ESB Power Stations West Offaly (Shannonbridge) Aquatic ... · ESB Power Stations West Offaly (Shannonbridge) Aquatic Ecological Monitoring ... while at others there was rapid descent

ESB Power Stations

West Offaly (Shannonbridge) Aquatic Ecological Monitoring

(August 2016)

Aquatic Services Unit (ASU) University College Cork (UCC) ERI Building, Lee Road, Cork P: +353 21 490 1935/ F: +353 21 490 1940 (October 2016)

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Contents

1. Executive Summary ..................................................................................................................... 3

2. Introduction ................................................................................................................................. 4

3. Methodology ............................................................................................................................... 4

3.1 Site Selection ............................................................................................................................... 4

3.2 Macrophyte Survey ..................................................................................................................... 5

3.3 Diatom Sampling ......................................................................................................................... 6

3.4 Benthic Grab Sampling ................................................................................................................ 6

3.5 Water Temperature .................................................................................................................... 7

4. Results ......................................................................................................................................... 8

4.1 Macrophytes ............................................................................................................................... 8

4.2 Diatoms ....................................................................................................................................... 9

4.3 Benthic Fauna ............................................................................................................................ 14

5. Discussion .................................................................................................................................. 16

6. Conclusions ................................................................................................................................ 17

7. References ................................................................................................................................. 19

APPENDICES ...................................................................................................................................... 20

APPENDIX 1 Aquatic Macrophyte Data ....................................................................................... 21

APPENDIX 2 Site photographs ..................................................................................................... 23

APPENDIX 3 Diatom data August 2016 ....................................................................................... 25

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1. Executive Summary

The Aquatic Services Unit (ASU) was commissioned to carry out aquatic surveys in relation to a thermal discharge to the River Shannon arising from ESB’s West Offaly power station located at Shannonbridge Lanesborough, Co. Offaly. Surveys were conducted on August 18th, 2016, and were a repeat of aquatic surveys conducted by ASU in August 2014 and 2015.

Aquatic communities were sampled at various distances upstream and downstream of the thermal discharge to allow for comparisons in relation to the thermal discharge. Sampling locations were identical between 2015 and 2016. Biotic communities sampled and analysed for composition and abundance were: (i) aquatic macrophytes, (ii) diatoms, and (iii) benthic macroinvertebrates.

At sites of a similar hydromorphological nature the aquatic macrophyte communities were broadly similar upstream and downstream of the discharge, although the freshwater red algae Thorea hispida only occurred downstream of the discharge. This is more than likely linked to temperature since the species is known to prefer warmer waters. As in previous surveys, the effect of depth/light and turbidity is likely the strongest determinant of communities present. There were no fundamental changes in the macrophyte species composition between 2015 and 2016, but T. hispida, was recorded in a greater number of transects downstream of the discharge in 2016 compared to previous years. Other minor upstream/downstream differences detected in the aquatic macrophyte community present just downstream of the thermal outfall are likely to be related to hydromorphology, i.e., shallower, faster flows and engineered banks.

Diatom assemblages showed upstream/downstream differences in relation to the thermal outflow. The two upstream sites were at ‘High’ status in 2016, declining to ‘Good’ status at the three downstream sites nearest the outfall (up to 101m downstream). All remaining sites downstream; beginning at 184m from the outfall; were at ‘High’ status. The zone of impact according to diatom EQR was therefore quite localised.

The 2016 study demonstrated links between monthly average water temperature and: (i) diatom species richness and; (ii) % A. minutissmum. Species richness tended to increase and % A. minutissimum declined markedly, coinciding with higher average temperatures, i.e., at sites nearest downstream of the discharge.

The distribution patterns of dominant macroinvertebrate groups appear to be more influenced by the availability of suitable substrate than to any clear effect of elevated temperature associated with the thermal discharge. Nevertheless, there may me some limited temperature-related enhancement of the Asian clam, but the effect, would appear to be limited in the main to the immediate area downstream of the thermal discharge.

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2. Introduction

ESB’s West Offaly power station generates a thermal discharge to the River Shannon at Shannonbridge, Co. Offaly. Aquatic surveys were initially conducted in August 2014 and were repeated in August of both 2015 and 2016; upstream and downstream of the discharge. The biotic communities sampled, and analysed for composition and abundance, were: (i) aquatic macrophytes, (ii) benthic diatoms, and (iii) benthic macroinvertebrates. The current report presents results of August 2016 studies and compares the results of the three survey rounds to date.

3. Methodology

3.1 Site Selection

Sampling sites in 2016 were identical to those selected for the 2015 survey. The sites were chosen in 2015 at distances upstream and downstream of the discharge having regard to: (i) results of thermal plume studies undertaken in 2014 at the station, and; (ii) the need to increase the number of sample points closer to the discharge. There were therefore ten (10) sampling sites in total in 2015 and 2016: 2 upstream and 8 downstream of the thermal discharge. The locations of sample sites are shown in Figure 1.

Figure 1 - Survey site locations at Shannonbridge – West Offaly Power Station

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The sampling regime at each site consisted of a combination of the following: a transect along which macrophytes were recorded, a diatom sample and a benthic dredge sample taken from the boat. Each of these parameters was measured at every site.

