ECOLOGY OF FRESH WATER ECOSYSTEMS Freshwater ecology is a specialized sub category of the overall study of organisms and the environment. Unlike biology, ecology refers to the study of not just organisms but how they react, and are affected by the natural surrounding environment or ecosystem. By studying the plants and animals in a body of water as well as the components of the water itself, a scientist specializing in freshwater ecology can discover vital information about the health and needs of a freshwater system. Freshwater Ecology is a study of the interrelationships between freshwater organisms and their natural and cultural environments.

Freshwater ecosystems include: • sluggish waters of lakes and ponds • moving waters of rivers and streams • Wetlands = areas of land periodically covered by water. Factors that determine where organisms live in the water include: • Temperature • Sunlight • Oxygen • Nutrients Aquatic organisms are grouped by their location and their adaptation. • There are 3 main groups of organisms in the freshwater ecosystem: PLANKTON - organisms that float near the surface of the water Two main types of plankton are: • Phytoplankton – microscopic plants that produce most of the food for an aquatic ecosystem • Zooplankton – microscopic animals, some are large enough to be seen with the eye. • many are larvae of aquatic mollusc’s or crustaceans. NEKTON – free-swimming organisms • Fish, turtles, etc. BENTHOS – bottom-dwelling organisms • Mussels, worms, many decomposers. • Many benthic organisms live attached to the hard surfaces of the bottom.

ECOLOGY OF POND AND LAKE Life Zones in a Lake or Pond Lakes and ponds can be structured into horizontal and vertical zones that include: LITTORAL ZONE – nutrient-rich, near shore, aquatic life is diverse and abundant. • Plants, such as cattails and reeds are rooted in the mud underwater, and their upper leaves and stems emerge above the water. • Plants with floating leaves, like pond lillies, are also rooted here. • Many fish live here as there is good hiding and food in the plants. LIMNETIC ZONE – well-lit, open surface waters, away from the shore • Further out from the shore in the open waters there are other plants, algae, and some bacteria that make food through photosynthesis. • Many fish swim freely in this zone. • Algae, phytoplankton, and zooplankton live (float freely) here as well. • Most photosynthesis occurs in this part of the lake. • Near the surface there is plenty of light penetrating down through the waters. As waters deepen it becomes darker. PROFUNDAL ZONE (aphotic zone) – deeper open waters away from shore, colder and darker zone • located below the range of light penetration – so little to no light. • Temperatures typically colder (because sunlight does not penetrate) • Fish adapted to live in darker, cooler water live here. BENTHIC ZONE – bottom of a pond or lake, predominately inhabited by decomposers, insect larvae, and clams. • Sometimes little to no light, depending on the depth. • Bacteria live here to decompose dead plants and animals that drift down from the land and water above. • Fish adapted to live in darker, cooler water also live here. A pond ecosystem is a complex interdependent system of plants, animals and microorganisms along with the physical environment in which they live. Pond ecology depends first and foremost on the freshwater environment for nutrients and survival. Ponds are usually shallow, which allows sunlight to reach organisms growing on the bottom. A freshwater pond ecosystem consists of a four habitats, populated by three types of organisms that live in four different habitats. Every element of a pond ecosystem works in conjunction with the others to maintain balance. Fishes, plants, algae, fungi, and microorganisms in the pond ecology fall into three categories:  Producers - those that provide or are food for other species.  Consumers - those that partake of the food provided by Producers.  Decomposers - those that decompose and consume dead organisms

Habitats in the Pond Ecology Ecosystem A habitat is a structure or environment which provides the needed elements for the life of an organism. A pond is made up of four interdependent habitats:  Shore Habitat - The organisms that inhabit the shore habitat are dependent upon what kind of shoreline exists. Some shorelines may not be conducive to plant growth, where others may contain all four of the predominant pond ecosystem organisms.  Surface Film - Insects such as water striders and other organisms able to walk or float on the surface inhabit the surface of the pond ecosystem. They feed on the floating plants, dead insects and even each other when need arises.  Open Water - Fishes and plankton inhabit this third habitat of the pond. Phytoplankton (algae) and zooplankton (insect larvae, invertebrates, rotifier, and tiny crustaceans) are present as well.  Bottom Water - Bottom habitat varies according to the depth of the pond. Shallow ponds with sandy bottoms may contain insects, earthworms, and snails. A deep pond with a muddy bottom will contain dragonfly nymphs, microorganisms, maggots, and flatworms.

 The Pond Ecosystem Food Chain In order to live, all organisms must eat. A food chain is a hierarchical system of consumption. There are three basic levels in the food chain of a pond.

