AQUATIC PLANT COMMUNITIES AND RAPID WATER LEVEL CHANGE: EXAMINING LONG-TERM PATTERNS IN FISH LAKE, WISCONSIN, USA

Fish Lake, a core study site in southern Wisconsin for the North Temperate Lakes Long-Term Ecological Research (NTL-LTER) program, provides an extreme example of lake level rise. Surface water elevation has steadily risen >5m since the 1960s then rapidly increased by 3m from 2017 to 2021. Rising water has displaced the littoral zone upwards and inundated houses, roads, trees, and other terrestrial substrates to create novel littoral habitats in the lake. Our objectives were to determine how macrophyte communities have responded to water level fluctuations and which species have established in the novel nearshore habitats. An analysis of NTL-LTER data from 1995 to 2023 shows that species richness declined by at least 50% in 2008 and 2019 and coincided with dramatic increases in lake level. Submersed plants growing entirely below the water surface or rooted in the sediment including Potamogeton crispus and Vallisneria americana declined in years following a rise in water level while species that became more common can employ fast growth or possess flexible stems such as Stuckenia pectinata and Ceratophyllum demersum, respectively. Species that propagate by fragmentation or cloning such as Persicaria amphibia and Chara spp. were present in 2023 when lake levels reached record highs. We hypothesize that changes in macrophyte communities are being driven by water level fluctuations through unknown mechanisms and that some species may be better at colonizing the newly flooded substrate through an advantageous growth form, morphological feature, or reproductive strategy.

Primary Presenter: Cassandra Ceballos, University of Wisconsin-Madison (ceceballos@wisc.edu)

Authors:

Cassandra Ceballos, University of Wisconsin-Madison  (ceceballos@wisc.edu)

Emily Stanley, University of Wisconsin-Madison  (ehstanley@wisc.edu)