Photochemical production of dissolved organic carbon from resuspended sediments

Abstract

A series of controlled photolysis experiments using simulated sunlight was conducted in the presence and absence of estuarine bottom sediments to address the role of sediment resuspension on dissolved organic carbon (DOC) cycling in estuarine and coastal waters. In 0.2-mm-filtered estuarine water samples with no added sediment, DOC concentrations decreased from 0.4 to 3 mmol L 21 h 21 as a result of photooxidation. When 0.2-mm-filtered water samples with the addition of 1-2 grams of estuarine sediment per liter were irradiated, DOC was produced at rates of 3 to 150 mmol L 21 DOC per gram dry sediment. Photoproduction of DOC from resuspended sediments increased in direct proportion to the percent organic carbon content of the added sediment. Highenergy ultraviolet light was the most effective for photodegrading DOC in filtered samples and for photoproducing DOC from resuspended sediments. Photosynthetically active radiation (PAR; 400-700 nm) did not significantly degrade DOC in filtered water. However, PAR did produce half as much DOC from resuspended sediments in organic-rich regions of the estuary relative to full spectrum sunlight irradiations. The photoproduction of DOC from resuspended sediments, calculated for the top 1 m of coastal waters, resulted in fluxes that were significantly larger than benthic and riverine fluxes of DOC. Photoproduction from resuspended sediments therefore represents an episodically significant but previously unrecognized source of DOC to estuarine and coastal ecosystems receiving large sediment plumes.

Aerobic microbial transformation of pesticides in surface water

“…These authors pointed out the participation of different microbes depending on the trophic level of water, and they concluded that the slower energy gain at a lower concentration may not meet the demand by the small population of degrading microbes. A similar concentration effect on mineralization was reported for 2,4-d (10) and carbaryl (22) in stream water, 93) while (10) and propham (20) were more efficiently mineralized in lake water at lower concentrations. 87,140) In the case of isouron (31), no clear concentration effect was observed on the degradation and mineralization at 10 ppb-1 ppm.…”

“…Furthermore, the toxicity of metabolite(s) produced by one strain on another should also be considered for degradation by a community. 39) Through the biodegradation of 2,4-d (10) and 2,4,5-T (11) mixture by Pseudomonas and Alcaligenes sp., Haugland et al 133) reported that chlorohydroquinone from (10) inhibited the hydrolytic dechlorination of the phenols of both herbicides and (11) inhibited the formation of the phenol from (10).…”

“…9) Furthermore, sunlight with wavelengths shorter than 400 nm is reported to play a significant role in the production of dissolved organic carbons (DOC) from estuary sediments. 10) In this review, we first discuss the relative contribution of each environmental process to the dissipation of pesticide in surface water together with the importance of the microbial process especially by bacteria and fungi. After introduction of the study design assessing aerobic transformation with its kinetic analysis, the aerobic transformation profiles of pesticides are examined through a literature survey by considering the involvement of specific microbes in surface water.…”

The role of Fe(III) on phosphate released during the photo-decomposition of organic phosphorus in deionized and natural waters

“…Some studies demonstrated that dissolved nutrients, such as NH 4 þ and PO 4 3À could be released when marine and estuarine resuspended sediments were irradiated by sunlight (Kieber et al, 2006;Southwell et al, 2010Southwell et al, , 2011Zhang et al, 2016). After irradiation for 6 h, the release rate for total dissolved nitrogen and phosphate were 2.2 ± 0.5 mmol g À1 h À1 and 0.09 ± 0.005 mmol g À1 h À1 , respectively.…”

Seasonal changes in optical properties of two contrasting tropical freshwater systems

“…DOM represents a complex of compounds and derives from main sources: allochthonous material produced from degradation of humic substances coming from runoff of terrestrial origin (Kieber et al, 2006;Miller et al, 2009); and autochthonous material, produced by autotrophic and heterotrophic in situ activities, but mainly by the bacterial degradation of phytoplankton and macrophytes (Kritzberg et al, 2004;Hanamachi et al, 2008;Henderson et al, 2008;Guillenette and Del Giorgio, 2012). The two different sources of DOM can be distinguished from differences in their optical and chemical characteristics.…”