Water Resources Research Act Program

Details for Project ID 2012LA83B

Nutrient and harmful algal bloom (HAB) dynamics in Lake Pontchartrain during a non-spillway opening year

Institute: Louisiana
Year Established: 2012 Start Date: 2012-03-01 End Date: 2012-02-28
Total Federal Funds: $15,600 Total Non-Federal Funds: $37,948

Principal Investigators: John White, Sibel Bargu, Chunyan Li

Abstract: The Bonnet Carrpillway is a flood-release valve for the Mississippi River. The Spillway is only opened in years where the projected springtime flood stage of the river can threaten New Orleans and other downstream communities. The Bonnet Carre´ Spillway can alleviate pressure from dangerous flood stage river heights by directing up to 7080 m3 s-1 (250,000 ft3 s-1) of water (~ 20% of the flood volume Mississippi River capacity) into Lake Pontchartrain and out into the Gulf of Mexico. Coincident with the water, there is a large load of bioavailable N (>10,000 metric tons of N) in the form of nitrate as well as dissolved reactive P with the potential to trigger expressions of eutrophication in this important commercial and recreational fisheries water body. Our research team has documented the effects of these large nutrient pulses both in 2008 and 2011, however, we are missing the critical baseline data from a non-spillway opening year. In order to determine and model the impact of these nutrient pulses to the lake water quality and predict potential harmful algal blooms, we require spatially and temporally explicit data on the nutrient status, phytoplankton assemblages and toxin concentrations during a non-loaded year. We will sample surface and bottom waters along the salinity gradient along the east-west axis of the lake using previously established stations. Salinity, temperature, pH, dissolved oxygen, secchi disk depth, pigments, nutrients (NO3, PO4, NH4, Si, TKN, TP, DOC, DON), phytoplankton assemblages, toxin concentrations will be measured at each station. We will then compare these results with similar measurements taken during and after closure of the spillway in 2008 and 2011 in order to more accurately predict the effects of these large nutrient loading events on lake water quality. This information is critically important for lake managers as well as fisheries groups as harmful algal blooms produce toxins which have the potential to contaminate the entire food web and affect human health. In addition, as the state of Louisiana plans for larger Mississippi River diversion like the White’s Ditch diversion, this data can be used to predict the effects of those new, larger diversions on the receiving water body.