Assessment of recent sediment influence in an urban polluted subantarctic coastal ecosystem. Beagle Channel (Southern Argentina) (original) (raw)
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The effect of benthic sediments on the dissolved nutrient concentrations and fluxes
2006
The Ria Formosa is a meso-tidal coastal lagoon experiencing enhanced nutrient concentrations. Assessment of sediment–seawater interaction is essential if nutrient dynamics and the risk of eutrophication are to be fully understood. Pore water concentrations of dissolved inorganic and organic phosphorus, ammonium, nitrate and nitrite were determined in cores from six sites. Changes in nutrients concentrations were measured in intertidal pools on sand and mud between tides. Dissolved inorganic phosphorus (DIP) concentrations (~200 µmol l−1) and effluxes (123 ± 14 µmol m−2 h−1) were greater from sand than mud (37 ± 10 µmol m−2 h−1), possibly due to the binding of P with the <63 µm fraction. NH 4 + effluxes were high outside the Ancão Basin (821 ± 106 µmol m−2 h−1) and were associated with Enteromorpha sp. mats. The greatest NO 3 − efflux was from sediments near a salt marsh (170 ± 67 µmol m−2 h−1). These sediment fluxes of P were not sufficient to account for elevated P concentrations seen by other workers on the ebb tide from the Ancão Basin. Intertidal pools were sinks for Dissolved Inorganic Nitrogen (DIN) and DIP over the 6 h exposure period. Thus, tidepools may be an important route of nutrients into sediments that enhances the effects of sediments on seawater nutrient concentrations.
Significance of euphotic sediments to oxygen and nutrient cycling in a temperate estuary
Marine Ecology Progress Series, 1992
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.
Marine Pollution Bulletin, 2002
We used a biochemical approach based on the analysis of the quality and quantity of sedimentary organic matter for identifying new descriptors of the trophic state and environmental quality of coastal marine systems. A large-scale study, including 99 stations, belonging to 33 transects, was carried out along 250 km of the Apulian coasts (Mediterranean Sea) in March and September 2000. The investigated area covered a wide range of anthropogenic impacts (industrial ports, tourist harbours, areas affected by power plants and industrial wastes, mariculture areas). Other sites, including marine protected areas (i.e., without any apparent impact), were used as ''control''. Water column and benthic parameters provided different indications and classifications of the trophic state of coastal marine systems. We found that phytopigment content of the sediments changed in response to all different sources of anthropogenic impact and resulted in a useful descriptor of the trophic state and environmental quality. Highest sediment chlorophyll-a concentrations, indicating conditions of increasing eutrophication, were found in areas impacted by the discharge of heated waters from a power plant. In particular, the contribution of the autotrophic biomass to the biopolymeric carbon pool appeared to be a good descriptor of the decreasing environmental quality. Independently from the sampling period or the pollution source such contribution was significantly lower in transects subjected to anthropogenic impact than in control areas. Differences in trophic conditions were evident both in terms of quantity (i.e., total organic matter content) and quality (i.e., biochemical composition) of sediment organic matter. In particular, sediment protein concentration appeared to be a good descriptor of the trophic state of the benthic systems at different spatial scales. Multivariate (MDS) analysis allowed identifying areas characterised by hypertrophic, eutrophic and meso-oligotrophic conditions and to define relative threshold levels. A classification of the trophic state of coastal systems based on protein and carbohydrate concentrations is proposed.
The effect of benthic sediments on dissolved nutrient concentrations and fluxes
Biogeochemistry, 2006
The Ria Formosa is a meso-tidal coastal lagoon experiencing enhanced nutrient concentrations. Assessment of sediment-seawater interaction is essential if nutrient dynamics and the risk of eutrophication are to be fully understood. Pore water concentrations of dissolved inorganic and organic phosphorus, ammonium, nitrate and nitrite were determined in cores from six sites. Changes in nutrients concentrations were measured in intertidal pools on sand and mud between tides. Dissolved inorganic phosphorus (DIP) concentrations (~200 lmol l -1 ) and effluxes (123 ± 14 lmol m -2 h -1 ) were greater from sand than mud (37 ± 10 lmol m -2 h -1 ), possibly due to the binding of P with the <63 lm fraction. NH 4
Marine Ecology Progress Series, 2007
We tested the effect of additions of organic matter of different quality (C:N ratio) and quantity on benthic fluxes of ammonium, nitrate, silicate, oxygen and dissolved inorganic carbon (DIC). Additions were made to intact sediment boxes, according to a 2-level factorial design, and the magnitude and temporal scale of the response were evaluated with Partial Least Square (PLS) regression analysis. Response patterns were followed over a 40 d period following the addition, but only fluxes of ammonium, nitrate, silicate and oxygen for the first 2 d after addition, and nitrate fluxes for the first 8 d after addition, could be used for predictive modelling. The results showed that the response of the microbial community to different qualities and quantities of organic matter may initially be related to its capacity to sequester organic matter, and in the long term, to its growth in response to the respective nutritional supply. The results also suggest that such an experimental approach can be a useful tool for classification of areas with potential risk of eutrophication.
Coastal hypoxia and sediment biogeochemistry
2009
The intensity, duration and frequency of coastal hypoxia (oxygen concentration <63 µM) are increasing due to human alteration of coastal ecosystems and changes in oceanographic conditions due to global warming. Here we provide a concise review of the consequences of coastal hypoxia for sediment biogeochemistry. Changes in bottomwater oxygen levels have consequences for early diagenetic pathways (more anaerobic at expense of aerobic pathways), the efficiency of re-oxidation of reduced metabolites and the nature, direction and magnitude of sediment-water exchange fluxes. Hypoxia may also lead to more organic matter accumulation and burial and the organic matter eventually buried is also of higher quality, i.e. less degraded. Bottom-water oxygen levels also affect the organisms involved in organic matter processing with the contribution of metazoans decreasing as oxygen levels drop. Hypoxia has a significant effect on benthic animals with the consequences that ecosystem functions related to macrofauna such as bio-irrigation and bioturbation are significantly affected by hypoxia as well. Since many microbes and microbial-mediated biogeochemical processes depend on animal-induced transport processes (e.g. re-oxidation of particulate reduced sulphur and denitrification), there are indirect hypoxia effects on biogeochemistry via the benthos. Severe long-lasting hypoxia and anoxia may result in the accumulation of reduced compounds in sediments and elimination of macrobenthic communities with the consequences that biogeochemical properties during trajectories of decreasing and increasing oxygen may be different (hysteresis) with consequences for coastal ecosystem dynamics.