Long-Term Nutrients Trends, Extreme Hydrologic Conditions and Unprecedented Toxigenic Cyanobacterial Blooms in the Ohio River
Abstract
In 2015 and 2019, unprecedented Microcystis-dominated blooms were reported in the Ohio River and extended 600 and 300 miles, respectively. Given the unusual nature of these extensive blooms, it is imperative to understand nutrient fluxes to the Ohio River system and long-term trends as potential factors driving bloom proliferation. Here, we explored long-term and seasonal trends in the concentration and flux of nutrients in the Ohio River using the Weighted Regressions on Time, Discharge, and Season method (WRTDS). USGS discharge records at four monitoring sites were coupled with nutrient chemistry measured by the Ohio River Valley Water Sanitation Commission (ORSANCO). We also evaluated hydrological shifts in Ohio River discharge using long-term daily average flow during bloom years in 2015 and 2019. Our results indicate that water year flow-normalized (FN) total nitrogen (TN) concentration and flux at the three upstream sites between 1994 and 2019, decreased by -45% and -45%, respectively. In contrast, FN TN concentration and flux increased by 13% and 25%, respectively, at the most downstream site. During the same period, FN TP concentration decreased by -25% and flux increased by 4% at the most upstream site, while FN TP concentration and flux increased by 1.6% and 5.7%, respectively, at the most downstream site. TN and TP fluxes were highest during winter and spring, with lower fluxes in the summer and fall. Our analyses revealed that both bloom years were characterized by extreme wet conditions followed by extreme dry conditions in late summer. Our findings indicate that abnormally long residence times, coupled with warm water and low-flow drought periods, fueled excessive Microcystis growth in 2015 and 2019. Our results highlight the need to develop 1) best management practices that decouple extreme precipitation events from nutrient delivery, and 2) reservoir management approaches that modulate discharge during drought conditions.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.B45L1772B