Stream hydraulics as a major determinant of benthic invertebrate zonation patterns

SUMMARY. 1. Studies on the zonation of benthic fauna in fourteen streams situated in a variety of latitudes from Alaska to New Zealand have been evaluated.
2. We suggest that physical characteristics of flow ('stream hydraulics') are the most important environmental factor governing the zonation of stream benthos on a world-wide scale.
3. From the source to the mouth of a stream, zones of transition in stream hydraulics' occur, to which the general pattern of stream invertebrate assemblages can be related. In these zones benthic community stability and resilience must be different from those upstream and downstream of the hydraulic transition zones.     

Focusing environmental management budgets on non-linear system responses: potential for significant improvements to freshwater ecosystems

1. The non-linear responses of environmental systems to changes imposed upon them is well known to scientists. Environmental managers rarely act accordingly, however, because of communication problems, a lack of imagination and various other constraints. Therefore, we illustrate such non-linear responses to demonstrate that gains in efficiency (benefit per money spent) can be made by integrating these characteristics into decision making.
2. Identifying three measures that are currently the focus of large freshwater management budgets (waste-water treatment, riparian buffer strips and discharge allocations to regulated rivers), we relate the costs of these measures to the environmental improvements achievable in running waters. For each of these measures, the environmental improvement achieved per currency unit significantly decreases with an increase in total money spent.
3. Traditional environmental management ignores this system behaviour because it invests important parts of budgets in a particular measure before focusing on the next among other measures. We therefore advocate alternating investments in that measure which achieves the greatest environmental improvement in the next possible investment step. Compared with traditional management, this alternating decision-making strategy will achieve greater environmental improvements for a given total budget.     

Focusing environmental management budgets on non-linear system responses: potential for significant improvements to freshwater ecosystems

1. The non-linear responses of environmental systems to changes imposed upon them is well known to scientists. Environmental managers rarely act accordingly, however, because of communication problems, a lack of imagination and various other constraints. Therefore, we illustrate such non-linear responses to demonstrate that gains in efficiency (benefit per money spent) can be made by integrating these characteristics into decision making.
2. Identifying three measures that are currently the focus of large freshwater management budgets (waste-water treatment, riparian buffer strips and discharge allocations to regulated rivers), we relate the costs of these measures to the environmental improvements achievable in running waters. For each of these measures, the environmental improvement achieved per currency unit significantly decreases with an increase in total money spent.
3. Traditional environmental management ignores this system behaviour because it invests important parts of budgets in a particular measure before focusing on the next among other measures. We therefore advocate alternating investments in that measure which achieves the greatest environmental improvement in the next possible investment step. Compared with traditional management, this alternating decision-making strategy will achieve greater environmental improvements for a given total budget.     

Restoration of lowland streams: an introduction*

• 1 This paper introduces the Lowland Streams Restoration Workshop that was held in Lund, Sweden in August 1991.
• 2 Attenders at the Workshop participated in working groups which discussed and reported on the state of knowledge of stream restoration and identified critical areas of information need. Currently, most restoration efforts are emission-orientated (i.e. waste-water management), while the imitation of the geomorphology or of the riparian vegetation of a quasi-natural or natural reference channel receives less attention.
• 3 Successful stream restoration requires a multidisciplinary approach within a holistic system framework. Monitoring the outcome of past, existing and future steam-restoration projects is required for information on the feasibility of alternative techniques and approaches.
• 4 It was recommended that systems in pristine condition serve as a point of reference and not as a goal for most stream restoration projects. Restoration goals must be carefully defined so that everyone at every level understands the aim of the project. At the very least, all restoration programmes should consider geomorphic, hydrological, biological, aesthetic, and water quality aspects of the system.
• 5 Restoration programmes should aim to create a system with a stable channel, or a channel in dynamic equilibrium that supports a self-sustaining and functionally diverse community assemblage; it should not concentrate on one species or group, except at the local level. Preserving the terrestrial -aquatic interface by setting aside riparian land corridors is critical to all stages of restoration. Additional information on the temporal and regional variability in important system processes and functions is needed.

     

The riparian community of north-west European lowland streams

• 1 Riparian plant communities along lowland streams have been affected by man for the past 15000 years. During this period climatological changes have also taken place. The present situation in north-west Europe is a result of these influences so that the choice of reference situations is necessarily arbitrary.
• 2 Dominant abiotic factors that influence riparian vegetation are local hydrology and soil composition, and the pH, lime content and nutrient concentration of the feeding ground water.
• 3 Riparian plant communities are described as phytosociological units. Depending on abiotic characteristics, sequences from spring to lower course and from the stream bank to the boundaries of the stream valley are reported. The Pruno-Fraxinetum association is, and has been for thousands of years, one of the main riparian vegetation types of (lowland) streams.
• 4 In many European countries, restoration projects are being performed or planned. One of the restoration measures is the planting of trees or shrubs along streams as buffer strips. A phytosociological approach, based on knowledge of the local hydrology and nutrient/ion availability, is better by far than the general practice of standard plantation. Such an approach requires research in advance, which increases the initial costs of projects, but can be expected to provide far better results in the long term, and ultimately save money.

     

Reactions of some caddis larvae (Trichoptera) to different types of substrate in an experimental stream *

In laboratory experiments with full-grown larvae of three Trichoptera species (Limnephilus rhombicus, Potamophylax rotundipennis and Sericostoma pedemontanum) in an artificial stream, four types of bottom material were provided in combination with various currents. Only L. rhombicus reacted to low current speed (9 cm/sec), moving downstream when a bottom current was present. L. rhombicus and P. rotundipennis showed a distinct preference for pebbles over sand and for coarse pebbles over crushed brick. S. pedemontanum burrowed under pebbles or stones. L. rhombicus showed a distinct tendency to climb onto the dividing gauze or vertical sticks. All three species preferred shaded parts of the experimental stream to the illuminated parts. The results are related to field observations. Limnephilus rhombicus occurs in stagnant and slow-running waters. Potamophylax rotundipennis is restricted to rather fast-running streams with a perpetual flow, while Sericostoma pedemontanum occurs in the same type of stream.