Underway Mapping of Alkaline Phosphatase Activity in the Mississippi River Plume: Real-Time Evidence for Phosphorus Limitation

Texas A&M Research Foundation, College Station TX

Investigators

Abstract

Microbial ectoenzyme activities in aquatic environments are important agents of polymer hydrolysis and indicators of the state of microbial carbon, nitrogen, or phosphorus nutrition. Alkaline phosphatase, in particular, is a good indicator of phosphorus limitation. However, like most other biochemical and molecular measurements, ectoenzyme activities, including alkaline phosphatase, have been limited to discreet water samples. We have developed a continuous underway method for measuring alkaline phosphatase and other microbial enzyme activities using high-sensitivity fluorescent substrates. This method has been successfully employed to map surface alkaline phosphatase activity in a limited area of the Mississippi River plume and the Louisiana shelf, the area where phosphorus limitation is likely to be most intense. This proposed study will use an improved automated enzyme measurement system for extensive seasonal mapping of surface water alkaline phosphatase activity in the Mississippi plume and along the Louisiana coast. This system will be coupled with continuous underway measurements of temperature, salinity, in vivo fluorescence and other parameters provided by the ship. This work will be conducted in conjunction with a previously-funded comprehensive process study of nitrogen, phosphorus, and silica limitation in this area to be conducted by Quay Dortch and David Nelson. The seasonal alkaline phosphatase mapping will provide important information on the spatial and temporal extent of phosphorus limitation, which will aid in the selection of stations for detailed nutrient enrichment experiments by Dortch and Nelson. These nutrient enrichment experiments, in turn, will supply detailed information on the response of the community to nutrient enrichment, which will help in the interpretation of the mapping data. Additional alkaline phosphatase measurements will be made on samples from the nutrient enrichment experiments to help in the interpretation of their physiological status.