Connectivity and zebra mussel invasion offer short‐term buffering of eutrophication impacts on floodplain lake landscape biodiversity

Abstract

Aim To investigate if connectivity and zebra mussel (Dreissena polymorpha) occurrence can mitigate effects of eutrophication in a lowland lake landscape. Location Upper Lough Erne, Northern Ireland, UK. Methods Data on environment, macrophytes and invertebrates were assembled for three basins of a large central lake and its satellite floodplain lakes via field surveys and palaeolimnological analyses. Space–time interaction analyses of palaeoecological data were compared pre‐1950 and post‐1950. Multivariate analyses examined how connectivity, environment and zebra mussels influenced contemporary lake communities, and explain their divergence from historical communities in the past. Results Pre‐1950, we found high community variation across sites and low within‐lake variation in macrophytes, but progressive eutrophication accentuated within‐lake community variation after 1950. Partitioning analysis showed larger effects of connectivity than nutrient enrichment on contemporary macrophyte composition, while local effects structured invertebrate communities. Three clusters of lakes were revealed according to variation in macrophyte composition, isolation from the central lake and nutrient enrichment: Group 1– the central lake and six nearby lakes were meso‐eutrophic (TP = 66.7 ± 47.6 μg/L; TN = 0.79 ± 0.41 mg/L) and had the highest zebra mussel abundances and organismal biodiversity; Group 2– Eight eutrophic (TP = 112±36.6 μg/L; TN = 1.25 ± 0.5 mg/L) and connected lakes; Group 3– Seven isolated and hypertrophic (TP = 163.2 ± 101.5 μg/L; TN = 1.55 ± 0.3 mg/L) lakes. Pre‐1950 palaeolimnological data for macrophytes and invertebrates for 5 lakes and a basin in the central lake most resembled extant lake communities of Group 1. However, palaeo‐records revealed that macrophytes and invertebrates subsequently converged towards those of Groups 2 and 3. Main conclusions Our study reveals that the central “mother” lake acts as a hub for preserving biodiversity via shared hydrological connectivity with satellite lakes and high zebra mussel abundances. These may buffer the impoverishing effects of eutrophication and sustain unexpectedly high biodiversity in the short term. Such protective buffering, however, cannot be relied upon indefinitely to conserve biodiversity.

River connectivity and climate behind the long‐term evolution of tropical American floodplain lakes

“…However, the marked temporal successional trend in diatom species and the more recent (post-1960s) increases in diatom species associated with productive environments (Nitzschia spp., C. cuspidata and G. eriense; Table 2), coupled with gradual increases in P, OM, and sedimentation rates, all indicate greater importance F I G U R E 6 Multiple factor analysis (MFA) plots for the core LBARB1, showing (a) the variation and contribution of diatoms functional groups (plankton in green, acidic/dystrophic in yellow, and benthic/productive in gray), selected geochemical ratios and elements (purple) Fe/Mn, Ti/Ca, Zr/Fe, and P, organic matter content (LOI), and sedimentation rates and SPEI data (SPEI = annual average; < minimum annual value; > maximum annual value). Major zones of diatom community change detected by coniss analysis are indicated with brown (Zone 1), green (Zone 2), and blue (Zone (Bennion et al, 2004;Salgado et al, 2019).…”

“…eriense ; Table 2 ), coupled with gradual increases in P, OM, and sedimentation rates, all indicate greater importance of in‐lake factors in driving the diatom communities. The more enclosed nature of the San Juana Lake may therefore facilitate a quicker response to localized stressors such as deforestation, and nutrient runoff from agriculture and husbandry (Bennion et al., 2004 ; Salgado et al., 2019 ).…”

“…In large riverine ecosystems, the way in which aquatic communities are organized and respond to climatic or human‐derived stressors largely depends on the degree and magnitude of the disturbance, and on the spatial arrangement of lakes within the main hydrological network (Eros et al., 2012 ; González‐Trujillo et al., 2020 ; Grant et al., 2007 ;). Connected lakes to the main river channel may be for instance, more dependent on the hydrological dynamics of the main river, and hence be prone to greater biological resilience and recovery through source–sink dynamics than in isolated lakes (Salgado et al., 2019 ). In turn, isolated lakes are likely to present lower dispersal, and thus, local environmental change such as nutrient inputs (eutrophication) is likely to exert a greater control over the community structure through temporal species turnover (Salgado et al., 2019 ).…”

“…Connected lakes to the main river channel may be for instance, more dependent on the hydrological dynamics of the main river, and hence be prone to greater biological resilience and recovery through source–sink dynamics than in isolated lakes (Salgado et al., 2019 ). In turn, isolated lakes are likely to present lower dispersal, and thus, local environmental change such as nutrient inputs (eutrophication) is likely to exert a greater control over the community structure through temporal species turnover (Salgado et al., 2019 ). However, increased habitat connectivity may also disrupt ecosystem resilience by homogenizing lake communities (Strecker & Brittain, 2017 ).…”

“…However, increased habitat connectivity may also disrupt ecosystem resilience by homogenizing lake communities (Strecker & Brittain, 2017 ). A long‐term perspective is of particular value, as it captures environmental and hydrological change at centennial and millennial scales (Salgado et al., 2018 , 2019 ; Salgado, Sayer, Brooks, Davidson, Goldsmith, et al., 2018 ) and supplies limnological information from a scarcely monitored region. This approach has shown to provide continuous data on sedimentological changes and aquatic communities over time allowing to track back in time the effects of land‐use change and its hydrological and limnological effects (Liu et al., 2012 ; Salgado et al., 2020 ; Zeng et al., 2018 ).…”