| 11. |
- Bargues Tobella, Aida, et al.
(författare)
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Strategies trees use to overcome seasonal water limitation in an agroforestry system in semiarid West Africa
- 2017
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Ingår i: Ecohydrology. - : Wiley. - 1936-0584 .- 1936-0592. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Agroforestry parklands, in which annual crops are grown under scattered mature trees, constitute the most prevalent farming system in semiarid West Africa, covering vast areas of land. The most dominant tree species in these systems is Vitellaria paradoxa, an indigenous tree to West Africa. Despite the importance of this tree in the region, no study to our knowledge has examined its sources and patterns of water uptake. In this study, we used oxygen stable isotopes at natural abundance levels to investigate water sources used by V. paradoxa both in the dry and wet season in an agroforestry parkland in Burkina Faso. We found that during the wet season soil moisture was highest near the soil surface (< 10 cm depth), yet during this time V. paradoxa preferentially accessed water from slightly deeper soil depths, obtaining ca. 90% of its water from 10 to 50 cm depth. In contrast, soil moisture in the upper soil layers was significantly lower during the dry season and as a result V. paradoxa shifted to deeper water sources, obtaining ca. 30% of its water from groundwater and ca. 50% from 30 to 600 cm depth. We also found a negative relationship between tree size and the contribution of groundwater during the dry season, whereas during the wet season V. paradoxa predominantly used water near the soil surface regardless of tree size. Knowledge about the sources and patterns of tree water uptake provides crucial information to better understand how trees influence the local water balance.
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| 12. |
- Bargues Tobella, Aida, et al.
(författare)
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The effect of trees on preferential flow and soil infiltrability in an agroforestry parkland in semiarid Burkina Faso
- 2014
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Ingår i: Water Resources Research. - 0043-1397 .- 1944-7973. ; 50, s. 3342-3354
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Tidskriftsartikel (refereegranskat)abstract
- Water scarcity constrains the livelihoods of millions of people in tropical drylands. Tree planting in these environments is generally discouraged due to the large water consumption by trees, but this view may neglect their potential positive impacts on water availability. The effect of trees on soil hydraulic properties linked to groundwater recharge is poorly understood. In this study, we performed 18 rainfall simulations and tracer experiments in an agroforestry parkland in Burkina Faso to investigate the effect of trees and associated termite mounds on soil infiltrability and preferential flow. The sampling points were distributed in transects each consisting of three positions: (i) under a single tree, (ii) in the middle of an open area, and (iii) under a tree associated with a termite mound. The degree of preferential flow was quantified through parameters based on the dye infiltration patterns, which were analyzed using image analysis of photographs. Our results show that the degree of preferential flow was highest under trees associated with termite mounds, intermediate under single trees, and minimal in the open areas. Tree density also had an influence on the degree of preferential flow, with small open areas having more preferential flow than large ones. Soil infiltrability was higher under single trees than in the open areas or under trees associated with a termite mound. The findings from this study demonstrate that trees have a positive impact on soil hydraulic properties influencing groundwater recharge, and thus such effects must be considered when evaluating the impact of trees on water resources in drylands.
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| 13. |
- Bargues Tobella, Aida, et al.
(författare)
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Trees in African drylands can promote deep soil and groundwater recharge in a future climate with more intense rainfall
- 2020
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Ingår i: Land Degradation and Development. - : Wiley. - 1085-3278 .- 1099-145X. ; 31, s. 81-95
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Tidskriftsartikel (refereegranskat)abstract
- Tropical regions are likely to experience more intense rainfall events in the future. Such an increase in rainfall intensities will affect soil and groundwater recharge, with potential consequences for millions of people. However, little is known about the impact of tree cover on soil and groundwater recharge under higher rainfall intensities. Here, we investigated the effect of tree cover and rainfall intensity on soil water drainage in an agroforestry parkland in West Africa. We collected soil water drainage from lysimeters located at 50 and 150 cm depth in both small and large open areas among trees, which represent contrasting degrees of tree cover, and analyzed a subset of water samples for delta O-18 and delta H-2 to gain insights into the mechanisms of water flow within the soil profile. We found that under high rainfall intensities (>20 mm d(-1)), the median daily soil water drainage amount at 150 cm was 13 times higher in the small compared with the large open areas, whereas at 50 cm, there were no significant differences. Low rainfall intensities (<10 mm d(-1)) resulted in little soil water drainage both at 50 and 150 cm depth, regardless of canopy opening size. The isotopic signature of soil water drainage suggested less evaporation and a higher degree of preferential flow in small compared with large open areas. Our results suggest that maintaining or promoting an appropriate tree cover in tropical African drylands may be key to improving deep soil and groundwater recharge under a future climate with more heavy rainfall.
