Artificial Ponds in the Cayman Islands

ARTIFICIAL PONDS IN THE CAYMAN ISLANDS

GUIDELINES TO MAXIMIZING WILDLIFE VALUE AND MINIMIZING WATER QUALITY ISSUES

INTRODUCTION

Due to the low-lying nature of land in the Cayman Islands new developments often encounter and impact natural wetland areas. Some developments deliberately engineerartificial ponds and pools to excavate fill and raise the level of surrounding areas. Natural freshwater pools are a rare habitat in the islands and one which has been much eroded by development in recent years. To these ends, if properly constructed, the creation of artificial wildlife ponds has the potential to generate valuable areas for wildlife.Unfortunately, in the past, poor planning of artificial pools has meant that far from providing new habitat, badly thought-out excavations have resulted in areas unusable by most wildlife. Additionally, poorly designed ponds have causedserious water quality issues. This has given rise to the death of wildlife and unpleasant conditions for people living close by.

The Department of Environment has produced this simple list of guidelines for the construction of ponds with the objective ofmaximizing the value of artificial ponds for wildlife and minimizing the water quality issues associated with inappropriate designs.

1 - PLANNING YOUR POND

1.1 – HEALTH AND SAFETY

Ponds can present a potential hazard to young children. Dangers can be minimized by ensuring that ponds are appropriately sited within a development and access is suitably restricted through fencing, gating and landscaping design.

1.2 - STORM WATER MANAGEMENT

Provision of ponds and pools, both natural and manmade, can form part of an effective storm water management strategy for your development. Equally, the filling of natural ponds and blocking of natural water courses can result in flooding issues, both on site and off.

1.3 - LOCATION

Pick an appropriate site for your pond. While most locations are suitable for wildlife ponds, some are better than others. If your land is in close proximity to an air strip, the birds attracted by freshwater areas may present a birdstrike hazard. Areas adjacent busy roadsides, power lines and floodlights are also to be avoided where possible. Ponds should also be sited away from areas of nutrient enrichment, e.g. septic tanks, if water quality issues are to be avoided. In all cases, working with the natural environment will make for the best results – where possible, natural low-lying areas and pre-existing native vegetation should be incorporated into your design.

1.4 – WATER LEVEL

The wildlife value and aesthetics of your pond will depend to a large extent on the water level it maintains. To these ends, it is best to understand the depth of the water table and the dynamics of the hydrology in your area prior to commencing excavations.

1.5 – EQUIPMENT

A bulldozer or scraper is best for constructing larger ponds and sculpting slopes and edges. A backhoe or excavator may be required to work in deeper, wetter sections.

2 – DESIGNING YOUR POND

2.1 – THINGS TO AVOID

Excavations for fill are typically large, deep and steep-sided. Ponds of this nature are of little or no value for wildlife. They can also represent a public health hazard and are most prone to water quality issues.

2.2 - SHAPE AND SIZE

Generally speaking, larger ponds (e.g. 2500 sqft) have the potential to attract most wildlife if properly designed.

Introduction of curves into your pond design will improve its aesthetic value, complementing and adding value to associated developments. Ponds can be constructed in unusual shapes, to complement the natural and built environment.

A mosaic of water areasinterspersed with native landscaping will support the greatest possible variety of wildlife. With appropriate design and landscaping, even the smallest ponds and scrapes can support a significant number of species.

2.3 – MAXIMIZING VALUE FOR WILDLIFE

The key to maximizing the wildlife value of ponds is to incorporate as many different habitats into your designas possible:

• ponds should be surrounded by a broad belt of vegetation – the wider the better, but should be at least 30ft.
• surroundingvegetation should be low in some areas (cut grass or, preferably, native ground cover), incorporate reed beds (Typha) and water-tolerant native trees and shrubs (see 2.5). Trees and shrubs can be used as cover by wildlife, shielding sensitive species from disturbance. Vegetation can also be used to control access to the pond by people.
• surrounding vegetation should overhang the pond wherever possible, providing shade and cover over the water. This will contribute greatly to the pond’s biodiversity and also support better water quality.
• from the edges, ponds should shelve gently downward. The slope should be as gentle as possible (10:1 or less).
• pond edges should incorporate significant shallow areas – (0-1 ½ ft deep) - these areas function as habitat for wading birds and are a practicalhealth and safety measure. Ideally, such shallow areas should constitute 25-40% of the pond area. Intermediate depth areas should vary from 1 ½ -3 ft deep; constituting 25-40% of the pond area. Deeper areas should be 3-4 ft in depth; constituting 25-40% of the pond area.
• waterdepths greater than 6feet have reduced value for wildlife, benefit less from wind-driven aeration and circulation which helps to maintain well-oxygenated pond water and bottom sediments, and become increasingly susceptible to water quality issues.Provision of some deeper areas will ensure the presence of water year round in the event of drought – annualfluctuations in water level of 3-4ft can be expected in most places.
• the base of the pond should be smooth and undulating - this encourages a mosaic of open water and underwater vegetation to develop, which is attractive to waterfowl.
• wildlife and aesthetic value can be further augmented by the provision of vegetated islands, which will attract roosting and possibly nesting birds. In the absence of islands, tethered floating platforms can be used as an alternative. Loose gravel islands may attract unusual species such as Antillean Nighthawk and Least Tern.

2.4 – LANDSCAPING

The importance of landscaping to the aesthetic and wildlife value of ponds has been touched on in previous sections. In all cases, attempts should be made to maintain any native vegetation already present on site. The maintenance of mature, overhanging trees, which can shade the water, will greatly add to the wildlife and aesthetic value of the pond. Shading of water also contributes to the maintenance of good water quality. Landscaping with native trees will help attract native species to the pond, particularly birdlife.