Table 1 summarises the sampling programme to date (2014, 2015, 2016). Water temperature was taken from automatic temperature loggers that were installed by Irish Hydrodata. The alkalinity values arising from water samples taken in 2015 were used to calculate diatom EQR.

Note that the 2014 sites were all located along the left (eastern) side of the channel, whereas, in 2015 and 2016, sites 6d/s and 8d/s were positioned on the opposite side and 5 d/s slightly toward the centre of the channel. These positions were selected based on a detailed examination of the thermal plume survey of 2014 (which wasn’t available sufficiently in advance of the 2014 survey to inform a similar choice of sites at the time).

Table 1 - Sampling sites showing distance from the outfall and parameters surveyed at each site

Station Code 2015 & 2016

Station Code 2014

Distance from Outfall (m)

Diatoms Macrophytes Invertebrates

1 u/s -910m

2 u/s 3u/s -58m

3 d/s + 21m

4 d/s +72

5 d/s 4d/s +101

6 d/s +184

7 d/s 5d/s +218

8 d/s +323

9 d/s 6d/s +430

10 d/s +1029

3.2 Macrophyte Survey

Up to 5 macrophyte quadrats (size 1m x 1m) per transect were visually assessed on the river bed for macrophyte composition and relative abundance. The quadrats were selected along the transect line extending perpendicular from the shore to a maximum depth of 2m. Quadrat locations were selected on-site in order to assess the main community types encountered along each transect. Macrophyte surveys were carried out by snorkelling and the start and end positions of each transect were recorded using handheld GPS from a boat. A weighted float was used to mark the 2m depth end of each transect and a landmark was used at the other end.

Transects varied in length depending on the profile of the river bed cross section. At some sites there was a gently sloping cross-section, while at others there was rapid descent to >2m within a few metres of the river bank. Transect lengths therefore varied, from 6-30m. The number of quadrats assessed along each transect was determined by transitions in macrophyte community type, which was apparently influenced

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by depth along each transect. Anything between 2 and 5 quadrats per transect were required depending on river depth profile.

3.3 Diatom Sampling

Diatom communities were assessed in accordance to the Diatoms for Assessing River Ecological Status (DARES) protocol including: (i) Identification of diatom community assemblage, and (ii) calculation of Trophic Diatom Index (TDI) and Ecological Quality Ratio (EQR). Samples were collected from stems of waterlily (Nuphar lutea) at all locations except site 3d/s, where diatoms were sampled from submerged cobbles using standard methods.

EQRs represent the relationship between the TDI observed for a given body of surface water and the expected TDI value for reference conditions applicable to that waterbody. “Expected TDI” (eTDI) is adjusted on a per site basis for alkalinity and season (Kelly et al., 2008). Mean alkalinity data was derived from a water sample taken on the day of sampling, analysed in ASU’s in-house laboratory. Alkalinity values recorded in 2015 (156mg/l CaCO3) were used which for the purpose of EQR calculation was capped at 150mg/l as per DARES protocols. Table 2 shows how diatom EQR translates to WFD ecological status classifications of High, Good, Moderate, Poor and Bad. The EQR allows comparison of water quality status across the European Union as each member state has an EQR value for ‘High’; ‘Good’ etc., based on an inter-calibration of boundaries between water quality categories (Kelly et al., 2008).

Table 2 - Status class boundaries for diatom EQR

Diatom EQR WFD Status

≥0.93 High

≥0.78 – < 0.93 Good

≥0.52 – < 0.78 Moderate

≥0.26 - < 0.52 Poor

< 0.26 Bad

3.4 Benthic Grab Sampling

In the present survey, every effort was made to obtain benthic sample from the same depth (~2m) and in the same type of coarse substrate in order to reduce the influence of this factor in upstream/downstream data trends. In 2014 samples were taken using a Van-veen grab (0.045m2) while in 2015 and 2016 they were obtained using a freshwater dredge (Figure 2) with an opening of 45cm x 18.5cm and a 1mm mesh net bag. This was anticipated to perform better on coarse substrates than the grab. In reality, the dredge only proved to be marginally better than the grab and at some sites required to be physically pressed into the substrate due to its coarseness. The dredge samples were sieved on site through a 1mm sieve to extract biota. These were placed in a labelled container, preserved in formalin solution and transported back to the laboratory for identification and enumeration. Macroinvertebrates were classified according to the EPA Q-value biotic index system, even though actual Q-rating couldn’t be assigned to the sites due to the unsuitability of the hydromorphology of the sampling locations for that purpose.

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Figure 2 - Benthic freshwater dredge - 2015/2016 sampling

3.5 Water Temperature

Average monthly water temperature data was provided by Irish Hydrodata Ltd. Arising from water temperature data loggers installed at locations upstream and downstream of the thermal discharge at Shannonbridge. The time period used to obtain monthly average temperatures was 11:40 on 15 July 2016 to 11:35 on 15 August 2016 (5 mins sampling rate). This covers the month preceding recent aquatic surveys of 18 August 2016. For the purposes of comparing water temperature trends with biological metrics in the current report, a simple method of normalization was used to convert per site temperature data to a fraction of the site with the maximum average monthly water temperature. This allowed a 0-1 scale for monthly average temperature data, which could be more practicably compared with, for example, diatom EQR, which also has a 0-1 scale.

