Significance of euphotic sediments to oxygen and nutrient cycling in a temperate estuary

Abstract

Sediment-water nutrient and oxygen exchanges were measured under light and dark conditions at 1 oligohaline (Stn D) and 1 mesohaline (Stn A) shallow (1 m) site in the Neuse River estuary, North Carolina. USA. Mean respiration rates were very similar between sites (11 to 12 mg 0 2 m-' h-'), but maximum net productivity at the mesohaline site (74 mg Oz m-' h-') was nearly twice that of the oligohaline site (40 mg O2 m-2 h-'). NH4 fluxes were also significantly different. On average, releases of NH, from sediments at both sites occurred in the dark (13 to 22 pm01 N h-' for Stns D and A, respectively) and, slightly, at the lowest irradiance (67 E m-' S-'. 0.3 to 5 pm01 N h-'). NH, was taken up at average rates between 3 and 12 pm01 N m-' h-' at 3 higher irradiances. Mean NO, (nitrate + nitnte) fluxes were very low ( < l 0 pm01 N m-2 h-'), nearly always directed out of the sediment, and not significantly different. Filterable reactive phosphorus fluxes also did not follow any consistent response to changes in irradiance. Flux vs irradiance curves were used in conjunction with estimates of in situ light availability to the benthos to compute ecosystem-level influence of autotrophy on material exchanges. The autotropic-heterotrophic transitions were 1 to 2 m (oligohaline) and 3 to 4 m (mesohaline). When integrated over depth and area the mesohaline sediments were always net NH, sources to the water column, net O2 sources in fall and winter and net O2 sinks in spring and summer. Oligohaline sediments were O2 sinks except during fall, and NH, sources only in winter and summer. Cultural eutrophication has the potential to alter the balance of benthic autotrophy and heterotrophy which in turn may foster phytoplanktonic productivity.

Nitrogen and Phosphorus Flux Rates from Sediment in the Lower St. Johns River Estuary

“…Several studies have been performed on NH 4 –N fluxes in a variety of aquatic systems using intact core incubation (Table 7) When comparing flux rates from the fine‐grained muddy sediment of the LSJR (13.1–23.9 mg m −2 d −1 ) to similar intact core studies, the mean average anaerobic NH 4 –N flux rates in the LSJR are within the range of flux rates from mud sediment of Morlaix Bay, France (21.0 mg m −2 d −1 ) (Lerat et al, 1990) and higher than fluxes from the sand sediment of the Neuse River estuary (9.50 mg m −2 d −1 ) (Rizzo et al, 1992), while being comparable or slightly greater than fluxes reported in the Indian River Lagoon (17.6–36.3 mg m −2 d −1 ) (Reddy et al, 2001).…”

Nutrient fluxes on an intertidal mudflat in Marennes-Oléron Bay, and influence of the emersion period

“…Nutrient fluxes at the sediment-water interface can indeed influence or regulate the nutrient composition of the water column since the sediment can behave as a sink or as a source of inorganic nitrogen , phosphorus and silica through different biogeochemical processes (Nixon et al, 1976;Billen, 1978;Peterson, 1979;Kemp et al, 1990). Moreover, in the most shallow waters, where a sufficient amount of light reaches the sediment surface, microphytobenthos photosynthesis is also tightly coupled to fluxes of dissolved inorganic nutrients through the sedimentwater interface (Nowicki and Nixon, 1985;Rizzo, 1990;Nilsson et al, 1991;Sundbiick et al, 1991;Rizzo et al, 1992;Riera and Richard, 1996) sa that the autotrophic activity of the sediment has to be taken into account if a total understanding of the cycling of matter in coastal areas is to be achieved.…”

Ecosystem impacts of three sequential hurricanes (Dennis, Floyd, and Irene) on the United States' largest lagoonal estuary, Pamlico Sound, NC

“…Preliminary examinations of the Sound's surface sediments indicate organic matter enrichment from both nutrient-enhanced primary production and sediments transported to the Sound from the riverine tributaries by flood flows. Increased rates of oxygen consumption and inorganic nutrient release from sediment diagenesis have been observed in the Neuse and Pamlico estuaries in response to organic matter enrichment (8,10,29). The inorganic nutrient release should further stimulate primary production, as occurred in Chesapeake Bay after Hurricane Agnes (20).…”