TY  - JOUR
A1  - Zimmermann, Beate
A1  - Zimmermann, Alexander
A1  - Turner, Benjamin L.
A1  - Francke, Till
A1  - Elsenbeer, Helmut
T1  - Connectivity of overland flow by drainage network expansion in a rain forest catchment
JF  - Water resources research
N2  - Soils in various places of the Panama Canal Watershed feature a low saturated hydraulic conductivity (K-s) at shallow depth, which promotes overland-flow generation and associated flashy catchment responses. In undisturbed forests of these areas, overland flow is concentrated in flow lines that extend the channel network and provide hydrological connectivity between hillslopes and streams. To understand the dynamics of overland-flow connectivity, as well as the impact of connectivity on catchment response, we studied an undisturbed headwater catchment by monitoring overland-flow occurrence in all flow lines and discharge, suspended sediment, and total phosphorus at the catchment outlet. We find that connectivity is strongly influenced by seasonal variation in antecedent wetness and can develop even under light rainfall conditions. Connectivity increased rapidly as rainfall frequency increased, eventually leading to full connectivity and surficial drainage of entire hillslopes. Connectivity was nonlinearly related to catchment response. However, additional information on factors such as overland-flow volume would be required to constrain relationships between connectivity, stormflow, and the export of suspended sediment and phosphorus. The effort to monitor those factors would be substantial, so we advocate applying the established links between rain event characteristics, drainage network expansion by flow lines, and catchment response for predictive modeling and catchment classification in forests of the Panama Canal Watershed and in similar regions elsewhere.
KW  - connectivity
KW  - overland flow
KW  - stormflow
KW  - suspended sediment
KW  - phosphorus
KW  - drainage network expansion
Y1  - 2014
U6  - https://doi.org/10.1002/2012WR012660
SN  - 0043-1397
SN  - 1944-7973
VL  - 50
IS  - 2
SP  - 1457
EP  - 1473
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Lukas, Marcus
A1  - Wacker, Alexander
T1  - Constraints by oxygen and food quality on carbon pathway regulation: a co-limitation study with an aquatic key herbivore
JF  - Ecology : a publication of the Ecological Society of America
N2  - In food webs, herbivores are often constrained by low food quality in terms of mineral and biochemical limitations, which in aquatic ecosystems can co-occur with limited oxygen conditions. As low food quality implies that carbon (C) is available in excess, and therefore a regulation to get rid of excess C is crucial for the performance of consumers, we examined the C pathways (ingestion, feces release, excretion, and respiration) of a planktonic key herbivore (Daphnia magna). We tested whether consumer C pathways increase due to mineral (phosphorus, P) or biochemical (cholesterol and fatty acid) limitations and how these regulations vary when in addition oxygen is low. Under such conditions, at least the capability of the upregulation of respiration may be restricted. Furthermore, we discussed the potential role of the oxygen-transporting protein hemoglobin (Hb) in the regulation of C budgets. Different food quality constraints led to certain C regulation patterns to increase the removal of excess dietary C: P-limited D. magna increased excretion and respiration, while cholesterol-limited Daphnia in addition upregulated the release of feces. In contrast, the regulative effort was low and only feces release increased when D. magna was limited by a long-chain polyunsaturated fatty acid (eicosapentaenoic acid, EPA). Co-limiting oxygen did not always impact the discharge of excess C. We found the food-quality-induced upregulation of respiration was still present at low oxygen. In contrast, higher excretion of excess C was diminished at low oxygen supply. Besides the effect that the Hb concentration increased under low oxygen, our results indicate a low food-quality-induced increase in the Hb content of the animals. Overall, C budgeting is phenotypically plastic towards different (co-) limiting scenarios. These trigger specific regulation responses that could be the result of evolutionary adaptations.
KW  - carbon budget
KW  - carbon stoichiometry
KW  - cholesterol
KW  - co-limitation
KW  - Daphnia
KW  - EPA
KW  - hemoglobin
KW  - oxygen
KW  - phosphorus
KW  - polyunsaturated fatty acid
KW  - zooplankton
Y1  - 2014
SN  - 0012-9658
SN  - 1939-9170
VL  - 95
IS  - 11
SP  - 3068
EP  - 3079
PB  - Wiley
CY  - Washington
ER  -