DROUGHT AFFECTS SURFACE WATER QUALITY

by: Dr. Lee Jones
DVM, MS

As surface water evaporates and isn't recharged by fresh rains, it increases the concentration of water contents such as nitrates, phosphorus and other elements. This makes for an excellent place for growth of potentially toxic substances such as blue-green algae. Recently we received reports of livestock found dead near a shallow pond. The local veterinarian suspected an algal bloom or rapid growth. The water was tested for cyanotoxins. According to Gary Burtle of the aquaculture unit of the animal and dairy science department in Tifton, "We have few cases of cyanobacterial toxins reported in Georgia. However, I expect that to change if the dry weather continues."

Cyanobacteria, often referred to as blue-green algae, are microscopic organisms that live in all types of water. Cyanobacteria grow quickly or bloom, sometimes even overnight, when water is warm, slow moving or stagnant and there is an increase in the concentration of nutrients. Farm ponds are excellent places for algal blooms under certain circumstances.

Though algal blooms typically occur in the summer or early fall they have been known to happen during other times as well under the right environmental conditions. Usually, scum forms on the water surface when a bloom occurs, but a bloom can take place below the surface. Blooms aren't always green but can be reddish brown or some combination of colors. As it dies off it may smell like rotting plants but there may be no odor at all. Not every bloom is toxic, but the toxins, such as microcystins, may be in the water or algae and are toxic to pets, people, livestock and wildlife.

The toxin levels of blooms vary and toxicity depends on the amount the animal drinks. There are three types of toxins: Neural, liver --otherwise known as hepatic -- and a skin toxin. If an animal drinks enough of the neurotoxin, death can come quickly and often these animals are found very close to the water. The liver toxin or hepatotoxin usually does not cause sudden death. Sometimes the affected animal may have colic symptoms, abdominal cramps, excessive drooling, lose their appetite and be very lethargic. The skin toxin causes a contact irritation that can be severe if exposed to high levels.

It is not possible to tell if a bloom is toxic without testing the water so it is best to avoid blooms and keep all livestock and pets away from water when the bloom scum is present. There is no way to predict when or if a bloom will occur.

The presence of harmful bacteria can be suspected if there is a scum on the surface or the water has a bluish or green color. The presence of potentially toxic algae is determined microscopically, but the presence and level of toxins have to be confirmed by a lab test.

Wind will concentrate the bloom to the downwind side or corner of a pond, so it is best to keep cattle away from that end. If dead wildlife is found around a pond it is a good idea to get the cattle away from it as soon as possible: Some cattle develop a taste for the dried crust of pond scum on the banks.

Livestock affected by the neurotoxin may not die immediately but may be disoriented, stagger or refuse to get up. There is no antidote or treatment for poisoned animals. In the case of liver toxins, the effects may be delayed and animals get sick three to four weeks after drinking from the contaminated water source. Occasionally, a condition called secondary photosensitivity occurs following severe liver damage. The liver breaks down chlorophyll from ingested green plants and removes it from the body, but when it is damaged the chlorophyll breakdown products circulate in the bloodstream. When the product is in the capillaries of white areas of skin it reacts to light and causes a toxic reaction and sloughing of the white areas of skin. Some of these animals can get well but have to be kept out of the sun until the liver and skin heal. A blood test can show if there is liver damage.

Ponds contaminated with algae blooms can be treated with copper sulfate. These products can be purchased at many farm livestock supply stores. Always follow label directions when applying the solution. Copper is especially toxic to sheep so they should not be allowed to drink from treated ponds. Copper sulfate is toxic to fish and eating fish from treated ponds is not recommended. The pond should be safe after a few weeks.

Stagnant ponds can also be a source of other bacteria such as Aeromonas, which have even been known to kill fish in hatcheries. Animals or people with an open sore that gets infected with Aeromonas or other bacteria growing in stagnate water may have severe, even life-threatening infections. It is best to avoid stagnant water altogether and to prevent livestock or horses from wading into stagnate ponds, especially those covered with slime. Sediment bacteria are suspended or mixed in the water more often during lower water levels, too. Levels of E. coli in water from rivers have been shown to increase during drought years when the sediment was distributed.

Producers who suspect their ponds may have potentially toxic algal bloom should contact their local veterinarian or Extension agent immediately. Many veterinary clinics can evaluate blood samples to see if animals have liver damage. A necropsy should be done of all animals suddenly found dead and appropriate samples should be submitted.







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