Student Number: 1595137

THE CHEMICAL AND BIOLOGICAL RESTORATION OF ACIDIFIED STREAMS

Acidification of streams is one of the major problems facing freshwater ecosystems today. Short-term acid episodes or long-term acidification directly affects acid-sensitive invertebrates, snails, crayfish, clams and freshwater shrimps (Økland and Økland, 1986; Muniz, 1990; Ormerod, 2005). Acidification has been found as the main culprit for the loss of fish in significant parts of Norway and Sweden (Howells and Brown, 1992; Muniz, 1990). Acid waters release toxic amount of Al3+ which damages internal organs of fishes and negatively affecting fish eggs and fries (Rosseland and Henriksen, 1990). Acidified streams are characterised by reduced density and species richness, potentially resulting in major loss of biodiversity.

This essay will discuss about chemical restoration, particularly liming, and the subsequent biological restoration of acidified rivers; its impact and effectiveness.

It is of high significance to determine the causes of stream acidification before introducing restoration solutions. Atmospheric deposition or “acid rain” is one of the prime cause of freshwater acidification (Gee & Stoner, 1989)(Driscoll et al., 2001). The main acidifying substances are the sulphur and nitrogen oxides (SOx and NOx), and ammonia, derived mostly from commercial agriculture (UKAWMN, 2001; Driscoll et al., 2001). SOx and NOx may come from natural sources like volcanoes, oceans, biological decay, lightning and forest fires; and anthropogenic sources like burned coal and petroleum fuels (UKAWMN, 2001) (EPA, 2016). Acid deposition can be classified as “dry deposition” of air pollutants or “wet deposition” of sulphuric and nitric acids. Improper disposal of waste such as acid mine drainage also lowers pH levels in rivers. Although acid deposition is a major factor in aquatic acidification it can still be mitigated if there is a high buffering system by the vegetation and soil (Gee & Stoner, 1989). Livestock introduction to river catchment also lowers river pH by adding large amounts of nitrates through urine to the soil which then reacts to produce nitric acid that is later leached to the water systems (Martins et al., 2014). Aside from acid deposition, buffering and livestock introduction, afforestation by conifers also lowers river since forest canopies to capture more sulphur and nitrogen pollutants from the atmosphere than shorter types of vegetation which is then released to the soil through plant-soil interactions (Department of the Environment, 1991 as cited by Forestry Commisssion, 2014)

Sudden drop in fish population in Scandinavian lakes in the 1970s was found out to be caused by lower pH due to acid deposition (UKAWMN, 2001; Bradley and Ormerod, 2002). Similar events also took place in UK and US streams and lakes thus urging the respective governments to find ways to restore freshwater fish populations through lobbying by anglers which eventually became the start of present and on-going, chemical and biological restoration of acidified streams (Howells and Brown, 1992). Restoration, in freshwater systems, is defined by Roni and Beechie (2013) as a “return of an aquatic system or habitat to its original or undisturbed state”. One of the earlier acid restoration projects were done on Scandinavian lakes and streams (Howells and Brown, 1992; UKAWMN, 2001).

Minimizing SOx and NOx emission are one of the major solutions in mitigating stream acidification (Hildrew and Ormerod, 1995; Gee & Stoner, 1989). Another solution also is proper land-use. Afforestation of catchment with conifers lowers soil pH. Tree planting can enhance acidification by the scavenging of acid deposition, base cation uptake, the scavenging and concentration of sea salts, soil drying and the formation of an acid litter layer at the soil surface (Forestry Commission, 2014).

Aside from the abovementioned solutions, a short-term method is the direct chemical restoration of streams by spreading calcium carbonate (liming) of catchment or lakes. It has already been used operationally in the UK particularly in the Llyn Brianne catchments and in Scandinavia (UKAWMN,

Student Number: 1595137

2001; Howells, G. and Brown, D. 1992). The most common liming material is ground limestone (Clair and Hindar, 2005). Lake liming, wherein liming agent is directly dumped to the lake to increase pH of the lake and its outlet streams, has been done ever since the early reports of freshwater acidification in Scandinavia. Each year 30 000 - 50 000 tonnes are spread in Norwegian rivers and lakes (Norwegian Environment Agency, 2016). On the other hand, catchment liming has demonstrated to be effective in reducing Al3+ in catchment soils (Clair and Hindar, 2005). Mant et al. (2013) suggested that liming might be advocated by the European Union (EU) due to the Water Framework Directive requiring member nations to reach or maintain “good ecological status” of their surface waters.

Figure 1. Lake Liming in Norway (image taken from Norwegian Environment Agency)

Immediate and medium term impacts of liming have been reported. Monteith (2005) stated that catchment liming in Wales showed first clear evidence of chemical recovery from acidification at a national scale. In summer 1987, catchment liming of Llyn Brianne was reported to have increased mean pH from 5.2 to >6.5 since treatment (Welsh Water, 1988 as cited by Gee and Stoner, 1989).

