Quantifying water sources to a semiarid riparian ecosystem, San Pedro River, Arizona

Abstract

The Upper San Pedro River Basin (Southeastern Arizona, United States) contains one of the few desert riparian areas in the Southwest, a system that is dependent on both shallow groundwater to support phreatic vegetation and baseflow for aquatic plants and animals. Proper management decisions for sustaining this biodiversity hotspot require understanding the hydrology of the riparian system and its interaction with the basin aquifer. To meet this need and to assess whether the techniques used would be efficient for evaluating other semiarid riparian ecosystems, we addressed the following questions. What are the contributions of different water sources (e.g., local recharge during monsoon flood events versus inflow of basin groundwater) to riparian groundwater and river baseflow? How does the spatial variability in water sources relate to gaining and losing reaches along of the river? We first characterize the possible water sources to the riparian system using a suite of geochemical tracers. Results indicate that, of the possible sources, basin groundwater recharged along the Huachuca Mountains to the west and local recharge of monsoon floodwaters are the dominant riparian water sources. Then, using their geochemical composition, we quantify these sources using a two end‐member mixing model. We find that riparian groundwater composition varies between gaining and losing reaches. