TY - JOUR A1 - Périllon, Cécile A1 - Pöschke, Franziska A1 - Lewandowski, Jörg A1 - Hupfer, Michael A1 - Hilt, Sabine T1 - Stimulation of epiphyton growth by lacustrine groundwater discharge to an oligo-mesotrophic hard-water lake JF - Freshwater Science N2 - Periphyton is a major contributor to aquatic primary production and often competes with phytoplankton and submerged macrophytes for resources. In nutrient-limited environments, mobilization of sediment nutrients by groundwater can significantly affect periphyton (including epiphyton) development in shallow littoral zones and may affect other lake primary producers. We hypothesized that epiphyton growth in the littoral zone of temperate oligomesotrophic hard-water lakes could be stimulated by nutrient (especially P) supply via lacustrine groundwater discharge (LGD). We compared the dry mass, chlorophyll a (chl a), and nutrient content of epiphyton grown on artificial substrates at different sites in a groundwater-fed lake and in experimental chambers with and without LGD. During the spring-summer periods, epiphyton accumulated more biomass, especially algae, in littoral LGD sites and in experimental chambers with LGD compared to controls without LGD. Epiphyton chl a accumulation reached up to 46 mg chl a/m(2) after 4 wk when exposed to LGD, compared to a maximum of 23 mg chl a/m(2) at control (C) sites. In the field survey, differences in epiphyton biomass between LGD and C sites were most pronounced at the end of summer, when epilimnetic P concentrations were lowest and epiphyton C:P ratios indicated P limitation. Groundwater-borne P may have facilitated epiphyton growth on macrophytes and periphyton growth on littoral sediments. Epiphyton stored up to 35 mg P/m(2) in 4 wk (which corresponds to 13% of the total P content of the littoral waters), preventing its use by phytoplankton, and possibly contributing to the stabilization of a clear-water state. However, promotion of epiphyton growth by LGD may have contributed to an observed decline in macrophyte abundance caused by epiphyton shading and a decreased resilience of small charophytes to drag forces in shallow littoral areas of the studied lake in recent decades. KW - lacustrine groundwater discharge KW - periphyton KW - littoral KW - nutrients KW - benthic KW - macrophytes KW - seepage Y1 - 2017 U6 - https://doi.org/10.1086/692832 SN - 2161-9549 SN - 2161-9565 VL - 36 SP - 555 EP - 570 PB - Univ. of Chicago Press CY - Chicago ER - TY - JOUR A1 - Lehr, C. A1 - Pöschke, Franziska A1 - Lewandowski, Jörg A1 - Lischeid, Gunnar T1 - A novel method to evaluate the effect of a stream restoration on the spatial pattern of hydraulic connection of stream and groundwater JF - Journal of hydrology N2 - Stream restoration aims at an enhancement of ecological habitats, an increase of water retention within a landscape and sometimes even at an improvement of biogeochemical functions of lotic ecosystems. For the latter, good exchange between groundwater and stream water is often considered to be of major importance. In this study hydraulic connectivity between river and aquifer was investigated for a four years period, covering the restoration of an old oxbow after the second year. The oxbow became reconnected to the stream and the clogging layer in the oxbow was excavated. We expected increasing hydraulic connectivity between oxbow and aquifer after restoration of the stream, and decreasing hydraulic connectivity for the former shortcut due to increased clogging. To test that hypothesis, the spatial and temporal characteristics of the coupled groundwater-stream water system before and after the restoration were analysed by principal component analyses of time series of groundwater heads and stream water levels. The first component depicted between 53% and 70% of the total variance in the dataset for the different years. It captured the propagation of the pressure signal induced by stream water level fluctuations throughout the adjacent aquifer. Thus it could be used as a measure of hydraulic connectivity between stream and aquifer. During the first year, the impact of stream water level fluctuations decreased with distance from the regulated river (shortcut), whereas the hydraulic connection of the oxbow to the adjacent aquifer was very low. After restoration of the stream we observed a slight but not significant increase of hydraulic connectivity in the oxbow in the second year after restoration, but no change for the former shortcut. There is some evidence that the pattern of hydraulic connectivity at the study site is by far more determined by the natural heterogeneity of hydraulic conductivities of the floodplain sediments and the initial construction of the shortcut rather than by the clogging layer in the oxbow. (C) 2015 The Authors. Published by Elsevier B.V. KW - Groundwater-stream water interactions KW - Principal component analysis KW - Signal propagation KW - Hydraulic connectivity KW - Clogging KW - Riparian zone Y1 - 2015 U6 - https://doi.org/10.1016/j.jhydrol.2015.04.075 SN - 0022-1694 SN - 1879-2707 VL - 527 SP - 394 EP - 401 PB - Elsevier CY - Amsterdam ER -