(BIO 386) Lecture 10 - Running Waters

Hydrography

Change in structure of the channel and effects on flow (patterns)

Role of running waters in global cycles

• short retention time

• responsible for fluxes between terrestriala and ocean reservoirs

  • dissolved and particulate substances

• rivers and streams associated with wetlands

Dissolved substances

weathering/organismal uptake

Particulate substances

deposition/feeding/erosion

Transpiration water budget

Movement of water vapor through stomata of leaves to the atmosphere

• Trade-off: water conservation vs. nutrient acquisition

• Plants differ in amount of transpiration

Evapotranspiration water budget

Total flux of water from an ecosystem

• Made up of evaporation and transpiration

Watershed water budget

The area of the landscape that contributes to flow of water at a particular point in the stream

Groundwater recharge

depends on soil structure and nature and depth of bedrock

Plants affect terrestrial water balance

Difference between precipiation and discharge due to transpiration by plants in summer; plants suck up all the water.

Water flow paths

• Baseflow: from groundwater

• Overland flow: over surface

• Through flow (interflow?): through surface soils

Baseflow

From groundwater, varies as water table rises and falls

Overland flow

Over surface, responds fastest but only due to soil hardening or saturation

Through flow

Faster to respond to precipitation and recedes faster than baseflow

Stream Order

How far a stream is from its origin

Stream characteristics that change with order

Flow of running water influences…

the shape of the stream channel itself, because they carry particles

Eddies

Whirlpools of flowing water that are caused by differences in speed

Eddies cause variations in current speed, which leads to

Movement of particles:

• When flow is fast: Erosion

• When flow is slow: Settling and deposition

Resistance of surrounding materials affect

Structure of rivers/streams

• When resistant to erosion: streams follow solid banks

• When erodable: streams meander and positions change over time

Riffles

Zones of erosion and loss of material (Only coarse material remains)

Pools

Places of slow water flow and deposition of slit

Floodplains

Periodically flooded areas

• water is reduced due to friction of nearby river bottom

• particles sink out because of slower flow

• Fertile, nutrient-rich

Riverflow is directly related to…

flux of materials

Particle load

Mass flux of particles per year (flow x concentration)

• Load is higher for steeper rivers with fast flow

• Load is lower for flatter rivers with slower flow

Succession of vegetation

Starts with open land affected by fire, ice, etc. starts to grow annual plants →

Succession affects nutrient retention

Mid succession:

• Limiting nutrient is needed to make more biomass → Starts to decrease

Later succession:

• Outputs to streams < input from atmosphere

• Limiting elements increases

• Plants are CHANGING characteristics of water in soils that are reaching the streams → Output to streams =i input from atmosphere

Dissolved organic carbon (DOC) makes up…

70-90% of organic matter in surface waters

Allocthonous

inputs originate from outside system

Autochthonous

inputs originate from inside system

Three sources of food

1) Algae/plants growing in stream

2) Dissolved organic matter from watershed

3) Particulate organic matter from watershed

Scrapers

eat algae and bacteria off of rocks and plants

Shredders

Shred and ingest large organic material

• digest associated algae, bacteria, fungi

• facilitate decomposition by making particles smaller

Collectors

Collect particles floating in water or in sediment

• deposit feeders: feed on sediment

• filter feeders: collect particles

River continuum concept

Primary source of carbon to food webs shift with distances from source waters

• results in shifting ratios of production and respiration (P:R)

• some sections are more dependent on local production, some on remote production

Upper river

• light is low and vegetation nearby

• primary source of carbon: terrestrial plant material

• P:R <1 (heterotrophic)

• Shredders dominate

Middle river

• Light is high as river widens

• Carbon produced by photosynthesis within river

• P:R>1 (autotrophic)

• Scrapers dominate

Lower river

• River deep and filled with sediments

• Source of carbon from upstream

• P:R<1 (heterotrophic)

• Filter feeders collectors dominate

Nutrient movement

• Nutrients move downstream fastest when dissolved/suspended in flowing water

• Organisms take up dissolved substances into sediments, preventing downstream loss

  • Algae/plants

  • Bacteria

• Fast flow loosens sediments and organisms, taking them downstream, and vice versa.

Channel shape influences

Spiraling and nutrient loss

Long Spirals:

• Smaller surface area to volume

Shorter Spirals:

• Larger surface area to volume