The effects of nutrients and hydrology on shallow lake plankton at Attenborough Nature Reserve, Nottinghamshire
Cross, Iain David
PublisherUniversity of Nottingham
MetadataShow full item record
Eutrophication results in the loss of conservation and amenity value from shallow lakes. Efforts have been made to restore shallow lakes by reducing the external nutrient loading. Removing nutrient-rich inflows can reduce nutrient loading but may alter lake hydrology. This thesis is primarily aimed at investigating the effects of a nutrient-rich river on water chemistry and plankton by comparing six shallow (<3.5 m) lakes that are connected to and isolated from the River Erewash, in the Attenborough Nature Reserve, Nottinghamshire, U.K. Lakes that received River Erewash discharge had higher nutrient concentrations and higher phytoplankton biomass than those that were isolated from it. Turbid water was also found in a lake isolated from the River Erewash but with a nutrient-rich inflow stream. Lakes isolated from the inflows had abundant submerged macrophytes and clear water but other lakes were turbid and devoid of macrophytes. In lakes without inflows, cyanobacteria were proportionally more abundant. Lakes receiving nutrient-rich water were generally dominated by small chlorophytes and centric diatoms. Phosphorus concentrations had little effect on the phytoplankton. N and Si in the connected lakes, and zooplankton grazing and N in the isolated lakes, probably limited phytoplankton. A mesocosm experiment found chlorophyll-a concentrations were reduced by the addition of silica, and that the biovolume of dinophytes increased in the mesocosms without nitrate addition. Total zooplankton biomass did not change significantly between treatments. Summer floods reduced P concentrations in the connected lakes, suggesting that internal P loading was diluted and flushed out. Phytoplankton biomass was also lower during floods. Cryptophytes and diatoms dominated the phytoplankton and cyanobacteria were rare during flooding. A simulation of lake restoration by river diversion using mesocosms confirmed the importance of lake flushing for reducing internal loading. Diverting the River Erewash in order to reduce the nutrient loading to Attenborough Nature Reserve may be problematic in the short-term, because the lack of flushing may increase the effect of internal P loading and favour cyanobacterial growth. Reducing the external supply of N may further stimulate the dominance of cyanobacteria while P concentrations remain high.