Effects of sunlight on the production of dissolved organic and inorganic nutrients from resuspended sediments

A series of laboratory-based and field experiments was conducted to address the effects of sunlight-exposed resuspended sediments on dissolved nutrient fluxes in two different water bodies. In suspensions of tidal creek sediments in 0.2 μm-filtered creek water, measurable increases in dissolved nutrients occurred after only 2 h of exposure to simulated sunlight. During a 6-h irradiation, nutrient release rates for total dissolved nitrogen (TDN) and phosphate were 2.2 ± 0.5 (standard error; S.E.) μmol g^?1 h^?1 and 0.09 ± 0.005 μmol g^?1 h^?1 (S.E.), compared to no significant changes in dark controls. The majority of nitrogen was released as dissolved organic nitrogen (87% on average) with lesser amounts of ammonium (13%). Continental shelf sediments resuspended in unfiltered seawater also released phosphate and TDN when exposed to sunlight, suggesting that this process can occur in a variety of marine and estuarine environments. The source material for inorganic nutrients appears to be associated with sediments rather than dissolved organic matter, as no significant changes in nutrient concentrations occurred in experiments with 0.2 μm-filtered creek water or seawater alone. Results suggest that photoproduction of dissolved nutrients from resuspended sediments could be an episodically significant and previously unrecognized source of dissolved organic and inorganic nutrients to coastal ecosystems. This process may be especially important for continental margins where episodic resuspension events occur, as well as in regions experiencing high riverine sediment fluxes resulting from erosion associated with deforestation and desertification.