Title| Summary|Strategy|Impacts/Products|Collaborators/Clients|Task 1|Task 2 |Task 3|Task 4|Task 5|Task 6|Task 7

GEOLOGIC DIVISION CONTINUING PROJECT WORK PLAN - FL 2001

Background Narratives - Objectives and Strategy

Almost all (>92%) of the trace element load in the Mississippi River is transported downstream in particulate form, either as suspended sediment or bedload. Seasonal sediment storage and remobilization in the Atchafalaya/Mississippi River system, as well as physico-chemical shelf effects thus control the ultimate delivery of reactive pollutants to the Gulf of Mexico. In the lower reaches of the Mississippi River sediments are typically stored during low discharge (Q 14,000 m³/sec) and remobilized during high discharge stages (Q>20,000 m³/sec). During such periods of storage, key diagenetic reactions such a remineralization and the reduction of Fe/Mn carrier phases can significantly change the solubility of certain contaminants. Similar geochemical reactions also occur in floodplain, deltaic or shelf sediments, and thus the fate of sediment-hosted contaminants during down-stream and across-shelf transport collectively define pollutant loading to the Gulf of Mexico.

Figure 1

Our hypothesis is that differential processing of terrigenous, sediment-hosted contaminants in the lower Atchafalaya and Mississippi Rivers and their respective receiving basins (shelf vs shelf break) and flood plains can significantly alter the environmental fate and ultimate availability of these constituents. This differential processing is primarily due to the discharge of Atchafalaya River waters into a broad, shallow inner shelf environment, while Mississippi River waters discharge into the Gulf of Mexico, beyond the shelf break (Fig.1). We will directly address this differential processing by collecting dissolved, suspended sediment and bottom sediment samples in these two river systems (i.e., lower river, floodplain and shelf), following NASQAN procedures. Our stations will include historic NASQAN sites in the lower river that have been recently discontinued due to budgetary constraints within USGS WRD.

The overall objective is to evaluate the effect of seasonal sediment storage, early diagenetic reactions, remobilization and eventual deposition on the following subset of sediment-hosted pollutants:

1. pesticides and fertilizers, PAHs and other organic pollutants,
2. trace metals that exhibit variable particle affinities or bioavailabilities (e.g., U, V, Mo, Ba, Sr, Fe and Mn) and
3. organic carbon and nutrients.

The following specific objectives will be addressed for each river system under variable discharge regimes:

1. examine diagenetic/carrier phase transformations (Fe/Mn, U, Mo, V and nutrients);
2. examine biogeochemical transformations that occur as a result of sediment storage/remobilization (resetting geochemical gradients);
3. assess historical inventory of pollutants and their environmental reactivity/lability;
4. evaluate overall delivery of sediment-hosted pollutants that eventually reach the Gulf of Mexico, including a component of water/particles that may be introduced to wetland ecosystems during high discharge.

Results from (a-d) will be used to develop flux models (as per NASQAN) of pollutant transport and ecosystem health.

Strategy

Key NASQAN leaders (Meade, Goolsby, Horovitz, Demas) have provided essential direction and linkages to the ongoing NASQAN Mississippi River program. Such guidance has established critical scientific issues that warrant an investigation of this scope, and from this input the following approach has been formulated, as described by the following tasks.

1. review of past work and a workshop to introduce the project and its members/linkages (PWS/JLK),
2. sampling procedures (PWS/JLK),
3. inorganic geochemistry (AJH, USGS-WRD/PWS),
4. organic geochemistry (KAK/BHO/RJR/TDS),
5. geo-framework (JLK/Allison-Tulane coop),
6. river plume dynamics (Muller-Karger-USF coop),
7. knowledge bank-data archiving (all).

Note that to complete these tasks requires active participation of WRD, BRD, NMD as well as linked state and academic institutions.

Title|Summary|Strategy|Impacts/Products|Collaborators/Clients|Task 1|Task 2 |Task 3|Task 4|Task 5|Task 6|Task 7