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4. Results

4.1 Macrophytes

Appendix 1 shows composition and cover values for macrophytes in quadrats assessed along transects during August 2016. Appendix 2 contains photographs of each transect location.

As in previous surveys; the pattern of vegetation distribution was that of a number of vegetation zones that altered with depth out from the river bank. There was generally: (1) fringing reeds and rushes comprised mainly of a band of Common reed (Phragmites australis) towards the drier banks and shallow littoral zone; (2) a band of emergent Club rush (Schoenoplectus lacustris) and some Branched Burr-reed (Sparganium erectum) in the slightly deeper littoral with some Equisetum fluviatile. At a depth ranging from around 0.4m to 1.6m the communities were generally ((3) a mosaic of submerged species comprised mainly of adult and juvenile Nuphar lutea, plus Myriophyllum spicatum, Sagattaria sagittifolia, Sparganium emersum, the moss Fontinalis antipyretica and in places, stands of Potamogeton perfoliatus and Potamogeton crispus. Between 1.6 and 1.8m there was: (4) notably less abundance of the species found in zone (3), mainly just N. lutea and tall S. sagittifolia with some blue-green algae. The moss Fontinalis antipyretica could be found at any depth up to about 1.8m, its distribution depending on flow and substrate type – it was more common on bouldery substrates in swifter flows. As in previous years, a depth of 2m appeared to be the limit of the photic zone for submersed macrophyte species, apart from: (5) a layer of blue-green algae on benthic substrates.

The freshwater red algae, Thorea hispida (Plates 2) was common in the thermal race just downstream of the outfall location at sites 3d/s, 4d/s and 5d/s. T. hispida was also found in reasonable abundance at a number of sites well downstream of the discharge during 2016 sampling, including: 7d/s; 9d/s and 10d/s. Blue-green algae occurred in two forms: a thin layer (mainly in deeper waters) and as “feathery” masses (Plate 1). These “feathery” blue-greens were more prolific in 2016 compared to 2015.

Plate 1: Mass of “feathery” blue-green algae common at sites downstream of the thermal discharge (18/08/16).

Plate 2: Thorea hispida most abundant at site 5d/s, but also present at other sites downstream of the thermal discharge in 2016 (18/08/16).

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ESB Aquatic Surveys Aquatic Services Unit, UCC

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The main upstream/downstream difference between sites of a similar hydromorphological nature was that T. hispida was included in transects downstream of the thermal discharge, but not upstream (1u/s; 2u/s).

Species composition at sites 3d/s, 4d/s and 5d/s differed from all other sites upstream and downstream in that they were dominated by T. hispida plus growths of blue-green algae. These sites were swifter and shallower with more engineered banks that did not allow for growth of the common fringing reeds and rushes. The differences between these sites and other sites could not be attributed to the thermal discharge alone. Although they are typically much warmer sites: they are also shallower with swifter flows.

As in previous years, depth/light and river hydromorphology were considered the primary determinants of macrophyte community type. Higher frequency and coverage of T. hispida was linked to presence of warmer waters.

Plate 3: Nuphar lutea; Thorea hispida and mats of blue-green algae near the thermal discharge at site 4d/s. (18/08/16).

Plate 4: “Feathery” blue-green algae at site 8d/s with Freshwater sponge (18/08/16).

4.2 Diatoms

Appendix 3 presents the diatom communities at each sampling location in August 2016. Table 3 summarises TDI, EQR and WFD ecological status classifications for August 2014, 2015 and 2016. Figures 3 and 4 show the trends in TDI and EQR, respectively, for 2016 data. Green dashed lines represent the thermal outfall located between sites 2u/s and 3d/s.

In 2016, as in previous years, there was a significant increase in TDI and a decline in the ecological quality classification (compared to upstream sites) at Site 3d/s located immediately downstream of the thermal discharge. In general, a change of +/- 7 TDI points signifies a significant difference between sites (Dr M. Kelly, pers. comm.).

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Table 3 - Diatom metric summary and 2014/2015 comparisons

Site TDI EQR Ecological Status

2014 2015/2016 2014 2015 2016 2014 2015 2016 2014 2015 2016

1u/s 33.49 38.67 33.86 0.97 1.00 H H H

1u/s 33.49 1.00 G

2u/s 39.18 0.92 G

3u/s 2u/s 40.81 34.11 31.82 0.89 1.00 1.00 G H H

3d/s 55.20 51.33 0.71 0.81 M G

4d/s 40.60 44.95 0.94 0.92 H G

4d/s 5d/s 48.92 41.95 46.69 0.77 0.92 0.89 M G G

6d/s 36.16 33.13 1.00 1.00 H H

5d/s 7d/s 47.19 37.08 40.50 0.80 1.00 0.99 G H H

8d/s 38.96 34.28 0.97 1.00

H H

6d/s 9d/s 44.13 34.75 39.89 0.84 1.00 1.00 G H H

7d/s 35.75 0.97 H

8d/s 33.78 1.00 H

10d/s 31.02 36.60 1.00 1.00

H H

Ecological status according to diatoms was ‘High’ upstream of the discharge, declining to ‘Good’ status downstream for sites 3d/s, 4d/s and 5d/s (a distance of 101m downstream); returning to ‘High’ status at site 6d/s (184m downstream of outfall) and remaining ‘High’ status for all other sites downstream of the outfall.

