Nutrient and Ecosystem Dynamics in Ireland's Only Marine Nature Reserve (NEIDIN) datasets

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Resource or Project Abstract

Humans now strongly influence almost every major aquatic ecosystem, and their activities have dramatically altered the fluxes of growth-limiting nutrients from the landscape to receiving waters. Increased incidence of algal blooms and necrotic patches in jewel anemone colonies suggest that anthropogenic nutrient enrichment may be negatively impacting Ireland?s only statutory marine reserve, Lough Hyne. This project aimed to address the nutrient and ecosystem dynamics within Lough Hyne, with additional reference to the candidate SACs at Tragumna and Tranabo bays.

Water quality and nutrient analysis was conducted monthly for 23 months. Initial high values of total nitrogen at the beginning of the study reduced over the course of the year, but remained much higher than historical values. The atomic ratio of N:P in water samples greatly exceeded the 16:1 ratio for optimum phytoplankton growth, suggesting that the coastal environment is P limited. There were no significant differences in nutrient levels between Lough Hyne and adjacent coastal areas, suggesting that high nutrient levels are part of a wider coastal problem, and not from localised inputs. Potentially eutrophic conditions where TN>350 mg m-3 and TP>30 mg m-3 occurred in 101 and 27 out of 131 samples respectively, indicating a high degree of N enrichment in coastal waters. Bloom conditions (where phytoplankton cell abundance exceeded 106 cells l-1) occurred on 27 sampling occasions.

Phytoplankton assemblages were studied for 18 months in Lough Hyne and the adjacent coast, and the influence of nutrients on structuring phytoplankton assemblages was investigated. Lough Hyne had higher phytoplankton abundances, yet lower Shannon-Weiner diversity, indicating a proliferation of relatively few dominant species. Non-metric multidimensional scaling plots showed a general separation of reserve and adjacent coastal areas, with significant differences between Lough Hyne and adjacent coastal areas being detected. Lough Hyne tended to be characterized by higher abundances of tintinids, microflagellates and dinoflagellates, while locations outside Lough Hyne had overall higher abundances of diatom species. Diatom abundance correlated with chlorophyll-a and P:Si ratio, suggesting that phosphorus may be the limiting nutrient to diatom production. Dinoflagellates correlated with salinity, temperature, and total N, indicating that the high N levels observed in marine waters are favouring dinoflagellate production.

A series of phytoplankton growth and microzooplankton grazing experiments were run in Lough Hyne and Tranabo bay to investigate the extent to which top-down and bottom-up processes influence the observed differences in phytoplankton assemblages noted between Lough Hyne and adjacent coastal areas. Negative phytoplankton growth rates were observed in both locations, indicating that microzooplankton grazing was greater than phytoplankton growth at the time of the experiment. Microzooplankton grazing in Tranabo Bay was high, while in Lough Hyne the grazing rate was weak and non-significant. Phytoplankton growth rate was much higher in samples containing mesozooplankton grazers, suggesting mesozooplankton grazing on the abundant ciliates and heterotrophic dinoflagellates, which in turn reduced overall grazing pressure on phytoplankton. This suggests that top-down processes play a greater role in structuring phytoplankton assemblages at Lough Hyne.

Finally, the catchment and hydrodynamics of Lough Hyne were characterized. Catchment areas for Lough Hyne, Tranabo bay, and Tragumna bay were calculated as 2.89, 0.37, and 11.77km2 respectively. Given that Tragumna bay has a large catchment relative to its size, it may be more susceptible to anthropogenic nutrient enrichment associated with runoff into its coastal waters. A 2-dimensional, depth-averaged hydrodynamic model of Lough Hyne was developed that successfully modelled the unique 8-hour ebb and 4-hour flood tides observed in the lough. A revised tidal flushing time of 15 days was calculated. However, complete flushing of the lough was estimated at approximately 80 days, effectively double that of earlier estimates.

It is apparent that nutrient enrichment of the coastal waters is a wider problem than initially thought, and is adversely affecting a number of areas in the south-west of Ireland. Exceptional algal mats have been noted in Clonakilty and Rosscarbery estuaries as well as the blue flag beach in Inchydoney. A taskforce has recently been set up to address the problem, highlighting the importance of regular monitoring studies.

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Contact Information for This Resource

Dr. Mark Jessopp
University College Cork

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Data, Files, Information Objects Related To This Project Resource

This resource has SEMI-PUBLIC availability. This means that the metadata for the resource is available to the public but the data files and information objects connected to the resource are not. There are currently 7 data files and/or information objects connected to this resource. You will need to contact the owners of this resourceto seek their consent to access the files. Contact information for the owners of this resource can be found in the Responsible Parties information section of the metadata.


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Access Information For This Resource

SAFER-Data Display URL
Resource Keywordsnutrients, phytoplankton, biodiversity, eutrophication
EPA/ERTDI/STRIVE Project Code2007-FS-B-4-M5
EPA/ERTDI/STRIVE Project ThemeBiodiversity
Resource Availability: Non Owner-Users Cannot Download Files from This Resource
Limitations on the use of this ResourceNONE
Number of Attached Files (Publicly and Openly Available for Download): 3
Project Start Date Tuesday 1st January 2008 (01-01-2008)
Earliest Recorded Date within any attached datasets or digital objects Wednesday 30th January 2008 (30-01-2008)
Most Recent Recorded Date within any attached datasets or digital objects Tuesday 24th November 2009 (24-11-2009)
Published on SAFERThursday 17th December 2009 (17-12-2009)
Date of Last EditTuesday 12th April 2011 at 10:57:11 (12-04-2011)
Datasets or Files Updated On Tuesday 12th April 2011 at 10:57:11 (12-04-2011)

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Geographical and Spatial Information Related To This Resource

Description of Geographical Characteristics of This Project or Dataset
coastal areas of Lough Hyne, Tranabo Bay, Tragumna Bay (southwest Cork). Nearest town: Skibbereen.

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Supplementary Information About This Resource

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Lineage information about this project or dataset
Water Framework Directive
Supplementary Information
-Dissolved O2 data taken at 1m intervals down the western trough at Lough Hyne to record development and persistence of seasonal thermocline and anoxic zone

-Phytoplankton abundance data from locations within Lough Hyne, Tranabo Bay, Tragumna Bay and adjacent coast. species abundances given as cells/L

-Nutrient data (total N, total P, Total Si, chlorophyll-a) taken from 10m integrated water sample for marine locations, and from freshwater inputs to bays. Nutrient analysis carried out by University College Cork Aquatic Services Unit. Dissolved O2, temperature and salinity readings taken from surface waters using portable field meters.

-Dilution experiment data gives Chlorophyll-a levels (using acetone extraction method) for seawater replicates as well as phytoplankton abundances associated with the samples. Spreadsheet also includes zooplankton abundances from the water column (0-10m)
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