1. Periphyton chlorophyll a was measured at weekly or 2 weekly intervals from October 1992 to March 1994 at four sites in a Swiss prealpine gravel bed river that was frequently disturbed by unpredictable spates. 2. To evaluate the dominant processes that control periphyton biomass, measured data were compared with a set of simulations from an empirical dynamic periphyton model. Different combinations of process hypotheses were systematically activated and deactivated in order to assess their importance. 3. The simplest model leading to an acceptable agreement with measured data employs a biomass‐dependent growth rate, a detachment rate directly proportional to discharge and biomass, and a catastrophic loss rate during bed moving spates. Terms describing light or temperature dependence had a minor effect on the model fit. 4. The model describes the temporal pattern of the periphyton biomass as a series of growth curves periodically truncated by spates. Within the uncertainties of the measurements, mainly caused by the spatial heterogeneity of periphyton, the biomass recovered along deterministic trajectories. 5. Sensitivity analyses with respect to model parameters and model structure showed that site‐specific model parameters could not be unequivocally determined, and that the model yields similar results with slightly different formulations of processes. This indicates that the data base with respect to periphyton biomass was too small for a unique identification of model details but that the main conclusions on the significance of processes did not depend on arbitrary choices of the model formulation.

1. Temporal variation in ecosystem metabolism over a 15-year period (1986-2000) was evaluated in a seventh order channelised gravel bed river (mean annual discharge 48.7 m 3 s )1 ) of the Swiss Plateau. The river is subject to frequent disturbance by bedmoving spates. Daily integrals of gross primary production (GPP) and ecosystem respiration (ER) were calculated based on single-station diel oxygen curves. 2. Seasonal decomposition of the time series of monthly metabolism rates showed that approximately 50% of the variation of GPP and ER can be attributed to season. Annual GPP averaged 5.0 ± 0.6 g O 2 m )2 day )1 and showed no long-term trend. 3. Ecosystem respiration, averaging 6.2 ± 1.4 g O 2 m )2 day )1 , declined from 8.8 to 4.1 g O 2 m )2 day )1 during the 15-year period. This significant trend paralleled a decline in nitrate and soluble reactive phosphorus concentrations, and the biochemical oxygen demand discharged by sewage treatment facilities upstream of the study reach. The ratio of GPP to ER (P/R) increased from 0.53 to about 1 as consequence of ER reduction. 4. Bed moving spates reduced GPP by 49% and ER by 19%. Postspate recovery of GPP was rapid between spring and autumn and slow during winter. Recovery of ER lacked any seasonal pattern. Annual patterns of daily GPP and to a minor extent of daily ER can be described as a sequence of recovery periods frequently truncated by spates. 5. The study showed that disturbance by frequent bed-moving spates resulted in major stochastic variation in GPP and ER but annual patterns were still characterised by a distinct seasonal cycle. It also became evident that stream metabolism is a suitable method to assess effects of gradual changes in water quality.

1. Single-station diel oxygen curves were used to monitor the oxygen metabolism of an intermittent, forested third-order stream (Fuirosos) in the Mediterranean area, over a period of 22 months. Ecosystem respiration (ER) and gross primary production (GPP) were estimated and related to organic matter inputs and photosynthetically active radiation (PAR) in order to understand the effect of the riparian forest on stream metabolism. 2. Annual ER was 1690 g O 2 m )2 year )1 and annual GPP was 275 g O 2 m )2 year )1 . Fuirosos was therefore a heterotrophic stream, with P : R ratios averaging 0.16. 3. GPP rates were relatively low, ranging from 0.05 to 1.9 g O 2 m )2 day )1 . The maximum values of GPP occurred during a few weeks in spring, and ended when the riparian canopy was fully closed. The phenology of the riparian vegetation was an important determinant of light availability, and consequently, of GPP. 4. On a daily scale, light and temperature were the most important factors governing the shape of photosynthesis-irradiance (P-I) curves. Several patterns could be generalised in the P-I relationships. Hysteresis-type curves were characteristic of late autumn and winter. Light saturation responses (that occurred at irradiances higher than 90 lE m )2 s )1 ) were characteristic of early spring. Linear responses occurred during late spring, summer and early autumn when there was no evidence of light saturation. 5. Rates of ER were high when compared with analogous streams, ranging from 0.4 to 32 g O 2 m )2 day )1 . ER was highest in autumn 2001, when organic matter accumulations on the streambed were extremely high. By contrast, the higher discharge in autumn 2002 prevented these accumulations and caused lower ER. The Mediterranean climate, and in its effect the hydrological regime, were mainly responsible for the temporal variation in benthic organic matter, and consequently of ER.

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With 10 figures and 5 tables in the text Abstract: Val Roseg in the Swiss Alps is a complex alluvial valley formed in glacial outwash. The braided flood plain, 2.6 km long and 130-510 m wide, begins 1.2 km downstream of the glacier terminus and extends to a "knickpoint" at 1990 m a.s.!. where water upwells before entering a constrained reach. A long-term study has been initiated to investigate habitat heterogeneity and how such heterogeneity (I) contribu tes to the biodiversity of benthos, groundwater fauna, and periphyton in a harsh envi ronment and (2) influences ecosystem processes such as productivity and decomposi tion dynamics. As a first step we have distinguished different channel types based on the correspondence between hydrological connectivity and physico-chemical attrib utes. This functional characterization will serve as a habitat template to structure future ecological research in the Val Roseg flood plain. Six distinct channel types have been identified within the fl oodplain ecosystem: (i) Main channel. (ii) Side channels, (iii) Intermittently-connected channels. (iv) Mixed channels, (v) Ground water channels, and (vi) Tributaries. Distinct seasonal and daily runoff patterns, caused by ice melt, change the hydrological connectivity between individual channel types. Results clearly demonstrate that the whole flood plain shifts from dominance by surface water at high summer discharge to a groundwater-controlled system in winter. Temporal variability, rather than the means of environmental values, has been used to differentiate between individual floodplain channel types. Groundwater chan nels exhibit the highest spatial but the lowest temporal variability. In contrast, inter mittently-connected channels are characterized by a low spatial but an extraordinary temporal variability. High spatio-temporal heterogeneity resulting from a diversity of channel types is believed to play a major role in maintaining what appears to be re markably high biodiversity in this glacial flood plain.

Running water ecology is a young science, the conceptual foundations of which were derived largely from research conducted in Europe and North America. However, virtually all European river corridors were substantially regulated well before the science of river ecology developed. While regulation of North American river systems occurred later than in European systems, river ecology also developed later. Therefore, there is a general impression of rivers as being much less heterogeneous and much more stable than they actually are in the natural state. The thesis of this paper is that established research and management concepts may fail to fully recognize the crucial roles of habitat heterogeneity and fluvial dynamics owing to a lack of fundamental knowledge of the structural and functional features of morphologically intact river corridors. Until quite recently, most concepts in river ecology were based on the implicit assumption that rivers are stable, single-thread channels isolated from adjacent floodplains. Unfortunately, many rivers are in just such a state, but it should be recognized that this is not the natural condition. This incomplete understanding constrains scientific advances in river ecology and renders management and restoration initiatives less effective. Examples are given of the high level of spatio-temporal heterogeneity that may be attained in rivers where natural processes still operate on a large scale. The objective of this paper is to promulgate a broader and more integrative understanding of natural processes in river corridors as a necessary prelude to effective river conservation and management.

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