Surface Water Exam 2

What are three of the most common water quality problems in streams/rivers?

Pathogens, Nutrients, Siltation

Possible water quality issues in rivers include:

1. Endocrine disruptors, microplastics, and volatile organic chemicals;

2. Organic wastes, pathogens, and toxic substances;

3. Silt (sediment), nutrients, pathogens;

4. Nutrients, pesticides, organic wastes;

List three common impairments to rivers other than contaminants, nutrients and silt:

1. Habitat destruction (agriculture to river edge, urban, residential construction and runoff, levees that restrict flood plain replenishment)

2. Flow & hydrology alterations (dams, levees, water withdrawals)

3. Temperature change associated with climate change

What percentage of U.S. rivers have been assessed?

< 50%

What sector of the economy is responsible for the most degraded river miles?

Agriculture

From what source does most of the phosphorus pollution in rivers come?

Municipal Wastewater discharges

From what source does most of the anthropogenic nitrogen in rivers come?

Agriculture

 In addition to the amount of respirable (decomposable) organic matter (i.e., CBOD), what other characteristic of effluent can significantly contribute to oxygen depletion downstream of a discharge?

Nitrogenous biological oxygen demand (NBOD)

A river reach is:

A stretch with constant velocity and dimensions

The Peclet number is a ratio of

Rate of Advection to Rate of Dispersion

The Estuary number is used to compare rates of

Dispersion and advection

The Peclet number is calculated as u•L/K_x.  A value of Pe > 10 would indicate:

Use of a PFR model is justified

Which is the correct ranking for the magnitudes of dispersion coefficients in rivers?

Kx>Ky>Kz

Hypoxia refers to:

Low dissolved oxygen content

What are typical flow velocities in rivers?

0.3-1m/s

The riparian zone refers to:

the area of land and vegetation bordering the body of surface water

  How do food webs differ in lakes and streams?

In lakes, the base of the food web is phytoplankton, while in rivers it is organic matter from the catchment.

List three zones of a river ecosystem.

1. Hyporheic zone

2. Riparian Zone

3. Flood plain, main channel

List three structural characteristics of a river.

1. Flow depth, water source, water chemistry

2. Substrate, riffles and pools, large woody debris

3. Components of food web, sun vs. shade, turbidity

Which of the following selections lists two functions of rivers/streams in the global landscape?

1. Draining water, carrying dissolved minerals from continents to oceans

2. Supporting biodiversity, supporting global elemental cycles

Structural elements of natural river/stream ecosystems include:

Flow velocity, depth, steepness or river corridor, amount of shade vs. direct sunlight

Functions within stream/river ecosystems include:

Primary and secondary reproduction, decomposition, gas exchange, sediment accumulation and erosion, greenhouse gas emissions, spiraling

The hyporheic zone is:

The sediment zone below a river where dissolved substances are exchanged with the flowing water

Which of the following is true?

The distance downstream where a contaminant discharge plume is well mixed horizontally across a stream will be longer than the distance at which it is well mixed top-to-bottom. 

Distances downstream from a discharge where the plume is well-mixed across the width of a river are typically:

1-100km

To model an instantaneous spill in a river, which of the following equations could be used?

1. C=C₀exp(-ku/x)

2. C_x,t=(Me^(-k(x/u))/Asqr(4piKxt)exp[(-x(x+ut)²/4kxt]

Whether the medium-duration spill model is appropriate depends on what factor besides the duration of the spill?

The time to flow to the point being modeled (point of interest)

 List three processes that can contribute to dissolved oxygen depletion in rivers.

1. CBOD

2. NBOD

3. SOD

What are three characteristics of a river that influence its reaeration rate.

Width, Depth, Flow velocity

Which of the factors below would act to increase the oxygen deficit in a river?

Ice, Low flow, High temperature

Which of the following factors can affect the distance of the critical deficit from the discharge location?

Flow velocity, the biodegradability of the waste, the amount of nitrogenous BOD

The assimilation capacity of a lake is 

1. In units of volume per time

2. A measure of the amount of a pollutant that a lake can withstand

3. The ratio of loading to concentration