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Solar radiation-enhanced dissolution (photodissolution) of particulate organic matter (POM) has the potential to provide a substantial pool of dissolved organic matter (DOM) to surrounding waters in a variety of aquatic systems. This study focused on the magnitude of photodissolution in south Texas estuaries and the influence of environmental factors such as sediment desiccation and water chemistry on the production of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) via photodissolution. Substantial photoproduction of DOM from POM was observed during 24-h irradiations, with the potential to augment DOC and TDN loads in Texas estuarine waters by as much as 85 and 75 %, respectively. Excitation-emission matrix (EEM) fluorescence analysis revealed that fluorescent DOM (FDOM) produced during photodissolution is primarily humic-like. Experimental evidence suggested that photochemical degradation of POM was a major pathway for DOM photoproduction, at least a strong supplement to microbial-mediated degradation and/or stimulation of benthic primary production by benthic phytoplankton or algae. Sediment dry-wet cycles strongly influenced photodissolution as sediment desiccation augmented the photoproduction of DOC and TDN in organic-poor water. The organic content of ambient water by itself did not significantly affect the magnitude of DOM photoproduction, but the combined influence of water organic content and sediment desiccation played a substantial role in controlling the extent of photodissolution. Thus, photodissolution is likely an important source of DOC and TDN to shallow Texas estuarine waters especially for habitats where organic-rich sediments undergo dry-wet cycles.

This study examined freshwater discharge of dissolved organic matter (DOM) to the shallow Lavaca–Matagorda (LM) Bay estuarine system along the central Texas coast and investigated whether chromophoric DOM (CDOM) photochemical reactions have the potential to stimulate microbial activity within LM estuarine waters. Dissolved organic carbon (DOC) concentrations ranged from 3 to 10 mg C l−1 and CDOM levels (reported as a 305) ranged from 8 to 77 m−1 during April and July, 2007, when the LM system was experiencing very high freshwater inputs. DOC and CDOM levels were well-correlated with salinities > 3, but exhibited considerable variability at salinities

Phytoplankton nutrient limitation experiments were performed from 1994 to 1996 at three stations in the Cape Fear River Estuary, a riverine system originating in the North Carolina piedmont. Nutrient addition bioassays were conducted by spiking triplicate cubitainers with various nutrient combinations and determining algal response by analyzing chlorophyll a production and 14C uptake daily for 3 d. Ambient chlorophyll a, nutrient concentration, and associated physical data were collected throughout the estuary as well. At a turbid, nutrient-rich oligohaline station, significant responses to nutrient additions were rare, with light the likely principal factor limiting phytoplankton production. During summer at a mesohaline station, phytoplankton community displayed significant nitrogen (N) limitation, while both phosphorus (P) and N were occasionally limiting in spring with some N+P co-limitation. Light was apparently limiting during fall and winter when the water was turid and nutrient-rich, as well as during other months of heavy rainfall and runoff. A polyhaline station in the lower estuary had clearer water and displayed significant responses to nutrient additions during all enrichment experiments. At this site N limitation occurred in summer and fall, and P limitation (with strong N+P co-limitation) occurred in winter and spring. The data suggest there are two patterns controlling phytoplankton productivity in the Cape Fear system: 1) a longitudinal pattern of decreasing light limitation and increasing nutrient sensitivity along the salinity gradient, and 2) a seasonal alternation of N limitation, light limitation, and P limitation in the middle-to-lower estuary. Statistical analyses indicated upper watershed precipitation events led to increased flow, turbidity, light attenuation, and nutrient loading, and decreased chlorophyll a and nutrient limitation potential in the estuary. Periods of low rainfall and river flow led to reduced estuarine turbidity, higher chlorophyll a, lower ambient nutrients, and more pronounced nutrient limitation.