Figure 3 - TDI trend August 2016 (green dashed line = thermal outfall)

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Figure 4 – Diatom EQR trend August 2016 (green dashed line = thermal outfall)

The relationship between water temperature (normalised) and diatom EQR at Shannonbridge study sites is illustrated in Figure 5, showing that EQRs are lowest (poorest) when average monthly water temperatures are higher.

0.5

0.6

0.7

0.8

0.9

1

1.1

1u/s 2u/s 3d/s 4d/s 5d/s 6d/s 7d/s 8d/s 9d/s 10d/s

EQR

Temp.

Figure 5 – Water Temperature (normalised) vs Diatom EQR (thermal outfall = green dashed line)

Figure 6 shows diatom samples recorded a marked increase in species richness just downstream of the thermal discharge compared to upstream sites. Figure 7 shows there was apparently a strong correlation between average monthly water temperature data and diatom species richness. Note that sites 6d/s and 8d/s are located on the west bank of the Shannon River. These sites recorded slightly lower monthly average temperatures compared to sites 7d/s, 9d/s and 10d/s downstream of the outfall

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on the river’s east bank. There was a corresponding decrease in species richness at 6d/s and 8d/s (slightly cooler sites on average) compared to 7d/s, 9d/s and 10d/s (slightly warmer sites on average).

Figure 6- Diatom species richness in relation to thermal outfall (green dashed line)

Figure 7- Diatom species richness vs temperature (normalised) (thermal outfall = green dashed line)

Figure 8 shows % Achnanthidium minutissimum for Shannonbridge sites in August 2016. Similar to trends recorded in 2014 and 2015, there was a significant decline in relative abundance of A. minutissimum in relation to the thermal outfall. Relative abundance of A. minutissimum then gradually increases with increasing distance downstream. Note that only sites 6d/s and 8d/s, located on the river’s west bank and slightly cooler on average, had similar levels as upstream sites.

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Figure 9 further demonstrates the relationship between (normalised) average monthly water temperature and relative abundance of A. minutissimum, showing quite a clear relationship between higher water temperature and decreased % A. minutissimum.

Figure 8 - Relative abundance of A. minutissimum in relation to thermal outfall (green dashed line)

0.00

0.20

0.40

0.60

0.80

1.00

1.20


Temp.

A. minutissimum

Figure 9- Relative abundance A.minutissimum vs temperature (thermal outfall = green dashed line)

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4.3 Benthic Fauna

All of the same dominant, and most of the same minor, macroinvertebrate species that were collected in 2015 were again obtained in samples in 2016. A notable exception was the presence of a single specimen of the Group A (pollution sensitive) mayfly species Heptagenia sulphurea at S3d/s and again at 9d/s. Apart from this, and one Group B genus (the cased caddis Ceraclea sp.) the fauna (Table 4) was characterised by pollution tolerant or very tolerant macroinvertebrates mainly from the EPA Quality groups C, D and E. It isn’t possible to give a Q-rating for the sites because hydromorphology was unsuitable for the normal kick-sample based Q-value system, the study reach being too deep and sluggish in nature. The nearest EPA monitoring point to the Shannonbridge study site is at Clonmacnoise (jetty) about 9km upstream where in 2014 a Q3 rating was assigned i.e. Poor Ecological Status under the WFD and slightly polluted. Some 18km downstream, at Incherky Quay d/s Banagher a Q4 rating was assigned in 2014, i.e., Good Ecological Status under the WFD and non-polluted. While habitat conditions at the sampled sites indicate that they are unsuitable for a standard Q-rating system, the data does suggest a level of nutrient enrichment and therefore the quality is believed to be much closer to Q3-4 or Q3 than to Q4 overall.

The most widespread and abundant species in 2015 were again present in 2016 namely, the amphipod crustacean Chelicorpohium curvispinum, by far the most numerous species in terms of density, followed by zebra mussels (Dreissena polymorpha) the most abundant bivalve and the Asian clam (Corbicula fluminia), the other abundant bivalve in the survey area. Other frequently occurring species but in more modest numbers included crustaceans Gammarus and Asellus, molluscs Bithynia tentaculata and Theodoxus fluviatilis (the freshwater nerite) and flatworms of the genera Dugesia. There is a strong association between the numbers of Zebra mussels in the samples and Chelicorophium which appears to arise from the preference of the amphipod for concentrations of zebra mussels, an observation made previously in Ireland (Lucy et al, 2004). Corbicula was again quite patchy in its distribution in 2016 occurring only in higher densities at two sites 3d/s, immediately below the thermal discharge, and to a much lesser extent at 9d/s toward the downstream end of the survey reach. This distribution may be explainable by its preference for silty sandy substrates and the likely patchiness in the distribution of the latter within the survey areas. However, given that the Asian clam comes from naturally warmer waters than occur in Ireland, would suggest that they could be favoured by elevated temperatures, which is borne out by the findings of a detailed survey of the species near Lanesborough by IFI in 2014 (Caffrey and Millane, 2004). Despite this however, the current and previous survey data in West Offaly Power survey reach, suggests that the species is significantly less prominent at this site than in the Lough Ree Power survey area.

