Трофика экосистем водотоков

Водотоки: роль фитофагов.

Фитофаги в кисловодных водотоках.

Herbivory in an acid stream

Mark E. Ledger and Alan G. Hildrew

Summary

1. Spatial and temporal variation in the distribution and feeding of non-

in the Ashdown Forest, southern England.

2. Stonefly (Nemouridae) and chironomid (Orthocladiinae) larvae were

abundant on the upper surfaces of mineral substrata of three sizes (small

stones, large stones, bedrock). The density of larvae in each taxonomic

group did not vary among substrata of different sizes, although strong

seasonal variation existed.

3. Nemourids and chironomids (H. marcidus) collected from the upper

surfaces of substrata exhibited generalist feeding habits, consuming algae

(diatoms, coccoid and filamentous green algae), detritus (biofilm matrix

material and fine particulate organic matter (FPOM)) and inorganic debris.

4. There was spatial variation in the gut contents of nemourids. The

proportion of algae in the guts of larvae often increased with the size of the

substratum from which they were collected. Strong temporal variation in the

composition of the diet also existed. Nemourids ingested a large quantity of

attached algae and biofilm matrix from the biofilm in spring and winter, but

consumed loose FPOM and associated microflora in summer and autumn.

5. We conclude that, in this acid stream, the trophic linkage between algae and

grazers is maintained by detritivorous stonefly and chironomid species. The

relationship between the feeding habits of these larvae and other life-history

attributes, such as mouthpart morphology and mobility, is discussed.

Водотоки: роль микроорганизмов

Volume 40 Issue 3 Page 453-495 - November 1998

The role of micro-organisms in the ecological connectivity of running waters

M. Pusch D. Fiebig I. Brettar H. Eisenmann B. K. Ellis L. A. Kaplan M. A. Lock M. W. Naegeli W. Traunspurger

Summary

1. Riparian zones hold a central place in the hydrological cycle, owing to the

quality of exfiltrating water is heavily influenced by microbial activities within the

bed sediments. This paper reviews the role of micro-organisms in biogeochemical

cycling in the riparian-hyporheic ecotone.

2. The production of organic substances, such as cellulose and lignin, by riparian

vegetation is an important factor influencing the pathways of microbial processing

in the riparian zone. For example, anaerobic sediment patches, created by

entrainment of allochthonous organic matter, are focal sites of microbial

denitrification.

3. The biophysical structure of the riparian zone largely influences in-stream

microbial transformations through the retention of organic matter. Particulate and

dissolved organic matter (POM and DOM) is retained effectively in the hyporheic

zone, which drives biofilm development and associated microbial activity.

4. The structure of the riparian zone, the mechanisms of POM retention, the

hydrological linkages to the stream and the intensity of key biogeochemical

processes vary greatly along the river continuum and in relation to the geomorphic

setting. However, the present state of knowledge of organic matter metabolism in

the hyporheic zone suggests that lateral ecological connectivity is a basic attribute

of lotic ecosystems.

5. Due to their efficiency in transforming POM into heterotrophic microbial

biomass, attached biofilms form an abundant food resource for an array of

predators and grazers in the interstitial environments of rivers and streams. The

interstitial microbial loop, and the intensity of microbial production within the bed

sediments, may be a primary driver of the celebrated high productivity and

biodiversity of the riparian zone.

6. New molecular methods based on the analysis of the low molecular weight RNA

(LMW RNA) allow unprecedented insights into the community structure of natural

bacterial assemblages and also allow identification and study of specific strains

hitherto largely unknown.

7. Research is needed on the development and evaluation of sampling methods for

interstitial micro-organisms, on the characterization of biofilm structure, on the

analysis of the biodegradable matter in the riparian-hyporheic ecotone, on the

regulation mechanisms exerted on microbiota by interstitial predators and grazers,

and on measures of microbial respiration and other key activities that influence

biogeochemical cycles in running waters.

