Nature and variability of water resources in the Rio Santa upper watershed, Peru
The ongoing global retreat of mountain glaciers is stressing the water resources availability for regions where glacial melt water represents a significant part of the annual water budget. The Cordillera Blanca, Peru, has the highest density of glaciers in the tropics. The majority of the region's population and economical activity are located along the arid Pacific coast plains and the western slopes of the Andes where the land is typically dry and dependent on runoff from the Cordillera Blanca. The impact of glacial retreat on water resources is a function of not only glacial melt water but also other sources of water such as groundwater and runoff. To date, there has been very little research studying the relative contributions of non-glacial melt water to pro-glacial systems in the tropics. We present research using a new distributed hydrochemical basin characterization method (HBCM) to analyze hydrologic end-members contribution to 4 glacially fed watersheds within the mountain range. Water samples from streams, glacial melt, runoff, and groundwater, were collected in the dry and wet seasons 2008. Samples were analyzed for major ions (e.g., SO42-, Mg2+) and the stable isotopes of water (ä18O and ä2H). These tracers are used to distinguishing significant characteristics of individual end members and their chemical behaviour. The HBCM combines mass-based end-member mixing with geospatial component contributions in order to evaluate both source contributions and where these sources enter the hydrologic system.. The results show that surface runoff is the major contributor to streams flows during the wet season and that melt water and groundwater dominate during the dry season. With dry season specific discharges above 0.4 mm per day at all valleys, groundwater comes out as a critical contributor to tropical proglacial hydrologic systems. Differences observed in hydrochemical signature between groundwater samples indicate that the groundwater system is complex, likely the result of multifaceted flow system through unconsolidated pro- glacial deposits.
In Lieu of the Paired-Catchment Approach - Hydrologic Model Change Detection at the Catchment Scale
Knowledge of the effects of forest management on hydrology primarily comes from paired-catchment studies conducted world-wide. While this approach has been useful for discerning changes in small experimental catchments and has contributed fundamental knowledge of the effects of forest and natural resources management on hydrology, results from experimental catchment studies exhibit temporal variability, have limited spatial inference, and lack insight into internal catchment processes. To address these limitations, traditional field experiments can be supplemented with numerical models to isolate the effects of disturbance on catchment behavior. Outlined in this study is an alternative method of change detection for daily time-series streamflow that integrates hydrologic modeling and statistical change detection methods used to discern the effects of contemporary forest management on the hydrology of western Oregon Cascades headwater catchments. In this study, a simple rainfall-runoff model was used to generate virtual reference catchments using attributes that reflect streamflow conditions absent of forest disturbance. Streamflow was simulated under three levels of model uncertainty using GLUE and were used to construct generalized least squares regression models to discern changes in hydrologic behavior. By considering processes within a single experimental catchment rather than the two spatially explicit catchments used in traditional paired experiments, it was possible to reduce unexplained variation and increase the likelihood of correctly detecting hydrologic effects following forest harvesting. In order to evaluate the stability of the hydrologic and statistical models and catchment behavior over time, the change detection method was applied to a contemporary reference catchment. By applying the change detection model to reference catchments, it was possible to eliminate unexpected variation as a cause for detected changes in observed hydrology. Further, it was possible to attribute increased streamflow to forest management with greater certainty. Shown is the importance and necessity of coupling hydrologic modeling studies with reference catchments in order to evaluate model performance and reduce false detections from statistical models. The proposed method appears to be a useful alternative to change detection using highly variable daily streamflow.
Mountain pine beetle and hydrology: addressing scale issues with process research in experimental hydrology
Mountain pine beetle (MPB) is a major forest disturbance that has affected large areas of Western North America's forested land base. Hydrologic impacts of MPB are driven by changes to stand scale processes regulating evaporative fluxes, soil/groundwater recharge, and runoff generation. However, while recent studies have provided detailed process knowledge of some of the stand-scale hydrologic impacts of infestation, scaling of stand level insights to the watershed scale remains a formidable challenge. While numerical models are beginning to assess likely watershed-scale impacts, few field-based process studies have been completed at this scale to address these questions. This talk builds on stand-scale process studies of snow-forest interactions in beetle-killed forests in northern British Columbia, and outlines a new research approach at a research basin in southwestern Alberta. This new study will apply the paired catchment approach common in experimental watershed hydrology to assess the impacts of both increasing MPB infestation intensity and associated management interventions on watershed-scale hydrology, and to assess impacts on montane versus alpine/sub-alpine regions of these watersheds.
Evapotranspiration From Above and Within a Western Boreal Plain Aspen Forest
The Western Boreal Plain (WBP) of North Central Alberta consists of a mosaic of wetlands and aspen (Populous tremuloides) dominated uplands. This region operates within a moisture deficit regime where precipitation (P) and evapotranspiration (ET) are the dominant hydrologic fluxes. Upland ET was characterized over three scales during the 2005 and 2006 snow-free seasons. Above canopy (ETC) and within canopy (ETB) were examined using the eddy covariance (EC) technique situated at 25.5 m (7.5 m above crown) and 4.0 m above the ground surface respectively. Soil evaporation (ES) was examined using a closed dynamic chamber system to gather data on surface evaporation for upland soils. ETC and ETB were controlled primarily through atmospheric demand (VPD) while ES was controlled by soil moisture (è). During peak growth periods ETC averaged 3.08 mm d-1 and 3.45 mm d-1 in 2005 and 2006 respectively while ETB averaged 1.56 mm d-1 and 1.95 mm d-1. ES was consistent across both snow-free seasons and averaged 0.28 mm hr-1 in 2005 and 0.31 mm hr-1 in 2006. The nature of Populous tremuloides canopies permits ample energy availability within the canopy during the early season green up periods which promotes the development of a lush understory consisting of Rosa acicularis and Viburnum edule. ETB fluxes were equal to or greater than the ETC fluxes once understory development had occurred. Upon crown growth ETB fluxes were reduced as a reduction in available energy existed. ETB fluxes ranged from 42 to 56% of ETC fluxes over the remainder of the snow-free seasons. Vapour pressure deficit (VPD) and soil moisture (è) displayed strong controls on both ETC and ETB fluxes. ETC fluxes responded to precipitation events as the developed crown intercepted and held available water which contributed to peak ETC fluxes following precipitation events >10 mm. This indicates the importance of interception in aspen dominated forest canopies of the WBF.
