Nutrient‐enhanced coastal ocean productivity explored in the Gulf of Mexico

Abstract

Nutrient enrichment from anthropogenic sources is one of the major stresses imposed on our coastal ecosystems. This is particularly true in the northern Gulf of Mexico where the nation's largest river discharges into an otherwise oligotrophic subtropical system. To better understand coastal ecosystem response to nutrient enrichment, 30 federal and academic scientists joined forces from 1989 to 1994 in an interdisciplinary investigation of the continental shelf of the northern Gulf of Mexico. Through the Nutrient Enhanced Coastal Ocean Productivity (NECOP) Program of NOAA's Coastal Ocean Program, the researchers conducted a series of closely integrated retrospective analyses, process and monitoring studies, and modeling exercises. The results obtained confirm current and historical linkages between nutrients derived from the extensive Mississippi drainage basin and the coastal ecosystem of the Northern Gulf of Mexico and document its current status. Most of the extensive physical, biological, and chemical data generated are stored in a permanent NECOP data repository and are available on‐line to researchers and environmental managers.

Mesozooplankton consumption of microplankton in the Mississippi River plume, with special emphasis on planktonic ciliates

“…Discharge of freshwater and its dissolved and particulate constituents affect broad areas of the northern Gulf of Mexico (Ortner & Dagg 1995). According to the conceptual model of Dagg & Breed (2003), conditions for phytoplankton growth in the lower river are poor because of high concentrations of suspended sediments, but immediately after discharge and formation of a surface plume, the settling of large lithogenic particles results in a greatly improved light environment.…”

Numerical increases and distributional shifts of Chrysaora quinquecirrha (Desor) and Aurelia aurita (Linné) (Cnidaria: Scyphozoa) in the northern Gulf of Mexico

“…Light limitation due to turbidity is responsible for a lag in primary production away from the river mouth (Randall & Day, 1987;Lohrenz et ai., 1990). Peak nutrient utilization by phytoplankton (Lohrenz et ai., 1990) and subsequent secondary production (Dagg, 1995;Ortner & Dagg, 1995) occurs well downstream of the discharge point. This is typically toward the west along the Louisiana shelf (Wiseman & Garvine, 1995).…”

“…The greatest seasonal primary production rates in the northern Gulf of Mexico are associated with the Mississippi-Atchafalya River system and Mobile Bay estuary outflows; productivity rates are depressed accordingly with the lower-discharge estuaries of Texas (reviewed in Pennock et a!., 1999). Zooplankton grazing and secondary production are intense at the coastal transition zone (Dagg & Whitledge, 1991;Dagg, 1995;Ortner & Dagg, 1995) and trophic transfer of this energy to fish is highly coupled to estuarine delivery in the Gulf (Deegan et a!., 1986). The alternate pathway of energy to gelatinous zooplankton predators has thus far received little, if any, attention.…”

Summertime Nutrient Supply to Near-Surface Waters of the Northeastern Gulf of Mexico: 1998, 1999, and 2000

“…This entrainedlow-salinit:ywater can be rich in nutrients and contributes to enhanced productivity along the outer shelf, particularly west of the delta. Ortner and Dagg (1995) and Lohrenz et al (1990Lohrenz et al ( , 1999 reported high levels of phytoplankton production, occasionally greater that 8 g·C·m-2·d-1 in the river plume, especially after the settling of suspended matter allowed deeper light penetration. High chlorophyll a concentrations associated with the Mississippi River plume east of the delta have been reported by Hu et al (2003).…”