Small Water Bodies in Great Britain and Ireland: Ecosystem function, human-generated degradation, and options for restorative action.

Small, 1st and 2nd-order, headwater streams and ponds play essential roles in providing natural flood control, trapping sediments and contaminants, retaining nutrients, and maintaining biological diversity, which extend into downstream reaches, lakes and estuaries. However, the large geographic extent and high connectivity of these small water bodies with the surrounding terrestrial ecosystem makes them particularly vulnerable to growing land-use pressures and environmental change. The greatest pressure on the physical processes in these waters has been their extension and modification for agricultural and forestry drainage, resulting in highly modified discharge and temperature regimes that have implications for flood and drought control further downstream. The extensive length of the small stream network exposes rivers to a wide range of inputs, including nutrients, pesticides, heavy metals, sediment and emerging contaminants. Small water bodies have also been affected by invasions of non-native species, which along with the physical and chemical pressures, have affected most groups of organisms with consequent implications for the wider biodiversity within the catchment. Reducing the impacts and restoring the natural ecosystem function of these water bodies requires a three-tiered approach based on: restoration of channel hydromorphological dynamics; restoration and management of the riparian zone; and management of activities in the wider catchment that have both point-source and diffuse impacts. Such activities are expensive and so emphasis must be placed on integrated programmes that provide multiple benefits. Practical options need to be promoted through legislative regulation, financial incentives, markets for resource services and voluntary codes and actions.

Photosynthetic carbon assimilation by Crassula helmsii.

Photosynthesis of Crassula helmsii, an amphibious aquatic macrophyte weed species, has been measured with respect to pH and irradiance. C. helmsii shows a marked diel fluctuation in titratable acidity, which can be accounted for by changing levels of malic acid. C. helmsii is unable to use HCO inf3sup- for photosynthesis and exhibits generally low photosynthetic rates when CO2 is not limiting. The photon flux density at which the onset of light saturation of photosynthesis is reached (E K ) is low for aquatic macrophytes. Some advantages conferred on C. helmsii by the possession of crassulacean acid metabolism are an extension of the period of assimilation of dissolved inorganic carbon, resulting in a reduction in the limitation imposed on photosynthesis in aquatic environments by a very high CO2 diffusion resistance.

Herbicide risk assessment for non-target aquatic plants: sulfosulfuron--a case study.

Herbicides entering the aquatic environment by spray drift, run-off and leaching to field drains may cause adverse effects on non-target aquatic vegetation. The potential for such effects has typically been evaluated from tests with floating, monocotyledonous Lemna sp. However, concern has been expressed as to whether this species could be used to indicate potential effects on other vegetation types, particularly rooted, submerged, emergent or dicotyledonous species. In 1997, the Centre for Aquatic Plant Management undertook development of new tests based on the additional species, Glyceria maxima (Hartm) Holmb, Lagarosiphon major (Ridl) Moss and Myriophyllum spicatum L. The resulting methodology was used to assess the effects of the sulfonylurea herbicide, sulfosulfuron on these species. Data presented here demonstrate that exposure to initial sulfosulfuron concentrations of 3.33 microg litre(-1) for up to 21 days was tolerated by these species and that adverse effects were observed only when plants were exposed to initial concentrations of 3.33 and 10 microg litre(-1) for 70 days. As the occurrence of such high initial concentrations for long periods is unlikely in the aquatic environment, sulfosulfuron is not expected to have adverse effects on the growth of these species. This study has also demonstrated that G maxima, L major and M spicatum grown in small outdoor tanks can be used successfully to assess the effects of crop-protection products on non-target aquatic flora.

The British river of the future: how climate change and human activity might affect two contrasting river ecosystems in England.

The possible effects of changing climate on a southern and a north-eastern English river (the Thames and the Yorkshire Ouse, respectively) were examined in relation to water and ecological quality throughout the food web. The CLASSIC hydrological model, driven by output from the Hadley Centre climate model (HadCM3), based on IPCC low and high CO(2) emission scenarios for 2080 were used as the basis for the analysis. Compared to current conditions, the CLASSIC model predicted lower flows for both rivers, in all seasons except winter. Such an outcome would lead to longer residence times (by up to a month in the Thames), with nutrient, organic and biological contaminant concentrations elevated by 70-100% pro-rata, assuming sewage treatment effectiveness remains unchanged. Greater opportunities for phytoplankton growth will arise, and this may be significant in the Thames. Warmer winters and milder springs will favour riverine birds and increase the recruitment of many coarse fish species. However, warm, slow-flowing, shallower water would increase the incidence of fish diseases. These changing conditions would make southern UK rivers in general a less favourable habitat for some species of fish, such as the Atlantic salmon (Salmo salar). Accidental or deliberate, introductions of alien macrophytes and fish may change the range of species in the rivers. In some areas, it is possible that a concurrence of different pressures may give rise to the temporary loss of ecosystem services, such as providing acceptable quality water for humans and industry. An increasing demand for water in southern England due to an expanding population, a possibly reduced flow due to climate change, together with the Water Framework Directive obligation to maintain water quality, will put extreme pressure on river ecosystems, such as the Thames.