Original paper

Low retention of nitrogen in a clear-water, shallow, temperate lake

Irfanullah, Haseeb M.d.; Moss, Brian


Little Budworth Pool in Cheshire, UK is a small (5 ha), shallow (maximum depth < 1 m) lake with very high total nitrogen (tn) concentration (96 % as no3-N), without any submerged macrophyte beds but with abundance of filamentous green algae. The pool has one inflow surrounded by a reed bed at its entry to the lake, and one outflow. A two-year study revealed high nitrogen loading (mean 15.8 ± SEM 1.1 kg TN ha−1 d−1), high annual loss of nitrogen through the outflow (mean 14.2 ± 1.1 kg TN ha−1 d−1), and low annual nitrogen retention (mean 1.6 ± 0.3 kg TN ha−1 d−1). The small surface area, shallowness, high water discharge (mean 4.3 ± 0.3 × 103 m3 d−1), short water residence time (mean 6.5 ± 0.4 day), and a lack of submerged macrophytes for removing nutrients as well as promoting sedimentation by reducing water velocity could explain low nitrogen retention in Little Budworth Pool. The lake, however, acted as an efficient sink for NO3-N and TN in summer apparently due to denitrification and uptake of nitrogen by the filamentous green algae (mostly Spirogyra sp.). The reed bed, on the contrary, did not act as a significant source or sink of nutrients probably because of its small area compared with the catchment, and the catchment slope.


macrophytesnitratenitrogen loadingnitrogen retention