Comparative biodiversity of rivers, streams, ditches and ponds in an agricultural landscape in Southern England
Introduction
Over the last 10 years, the concept of integrated catchment management has begun to gain wide acceptance amongst water managers (Gardiner, 1994, Everard, 1999, Verdonschot, 2000). Its central premise, that land and water need to be managed together at a catchment level to ensure long-term ecological and socio-economic sustainability, has also been increasingly emphasised in legislation and policy. Most recently, the new EC Water Framework Directive (2000/60/EC) has placed catchment management at the centre of European water protection policy by requiring Member States to maintain the ecological quality of all fresh waters in a catchment context.
Achieving sustainable catchment management requires, inter alia, knowledge of the biodiversity characteristics and importance of different waterbody types within catchments (Schneiders and Verheyen, 1998). This includes information about the relative richness of different waterbody types, their variability across the landscape, and net contribution to catchment biodiversity. In practice, however, such data are exceptionally scarce. This is, in part, because traditional freshwater research has generally been waterbody-specific with very few comparisons made between different waterbody types. In addition, most research on specific waterbody types has focused on rivers, streams and lakes with little data describing other smaller natural or man-made habitats such as ditches, ponds, headwater streams, springs and flushes. In the few cases where wider catchment studies have been undertaken, their relevance and applicability has usually been restricted, because they either cover a limited range of taxa (Gontcharov, 1996, Sanoamuang, 1998), focus on restricted or atypical habitat types (Abernethy and Willby, 1999, Godreau et al., 1999, Pollock et al., 1998, Vincent and James, 1996, Ward et al., 1999) or use methodologies which differ between the waterbody types, making direct comparison difficult (Doledec and Statzner, 1994, Verdonschot, 1990). There remains, therefore, a paucity of information describing freshwater biodiversity across wider catchment areas, either semi-natural or managed. The need for such data is particularly urgent because it has immediate relevance for many areas of catchment management including the strategic location of agri-environment schemes, water resource management, pesticide strategic risk assessment and catchment restoration.
The aim of this paper is to present some of the first data to compare the biodiversity of different freshwater ecosystems in a lowland agricultural landscape. The survey area, on the Oxfordshire/Wiltshire border of southern England, includes a representative range of waterbody types, both permanent and seasonal, including streams, ponds, ditches, rivers and lakes. The comparative biodiversity of these waterbodies was assessed in terms of their wetland macrophytes and aquatic macroinvertebrates, with comparisons made of assemblage type, the occurrence of rare species and the alpha, beta and gamma diversity of each waterbody type.
Section snippets
Study area
The study area comprised an 80 km2 square (ca 9×9 km), centred on the River Cole at Coleshill, Oxfordshire (national grid reference SU234935) (Fig. 1). Land use in the region was mainly mixed grassland and arable agriculture with ca 9% of the area woodland and 8% urban. The geology is largely Oxford Clay to the south and mixed strata of limestone, sands and clays of Corallian age to the north. Topographically, the region is dominated by low rolling hills with ca 10% of the area lying within the
Sampling strategy
In total, 80 sites were sampled within the survey area. Of these, half were surveyed in spring 2000 (April and May) and the remainder in autumn 2000 (October and November). Sample sites were stratified by waterbody type with 20 sites surveyed in each of the following categories: (i) ditches, (ii) streams, (iii) rivers, and (iv) ponds and lakes. In each season, equal numbers of each waterbody type were surveyed (i.e. 10 in spring, 10 in autumn). Within this stratification, sites were selected
Chemical data
Data summarising the chemical characteristics of the four main waterbody types are given in Table 4. As a whole, the waterbodies were circum-neutral to slightly alkaline with similar mean and range pH values. Mean conductivity and dissolved oxygen levels were also similar across the waterbody types. Ponds had the lowest mean values for nitrate-nitrogen and suspended solids but also by far the widest range values for these parameters. The mean total phosphorus concentrations for streams was
Patterns in catchment aquatic biodiversity
The limited availability of multi-waterbody biodiversity data makes it difficult to identify how typical the current findings are of other regions and landscape types. A preliminary evaluation can, however, be undertaken using data from studies that have made pair-wise comparisons between waterbody types.
Acknowledgments
This work was funded under the CONNECT B programme by NERC (grant number GR3/C0018), the Environment Agency, the Rivers Agency (Northern Ireland), Vale of White Horse District Council and Northumbrian Water. Water samples were analysed by ADAS as part of DEFRA project CTD0004 2000–2003. We would also like to thank the following: staff from Syngenta Ltd for help in collection of water samples, Katia Bresso for map calculations, Garth Foster for confirmation of Notable species, Brian Davis and
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