None of the less dominant species showed any discernible or consistent distribution pattern that could be attributed to temperature effects. It is possible that with continued annual sampling at the same sites over several years that a pattern might emerge in some cases. However, given that the numbers in the case of these latter species tend to be low, there is no guarantee that such a pattern would emerge and its value in any case would arguably be of lesser ecological significance, given the lower densities involved.

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Table 4 - Benthic macroinvertebrates taken in dredge samples

EPA WQ Class


Ephemeroptera – Mayflies

Heptagenia sulphurea A 1 1

Trichoptera - Caddisfly larvae

Polycentropus flavomaculatus

C 1

Neureclipsis bimaculata C 1

Ceraclea sp. B 1 1

Cased caddis indet (early instar)

1

Diptera - True Flies

Chironomidae C 5 3 4 7 14 14 26

Crustacea - Freshwater Shrimps

Gammarus C 14 5 1 1 2 2 6 4

Asellus D 25 5

6 27 4

Chelicorophium curvispinum - 50 10 73 52 136 103 241 840 123

Mollusca -Snails and Bivalves

Corbicula fluminea - 145 1 2 18

Dreissena polymorpha - 34 15 1 8 26 198 61 89 596 18

Theodoxus fluviatilis C 10 1 8

Bithnyia tentaculata C 1 1 2 8 1

Potamopyrgus jenkinsii C 1

Oligochaetae - Segmented worms

E 1 1 1

Turbelaria - Flat worms

Dugesia sp C 6 3 1 2 6 22 1

Dendrocoelum lacteum C 1 1 1 1 5 1

Freshwater Sponge + + + +

No of Taxa 5 4 8 9 6 10 6 9 14 8

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5. Discussion

There were no fundamental changes in the macrophyte species composition between 2015 and 2016. As concluded in previous survey rounds, the effect of depth / light and turbidity is likely the strongest determinant of the communities present. At sites of a similar hydromorphological nature the aquatic macrophyte communities were broadly similar upstream and downstream of the discharge, with a distinct zonation pattern in the macrophyte distribution. In most transects (running perpendicular to the bank), fringing reeds and rushes gave way to submerged species mainly those with floating leaves such as Nuphar lutea, Saggitaria saggitifolia and pondweeds. During 2016 sampling, feathery blur-green algal masses were common in the photic zone and the filamentous green algae: Cladophora was quite frequent. At all sites, 2m water depth was pretty much the limit of the photic zone, with only encrusting blue-green algae present on benthic substrates. As in previous years, the macrophyte species recorded at Shannonbridge sites were generally typical of large, slow flowing, slight-to-moderately enriched waters (Holmes et al., 1999).

In 2016 the freshwater red algae, Thorea hispida, was most frequent at sites nearest the thermal discharge (4d/s and 5d/s), but was also recorded at a number of transects further downstream. It was absent from upstream sites. Overall, it appears very likely that occurrence of T. hispida is influenced by the thermal discharge.

Other minor upstream/downstream differences detected in the aquatic macrophyte community present just downstream of the thermal outfall are more than likely related to hydromorphology, i.e., shallower, faster flows and engineered banks.

Diatom assemblages showed upstream/downstream differences in relation to the thermal outflow in 2016. The two upstream sites were at ‘High’ status, declining to ‘Good’ status at the three downstream sites nearest the outfall (up to 101m). All remaining sites downstream (beginning at 6d/s, 184m from the outfall) were at ‘High’ status. Similar to 2015, the impact zone was quite localised in 2016 (101m).

The 2016 study demonstrated links between monthly average water temperature and: (i) diatom species richness and; (ii) % A. minutissmum. Species richness tended to increase and % A. minutissimum declined markedly coinciding with higher temperatures downstream of the discharge. As discussed in previous reports, it is suggested that A. minutissimum a cool water species (Smith & Manoylov, 2013). The results of 2016 sampling at Shannonbridge tend to support this premise. Relative abundance of A. minutissimum often has a strong bearing on diatom EQR as it is generally imparts a good water quality signal.

The macroinvertebrate faunal community upstream and downstream of the thermal discharge at West Offaly Power in 2016 was again typified by the dominance of species tolerant of degraded water quality and the near absence of any pollution sensitive species. Moreover the most abundant invertebrates, as in 2015, belonged to 3 highly invasive species, whose distribution patterns appear to be more influenced by the availability of suitable substrate than to any clear effect of elevated temperature associated with the thermal discharge. Nevertheless, there may me some limited temperature-related enhancement of the Asian clam, but the effect, would appear to be limited in the main to the immediate area downstream of the thermal discharge.

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6. Conclusions

Overview

There were no discernable upstream/downstream differences in the macrophyte communities that could be attributed to temperature alone, although the warm water red algae, T. hispida, was notably only present at downstream sites.

