Rising CO2 concentration in the atmosphere, global climate change, and the sustainability of the Earth's biosphere are great societal concerns for the 21st century. Global climate change has, in part, resulted in a higher frequency of flooding events, which allow for greater exchange between soil/plant litter and aquatic carbon pools. Here we demonstrate that the summer 2011 flood in the Mississippi River basin, caused by extreme precipitation events, resulted in a “flushing” of terrestrially derived dissolved organic carbon (TDOC) to the northern Gulf of Mexico. Data from the lower Atchafalaya and Mississippi rivers showed that the DOC flux to the northern Gulf of Mexico during this flood was significantly higher than in previous years. We also show that consumption of radiocarbon‐modern TDOC by bacteria in floodwaters in the lower Atchafalaya River and along the adjacent shelf contributed to northern Gulf shelf waters changing from a net sink to a net source of CO2 to the atmosphere in June and August 2011. This work shows that enhanced flooding, which may or may not be caused by climate change, can result in rapid losses of stored carbon in soils to the atmosphere via processes in aquatic ecosystems.

Solar ultraviolet (UV) radiation can have deleterious effects on coral assemblages in tropical and subtropical marine environments, but little information is available on UV penetration into ocean waters surrounding corals. Here we provide an extensive data set of optical properties in the UV domain (280[en]400 nm) that were obtained during 1998‐2005 at sites located in the Lower and Middle Keys and the Dry Tortugas. Absorption coefficients of the colored component of the dissolved organic carbon (DOC; colored dissolved organic matter [CDOM]) were 6× to 25× larger than particulate absorption coefficients in the UV region, indicating that CDOM controls UV penetration in the inshore coastal waters and reef tract. CDOM absorption coefficients (αCDOM) and DOC were highly correlated to diffuse attenuation coefficients (Kd) in the UV spectral region. Measurements using moored sensors showed that UV penetration at the reef tract in the Lower Keys varies significantly from day to day and diurnally. The diurnal variations were linked to tidal currents that transport CDOM over the reef tract. Summertime stratification of Case 1 bluewaters near the reef tract during periods of low wind resulted in higher temperatures and UV penetration than that observed during well‐mixed conditions. This result suggests that higher UV exposure accompanying ocean warming during low‐wind doldrums conditions significantly contributes to coral bleaching. Modeling results indicate that changes in underwater sunlight attenuation over the coral reefs can affect UV‐induced deoxyribonucleic acid (DNA) damage and inhibition of coral photosynthesis much more strongly than changes in the stratospheric ozone layer.

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We tracked a swine waste spill (4.13 x 10' L) into a small receiving river and estuary. After 2 d, a 29-km freshwater segment that the wastes had traversed was anoxic, with ca. 4000 dead fish floating and hung in shoreline vegetation. Suspended solids, nutrients, and fecal coliforms were IO-to lOO-fold higher at the plume's edge (71.7 mg SSIL, 39.

In the summer of 1996, southeastern North Carolina, United States, was struck by two hurricanes, with the second (Hurricane Fran) doing considerably more damage than the first (Hurricane Bertha). The Cape Fear watershed, largest in North Carolina, suffered from severe water quality problems for weeks following Fran, including a massive fish kill in the Northeast Cape Fear River. Post-hurricane flooding caused inputs of riparian swamp water to river channels, and sewage treatment plant and pump station power failures caused diversions of millions of liters of raw and partially treated human waste into rivers. Additionally, several swine waste lagoons were breached, overtopped, or inundated, discharging large quantities of concentrated organic waste into the system, particularly into the Northeast Cape Fear River. Dissolved oxygen (DO) decreased to 2 mg/L in the mainstem Cape Fear River, and fell to zero in the Northeast Cape Fear River for Ͼ3 wk. Biochemical oxygen demand in the Northeast Cape Fear River was sixfold greater than in the other tributaries, probably as a result of anthropogenically derived inputs. The Cape Fear Estuary also suffered from hypoxia for several weeks. Following Hurricane Fran, ammonium levels in the Northeast Cape Fear River displayed a distinct increase, and total phosphorus reached its highest concentration in 27 yr. The benthic community, which is dominated by opportunistic species typical of oligohaline to mesohaline estuarine areas, showed a mixed response. There was a significant decline in total benthic abundances immediately after Hurricane Fran at an oligohaline station in the Northeast Cape Fear River, with recovery occurring in ϳ3 mo. An oligohaline station in the mainstem Cape Fear River, which had relatively rapid DO recovery, did not display significant declines. A mesohaline station 5 km below the confluence of these rivers showed broad and long-lasting benthic declines, but benthic declines were less severe in the lowest reaches of the estuary sampled. The natural hurricane effect of swamp water flooding into river basins led to reduced dissolved oxygen levels and increased light attenuation. However, environmental damage was considerably increased by anthropogenic practices, including the lack of backup generating systems for waste treatment systems and subsequent sewage diversions into rivers, as well as accidents occurring at swine waste lagoons sited on river floodplains.