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Brackish waters are commonly characterised by high productivity due to frequent if not continuous inputs of nutrients from both freshwater (notably nitrogen) and marine (notably phosphorous) sources (Nixon 1995). Significant settlement of particulate matter, itself often rich in nutrients (including organic carbon), occurs in estuaries and can result in high levels of production of benthic (seabed) fauna and flora, and form a source of nutrients to the water column. These nutrients promote the growth of phytoplankton and algal blooms may occur. Such high productivity, combined with alternating salinity and temperature conditions, can result in fluctuating oxygen levels. These disturbances, and often extreme environmental conditions, result in estuaries and brackish environmental waters being characterised by a low biodiversity, but often high production of plants and animals.
Alga blooms can produce toxins which stress or kill aquatic life, contaminate shellfish and limit the value of the water body for public and recreational use. Toxic blooms in freshwater are correlated with nutrient enrichment (Petersen et al. 1999) and such pollution may also have a role in marine and estuarine toxic alga blooms.

Disturbed ecosystem conditions and low biodiversity in brackish waters are natural and not a management problem. However, if eutrophic conditions develop then benthic and/or planktonic alga blooms, and loss of species of economic importance (e.g. fisheries) can be a problem (e.g. Caddy 1993). Alga blooms can be unsightly, and can die on-mass and cause severe local anoxic conditions with hydrogen sulphide emissions. Apart from the upset such smells and pollution of seashores may cause to the public, they also kill off other fauna and flora. In 1988, the hydrogen sulphide released from the decay of over 1 million tons of the benthic alga Ulva in the Venice lagoon was so severe that evacuation of the city was considered (Runca et al. 1996).

The fauna living on the riverbed is routinely used as an indicator of river quality. Similarly marine seabed (i.e. benthic) fauna can indicate organic enrichment. However, within an estuary the benthic fauna can be exposed to salinity and temperature changes, and natural enrichment from settlement of particulate organic matter (i.e. mud). It can thus be difficult to discriminate impacts on estuarine benthos due to human activities. However, indices of estuarine quality have been developed that utilise information on the benthos (e.g. Jeffrey et al. 1985a, Jeffrey et al. 1985b).

Benthic fauna can be important in grazing algae, and aerating and stabilising sediments. Stabilisation of sediments by benthic plants (e.g. sea grass) and animals (e.g. tubeworms, hydroids) can reduce re-suspension of organic carbon into the water column. Furthermore, degradation of organic matter is faster under aerobic conditions through both microbial and
faunal activity. The extinction of fauna due to anoxia following alga blooms may thus make the recurrence of such blooms more likely in the future. For these reasons, regular surveys of species? distributions form a useful indicator of ecosystem health, complement monitoring of anthropogenic waste inputs, and provide a baseline for comparison against future surveys.

The best indicators of estuary trophic status may be the frequency (in time) and spatial extent of alga blooms, hypoxia in the water column, and the occurrence of impoverished benthos due to anoxia or other pollution. Service et al. (1996) considered eutrophic estuaries to exhibit a selection of the following: elevated nitrate concentrations in water; exceptional algal concentrations; long-lasting algal blooms; oxygen deficiency; changes in benthic fauna; changes in macrophyte growth; occurrence of shellfish poisoning; formation of algal scums.

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Contact Information for This Resource

Mark J. Costello
Ecological Consultancy Services Ltd (EcoServe)

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Data, Files, Information Objects Related To This Project Resource

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Att 1    R&D_94-99_Costello_Nutrient_Dynamics_syn.pdf   (2.16 Mb)

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Author(s)Costello, J.
Title Of WebsiteSecure Archive For Environmental Research Data
Name of OrganisationEnvironmental Protection Agency Ireland
Electronic Address or URL
Unique Identifierc71de499-204a-102f-a0a4-f81fb11d7d1c
Date of AccessLast Updated on SAFER: 2024-04-17

An example of this citation in proper usage:

Costello, J.   "MEASUREMENT AND MODELLING OF NUTRIENT DYNAMICS OF TWO ESTUARIES IN IRELAND, WEXFORD AND CORK HARBOURS". Associated datasets and digitial information objects connected to this resource are available at: Secure Archive For Environmental Research Data (SAFER) managed by Environmental Protection Agency Ireland (Last Accessed: 2024-04-17)


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Access Information For This Resource

SAFER-Data Display URL
Resource KeywordsNutrient Dynamics, Urbanisation, Drainage, Estuary
EPA/ERTDI/STRIVE Project ThemeWater Quality
Resource Availability: Any User Can Download Files From This Resource
Limitations on the use of this ResourceAny attached datasets, data files, or information objects can be downloaded for further use in scientific applications under the condition that the source is properly quoted and cited in published papers, journals, websites, presentations, books, etc. Before downloading, users must agree to the "Conditions of Download and Access" from SAFER-Data. These appear before download. Users of the data should also communicate with the original authors/owners of this resource if they are uncertain about any aspect of the data or information provided before further usage.
Number of Attached Files (Publicly and Openly Available for Download): 1
Project Start Date Monday 19th January 1998 (19-01-1998)
Earliest Recorded Date within any attached datasets or digital objects Monday 19th January 1998 (19-01-1998)
Most Recent Recorded Date within any attached datasets or digital objects Monday 18th December 2000 (18-12-2000)
Published on SAFERThursday 25th August 2011 (25-08-2011)
Date of Last EditThursday 25th August 2011 at 10:29:56 (25-08-2011)
Datasets or Files Updated On Thursday 25th August 2011 at 10:29:56 (25-08-2011)

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Geographical and Spatial Information Related To This Resource

Description of Geographical Characteristics of This Project or Dataset
The main rivers entering Wexford and Cork Harbours are the Slaney and Lee. In both cases, the entire estuary from the freshwater river to marine entrance to the sea is termed the ?Harbour?. Their freshwater catchment areas are similar, but freshwater runoff is greater in Cork due to a generally higher rainfall (Table 3). Wexford is smaller and shallower, and although it has a larger tidal range a greater proportion of its volume (39 %) is potentially exchanged on each tide than for Cork (10 %) (Table 3). They differ markedly in shape, the Slaney discharging into a very wide shallow bay (Figure 3), but the Lee into a narrower complex inlet (Figure 4). Both receive untreated sewage discharges, and Cork Harbour has a greater concentration of industrial discharges and a larger human population (Table 3). In Wexford Harbour, considerable areas of saltmarsh have been dyked off and drained for use as agricultural land. Large beds of mussels (Mytilus edulis) are managed as a fishery in Wexford Harbour, and Cork Harbour has a large native oyster (Ostrea edulis) farm. Phytoplankton blooms have caused concern in both estuaries. These were toxic dinoflagellates in Cork and nuisance mats of Phaeocystis washed ashore in Wexford Harbour.

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Supplementary Information About This Resource

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Lineage information about this project or dataset
This study was part financed by the European Regional Development Fund through the Environmental Monitoring, R & D Sub-Programme, Operational Programme for Environmental Sciences (1994-1999).
Supplementary Information
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