Weed Control Methods for Public Health Applications

E.O. Gangstad

• Publisher: CRC Press
• Year: 2018
• Print ISBN: 9781315898599
• eBook ISBN: 9781351094597
• Topic: Biological Sciences
• Subtopic: Biology
• Index: Biological Sciences

This volume includes measures of control of aquatic vegetation that harms human health, since water-related diseases exist in this environment. Although malaria has receded internationally due to the combined chemotherapeutic-insecticidal programs, recently it has resisted both medicines and insecticide control. Active malaria cases in the U.S. were fewer than a dozen before the Vietnam War, but in 1973 the figure was ab out 700, almost all traceable to returning military personnel. The disease could again become prevalent. Other diseases exist whose transmission is indirectly affected by aquatic weed conditions including filariasis, and various trematodiases, especially from the schistosomes, Chinese liver fluke, cattle liver fluke, Guinea worm, giant intestinal fluke, Asiatic lung fluke, and broad tapeworm. Waterweeds also support disease-pest arthropods, i.e., snipe flies, tabanids (horse, gad, deer, and greenheads), Clear Lake gnats, Mayflies, black flies, sandflies, and sewage flies.Ecosystem studies of impounded water research and development of herbivorous fish, and utilization of herbivorous fish in China, are also included in this volume.

Part I

Aquatic Plant Survey and Assessment

Chapter 1

AQUATIC WEEDS AND MAN’S WELL-BEING*

INTRODUCTION

Aquatic vegetation harms human health in several ways since water-related diseases are part of our environment. Malaria has receded internationally due to chemo-therapeutic-insecticidal programs, but recently has resisted both medicines and insecticides. Lately, active malaria cases in the U.S. were kept to fewer than a dozen annually; in 1967, the figure was about 700, almost all traceable to returning military personnel. Other diseases exist whose transmission is indirectly affected by aquatic weed conditions: filariasis, and various trematodiases especially the schistosomes, Chinese liver fluke, cattle liver fluke, Guinea worm, giant intestinal fluke, Asiatic lung fluke, and the broad tapeworm.

Water weeds support the other disease pest arthropods: snipe flies, tabanids (horse, gad, deer, and greenheads), Clear Lake gnats, May flies, black flies, sandflies, and sewage flies.

Bacteria in the wrong place and in harmful population density degrade the health of urbanized man and as water pollutants require upgrading and maintenance of all water bodies. Lay understanding of conservation must include aquatic vegetation management. A pest plant should be removed mechanically, by chemical herbiciding, or by recently developed biocontrol techniques using several plant-eating snails, fishes, ducks, and manatee and aquatic insects. Weed removal allows the natural or introduced predators of larval stages of fluke infections to operate without mechanical hindrance near habitations in endemic areas. Seaweeds must be protected from coastal pollution to insure the future of a growing industry giving human and animal food, medicinais, mucilages, bacterial media, fertilizers, and various organic compounds. Marine Protista toxify edible shellfish and fish and seriously threaten consumers. Blooms (red tides) of the Protista somehow destroy fish and other marine life. Control of fresh water aquatic weeds strengthens the alliance between agriculture, navigation, and public health and will serve man’s survival in the 21 st Century.

What is the value of considering the relation of water weeds to man’s physical and mental state? The subject forms no composite whole and will never form one. Yet the ancient problem can be viewed from angles usually overlooked. Current public acceptance of some unpleasant facts about increased human population, food and water supply, and air and water pollution spurs growing reverence for conservation of natural resources whether it be expressed as a birth control pill, development of fungus resistant wheat, conversion of salt to fresh water, regulated usage of exhaust reducers in vehicles, or the simple contemplation of the present condition of the stream in which one swam as a child. Within this melancholy framework, there is room to outline some ways natural plants living in or near water bodies affect man’s health and equanimity. Such an art cuts across several disciplines of natural history, and the supporting data are hidden in many bibliographic niches and in the memories of biologists.²²

Water then is our basic interest, and weeds (plants in the wrong place, wrong population density, and serving wrongly) are defined as pollutants. To the farmer whose pond use has been curtailed by an almost impenetrable cover of water lettuce (Pistia stretioties), each plant is a particulate pollutant. According to the lay concept, water pollution means sewage contamination firstly and industrial wastes secondly. According to the technical concept, the most important vital component of the debased aquatic ecosystem is the bacterial-mycotic complex.^27,32 Here we think of bacteria as aquatic plant life in the polluted maze. Although chemical control is a necessary part of current programs, the current list of known organisms useful as biocontrol agents of aquatic weeds¹⁸ includes the snails, Marisa and two Pomacea; ducks—for example, black muscovies;⁵ several fishes (species of Tilapia and the Chinese grass carp, Ctenopharyngodon ideila); the beetle, Agasicles, consumer of alligator weed;³⁶ the aquatic wingless grasshopper, Paulinia, eater of water fern;⁸ and the manatee which ingests both floating and rooted plants.

SPECIFIC PROBLEMS

Water Supply and Pollution

By the year 2000, we will need 35% more unpolluted water than will be available. The present supply must be maintained for use and re-use. The aquatic budget is limited. All we can do is locate water, decontaminate it, transport it, and be prepared to exert eternal vigilance for its proper maintenance.² Of the total annual precipitation in the U.S. in 1966, only 8% was used by man, 71% evaporated, and 21% was returned to the ocean.³²

Although the term “bacterial flora” is glibly used to refer to microbiotic residents of the human gut, the public does not connote these key organisms as the plant life they are. The current pollution problem in American water bodies is an appalling example of the significance of bacteria whether the bacteria are pathogenic or not. The natural biological cycle in aquatic environments is still a fact. The key element in the normal cycle is oxygen; the key aquatic plant is the bacterium that converts soluble organic matter into other bacterial cells and inorganic elements. The inorganics are absorbed by algae and metabolized into other algal cells. Both cell types become food for protozoans, rotifers, and crustaceans. Some bacteria, algae, and animal life serve as basic food for minnows and young fish; small fish are devoured by large fish. Man discharges his wastes into the water body where bacteria metabolize organics. The cycle is then completed.^2,4,15,27,32 Thus, a certain amount of waste discharged into water bodies is normal and biologically required.

However, if organic waste concentrations increase over normal, bacterial populations explode with increased oxygen (BOD). As this life-giving element decreases, the higher animal forms perish – game fish first, then crustaceans, rotifers, and the higher protozoa.³² Bacteria remain dominant and in the absence of dissolved oxygen (DO) undergo anaerobic metabolism producing vile odors and black water. Man thus fouls his aquatic ecosystem. That it required 100 years of varied pollution to bring Lake Erie to its current status as a massive cesspool is a monument to the strength of the elemental aquatic plant, water-fouling bacterium.¹² In contrast, management of fishing ponds and lakes is now an advanced art providing both beauty and recreation.²⁵

Taste-Odor Problem in Water Supply

Public acceptance of drinking water supplies, whether purified or not, hinges to a great degree on absence of detrimental tastes and odors. If poor taste and odor are of chemical origin (saline or sulphurous) the public is resigned to its fate; but if these are of microbiotic origin, great clamor is raised and the sanitary engineer is expected to defy nature and quickly bring the supply back to levels to which the user is accustomed.¹⁵ Remarkably enough, publication of Standard Methods has stimulated codification and description of common odors that may emanate from the domestic tap.⁴ These are spicy, balsamic, geranium, nasturtium, sweetish, violet, chlorinous, hydrocarbon, medicinal, sulferetted, earthy, peaty, grassy, musty, moldy, vegetable, septic, fish and pigpen! Abatement of taste-odors is not easy and at times impossible for a particular season.

Much accumulated information on the kinds of algae implicated exists, and recent studies show that the actinomycetes are potential troublemakers. Blooms of microorganisms die and release certain oils that cause undesirable taste-odor problems. Good algae and actinomycetes result in agricultural areas where run-off water carries fertilizer residues into impoundments increasing the phosphorous content.⁷ In impoundments that receive treated or untreated sewage, algal problems may be increased by use of polyphosphates in household detergents. At certain population levels, algacides must be applied.⁵ The most common one is copper sulfate applied at 0.1 to 1.0 ppm in only the upper 10 ft of the reservoir.²⁷ Since the algacide kills the protozoan predators of bacteria there is a temporary surge of these organisms. In treatment plants, activated carbon, chlorination, and aeration are indicated treatments to alleviate the problem should reservoir source treatment be insufficient.¹⁵

Toxic Shellfish and Fish

Seaweed and certain types of plankton (termed Protista) cause a serious form of human intoxication – shellfish poisoning – and produce disasters in marine biology.³³ Shellfish poison is one of the most lethal known; the minimal lethal oral dose for man is thought to be between 1 and 4 mg/kg of body weight. Clinical effects are not completely understood, but the heart is definitely harmed. Death is usually attributed to respiratory paralysis. Protista are single-celled, animal-plant organisms in that their energy is derived by photosynthesis and their motion by flagellation. Widely distributed in marine waters, they reach public attention as blooms called “red tide” and “red water.” Massive fish destruction may accompany these blooms produced by a variety of environmental changes. The cause of mass mortality of marine life during and after the blooms is not clear, yet the best evidence points to physical rather than chemical factors.

Paralytic shellfish intoxication is caused by certain molluscs and a few echinoderms and arthropods that eat toxic Protista (dinoflagellates) and are then ingested by man.³³ Some 21 dinoflagellates have been implicated; the best known is Gonyaulax catenella of the Pacific coast of North America. How the poison accumulates in molluscs is unknown. At least 28 species are involved including commonly known forms – clams, mussels, and oysters. Mostly the toxin is concentrated in the digestive glands of the mollusc. In Japan, nonparalytic form of poisoning may be contracted by ingestion of certain clams, oysters, and gastropods that consume toxic plankton.

Ichthyotoxism is a very complex subject^24,33 viewed either scientifically or as a basis for folklore. At least 16 factors have been studied as probable causes of concentration of very potent toxins in tissues of various marine fishes. The most important form of fish poisoning implicating over 300 species is ciguatera. It seems certain that it is associated with the food chain relationship of fishes. Probably the toxin originates in a benthonic organism eaten by herbivorous fishes and in turn consumed by carnivorous ones. The latter fishes accumulate poison without harm. Herbivores feed on toxic algae, fungi, or Protista, and current evidence favors the blue-green algae as the most probable causative factor. Clinical symptoms resemble those of shellfish ...

Table of contents

• Cover
• Title Page
• Copyright Page
• Table of Contents
• Part I: Aquatic Plant Survey and Assessment
• Part II: Ecosystem Studies of Impounded Water
• Part III: Research and Development Studies for the Control of Hydrilla with Herbivorous Fish
• Part IV: Utilization of Herbivororous Fish in China
• Appendix A Conversion Factors for U.S. annd Metric Units
• Glossary of Biomedical Terms
• Index