Eutrophication Forum Position Paper No. 1

Introductory Note. Eutrophication Forum Position Papers are intended to cover particular aspects of eutrophication and related causes and effects. They are pitched at the level of the person who wants to be well informed and who has a reasonable scientific understanding but is not a specialist. [Any controversial aspects are tackled openly and any uncertainties acknowledged.] The content of Eutrophication Forum Position Papers represents a broad consensus of the views of members of the Eutrophication Forum Committee but is limited in its level of detail in order to fulfil the need to inform its target audience in a reasonably concise manner. The content does not, therefore, necessarily reflect the definitive position of each individual member or the organisation he/she represents.

ADVERSE EFFECTS OF AQUATIC EUTROPHICATION

Aquatic eutrophication is the enrichment of water bodies by plant nutrients, primarily as a result of human activities, creating a range of atypical effects. These may be categorised as follows:

  1. Direct biological effects (e.g. enhanced growth of plants and algae and changes in their species composition).
  2. Indirect ecological effects on water quality, water flow, the beds of water bodies and the biota (animal and plant life) as a result of A. (A and B can be self perpetuating.)
  3. Effects on water uses as a result of A and/or B.
  4. Other effects (e.g. flooding).

The extent to which effects are seen as "problems" is naturally open to debate, involving value judgements in which different sectors of society and individuals may have differing perspectives. Adverse effects on water uses are generally the most obvious to the general public and water users. Ecological and wildlife conservation impacts are often less immediately tangible to the public (except extreme events such as fish kills and lakes which have become "pea soups") but are of great importance to those with an interest in the "health" of the water environment.

The main adverse effects caused by aquatic eutrophication are listed below, categorised in terms of the type of waters in which they occur (fresh or saline), the type of plant/algal growth involved and the types of effect (A-D above).

Eutrophication is considered to be a "problem" when nutrient enrichment causes adverse effects of the types A-D above (and as expanded upon in 1 and 2 below), or when the risk of such adverse effects arising is judged to be significant. The effects listed below are not presented in any particular order and no indication is given of their respective frequency, extent and severity of occurrence. It should be noted that not all of the adverse effects will occur and that some adverse effects may occur naturally. The difficulties and costs (to different sections of society) associated with the assessment, management and control of the causes and effects of eutrophication present their own problems but are not expanded upon in this paper.

1.FRESH WATERS

1.1 EFFECTS ASSOCIATED WITH BLUE-GREEN ALGAL BLOOMS/SCUMS AND THEIR TOXINS (STANDING AND SLOW-FLOWING FRESH WATERS)

1.1.1Ecological impacts of toxins on other biota (A)

1.1.2Loss of water-based recreational facilities (e.g. swimming, windsurfing, boating and angling) due to risk to human health (C)

1.1.3Hazard and impact of toxins on pets and livestock (illness and death) from drinking direct from lakes, reservoirs or slow flowing rivers (C)

1.1.4Reduced general amenity value of water bodies, due to hazard from toxins, unsightly, decomposing algal scums on shorelines, noxious odours and aesthetic nuisance (C)

1.1.5Reduced ability to abstract water for public water supply, industrial water supply, spray irrigation or livestock watering, with potential need to provide alternative sources (C)

1.1.6Need for increased treatment of abstracted water (by water companies) to remove toxins (C)

1.1.7Adverse effects on crops following spray irrigation (C)

1.1.8Reduced value of waterside properties (e.g. to British Waterways) (linked to 1.1.4) (D)

1.2EFFECTS ASSOCIATED WITH INCREASED GROWTH AND CHANGING SPECIES COMPOSITION OF ALGAE (MAINLY IN STANDING FRESH WATERS)

1.2.1A flip from clear water to algal dominance (with turbid water) in shallow lakes, leading (through a series of inter-related effects) to adverse impacts on the whole ecology (eventually reducing biodiversity) including plant life, zooplankton (microscopic animals) and fisheries, reducing wildlife conservation and amenity values (A, B and C)

1.2.2Algal blooms causing reduced dissolved oxygen levels through respiration and decay, affecting aquatic flora and fauna (including fish kills) and human uses (abstraction, amenity, angling) (B & C)

1.2.3Loss of sensitive and rare elements of the biota (e.g. fish such as vendace), particularly in lakes, as a result of algal decay reducing oxygen in the lower water layer of lakes (the hypolimnion) and changing the pH, thereby reducing the wildlife conservation value of water bodies (B & C).