The biological recovery of an acidified river is always preceded by chemical recovery (Driscoll et al., 2001). Increasing stream pH to circumneutral levels is expected to increase stream biodiversity to its original or near-original state (Howells, G. and Brown, D., 1992). Liming projects in UK, Europe and USA have been accompanied by increase in fish population and acid-sensitive invertebrates (Mant et al., 2013). In Enningdal, a watershed shared by Norway and Sweden, crustaceans were observed to respond better than fishes to improved water quality after more than 20 years of liming (Hesthagen et al., 2007). Reintroduction of salmon and brown trout were found to thrive after being absent in the watershed in the 1980s. The salmon catch has increased from 5 tonnes prior to liming in the early 1980s and up to 40 tonnes the recent years (North Atlantic Salmon Conservation Organization, 2005).

Student Number: 1595137

Figure 2. Trends in dissolved organic carbon (DOC) at 3 UKAWMN lakes (image taken from UKAWMN (2001)

Despite liming has been found to increase pH in acidified streams and lakes in UK and Norway (Mant et al., 2013), in some parts of Llyn Brianne, liming was suggested to increase the dissolve organic carbon (DOC) (Figure 1) (UKAWMN, 2001). DOC offsets the direct effects of liming by providing additional acidity. Liming of catchment without existing knowledge of existing ecosystems may be detrimental especially on naturally oligotrophic, base-poor, and of high conservation ecosystems (Ormerod, 1989; Woodin & Skiba, 1990; Farmer, 1992 as cited by Buckton &Ormerod, 1996)

The mixing zone that occurs where an acidic tributary enters a limed river can be highly toxic to the Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.) in the limed River Audna, southern Norway (Åtland and Barlaup, 1995). Acid episodes may contribute to slow biological recovery. Some stream diatoms are highly sensitive to short-term acidification (Hirst et al., 2004) as well insects. . This is supported by Lepori and Ormerod (2005) wherein they observed that the spring distribution of Baetis alpinus in acid sensitive parts of the Alps directly reflects the toxicity of acid runoff during snowmelt. The study also demonstrated that even mild episodic acidification can have significant impact in Alpine streams for highly acid-sensitive insects like the B. alpinus. Previously held belief that only limited dispersal hinders biological recovery from acidification was refuted by a study in the Llyne Brianne by Masters et al.(2007). The study states that aside from insect mating behaviour, acid episodes are also involved in the delayed macroinvertebrate increase in limed catchments.

Acid episodes sometimes occur due to base cation dilution to precipitation, sea salt inputs and NO 3-

pulses as was observed in Afon Gwy (Evans et al., 2008b). A related study by Evans et al (2008a) showed that although sulphur concentrations have declined, dissolved organic carbon (DOC) have increased which resulted in increased organic acidity thus offsetting the benefits of a decrease in mineral (sulphate) acidity.

Between 1989 and 1998, UKAWMN reported a slow decline in sulphate concentrations in some catchments in Wales and England despite the significant reduction of sulphur oxides in the UK. UKAWMN (2001) attributed this to catchments releasing stored sulphate, which has accumulated within them over the past 150 years. Climatic changes like droughts may cause previously inert sulphur compounds, stored deep in catchment soils, to re-oxidise as sulphate which subsequently increase sulphate concentration temporarily once rain returns (UKAWMN, 2001). There is also uncertainty about how the acidified stream recovery process will be influenced by future nitrogen deposition and anthropogenic climate change (Forestry Commission, 2014).

Chemical and biological restoration of acidified streams just like any restoration projects are not straightforward. This is due to the fact that there are several aspects needed to be considered like

Student Number: 1595137

acid episodes, land-use management, disturbance caused by restoration, climate and other abiotic factors (Ormerod, 2004) aside from biotic factors such as dispersal (Petersen et al., 2004), colonisation, competition, (Frame, 2009) (Berger 2006) among others. Though liming has immediate positive impacts nevertheless we should be cautious also of its downsides like risking of liming of naturally base-poor ecosystems, uncertainties related to climate and climate change; and its variable impacts on different acidified streams (e.g. negative impacts on fish and invertebrates (Mant et al., 2013).

REFERENCES

Åtland, Å. and Barlaup, B. (1995). Avoidance of toxic mixing zones by Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.) in the limed River Audna, southern Norway. Environmental Pollution, 90(2), pp.203-208.

Bradley, D. and Ormerod, S. (2002). Long-term effects of catchment liming on invertebrates in upland streams. Freshwater Biology, 47(1), pp.161-171.

Clair, T.A., Hindar, A., 2005. Liming for the mitigation of acid rain effects in fresh-waters: a review of recent results. Environmental Reviews 13, 91-128.

Environment Protection Agency (EPA), (2016). Causes of Acid Rain. [online] Available at: http://www3.epa.gov/region1/eco/acidrain/causes.html [Accessed 16 Jan. 2016].

Evans, C., Monteith, D., Reynolds, B. and Clark, J. (2008a). Buffering of recovery from acidification by organic acids. Science of The Total Environment, 404(2-3), pp.316-325.

