RAPID CHANGES IN A SHALLOW SEEPAGE LAKE IN THE NORTH CAROLINA COASTAL PLAIN (USA): THE INFLUENCES OF ATMOSPHERIC DEPOSITION AND BIG RAINS

Shallow lakes have large surface area to volume ratios, so atmospheric deposition can be more impactful, and change can be relatively rapid. A small, clear water lake (White Lake, >90% rainwater source) in NC has seen 3x increases in Total Nitrogen since the 1970s, while shallow blackwater lakes in the area have seen 2x increases. Total Phosphorus levels in the lakes have remained generally stable over the same period. A nearby National Atmospheric Deposition Program station has measured a 4x increase in ammonium ion deposition while nitrate/nitrite deposition has declined; rainfall pH has increased 1.5 units. Limited rainfall sampling at White Lake found TP ranging from <2 to 45 mg/L, with TN ranges of 190 to 1350 mg/L; DIN ranged from 14-92% of TN. Benthic zone productivity has been and remains relatively high but variable from year to year; hydrilla was widespread in 2017, when pH levels were elevated, but since 2018 its occurrence has been low, and taxa characteristic of the lake have dominated. There has been a notable change in water column productivity, and a cyanobacterial bloom (Planktolyngbya limnetica) developed in 2017 (causing elevated pH) and persisted over that winter; a P-stripping alum treatment was applied in May 2018 and since then cyanobacterial biovolume has remained <5% of total BV. The present phytoplankton community is very dynamic and diverse and is often dominated by taxa groups such as desmids and picocyanobacteria, and short-duration blooms are often associated with high rainfall.

Primary Presenter: Diane Lauritsen, LIMNOSCIENCES (ddlauritsen@comcast.net)

Authors:

Diane Lauritsen, LIMNOSCIENCES  (ddlauritsen@comcast.net)

Linda Ehrlich, Spirogyra Diversified Environmental Services  (spirogyra@juno.com)

Rob Richardson, North Carolina State University  (rob_richardson@ncsu.edu)