Hydrology

River Ecosystems and Humans

Dimensions of river ecosystems

• Longitudinal

• Lateral

• Vertical

• Temporal

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Longitudinal Changes in Streams

• Certain characteristics of streams change predictably from upstream to downsteam– Channels become

wider– Flow becomes

slower, but greater in volume

– Streams become deeper

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Longitudinal Changes – Reach Scale

• Longitudinal changes are also observed at shorter scales than the entire river length

• We call this shorter scale the “reach” scale

• One example of reach scale changes is the pool-riffle pattern found in many streams draining areas with medium gradient

• Riffle is an area of rapid flow over coarse substrate (rocks) whereas the pool is a slower flowing stretch with finer substrate

• Path of flow - thalweg

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Lateral Patterns• There are also some

predictable changes laterally

• The stream has a low flow channel; the fastest flow is called the thalweg

• The stream has banks which define its frequent flow limit

• The stream has a floodplain which defines its flow limit on less frequent events, annual or lesser frequency

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Lateral Patterns

• Some streams and rivers will have a single dominant channel while others will have a network of interwoven channels

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Lateral Features

• As rivers increase in size they may develop a complex floodplain system

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Vertical dimensions

• Velocity changes with depth in stream channel• Discharge (Q) = VA

Diagram by:Eric G. PatersonDepartment of Mechanical and Nuclear EngineeringThe Pennsylvania State University

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Vertical Features

• Hyporheic (below stream) inter-actions

• Exchanges occur with groundwater just below the stream

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Lateral and Vertical Patterns

• In many large alluvial valleys, creatures that live in ground water and hyporheic water can be found in the subsurface water kilometers from the stream. In other words the stream extends well beyond its channel.

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Temporal dimension

• Stream flow changesSecond by secondHourlyDailyMonthlySeasonallyAnnuallyMilleniumly

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Selected Important Habitat Factors

• Substrate• Temperature• Oxygen levels• Flow velocity• Food availability• pH• Nutrient and sediment regimes• Organic input and transport

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How are species distributed in space and time?

-- Environments contributing to riverine biodiversity

Surface water Subsurface water Riparian system

Streams

Springs

LakesHyporheic

ZoneGroundWater

ConfinedReaches

UnconfinedReaches

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River --------------------------------------------- Floodplain Edge

Spatial distribution of species across a floodplain (lateral dimension)

Species Richness

0

50

100

Per

cen

t o

f m

axim

um

ric

hn

ess

fish

Mollusca

Odonata

Amphibia

Macrophytes

(Ward and Tockner 2001 fig. 9.3)

Species Richness

0

100

Eg.FishSnails, slugs, mussels,Dragonflies, damselfliesFrogs, salamanders, toadsAquatic plants

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How do humans affect watersheds and the hydrologic

cycle?

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Human caused disturbances

• Agriculture

• Timber harvest

• Mining

• Urbanization

• Introduction of exotic species

• Harvesting of fish and wildlife

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Land use/cover and vegetation

Physiography Climate

Landscape controls

NutrientInputs

Solar energy and

Organic input Regime

Gross reachmorphology

Habitat FormingProcesses

Species assemblages

Stream Morphology andConditions

Biodiversity

Habitat complexes and conditionse.g., pools, riffles, temperature, etc.

Sedimentand HydrologicRegime

Modified from Roni et al. 2002.

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Physical, chemical, and biological components related to water quality

• Light• Temperature• Dissolved ions• Suspended solids• Nutrients and gases• Toxics such as metals and pesticides/herbicides• Biological features• PPCPs (Pharmaceuticals & Personal Care Products)

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Photos by R.S. Lindsay

Photo by Carrie Inman

Agriculture

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FORESTRY

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Aggregate Mining

In-channel mining

In-channel and floodplain miningPhotos by M. Kondolf

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URBANIZATION

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Forestry, agriculture and urbanization

• Remove trees and other vegetation

• Reduce organic matter delivery

• Build roads

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Large storage in soil, channel and valley floor Recharge

Natural cleaning

Pollutant wash off

No recharge

Rapid flow limited storage

Slow flow

Natural Developed

Reduced soil storageLimited infiltration

Precipitation

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Floods and Urbanization

surface runoff vs. infiltrationnatural land cover vs. urban area

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How do we manage watershed?

• Dept of Natural Resources Regulations

• U.S. Forest Service Regulations

• Clean water act

• Endangered Species Act

• Total Maximum Daily Loads (TMDLs)

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Take Home Messages

• Understand the interactions between land use/land cover and components of the hydrologic cycle

• Be able to describe what is typically measured in watersheds and why

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Hydrology Report

~ 2-3 pages due May 25 individually

Include: Name, Date, Title IntroductionMethodsResults and Discussion (w tables) ConclusionsAppendix (if needed for raw calculations)

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