Download Complete Bulletin (215 KB)
Eutrophication is essentially the nutrient enrichment of waterways leading to algal growth. It must be controlled to maintain sustainable agricultural systems and the main mechanisms of control are stabilising catchment processes and reducing nutrient output.
Eutrophication can be defined as 'the nutrient enrichment of waters which results in the stimulation of an array of symptomatic changes, among which increased production of algae and macrophytes, deterioration of water quality and other symptomatic changes, are found to be undesirable and interfere with water uses' (OECD 1982). The word eutrophic is a Greek word that means 'well fed'. The food referred to is plant nutrients, such as nitrogen (N) and phosphorus (P) and as such the definition simply means 'an undesirable addition of plant nutrients to a waterbody'. The visible sign of nutrient enrichment is the proliferation of algae in waterways. Algae flourish in nutrient rich waters, most often to the detriment of other species of aquatic plants and fauna. Algae may block light to other aquatic plants such as seagrasses resulting in reduced biomass, thus threatening parts of the ecosystem reliant on seagrass. The decomposition of algae consumes oxygen, which can lead to the death of fish and the release of nutrients from sediments into the water column.
Eutrophication is a natural aging process. Over millennia waterbodies are slowly filled with soil and other materials entering with inflowing waters. In this natural process water quality is usually good, there is a diverse biological community and little algae. Human activities accelerate these natural processes. Human settlement, the clearing of forests, development of cities, agriculture and industry have increased the addition of nutrients to catchments and increased water erosion and flow from catchments to downstream waterways at a rate exceeding that of the system to assimilate.
Eutrophication leads to social and economic problems at a local scale including visual pollution for residents and recreational users and declining property values because of the stigma of pollution. An increase in nutrients can increase fish productivity, however algae fouls fishing nets making fish catching difficult. Algae decomposition results in the release of foul smelling gases (including hydrogen sulphide) which can be a problem for some residents. At an international scale overseas consumers demand products that are produced in a sustainable manner and this generates barriers to trade.
The nutrient most implicated in eutrophication in Western Australia is phosphorus (P) which generally limits algae growth to the greatest extent. However, just as the supply of other nutrients influences pasture growth, the addition of other micro- and macro-nutrients may also influence algal growth. The major areas of concern are the coastal zones, particularly in the south west and along the south coast (Figure 7.3.1) (Hodgkin and Hamilton 1993). These are also the most heavily populated and developed areas of Western Australia. Some waterbodies that have received particular attention, both in the media and by research organisations are the Peel Inlet and Harvey Estuary, Leschenault Inlet, Princess Royal Harbour and Oyster Harbour, Wilson Inlet and Swan Estuary. There are also numerous reports of the effects of nutrient enrichment of many wetlands, lakes and rivers throughout the south-west of WA.
Soils are closely linked to eutrophication processes because soil characteristics influence the delivery of soil and nutrients to waterways. This section describes some of the principles of eutrophication and then elaborates on some soil criteria influencing the problem.
Department of Agriculture and Food, Western Australia
Eutrophication, soil type, management practices, water quality
Agriculture | Natural Resources Management and Policy | Soil Science | Water Resource Management
Weaver, D, and Summers, R. (2001), Soil factors influencing eutrophication. In Soilguide. A handbook for understanding and managing agricultural soils. (ed. Geoff Moore). Department of Agriculture and Food, Western Australia. Bulletin 4343, 243-250 of 381p.