LOW TECHNOLOGY INNOVATIONS TO REDUCE WATER EVAPORATION, VECTOR AND ALGAE GROWTH IN OPEN WATER HARVEST SYSTEMSBy : Jervis E Rowe( Abbey Garden Farm, Central Greenhouse Supplies & Services)

BAUXITE PIT TURN POND

OBSERVATIONS

Rainfall is declining

Evaporation rates are increasing

Climate is warming up

THE GENERAL PICTURE

Quantity of water reaching reservoirs, rivers and streams is decreasing

Evaporation losses from the above sources is increasing

Irrigated plants are demanding more water as temperature rises

REALITY OF THE SITUATION

To purchase and transport water for Agriculture is too expensive

To implement measures to reduce evaporation will increase your cost of production

To do Agriculture with out water is impossible

UNDERSTANDING WATER EVAPORATION

Evaporation of water occurs when the exposed surface looses molecules to the atmosphere in the for of water vapor

Water vapor rises to form clouds

FACTORS AFFECTING THE RATE OF EVAPORATION

Humidity

Speed of air passing over the water

Temperature , ( 1degree C reduction in temp. can mean 2,900 gallons water saved /acre/day.)

FACTORS AFFECTING RATE OF EVAPORATION

SOME PRE-REQUISITES TO REDUCING EVAPORATION

Keep water cool

Keep water depth above 3 ft

Cover water

ECONOMICAL WAYS TO REDUCE EVAPORATION

Floating covers

WER ( Water Evaporation Retardants)

Aquatic Plants

Trees, shrubs and bushes

Trellising system with a vine crop

Less disturbance to water surface

FLOATING COVERS

Acts as a barrier between water surface and the air

Reduces speed of air passing over the water

Reduces contamination of water, falling debris , algae and other water plants

Reduces break down of pond liners

FLOATING COVER

WER ( Water Evaporation Retardants)

Creates a film over the water surface

Example : Acilol TA 618 , emulsion made from a fatty alcohol

AQUATIC PLANTS

Shades the water below

Absorbs some of the solar radiation

Examples: water lilies, floating hearts

Far less expensive when compared to floating covers

WATER LILIES

TREES, SHRUBS AND BUSHES Planted outside and around the pond

Use plants that do not shed a lot of leaves or pods eg. Evergreens

TRELLIS WITH VINE CROP

Provides shade and wind break

Example: beans, passion fruit

REDUCE AGGITATION

Reduce splashing at water surface

Allow inlet pipes to touch water

Avoid the use or water wheels where possible

WHAT IS ALGAE ?

Chlorophyll containing plant existing very low on the evolutionary chain

3 main groups , filamentous , branched , planktonic

May occur single, colonies or mat

Reproduces asexually AND asexually

COMMON STRING AND GREEN ALGAE

FACTORS AFFECTING ALGAE GROWTH

Pond size and depth

Water stagnation

High nutrients and light

POND SIZE AND DEPTH

Small & shallow=high light & temp=algae

Stagnant water, limited wave action promotes growth

High P & N is food for Algae

ALGAE IN IRRIGATION WATER

Creates blockages ( pumps, filters, emitters, meters, wheels and gates

Reduces water quality( reduces oxygen, causes contamination)

When algae die they sink to the bottom of the pond and contributes to the build up of sludge

ALGAE MANAGEMENT IN SURFACE PONDS

Physical/ Mechanical control

Chemical Control

Biological Control

PHYSICAL / MECHANICAL CONTROL

Rake out mat form algae

Result is immediate

No chemical cost or risk

Algae removed can be used as mulch

CHEMICAL CONTROL( Hydrogen peroxide)

Organic

Oxidizing agent

Breaks down to water and oxygen( relatively expensive)

CHEMICAL CONTROL ( copper) In use for several years

Used as recommended has no adverse effects

CHEMICAL CONTROL ( Dyes) Blocks part of the light spectrum that

algae need to photosynthesize

Example : Aquashade ( product name)

BIOLOGICAL CONTROL OF ALGAE Use of organism that feed on or rob

algae of their food or oxygen

Triploid grass carp eat algae when other food is limited

PATHOGENIC MICRO ORGANISMS IN POND WATER

These may include but not limited to :

Bacteria eg. Salmonella E Coli

Protozoa eg. Crytosporidium , Giardia

Viruses eg. Noroviruses

CONDITIONS FAVORING BACTERIAL GROWTH IN POND WATER

Ph 4.5-6.5

Temperature above 45degrees F

0.2- 1.0 ppm iron in water

0.1 or more ppm of Hydrogen Sulfide in water

Bacteria produces slime which affects water quality

MANAGEMENT OF BACTERIA IN POND WATER

Best done locally with chlorine

Ultra violet ray flow cells ( expensive)

Osmosis (expensive)

Water Chlorination

Chlorine disrupts cell membrane

Cell looses contents

Cell looses function

Micro-organism dies

UV light treatment

Light penetrates cell Disrupts DNA , prevents reproduction Kills up to 99.99% bacteria and

viruses Does not alter water ( taste and

odor) Does not add chemical Use very little energy Low maintenance ( change bulb

annually)

Ozone water treatment Oxygen is electrically charged to produce

ozone ( O2--- O3) Ozone is very unstable and will react with

material in an oxidizing reaction

Ozone is one of the strongest sterilizing agents

Apply ozone using a venturi or centrifugal pump

After oxidation of ozone oxygen is left in solution

LOOKING AHEAD Rain water which sometime gets to the

Island from other region must be harvested and effectively stored

Water already here must be screened for quality, corrected accordingly and properly stored

Surface water from roads, parking lots or other paved areas can be harvested and treated for certain agricultural uses

Irrigation techniques must be efficient and reflect best practices

THANK YOU