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| 14. |
- Berggren, Martin, 1981-, et al.
(författare)
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Aging of allochthonous organic carbon regulates bacterial production in unproductive boreal lakes
- 2009
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 54:4, s. 1333-1342
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Tidskriftsartikel (refereegranskat)abstract
- We calculated average aquatic dissolved organic carbon (DOC) age (the time span from soil discharge to observation) in water from the inlets and outlets of two unproductive Swedish lakes at different times during an annual cycle. Bacterial production (BP) and bacterial growth efficiency (BGE) determined during 7-d bioassays decreased with increasing average aquatic DOC age. Parallel to the declines in BP and BGE there was a rise in specific ultraviolet absorbance at the wavelength of 254 nm (SUVA254), which indicates that decreasing BP and BGE were connected to a shift to a more aromatic and recalcitrant DOC pool. The relationships between bacterial metabolism and DOC age were stronger after a Q10 correction of the DOC age, showing that temperature affected rates of DOC quality changes over time and should be taken into account when relating lake bacterial growth to substrate aging in natural environments. We propose that hydrological variability in combination with lake size (water renewal time) have a large influence on pelagic BP in lakes with high input of terrigenous DOC.
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| 15. |
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| 16. |
- Berggren, Martin, 1981-, et al.
(författare)
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Efficient aquatic bacterial metabolism of dissolved low-molecular-weight compounds from terrestrial sources
- 2010
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Ingår i: The ISME Journal. - London : Nature Publishing Group. - 1751-7362 .- 1751-7370. ; 4:3, s. 408-416
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Tidskriftsartikel (refereegranskat)abstract
- Carboxylic acids (CAs), amino acids (AAs) and carbohydrates (CHs) in dissolved free forms can be readily assimilated by aquatic bacteria and metabolized at high growth efficiencies. Previous studies have shown that these low-molecular-weight (LMW) substrates are released by phytoplankton but also that unidentified LMW compounds of terrestrial origin is a subsidy for bacterial metabolism in unproductive freshwater systems. We tested the hypothesis that different terrestrially derived CA, AA and CH compounds can offer substantial support for aquatic bacterial metabolism in fresh waters that are dominated by allochthonous dissolved organic matter (DOM). Drainage water from three catchments of different characters in the Krycklan experimental area in Northern Sweden were studied at the rising and falling limb of the spring flood, using a 2-week bioassay approach. A variety of CA, AA and CH compounds were significantly assimilated by bacteria, meeting 15–100% of the bacterial carbon demand and explaining most of the observed variation in bacterial growth efficiency (BGE; R2=0.66). Of the 29 chemical species that was detected, acetate was the most important, representing 45% of the total bacterial consumption of all LMW compounds. We suggest that LMW organic compounds in boreal spring flood drainage could potentially support all in situ bacterial production in receiving lake waters during periods of weeks to months after the spring flood.
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| 17. |
- Berggren, Martin, 1981-, et al.
(författare)
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Hydrological control of organic carbon support for bacterial growth in boreal headwater streams
- 2009
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Ingår i: Microbial Ecology. - : Springer Science and Business Media LLC. - 0095-3628 .- 1432-184X. ; 57:1, s. 170-178
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Tidskriftsartikel (refereegranskat)abstract
- Terrestrial organic carbon is exported to freshwater systems where it serves as substrate for bacterial growth. Temporal variations in the terrigenous organic carbon support for aquatic bacteria are not well understood. In this paper, we demonstrate how the combined influence of landscape characteristics and hydrology can shape such variations. Using a 13-day bioassay approach, the production and respiration of bacteria were measured in water samples from six small Swedish streams (64° N, 19° E), draining coniferous forests, peat mires, and mixed catchments with typical boreal proportions between forest and mire coverage. Forest drainage supported higher bacterial production and higher bacterial growth efficiency than drainage from mires. The areal export of organic carbon was several times higher from mire than from forest at low runoff, while there was no difference at high flow. As a consequence, mixed streams (catchments including both mire and forest) were dominated by mire organic carbon with low support of bacterial production at low discharge situations but dominated by forest carbon supporting higher bacterial production at high flow. The stimulation of bacterial growth during high-flow episodes was a result of higher relative export of organic carbon via forest drainage rather than increased drainage of specific “high-quality” carbon pools in mire or forest soils.
