AUTHOR=Harrow-Lyle Tyler J. , Kirkwood Andrea E. 

TITLE=Low Benthic Oxygen and High Internal Phosphorus-Loading are Strongly Associated With the Invasive Macrophyte Nitellopsis obtusa (starry stonewort) in a Large, Polymictic Lake

JOURNAL=Frontiers in Environmental Science

VOLUME=9

YEAR=2021

URL=https://www.frontiersin.org/journals/environmental-science/articles/10.3389/fenvs.2021.735509

DOI=10.3389/fenvs.2021.735509

ISSN=2296-665X

ABSTRACT=<p>Lake Scugog is an important headwater to the Trent Severn-Waterway in Ontario, Canada. In recent years, notable ecosystem-level changes have occurred coinciding with the emergence of the non-native invasive charophyte <italic>Nitellopsis obtusa</italic>. Despite <italic>N. obtusa</italic> arriving in North America in the early 1970s, studies documenting the impact of <italic>N. obtusa</italic> on invaded ecosystems are scarce. Given the increasing dominance of <italic>N. obtusa</italic> in inland waters of the Great Lakes basin, we investigated the ecosystem-level impacts of <italic>N. obtusa</italic> in Lake Scugog over a 3-year period. We show for the first time a strong association between <italic>N. obtusa</italic> occurrence and biomass with benthic anoxia in this shallow, polymictic lake. Benthic dissolved oxygen concentrations were significantly lower (<italic>p</italic>-value &lt; 0.001) at sites with <italic>N. obtusa</italic> compared to sites without <italic>N. obtusa</italic>. Additionally, <italic>N. obtusa</italic> biomass was a negative predictor of near-bed oxygen concentration (<italic>R</italic><sup>2</sup> = 0.59, <italic>p</italic>-value &lt; 0.001). Knowing that anoxia can promote the internal loading of phosphorus, we measured soluble reactive phosphorus (SRP) in the pore-water of sediments at each site, and found <italic>N. obtusa</italic> biomass explained 90% of sediment pore-water SRP (<italic>R</italic><sup>2</sup> = 0.90, <italic>p</italic>-value &lt; 0.001). These notable associations between <italic>N. obtusa</italic> and key lake elements indicates that <italic>N. obtusa</italic> may be acting as an ecosystem engineer in invaded lakes by altering the biogeochemical fate of oxygen and phosphorus.</p>