The San Diego Unified Port District (Applicant) proposes to receive grant funding from the U.S. Department of Transportation Maritime Administration’s (MARAD) Maritime Environmental Technical Assistance (META) program to conduct a San Diego Bay-wide evaluation and inventory of carbon storage and sequestration potential (often referred to as “blue carbon”) of two species of eelgrass (proposed project). The MARAD META program promotes the research, demonstration, and development of emerging technologies, practices, and processes that improve maritime industrial environmental sustainability. The Applicant’s proposed study of carbon storage and sequestration in eelgrass (Blue Carbon Eelgrass Study or Study) would be the first quantitative effort to characterize carbon sequestration rates within eelgrass beds throughout San Diego Bay. Results from the Study would provide baseline data on carbon stocks and sequestration rates, which would support future sampling and restoration efforts, and could provide guidance on future greenhouse gas emissions reduction strategies.
The Study would focus on two species of eelgrass present in San Diego Bay: common eelgrass (Zostera marina) and wide-leaved eelgrass (Z. pacifica). It is anticipated that the Study would occur between Fall 2021 and Summer 2022, during the peak growth season for eelgrass, and may continue to occur annually as a multi-year study (dependent upon budget or funding availability). Biomass and sediment analysis would occur at up to ten sites with up 12 sampling locations (time and budget permitting) over a ten- to fourteen-day sampling period. Descriptions of each location are included below:
1. Site A (East of Zuniga Jetty): sampling would occur at western end of eelgrass transect line (start location of transect: 479072.77 mE, 3615685.66 mN, end location of transect: 480125.88 mE, 3615857.96 mN). Depth of sampling location: -4 ft MLLW.
2. Site B (East of Zuniga Jetty): sampling would occur at eastern end of eelgrass transect line (start location of transect: 479072.77 mE, 3615685.66 mN, end location of transect: 480125.88 mE, 3615857.96 mN). Depth of sampling location: -4 ft MLLW.
3. Site C (Entrance of Shelter Island Yacht Basin): sampling would occur along eelgrass transect line (start location of transect: 478133.17 mE, 3618846.88 mN, end location of transect: 478146.21 mE, 3618653.29 mN). Depth of sampling location: -4 ft MLLW.
4. Site D (South of the Coronado Bridge): sampling would occur along eelgrass transect line (start location of transect: 485096.94 mE, 3616261.04 mN, end location of transect: 484613.27 mE, 3616253.50 mN). Three sampling locations at this site at three different depths: 0 ft MLLW, -4 ft MLLW, and -6 MLLW.
5. Site E (Inshore of Homeport Island): sampling would occur along eelgrass transect line (start location of transect: 484988.77 mE, 3614913.87 mN, end location of transect: 485340.45 mE, 3614908.16 mN). Depth of sampling location: -4 ft MLLW.
6. Site F (South of Entrance to Chula Vista Marina): sampling would occur along eelgrass transect line (start location of transect: 490227.92 mE, 3609183.78 mN, end location of transect: 489552.07 mE, 3609170.16 mN). Depth of sampling location: -4 ft MLLW.
7. Site G (Northwest of the Chula Vista Wildlife Reserve): sampling would occur at an existing eelgrass restoration site (489,551 mE, 3,608,987 mN). Depth of sampling location: -4 ft MLLW.
8. Site H (West of the Chula Vista Bayfront): sampling would occur at South Bay Borrow Pit (3,609,445E; 489,142N - UTM, Zone 11 (NAD83)). Depth of sampling location: -4 ft MLLW.
9. Site I (East of Crown Isle): sampling would occur south of eelgrass transect line (start location of transect: 486833.63 mE, 3610996.46 mN, end location of transect: 488574.09 mE, 3611161.79 mN). Depth of sampling location: -4 ft MLLW.
10. Site J (Along the Northern Shoreline of the Chula Vista Wildlife Reserve): sampling would occur north of the Chula Vista Wildlife Reserve (32.36.49 N, 117. 06.14 W). Depth of sampling location: -4 to 0 ft MLLW.
