Coastal Salinity Index Monitoring Drought on the Gulf

Coastal Salinity Index: Monitoring Drought on the Gulf and Atlantic Coasts PRESENTER: Kirsten Lackstrom, Carolinas Integrated Sciences & Assessments (CISA) CO-AUTHORS: Paul Conrads (USGS), Bryan Mc. Closkey (USGS), Lauren Rouen (CISA) 98 th American Meteorological Society Annual Meeting January 8, 2018

What does drought look like… … on the coast? Source: Dan Tufford Source: Ed Christopher Source: CISA Coastal Salinity Index: Monitoring Drought on the Gulf and Atlantic Coasts Source: USFS

Drought and coastal ecosystems • Salinity is a key stressor • Focus of the Coastal Carolinas Drought Early Warning System (DEWS) • “Can a unique index be developed to characterize coastal drought? ” Coastal Salinity Index: Monitoring Drought on the Gulf and Atlantic Coasts

Coastal Salinity Index (CSI) • Similar approach to the Standardized Precipitation Index (SPI) • Conrads and Darby (2017) https: //doi. org/10. 1175/BAMS-D-15 -00171. 1 • Indicates drought and wetter conditions over multiple time periods • 1 - to 24 -months • Indicator of salinity changes and location of the freshwater-saltwater interface Coastal Salinity Index: Monitoring Drought on the Gulf and Atlantic Coasts

Computation • Calculated at 30 sites • Florida • South Carolina • R-package for consistent calculation created in 2017 • Next step is testing Coastal Salinity Index: Monitoring Drought on the Gulf and Atlantic Coasts

Salinity Data • Sources ◦ ◦ USGS NERRS University research State agencies • Availability ◦ Earliest ongoing records begin in the 1980 s • Frequency ◦ 15 -minutes to monthly Coastal Salinity Index: Monitoring Drought on the Gulf and Atlantic Coasts

The arrow indicates a period when longterm CSI values indicate drought conditions, but short-term conditions were fresh, suggesting recovery from drought. These were the driest conditions (CD 4) experienced by this station over its history. Coastal Salinity Index interval (months) Period of record values and estuarine salinity ranges (in psu) The CSI values shown here (CW 4) indicate that these were the wettest, long-term conditions experienced by this station over its history. The overall site mean (approx. 28 psu), dark gray A 12 -month rolling average of salinity values, light blue The 25 th percentile (approx. 26 psu) and 75 th percentile (approx. 32 psu) values, light gray CSI Plot for St. Pierre Creek, Ashepoo-Combahee-Edisto (ACE) Basin, SC

Low average salinity dampens CSI sensitivity to extreme floods FC MC SP BB High average salinity dampens CSI sensitivity to extreme drought ACE Basin National Estuarine Research Reserve Water Quality Stations

Dissemination • The Coastal EDEN webpage currently provides plots for South Florida sites https: //sofia. usgs. gov/eden/coastal. php

Applications: Coastal Carolinas DEWS • Quarterly working group meetings, began late 2016 • Literature review to identify ecological response variables • CSI correlations with ecological response variables • User Guide Coastal Salinity Index: Monitoring Drought on the Gulf and Atlantic Coasts

Freshwater availability and timing Estuarine conditions and resources Coastal Salinity Index: Monitoring Drought on the Gulf and Atlantic Coasts Adapted from Crausbay et al. (2017)

Blue crab response to drought

• Annual CSI is a better fit, compared to annual river discharge. r 2 = 0. 0525 r 2 = 0. 1767 • Strongest correlation is with blue crab landings three years later. r 2 = 0. 1251 r 2 = 0. 2576 • This suggests that salinity impacts accrue across a generation of blue crabs. r 2 = 0. 1959 r 2 = 0. 3562 Model Fit Source: Michael Childress, Clemson University 1 Yr Lag r 2 = 0. 0670 2 Yr Lag r 2 = 0. 0540 0 Yr Lag Coastal Salinity Index 3 Yr Lag River Discharge

Other responses • A long term study of marsh vegetation in Savannah, GA (Wetzel & Kitchens, 2007) found shifts in marsh species composition as a result of a severe drought from 1998 to 2002 • Studies of Vibrio vulnificus rates in oysters have found a relationship between increased salinities (caused by drought) and reduced presence of this bacteria in oysters (Wetz et al. , 2014; Froelich et al. , 2012) Coastal Salinity Index: Monitoring Drought on the Gulf and Atlantic Coasts

Questions? USGS South Atlantic Water Science Center https: //www. usgs. gov/centers/sa-water/science/development-a-coastalsalinity-index? qt-science_center_objects=0#qt-science_center_objects Carolinas Integrated Sciences & Assessments (CISA) http: //cisa. sc. edu/projects__salinity. html Contact Kirsten Lackstrom at lackstro@mailbox. sc. edu Coastal Salinity Index: Monitoring Drought on the Gulf and Atlantic Coasts