Arctic rivers, underscoring the importance of diatoms as bioindicators in Arctic ecosystems. It serves as an important resource for researchers studying nutrient dynamics, ecological monitoring, and the impacts of climate change on Arctic freshwater systems. 

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2. Toolik Lake soil biogeochemical data from 35 year long term fertilization experiment, 2015

   https://doi.org/10.18739/a2833n104  

   Machmuller, Megan (January 2024, NSF Arctic Data Center)

   Dataset from a nutrient addition experiment in moist acidic tundra at the Arctic Long-Term Ecological Research site near Toolik Lake, Alaska. Established in 1981, the field experiment was originally designed to test the response of Arctic tundra vegetation to chronic press disturbances. The split-block design consisted of 5 x 20 meter (m) fertilized and unfertilized plots in four replicate blocks with 1 m buffer strips that were continuously fertilized since 1981 (10 grams (g) Nitrogen (N )and 5 g Phosphorus (P) square meters (m-2) per year (yr-1)). In the 35th year of fertilization (2015) we collected soil samples to quantify the effect of long-term fertilization on soil carbon and nitrogen stocks. We used an isotope labeling laboratory incubation to evaluate how the observed transition from graminoid- to shrub-dominated tundra influenced microbial metabolism and soil carbon dynamics. 

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3. Long-Term Nutrient Enrichment of an Oligotroph-Dominated Wetland Increases Bacterial Diversity in Bulk Soils and Plant Rhizospheres

   https://doi.org/10.1128/mSphere.00035-20  

   Bledsoe, Regina B.; Goodwillie, Carol; Peralta, Ariane L. (June 2020, mSphere)

   Campbell, Barbara J. (Ed.)

   ABSTRACT In nutrient-limited conditions, plants rely on rhizosphere microbial members to facilitate nutrient acquisition, and in return, plants provide carbon resources to these root-associated microorganisms. However, atmospheric nutrient deposition can affect plant-microbe relationships by changing soil bacterial composition and by reducing cooperation between microbial taxa and plants. To examine how long-term nutrient addition shapes rhizosphere community composition, we compared traits associated with bacterial (fast-growing copiotrophs, slow-growing oligotrophs) and plant (C 3 forb, C 4 grass) communities residing in a nutrient-poor wetland ecosystem. Results revealed that oligotrophic taxa dominated soil bacterial communities and that fertilization increased the presence of oligotrophs in bulk and rhizosphere communities. Additionally, bacterial species diversity was greatest in fertilized soils, particularly in bulk soils. Nutrient enrichment (fertilized versus unfertilized) and plant association (bulk versus rhizosphere) determined bacterial community composition; bacterial community structure associated with plant functional group (grass versus forb) was similar within treatments but differed between fertilization treatments. The core forb microbiome consisted of 602 unique taxa, and the core grass microbiome consisted of 372 unique taxa. Forb rhizospheres were enriched in potentially disease-suppressive bacterial taxa, and grass rhizospheres were enriched in bacterial taxa associated with complex carbon decomposition. Results from this study demonstrate that fertilization serves as a strong environmental filter on the soil microbiome, which leads to distinct rhizosphere communities and can shift plant effects on the rhizosphere microbiome. These taxonomic shifts within plant rhizospheres could have implications for plant health and ecosystem functions associated with carbon and nitrogen cycling. IMPORTANCE Over the last century, humans have substantially altered nitrogen and phosphorus cycling. Use of synthetic fertilizer and burning of fossil fuels and biomass have increased nitrogen and phosphorus deposition, which results in unintended fertilization of historically low-nutrient ecosystems. With increased nutrient availability, plant biodiversity is expected to decline, and the abundance of copiotrophic taxa is anticipated to increase in bacterial communities. Here, we address how bacterial communities associated with different plant functional types (forb, grass) shift due to long-term nutrient enrichment. Unlike other studies, results revealed an increase in bacterial diversity, particularly of oligotrophic bacteria in fertilized plots. We observed that nutrient addition strongly determines forb and grass rhizosphere composition, which could indicate different metabolic preferences in the bacterial communities. This study highlights how long-term fertilization of oligotroph-dominated wetlands could alter diversity and metabolism of rhizosphere bacterial communities in unexpected ways. 

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4. Plant community re-organization and increased productivity due to multi-year nutrient enrichment of a coastal grassland

   https://doi.org/10.1371/journal.pone.0270798  

   Brown, Joseph K.; Moulton, Ashley; Zinnert, Julie C. (July 2022, PLOS ONE)

   Kim, Daehyun (Ed.)

   Nutrient enrichment alters plant community structure and function at a global scale. Coastal plant systems are expected to experience increased rates of nitrogen and phosphorus deposition by 2100, caused mostly by anthropogenic activity. Despite high density of studies investigating connections between plant community structure and ecosystem function in response to nutrient addition, inconsistencies in system response based on the ecosystem in question calls for more detailed analyses of nutrient impacts on community organization and resulting productivity response. Here, we focus on nutrient addition impacts on community structure and organization as well as productivity of different lifeforms in a coastal grassland. We established long-term nutrient enrichment plots in 2015 consisting of control (C), nitrogen (N), phosphorus (P), and nitrogen + phosphorus (NP) treatments. In 2017 we collected graminoid and forb productivity, root productivity, and community composition for each plot. We found no N x P interaction, but N enrichment was a significant main effect on productivity, highlighting N limitation in coastal systems. Importantly, nutrient enrichment treatments did not alter root productivity. However, all treatments caused significant differences in community composition. Using rank abundance curves, we determined that community composition differences were driven by increased dominance of nitrophilous graminoids, re-organization of subordinate species, and species absences in N and NP plots. Results of this study highlight how coastal grassland communities are impacted by nutrient enrichment. We show that community re-organization, increased dominance, and absence of critical species are all important mechanisms that reflect community-level impacts of nutrient enrichment in our coastal grassland site. 

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5. An examination of environmental factors that influence the composition of diatom communities in northern hardwood streams (USA)

   https://doi.org/10.1016/j.indic.2025.100697  

   Sahlmann, Lindsey; Edlund, Mark B; Thellman, Audrey N; Solomon, Christopher T; Morales, Ana M; Keeton, William Scott; Bowden, William B (May 2025, Environmental and Sustainability Indicators)

   Headwater streams draining northern hardwood forests are vulnerable to environmental pressures, including climate change, atmospheric deposition, land-use changes, and recreational impacts. These streams play a crucial role in the forest ecosystem by influencing nutrient dynamics, water quality, and serving as refugia for aquatic species. This study focuses on epiphytic diatom communities that colonize bryophytes within Hubbard Brook Experimental Forest (HBEF), where extensive ecological research exists but with limited data on diatom community composition. Bryophytes provide stable, nutrient-rich microhabitats that support diatom growth, offering refugia from flood scour and accumulating stream sediments, making them useful for studying diatom dynamics. We compared diatom communities colonizing artificial bryophytes across seven streams weir ponds in HBEF in New Hampshire and explored the influence of various environmental factors on species richness. Distinct diatom communities were observed, along with increased species richness under higher light exposure. Further analysis reveals significant variability in diatom communities driven by watershed-specific environmental conditions and temporal changes. A total of 86 diatom taxa spanning 43 genera were identified, with species presence significantly associated with environmental variables such as light intensity (lux), dissolved organic carbon, pH, and total dissolved nitrogen. These findings reinforce the value of Diatoms are sensitive environmental indicators in this study, provide useful insights into ecosystem health and resilience of streams flowing through northern hardwood forests in the face of environmental stressors. 

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