Sources, production and fate of nutrients in Clew Bay, County Mayo and its catchment.

1. Presented to the Clew Bay Forum February 21st 2002 Sources, production and fate of nutrients in Clew Bay, County Mayo and its catchment. Dr Neil Bass Watermark aqua-environmental

2. What people say about salmon farms wastes:- • Håkanssen et al (1988):- 1 tonne salmon production ~ 150 people. Invalidated by Ackefors (1990), an environmental scientist. • David Suzuki Foundation (1988):- 1 tonne salmon production ~ 1,500 people. Suzuki’s claims have often been cited (Friends of the Earth, WWF) but they have never achieved peer-reviewed publication in the scientificpress . They have been generally regarded as sensationalist and politically motivated by the scientific community (Hardy 2000). • Letters to Mayo News (2001):- Quoting Commercial fishing fish farming and fish eating; “1 tonne of farmed fish produces pollution equal to the untreated sewage of 2-300 people”. • Article; Irish Times, Feb 11th 2002; quoted source:- “The larger the (salmon farming) industry grows, the more likely it is to burst, (due) to uncontrollable pollution and disease”. Watermark aqua-environmental

3. Let’s examine the facts. A number of opportunities to do this arose in 2001:- • Desk study of nutrient discharges into Lough Swilly (for Lough Swilly CLAMS group). • Desk study of nutrient discharges into Clew Bay (for Clew Bay CLAMS group). • EIS and Aquaculture license submission; (in an answer to query from the Irish Aquaculture License Vetting Committee, regarding the “carrying capacity” of Kenmare Bay). Watermark aqua-environmental

4. What’s the plan? • We will take a look at the total production of nutrients by the main inhabitant groups in the Clew Bay catchment. • Next, we will estimate what proportion of all nutrients produced in the catchment enter the bay. • Then we will look at what happens to nutrients, once in the bay. • Finally we will look at their subsequent fate. Watermark aqua-environmental

5. A few definitions. • Nutrients are inorganic chemicals, which are required by plants for primary production. • Primary production is the process of plant growth, (phytoplankton and algae / seaweed in freshwater / seawater; grass and other plants on land), by which nutrients, carbon and oxygen (CO2) are combined into plant matter, with the help of photo-synthesis and solar energy. Plant matter is at the bottom of the food chain, through which all animal nutrition arises. • Nitrate is the first limiting nutrient to primary production in marine systems, where phosphate is plentiful. • Phosphate is the first limiting nutrient to primary production in freshwater systems, where it is scarce. • Biochemical oxidation demand (BOD) is the total amount of oxygen required to neutralise the environmental impact of a given waste. • Suspended / settleable solids (SS) are the insoluble fraction of a waste. • Feed conversion ratio (FCR) is the ratio of dry feed fed to wet weight gain (example 1.20 : 1). Watermark aqua-environmental

6. Fishfarm wastes. Fishfarm wastes can be easily calculated:- (Not such an easy task for some other sources of waste). • Develop a growth model. • Select ration type; establish its and protein (nitrogen) and phosphorus content. • Calculate feed usage and FCR by month. • Calculate monthly N and P feed intake, from the feed analysis data. • Use standard formulae to calculate monthly production of BOD, SS, N and P, from the feed intake data. Watermark aqua-environmental

7. Clew Bay salmonid farms; combined nutrient production.(Clare Island Seafarm and Seastream Trout Farm sites) Nitrogen and phosphorus production; tonnes per month. • Licensed production ~ 4,500 tonne pa. • September transfer, harvest the following October. • Mean transfer weight = 733gm; mean harvest weight = 4.5kg • Mean FCR ~ 1.20 : 1 • Total inorganic N production = 9.8 - 29.8 tonnes pm = 208.0 tonnes pa. • Total inorganic P production = 2.5 – 7.5 tonnes pm = 52.3 tonnes pa. Nuttrient prodctuion tonnes Watermark aqua-environmental

