Temperature profoundly influences the occurrence and organic production of algae in inland waters. Correlations deduced from seasonality of species are limited by numerous interactions. The kinetics of growth and photosynthesis are more unequivocal, although light and nutrient conditions affect rate-response to temperature, with reduced sensitivity at low irradiance. Specific growth rates, species-characteristic, have rarely been measured systematically with numerous common species and short intervals over an extended range of temperature.

Different bases of quantitative analysis are cited; they include cardinal points, neo-Blackman behaviour, and the van't Hoff (Q₁₀), Arrhenius (degrees K) and Bğlehrádek (with ‘biological zero’) formulations. Temperature-limits of specific growth rate are widely found, and variable with species, outside the 10–20 °C range. Low-temperature stenothermy is apparently uncommon, and high temperature (35+ °C) species and strains are known. Maximum rates fall below an upper limiting envelope. In nature, species are only rarely most abundant at their optima for specific growth rate. Differences of temperature have indirect effects on algal distribution in a stratified water-column. Geographical distributions partly relate to temperature, although experimental elucidation is rare; there is indirect influence through ice-cover and altitude. Some prediction of rate-limitation is possible, both with latitude and globally.

Quantifying the contributions of carbon sources that support food webs in large rivers is an important and growing field of ecological research with implications for future management and rehabilitation. Here we review theoretical concepts and recent empirical evidence that address carbon flow through aquatic food webs in large rivers. The literature reviewed focuses on studies using stable isotope analysis, which is a tested framework for identifying the origin of carbon sources that are assimilated by primary consumers and subsequently transferred through the food web to support higher consumers. Theoretical concepts addressing carbon flow in large river food webs have tended to stress the importance of organic matter originating from different sources, such as floodplains (Flood Pulse Concept), local riparian and aquatic primary producers (Riverine Productivity Model), or leakage from upstream processing of terrestrial organic matter (River Continuum Concept). Recent empirical evidence from a range of studies has highlighted the importance of autochthonous carbon, especially in the form of benthic algae and phytoplankton, to food webs in a variety of large rivers. However, some flexibility is apparent within food webs and several studies have identified a range of secondary carbon sources that can also be consistently important, depending on the temporal and spatial patterns of hydrogeomorphic conditions. The geographic spread of studies addressing carbon flow in large river food webs is steadily increasing, although long term data sets remain sparse. Despite this, opportunities exist to improve our understanding of historical changes in river food webs and to develop predictive models of future responses to environmental change through the use of museum collections and rehabilitation case-studies.

‘Ecological status’ is a core concept of the Water Framework Directive (WFD). Many papers have been published throughout Europe describing methods for assessing ecological status by comparing observed assemblages with those expected under unimpacted conditions. However, the quantitative rigour necessary to develop these methods has been achieved by reducing complex community structure to simple metrics. One of the costs associated with this is the loss of higher level understanding of community structure which otherwise may have informed data interpretation. It also pushes the debate about ecological status further into the realm of abstract scientific ideas and away from engagement with stakeholders, another core concept of the WFD. These matters are particularly acute for microscopic organisms such as the algae, which play a key role in freshwater ecosystem functioning but are little known beyond a narrow group of specialists. Examples of phytobenthos communities from streams and rivers in the UK are used to show how visual representation can inform both peer-to-peer debate within the scientific community and communication with non-technical stakeholders.

Airborne remote sensing provides an ideal means of mapping the physical structure of lakes and studying the effects of mixing on the horizontal distribution of phytoplankton. Airborne surveys are easier to integrate with field studies than satellite measurements and currently provide the only means of collecting high resolution spectral and spatial data. In this review, I present some results from a series of airborne campaigns organised in the English Lake District between 1986 and 1991. The main instrument used for the surveys was a Daedalus 1268 Airborne Thematic Mapper. This instrument acquires data in 11 spectral bands ranging from the blue visible to the thermal infrared. The visible band data was used to study the spatial distribution of the phytoplankton and the thermal data to map the surface temperature of the lakes. Examples are presented to show how the instrument was used to track the trajectory of surface currents, study exchange processes with the shallow littoral and map the spatial distribution of phytoplankton. Some of the acquired images highlight patterns and processes that could not have been identified by any other means. These included the development of poorly mixed areas (‘dead zones’) in the littoral zone and the effect of power-boat movements on the surface temperature of Windermere. The review describes some of the methods used to process the acquired imagery and includes an introduction to the procedures used to analyse the spectral data now being gathered by a new generation of airborne instruments.

The construction of river crossings to facilitate road schemes can potentially impact upon adjacent aquatic ecosystems. Such construction activity can pose a risk both to the physico-chemical and ecological quality of the aquatic environment. The EU Water Framework Directive requires member states to ensure that there is no further ‘degradation in water quality’ and to maintain ‘good ecological and chemical status’ of surface waters by 2015. In this context, it is important to understand the potential impacts of river-crossing construction and the methods for mitigating such impacts. This paper presents a critical review of current knowledge on such impacts, which is presented under three headings: water quality, river hydraulics and aquatic ecology. The review has identified knowledge gaps in all three areas, with the issue of the impact of suspended solids on aquatic ecosystems being a priority. The review concludes that some water quality standards may not provide sufficient regulatory control of discharges to the aquatic environment from river-crossing construction activities.