The two sites (3d/s and 4d/s), close to the thermal outflow, differed slightly in their macrophyte communities from other sites both upstream and downstream: but these are shallower, swifter flowing sites and the effects of temperature and hydromorphology on the aquatic plant community cannot be separated.

Summer macrophyte communities appear to primarily be influenced by depth/light and very likely, turbidity, as apparent from the clear zonation pattern observed along each transect and the absence of any macrophyte growth at depths of ≥2m.

Diatom EQR showed a decline in ecological quality immediately downstream of the outflow: from ‘High’ down to ‘Good’ status persisting for at least 101m; with improvement back to ‘High’ status a little further downstream (184m). High status then persisted at all sites downstream of there.

The zone of impact of the thermal discharge on ecological classification according to diatom EQR was again quite localised in 2016 (101m).

Macrophytes

As in 2016, the warm water red algae, Thorea hispida, was abundant in the outflow zone immediately downstream of the thermal discharge location and was also recorded at a number of transects further downstream. It was absent from upstream sites.

As in previous years, depth/light and river hydromorphology were considered the primary determinants of macrophyte community type, but occurrence of T. hispida was only recorded downstream, so this is likely to be linked to the thermal discharge since this is considered a warmer water species.

Diatoms

Ecological status according to Diatom EQR declined from ‘High’ at the 2 sites upstream of the discharge to ‘Good’ at the 3 sites nearest downstream of the outfall (101m), then returned back to High status at site 6d/s (184m) and for the remaining 5 sites downstream.

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The 2016 study demonstrates a good relationship between average preceding monthly water temperature and diatom EQR. Sites with higher average monthly temperature showed lower (poorer) diatom EQR.

The 2016 study demonstrated a good relationship between average preceding monthly water temperature and both diatom species richness and relative abundance of A. minutissimum. Species richness tended to increase and % A. minutissimum declined quite significantly coinciding with higher temperatures downstream of the discharge.

Benthic fauna

Macroinvertebrates taken in the 2016 survey, both upstream and downstream of the discharge, were again dominated with minor exceptions by species tolerant of poorer water quality. This is consistent with the EPA’s own monitoring data for this general area of the Shannon in 2014, when a site about 6km upstream was rated Q3 i.e. poor status.

In most cases, the macroinvertebrate data doesn’t reveal a trend that can clearly be attributed to a temperature impact. The only possible exception to this is the presence of the highest densities of Asian clam at stations close to and immediately downstream of the discharge. This effect, however, is very confined spatially.

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7. References

Caffrey, J. and Millane, M. (2004) Status of the Asian clam in the mid- River Shannon and recommendations for its management. Inland Fisheries Ireland, City West Business Campus. Dublin 14, Ireland

Holmes, N. T. R., Newman J. R., Chadd, S., Rouen, K. J., Saint, L. and Dawson F. H. (1999) Mean Trophic Rank: A User’s Manual. R&D Technical Report E38. Environment Agency, Rio House, Waterside Drive, Aztec West, Almondsbury, Bristol, BS32 4UD.

Hydrodata (2016) Longterm Continuous Water Temperature Measurements: Data Download #1 15th August 2016. Unpublished Report for ESB by Irish Hydrodata Ltd., Oak House, Rathmacullig West, Ballygarvan, Co. Cork.

Kelly, M., Juggins, S., Guthrie, R., Pritchard, S., Jamieson, J., Rippey, B., Hirst, H. and Yallop, M. 2008. Assessment of ecological status in UK rivers using diatoms. Freshwater Biology, 53, 403–422.

Lucy, F., Minchin, D and M. Sullivan (2004) First record of the Ponto-Caspian amphipod Chelicorophium curvispinum (Sars 1895) in Ireland. The Irish Naturalists Journal, 27 pp 461-464.

Smith, M. E. and Manoylov, K. M. (2013) Changes in Diatom Biodiversity in Lake Sinclair, Baldwin County, Georgia, USA. Journal of Water Resource and Protection, 2013 (5): 732-742.

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APPENDICES

AQUATIC MONITORING - WEST OFFALY POWER STATION

SHANNONBRIDGE (18/08/16)

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APPENDIX 1 Aquatic Macrophyte Data

SHANNONBRIDGE (Q=Quadrat) Q1 Q2 Q3 Q4 Q5

Approx. Depth 0 - 0.4m 0.4 – 1.0m 1.0 - 1.6m 1.6 - 1.8m 1.8 - 2.0m

Site Distance Length (m) Irish Grid X Y

10d/s (+)1029 20 M 98129 23603 19

81

29

22

36

03

Phragmites australis 60%; Schoenoplectus lacustris 40%; BG algae +; Cladophora +

Nuphar lutea 10%; Myriophyllum spicatum 30%; Fontinalis antipyretica 3%; Sagattaria sagittifolia 2%; Sparganium emersum 3%: Thorea hispida <1%.

Nuphar lutea 50%; Myriophyllum spicatum 30%; Sparganium emersum 2%; FW sponge <1%; BG algae tufts and layer on substrate 2%.

Thin BG algal layer (50%) + cobble/silt and some zebra mussel shell/gravel.

