Freshwater Biomes: Lotic Ecosystems

Quote by Heraclitus: "No man ever steps in the same river twice, for it’s not the same river and he is not the same man."

Definition: Freshwater ecosystems include various water bodies such as:
- Streams
- Rivers
- Lakes
- Ponds
- Inland wetlands
Salinity Levels:
- Freshwater ecosystems have a very low salinity level (less than 0.1%).
- Contrast with saltwater ecosystems that have a higher salinity of approximately 3.5%.
Categories:
- Lotic: Freshwater ecosystems with constantly moving water (e.g., streams and rivers).
- Term derives from Latin "Lotus/Lavere" meaning washing.
- Lentic: Freshwater ecosystems with standing (still) water (e.g., lakes, ponds, and wetlands).
- Term derives from Latin "Lentus" meaning slow or calm.

Lotic Ecosystems:
- Streams:
- Characteristics: Narrow channel of water, generally <15 m from bank to bank, rapid water movement, steep gradient, rockier bottoms, and shallow depths.
- Rivers:
- Characteristics: Wider channel formed when tributaries combine with runoff and groundwater inputs, generally >15 m
- from bank to bank, lower gradient, siltier (sediment-rich) bottoms, and deeper.

Characteristics:
- Moving water rather than still water.
- Flow generally in one direction (downhill) due to gravity.
- Create dynamic and varied habitats through weathering, erosion, and sedimentation/deposition processes.
- Higher geographical range and higher oxygen content compared to lentic systems.
- Can persist for many thousands of years.
Biodiversity Impact:
- Approximately 40% of global fish species (over 10,000 species) and 25% of vertebrates exist in lotic systems for support in food, water, and habitat.

Examples of Vertebrates that thrive in lotic systems include:
- Fish (e.g., salmon, trout)
- Amphibians (e.g., frogs, salamanders)
- Aquatic reptiles (e.g., crocodilians, turtles)
- Aquatic birds (e.g., ducks)
- Aquatic mammals (e.g., platypus, beavers, otters, river dolphins)

Streams and Rivers:
- Both systems drain watersheds, characterized by tributaries flowing into them.
- Tributary: A stream or river flowing into a larger waterbody.
- Watershed: A drainage area flowing to a common outlet.
- Source: Origin of a stream or river where water is supplied.
Watershed Features:
- Include lentic ecosystems, springs (groundwater exits), and snowmelt processes.
- Divide: An imaginary line separating watersheds.
- Confluence: The junction where two lotic water bodies meet.

Dimensions: Lotic systems can be measured in:
- Longitudinal: Length and flow direction.
- Lateral: Width and structure along banks.
- Vertical: Depth and profile of riverbed and channels.
Changes occur over time, influenced by temporal factors.

Source Zone:
- Where streams and rivers originate, characterized by cold, clear, high gradient, and swift turbulent water.
- High oxygen content, low nutrient levels.
Transition Zone:
- Area where streams widen to rivers.
- Features lower gradient, warmer water, and higher nutrient levels compared to the source zone.
Floodplain Zone:
- Flat, low elevation area where rivers meander and can flood.
- Features slower-moving water, decreasing oxygen levels, and increasing nutrient content.
Mouth:
- Area where the river joins a larger body of water (ocean or lake).
- Classifications:
- Delta: Fan-shaped, outward.
- Estuary: Funnel-shaped, inward.

Fluvial: Pertaining to a stream or river.
Profile: Side view of a lotic waterbody displaying gradient over its course.
Cross-Section: View from one bank across to the opposite bank, showing riverbed and land.
Precipitation: Water in the form of rain, snow, etc., contributing to water supply in streams.
Thalweg: A line following the valley's lowest part, where swift currents occur.
Rapids and Waterfalls: Fast-flowing water and steep falls, respectively.
Dendritic: Branch-like structure of rivers and tributaries forming a watershed.
Meander: Curves in rivers caused by erosion and deposition processes.
Oxbow Lake: A lake formed from a former meander of a river.
Flood Plain: Flat area next to a river, prone to flooding, composed of nutrient-rich alluvium.

Gradient: Slope or steepness of a waterbody.
Water Velocity: Speed of water flow, measurable in m/s or mph.
Discharge/Flow: Volume of water flowing through a specific area per unit time, often measured in cubic feet per second (cfs).
Sinuosity: Degree of bending in a river as measured by length relative to straight-line distance.
Weathering & Erosion: Breakdown and displacement of materials, some being moved away and others left behind during these processes.
Dissolved Oxygen (DO): Amount of oxygen dissolved in water crucial for aquatic life.
Temperature and Light: Integral factors influencing aquatic ecosystems.

Erosion and Deposition: Occur due to varying velocities across the meander (faster on outer banks, slower on inner banks).
Adaptations:
- Organisms exhibit unique adaptations for survival in rapids and pools.
- Macroinvertebrates and fish use physical attachments, streamlined bodies, specialized breathing adaptations, and specific microhabitats.

Riparian: Refers to areas adjacent to rivers and streams, critical for habitat diversity.
Riparian Zones serve various ecological functions:
- Flood protection, erosion control, habitat preservation.
Buffer Zones: Vegetative margin areas around water bodies reduce turbidity and mitigate temperature increases.

Water Column Chemistry is influenced by:
- Dissolved inorganic matter and nutrients.
- Presence of gases and trace metals crucial for ecosystem balance.
- Role of dissolved organic matter and pollutants.

Oxygen Cycle: Interplay of atmospheric and dissolved oxygen throughout different processes in aquatic ecosystems.
Nitrogen Cycle: Transfer and transformation of nitrogen affecting both biotic and abiotic components.

Lotic ecosystems are essential for biodiversity, provide critical habitats, and have complex interactions influenced by their physical characteristics and surrounding environments.