Abstract
This research examined water clarity in shallow, prairie lakes of southern Alberta. A combination of water column analyses from 20 lakes and paleolimnological analyses from ten of them were used to examine how water clarity has changed since 1850 and to identify possible explanations for the observed changes. Pigment data from sediment cores showed the lakes experienced accelerated eutrophication since 1850, but that the onset was not synchronous across lakes. The lakes showed evidence that regime shifts between clear and turbid lake regimes since 1850 were possible. Evidence was based based on paleolimnolgical analyses using pigment data and additional sediment core proxies (e.g. fossils, isotopes). Water quality data from 20 lakes did not provide additional support for the existence of alternate regimes based on multimodal distribution between regimes or dual relationships between nutrients and water clarity. Salinity and major ion composition may help explain why some lakes did not provide additional support for the existence of alternate clear and turbid regimes. In most lakes, turbidity was dominated by inorganic matter, rather than phytoplankton, and this was more prevalent in the more saline lakes. High proportions of heterocystous cyanobacteria from four of the 20 shallow lakes provided some evidence for nitrogen limitation in the lakes. It is possible that additional lakes were also nutrient limited. As a result, models that use nutrient-chlorophyll relationships developed in non-saline lakes do not accurately capture turbidity dynamics in the saline, shallow lakes on southern Alberta’s prairie.
