6. ANÁLISIS DE RESULTADOS
6.2 Análisis pretest – postest
In conclusion, the results show that discharge, stream size and position within the stream system affect the variation in riffle morphology. These results support the idea of a hierarchically nested physical stream ecosystem. Further, the study showed that disturbance affected the riffle habitats most severely, but depth, current velocity and substratum varied between riffles and pools in both disturbed and undisturbed streams.
This study highlights the importance of generating new knowledge on small-scale spatial and temporal differences in discrete morphological units such as riffles and pools, and how anthropogenic and natural disturbances affect these small-scale physical conditions. More knowledge is also needed on how riffles and pools vary in terms of physical structure and stability in lowland streams in time and space. We need to link process and form across multiple scales to understand the complex nature of the in-stream habitats and explain the distribution of the in- stream biota.
Acknowledgements
This study was partly financed by the Danish Research Academy (grant no. 641-00-49.65) and the National Environmental Research Institute. I thank Johnny Nielsen & Louise Korsgaard for field assistance and Dr. Nikolai Friberg and Professor Kaj Sand-Jensen for valuable comments on the manuscript.
References
Baattrup-Pedersen A & Riis T (1999): Macrophyte diversity and composition in relation to substratum characteristics in regulated and
unregulated Danish streams. Freshwater Biology,
42, 375-385.
Booker DJ, Sear DA & Payne AJ (2001): Modelling three-dimensional flow structures and patterns of boundary shear stress in a natural pool-riffle sequence. Earth Surface Processes and Landforms,
26, 553-576.
Brookes A (1987): The distribution and management of channelized streams in Denmark. Regulated
Rivers: Research and Management, 1, 3-16.
Brookes A (1988): Channelized Rivers - Perspectives for
Environmental Management. John Wiley and Sons,
Chichester.
Church M (1996): Channel morphology and typology. In: River flows and channel forms (Eds. GE Petts & P Calow), pp. 185-202. Blackwell Scientific Publications, Oxford.
Conover WJ (1980): Practical Nonparametric statistics.
2nd edition. John Wiley and Sons, New York.
Frissell CA, Liss WJ, Warren CE & Hurley MD (1986): A hierarchical framework for stream habitat classification - viewing streams in a watershed context. Environmental Management,
10, 199-214.
Hildrew AG & Townsend CR (1977): Influence of substrate on functional response of Plectrocnemia
conspersa (Curtis) larvae (Trichoptera,
Polycentropodidae). Oecologia, 31, 21-26.
Hooke JM & Harvey AM (1983): Meander changes in relation to bend morphology and secondary flows. In: Fluvial systems (eds. JD Collinson & J Lewin), pp. 121-132. Special Publication No. 6, International Association of Sedimentologists. Blackwell Scientific Publications, Oxford.
Iversen TM, Kronvang B, Madsen BL, Markmann P & Nielsen MB (1993): Reestablishment of Danish streams - restoration and maintenance measures.
Aquatic Conservation: Marine and Freshwater Ecosystems, 3, 73-92.
Kaenel BR & Uehlinger U (1998): Effects of plant cutting dredging on habitat conditions in streams. Archiv für Hydrobiologie, 143, 257-273. Kemp JL, Harper DM & Crosa GA (2000): The
habitat-scale ecohydraulics of rivers. Ecological
Engineering, 16, 17-29.
Lane SN & Richards KS (1997): Linking river channel form and process: time space and causality revisited. Earth Surface Processes and
Landforms, 22, 249-260.
Leopold LB, Wolman MG & Miller JP (1964): Fluvial
processes in geomorphology. WH Freeman & Co.,
San Francisco
Minshall, GW (1988): Stream ecosystem theory: a global perspective. Journal of the North American
Benthological Society, 7, 263-288.
Pedersen ML & Friberg N (2002a): Physical habitats and diversity of biological communities in low-
land streams with contrasting disturbance (submitted to Freshwater Biology).
Pedersen ML & Friberg N (2002b): Spatio-temporal variations in stability, substratum and macroinvertebrates in lowland stream-riffles (Submitted to Journal of the North American
Benthological Society).
Pool GC (2002): Fluvial landscape ecology addressing uniqueness within the river discontinuum. Freshwater Biology, 47, 641-660. Richards KS (1982): Rivers: Form and process in
alluvial channels. Methuen, London.
Sand-Jensen K (1998): Influence of submerged macrophytes on sediment composition and near- bed flow in lowland streams. Freshwater Biology,
39, 663-679.
Sand-Jensen K, Jeppesen E, Van Der Bijl L, Nielsen K, Wiggers-Nielsen L & Iversen, TM (1989): Growth of macrophytes and ecosystem consequences in a lowland Danish stream.
Freshwater Biology, 22, 15-32.
SAS Institute (2000): The SAS System Version 8.2. SAS Institute. Cary, USA.
Scarsbrook MR & Townsend CR (1993): Stream community structure in relation to spatial and temporal variation - a habitat templet study of 2 contrasting New Zealand streams. Freshwater
Biology, 29, 395-410.
Schumm SA (1977): The fluvial system. John Wiley and Sons, New York.
Sear DA (1995): Morphological and sedimentolo- gical changes in a gravel-bed river following 12 years of flow regulation for hydropower.
Regulated Rivers: Research and Management, 10,
247-264.
Smith C, Youdan T & Redmond C (1995): Practical aspects of restoration of channel diversity in physically degraded streams. In: The ecological
basis for river management (eds. DM Harper &
AJD Ferguson), pp. 269-273. John Wiley and Sons, Chichester.
Snedecor GW & Cochran WG (1989): Statistical
Methods. Iowa State College Press. Ames, Iowa.
ter Braak CJF (1995): Ordination. In: Data analysis in
community and landscape ecology (Eds. RHG
Jongman, CJF ter Braak & OFR van Tongeren), pp. 91-173. Cambridge University Press, Cambridge.
Thompson A (1986): Secondary flows and the pool- riffle unit: a case study of the processes of meander development. Earth Surface Processes
and Landforms, 11, 631-641.
Thorne CR (1997): Channel types and morphological classification. In: Applied fluvial
geomorphology for river engineering and management (Eds. CR Thorne, RD Hey & MD
Newson), pp. 175-222. John Wiley and Sons, Chichester.