9406585 Ruttenberg The overall objectives of this proposal are (1) to use selective leaching procedure (the SEDEX Method) to identify and quantify the chemical from of particulate-P in the lower Mississippi and Atchafalaya Rivers, at the interface between the Mississippi River and the deltaic marine shelf, and in proximal surficial deltaic marine sediments; (2) to identify spatial and temporal controls on processes modifying particulate-P during riverine transport; and (3) to identify spatial and temporal controls on chemical modification at the continent-ocean interface. Phosphorus (P) is an essential nutrient which can limit biological productivity in fresh, brackish, and saline natural waters. P associated with particulate matter in natural waters will enhance biological productivity to the extent that the P can be assimilated. Determining the bioavailable P associated with particulate matter is essential for placing constraints on sources of P for biological cycling in aquatic systems. Bulk P concentration is not a useful parameter as P-speciation is required for assessment of the fraction of particulate P which is bioavailable. The SEDEX method separately quantifies Fe-P, authigenic sedimentary apatite (ASAP), (phases likely to control soluble, and therefore bioavailable-P in natural waters), organic- P, loosely sorbed-P, and detrital apatite. P-distribution in Riverine Suspended Particulate Matter (RSPM) will be determined at a series of river stations chosen to permit comparisons of input from agricultural versus industrial land and between the levied lower Mississippi and the Atchafalaya hard-wood swamps. Temporal variability will be assessed by re-visiting the river study sites seasonal. This work will be carried out in conjunction with ongoing USGS monitoring programs, which provided an array of valuable supporting data and a long-term record. The effect of estuarine processes on RSPM P-distribution will be examined by coupling field measurements with P-desorption experiments. The latter will cover the range of salinity observed in the estuary. P-distribution of RSPM determined before and after mixing should permit direct identification of solid-phase P-reservoirs which liberate soluble (and therefore bioavailable ) P to solution. These results will be compared to P-distribution of in situ RSPM from the estuary. The riverine source of bioavailable-P to the coastal ocean will be assessed by contrasting the P-distribution of RSPM from these two rivers with that in proximal surficial marine sediments, and by contrasting P-loading calculations of separately quantified RSPM P-reservoirs to P-burial rates in proximal shelf sediments. The work focusses on a globally significant system, mechanisms of transformation, and physical and chemical controls that should be broadly applicable.
