Floral analysis of a ~140 yr sediment record using sedaDNA and diatoms, Summit Lake Nevada, USA

The sediment fill at Summit Lake shows strong potential for reconstructing past changes (Holocene to present) in the paleoecology and regional paleoclimate for the subalpine region of the Black Rock Range, northwestern Nevada, USA. Summit Lake is a high desert terminal lake with a surface elevation of 1780m.a.s.l. and is a eutrophic, alkaline (~8.4), dimictic lake with a maximum depth of ~10 m and a small surface area (2.8 km²). There is abundant growth of macrophytes, including Polygonium (smartweed), Myriophyllum (milfoil), and Ceratophyllum (coon tail), and growth progresses throughout the summer months. The lake falls within the domain of the Summit Lake Paiute Tribe, who has an inextricable cultural connection to the lake via the native Lahontan cutthroat fishery. The tribe’s original name, Agai Panina Ticutta, translates as the Summit Lake Fish Eaters.

In 2021 and 2022 C.E., we collected a series of surface and long sediment cores from multiple sites in the lake. This study focuses on sediments collected from the lake’s central depocenter. Preliminary age control of Summit Lake sediments is determined by ²¹⁰Pb-dating (corroborated by the stratigraphic profiles of the man-made radionuclides ¹³⁷Cs, ²⁴¹Am) for the upper ~40 cm, and the Mount Mazama tephra (~7.6 ka) at 410cm depth. The age model suggests high and increasing sedimentation rates between early 1900 C.E. and 2021 C.E. (from 0.05 to 1.87 cm/yr). In comparison, the mean sedimentation rate between the Mazama tephra and ~1900 C.E. is low (0.05 cm/yr). We present preliminary sedaDNA and diatom data for the last ca. 140 years. Plant sedaDNA shows good preservation, with a stable alpha diversity of ~40 ASVs. The plant record is dominated by the aquatic plants Myriophyllum and Potamogeton (pondweed) in the upper 40cm, and terrestrial plants are also represented, including sagebrush, willow, aspen, and a variety of herbaceous plants, including aster, rose, primrose, buckwheat, borage, lupin, and saxifrage. The diatom flora of the upper 40cm is dominated by the benthic epiphyte Cocconeis placentula, which is consistent with a large macrophyte community seen in the modern system and indicated by the plant sedaDNA. Modern sampling shows the epiphytic relationship between C. placentula and milfoil. Future work will include pairing and harmonizing the diatom record derived from traditional morphotaxonomy and eDNA, contextualizing the plant eDNA with the modern plant community, and refining the age model to better discern Holocene climate events that may be driving the changes in sediment flux and the floral community. These data will be extended down-core to reconstruct the past climate and lake levels, informing the Tribe’s management efforts for a resilient watershed and fishery in the future.