8. Past experiences from large-scale alterations of riparian zones by humans, such

as the River Rhine in central Europe, undeniably demonstrate the detrimental

consequences of disconnecting rivers from their riparian zones. A river management

approach that uses the natural services of micro-organisms within intact riparian

zones could substantially reduce the costs of clean, sustainable water supplies for

humans.

Водотоки: утилизация внешней органики.

Volume 41 Issue 4 Page 687 - June 1999

What happens to allochthonous material that falls into streams?

A synthesis of new and published information from Coweeta

J. R. Webster, E. F. Benfield, T. P. Ehrman*, M. A. Schaeffer, J. L. Tank, J. J. Hutchens and D. J. DAngelo

1. ,One of two things can happen to allochthonous material once it enters a stream:

it can be broken down or it can be transported downstream. The efficiency with

which allochthonous material is used is the result of these two opposing factors:

breakdown and transport.

2. ,The present synthesis of new and published studies at Coweeta Hydrologic

Laboratory compares biological use versus transport for four categories of

particulate organic material: (1) large wood (logs); (2) small wood (sticks); (3)

leaves; and (4) fine particulate organic matter (FPOM).

3. ,Over 8_years, logs showed no breakdown or movement.

4. ,The breakdown rate of sticks (3_cm diameter) ranged from 0.00017 to

0.00103_day1, while their rate of transport, although varying considerably with

discharge, ranged from 0 to 0.1_m_day1.

5. ,Based on 40 published measurements, the average rate of leaf breakdown was

0.0098_day1. The leaf transport rate depended on stream size and discharge.

6. ,The average respiration rate of FPOM was 1.4_mg_O2_g_AFDM1_day1 over a

temperature range of 6-22_°C, which implies a decomposition rate of 0.00104_day

1. Transport distances of both corn pollen and glass beads, surrogates of natural

FPOM, were short (<_10_m) except during high discharge.

7. , Estimates of transport rate were substantially larger than the breakdown rates

for sticks, leaves and FPOM. Thus, an organic particle on the stream bottom is

more likely to be transported than broken down by biological processes, although

estimates of turnover length suggest that sticks and leaves do not travel far.

However, once these larger particles are converted to refractory FPOM, either by

physical or biological processes, they may be transported long distances before

being metabolized.

Водотоки: трофические взаимосвязи.

Freshwater Biology

Volume 41 Issue 4 Page 771 - June 1999

Effects of prey dispersal on predator-prey interactions in streams

J. Dahl* and L. Greenberg

1. We studied the effect of mesh size (6 and 3mm) on interactions between brown

trout (Salmo trutta) and benthic invertebrates in enclosures placed in a stream in

southern Sweden. We also compared how different prey exchange rates affected

interactions between trout and invertebrates.

2. Trout had strong impacts on some benthic taxa, and different mesh sizes

produced different patterns. Trout affected the abundance of 10 of the 21 taxa

examined, six in enclosures with 3mm mesh and six in enclosures with 6mm mesh.

The abundance of nine of the prey taxa was lower in the presence of trout, only

leptocerids were more numerous in the presence of trout.

3. Our measurements of prey immigration/emigration, together with trout diet data,

suggest that direct consumption by trout, rather than avoidance behaviour by prey,

explains most decreases in prey abundance. There was avoidance behaviour by

only two of the twenty-one prey taxa, with trout inducing emigration of the mayflies

Baetis rhodani and Paraleptophlebia sp.

4. Trout indirectly increased periphyton biomass in both 3 and 6mm enclosures.

The effect of trout on periphyton was probably due to strong effects of trout on the

grazer, Baetis rhodani, Heptagenia sp. and Paralepthoplebia sp.

5. Our results suggest that mesh size, through its effects on exchange rates of prey,

may affect interactions between predators and prey in running waters, but that the

effects of dispersal and predation on invertebrates are taxon specific.

Водотоки: трофические взаимосвязи.

