An aquatic weed harvester, also known as a water mower, mowing boat and weed cutting boat, is an aquatic machine specifically designed for inland watercourse management to cut and harvest underwater weeds, reeds and other aquatic plant life. The action of removing aquatic plant life in such a manner has been referred to as "aquatic harvesting".

Overview

Water is an important resource and in many countries, waterways are increasingly clogged by aquatic plant growth. This is particularly so in tropical countries where warmer water means the plants grow more quickly, and increasing run-off of

fertiliser A fertilizer or fertiliser is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrition, plant nutrients. Fertilizers may be distinct from Liming (soil), liming materials or other non- ...

s and effluent has exacerbated the problem. Irrigation ditches and pumps can become overgrown with vegetation, power station and factory water intakes can get blocked, boats can get hindered, fish stocks can be disrupted, and water moves more slowly, resulting in greater

evapotranspiration Evapotranspiration (ET) refers to the combined processes which move water from the Earth's surface (open water and ice surfaces, bare soil and vegetation) into the Atmosphere of Earth, atmosphere. It covers both water evaporation (movement of w ...

and a greater risk of flooding. In some large irrigation projects in India, canals have become so overgrown with vegetation that water flow has been reduced to a fifth of its previous amount. In Bangladesh, floodwater has washed mats of

water hyacinth ''Pontederia crassipes'' (formerly ''Eichhornia crassipes''), commonly known as common water hyacinth, is an aquatic plant native to South America, naturalized throughout the world, and often invasive species, invasive outside its native rang ...

onto paddy fields, overwhelming the emerging rice crops. Small fish can become entangled in excessive algal growth.

Rice Rice is a cereal grain and in its Domestication, domesticated form is the staple food of over half of the world's population, particularly in Asia and Africa. Rice is the seed of the grass species ''Oryza sativa'' (Asian rice)—or, much l ...

is the main aquatic plant grown for human food, but smaller areas of

watercress Watercress or yellowcress (''Nasturtium officinale'') is a species of aquatic flowering plant in the cabbage family, Brassicaceae. Watercress is a rapidly growing perennial plant native to Eurasia. It is one of the oldest known leaf vegetabl ...

and water chestnut are also cultivated. In their native environments, aquatic weeds are part of a balanced ecosystem, and it is mainly introduced species of water plant that become invasive and cause problems by congesting water bodies. The worst culprits, found in both temperate and tropical waterways, are floating plants such as

water lettuce ''Pistia'' is a genus of aquatic plants in the arum family, Araceae. It is the sole genus in the tribe ''Pistieae'' which reflects its systematic isolation within the family. The single species it comprises, ''Pistia stratiotes'', is often call ...

and ''

Salvinia ''Salvinia'' or watermosses is a genus of free-floating aquatic ferns in the family Salviniaceae. The genus is named in honor of 17th-century Italian naturalist Anton Maria Salvini, and the generic name was first published in 1754 by French bo ...

'', fully submerged rooting plants such as ''

Hydrilla ''Hydrilla'' (waterthyme) is a genus of aquatic plant, usually treated as containing just one species, ''Hydrilla verticillata'', though some botanists divide it into several species. It is native to the cool and warm waters of the Old World in A ...

'' and

water milfoil ''Myriophyllum'' (water milfoil) is a genus of about 69 species of freshwater aquatic plants, with a cosmopolitan distribution. The centre of diversity for ''Myriophyllum'' is Australia with 43 recognized species (37 endemic). These submersed aq ...

and rooting plants that reach the surface such as

cattail ''Typha'' is a genus of about 30 species of monocotyledonous flowering plants in the family Typhaceae. These plants have a variety of common names, in British English as bulrushStreeter D, Hart-Davies C, Hardcastle A, Cole F, Harper L. 2009. ...

papyrus Papyrus ( ) is a material similar to thick paper that was used in ancient times as a writing surface. It was made from the pith of the papyrus plant, ''Cyperus papyrus'', a wetland sedge. ''Papyrus'' (plural: ''papyri'' or ''papyruses'') can a ...

bulrush Bulrush is a vernacular name for several large wetland graminoid, grass-like plants *Sedge family (Cyperaceae): **''Cyperus'' **''Scirpus'' **''Blysmus'' **''Bolboschoenus'' **''Scirpoides'' **''Isolepis'' **''Schoenoplectus'' **''Trichophorum'' ...

and reed.

Weed harvesting equipment

Weed cutting boats are developed to enable the maintenance of canals, lakes and rivers and to remove excessive aquatic life such as

algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...

and other plants that may negatively affect a waterway's

ecology Ecology () is the natural science of the relationships among living organisms and their Natural environment, environment. Ecology considers organisms at the individual, population, community (ecology), community, ecosystem, and biosphere lev ...

. Mechanical harvesters are large floating machines that have underwater cutting blades that sever the stems of underwater plants, gather the weeds and raise them on conveyor belts, storing the vegetation on board in a hold. Periodically this is discharged to a barge or an onshore facility. The harvested product can be

compost Compost is a mixture of ingredients used as plant fertilizer and to improve soil's physical, chemical, and biological properties. It is commonly prepared by Decomposition, decomposing plant and food waste, recycling organic materials, and man ...

ed, sent to a

landfill A landfill is a site for the disposal of waste materials. It is the oldest and most common form of waste disposal, although the systematic burial of waste with daily, intermediate and final covers only began in the 1940s. In the past, waste was ...

site or used in

land reclamation Land reclamation, often known as reclamation, and also known as land fill (not to be confused with a waste landfill), is the process of creating new Terrestrial ecoregion, land from oceans, list of seas, seas, Stream bed, riverbeds or lake ...

. In developing countries aquatic vegetation may be harvested by hand or by net from the shore, cut and harvested by boat and lifted ashore by hand, crane, pump or conveyor system. The harvested vegetation may be used for the feeding of livestock. To reduce the high moisture content and to make it easier to transport, the weed can be chopped and pressed. Other uses to which the harvested vegetation can be put include ensiling the material for livestock fodder, adding it to the soil as a bulky organic fertilizer, manufacturing the raw material into pulp, paper or fibre, and

fermenting Fermentation is a type of anaerobic metabolism which harnesses the redox potential of the reactants to make adenosine triphosphate (ATP) and organic end products. Organic molecules, such as glucose or other sugars, are catabolized and reduced ...

it to produce

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...

for energy production. Weed harvester 6520 from Berky

Advantages and disadvantages

Mechanical weed harvesters are effective at clearing aquatic weeds and the machines provide immediate relief from nuisance vegetation that interfere with navigation and recreation. Aquatic plants contain nitrogen, phosphorus and potassium that is bound in the vegetation, by removing the plants the nutrients are also removed. Removal of the biomass (plant material) prevents the build-up of muck and sediment on the bottom of the lake that occurs from the rotting weeds. Mechanical harvesters can also be used to improve the fishery by leaving behind aquatic vegetation for food and habitat. Aquatic weed machines are expensive and does require a capital investment and the process may need to be repeated several times in a growing season. Small fragments of weed may remain in the water and may spread to other locations thereby aiding in the dispersal of invasive species. However, a recent study by the Chautauqua Lake Association found that the harvesters lef
less than 1% of the loose plants behind
Some areas may be too shallow for the mechanical harvester and it may be unable to access restricted locations. Submerged tree stumps can damage the machine. Aquatic weeds can also be utilized as a source of

biofuel Biofuel is a fuel that is produced over a short time span from Biomass (energy), biomass, rather than by the very slow natural processes involved in the formation of fossil fuels such as oil. Biofuel can be produced from plants or from agricu ...

. An alternative to mechanical harvesting is the use of herbicides, which are easy to apply and less expensive, but may have unwanted adverse impacts on the environment. While many aquatic herbicides have received EPA approval and are considered safe for aquatic environments, long-term studies have found that aquatic herbicides can have major impacts on fish reproduction. Researchers at the University of Wisconsin-Madison found that fathead minnows exposed to concentrations of fluridone showed signs of endocrine disruption.

By region

Africa

Kenya Kisumu Harbour Hyacinths 1997ke09b21

In June 2015 in Uganda, use of the aquatic weed harvester was recommended by the country's Ministry of Agriculture to reduce

growth in

Lake Victoria Lake Victoria is one of the African Great Lakes. With a surface area of approximately , Lake Victoria is Africa's largest lake by area, the world's largest tropics, tropical lake, and the world's second-largest fresh water lake by surface are ...

, which has caused a scarcity of fish in the lake. The scarcity of fish has negatively-affected the livelihood of locals who live in the lake's region. Additional types of machines were recommended to address the problem, which were the hydraulic harvester, take out elevator and dredger.

India

In August 2015 in

Hyderabad Hyderabad is the capital and largest city of the Indian state of Telangana. It occupies on the Deccan Plateau along the banks of the Musi River (India), Musi River, in the northern part of Southern India. With an average altitude of , much ...

, India, an aquatic weed harvester was used to remove algal weeds and trash from Hussainsagar Lake. An amphibious hydraulic excavator was also used. The work was performed to address pollution problems at the lake, which had accumulated significant algae and rubbish such as plastic bags and

plastic waste Plastic pollution is the accumulation of plastic objects and particles (e.g. plastic bottles, bags and microbeads) in the Earth's environment that adversely affects humans, wildlife and their habitat. Plastics that act as pollutants are cate ...

, food wrappers, and various garbage, some of which was floating atop the lake.

United States

Some U.S. companies manufacture aquatic weed harvesters. One such machine manufactured by a U.S. company can cut around one-half an

acre The acre ( ) is a Unit of measurement, unit of land area used in the Imperial units, British imperial and the United States customary units#Area, United States customary systems. It is traditionally defined as the area of one Chain (unit), ch ...

of weeds a day, and costs over $100,000.

Tampa, Florida Tampa ( ) is a city on the Gulf Coast of the United States, Gulf Coast of the U.S. state of Florida. Tampa's borders include the north shore of Tampa Bay and the east shore of Old Tampa Bay. Tampa is the largest city in the Tampa Bay area and t ...

used an aquatic weed harvester in 2013 to clear aquatic plant life from lakes in the area. In 2012 in Leoni, Michigan, an aquatic weed harvester was used to remove

from Center Lake. The algae appeared to have roots, and other techniques such as attempting to kill it with chemicals were unsuccessful. The machine used collects algae and weeds that live at the bottom of the lake, removing them from the waterway.