8. Humans!Data; population from Central Statistics Office ; tourist numbers from Irish Tourist Board;Gross population mean human nutrient production rate data from OSPAR Neut 5/3E 1999;NB; Figures also make allowance for nutrients in domestic and industrial wastewater pc Clew Bay population statistics • Permanent residents; 18,000. • Tourists; 3,411-11,937 resident equivalents per month. • Estimated combined total weight of humans = 1,054 tonnes. • Mean human nutrient production = 9.0gm N and 2.7gm P / day. • Total N production = 5.9 – 8.2 tonnes pm = 82 tonnes pa. • Total P production = 1.8-2.5 tonnes pm = 24.7 tonnes pa. Watermark aqua-environmental

9. Livestock; cattleData; cattle numbers, types and weights; CSO 1991 data by electoral district (latest data).Excretion rates by type; “Agri-environmental Specifications for the Rural Environmental Protection Scheme (REPS); November 2000” ; Department of Agriculture, Dublin • The total population of cattle of all types is 37,838. • Their estimated total weight is 15,431 tonnes. • Total N production = 160 tonnes pm = 1.971 tonnes pa. • Total P production = 24 tonnes pm = 288 tonnes pa. Clew Bay cattle statistics (1991) Watermark aqua-environmental

10. Livestock; sheep.Data; sheep numbers, types and weights; CSO 1991 data by electoral district (latest data).Excretion rates by type; “Agri-environmental Specs for REPS 2000” ; DoA Dublin Clew bay sheep statistics (1991) • There are 163,598 sheep in the Swilly catchment. • Their estimated total weight is 8,129 tonnes. • Their total N production is 1,268 tonnes pa. • Their total P production is 194 tonnes pa. Watermark aqua-environmental

11. Let’s do some sums. Inhabitant populations by number Inhabitant populations by weight N and P production; tonnes pa. N and P production / inhabitant tonne Watermark aqua-environmental

12. Let’s do some more sums.Clew Bay catchment nutrient production by percent. Annual P production as % of total Salmon 4.4% Sheep 34.7% Salmon 7.0% Sheep 35.9% Trout 1.5% Trout 2.4% Humans 2.3% Humans 4.4% Annual N production as % of total Total catchment N production 3,529 tonnes pa Total catchment P production 560 tonnes pa Cattle 51.5% Cattle 55.8% Watermark aqua-environmental

13. What enters Clew Bay from its catchment?All transformation indices from nutrient production to input from OSPAR Neut 5/3E 1999. The fishfarms are in the bay, thus 100% of soluble nutrient production is input to the water column. Total = 185.1 tonnes N and 32.4 tonnes P pa Urban dwellers (14,000); after secondary treatment, 1.79kg N and 0.46kg P input to the bay pp pa. Rural dwellers (11,105); from septic tanks, 0.5kg N and 0.01kg P is input to the bay pp pa. Total = 30.6 tonnes N and 6.6 tonnes P pa Livestock (cattle and sheep); 20% of all N and 4% of all P produced inputs to lough. Total = 647.7 tonnes N and 19.3 tonnes P pa Fertilisers; Est. 50% national mean spread rate, 20% of N and 4% of P input to lough pa. Input = 506.3 tonnes N and 16.2 tonnes P Forestry 135.5km2; input = 73.4T N and 4.5 P pa Background deposition = 80.9T N and 5.4 T P pa. Have we missed anything? Yes! Watermark aqua-environmental

14. Here come the sums again.Catchment rainfall and inputs to the bay; % per month. • Rainfall is the controlling factor in inputs that originate on the land. • Net annual freshwater run-off arising from rainfall in the Clew Bay catchment is 1.2 billion m3 (=tonnes) pa. Net freshwater run-off to Clew Bay; % per month Watermark aqua-environmental

15. Nitrogen inputs into Clew Bay; % / month • Human inputs vary with population change (tourist flux). • Fishfarm nutrients vary with temperature, biomass and feeding. • Inputs from land vary in proportion to % monhtly freshwater run-off. Watermark aqua-environmental

16. How does that look annually?Nitrogen inputs from catchment sources by percent. Clew Bay Lough Swilly Fertiliser 26.82% Forestry1.88% Fertiliser 32.57% Forestry4.72% Background3.91% Background5.20% Fishfarms 2.84% Fishfarms11.91% Humans 3.94% Total annual N input 3,477 tonnes Total annual N input 1,578 tonnes Humans 1.97% Livestock 60.61% Livestock 41.66% Watermark aqua-environmental

17. What happens in the Bay?The contribution of the ocean to nutrients in Clew Bay • Mean inorganic N varies monthly from 16-168mgm/tonne water. • Mean inorganic P varies monthly from 8.7-18.0mgm/tonne water. (Source 10 years of 2-weekly sampling data from Clew Bay). • The mean low water volume of Clew Bay is 302km2 x 20m = 6,043,221,460 m3 (= tonnes weight) • The tidal range is 1.65 m (neap) to 3.75m (spring). • Using a tidal prism model, we can calculate that Lough Swilly flushes with the tide alone every 3-6.5 days (spring to neap) • Thus the volume of water flushing into Lough Swilly every month = 44,750,829,683 tonnes pm = almost 540 billion tonnes pa. • This is equivalent to the weight of 176 x the earth’s human population marching into Clew Bay every month. • Since it is the flushing action of tide and current that carries all nutrients into the bay, we can calculate that the total flux of nutrients is 38,769 tonnes of nitrogen and 7,243 tonnes of phosphorus per annum (windless conditions only). Watermark aqua-environmental

18. Mean nutrient flux into Clew Bay. Derived by multiplying the monthly tidal flow into Clew Bay by the mean monthly ambient nutrient concentration (ten-year database). The “wave form” of the graph reflects the natural, seasonal cycle of nutrient uptake, primary production die back and remineralisation in the oceans, hence the term “oceanic flux”. Watermark aqua-environmental

19. Total nutrient flux in percentages% contribitions to total flux from catchment and the ocean. Annual P flux as % of total Humans 0.07% Humans 0.07% Livestock 1.67% Livestock 0.27% Fertiliser 1.31% Fertiliser 0.22% Forestry0.06% Forestry0.19% Background0.07% Annual N flux as % of total Total annual N flux 14,817 tonnes Background0.21% Total annual P flux 2,921 tonnes Salmon 0.72% Salmon0.54% Oceanic98.59% Oceanic96.02% Watermark aqua-environmental

20. So? • The model tells us that we can infer absolutely no negative impact from nutrient inputs arising from the production of 4,500 tonnes of salmonids in Clew Bay, nor for that matter any other nutrient input. On the basis of nutrient inputs alone, the bay could support considerably more finfish culture. • Bearing in mind all the allegations made about “pollution from salmon farming”, should we be surprised that no lobby group seems to be as bothered about the nutrient impact of agriculture? As we have seen, agriculture sources account for well over 90% catchment nitrogen. • In freshwater systems, nutrient inputs from agriculture are now believed to be Ireland’s biggest single environmental issue, causing eutrophication and wiping out ame and coarse fish stocks. • We can see that the power of tide and ocean controls the nutrient balance in well-flushed sea areas very effectively. Indeed this is the dominant source of their nutrient flux. Watermark aqua-environmental

21. In case you wondered… In the case of the Clew Bay model model:- • One tonne of salmon production in Clew Bay produces the same nutrient nitrogen waste as about 14 humans (or 1.1 cows!!) • One tonne of salmon production in Clew Bay produces the same nutrient phosphorus waste as about 13 humans. • One tonne of salmon production in Clew produces the same BOD as about 15 adult humans. • Whichever way you look at it, Håkanssen was out by a factor of 10 and Suzuki by a factor of 100. The source recently quoted in the Mayo News was out by a factor of 15-20. Marine salmon farming is not a significant polluter in the well flushed waters of the west of Ireland. Anyone who thinks it is is talking a load of …. Watermark aqua-environmental

22. Bull…! Watermark aqua-environmental

23. Watermark aqua-environmental old conna bray county wicklow Ireland neilbass@iol.ie