Tim P. Duval

Disentangling the Effects of Precipitation Amount and Frequency on the Performance of 14 Grassland Species.

Climate change is causing shifts in the amount and frequency of precipitation in many regions, which is expected to have implications for plant performance. Most research has examined the impacts of the amount of precipitation on plants rather than the effects of both the amount and frequency of precipitation. To understand how climate-driven changes in precipitation can affect grassland plants, we asked: (i) How does the amount and frequency of precipitation affect plant performance? (ii) Do plant functional groups vary in their response to variable precipitation? To answer these questions we grew 14 monocot and eudicot grassland species and conducted a factorial manipulation of the amount (70 vs 90mm/month) and frequency (every 3, 15, or 30 days) of precipitation under rainout shelters. Our results show that both the amount and frequency of precipitation impact plant performance, with larger effects on eudicots than monocots. Above- and below-ground biomass were affected by the amount of precipitation and/or the interaction between the amount and frequency of precipitation. Above-ground biomass increased by 21–30% when the amount of precipitation was increased. When event frequency was decreased from 3 to 15 or 30 days, below-ground biomass generally decreased by 18–34% in the 70 mm treatment, but increased by 33–40% in the 90 mm treatment. Changes in stomatal conductance were largely driven by changes in event frequency. Our results show that it is important to consider changes in both the amount and frequency of precipitation when predicting how plant communities will respond to variable precipitation.

Effect of residential development on stream phosphorus dynamics in headwater suburbanizing watersheds of southern Ontario, Canada

Suburban landscapes are known to have degraded water quality relative to natural settings, including increased total phosphorus (TP) levels; however, the effect of subdivision construction activities on stream TP dynamics are less understood. This study measured TP and its constituents particulate, dissolved organic, and dissolved inorganic phosphorus (PP, DOP, and DIP, respectively) in two headwater streams of contrasting urbanization activity to examine whether the land-use conversion process itself contributed to TP concentrations and export. The nested watershed undergoing significant active residential community construction contained large areas of cleared former agricultural field and associated sediment mounds with elevated soil TP (~1000 mg kg-1), and twice as many stormwater management (SWM) ponds than the watershed with completed suburban communities. Daily stream sampling for six months revealed limited differences in TP between urbanized and urbanizing watersheds regardless of season or stream flow condition; however, the forms of TP varied significantly. The proportion of TP as DOP was consistently higher in the urbanizing stream relative to the urban stream, which was in line with significant decreases in DOP concentration as proportion of cleared former agricultural land decreased and density of SWM ponds increased. The DOP, and to a lesser extent DIP and PP, dynamics resulted in a 2.5× greater areal export of TP from a small watershed actively being suburbanized during the study period compared to the larger watershed with greater land urbanized 3-5 years ago. The results of this study suggest stream TP concentrations are relatively unresponsive to active versus established suburban cover, but the forms of TP can be quite different, and the period of home construction can increase phosphorus (P) delivery to and export through nearby streams. This information can aid land managers and urban planners update best management practices to mitigate the transfer of terrestrial P to the aquatic environment.

Effect of hydrogeomorphic setting on calcareous fen hydrology

Department of Geography, University of Toronto Mississauga, 3359 Mississauga Rd., Mississauga, ON L5L 1C6, Canada School of Geography and Earth Sciences, McMaster University, 1280 Main St. W.., Hamilton, ON L8S 4K1, Canada Correspondence Tim Duval, Department of Geography, University of Toronto Mississauga, 3359 Mississauga Rd, Mississauga, ON L5L 1C6, Canada. Email: tim.duval@utoronto.ca Funding information Natural Sciences and Engineering Research Council of Canada; NSERC; The Ontario Aggregate Resources Corporation

Response of herbaceous wetland plant species to changing precipitation regimes: Response of wetland plant species to changing precipitation regimes

Department of Geography, University of Toronto Mississauga, Mississauga, Ontario, Canada Department of Biology, University of Toronto Mississauga, Mississauga, Ontario, Canada Correspondence Tim P. Duval, Department of Geography, University of Toronto Mississauga, 3359 Mississauga Rd, Mississauga, ON, L5L 1C6 Canada. Email: tim.duval@utoronto.ca Funding information University of Toronto; Ontario Graduate Scholarship; NSERC, Grant/Award Number: 418197

Response of hydrology and CO 2 flux to experimentally-altered rainfall frequency in a temperate poor fen, southern Ontario, Canada

Predicted changes to the precipitation regime in many parts of the world include intensifying the distribution into lower frequency, large magnitude events. The corresponding alterations to the soil moisture regime may affect plant growth and soil respiration, particularly in peatlands, where large stores of organic carbon are due to gross ecosystem productivity (GEP) exceeding ecosystem respiration (ER). This study uses lab monoliths corroborated with field measurements to examine the effect of changing rainfall frequency on peatland moisture controls on CO2 uptake in an undisturbed cool temperate poor fen. Lab monoliths and field plots containing mosses, sedges, or shrubs received either 2.3, 1, or 0.5 precipitation events per week, with total rainfall held constant. Decreasing rain frequency led to lower near-surface volumetric moisture content (VMC), water table (WT), and soil tension for all vegetation types, with minimal effect on evapotranspiration. The presence of sedges in particular led to soil tensions of ≥ 100 cm of water for a sizeable duration (37 %) of the experiment. Altered rainfall frequencies affected GEP but had little effect on ER; overall, low-frequency rain led to a reduced net CO2 uptake for all three vegetation types. VMC had a strong control on GEP and net ecosystem exchange (NEE) of the Sphagnum capillifolium monoliths, and decreasing rainfall frequency influenced these relationships. Overall, communities dominated by mosses became net sources of CO2 after 3 days without rain, whereas sedge communities remained net sinks for up to 14 days without rain. The results of this study demonstrate the hydrological controls of peatland CO2 exchange dynamics influenced by changing precipitation frequency; furthermore, they suggest these predicted changes in frequency will lead to increased sedge GEP but limit the carbon-sink function of peatlands.