Hydrologic connectivity and runoff response in the METAALICUS experimental catchment
The response of fish methylmercury concentrations to changes in mercury deposition remains difficult to establish, in part, due to uncertainty about the hydrologic controls on the magnitude and timing of mercury release from upland soils and the export of upland mercury to the lake. Previous studies have measured large fluxes of mercury coincident with large runoff events, such as snowmelt and storms that generate quickflow, however, analysis of the mechanisms within the catchment that control these patterns remains sparse. Therefore, we examined the relationship between runoff response at the catchment outlet and hydrologic connectivity between different hydrologic response units within the catchment. This information will be used to better inform the interpretation and modeling of the response of upland mercury export to changes in atmospheric Hg loading. This study is part of METAALICUS (Mercury Experiment to Assess Atmospheric Loading in Canada and the United States), a unique whole-ecosystem experiment located at the Experimental Lakes Area in northwestern Ontario. The 7.75 ha upland experimental catchment is typical of the boreal Canadian Shield landscape in this region. Inter-year comparisons of rainfall and stream discharge response show that there is substantial variability from wet to drier conditions. Hydrograph separations of all storm events since 2001 indicate a threshold of 6 mm of rainfall required to generate a runoff response at the catchment outlet. Temporal variations in runoff response indicate that antecedent wetness conditions and the relative storage deficits of within-catchment landscape units exert a primary and predictable control on runoff generation by regulating subwatershed hydrologic connectivity. The frequency distribution of runoff coefficients and the analysis of a LIDAR-derived digital elevation model illustrate variability in the hydrologic contributing area and the "fill and spill" nature of this upland system. The hydrologic behavior of this catchment suggests that the timing and magnitude of mercury export will be influenced by not only the size of the runoff event, but also by the extent of hydrologic connectivity between different landscape units within the catchment.
Can Stream Hydrographs be Used to Estimate How Long Water Resides in the Catchment?
We test the hypothesis that transit time of water through a catchment can be derived from stream hydrograph recession analysis. We compare estimates of mean transit times generated using a stream hydrograph recession based technique with those from streamflow-precipitation O-18 derived convolution modeling for six gauged watersheds (0.10 to 62.4 km2) at the HJ Andrews Experimental Forest in Western Oregon, USA. Using an exponential model approximation of baseflow recession, watershed-scale hydraulic properties are estimated from master recession curves generated for each watershed from 11 years of daily streamflow data. Watershed-scale hydraulic properties are then used in a conjunction with an index of mean baseflow transit time to generate estimates for each watershed. The hydrograph recession based estimates of transit time were able to explain 84% of the variance in isotope-based transit times for the six watersheds and followed the same scaling behavior, where transit time was unrelated to watershed size, but highly correlated to internal topographic arrangement of sub-watersheds. Our analysis provides encouraging evidence that streamflow recession analysis can be used to approximate water transit time at the catchment scale, thus providing an alternative to the hitherto sole isotope-based transit time approach.
Assessing the Performance of two Stormwater Management Ponds in Waterloo, Ontario
Stormwater runoff in urban areas represents a major pathway for pollutant transfer to receiving waters. Stormwater management (SWM) ponds are used as a best management practice to help mitigate the negative effects of stormwater. This study examines the performance of two SWM pond designs (conventional and extended detention) in Waterloo, Ontario, Canada. A mass balance approach is used to quantify the concentration of total phosphorus (TP), soluble reactive phosphorus (SRP) and total suspended solids (TSS) at the inlet(s) and outlet of each pond. These parameters were sampled and characterized for 30 baseflow observations and 10 stormflow events in order to calculate the trap efficiency for each pond. The results show that, baseflow reduction for all constituents was low for both ponds. Pond 33 (extended detention design) was a source of TP and SRP during baseflow periods with trap efficiencies of -34% and -61% respectively. Pond 45 (conventional design) retained 65% of influent TP and 36% SRP. Both ponds were sinks for TSS during baseflow periods with 61% and 48% of SS retained for Pond 33 and Pond 45 respectively. Retention during storm events was higher compared to baseflow periods. Pond 33 retained 11%, 40% and 66% of TP, SRP and TSS, whereas Pond 45 had a higher trap efficiency of 90%, 93% and 97% for TP, SRP and TSS. Trap efficiency of these constituents are governed by pH, temperature and dissolved oxygen, as well as sediment geochemistry, P speciation and cycling at the sediment-water interface. Additional research focusing on P cycling in SWM ponds is required to improve trap efficiencies through improved pond design.