9d/s (+)430 15 M 97637 23877 19

76

37

22

38

77

Schoenoplectus lacustris 50%; Phragmites australis 50%; Sparganium emersum 2%

Schoenoplectus lacustris 50%; Nuphar lutea 30%; Fontinalis antipyretica 2%; Sparganium emersum 2%: tufts of BG algae 5%.

Nuphar lutea 20%; Fontinalis antipyretica 2%; Thorea hispida <1%; BG algae tufts and layer on substrate 5%.

BG algal layer (25%); FW sponge + large cobble/silt and some zebra mussel shell/gravel.

8d/s (+) 323 10 M 97474 23962 19

74

74

22

39

62

Schoenoplectus lacustris 10%; Sparganium erectum 50%

Schoenoplectus lacustris 3%; Nuphar lutea 20%; Sagattaria sagittifolia 10%; Fontinalis antipyretica 2%; Sparganium emersum 15%: Thorea hispida +

Nuphar lutea 5%; BG algae layer 20%; Thorea hispida +

BG algal layer (35%); FW sponge + bare gravel/silt.

7d/s (+)218 15 M 97484 24068 19

74

84

22

40

68

N

Phragmites australis 90%; Schoenoplectus lacustris +; Cladophora +; tufts of BG algae<1%.

Nuphar lutea 80%; Sagattaria sagittifolia 2% + silt /cobble (very silty).

Nuphar lutea 50%; Fontinalis antipyretica 1%; Sagattaria sagittifolia 5%; Thorea hispida 5%.

Nuphar lutea 3%; Thorea hispida 2%;

Gravel/silt; BG algae 25%

6d/s (+)184 14 M 9737024097 1

97

37

0

22

40

97

Schoenoplectus lacustris 50%; Sparganium erectum 50%.

Nuphar lutea 80%; Sagattaria sagittifolia 10%; Sparganium emersum 1%.

Nuphar lutea 10%; Fontinalis antipyretica 1%; Sparganium emersum 1%.

BG algae 5% + bare zebra mussel shell/gravel

5d/s (+101) 18 M 97431 24141 1

97

43

1

22

41

41

Schoenoplectus lacustris 40%; Nuphar lutea 20%; Myriophyllum spicatum 5%; Sparganium erectum 10%; Cladophora +.

Nuphar lutea 40%; Myriophyllum spicatum 2%; Fontinalis antipyretica 2%; Sparganium emersum 25%; BG algae 3%; Thorea hispida 5%; Cladophora +;

BG algae 40% + gravel and silt + zebra mussel shell/gravel

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4d/s (+)72 30 M 97422 24214 19

74

22

22

42

14

LHS: Schoenoplectus lacustris 5%; Nuphar lutea 50%; Myriophyllum spicatum 2%; Thorea hispida 2%; Phormidium <1% RHS: Thorea hispida 10%; Tufts of BG algae 20%; Myriophyllum spicatum 30%; Nuphar lutea 30%.

[Maximum depth = 1.0m] Nuphar lutea 1%; Zanichella palustris 1%; Thorea hispida 35%; Tufts of BG algae 40% + zebra mussel shell/gravel and cobble. N/A N/A

3d/s (+)21 10 M 97398 24254 1

97

39

8

22

42

54

LHS: Thorea hispida 50%; Tufts of BG algae 20%. RHS: Phragmites australis 50%; Thorea hispida 2%; Tufts of BG algae +.

[Maximum depth = 1m] Thorea hispida 5%; Layer of BG algae 70% + bare cobble with thick organic matrix. N/A N/A

Outfall M 97382 24196 19

73

82

22

41

96

2u/s (-)58 19 M 97363 24306 19

73

63

22

43

06

Phragmites australis 2%: Sparganium erectum 7%; Schoenoplectus lacustris 2%; Equisetum fluviatile 10%; Fontinalis antipyretica 15%; Myriophyllum spicatum <5%; Elodea Canadensis +.

Schoenoplectus lacustris 20%; Sparganium emersum 1%; Fontinalis antipyretica 30%; Potamogeton crispus 1%.

Potamogeton perfoliatus 1%; Myriophyllum spicatum 5%; Sparganium emersum 10%; Fontinalis antipyretica 5% + tufts of BG algae 2%.

BG algae layer 30% + bare mud/silt.

1u/s (-)910 6 M 96731 24820 19

67

31

22

48

20 Phragmites australis

60%; Cladophora spp, 10%.

Nuphar lutea 5%; Sagattaria sagittifolia 5%; FW sponge <1% + tufts of BG algae 10%

BG algae layer 10% + bare mud/silt.

