Abrupt diatom responses to recent climate and land use changes in the Cantabrian Mountains (NW Spain)

The multi-proxy study of sediment cores from Lake Isoba (43 degrees 02 ' N, 5 degrees 18 ' W; 1400 m a.s.l.) allows a detailed assessment of the past hydrological and environmental dynamics in north-western Iberia resulting from the interplay between climate variability and anthropogenic impact. The combination of diatom stratigraphy, sedimentology and high-resolution elemental geochemistry along with a robust chronological framework (established by Pb-210, Cs-137 and C-14 dating) provides a detailed environmental reconstruction for the past similar to 500 years. Abrupt changes in the fossil diatom assemblages indicate a high sensitivity of this small lake to past environmental change and allow identifying four major stages related to the main climate fluctuations of the Little Ice Age (LIA) and recent warming. High lake levels, enhanced runoff and higher productivity characterised the middle phase of the LIA (similar to 1550 to 1630 CE), indicating an overall wet climate. Conversely, shallow lake levels, decreased runoff and relatively low productivity prevailed during the last phase of the LIA and the onset of the Industrial Era (similar to 1630 to 1925 CE), likely due to colder and drier conditions. High lake levels and higher carbonate input occurred after similar to 1925 CE until the 1980s CE, when our data show an abrupt drop in lake levels probably caused by a regional negative rainfall anomaly related to climate warming during the past decades. Finally, since similar to 1997 CE a remarkable and abrupt increase in the lake nutrient load and turbidity is detected, probably associated with the replacement of transhumant sheep flocks with staying cattle. The main environmental changes reconstructed at Lake Isoba mostly agree with other palaeoclimatic records from northern Spain. However, the hydrological patterns reconstructed are opposed to those observed on the northern slopes of the Cantabrian Mountains. The recent and strong impact of land-use changes on the lake, causing more ecological disruptions than previous climate changes, is noteworthy and demonstrates the high sensitivity of mountain lakes to human activities in a global change context.

Automated summary

A multi-proxy study of sediment cores from Lake Isoba in northwestern Iberia provides a detailed assessment of past hydrological and environmental dynamics, highlighting the sensitivity of the lake to climate variability and human impact.