1.2.4Algal blooms causing reduced ability to abstract water for public water supply, or industrial water supply, with potential need to provide alternative sources (C)

1.2.5Algal blooms causing need for increased treatment of abstracted water (by water companies and industry), to remove algae, associated taste and odour problems and to address problems arising from algal decomposition products (e.g. formation of disinfection by-products) (C)

1.2.6Reduced general amenity value of water bodies due to "pea soup" appearance of water, decomposing algal scums on shorelines, noxious odours and aesthetic nuisance (C)

1.2.7Reduced value of waterside properties (e.g. to British Waterways) (linked to 1.2.6) (D)

1.3EFFECTS ASSOCIATED WITH INCREASED GROWTH OF BENTHIC (BOTTOM DWELLING OR ATTACHED) ALGAE (MAINLY IN RUNNING FRESH WATERS)

1.3.1Benthic algal mats in rivers can lead to reduced dissolved oxygen in spawning gravels, causing decline in salmon fisheries (sometimes termed "chalk stream malaise" but also affecting other river types) (B)

1.3.2Benthic algal growth in rivers, through reducing dissolved oxygen levels, can adversely affect the composition of benthic invertebrate(animal) communities, leading to loss of sensitive species (B)

1.3.3Benthic algal mats of oscillatoria (a type of blue-green algae) in rivers in the spring can pose a toxic hazard to human and animal health (C)

1.4EFFECTS ASSOCIATED WITH INCREASED GROWTH AND CHANGING SPECIES COMPOSITION OF LARGE PLANT FORMATIONS (MACROPHYTES/ MACROALGAE) IN STANDING AND RUNNING FRESH WATERS

1.4.1Proliferation and associated silt deposition contributing to "chalk stream malaise" (see also 1.3.1) through clogging the river bed, affecting oxygen levels and promoting benthic algal growth (A & B)

1.4.2Changing species composition (loss of sensitive macrophyte species) and abundance causing reduced wildlife conservation interest (A & C)

1.4.3Proliferation causing reduced night-time dissolved oxygen levels through respiration, leading to adverse effects (including death) for aquatic flora and fauna (B)

1.4.4Proliferation impeding navigation and water based recreation, (with associated need for weed cutting e.g. by Environment Agency and British Waterways) (C)

1.4.5Proliferation causing nuisance effect on angling (C)

1.4.6Proliferation reducing general amenity value of water body (C)

1.4.7Proliferation and associated silt deposition increasing flooding risk (D)

2.SALINE WATERS

2.1EFFECTS ASSOCIATED WITH INCREASED GROWTH AND CHANGING SPECIES COMPOSITION OF PHYTOPLANKTON (MICROSCOPIC PLANT ORGANISMS) AND BACTERIA

2.1.1Changing species composition of marine phytoplankton community, often with a shift away from diatoms to species considered less desirable (A)

2.1.2Changing plant community structure in estuaries, moving from vascular plants (seagrasses and saltmarsh), through macroalgae with eventual dominance by bloom-forming phytoplankton and reducing wildlife conservation interest (A and C)

2.1.3Decay of algal blooms in marine waters causing reduced dissolved oxygen levels, with potential production of methane and hydrogen sulphide, adversely affecting marine zooplankton, benthic fauna (including changing species composition) and fish (including fish kills and barriers to fish movement/migration) and human uses (commercial fisheries and shellfisheries) (B & C)

2.1.4Nuisance algal blooms (e.g. of Phaeocystis) causing aesthetic pollution (foaming, noxious odours) and reducing water and beach use for recreation (bathing, diving, windsurfing etc) and general amenity (C).

2.1.5Increased occurrence of blooms of toxic or tainting algae, presenting a hazard to other biota and to human health through the food chain, particularly via shellfish, and leading to loss of commercial production (C)

2.1.6Reduced tourist appeal (and revenues) due to perceived poor quality bathing waters as a result of algal blooms/foaming, decomposing algal scums on shorelines, noxious odours and aesthetic nuisance (D)

2.2EFFECTS ASSOCIATED WITH INCREASED GROWTH AND CHANGING SPECIES COMPOSITION OF MICROPHYTOBENTHOS (small bottom-dwelling algae) AND MACROALGAE (large algae)

2.2.1Proliferation and associated de-oxygenation of underlying muds in inter-tidal areas, affecting benthic faunal communities, restricting and reducing the quality of feeding areas for bird populations and fish (A & B)

2.2.2Changing species composition (e.g. loss of sensitive slow growing species) and abundance causing reduced wildlife conservation interest (A and C)

2.2.3Proliferation in inter-tidal areas impeding navigation, fishing and water based recreation (C)

2.2.4Proliferation reducing general amenity value of the waters (C)