Small lakes in big landscape: External drivers of littoral ecosystem in high elevation lakes

Abstract

Graphical abstract:\n\n\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=87 SRC=\"FIGDIR/small/034553_ab1.gif\" ALT=\"Figure 1\">\nView larger version (51K):\norg.highwire.dtl.DTLVardef@17b9e61org.highwire.dtl.DTLVardef@db2861org.highwire.dtl.DTLVardef@38125corg.highwire.dtl.DTLVardef@13d802f_HPS_FORMAT_FIGEXP M_FIG C_FIG In low nutrient alpine lakes, the littoral zone is the most productive part of the ecosystem, and it is a biodiversity hotspot. It is not entirely clear how the scale and physical heterogeneity of surrounding catchment, its ecological composition, and larger landscape gradients work together to sustain littoral communities.\n\nA total of 114 alpine lakes in the central Pyrenees were surveyed to evaluate the functional connectivity between catchment physical and ecological elements and littoral zoobenthos, and ascertain their effect on community formation. At each lake, the zoobenthic composition was assessed together with geolocation (altitude, latitude and longitude), catchment hydrodynamics, geomorphology, topography, riparian vegetation composition, the presence of trout and frogs, water pH and conductivity.\n\nUni- and multidimensional fuzzy set ordination models integrating benthic biota and environmental variables revealed that at geographical scale longitude surpassed altitude in its effect on littoral ecosystem, reflecting a sharp transition between Atlantic and Mediterranean bioregions. Topography (through its control of catchment type, summer snow coverage, and connectivity with other lakes) was the largest catchment-scale driver, followed by hydrodynamics (waterbody size, type and inflow/outflow volumes). Locally, riparian plant composition significantly related to littoral community structure, richness and morphotype diversity. These variables, directly and indirectly create habitats for aquatic and terrestrial stages of invertebrates, and control nutrient and water cycles. Three ecologically diverse associations characterised distinct lake sets. Vertebrate predation, water conductivity and pH (broad measures of total dissolved ions/nutrients and their bioavailability) had no major influence on littoral taxa.\n\nThe work provides exhaustive information from relatively pristine sites, which unveil a strong connection between littoral ecosystem and catchment heterogeneity at scales beyond the local environment. This underpins their role as sensors of local and large-scale environmental changes, and can be used to evaluate further impacts.