Effects of Closure of the Mississippi River Gulf Outlet on Saltwater Intrusion and Bottom Water Hypoxia in Lake Pontchartrain

The goal of this study was to determine if Mississippi River Gulf Outlet closure by hurricane flood protection projects stopped saltwater intrusion, salinity stratification, and associated low bottom water dissolved oxygen in Lake Pontchartrain

Rangia cuneata clam decline in Lake Pontchartrain from 2001 to 2014 due to an El Niño Southern Oscillation shift coupled with a period of high hurricane intensity and frequency

The clam, Rangia cuneata, occurs in low salinity zones of Atlantic and Gulf of Mexico estuaries. Prior to 2001, it was abundant in Lake Pontchartrain, a large and shallow oligohaline estuary, located north of New Orleans. However, abundance abruptly decreased by 96% after an extreme drought from an El Niño Southern Oscillation (ENSO) shift (1998-2000). Stable higher salinities resulted in the establishment of higher salinity communities. The hooked mussel, Ischadium recurvum, increased abruptly and colonized live R. cuneata. Competition from I. recurvum and the R. cuneata decline occurred at the end of the drought, despite a decrease in salinity. After the drought, there was a period of high hurricane intensity and frequency which stifled clam recovery. Their densities remained relatively low due to declines from hurricane disturbances in 2005, 2008 and 2012. In 2014, after two years without severe hurricane effects, density and biomass recovered to baseline years (1954 and 1997). Barrier island erosion caused by Hurricane Georges in 1998 and adverse effects of the ENSO drought on wetlands may have set the stage for increased effects of subsequent hurricanes. High relative sea level rise, wetland loss and erosion of barrier islands, which occurred with each successive storm, potentially increased the size of surges. Surges resuspended sediments which buried clams and abruptly increased salinity and lowered dissolved oxygen. Salinity stratification persisted after storms and caused hypoxia in bottom waters. Storm surge interactions with discharges from the Bonnet Carré Spillway, a Mississippi River flood diversion structure, and the MRGO, a ship channel, also exacerbated hurricane effects

Effects of Saltwater Intrusion from the Inner Harbor Navigation Canal on the Benthos of Lake Pontchartrain, Louisiana

A study of the benthos of southern Lake Pontchartrain, Louisiana, was conducted from July 1976 to July 1978. Seven offshore stations and three stations in the New Orleans Marina complex were sampled seasonally. Offshore stations formed a transect from the Lake Pontchartrain Causeway to the Inner Harbor Navigation Canal (I.H.N.C.). A west to east gradient of increasing salinity and salinity stratification was evident. Faunal differences among stations were assessed using indices of diversity, biological dominance, pollution, and station homogeneity. The fauna of the marina stations had a low species diversity and was dominated by annelids, indicative of a stressed environment. The fauna of stations near the I.H.N.C. were similar to the marina stations. Moving westward from the I.H.N.C., species diversity increased and the fauna became dominated by mollusks. Stressful conditions associated with the intrusion of water from the I.H.N.C. into Lake Pontchartrain appeared to be responsible for the faunal differences observed

Effects of Saltwater Intrusion from the Inner Harbor Navigation Canal on the Benthos of Lake Pontchartrain, Louisiana

A study of the benthos of southern Lake Pontchartrain, Louisiana, was conducted from July 1976 to July 1978. Seven offshore stations and three stations in the New Orleans Marina complex were sampled seasonally. Offshore stations formed a transect from the Lake Pontchartrain Causeway to the Inner Harbor Navigation Canal (I.H.N.C.). A west to east gradient of increasing salinity and salinity stratification was evident. Faunal differences among stations were assessed using indices of diversity, biological dominance, pollution, and station homogeneity. The fauna of the marina stations had a low species diversity and was dominated by annelids, indicative of a stressed environment. The fauna of stations near the I.H.N.C. were similar to the marina stations. Moving westward from the I.H.N.C., species diversity increased and the fauna became dominated by mollusks. Stressful conditions associated with the intrusion of water from the I.H.N.C. into Lake Pontchartrain appeared to be responsible for the faunal differences observed

Gentamicin Rapidly Inhibits Mitochondrial Metabolism in High-Frequency Cochlear Outer Hair Cells

Aminoglycosides (AG), including gentamicin (GM), are the most frequently used antibiotics in the world and are proposed to cause irreversible cochlear damage and hearing loss (HL) in 1/4 of the patients receiving these life-saving drugs. Akin to the results of AG ototoxicity studies, high-frequency, basal turn outer hair cells (OHCs) preferentially succumb to multiple HL pathologies while inner hair cells (IHCs) are much more resilient. To determine if endogenous differences in IHC and OHC mitochondrial metabolism dictate differential sensitivities to AG-induced HL, IHC- and OHC-specific changes in mitochondrial reduced nicotinamide adenine dinucleotide (NADH) fluorescence during acute (1 h) GM treatment were compared. GM-mediated decreases in NADH fluorescence and succinate dehydrogenase activity were observed shortly after GM application. High-frequency basal turn OHCs were found to be metabolically biased to rapidly respond to alterations in their microenvironment including GM and elevated glucose exposures. These metabolic biases may predispose high-frequency OHCs to preferentially produce cell-damaging reactive oxygen species during traumatic challenge. Noise-induced and age-related HL pathologies share key characteristics with AG ototoxicity, including preferential OHC loss and reactive oxygen species production. Data from this report highlight the need to address the role of mitochondrial metabolism in regulating AG ototoxicity and the need to illuminate how fundamental differences in IHC and OHC metabolism may dictate differences in HC fate during multiple HL pathologies

THE STATUS OF POTAMOGETON PERFOLIATUS (POTAMOGETONACEAE) IN LAKE PONTCHARTRAIN, LOUISIANA

Volume: 16Start Page: 757End Page: 76