Water Quality and Toxic Algal Presence in Borrow Pits in Eastern Lake Pontchartrain, 2021-2023

This dataset consists of sensor profile and water sample results from monitoring campaign to investigate  the effects of two dredged pits in eastern Lake Pontchartrain on dissolved oxygen conditions within the water column in and surrounding the pits  over a three-year period. The borrow pits were excavated to provide soil material to nourish three nearby protected marsh sites: Bayou Sauvage National Wildlife Refuge, Turtle Bayou Protected-Side Intermediate Marsh, and New Zydeco Ridge. The southern borrow pit occupies 418 acres and was monitored using a 9-point grid. The northern pit is 330 acres and was monitored using a 12-point grid. During 2021-2023, the U.S. Geological Survey, Lower Mississippi-Gulf Water Science Center, in cooperation with the U.S. Army Corp of Engineers New Orleans District collected data in the lake. Pit areas were sampled monthly in March, April, September, October, and November and twice a month during May, June, July, and August when possible.
A multi-parameter water quality sonde was used to measure dissolved oxygen concentration, pH, specific conductance, and salinity to monitor for the formation of hypoxic conditions. At each grid location, a 3-point vertical profile was measured. When hypoxic conditions were encountered (dissolved oxygen &lt;2 milligrams per liter (mg/L)) measurements were made at 1 foot intervals to define the extent of the hypoxic zone. 
During each sampling event, a surface and sub-surface water sample were collected at each pit to analyze for the presence of chlorophyll, phycocyanin, and microcystin at Auburn University. Sample water was first filtered through a glass fiber filter. To measure chlorophyll, filters were extracted with 90% aqueous ethanol for 24 hours at 4°C in the dark prior to being filtered through a glass fiber filter and analyzed with a fluorometer with a non-acidification chlorophyll module. To measure phycocyanin, filters were extracted while grinding in 50mM phosphate buffer and allowed to extract in the dark for 4 hours at room temperature before extract was purified using centrifugation and passing through a 0.2 um membrane filter and analyzed with a fluorometer. To measure microcystin, filters were extracted twice for 1 hour in acidic 75% aqueous methanol prior to pooling extracts, filtered through a glass fiber filter, dried on a sample concentrator, and redissolved in a phosphate buffer prior to analysis via enzyme-linked immunosorbent assay for intracellular microcystin content. Further information on these methods can be found in Belfiore and others, 2021.
In 2022-2023, at a subset of locations at each pit, additional sensor measurements for chlorophyll and phycocyanin were collected and water was sampled to measure turbidity and monitor for the presence of cyanobacteria and microcystin toxins at Tulane University. Turbidity was measured using an turbidimeter. A  handheld Harmful Algal Bloom indicator was used to determine a Phycocyanin:Chlorophyll-a ratio and a fluorometer was used to measure chlorophyll-a fluorescence. Samples to monitor for cyanobacteria and microcystin toxins were collected using sterile bottles and stored at -80°C until DNA extraction and quantitative real-time polymerase chain reaction (qPCR) was performed. Sample filtration followed protocol as described in Standard Methods for the Examination of Water and Waste Water, 19th edition. Further information on this method can be found in other published reports (Sipari and others, 2010, Rinta-Kanto and others, 2005, Rantala and others, 2004, and Doblin and others, 2007).

Tags: biota, cyanobacteria, gulf-coast, hypoxia, lake-pontchartrain, louisiana, microcystin, usgs-6585ac62d34eff134d435178, water-quality
Organization: Department of the Interior