 Producers or autotrophs: Made up of phytoplankton and plants, these organisms use sunlight and photosynthesis to create their own food.  Herbivores: Insects, invertebrates and crustaceans which consume the plants.  Carnivores: Fishes and other organisms which can feed on both plants and herbivores. The decomposers, or sapotrophs, are at the very bottom of the food chain. Mostly comprised of fungi and bacteria, these organisms are vital to the nutrient cycle, as they convert all dead organic matter into carbon dioxide and nutrients that can be readily use by algae and plants to produce food.

ECOLOGY OF RIVER In studies of the ecology of freshwater rivers, habitats are classified as upland and lowland. Upland habitats are cold, clear, rocky, fast flowing rivers in mountainous areas; lowland habitats are warm, slow flowing rivers found in relatively flat lowland areas, with water that is frequently coloured by sediment and organic matter. Classifying rivers and streams as upland or lowland is important in freshwater ecology as the two types of river habitat are very different, and usually support very different populations of fish and invertebrate species.

UPLAND In freshwater ecology, upland rivers and streams are the fast flowing rivers and streams that drain elevated or mountainous country, often onto broad alluvial plains (where they become lowland rivers). However, altitude is not the sole determinant of whether a river is upland or lowland. Arguably the most important determinants are that of stream power and course gradient. Rivers with a course that drops in altitude rapidly will have faster water flow and higher stream power or "force of water". This in turn produces the other characteristics of an upland river - an incised course, a river bed dominated by bedrock and coarse sediments, a riffle and pool structure and cooler water temperatures. Rivers with a course that drops in altitude very slowly will have slower water flow and lower force. This in turn produces the other characteristics of a lowland river - a meandering course lacking rapids, a river bed dominated by fine sediments and higher water temperatures. Lowland rivers tend to carry more suspended sediment and organic matter as well, but some lowland rivers have periods of high water clarity in seasonal low flow periods. The generally clear, cool, fast-flowing waters and bedrock and coarse sediment beds of upland rivers encourage fish species with limited temperature tolerances, high oxygen needs, strong swimming ability and specialized reproductive strategies to prevent eggs or larvae being swept away. These characteristics also encourage invertebrate species with limited temperature tolerances, high oxygen needs and ecologies revolving around coarse sediments and interstices or "gaps" between those coarse sediments. LOWLAND The generally more turbid, warm, slow-flowing waters and fine sediment beds of lowland rivers encourage fish species with broad temperature tolerances and greater tolerances to low oxygen levels, and life history and breeding strategies adapted to these and other traits of lowland rivers. These characteristics also encourage invertebrate species with broad temperature tolerances and greater tolerances to low oxygen levels and ecologies revolving around fine sediments or alternative habitats such as submerged woody debris ("snags") or submergent macrophytes ("water weed").

