A04 SOW.docx

STATEMENT OF WORK

I. GENERAL INFORMATION

A. Introduction Work involves (1) analyses of creek channel and marsh porewater samples for dissolved inorganic carbon (DIC) and alkalinity, (2) three 48-hr studies of porewater-tidal creek interactions to measure rates of exchange of dissolved carbon species between marsh and tidal creek during seasonally distinct hydrological conditions (flow-through Radon survey), (3) gamma spectroscopy dating of marsh soil accretion rates using Cs-137 and Pb-210 counters.

B. Background:

Hydrologic management has been used extensively in Louisiana coastal wetlands to maintain desirable habitat and sustainable ecosystems. Although less common, river diversions have the potential for large-scale impact, and there remains a critical need for a greater understanding of both short- and long-term impacts of river diversions on coastal wetlands and associated carbon cycling. To ensure successful restoration of these vital habitats, it is necessary to understand the cause of wetland loss as well as accurately measure the effectiveness of the restoration activity. We are measuring processes that represent ecosystem health and sustainability in coastal wetlands impacted by sea-level rise. This information will be used to identify mechanisms that lead to wetland loss and provide baseline data to assess the impacts and the effectiveness of existing and planned river diversions. Specifically, the research effort will assess how river diversions, which currently represent some of the largest climate adaptation management interventions ever implemented for coastal restoration, affect the carbon balance in receiving marshes. Porewater exchanges of dissolved carbon species represents a knowledge gap in our current understanding of carbon loss from marsh, as well as its implication on estuarine acidification in surrounding water bodies as high DIC in porewater results in lower pH (Still & Stolt, 2015). This information will help land managers identify vulnerable habitat, assess restoration effectiveness adaptively, and optimize restoration outcomes.

C. Definition and Applicable Documents

a. Porewater: water contained in marsh soil, difficult to extract large volumes

b. DIC and alkalinity: constituents for analysis in surface and porewater

c. Double chamber continuous flow dissolved Radon 222 detectors: instrument used to detect ultra-low levels of radon typical of mineral poor, high organic soils.

d. 25 mm germanium well detector: larger well size allowing use of greater soil mass to count activity in soil with low Cs-137.

D. Scope River diversions are a form of hydrologic management that has the potential for large-scale impact, but there remains a critical need for a greater understanding of both their short- and long-term effects on processes critical to sustaining the wetlands (Quirk et al 2019). Stakeholders within the outfall zone of these river diversions are concerned how large-scale mitigation activities will impact the health and sustainability of their wetlands. We have strategically located fresh and saltwater study sites within the impact zones of current and planned river diversions. The data collected will be used to provide a baseline of ecosystem function and health to accurately assess restoration effectiveness. To investigate the impacts of river diversions on saltwater marshes, a study site was established within the receiving basin of a planned diversion of the Mississippi River, the Mid-Barataria Sediment Diversion (scheduled to open 2022). This site is currently collecting the baseline information on processes controlling carbon accretion and flux in marshes, including the marsh-tidal creek exchange necessary to evaluate impacts of the planned diversion project when it becomes operational in 2022. Much like a heart-rate monitor on a hospital patient, this kind of high-resolution data on net ecosystem production is critical to evaluating the immediate impacts of the diversion in real-time, without waiting the years or even decades necessary for such impacts to appear.

E. Our objectives are to:

(1) Measure dissolved inorganic carbon (DIC) and alkalinity concentrations in water from both creek channels and marsh porewater over the course of a year;

(2) Quantify seasonal subsurface hydrologic exchange and marsh overland flow to creek channel to estimate baseline carbon flux rates including DIC using radon flow-through surveys;

(3) Measure carbon accretion rates in marsh soil using Cs-137 and Pb-210 dating

II. WORK REQUIREMENTS

A. Technical Requirements.

1. Specific work requirements and/or work products

a. Analyze porewater and creek channel water samples for DIC and alkalinity (240 samples for each constituent). Samples are collected throughout the year from multiple locations and delivered to the laboratory within 24 hours of collection

b. Technical services to collect and analyze soil and water samples during 48-hour synoptic surveys in situ using double channel radon detectors suitable for low activity levels. The synoptic surveys will be done during three field seasons, when either subsurface processes or overland flows dominate the marsh creek channel exchange, in the summer, fall and in late winter. During these synoptic surveys, porewater and creek water, and soil samples will be analyzed hourly.

c. Two marsh soil samples representing distinct geomorphological environments will be analyzed for Cs-137 and Pb-210 activity and carbon content characterized for each depth profile.

2. Criteria for acceptance of Product or Service

a. DIC and alkalinity analyses of porewater requires instruments that can make measurements using sample volumes < 10 ml, within few days of collection (to minimize gas loss) and that are not affected by presence of high sulfide and salinity.

b. Ability to detect low-level Radon-222 at concentrations less than femtomolar at hourly intervals for up to 48 hours during three synoptic surveys at the field site. The highly organic soils with extremely low radon concentration require the use of double chamber continuous flow detectors;

c. The highly organic, low mineral marsh soils make it necessary to collect large volume samples to measure Cs-137 with uncertainties less than 15%. This requires high efficiency germanium well detectors with well diameter of 25 mm to accommodate vials with greater soil volumes. Soil samples will be sectioned into 2 cm intervals and counted for 210Pb, 226Ra and 137Cs via their gamma emission at 46.5, 351 and 667.1 keV for individual depth horizon.

B. Deliverables.

1. Characteristics for work product described in II.A.1.

a. DIC and alkalinity analytical services

b. Technical services to measure hydrological exchange using radon detectors during three synoptic surveys of at least 48 hours.

c. Written report detailing hydrologic flux estimates

d. Report providing soil accretion rates for the two soil cores and activity profiles along with data for all counts along with all supporting data

2. Delivery dates for work/product to be completed and point of delivery.

a. Data for DIC and alkalinity analysis within 14 days of sample delivery

b. Technical report detailing radon activity and hydrologic flux calculations for each synoptic survey within six weeks of survey

c. Monthly oral progress discussions

d. Report detailing soil carbon accretion rates is due six months after collection of samples and delivery to contractor.

e. Final report containing all the data during the period of performance delivered to USGS Wetland and Aquatic Research Center, Lafayette, Louisiana

III. SUPPORTING INFORMATION

A. Place of Performance:

USGS data collection platform at Wilkinson Bayou Cutoff in Barataria Basin and adjacent marshes.

B. Period of Performance:

365 days from the date the contractor receives the purchase order.

C. Government Furnished Property (GFP):

USGS will provide all soil and water samples for analyses upon collection throughout the year.

D. Special Considerations.

1. Key personnel qualifications: Laboratory must have demonstrated ability to conduct the analyses required in accordance with the technical specifications. Proper interpretation of results depends on researcher possessing necessary combination of education and training

2. USGS Wetland and Aquatic Research Center will retain rights to the data resulting from these analyses and will follow established USGS protocols for releasing data when publishing results of this study.

Still, B.M. and Stolt, M.H. (2015), Subaqueous Soils and Coastal Acidification: A Hydropedology Perspective with Implications for Calcifying Organisms. Soil Science Society of America Journal, 79: 407-416. doi:10.2136/sssaj2014.09.0366