Evans, C., Reynolds, B., Hinton, C., Hughes, S., Norris, D., Grant, S. and Williams, B. (2008b). Effects of decreasing acid deposition and climate change on acid extremes in an upland stream. Hydrol. Earth Syst. Sci., 12(2), pp.337-351.

Forestry Commission, (2014). Forestry and surface water acidification. Forestry Commission.

Frame, J. (2009). Ecology Of Acidification And Recovery In Welsh Upland Streams. Ph.D. University of Birmingham.

Gee, A. and Stoner, J. (1989). A review of the causes and effects of acidification of surface waters in Wales and potential mitigation techniques. Arch. Environ. Contam. Toxicol., 18(1-2), pp.121-130.

Hesthagen, T., Walseng, B., Karlsen, L. and Langåker, R. (2007). Effects of Liming on the Aquatic Fauna in a Norwegian Watershed: Why Do Crustaceans and Fish Respond Differently?. Water Air Soil Pollut: Focus, 7(1-3), pp.339-345.

Hildrew A.G. & Ormerod S.J. (1995) Acidification: causes, consequences, solutions. In: The Ecological Basis for River Management (Eds D.M. Harper, A.J.D. Ferguson & R.W. Edwards), pp. 147-160. J. Wiley & Sons, Chichester

Student Number: 1595137

Hirst, H., Chaud, F., Delabie, C., Juttner, I. and Ormerod, S. (2004). Assessing the short-term response of stream diatoms to acidity using inter-basin transplantations and chemical diffusing substrates. Freshwater Biology, 49(8), pp.1072-1088.

Howells, G. and Brown, D. (1992). Acidification and Liming in Context. In: G. Howells and T. Dalziel, ed., Restoring Acid Waters: Loch Fleet 1984-1990, 1st ed. Salem, Massachussetts: Elsevier Science.

Ledger, M. and Hildrew, A. (2005). The ecology of acidification and recovery: changes in herbivore-algal food web linkages across a stream pH gradient. Environmental Pollution, 137(1), pp.103-118.

Mant, R., Jones, D., Reynolds, B., Ormerod, S. and Pullin, A. (2013). A systematic review of the effectiveness of liming to mitigate impacts of river acidification on fish and macro-invertebrates. Environmental Pollution, 179, pp.285-293.

Martins, A., Andrade Costa, S., Anghinoni, I., Kunrath, T., Balerini, F., Cecagno, D. and Carvalho, P. (2014). Soil acidification and basic cation use efficiency in an integrated no-till crop–livestock system under different grazing intensities. Agriculture, Ecosystems & Environment, 195, pp.18-28.

Masters, Z., Peteresen, I., Hildrew, A. and Ormerod, S. (2007). Insect dispersal does not limit the biological recovery of streams from acidification. Aquatic Conserv: Mar. Freshw. Ecosyst., 17(4), pp.375-383.

Monteith, D. and Evans, C. (2005). The United Kingdom Acid Waters Monitoring Network: a review of the first 15 years and introduction to the special issue. Environmental Pollution, 137(1), pp.3-13.

Muniz, I. (1990). Freshwater acidification: its effects on species and communities of freshwater microbes, plants and animals. Proc., Sect. B Biol. sci., 97, pp.227-254.

Norwegian Environment Agency, (2016). Liming lakes and rivers. [online] Available at: http://www.miljodirektoratet.no/en/Areas-of-activity1/Inland-waters/Liming-lakes-and-rivers/ [Accessed 17 Jan. 2016].

North Atlantic Salmon Conservation Organization, (2005). Liming as a Mitigation Measure in Acidified Salmon Rivers in Southern Norway has been a success. [online] North Atlantic Salmon Conservation Organization. Available at: http://www.nasco.int/pdf/2005%20papers/CNL(05)34.pdf [Accessed 19 Jan. 2016]. Ormerod, S. (2004). Golden age of River Restoration?.

Økland, J. and Økland, K. (1986). The effects of acid deposition on benthic animals in lakes and streams. Experientia, 42(5), pp.471-486.

PETERSEN, I., MASTERS, Z., HILDREW, A. and ORMEROD, S. (2004). Dispersal of adult aquatic insects in catchments of differing land use. Journal of Applied Ecology, 41(5), pp.934-950.

Roni, P. and Beechie, T. (2013). Introduction to Restoration: Key Steps for Designing Effective Programs and Projects. In: P. Roni and T. Beechie, ed., Stream and Watershed Restoration: A Guide to Restoring Riverine Processes and Habitats, 1st ed. [online] West Sussex, UK: Wiley-Blackwell, pp.1-8. Available at: http://lib.myilibrary.com/Open.aspx?id=395694.

Rosseland, B.O., Henriksen, A., 1990. Acidification in Norway – loss of fish populations and the 1000-lake survey 1986. The Science of the Total Environment 96(1-2), 45-56.

UKAWMN, (2001). UKAWMN 13-Year Summary Report. [online] Available at: http://awmn.defra.gov.uk/resources/interpreports/13yearSummaryRpt.pdf

Student Number: 1595137

UKAWMN, (2010). UK Acids Monitoring Network: 20-Year Interpretative Report. London: Environmental Change Research centre.