PRODUCTIVITY OF FRESHWATER ECOSYSTEMS All freshwater ecosystems (lakes, rivers, ponds, streams, wetlands) are home to various life forms, often collectively referred to as the food chain or food web. The numbers and variety of living organisms in a freshwater food web are dependent on the productivity of the ecosystem. This productivity depends on the availability of energy (usually solar) and raw materials (nutrients, minerals) within the ecosystem. Of course, the available energy is constantly changing with daily and seasonal cycles, and the raw materials are continuously cycling (water cycle, carbon cycle, nitrogen cycle, phosphorus cycle} through and within the ecosystem. These fluctuations also help to determine the shorter-term productivity of the system. In aquatic ecosystems, as on land, the basis of life and the resulting food web is photosynthesis. In simple terms, this is the conversion of solar energy and nutrients to living biomass in the form of green plants. These green plants take many forms. In aquatic systems, they are typically grouped as either macrophytes (large plants, often rooted) or algae (microscopic plants). Both types occur in shallow, nearshore areas, with the algae often attached to surfaces such as rocks, docks, and the large plants. In the deeper, open-water areas, algae are the dominant green plants. Collectively, these plants form the base of the freshwater food web. Their conversion, through photosynthesis, of inorganic nutrients and minerals to living (organic) matter is called primary production. Without this primary production, there would be no new biomass produced within the ecosystem to support other life forms. The greater the primary production within an ecosystem, the more living biomass that can be supported within the food web. The Algae The algae living in the open water are also referred to as phytoplankton (phyto = plant, plankton = wandering). Like many of the microscopic animals (zooplankton) that feed on them, these tiny “plants” float about in the open water, drifting with the slightest currents. They draw raw materials from the surrounding water and use energy from the sun to grow. When key nutrients (carbon, nitrogen, phosphorus) are available in abundance, they can grow and reproduce quickly. Algae are extremely diverse. While they are single-celled, plant-like organisms, many algal species form complex colonies consisting of many individual cells. Among the major freshwater algal groups are chlorophytes (green algae), diatoms, euglenophytes, dinoflagellates, and chrysophytes. Cyanophytes or “blue-greens” (more properly called cyanobacteria) are grouped with the other algae, but not related. Each group consists of hundreds of species, and hundreds of different species may occur in a given lake. The three photos at the top of the page 2 show (left) a mixture of filamentous cyanobacterial colonies and dinoflagellates, some diatom colonies, and ) a mixture of chlorophyte species. Each group and each species is adapted to certain conditions of nutrient availability, water temperature, solar energy, and other environmental factors. Thus, some species will commonly occur in certain types of lakes, or at certain times of year, or under certain special conditions. If conditions are ideal for a particular species, it will be present in high numbers and other algal species in the lake will be less abundant. If conditions change significantly, other species better adapted to the new conditions may outcompete the original species and begin to dominate within the phytoplankton. For instance, chrysophytes, such as Dinobryon sp. typically are found in Boreal Shield lakes, where nutrient concentrations are low. With limited availability of key nutrients, particularly phosphorus, these species can thrive in the cold, clear water of these lakes, but the overall biomass of the community will be low. On the other hand, cyanophytes, such as Anabaena sp. (above, right) are generally adapted to warmer, nutrient-rich water, such as is found in many prairie lakes. If phosphorus is available in abundance, either naturally or through human activities, many cyanophyte species can grow and multiply at a rapid pace, quickly dominating the Productivity of Freshwater Ecosystems phytoplankton community. Some of these blue-green species can form chains of specialized cells, some of which contain gas vacuoles that serve as flotation chambers to keep the chain floating at the surface where the other cells in the chain can utilize the abundant solar energy while taking the raw materials for rapid growth from the water. Some, similar to legumes on land, can fix nitrogen from the air and use it for rapid growth provided there is plenty of phosphorus also available. This can result in the formation of massive surface “blooms” that can block sunlight from reaching other species deeper in the water. When the cells forming the bloom die off, they leave large quantities of decomposing biomass. Bacteria carrying out this decomposition may remove much of the dissolved oxygen from the water, sometimes killing fish and other species of animals requiring considerable oxygen. THE INVERTEBRATES In general, where there is more algal growth (greater primary productivity), there will be more food for things that eat algae. Most of these algae eaters are invertebrates such as microcrustaceans, insect larvae, and mollusks. Many small fish, including minnows and the young of larger species, also feed directly on algae and other plants. However, not all algae are equally edible for these “critters”. Some algal species have spines and other structures that make their cells more difficult for small animals to consume. Some of the blue-greens and dinoflagellates can produce toxins that can be fatal. Below, left, is a transparent, sac-like animal called a rotifer, its gut filled with diatom cells. To the right is a tiny crustacean, Bosmina sp., its long gut filled with cells of the algae it has been eating. These small animals are food for larger animals, including fish. Lakes that produce more algae will normally produce more invertebrates and small fish. More invertebrates and small fish will normally mean more food to support large fish. Therefore, we would expect more fish biomass in a lake where primary productivity is high. However, high productivity lakes will not support all kinds of fish. Each species is best adapted to certain conditions, and will not do well where these conditions do not exist. THE FISHES Normally, when primary productivity in a lake is low, the lake will support only fish species that are adapted to this oligotrophic (low nutrition) system. Lake trout (below) are one such species. Because they are adapted to cold, well-oxygenated, clearwater lakes, with relatively little algal productivity, their food resources are limited. They tend to grow slowly, become sexually mature at a later age, and reproduce slowly. Therefore, lake trout populations are very susceptible to over-fishing. On the other hand, species, such as bass or walleye (below), that are adapted to life in warmer, shallower, more productive lakes, will have more food available. Thus, these fish can grow faster and reproduce more rapidly than lake trout. As a result, these fish populations are themselves more productive and can withstand heavier fishing pressures without suffering significant population losses. However, all fish populations, and particularly those that are piscivorous (eat other fish) and occupy a niche near the top of the lake food web, can be harmed by overfishing. Greatly increased fishing pressures result from continued construction of new roads and trails, easier access through use of all terrain and other off- road vehicles, and major advancements in fish finding technologies and techniques. In our modern world, wild fish populations have few places to hide. Productivity of Freshwater Ecosystems.