Nutrient cycling at Bakethin reservoir, Northumberland

Abstract

The aims of this research were to investigate the nutrient regime of a small upland water body, Bakethin Reservoir, situated in the middle of Kielder forest Northumberland, England. The research consisted of three main sections: to identify possible inputs of nutrients to the Reservoir, to investigate the seasonal changes in chemical variables and photosynthetic organisms, and to investigate whether certain organisms are P-limited at the Reservoir. Possible sources and sinks of nutrients were identified and it is likely that the major source of nutrients is the River North Tyne, which receives Butteryhaugh sewage treatment works and the Kielder Salmon hatchery. A small stream entering the Reservoir on the northern shore, termed here the Calcareous Flush, is very different in terms of water chemistry and flora to the Reservoir and other freshwater sites in the area. This inflow has a high merit in terms of conservation and general ecology and was therefore included in the study. Water samples were taken monthly from March 1993 until July 1994 at 6 sites around the Reservoir and from April 1993 until July 1994 at a site upstream of the STW. 18 physical and chemical variables were measured and these were all found to vary over the seasonal cycle and between sites. However, certain characteristics of the water can be highlighted and these are the low temperature (annual mean of 6.9ºC), the brown colouration (mean absorbance 0.05 at 420 nm), and the low transparency (mean annual Secchi depth of 0.94 m ). The annual range of inorganic combined N at Bakethin Reservoir is 46.2 to 166.3 ug 1(^-1) Total filtrable phosphate ranged from 11.4 to 49.7 ug 1(^-1) P. Sediment samples were collected on one occasion (28/04/1994) and analysed for organic matter, N and P. N levels were much lower than P. As part of a 'base-line' survey of photosynthetic organisms, and to gain an insight into the role that algae and aquatic macrophytes play in nutrient cycling at the Reservoir, algal samples were taken to coincide with the water samples. 210 algal taxa were recorded between April 1993 and June 1994 at 6 sites. These included 30 blue-green algae, 1 Rhodophyta, 7 Euglenophyta, 2 Cryptophyta, 4 Pyrrophyta, 4 Chrysophyta, 3 Xanthophyta, 114 Bacillariophyta (diatoms), and 45 Chlorophyta. 41 species of macrophytes were found at the sites including 2 lichens, 1 species of aquatic moss and 38 vascular plants. The algal samples were classified using TWINSPAN. To investigate whether organisms are P-limited, eight species were chosen for a preliminary study of their "surface" phosphatase activities. Five were algae: Ulothrix zonata, Stigeoclonium tenue, locally frequent in spring and early summer, Drapamaldia glomerata and Chaetophora incrassala, locally frequent in late summer and autumn, and Nitella flexilis, found in great abundance in May and June 1994 in a shallow bay at the Reservoir.. The other three were macrophytes: Potamogeton berchtoldii, P. obtusifolius, and P. natans. Phosphatase activity was associated with all eight species suggesting that the ability to hydrolyse organic phosphate is important for species at Bakethin Reservoir. The extent to which the phosphatase activity was attributable to the epiphytes is unclear.