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APPENDIX 2 Site photographs

ESB West Offaly Station - Shannonbridge (18/08/16)

Site 10d/s (18/08/16) Site 9d/s (18/08/16)

Site 8d/s (18/08/16) Site 7d/s (18/08/16)

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Site 6d/s (18/08/16) Site 5d/s (18/08/16)

Site 4d/s (18/08/16) Site 3d/s (18/08/16)

Site 2u/s (18/08/16) Site 1u/s (18/08/16)

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APPENDIX 3 Diatom data August 2016

Site Genus Species Infraspecific taxon N

1 u/s Caloneis bacillum 2

Pseudostaurosira brevistriata 1

Achnanthidium caledonicum cf 3

Navicula capitatoradiata 3

Navicula cryptotenella 2

Nitzschia dissipata 1

Cocconeis euglypta 22

Gomphonema exilissimum 4

Nitzschia fonticola 3

Navicula gregaria 1

Achnanthidium jackii 2

Amphora libyca 2

Site ID Sample Date No. Species % A. minutissimum

1u/s 08_16 22 67%

2u/s 08_16 21 73%

3d/s 08_16 41 18%

4d/s 08_16 34 33%

5d/s 08_16 36 41%

6d/s 08_16 23 69%

7d/s 08_16 39 55%

8d/s 08_16 24 75%

9d/s 08_16 36 58%

10d/s 08_16 32 59%

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Cocconeis lineata 5

Eolimna minima 3

Achnanthidium minutissimum 223

Fragilaria pectinalis 1

Amphora pediculus 8

Gomphonema pumilum 5

Achnanthidium saprophilum 35

Encyonema silesiacum 3

Nitzschia sp 1

Navicula tripunctata 1

2 u/s Rhoicosphenia abbreviata 1

Encyonema caespitosum 1

Gomphonema calcifugum 4






Amphora libyca 1

Cocconeis lineata 5

Encyonopsis microcephala 1


Gomphonema parvulum parvulum 1


Fragilaria perminuta 2




Nitzschia sociabilis 1

Diploneis sp 1

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3 d/s Rhoicosphenia abbreviata 1

Gyrosigma acuminatum 4

Caloneis bacillum 6


Navicula capitata capitata 2

Kareyvia clevei 3


Navicula cryptotenelloides 3

Simonsenia delognei 1




Planothidium frequentissimum 2

Fragilaria gracilis 3

Nitzschia lacuum 1

Amphora libyca 19

Cocconeis lineata 4

Eolimna minima 100


Diploneis oculata 8

Nitzschia paleacea 1



Amphora pediculus 23

Cocconeis pediculus 4

Cocconeis pseudolineata 4

Ctenophora pulchella 1


Fragilaria radians 3

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Navicula reichardtiana 1

Planothidium rostratum 1



Nitzschia sociabilis 1

Cyclotella sp 1

Nitzschia sp 1

Fallacia subhamulata 5

Staurosira subsalina 2


Navicula veneta 1

Diatoma vulgare 1

4 d/s Gyrosigma acuminatum 1

Navicula antonii 6

Caloneis bacillum 1







Cymbella excisa 3


Tabularia fasiculata 1




Navicula gregaria 1

Amphora libyca 10

Cocconeis lineata 24

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Amphipleura pellucida 1

Staurosirella pinnata 1

Ctenophora pulchella 1


Rossithidium pusillum 2

Fragilaria radians 1




Cymbella tumida 1

Melosira varians 5

Diatoma vulgare 3


Nitzschia amphibia 1









Cymbella excisa 1




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Navicula gregaria 3

Amphora libyca 3

Cocconeis lineata 9

Fragilaria mesolepta 4

Eolimna minima 2


Nitzschia palea debilis 3


Amphora pediculus 6




Achnanthidium pyrenaicum 4

Navicula reichardtiana 2



Nitzschia sp 1

Staurosira subsalina 11


Melosira varians 2

Fragilaria vaucheriae 1

Diatoma vulgare 1

6 d/s Navicula antonii 1




Fragilaria capucina capucina 1

Navicula cryptocephala 1



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Eolimna minima 1


Amphora pediculus 7

Kareyvia ploenensis gessneri 3




Nitzschia soratensis 1




Navicula antonii 2








Cymbella excisa 1




Nitzschia heufleuriana 1

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Stauroneis kriegeri 1

Amphora libyca 4


Eolimna minima 1


Gomphonema olivaceum 1


Amphora pediculus 4

Amphora pediculus 2




Cocconeis pseudolineata 1





Nitzschia soratensis 1

Cyclotella sp 2

Diploneis sp 1


Melosira varians 1

Encyonema ventricosum 1

Diatoma vulgare 1


Navicula antonii 1



Fragilaria capucina capucina 1

Navicula cryptocephala 1

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Cymbella excisa 1





Amphora ovalis 1



Kolbesia ploenensis 1




Diploneis sp 3

Gomphonema tergestinum 1




Navicula antonii 1

Gyrosigma attenuatum 1





Cymbella cistula 1

Kareyvia clevei 1



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Cymbella excisa 1




Navicula gregaria 1

Amphora libyca 2

Eolimna minima 1


Staurosira oldenburgiana 2


Amphora pediculus 9



Kolbesia ploenensis 2

Encyonema prostratum 1


Planothidium rostratum 1


Sellaphora seminulum 1


Encyonema sp 2




Navicula antonii 2

Surirella brebissonii kuetzingii 1




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Cymbella cistula 1

Achnanthes conspicua 1




Cymbella excisa 2








Nitzschia palea debilis 1


Gomphonema parvulum parvulum 1

Amphora pediculus 1





Cymatopleura solea 1



Melosira varians 3

Diatoma vulgare 1

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ESB Power Stations West Offaly (Shannonbridge) Aquatic ... · ESB Power Stations West Offaly (Shannonbridge) Aquatic Ecological Monitoring ... while at others there was rapid descent

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