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• 1. Basu, N. B.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK). Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
Nutrient loads exported from managed catchments reveal emergent biogeochemical stationarity2010In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 37, no L23404Article in journal (Refereed)

Complexity of heterogeneous catchments poses challenges in predicting biogeochemical responses to human alterations and stochastic hydro‐climatic drivers. Human interferences and climate change may have contributed to the demise of hydrologic stationarity, but our synthesis of a large body of observational data suggests that anthropogenic impacts have also resulted in the emergence of effective biogeochemical stationarity in managed catchments. Long‐term monitoring data from the Mississippi‐Atchafalaya River Basin (MARB) and the Baltic Sea Drainage Basin (BSDB) reveal that inter‐annual variations in loads (LT) for total‐N (TN) and total‐P (TP), exported from a catchment are dominantly controlled by discharge (QT) leading inevitably to temporal invariance of the annual, flow‐weighted concentration, $\overline{C_{f}}\mathit{}$ = (LT/QT). Emergence of this consistent pattern across diverse managed catchments is attributed to the anthropogenic legacy of accumulated nutrient sources generating memory, similar to ubiquitously present sources for geogenic constituents that also exhibit a linear LTQT relationship. These responses are characteristic of transport‐limited systems. In contrast, in the absence of legacy sources in less‐managed catchments, $\overline{C_{f}}\mathit{}$ values were highly variable and supply limited. We offer a theoretical explanation for the observed patterns at the event scale, and extend it to consider the stochastic nature of rainfall/flow patterns at annual scales. Our analysis suggests that: (1) expected inter‐annual variations in LT can be robustly predicted given discharge variations arising from hydro‐climatic or anthropogenic forcing, and (2) water‐quality problems in receiving inland and coastal waters would persist until the accumulated storages of nutrients have been substantially depleted. The finding has notable implications on catchment management to mitigate adverse water‐quality impacts, and on acceleration of global biogeochemical cycles.

• 2.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Land and Water Resources.
Long-term development, modeling and management of nutrient loading to inland and coastal waters2007Doctoral thesis, monograph (Other academic)
• 3.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Physical versus biogeochemical interpretations of nitrogen and phosphorus attenuation in streams and its dependence on stream characteristics2007In: Global Biogeochemical Cycles, Vol. 21, no GB3003Article in journal (Refereed)

We investigate the influence of biogeochemical nutrient attenuation rates versus physical solute travel times on nutrient transport and attenuation in streams with different characteristics. Comparative results indicate smaller biogeochemical in-stream attenuation rate and greater decrease of this rate with stream depth for phosphorus than for nitrogen. Because physical solute travel times also decrease with stream depth, equally for both nutrients, the resulting relative nutrient mass attenuation becomes essentially independent of stream depth for phosphorus but decreases with stream depth for nitrogen. Coarse interpretation models, without relevant representation of subgrid physical transport variability may lead to systematic misinterpretation of relative nitrogen mass attenuation behavior as a predominantly biogeochemical attenuation rate effect instead of a physical transport time effect. Incorrect understanding and distinction between

physical and biogeochemical processes and effects may generally induce misleading cause-effect conclusions on environmental loads and prevent us from reaching environmental goals of worldwide importance.

• 4.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Water resource informatics, management and adaptation under a warming climate2008Conference paper (Other (popular science, discussion, etc.))

International Workshop on The Sustainable City - Technologies and Systems for Sustainable Development, School of Environmental Studies, CUSAT-Cochin University of Science and Technology, Kerala State, India, December 10-12, 2008

• 5.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Quantification of advective solute travel times and mass transport through hydrological catchments2010In: Environmental Fluid Mechanics, ISSN 1567-7419, E-ISSN 1573-1510, Vol. 10, no 1-2, p. 103-120Article in journal (Refereed)

This study has investigated and outlined the possible quantification and mapping of the distributions of advective solute travel times through hydrological catchments. These distributions are essential for understanding how local water flow and solute transport and attenuation processes affect the catchment-scale transport of solute, for instance with regard to biogeochemical cycling, contamination persistence and water quality. The spatial and statistical distributions of advective travel times have been quantified based on reported hydrological flow and mass-transport modeling results for two coastal Swedish catchments. The results show that the combined travel time distributions for the groundwater-stream network continuum in these catchments depend largely on the groundwater system and model representation, in particular regarding the spatial variability of groundwater hydraulic parameters (conductivity, porosity and gradient), and the possible contributions of slower/deeper groundwater flow components. Model assumptions about the spatial variability of groundwater hydraulic properties can thus greatly affect model results of catchment-scale solute spreading. The importance of advective travel time variability for the total mass delivery of naturally attenuated solute (tracer, nutrient, pollutant) from a catchment to its downstream water recipient depends on the product of catchment-average physical travel time and attenuation rate.

• 6.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Scale and model resolution effects on the distributions of advective solute travel times in catchments2010In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 24, no 12, p. 1697-1710Article in journal (Refereed)

Advective solute travel times and their distributions in hydrological catchments are useful descriptors of the dynamics and variation of the physical mass transport among and along the different source-to-recipient pathways of solute transport through the catchments. This article investigates the scale dependence and the effects of model and data resolution on the quantification of advective travel times and their distributions in the Swedish catchment areas of Norrström and Forsmark. In the surface water networks of the investigated (sub)catchments, the mean advective travel time increases with (sub)catchment scale, whereas the relative travel time variability around the mean value (coefficient of variation, CV) is scale-invariant and insensitive to model resolution. In the groundwater and for the whole (sub)catchments, both the mean value and the CV of travel times are scale-invariant, but sensitive to model resolution and accuracy. Such quantifications and results of advective travel times constitute important steps in the development of improved understanding and modelling of nutrient, pollutant and tracer transport through catchments.

• 7.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Field study of phosphorous transport and retention in drainage reaches2009In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 365, no 1-2, p. 46-55Article in journal (Refereed)

Phosphorous (P) transport and retention is investigated here based on data from a 3-year field study of five drainage ditch reaches at Färingsö, west of Stockholm, Sweden. Results show that P retention rate in the drainage reaches greatly depends on and decreases with increasing water flow and watercourse depth. This supports previous simulation indications and implies that changing drainage reach depth and flow conditions may considerably change P loading to downstream waters. In deeper drainage reaches with tile-drained fields in their catchment areas, which are common in Nordic lowlands, particulate P amounted to about 80% of total P, with about half of this fraction being bio-available. As much as 70% of that particulate P was retained in a reach section that was flow- and depth-restricted by heavy vegetation. Retained P in sediments was found to be mostly bound to Fe and/or Al. Some of that PAl–Fe fraction may after dissolution become more permanently retained by re-binding to Ca.

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