Solar radiation–enhanced dissolution of particulate organic matter from coastal marine sediments

Abstract

We investigated the influence of solar radiation on the transfer of organic matter from the particulate to dissolved phase during resuspension of coastal sediments collected from seven sites across Florida Bay (organic carbon values ranged from 2% to 9% by weight). Sediments were resuspended in oligotrophic seawater for 48 h in 1‐liter quartz flasks in the dark and under simulated solar radiation (SunTest XLS+) at wet weight concentrations of 100 mg L−1 and 1 g L−1 (dry weights ranged from 27 to 630 mg L−1). There were little to no dissolved organic carbon (DOC) increases in dark resuspensions, but substantial DOC increases occurred in irradiated resuspensions. DOC levels increased 4 mg C L−1 in an irradiated 1 g L−1 suspension (dry weight 400 mg L−1) of an organic‐rich (7% organic carbon) sediment. At a particle load commonly found in coastal waters (dry weight 40 mg L−1), an irradiated suspension of the same organic‐rich sediment produced 1 mg C L−1. DOC increases in irradiated resuspensions were well‐correlated with particulate organic carbon (POC) added. Photodissolution of POC ranged from 6% to 15% at high sediment levels and 10% to 33% at low sediment levels. Parallel factor analysis modeling of excitation‐emission matrix fluorescence data (EEM PARAFAC) suggested the dissolved organic matter (DOM) produced during photodissolution included primarily humic‐like components and a less important input of protein‐like components. Principal component analysis (PCA) of EEM data revealed a marked similarity in the humic character of photodissolved DOM from organic‐rich sediments and the humic character of Florida Bay waters.