Impacts of Eutrophication

1. Impacts of Eutrophication Eutrophication in the Sea of Azov. Source: SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAG Developed by Richard Sandford with contributions from Martin Bloxham and Paul Worsfold,

2. Impacts of Eutrophication 3.1 Decrease in the transparency of water Light is essential for the growth of green plants and sunlight provides the energy for photosynthesis. The penetration of sunlight into a body of water determines the depth and quantity of algae and other underwater plants. Water transparency decreases as colour, suspended sediments and algae increase. Transparency of water can be measured using a Secchi disk. The Secchi disc is a simple scientific instrument used to measure water transparency. The Secchi disk is an eight-inch disk painted with alternating black and white quadrants. Which is lowered into a water body until it can no longer be seen. This depth of disappearance is a measure of the water's transparency. The Secchi disc depth indicates the water transparency and provides a rough estimate of light penetration in the water column. As a general rule, light can penetrate to a depth of two times the Secchi depth. For example, if the Secchi depth was 3m, then light can penetrate to a depth of 6m. As light penetration increases, so does the amount of plant growth and oxygen produced by algae and aquatic plants. The Secchi depth of muddy and eutrophic lakes, estuaries and big rivers ranges from 0 to 2 m but in oligotrophic or blue water oceans it can be as great as 40 m. In many lakes, the Secchi depth is approximately one-third of the depth of the photic zone. The clarity of lake water varies with season due to algal blooms or suspended sediment and these are well reflected by measurements of Secchi depth.

3. Impacts of Eutrophication 3.2 Development of anoxic conditions (low oxygen levels) The level of dissolved oxygen in surface and near surface water is an important measure of the state of the health of the aquatic environment. Dissolved oxygen levels become depressed as a result of the inability of natural processes to supply oxygen at the rate demanded for the oxidation of organic matter or reduced chemical substances. Dissolved oxygen deficiency may be particularly acute in the cases of eutrophication, discharge of sewage and the discharge of organic industrial, agricultural and aquacultural effluents. Extreme oxygen deficiencies (e.g., anoxia) can result in the elimination of all higher life forms. Anoxic conditions, especially in sediments, can also lead to the liberation of less reactive forms of metals from particles into aqueous phases. Under anoxic conditions anaerobic bacteria flourish. Anaerobic bacteria often produce foul smelling compounds such as hydrogen sulphide (H2S), thioalcohols (RSH) and ammonia (NH3). Levels of dissolved oxygen of >7mg/l in surface marine and freshwaters, depending upon temperature, represent essentially oxygen-saturated conditions. Levels below 4 mg/l represent serious oxygen depletion with some species exhibiting avoidance. Species mortalities can occur below these levels with severe prejudice to most aerobic organisms occurring below 3 mg/l. Fish kill in the Baltic Sea (Source: WVU (Wissenschaftsverbund Um-Welt), Germany

4. Impacts of Eutrophication 3.3 Increased algal blooms Algae are simple plants, which contain chlorophyll a as their primary photosynthetic pigment. Algae are found in fresh and marine waters and vary in size from large kelps (meters in length) to microscopic organisms. In low numbers, most algae are harmless and are an essential part of any healthy ecosystem because they produce oxygen and are a source of food for other aquatic animals. However, excessive algae growths or blooms can cause serious water quality problems including unpleasant tastes and odours, unsightly scums which significantly reduce the aesthetic and recreational amenity of the water body and blockages in pump valves and filters. In addition, dead or decomposing algae utilises oxygen in the water body which can contribute to fish kills and the death of other aquatic animals. Question: What are harmful algal blooms?

5. Impacts of Eutrophication 3.4 Loss of habitat (e.g. Sea grass beds) Pressures exerted on biodiversity can generally be divided into ecosystem loss, fragmentation, degradation and modification. This has resulted in the decline or extinction of many species of plants and animals. If sufficient amounts and types of suitable habitat cannot be maintained wildlife can be put at risk. Eutrophication can cause serious effects to living resources or their habitats. Marine or estuarine systems with biogenically structured habitat, such as coral reefs or seagrass beds, are especially vulnerable to eutrophication. Bays, lagoons, enclosed seas, and open coastal waters can also be affected. The accelerated increase in the input of nutrients to the marine system represents a serious threat to the integrity of marine ecosystems and the resources they support. Species losses may be short-term or even permanent in localised areas (e.g., the northern Gulf of Mexico, the Baltic Sea shelf, or the northwestern shelf of the Black Sea). There are no documented cases of a species extinction due to eutrophication, but there are many examples of localized or temporary loss of biodiversity, shifts in community structure in both pelagic and benthic systems, and many examples of degraded habitats, such as coral reefs, seagrass beds, and productive continental shelves with important commercial fisheries, that become unsuitable for the usual inhabitants. Eel grass (Zostera marina) in a saline lagoon. Source: Comhairle nan Eilean Siar Scotland

