Chapter 2- The Diving Environment The Diving Environment 47 Thermal stratification in lakes affects the amount of oxygen in the water and, therefore, fish distribution. The temperature also affects plankton populations which, in turn, affect visibility. In many lakes, isothermal conditions present the best times for diving unless wind action disturbs sediment and reduces the visibility. A halocline is a horizontal boundary between waters of differing salinity. In some situations where fresh water comes into contact with sea water, the waters remain separated in layers due to differences in density. At the boundary where the two layers come into contact, a mixing occurs. This boundary, which can be several feet deep, affects your perception as you pass through it, and can produce a feeling of disorientation. Although not physically dangerous, avoid lingering in a halocline if one should be encountered while diving. WEATHER CONSIDERATIONS Weather is an important factor affecting diving operations. You must be familiar with local weather conditions and monitor forecasts when planning dives. Different areas may have unique weather conditions. In some areas, offshore operations in small boats may be prohibited by weather and surface conditions. The following are examples of weather-related concerns for divers: • Squalls, which are brief, intense rainshowers, can occur on open water quite suddenly. • Storms, which produce wind and waves, and run-off that decreases visibility. Lightning, tornadoes, waterspouts, and driving rain can also be dangerous. • Low temperatures which can freeze equipment and cause chilling, frostbite, and hypothermia. • High temperatures and humidity which can cause hyperthermia, heat exhaustion, or heat stroke. • Sunlight, which is more intense near the equator, can cause eye strain and sunburn. • Winds, which affect surface conditions and can lower the temperature, also can cause currents and seasickness. BOTTOM CONDITIONS The type of bottom of the diving area can affect visibility, aquatic life, navigation, dive planning, and equipment requirements. Coral bottoms usually offer good visibility, warm water, abundant fish life, and exciting diving. Hazards include coral cuts, marine life stings, and exceeding planned depths due to the misleading visibility in very clear water. Wear protective clothing, avoid contact with the corals, and monitor your depth gauge frequently. Rocky bottoms exist in many colder areas and usually offer many of the benefits of coral reefs. Visibility varies by area and season. Hazards include slippery algal growth on rocks at entry and exit areas, surf, currents, and marine plants. Sandy bottoms are found everywhere and offer varying visibility, depending upon water movement. This environment may look like a desert to some divers, but is home for many animals. Diving on sandy bottoms requires that you maintain neutral buoyancy and minimize fin action near the bottom to avoid raising silt. Avoid dragging your equipment on the bottom, especially gauges and extra second stages. Muddy bottoms vary in consistency from compact, firm clay to a semi-fluid silt. These types of bottoms are found everywhere, but are most common in rivers, lakes, and bays. Many animals similar to those found in sand live in the mud. The visibility is generally poor because of the ease with which sediment can be disturbed. Muddy bottoms can significantly affect entries and exits. Beware of slipping and of sinking deeply into the mud. PRINCIPAL DIVING ENVIRONMENTS There are many different environments, in marine and fresh water, that are enjoyed by divers around the world. Ocean environments include coral reefs, temperate kelp forests, rocky shores, soft bottoms, and estuaries; while fresh water environments range from lakes and quarries, to rivers and springs. Coral reefs have many of the characteristics that divers love: warm, clear water; diverse species, and color. Coral reefs need water temperatures of at least 20°C
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