BZ471, Steam Biology & Ecology Exam

Transcription

1 BZ471, Eam1, p.1 BZ471, Steam Biology & Ecology Eam Name Multiple choice When benthic organisms enter the water column with a regular diel periodicity: a) catastrophic drift b) behavioral drift c) constant drift d) surface drift e) passive drift Stage between molts for all immature aquatic insects: a) egg b) juvenile c) nymph d) instar e) larva Upward force acting on benthic invertebrate in flowing water: a) drag b) lift c) skin friction d) shear stress e) turbulence Natural (not human-modified) factors that can influence the shape of the hydrograph for a small stream include a) topography of the watershed b) vegetation cover type in the watershed c) soil type in the watershed d) a and b e) a, b and c The lotic insect orders most characteristic of streams on a global basis a) Ephmeroptera, Coleoptera, Odonata b) Plecoptera, Ephemeroptera, Diptera c) Plecoptera, Trichoptera, Diptera d) Ephemeroptera, Trichoptera, Odonata e) Plecoptera, Ephemeroptera, Trichoptera

2 BZ471, Eam1, p.2 True/False. Please write the word True or False for each question in the space provided. False A meandering stream has a sinuosity < 1.5. False According to the Wentworth scale, boulder is larger than gravel but smaller than cobble. True An increase in shear stress increases stream competence. False The number of generations per year for all species of aquatic insects is fied across its entire geographic range. False The magnitude-frequency principle applied to sediment movement in streams argues that it is the most etreme events, occurring with low frequency, that transports the most sediment load over an annual cycle and thus is most important in maintaining the characteristic channel form of the stream. True In low-gradient streams characterized by fine sediments such as silts and sand, the greatest biomass of aquatic insects is often found on submerged woody debris. True Sand has a lower critical erosion velocity than clay, but once suspended clay is slower to settle back to the streambed. Definitions. Provide the word whose definition is given. Catchment Another term for "watershed." Dominant Discharge or Bankfull Discharge Term for the flood that occurs about once every 1.5 to 2 years in a stream (although the range can be once every 1 10 years) and is associated with maintaining the channel dimensions. bivoltie Name for the kind of aquatic insect that completes two generations in one year. meandering Name for a channel morphology when sinuosity is greater than 1.5. complete Type of development for an aquatic insect that includes egg, larva, pupa and adult. density Term referring to the number of individual organisms per square meter on a streambed.

3 BZ471, Eam1, p.3 invertivore Feeding guild of stream-dwelling fish that primarily eats invertebrates. Short Answer. Provide short answers to the following. (One to a few key words or concepts will usually suffice. Complete sentences not needed.) Give 2 reasons for why the invasion of freshwater habitats by terrestrial insects is thought to have occurred in headwater streams. (1) cool, oygen-rich habitats (2) permanent features of landscape through geologic time Give two reasons why organism abundance and species richness (diversity) is generally lower in sand than in gravel. (1) sand has limited interstitial space for habitat (2) sand is very mobile during high flows and therefore unstable habitat Poff et al. (1997, BioScience) indicate that a streamflow regime (i.e., temporal variation in discharge) for any particular river can be described by 5 components List 2 of the 5 components here. (Only first 2 listed will count.) (1) list two from: magnitude, duration, frequency, timing rate-of-change (2) Give 3 possible morphological adaptations of benthic macroinvertebrates to current velocity. (NOTE: Only your first 3 answers will be counted, so don't list more than 3.) 1) see table in lecture notes 2) 3) If an adjacent pool and riffle in a stream have the same width (W r = W p ), but the average velocity in the riffle is twice that in the pool, then what is the average depth of the riffle (D r ) compared to the pool (D p )? Discharge, Q is defined as W D * U (Wr * Dr * Ur = Wp * Dp * Up à eliminate width since same in both channels; therefore Dr * Ur = Dp * Up and if Ur = 2Up then Dr *2Up = Dp *Up, or Dr = ½ Dp

4 BZ471, Eam1, p.4 During very high flows, large particles such as boulders move along the streambed. Interestingly, these large substrate particles do not end up in pools; rather they get deposited in riffles. Eplain how this occurs using your understanding of the relationship between shear stress (τ), water depth (D) and stream slope (S). τ is proportional to D * S At high (flood) flows pools are deeper and have same S and shallower riffles, so pool shear stress is greater and large particles that enter pools are transported out of pools. As water levels recede, the depth of pools remains greater, but the slope of the water surface over pools declines, making shear stress greater in steeper riffles, even though riffles have a shallower slope. For the following stream network, Strahler stream order at point A = 3. Shreve link number at point A = 6. Graphs and Interpretation. Below are graphs showing 3 velocity profiles measured at 2 mm intervals for 3 stones in a stream. For a benthic invertebrate that protrudes 2 mm off the stone surface, which of the stones presents the greatest shear stress? Eplain why.

5 BZ471, Eam1, p.5 local shear stress is greatest where velocity gradient ((du/dy) is greatest. dy is the same for all 3 but du is greatest for B (about 50 cm/sec). Draw and label a figure that shows how water velocity (-ais) changes with depth (yais) from the bottom of a stream to the surface. Eplain the shape of the relationship and indicate the one point on the line where the average velocity occurs. [4 points] See Fig. 2.8 on page 9 of Lecture 2 notes posted on the class website. On the following graph draw the epected pattern of size-specific Baetis mayfly drift in two small, high mountain streams in Colorado, one which has no fish (indicate by the symbol o ) and one that has abundant fish (use symbol ). Ratio of # drifting by night vs. day 10.0 (N:D) Ho Actual Insect size (head width, mm)

6 BZ471, Eam1, p.6 The blue line is the fishless stream, where Baetis shows no diel pattern in numbers drifting or in the size drifting. Because there are fish in the red line stream, larger Baetis drift preferentially at night.