| Pollution: Algal Blooms | |||
|
|||
| Algal Blooms Algae are simple plants and form the basis of the food chain in fresh and saltwater. They vary considerably in size, from hundredths of a millimeter (Microcystis) to almost a hundred meters in the case of ocean kelps. They also vary in shape and colour, and are found in a large range of habitats. While a few algae are found in soils and in surfaces exposed to air, the great majority are truly aquatic and grow in ponds, lakes, water supply storages, stock drinking troughs, streams, geothermal hot pools, estuaries and oceans. The three most common freshwater algal phyla are the Chlorophyta (green), Cyanophyta or Cyanobacteria (blue-green) and the Chrysophyta (golden or brown-green). At times water bodies can suffer from an excess of algae which are called algal blooms. These often occur in nutrient-enriched (eutrophic) waters. Each algal group has special nutrient requirements for healthy growth. (e.g. blue-greens need phosphates or nitrates). When the specific nutrients are used up, the algae die back and the bloom is over. Some algae cause problems as they may produce toxins and other substances that can have lethal effects on aquatic organisms and stock. Toxic, or potentially toxic, algal blooms in fresh water are most commonly caused by several genera of blue-green algae. Most species are common throughout New Zealand lakes and algal blooms are a natural component of the aquatic environment. Problems occur when pollution provides additionalnutrients. Cyanobacterial (blue-green algae) blooms are not only a nuisance when they occur in lakes or reservoirs but can be a grave health risk. This is due to their ability to produce toxins such as the cyclic peptides microcystins which in the event of a bloom breakdown are released into the water and can reach high concentrations. Fish kills are a phenomenon often reported after cyanobacterial blooms in lakes. There are an increasing number of cyanobacteria genera and species which have been found to produce a suite of biologically active compounds. The cyanobacteria of concern are generally freshwater or brackish water species and are commonly found as 'blooms' in slow-flowing, nutrient-rich waters, usually in the warmer months of the year. Blooms are often found in farm dams or ponds where very little mixing occurs, allowing warm water layers to form near the surface. As a result, highly toxic 'scum' material often forms on the water surface, creating a potential danger not only for fish, but also livestock and humans. Routine testing by the Manawatu Regional Council in December 2001 confirmed a large bloom of Microcystis in Lake Horowhenua, a species of cyanobacteria that had been found in the lake in the previous summer. Tests have confirmed that the algae is toxic. The water in affected lakes and streams is not fit for drinking and all recreational use that involves significant skin contact should stop, as it can lead to serious health problems in some circumstances. Based on the experience of past years, the bloom in Lake Horowhenua is likely to continue for several months. At times the bloom will cause the lake to become discoloured and significant odour problems can be created when the organisms die off. At other times the water will appear to be quite normal to the naked eye. However, large numbers of organisms can still be present in what looks like normal clear water. Unless strict pollution control is enforced, closure of an increasing number of our waterways may become a regular feature of the New Zealand summer. Just when you thought it was safe to go back into the water: Pfiesteria piscicida is a toxic dinoflagellate that has been associated with fish kills in the USA and has been found in tidal rivers and estuaries in New Zealand. Pfiesteria normally exists in non-toxic forms, feeding on algae and bacteria in the water and in sediments. Scientists believe that Pfiesteria only becomes toxic in the presence of fish, particularly schooling fish, triggered by their secretions or excrement in the water. At that point, Pfiesteria cells change form and begin emitting a powerful toxin that stuns the fish, making them lethargic. Thirteen researchers who discovered Pfiesteria in 1988 worked with dilute laboratory cultures. All 13 sustained mild to severe adverse health impacts through water contact, or by inhaling toxic fumes from the cultures. The effects included symptoms such as narcosis (a "drugged" or lethargic effect), development of sores (in areas that had directly contacted water, as well as on the chest and face, suggestive of a systemic response), uniform reddening of the eyes, severe headaches, blurred vision, nausea/vomiting, sustained difficulty breathing (asthma-like effects), kidney and liver dysfunction, acute short-term memory loss, and severe cognitive impairment (i.e. serious difficulty in being able to read, remember one's name, dial a telephone number, or do simple arithmetic beyond 1 + 2 = 3). Most of the acute symptoms proved reversible over time, provided that the affected people were not allowed near the toxic cultures again. Some of the effects recurred following strenuous exercise, |
| Return to Category | Return To Main Index |
The comments are owned by the poster. We aren't responsible for their content.