Aquatic Science Lotic Ecosystems

Lotic Ecosystem The ecosystem of a river, stream, or spring. Lotic refers to flowing water. Included in the lotic environment are the biotic interactions (plants, animals and micro-organisms) as well as the abiotic interactions (physical and chemical).

Abiotic and Biotic Factors Abiotic Factors include: Flow Light Chemistry Temperature Substrate Biotic Factors include: Bacteria Primary Producers Insects and other Invertebrates Fish and other Vertebrates

Flow Lotic environments have water flowing in one direction, also called unidirectional (one-way). There is a state of continuous physical change as a result. Flowing waters can alter the shape of the streambed through erosion and deposition, creating a variety of habitats, including riffles, glides, and pools.

Riffle Riffles: a ripple in a stream or current of water. The Santa Cruz River riffles

Glide Habitat and Pool Glide Habitat: A nonturbulent, moderate-velocity, low-gradient macrohabitat with a wide channel and no thalweg that occurs at the transition between a pool and a riffle Thalweg: The line defining the lowest points along the length of a river bed or valley. Pool: a deep, still spot in a river

Flow Continued The strength of water flow can vary between systems, ranging from torrential rapids to slow backwaters that almost seem like lentic systems. The speed of the water flow can also vary within a system.

Speed of Flow The speed of flow is typically based on a variability of friction with the bottom or sides of the channel, sinuosity, obstructions, and the incline gradient. Sinuosity: A river’s sinuosity is the rivers tendency to move back and forth across the floodplain, in an S-shaped pattern, over time. As the stream moves back and forth across the flood plain, it leaves behind scars of where the river channel once was. The amount of water input into the system from direct precipitation, snowmelt, and/or groundwater can affect flow rate.

Light Light is important to lotic systems, because it provides the energy necessary to drive primary production via photosynthesis. Primary production: The total amount of new organic matter produced by photosynthesis. Light can also provide refuge for prey species in shadows it casts.

Amount of Light The amount of light that a system receives can be related to a combination of internal and external stream variables. The area surrounding a small stream, for example, might be shaded by surrounding forests or by valley walls. Larger river systems tend to be wide so the influence of external variables is minimized, and the sun reaches the surface. Additional influences on light availability include cloud cover, altitude, and geographic position.

Temperature Most lotic species are poikilotherms whose internal temperature varies with their environment. As a result, temperature is a key abiotic factor for them. Poikilotherms: Organisms, plant or animal, having an internal temperature that varies with the temperature of its surroundings. Water can be heated or cooled through radiation at the surface and conduction to or from the air and surrounding substrate.

Temperature Continued Shallow streams are typically well mixed and maintain a relatively uniform temperature within an area. In deeper, slower moving water systems, however, a strong difference between the bottom and surface temperatures may develop. The amount of shading, climate and elevation can also influence the temperature of lotic systems.

Chemistry Water chemistry between systems varies tremendously. The chemistry is foremost determined by inputs from the geology of its watershed, or catchment area, but can also be influenced by precipitation and the addition of pollutants from human sources. Watershed: The region draining into a river, river system, or other body of water. Large differences in chemistry do not usually exist within small lotic systems due to a high rate of mixing. In larger river systems, however, the concentrations of most nutrients, dissolved salts, and pH decrease as distance increases from the river’s source

Oxygen Oxygen is likely the most important chemical constituent of lotic systems, as all aerobic organisms require it for survival. It enters the water mostly via diffusion at the water-air interface. Oxygen’s solubility in water decreases as water temperature increases. Fast, turbulent streams expose more of the water’s surface area to the air and tend to have low temperatures and thus more oxygen than slow, backwaters.

Oxygen and Photosynthesis Oxygen is a byproduct of photosynthesis, so systems with a high abundance of aquatic algae and plants may also have high concentrations of oxygen during the day. These levels can decrease significantly during the night when primary producers switch to respiration. Oxygen can be limiting if circulation between the surface and deeper layers is poor, if the activity of lotic animals is very high, or if there is a large amount of organic decay occurring

Substrate The inorganic substrate of lotic systems is composed of the geologic material present in the catchment that is eroded, transported, sorted, and deposited by the current. Substrate: An underlying layer; a substratum. Inorganic substrates range from boulders, to pebbles, to gravel, to sand, and to silt. Substrate can also be organic and may include fine particles, autumn shed leaves, submerged wood, moss, and more evolved plants.

Substrate Particle Size Typically, particle size decreases downstream with larger boulders and stones in more mountainous areas and sandy bottoms in lowland rivers. This is because the higher gradients of mountain streams facilitate a faster flow, moving smaller substrate materials further downstream for deposition.