6. Impacts of Eutrophication 3.5 Change in dominant biota: Changes in plankton and macrophyte community structure The production of aquatic macrophytes and algae is an important component of wetland food chains. Aquatic macrophytes provide structural habitat for invertebrate and vertebrate life and also provide substrates for colonization by epiphytic algae and microbes that are important foods of aquatic invertebrates. Once macrophytes senescence, they contribute litter for colonization by microbes which provide additional food resources for aquatic invertebrates. In addition to epiphytic algae, phytoplankton and epibenthic algae are also major sources of carbon in wetlands and are important food resources of aquatic invertebrates. Anthropogenic sedimentation has potential to suppress primary production and alter natural food chain interactions. Increased sediment in the water column generally reduces the depth of the photic zone and hence reduces the light available for primary production by aquatic macrophytes and algae. As sediment falls out of suspension, deposition may be adequate to bury epibenthic algae, macrophytic photosynthetic substrates, and seed. Question: What are the basic classes of macrophyte?

7. Question: What are Harmful algal blooms? Among the thousands of species of microscopic algae there are a number that produce potent toxins. Under the appropriate conditions of nutrients and temperature these species can multiply at high rates causing ``red tides''. Such events can cause detrimental effects on marine and estuarine ecosystems through reduced light, oxygen and occasionally the production of toxins. The impacts of these phenomena include mass mortalities of wild and farmed fish and shellfish, human intoxications or even death from contaminated shellfish or fish. Alterations of marine trophic structure through adverse effects on larvae and other life history stages of commercial fisheries species and death of marine mammals, seabirds, and other animals can also occur. Given the confusion surrounding the meaning of ``red tide,'' the scientific community now prefers the term harmful algal bloom (HAB). This new descriptor applies not only to microscopic algae but also to benthic or planktonic macroalgae which can proliferate in response to anthropogenic nutrient enrichment, leading to major ecological impacts such as the displacement of indigenous species, habitat alteration, or oxygen depletion. The causes and effects of macroalgal blooms are thus similar in many ways to those associated with harmful microscopic phytoplankton species. The cause of marine algal blooms is not always clear. The key trigger could be appropriate conditions of nutrients and temperature, although incidents of algal blooms triggered by pollution have occurred in a number of countries. However, in tracking this indicator, we may be alerted to anthropogenic activities which are influencing the incidence of algal blooms. For pictures of HABs, click Here References: Harmful Algae Page, National Office for Marine Biotoxins and Harmful Algal Blooms, Woods Hole Oceanographic Institution, Woods Hole, MA 02543

8. Impacts of Eutrophication Dinoflagellate algae Alexandrium tamarense Gulf of Maine Sea Surface Temperature image of an Alexandrium sp. Bloom 1999 Hong Kong Red Tide (Unidentified species) Blue-green algae can occur in both urban and rural locations

9. Question: What are the basic classes of macrophytes? There are 4* basic classes of macrophytes: Submerged macrophytes Grow primarily under water, although some can resist and respond to exposure. Reproductive organs can be submerged, emergent or floating. Examples include teridophytes (mosses and charophytes) and angiosperms. Floating leafed macrophytes Possess at least some leaves floating at the surface attached by stems to the substrate. Many also have submerged leaves. Examples include lilies such as Nuphar spp., Nymphaea spp or Potamogeton natans. Emergent macrophytes Include plants whose aerial structures are produced in a similar fashion to terrestrial plants. Many species grow well on exposed substrate as well as surviving completely submerged. Examples include Phragmites, Scirpus spp. (bulrushes), Typha spp. (cattails). Free floating macrophytes Grow primarily unattached to the substrate. Some float on the surface with much of the emergent structure growing clear of the water, whilst others lie under the water surface. Examples include Lemna spp. (duckweed). *Intertidal algae (seaweeds) are often consdered as a separate class because they do fit into the other macrophyte classes. For pictures of macrophytes, click Here

10. Cattail, common (Typha latifolia Fragrant white water lily (Nymphaea odorata) Duckweed, lesser (Lemna minor)