Energy Flow Ws

8/10/2019 Energy Flow Ws

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1. A river is an ecosystem which is influenced by the biotic and abiotic factors that are present

within the river itself. The water in a river drains into it from its catchment area.

Factors within the catchment area also have an effect on the rivers ecosystem.

In a river, there are two sources of plant material that contribute towards the net primary

production. The first source is the living plants which grow within the river itself. Most of theseare algae forming a surface covering on rocks near the surface or suspended in the upper layers

of water. The second source is dead plant material, such as leaves, that is brought in from the

surrounding land. This forms most of the layer of decomposing organic material detritus! found

on the bed of the river.

The relative "uantities of these two types of plant material can determine the types of consumers

in the dependent food chains. The gra#ing invertebrates that feed on algae tend to form the main

food source for trout and other carnivorous river fish. Invertebrates that feed in the detritus

layers are not easily seen and do not form a ma$or part of the diet of most of these fish.

In %ew &ealand, the 'angapeka (iver and the Motupiko (iver meet to form the Motueka (iver

which flows into the sea. A study of the Motueka (iver was carried out to estimate the influence

of dead plant material from the catchment area on the ecosystem. %ine sampling sites between

the sources of the rivers and the sea were selected. The three rivers and the sampling sites in the

catchment area of the study are shown in Figure ).

At each of the sampling sites, gross primary production *++! of algae was estimated by

measuring the production of oygen in the water over a - hour period. As oygen is released, a

proportion of it will be used during respiration of all organisms in the river community. This

uptake of oygen, which was also estimated, is known as community respiration /(!. The

estimates were made during winter and summer. These results are shown in Figure - and

Figure 0.

[Data adapted from Cawthron Research News September 2002]

Al-NAjah Private School 1


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Figure 1 The Wangapeka, Motupiko and Motueka river system.

1 i r e c t i o n o f

w a t e r f o w

' A % * A + 2 3 A

( I 4 2 (

% o r t h

M 5 T 6 2 3 A

( I 4 2 (

M 5 T 6 + I 3 5

( I 4 2 (

7 8 a m p l i n g s i t e

8 2 A



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Figure 2 Gross primary production in the Motueka River catchment area.

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(a) (i) Explain what is meant b the term gross primary production!

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(ii) State two abiotic factors that can affect "ross primar prod#ction in thisri$er sstem!

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(2)

(b) (i) &ith reference to 'i"#re compare the trend in comm#nit respiration inwinter with that in s#mmer for the *ot#e+a Ri$er catchment area!

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(ii) S#""est wh comm#nit respiration shows this trend!



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(c) (i) ,he n#mbers of carni$oro#s fish s#ch as tro#t are hi"her in the *ot#e+aRi$er than in the other two ri$ers! &ith reference to 'i"#re 2 s#""estreasons for this!

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(ii) &ith reference to 'i"#re s#""est how the pop#lation of thesecarni$oro#s fish mi"ht chan"e in the winter!

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(3)(Total 14 marks)



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2. (a) Explain what is meant b the term gross primary production(-..)!

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(2)

(b) ,he table below shows the flow of ener" in a tropical rainforest!

,rophic le$el Ener" enterin" trophic le$el/+ m?-

ear?)

.rod#cers %10!0 @ ):

.rimar cons#mers !0 @ ):

Secondar cons#mers 3! @ ):

,ertiar cons#mers !3 @ ):

Decomposers 21!3 @ ):

(i) Ener" is transferred between trophic le$els! 4f the prod#cers lose %3 @

):+ m

?-ear

?)in respiration calc#late the percenta"e of net primar

prod#ction (N..) which is passed to the primar cons#mers! Show o#rwor+in"!



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5nswer !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! 6(3)



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(ii) Explain the role of decomposers in a food chain!

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(iii) ,he prod#cti$it of a temperate forest in E#rope is m#ch lower than that ofa tropical rainforest! S#""est reasons for this difference!

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(2)(Total 9 marks)



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3. S#nflower seedlin"s were planted and +ept #nder controlled conditions for 20 das!,he "ross primar prod#cti$it (-..) and the net primar prod#cti$it (N..) weremeas#red each da! ,he res#lts are shown in the "raph below!

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+ r i m a r yp r o d u c t i v i t y >

a r b i t r a r y u n i t s

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