Most of the sampling locations would occur along existing eelgrass transect lines utilized by the U.S. Navy in their evaluations of San Diego Bay eelgrass beds. All locations would be accessed by boat and divers would conduct the activities detailed below for the biomass analysis and the sediment analysis.
The biomass analysis portion of the Study includes three components: quadrat measurements, biomass sampling, and productivity sampling.
Quadrat measurements: At the beginning of the Study, three replicate biomass quadrats of eelgrass would be measured at each location (up to 36 total quadrats). The quadrats are composed of PVC pipe and would be 25 centimeters (cm) by 25 cm. A diver would bring down the quadrat, place it in the sample area, take a photo of the quadrat, count and record the number of eelgrass shoots within the quadrat, and measure and record the height and width of each shoot within the turions within each quadrat. The quadrats would be brought back to the boat with the diver.
Biomass sampling: At the beginning of the sampling period, 50 individual shoots over a range of heights and widths would be collected within one quadrat for each of the two eelgrass species (100 total shoots). The shoots would be collected with the use of vegetable shears. These shoots would be used for analysis at an off-Tidelands facility.
Productivity sampling: At the beginning of the sampling period, 10 turion sheaths from a mature individual eelgrass plant would be identified within one quadrat for each of the two eelgrass species (20 total turion sheaths). At the blade-sheath junction of the most mature intact eelgrass blade, the diver would use a hypodermic needle to mark a reference hole on the blade. The diver would wrap colorful zip-ties at the base of the plant and place a stake at the location of the marked shoots to be able to identify the plant on the last day of the sampling period. On the last day of the sampling period, the diver would re-visit the marked shoots and visually identify newly formed blade material based on upward displacement of the reference hole and record the area of the new blade material and total blade material. On the last day of the sampling period, between five (5) and twenty (20) of the marked blades would be collected using vegetable shears, and the zip-ties and stakes would be removed. The collected blades would be used for analysis at an off-Tidelands facility.
The sediment analysis portion of the Study includes two components: sediment coring and sediment sampling.
Sediment coring: During the sampling period, three (3) sediment core samples would be taken at each location during the sampling period (approximately 36 samples total). The core tubes would be either two (2) or three (3) inches in diameter, depending on stiffness of sediment. Additional core samples may be necessary if the two-inch diameter core tube is used to meet sediment volume requirements for analysis. To take a sediment core sample, a three-point anchoring system would be set up over the sample location and the location and elevation of the site would be recorded. A vibracore would be attached to the anchoring system and used to drive the core tube into the ground. The majority of the cores would be collected down to one-meter-depth, however five (5) of the cores would be collected down to three-meter-depth (one at five different regions throughout the Bay). Collected core samples would be used for analysis at an off-Tidelands facility.
Sediment sampling: This component would rely upon the cores collected during sediment coring. For the one-meter-depth cores, six samples would be collected (one every 10 cm for the first 50 cm, and one sample for the rest of the core). For the three-meter-depth cores, ten samples would be collected (one every 10 cm for the first 50 cm, and one sample every 50 cm for the rest of the core). Each sample would be photographed, recorded, and used for analysis at an off-Tidelands facility.
In addition to the biomass analysis and sediment analysis, the MARAD META program would also fund an effort to model the evolution of eelgrass habitat in San Diego Bay with sea level rise and project how blue carbon may change over time, as a part of the Study. Finally, administration and grant management would also be funded and would include coordination with consultants, site visits, permitting, environmental and coastal review, review of draft and final reports, and quarterly reporting on the grant.
Due to its nature and limited scope, construction of the proposed project would generate a minor amount of vehicle trips and would require limited use of equipment. Therefore, impacts related to air quality, greenhouse gas emissions, and transportation and traffic are not anticipated to occur. Furthermore, the Applicant would be responsible for complying with all applicable federal, state, and local laws regarding construction demolition debris, hazards and hazardous materials, and stormwater.