Introduction

Introduction

The severe impact on river health of excessive nutrient inputs from point sources, such as sewage outlets, has led to a Europe-wide drive to curb such discharges to ensure that rivers maintain generally good water quality (WFD, European Commission 2000). The reduction of diffuse inputs, however, is far more difficult as these have less obvious points of entry to a system and will require complicated catchment management programmes.

In Ireland, nitrogen and phosphorus applications to farmland increased approximately 40-fold and 2.5-fold respectively between 1950 and 1990 and are still increasing (Tunney et al. 1998). The imbalance between phosphorus input in the form of artificial fertiliser and animal manure (derived from P in feed) and output in the form of milk and meat (live or dead) is leading to the creation of an increasing reservoir of P in soils. As the total amount of phosphorus exported in farm run-off from the landscape to surface waters increases linearly with the soil P content, this build up of P in soils is leading to long-term threats to Irish water courses in intensively farmed areas (Tunney et al. 1998; Smith et al.1999).

Eutrophication of river and lakes due to diffuse phosphorus losses from agriculture is considered the greatest threat to Irish freshwaters. Trends from 1971 to 2000 show a strong decline in the numbers of unpolluted rivers and a concomitant increase in the numbers of slightly and moderately polluted rivers (EPA 2004). This increase is attributed to diffuse sources of agricultural pollution (Bowman & Clabby 1998). The long-term history of over-application of phosphorus on farmland has built up stores of soil phosphorus that may take many decades to reduce to levels compatible with environmental protection. Unless urgent action is taken, it may prove to be impossible to prevent a long-term ongoing eutrophication problem in certain catchments (EPA 2004).

Despite the considerable information about the trophic state of many rivers in Ireland (EPA water in Ireland), little is known about the risk of ecosystem degradation for an individual river. Although there have been correlative links made between phosphorus levels in running waters and indicators of river health (the macroinvertebrate Q-value system – McGarrigle 1998), little is known about the direct impacts of nutrients on primary producers and secondary consumers. Furthermore, the impacts of factors such as hydraulic disturbance, water chemistry and shade that may potentially mitigate the degrading effects of eutrophication, have not been studied in detail. Relationships between phosphorus and algal growth have been firmly established for Irish lakes (although exact relationships remain to be investigated), but few studies have focussed on flowing waters.

Given the high likelihood of widespread, long-term eutrophication of Irish waters, there is a clear and pressing need to understand how such a disturbance will affect the ecosystem health of running waters. To specifically address this issue, we propose an innovative approach to quantitatively establish the role of environmental parameters in stream degradation, based on combining analytical field surveys with complementary laboratory experiments. The consequent understanding of the fundamental mechanisms underlying the nutrient economies of Irish streams, will lead to the identification of streams most at risk from ecological degradation through excessive nutrient inputs. Thus this project directly underpins the Irish research capacity in stream management by developing methodology for targeted monitoring of streams most at risk from degradation and by developing management guidelines aimed at mitigating the impact of eutrophication in flowing waters.

  • Bowman JJ & Clabby KJ (1998). Water quality or rivers and lakes in the Republic of Ireland. In: Eutrophication in Irish Waters (ed. JGW Wilson). Royal Irish Academy, Dublin.
  • Environmental Protection Agency (2004). Eutrophication of inland and estuarine waters. In: Ireland's Environment 2004 - The State of the Environment. EPA, Dublin.
  • McGarrigle, M (1998). Impact of eutrophication on Irish river water quality In: Eutrophication in Irish Waters (ed. JGW Wilson). Royal Irish Academy, Dublin.
  • Smith, V.H., Tilnan, G.D., Nekola, J.C. (1999). Eutrophication: impacts of excess nutrient inputs of freshwater, marine and terrestrial ecosystems. Environmental Pollution, 100, 179-196.
  • Tunney H, Foy RH & Carton OT (1998). Phosphorus inputs to water from diffuse agricultural sources. In: Eutrophication in Irish Waters (ed. JGW Wilson). Royal Irish Academy, Dublin.
  • Water Framework Directive. Establishing a framework for Community action in the field of water policy. DIRECTIVE 2000/60/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 23 October 2000
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