Spatial and temporal variability in modelled nutrient fluxes from the unpolluted Shannon estuary, Ireland, and the implications for microphytobenthic productivity

Wilson, James G.; Brennan, M.

doi:10.1016/j.ecss.2003.12.007

Cited by 12 publications

(9 citation statements)

References 31 publications

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“…Sediment-water exchange flux studies are rare in Ireland and there is little data available for Irish systems. However, the fluxes measured in Kinvara compare well with those reported (Wilson and Brennan 2004) for finer sediments containing 1.21-1.58 % organic carbon from the nearby Shannon estuary of 1.75 to -82.3 (uptake) lmol N m -2 h -1 (NO x ) and 2.82 to 26.2 lmol N m -2 h -1 (NH 4 ? ).…”

Section: Benthic Nitrogen Mineralization and Turnoversupporting

confidence: 73%

Retention and fate of groundwater-borne nitrogen in a coastal bay (Kinvara Bay, Western Ireland) during summer

Rocha

Wilson

Scholten³

et al. 2015

Biogeochemistry

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The magnitude of submarine groundwater discharge (SGD) and its contribution to nitrogen biogeochemistry in a small embayment in the Western Coast of Ireland subject to occasional hypoxia were investigated during summer. Time series (24 h) of 222 Rn, NO 3 -, NO 2 -, NH 4 ?, dissolved reactive silicate (DRSi) and salinity (and dissolved organic nitrogen (DON) (July 2013) were measured at the mouth of the bay and coupled with relevant sediment-water fluxes and input loadings to derive nutrient budgets. In-situ activity ratios of the naturally occurring radium isotopes 224 Ra and 223 Ra were employed in parallel to the freshwater fraction method to determine the timescale of freshwater retention in the system. Based on 222 Rn mass balances (n = 4), the mean groundwater (±SE) discharge into Kinvara Bay was 10.4 ± 6.3910 4 m 3 days -1 , delivering average loads of 376 ± 67 kg Si day -1 (as DRSi), 1.6 ± 0.2 kg P day -1 (as TDP) and *280 kg N day -1 of dissolved nitrogen (272 ± 49 DIN, essentially as NO 3 -, and 8.2 ± 1.6 DON), which correspond to *98.8, 49.1 and *93.5 % of total allochthonous nutrient inputs respectively. Expressed on an areal basis and annual scale the exogenous N summer loading of Kinvara is equivalent to 25.9 g N m -2 year -1 . Our biogeochemical budgets indicate that tight benthicpelagic coupling contributes to the very high retention levels of N within the bay with subtidal sediments acting as a link in the internal N cycle via DNRA, while *18 % of the exogenous N load is removed by benthic denitrification. Rapid cycling of DON into bioavailable forms of N within the timescale of freshwater retention in the system (*7 days) contributes *50 % to local biological N fixation. Nutrient availability ratios are N:P *173 and Si:P *503, indicating that primary production is P-limited while the carbon yield (*3.01 9 10 5 mol C day -1 , or *0.313 kg C m -2 year -1 ) suggests the bay is eutrophic during the summer. SGD-borne Nitrogen loading is therefore the major driver of eutrophication in Kinvara Bay. Our biogeochemical characterization is consistent with the observed phytoplankton community composition and species succession and justifies the local observation of HAB's. In addition, the relative magnitude of DNRA-promoted N retention compared to N removal by denitrification, coupled with seasonal hypoxia, suggests that the system is advanced in Responsible Editor:

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Section: Benthic Nitrogen Mineralization and Turnoversupporting

confidence: 73%

Retention and fate of groundwater-borne nitrogen in a coastal bay (Kinvara Bay, Western Ireland) during summer

Rocha

Wilson

Scholten³

et al. 2015

Biogeochemistry

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“…These values, 2-3 orders of magnitude lower than those found in porewater lead to concentration gradients between sediment and overlying water that drives nutrient sedimentwater exchanges (Trimmer et al 1998;Wilson and Brennan 2004). Solute diffusion is particularly important for nutrient cycling in muddy sediments where diagenesis takes an active part in the biogeochemical cycles of elements (Aller 1980;Nowicki and Nixon 1985;Lerat et al 1990;Bally et al 2004).…”

Section: Discussionmentioning

confidence: 99%

“…Organic material, settled in the upper sediment layers associated to high temperatures, accelerates mineralization processes due to an increase in the microbial metabolism, leading to intense NH 4 + production during that period (Nowicki and Nixon 1985;Van Raaphorst et al 1992;Kristensen 1993;Chapelle 1995;Asmus et al 2000;Wilson and Brennan 2004). On the other hand, nitrification/denitrification processes are also temperature-dependent (Cartaxana et al 1999).…”

Section: Discussionmentioning

confidence: 99%

“…The present fluxes were also comparable with those found in other marine systems (Pregnall and Miller 1988;Lerat et al 1990;Kristensen 1993;Asmus et al 2000). Maximum NH 4 + exchange rates of 96 and 144 nmol cm -2 d -1 have been reported for marine environments in the coast of Ireland (Wilson and Brennan 2004). In the organically-rich Tamar estuary (SW of England), a broader range of NH 4 + (-57-408 nmol cm -2 d -1 ) and HPO 4 2-fluxes (-17-48 nmol cm -2 d -1 ) were referred by Watson et al (1993), while in the carbonate-rich sands of the Great Barrier Reef (Australia), NH 4 + effluxes varied from 14 nmol cm -2 d -1 to 48 nmol cm -2 d -1 and HPO 4 2-from 0 nmol cm -2 d -1 to 3 nmol cm -2 d -1 (Hansen et al 1987).…”