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| 18. |
- Berggren, Martin, et al.
(författare)
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Lake secondary production fueled by rapid transfer of low molecular weight organic carbon from terrestrial sources to aquatic consumers
- 2010
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 13:7, s. 870-880
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Tidskriftsartikel (refereegranskat)abstract
- P>Carbon of terrestrial origin often makes up a significant share of consumer biomass in unproductive lake ecosystems. However, the mechanisms for terrestrial support of lake secondary production are largely unclear. By using a modelling approach, we show that terrestrial export of dissolved labile low molecular weight carbon (LMWC) compounds supported 80% (34-95%), 54% (19-90%) and 23% (7-45%) of the secondary production by bacteria, protozoa and metazoa, respectively, in a 7-km2 boreal lake (conservative to liberal estimates in brackets). Bacterial growth on LMWC was of similar magnitude as that of primary production (PP), and grazing on bacteria effectively channelled the LMWC carbon to higher trophic levels. We suggest that rapid turnover of forest LMWC pools enables continuous export of fresh photosynthates and other labile metabolites to aquatic systems, and that substantial transfer of LMWC from terrestrial sources to lake consumers can occur within a few days. Sequestration of LMWC of terrestrial origin, thus, helps explain high shares of terrestrial carbon in lake organisms and implies that lake food webs can be closely dependent on recent terrestrial PP.
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| 19. |
- Berggren, Martin, 1981-, et al.
(författare)
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Landscape regulation of bacterial growth efficiency in boreal freshwaters
- 2007
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Ingår i: Global Biogeochemical Cycles. - : American Geophysical Union. - 0886-6236 .- 1944-9224. ; 21
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Tidskriftsartikel (refereegranskat)abstract
- Allochthonous organic carbon in aquatic systems is metabolized by heterotrophic bacteria, with significant consequences for the biostructure and energy pathways of freshwater ecosystems. The degree to which allochthonous substrates support growth of bacteria is largely dependent on bacterial growth efficiency (BGE), i.e., bacterial production (BP) per unit of assimilated carbon. Here we show how the spatial variability of BGE in the boreal region can be mediated by the distribution of the two dominating landscape elements forest and mires. Using an 11 days bioassay approach, the production and respiration of bacteria were measured in water samples from nine small Swedish streams (64°N 19°E), representing a gradient ranging from organic carbon supplied mainly from peat mires to carbon supplied mainly from coniferous forests. BP was positively correlated to forest coverage (%) of the catchment, while bacterial respiration was similar in all streams. Consequently, BGE showed a strong positive correlation with forest coverage. Partial least square regression showed that BGE was chiefly regulated by qualitative properties of the organic material, indicated by the absorbance ratio a254/a365 plus C/N and C/P ratios. The data suggest that a share of the organic carbon pool, drained mainly from forest soils, had a potential of being incorporated into bacterial biomass with great efficiency. Its potential for supporting growth was probably nutrient regulated as indicated by inorganic nutrient enrichment experiments.
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| 20. |
- Berggren, Martin, 1981-, et al.
(författare)
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Nutrient constraints on metabolism affect the temperature regulation of aquatic bacterial growth efficiency
- 2010
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Ingår i: Microbial Ecology. - : Springer. - 0095-3628 .- 1432-184X. ; 60:4, s. 894-902
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Tidskriftsartikel (refereegranskat)abstract
- Inorganic nutrient availability and temperature are recognized as major regulators of organic carbon processing by aquatic bacteria, but little is known about how these two factors interact to control bacterial metabolic processes. We manipulated the temperature of boreal humic stream water samples within 0–25°C and measured bacterial production (BP) and respiration (BR) with and without inorganic nitrogen + phosphorus addition. Both BP and BR increased exponentially with temperature in all experiments, with Q 10 values varying between 1.2 and 2.4. The bacterial growth efficiency (BGE) showed strong negative relationships with temperature in nutrient-enriched samples and in natural stream water where community-level BP and BR were not limited by nutrients. However, there were no relationships between BGE and temperature in samples where BP and BR were significantly constrained by the inorganic nutrient availability. The results suggest that metabolic responses of aquatic bacterial communities to temperature variations can be strongly dependent on whether the bacterial metabolism is limited by inorganic nutrients or not. Such responses can have consequences for both the carbon flux through aquatic food webs and for the flux of CO2 from aquatic systems to the atmosphere.
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