TY - JOUR A1 - Musolff, Andreas A1 - Schmidt, Christian A1 - Rode, Michael A1 - Lischeid, Gunnar A1 - Weise, Stephan M. A1 - Fleckenstein, Jan H. T1 - Groundwater head controls nitrate export from an agricultural lowland catchment JF - Advances in water resources N2 - Solute concentration variability is of fundamental importance for the chemical and ecological state of streams. It is often closely related to discharge variability and can be characterized in terms of a solute export regime. Previous studies, especially in lowland catchments, report that nitrate is often exported with an accretion pattern of increasing concentrations with increasing discharge. Several modeling approaches exist to predict the export regime of solutes from the spatial relationship of discharge generating zones with solute availability in the catchment. For a small agriculturally managed lowland catchment in central Germany, we show that this relationship is controlled by the depth to groundwater table and its temporal dynamics. Principal component analysis of groundwater level time series from wells distributed throughout the catchment allowed derivation of a representative groundwater level time series that explained most of the discharge variability. Groundwater sampling revealed consistently decreasing nitrate concentrations with an increasing thickness of the unsaturated zone. The relationships of depth to groundwater table to discharge and to nitrate concentration were parameterized and integrated to successfully model catchment discharge and nitrate export on the basis of groundwater level variations alone. This study shows that intensive and uniform agricultural land use likely results in a clear and consistent concentration-depth relationship of nitrate, which can be utilized in simple approaches to predict stream nitrate export dynamics at the catchment scale. (C) 2016 Elsevier Ltd. All rights reserved. KW - Water quality KW - Nitrate KW - Lowland catchment KW - Export regime KW - Concentration-discharge relationship Y1 - 2016 U6 - https://doi.org/10.1016/j.advwatres.2016.07.003 SN - 0309-1708 SN - 1872-9657 VL - 96 SP - 95 EP - 107 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Lischeid, Gunnar A1 - Kalettka, Thomas A1 - Holländer, Matthias A1 - Steidl, Jörg A1 - Merz, Christoph A1 - Dannowski, Ralf A1 - Hohenbrink, Tobias Ludwig A1 - Lehr, Christian A1 - Onandia, Gabriela A1 - Reverey, Florian A1 - Pätzig, Marlene T1 - Natural ponds in an agricultural landscape BT - external drivers, internal processes, and the role of the terrestrial-aquatic interface JF - Limnologica : ecology and management of inland waters N2 - The pleistocenic landscape in North Europe, North Asia and North America is spotted with thousands of natural ponds called kettle holes. They are biological and biogeochemical hotspots. Due to small size, small perimeter and shallow depth biological and biogeochemical processes in kettle holes are closely linked to the dynamics and the emissions of the terrestrial environment. On the other hand, their intriguing high spatial and temporal variability makes a sound understanding of the terrestrial-aquatic link very difficult. It is presumed that intensive agricultural land use during the last decades has resulted in a ubiquitous high nutrient load. However, the water quality encountered at single sites highly depends on internal biogeochemical processes and thus can differ substantially even between adjacent sites. This study aimed at elucidating the interplay between external drivers and internal processes based on a thorough analysis of a comprehensive kettle hole water quality data set. To study the role of external drivers, effects of land use in the adjacent terrestrial environment, effects of vegetation at the interface between terrestrial and aquatic systems, and that of kettle hole morphology on water quality was investigated. None of these drivers was prone to strong with-in year variability. Thus temporal variability of spatial patterns could point to the role of internal biogeochemical processes. To that end, the temporal stability of the respective spatial patterns was studied as well for various solutes. All of these analyses were performed for a set of different variables. Different results for different solutes were then used as a source of information about the respective driving processes. In the Quillow catchment in the Uckermark region, about 100 km north of Berlin, Germany, 62 kettle holes have been regularly sampled since 2013. Kettle hole catchments were determined based on a groundwater level map of the uppermost aquifer. The catchments were not clearly related to topography. Spatial patterns of kettle hole water concentration of (earth) alkaline metals and chloride were fairly stable, presumably reflecting solute concentration of the uppermost aquifer. In contrast, spatial patterns of nutrients and redox-sensitive solutes within the kettle holes were hardly correlated between different sampling campaigns. Correspondingly, effects of season, hydrogeomorphic kettle hole type, shore vegetation or land use in the respective catchments were significant but explained only a minor portion of the total variance. It is concluded that internal processes mask effects of the terrestrial environment. There is some evidence that denitrification and phosphorus release from the sediment during frequent periods of hypoxia might play a major role. The latter seems to boost primary production occasionally. These processes do not follow a clear seasonal pattern and are still not well understood. KW - Ponds KW - Kettle holes KW - Water quality KW - Land use KW - Hydrogeomorphic type KW - Shore vegetationa Y1 - 2018 U6 - https://doi.org/10.1016/j.limno.2017.01.003 SN - 0075-9511 SN - 1873-5851 VL - 68 SP - 5 EP - 16 PB - Elsevier GMBH CY - München ER - TY - JOUR A1 - Lischeid, Gunnar A1 - Kalettka, Thomas T1 - Grasping the heterogeneity of kettle hole water quality in Northeast Germany JF - Hydrobiologia : acta hydrobiologica, hydrographica, limnologica et protistologica N2 - In the young moraine landscape in Northeast Germany, small glacially created ponds, the so-called kettle holes, are very abundant. They exhibit large spatial heterogeneity, seemingly rendering each kettle hole unique. However, this would not be consistent with any scientific approach. Thus, a classification scheme has been developed for kettle holes in Northeast Germany based on morphology, hydrodynamics and connection to stream networks of the kettle holes as well as size, topography and land use of the respective catchment. These indices are assumed to be related both to water quality as well as to biological issues of the kettle holes. Starting in the mid-1990s, an extensive monitoring program has been established in the federal state of Brandenburg, Germany. In this study, a subset comprising 1,316 samples from 79 kettle holes was analysed, where 21 parameters had been determined. Sampling intervals varied widely, and were between bi-weekly and three-monthly at most sites. A nonlinear principal component analysis was performed. The first four components explained 90% of the variance. These components seem to provide quantitative measures of phosphorus release from the sediments during hypoxic periods, agricultural solute input, algae primary production, and geogenic compounds. This allowed differentiating between the natural and anthropogenic impact factors on water quality. In addition, scores of single components were related to properties of the kettle holes and their environments. The results contribute to a better understanding of biological and biogeochemical processes and can be used to verify the effects of conservation and management strategies for kettle holes. KW - Kettle holes KW - Water quality KW - Monitoring KW - Land use KW - Isomap Y1 - 2012 U6 - https://doi.org/10.1007/s10750-011-0764-7 SN - 0018-8158 SN - 1573-5117 VL - 689 IS - 1 SP - 63 EP - 77 PB - Springer CY - Dordrecht ER -