1. Aquatic Science—Lotic
Biotic Lotic Ecosystems

2. Bacteria Bacteria is present in large numbers in lotic waters.
Free-living forms decompose organic material.
Other forms are in the guts of organisms as parasites, or in a commensal relationship.
Bacteria recycle energy.

3. Primary Producers
Algae, consisting of phytoplankton and periphyton, are the most significant sources of primary production in most streams and rivers.
Plants exhibit limited adaptations to fast flow and are most successful in reduced currents.

4. Plants
Primitive plants, such as mosses and liverworts attach themselves to solid objects.
Others are rooted and may be classified as submerged or emergent.
Algae and plants are important to lotic systems as sources of energy, for forming microhabitats that shelter other fauna from predators and the current, and as a food resource .

5. Insects and Other Invertebrates
Up to 90% of invertebrates in some lotic systems are insects.
Insects have developed several strategies for living in the diverse flows of lotic systems. Some avoid high current areas, inhabiting the substratum or the sheltered side of rocks. In stronger current, species have developed weighted cases, attachments to anchored pads of silk, recurved clinging claws, suction cup like devices, and flattened, streamlined bodies.
Mayfly nymph

6. Insects and Invertebrates Continued
Invertebrate taxa common to flowing waters include mollusks such as snails, limpets, clams, mussels, as well as crustaceans like crayfish and crabs.
Like most of the primary consumers, lotic invertebrates often rely heavily on the current to bring them food and oxygen.
Invertebrates, especially insects, are important as both consumers and prey items in lotic systems.
Crayfish
Mussels

7. Fish and Other Invertebrates
Fishes are probably the best-known inhabitants of lotic systems.
The ability of a fish species to live in flowing waters depends upon the speed at which it can swim and the duration that its speed can be maintained.
Continuous swimming expends a tremendous amount of energy and, therefore, fishes spend only short periods in full current.

8. Anadromous vs Catadromous
Lotic systems typically connect to each other, forming a path to the ocean (spring → stream → river → ocean), and many fishes have life cycles that require stages in both fresh and salt water.
Salmon, for example, are anadromous species that are born and develop in freshwater and then move to the ocean as adults.
Eels are catadromous, and are born and develop in the ocean and then move into freshwater as adults

9. Fish and Other Vertebrates
Other vertebrates that inhabit lotic systems include snakes, turtles, crocodiles, and alligators.
Mammals like otters, beavers, hippos, and river dolphins.
With the exception of a few species, these vertebrates are not tied to water as fishes are, and spend part of their time in terrestrial habitats.

10. Pollution
Agricultural fields often deliver large quantities of sediments, nutrients, and chemicals to nearby streams and rivers.
Urban and residential areas can also add to this pollution when contaminants are accumulated on impervious surfaces such as roads and parking lots that then drain into the system.

11. Nitrogen and Phosphorus Pollution
Elevated nutrient concentrations, especially nitrogen and phosphorus which are key components of fertilizers, can increase periphyton growth.
Periphyton: Algae and associated microorganisms growing attached to any submerged surface.

12. Acid Rain
Acid rain, forms from sulfur dioxide and nitrous oxide emitted from factories and power stations.
These substances readily dissolve in atmospheric moisture and enter lotic systems through precipitation.
This can lower the pH of these sites, affecting all trophic levels from algae to vertebrates.

13. Dams
Dams alter the flow, temperature, and sediment regime of lotic systems.
Additionally, many rivers are dammed at multiple locations, amplifying the impact.
Invertebrates immediately below a dam can show reductions in species richness due to an overall reduction in habitat heterogeneity.
dams fragment river systems, isolating previously continuous populations, and preventing the migrations of anadromous and catadromous species.