Silicon Levels In Mobile Bay And The Gulf Of Mexico

Silicon Levels In Mobile Bay And The Gulf Of Mexicoi Introductionsili

Silicate is a very important nutrient in the ocean. Silicate is essential for diatoms, particularly, and also for sponges and radiolarians. Even though sponges are benthic, many use silicate to support their structure. Radiolarians are microscopic. Diatoms are also microscopic and photosynthetic organisms. Areas that are surrounded by rivers receive a great deal of volume of sediment at a very high delivery rate (Davis, 2017). Nearly five million metric tons of large amounts of sediment are carried into Mobile Bay every year (Davis, 2017). While 33% of it stays in the delta at the mouth of the Mobile River, half of it settles to the bottom of Mobile Bay. Only about 15% of it makes it into the Gulf (Davis, 2017). Silicate is very specifically important for diatoms, siliceous sponges, and radiolarians. The majority of how silicate returns back into the ocean is through weathering and fresh water sends it back towards the ocean through rivers. Given the large amount of freshwater input in Mobile Bay, I hypothesize that silicate levels will be significantly higher in Mobile Bay than in the Gulf of Mexico.

Materials and Methods

Samples were collected on June 12th, and nutrient samples were taken at five different stations. At each station, samples were collected at three different depths: surface, middle, and deep. The Niskin bottle was used to collect water at each depth. Sixty milliliters of unfiltered water was collected at each depth, filtered, and then 15 mL of the sample was stored on ice until returned to the lab. Sampling began in Mobile Bay and continued southward towards the Gulf of Mexico. CTD data was processed by DISL technical support and provided to us for analysis.

Results

The silica concentration results indicate higher levels at the surface than at deeper depths in both Mobile Bay and the Gulf of Mexico. The exception was at station 12, where surface Si was 18.02 μmol Si/L and bottom Si was 25.45 μmol Si/L, making it the only station displaying higher silicate levels at depth. Data from the middle depth was unavailable for the first station. Overall, the levels at middle depths were similar to those at the bottom depth within the same station. The surface Si levels ranged from 18.02 μmol/L at station 12 in the Gulf to over 82 μmol/L at station 6 in Mobile Bay. The bottom depths had notably lower concentrations, with the highest bottom level at station 1 (29.83 μmol/L) and the lowest at station 6 (14.42 μmol/L).

Discussion

The analysis reveals that surface silicate levels were generally higher than those at the bottom across most stations. The highest surface concentration was observed at station 6 in Mobile Bay (82.34 μmol/L), while the lowest was at station 12 in the Gulf (18.02 μmol/L). The bottom depths consistently showed lower silicate concentrations with some variability, notably with station 1 exhibiting a relatively high bottom level (29.83 μmol/L). This suggests that silicate availability is influenced by multiple factors, including riverine input, sedimentation, and biological uptake. The elevated silicate levels at station 6 may be linked to substantial nutrient inflow from nearby rivers, supporting diatom blooms, which need silicate to form their silica-based cell walls. The lower levels at station 12 could be due to increased biological consumption or dilution effects from oceanic processes. Understanding these spatial variations is critical for assessing nutrient cycling and productivity in the Gulf of Mexico and adjacent coastal areas, especially under the influence of ongoing environmental changes and human activities.

References

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