DO AQUATIC ECOSYSTEMS HAVE AN UNLIMITED CAPACITY TO MAINTAIN THEIR QUALITY?

Not exactly, but believe it or not, we once thought they did, and that's why we dumped many industrial chemicals over the past century. In nature nothing exists alone. Living things relate to each other as well as to their non-living, but supporting, environments. These complex relationships are called ecosystems.

Aquatic ecosystems include oceans, lakes, rivers, streams, estuaries, and wetlands. Within these aquatic ecosystems are living things that depend on the water for survival, such as fish, plants, and microorganisms. Aquatic ecosystems usually contain a wide variety of life forms including bacteria, fungi, and protozoan; bottom-dwelling organisms such as insect larvae, snails, and worms; free-floating microscopic plants and animals known as plankton; large plants such as cattails, bulrushes, grasses, and reeds; and also fish, amphibians, reptiles, and birds. The assemblages of these organisms vary from one ecosystem to another because the habitat conditions unique to each type of ecosystem tend to affect species distributions. For example, many rivers are relatively oxygen-rich and fast-flowing compared to lakes. The species adapted to these particular river conditions are rare or absent in the still waters of lakes and ponds.

These ecosystems are very fragile and can be easily disturbed by pollution. Each body of water is a delicately balanced ecosystem in continuous interaction with the surrounding air and land. Whatever occurs on the land and in the air also affects the water. If a substance enters a river or lake, the water can purify itself biologically - but only to a degree. Whether it is in the smallest stream or lake - or even in the mighty oceans - the water can absorb only so much. It reaches a point where the natural cleaning processes can no longer cope.

The ecosystem, like most systems in nature in general, have a process by which they work. Energy from the sun is the driving force of an ecosystem. This light energy is captured by primary producers (mainly green plants and algae) and converted by a process called photosynthesis into chemical energy such as carbohydrates. The chemical energy is then used by the plants to perform a variety of functions including the production of plant parts such as leaves, stems, and flowers. The raw materials used for this purpose are nutrients (e.g., nitrogen, phosphorus, oxygen, and calcium): substances necessary for the growth of all plants and animals. Animals are incapable of photosynthesis. They therefore eat either plants, other animals, or dead tissue to obtain their energy and required nutrients.

In ecosystems, the transfer of energy and nutrients from plants to animals occurs along pathways called food chains. The first link in a food chain consists of primary producers: green plants and other organisms capable of photosynthesis. Plant-eating organisms, known as primary consumers, are the next link in the food chain. They, in turn, are eaten by secondary consumers: carnivores (flesh eaters) or omnivores (plant and animal eaters). Decomposers such as bacteria and fungi make up the final link in the food chain. They break down dead tissues and cells, providing nutrients for a new generation of producers. Most organisms in an ecosystem have more than one food source (e.g., fish feed on both insects and plants) and therefore belong to more than one food chain. The consequent overlapping food chains make up food webs: complex phenomena with links that are constantly changing.

In some ways, there are some indicators that an aquatic ecosystem may not be healthy. Unhealthy aquatic ecosystems are those where human disturbances have impaired the natural functioning (e.g., nutrient cycling) or appreciably altered the structure (e.g., species composition) of the system. These disturbances can be physical (e.g., injection of abnormally hot water into a stream), chemical (e.g., introduction of toxic wastes at concentrations harmful to the organisms) or biological. Introduction and propagation of non-native animal or plant species is one such example of biological disturbance. There are more than 900 exotic plant species in Florida, accounting for more than one-fourth of the total number of plant species found in the state. Most were introduced to Florida on purpose, as ornamental plants, while a handful were introduced accidentally. Many of the characteristics that make a plant easy to grow and propagate are also characteristics of invasive plants. The lack of predators (insects, animals or fungi) has given many invasive exotic plants a huge advantage over native species.

Nature reveals more every decade through great research and application on the behalf of humans, that each of its ecological systems are connected. An aquatic ecosystem can no more self-repair itself once it reaches a breakpoint, than can a rainforest or a wetlands.