Exotic landscaping is costly and many introduce unwanted invasive species to a wildlife pond, however, some exotic species can be added to bring some added colour or variety to a native landscaping scheme.

2.5 – WATER QUALITY

Poor water quality is an issue for wildlife as it brings with it a reduction in biodiversity.

Poor water quality is also an issue for residents living adjacent to ponds, bringing with it aesthetic issues, including visually unappealing algal blooms and scum, foul odors and noxious fumes, fish kills and, in the worst cases, water toxicity and health issues for people and pets.

Poor water quality arises from

• nutrient run-off:most commonly, the source is fertilizer runoff from landscaping and agricultural land, washed into the pond during heavy rain. This can be avoided by reducing the amount of fertilizeradded to land nearby,by surrounding the pond with an appropriate buffer of vegetation.
• nutrient leaching: most commonly, the source of enriching leachatessuch as nitrogen and phosphorus is sewage systems and deep wells. This can be avoided by siting your pond away from deep wells and sewage systems.
• nutrient loading: this may occur when people feed wildfowl or add fish to a pond, artificially increasing its nutrient content. This can be avoided by allowing a pond to populate and equilibrate naturally.
• poor mixing of the water column: this usually arises from ponds being dug too deeply, and can be exacerbated by the addition of nutrients, physical constrictions, and direct sunlight. Poor mixing can be avoided by not digging ponds too deeply, and further mitigated by the addition of water pumps and water features.
• lack of oxygen: this usually arises when a pond does not possess enough oxygenating plant life. Aquatic plants will not thrive if the water column is too deep, as they will not receive sufficient sunlight. Algal blooms will also block out sunlight to oxygenating plants belowand absorb oxygen at night.This situation can be avoided by not digging your pond too deeply, and also by maintaining elevated ridges within the pond which are able to support oxygenating vegetation.
• ecological collapse: when water quality issues are extreme and persist, “ecological collapse” can occur. Under such circumstances, the ecological structure of a pond can “flip” from supporting a diverse natural complement of species, to a self-perpetuating species-poor slump. Such ponds are characterized by dense algal blooms (e.g.“pea-soup” color) and fish kills, which respectively further deoxygenate the water and add further nutrients, perpetuating the collapsed state of the pond. Once in this state, the slump species maintain their own ecological balance, preventing the pond from recovering. This makes active (and expensive) remedial action necessary, (such as draining the pond and removal of dead fish), if the pond is to recover its natural balance.Algal blooms can be monitored by using a “secchi disc”. In a healthy pond secchi disc visibilities should not fall below 30-45 cm (12-18 inches), for details see A secchi disc is easy to make, and can provide a usefulwarning of impending algal blooms associated with low oxygen levels especially at night.
• For more information see

2.5 – NATIVE LANDSCAPING FOR PONDS

LARGERTREES

Royal Palm
Roystonearegia / Bitter Plum
Picrodendronbaccatum / Red Birch
Burserasimaruba / Mahogany
Swieteniamahagoni
Smokewood
Erythroxylumaureolatum / Pepper Cinnamon
Canella winterana / Fig
Ficusaurea / White MangroveLagunculariaracemosa

SMALLER TREES

Buttonwood
Conocarpus erectus / Cabbage Tree
Guapira discolor / Wild Cocoplum
Saviaerythroxyloides / Christmas bush
Allophyluscominia

SHRUBS AND FLOWERS

Swamp fern
Acrostichum sp. / Mangrove vine
Rhabdadeniabiflora / Bloody Head Raw Bones
Capparisflexuosa / Snow Berry
Chiococca alba

3 – FILLING YOUR POND

3.1 – WATER

Your pond should be dug to such a depth that it is filled for the majority of the year by virtue of the natural water table.

If your pond dries out and you wish to replenish it, rainwater from a cisternorground water from a well,rather than tap water, will be the most beneficial.

If you wish to encourage introduction of natural pond life and native species to a newly dug pond, the addition of a few buckets of water from a neighboring well-established pond will give your pond a head start.

3.2 – AQUATIC PLANTS

If your pond is excavated into rock, adding an organic base (such as a thin layer of topsoil, perhaps 6 inches) to the excavated base will encourage the more rapid establishment of water plants.If you provide an organic base, aquatic plants should naturally establish in due course (additional planting is not necessary).

3.3 – FISH

Native species and non-native species do not generally mix well in ponds. It is often thought that adding fish will help keep algae and greening of ponds down, but fish generally add to the nutrient loading of ponds. Wildlife ponds for native species and ornamental ponds which feature exotic species (such as goldfish, koicarp, and introduced waterfowl) are best kept separate. Tilapia should not be stocked because of their potential to become a pest fish,capable of competing with native fish for food and living space. DoE investigations since 1991 have shown Tilapia to be the species of fish most commonly involved in fish-kill events in Grand Cayman.

3.4 – ATTRACTING BIRDS

With appropriate design and landscaping, your pond will naturally attract wild birds in time.Attracting larger numbers of birds, particularly by feeding waterfowl at the edges of ponds, will introduce additional nutrients to the pond. If your pond does not have the capacity to adapt to this elevation in nutrient levels, water quality issues will quickly result. The feeding of waterfowl is a seemingly generous act, however inappropriate feeding can have serious repercussions for waterfowl including nutrient deficiencies such as “Angelwing”, resulting in deformity and even death. Feeding also encourages unnatural behaviour, including delayed migration and aggressive behaviour towards people.

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These guidelines were adapted from the Excavated Ponds for Wildlife guidelines, developed by the Minnesota Department of Natural Resources.