Freshwater Biology

Volume 41 Issue 3 Page 553 - May 1999

Associations between stream fish and benthos across environmental gradients

in southern Ontario, Canada

Bruce W. Kilgour* and David R. Barton

Summary

1.The relationship between fish and benthic invertebrate communities in wadeable

streams in southern Ontario, Canada, was examined using three independent and

spatially distinct data sets.

2.Associations between fish and benthos were always significant when benthos

were identified to family and often at the level of phylum. Identification to genus

improved the strength of the fish-benthos association in one case. In contrast,

identification to species did not improve the strength of the fish-benthos

association. Associations between benthos and fish were weaker for one study

utilizing a rapid bio-assessment protocol involving field sorting and identification,

and a second study which utilized winter benthic collections.

3.In two surveys, stream temperatures were important to the distributions of both

fish and benthos, while in a third survey, fish and benthos were primarily influenced

by stream size. In all three studies, fish and benthos were associated with similar

suites of environmental variables, suggesting that the fish-benthos associations in

these streams was driven by corresponding environmental tolerances.

4.Although there was significant variation in the strength of the fish-benthos

association which could be attributed to differences in sampling methodologies, the

findings from the present study confirm that stream fish and benthos are

significantly associated. Therefore, surveys of benthos can be used to make

inferences on the condition of fish community composition.

Водотоки: источники органики.

Freshwater Biology

Volume 40 Issue 1 Page 145-158 - August 1998

Primary nutrients and the biotic integrity of rivers and streams

Robert J. Miltner & And Edward T. Rankin

1. Controls to reduce loadings of primary nutrients to maintain biotic integrity in

rivers and streams have not been widely implemented because the relation between

nutrients and chlorophyll, and its consequences for higher trophic levels, is

confounded in lotic ecosystems by their openness, the variable degree of nutrient

limitation and by the effect of physical factors.

2. The relationship between primary nutrients and biotic integrity in rivers and

streams was tested using biological, physical and chemical information collected

since 1982 from similar locations in streams throughout Ohio using standard

procedures.

3. There was a negative correlation between nutrients, especially total phosphorus,

and biotic integrity. The deleterious effect of increasing nutrient concentration on

fish communities in low order streams was detectable when nutrient concentrations

exceeded background conditions (total inorganic nitrogen and phosphorus > 0.61

mg L1 and 0.06 mg L1, respectively).

4. These results suggest that the control of release of toxins and oxygendemanding

wastes to rivers is insufficient to protect aquatic life, and confirm the importance of

nonpoint sources of pollution in catchment planning as well as the combined effect

of habitat and riparian quality on nutrient assimilation.

Водотоки: влияние бентоса на фитопланктон.

Freshwater Biology

Volume 39 Issue 1 Page 9-24 February 1998

Can a community of small-bodied grazers control phytoplankton in rivers?

V. Gosselain, L. Viroux AND J. -P. Descy*

1. Phytoplankton, zooplankton and grazing were monitored throughout the growing

season for three years (1994-96) in the Belgian section of the River Meuse.

2. A size structure analysis of the algal community shows that there was a summer

shift toward larger algal units, following a decline in phytoplankton biomass. These

changes occurred after an increase in zooplankton biomass and diversity.

3. Daily filtration rates of grazers ranged from 1 to 113%day1 and maxima were

observed during the summer period. Higher rates tended to correspond with peaks

of rotifer biomass. A decline in total phytoplankton biomass within two weeks

followed the increase in zooplankton biomass and filtration rate. A rapid biomass

recovery was then observed, along with a shift of the algal community toward larger

units. When grazing activity was not sustained, due to zooplankton fluctuations, the

change in phytoplankton size structure was less marked.

4. We suggest that the composition of the phytoplankton community of large rivers

may at times be controlled by grazers. However, such biotic interactions can take

place only when physical constraints are reduced, i.e. when discharge is low, and

when increased transfer time, high temperature and availability of grazeable algae

allow high zooplankton biomass.

жүктеу/скачать 1.21 Mb.

Достарыңызбен бөлісу: