Abstract
Phosphorus (P) cycling and possible P limitation in the Mississippi River Plume (MRP) and Louisiana shelf (LS) were studied during two Nutrient Enhanced Coastal Ocean Productivity (NECOP) cruises in May 1992. Horizontal and vertical distribution of P pools, nutrient ratios, alkaline phosphatase (AP) activities, and orthophosphate (Pi) uptake rates were examined. Dissolved inorganic phosphorus (DIP) concentrations were up to 3.5 jiM in the freshwater portions of each river and decreased to less than 0.5 liM at 30 psu during leg 1. Dissolved organic phosphorus (DOP) and particulate phosphorus (PP) also decreased with increasing salinity. Maximum DIP concentrations near Southwest Pass were less during leg 2 than leg 1. The entire area of the MRP and LS showed low DIP concentrations, from 0 to 0.5 gM, during both cruises. Highest N/P and many high Si/P were found off of Southwest Pass. The area with a high N/P was smaller during leg 2. The low DIP (< 0.2 IiM) and high N/P (>30:1) suggest likely P-limited area near Southwest Pass during leg 1. Highest chlorophyll a concentrations were found west of Southwest Pass. The highest values of in vivo fluorescence were found directly west of Southwest Pass. High AP activities and Pi uptake rates were found in Surface AP activities were fluorescence. AP activities up a e rates were found in nearshore areas near Barataria Bay. Surface AP activities were highest in the same area as in vivo fluorescence. AP activities and Pi uptake rates suggest P limitation from west of Southwest Pass to n . ear Atchafalaya Bay during leg 1, while AP activities suggest P-limitation From west of Southwest Pass to near Atchafalaya Bay during leg1, while AP activities suggest P-limitation in large area near Southwest Pass and southwest of Atchafalaya Bay during leg 2.
Kim, Jin-Seok (1996). Phosphorus limitation in the Mississippi River Plume (MRP) and Louisiana shelf (LS) during May 1992. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1996 -THESIS -K565.