Section: Discussionmentioning

confidence: 99%

“…As diagenetic processes depend on organic matter, temperature, oxygen availability and sediment grain size (Lerat et al 1990;Kristensen 1993;Forja et al 1994;Chapelle 1995;Asmus et al 2000), benthic fluxes are influenced by these environmental factors (Nowicki and Nixon 1985;Van Raaphorst et al 1992;Kristensen 1993;Wilson and Brennan 2004) leading to a spatial and temporal variability in sediment-water nutrient exchanges in most coastal environments (Lerat et al 1990;Forja et al 1994;Vidal and Morguí 1995).…”

Section: Introductionmentioning

confidence: 99%

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Evaluation of ammonium and phosphate release from intertidal and subtidal sediments of a shallow coastal lagoon (Ria Formosa – Portugal): a modelling approach

et al. 2007

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During an annual cycle, overlying water and sediment cores were collected simultaneously at three sites (Tavira, Culatra and Ramalhete) of Ria Formosa's intertidal muddy and subtidal sandy sediments to determine ammonium, nitrates plus nitrites and phosphate. Organic carbon, nitrogen and phosphorus were also determined in superficial sediments. Ammonium and phosphate dissolved in porewater were positively correlated with temperature (P < 0.01) in muddy and sandy sediments, while the nitrogen-oxidized forms had a negative correlation (P < 0.02) in muddy sediments probably because mineralization and nitrification/denitrification processes vary seasonally. Porewater ammonium profiles evidenced a peak in the top-most muddy sediment (380 lM) suggesting higher mineralization rate when oxygen is more available, while maximum phosphate concentration (113 lM) occurred in the sub-oxic layer probably due to phosphorus desorption under reduced conditions. In organically poor subtidal sandy sediments, nutrient porewater concentrations were always lower than in intertidal muddy sediments, ranging annually from 20 lM to 100 lM for ammonium and from 0.05 lM to 16 lM for phosphate. Nutrient diffusive fluxes predicted by a mathematical model were higher during summer, in both muddy (104 nmol -2 ), while during lower temperature periods these fluxes were 3-4 times lower. Based on simulated nutrient effluxes, the estimated annual amount of ammonium and phosphate exported from intertidal areas was three times higher than that released from subtidal areas (22 ton year -1 --NH 4 + ; 2 ton year -1 --HPO 4 -2 ), emphasizing the importance of tidal flats to maintain the high productivity of the lagoon. Global warming scenarios simulated with the model, revealed that an increase in lagoon water temperature only produces significant variations (P < 0.05) for NH 291-304 DOI 10.1007/s10533-007-9076-4 will probably affect the system productivity due to a N/P ratio unbalance.

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Spatial and seasonal variation of water quality in an impacted coastal lagoon (Óbidos Lagoon, Portugal)

Pereira¹,

Pablo²,

Vale³

et al. 2008

Environ Monit Assess

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The spatial distribution of silicate, ammonium, nitrate, nitrite, phosphate, chlorophyll a and dissolved oxygen in Obidos lagoon was obtained by surveying five sites in eight campaigns, between October 2004 and October 2006. A confined inner branch of the lagoon showed higher availability of ammonium (1.2-81 micromol l(-1)), phosphate (1.9-17 micromol l(-1)), silicate (0.85-86 micromol l(-1)) and chlorophyll a (0.30-18 microg l(-1)) than other sites (0.47-25 micromol l(-1), 0.10-3.9 micromol l(-1), 0.47-25 micromol l(-1), 0.25-11 microg l(-1), respectively). According to several trophic classification tools, that branch is considered eutrophic to polytrophic, emphasising its deteriorated conditions, while the rest of the lagoon is of better quality. In autumn/winter nutrients were inversely correlated to salinity (r > 0.93) reflecting the freshwater inputs enriched in nitrogen and phosphorous compounds to the inner branch. In warmer periods, dissolved oxygen concentrations dropped during the night, and sediments of the branch become an important source of ammonium and phosphate. The low DIN:P ratio (median = 10) obtained in the branch, which suggests an excess of phosphate, that increased in warmer periods and changed the limiting nutrient in the entire lagoon. These results emphasize the spatial heterogeneity of water quality in Obidos lagoon, its seasonal variability, and the importance of recognising these distributions before defining homogenous water body on the scope of Water Framework Directive.

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Spatial and temporal variability in modelled nutrient fluxes from the unpolluted Shannon estuary, Ireland, and the implications for microphytobenthic productivity

Cited by 12 publications

References 31 publications

Retention and fate of groundwater-borne nitrogen in a coastal bay (Kinvara Bay, Western Ireland) during summer

Retention and fate of groundwater-borne nitrogen in a coastal bay (Kinvara Bay, Western Ireland) during summer

Evaluation of ammonium and phosphate release from intertidal and subtidal sediments of a shallow coastal lagoon (Ria Formosa – Portugal): a modelling approach

Spatial and seasonal variation of water quality in an impacted coastal lagoon (Óbidos Lagoon, Portugal)

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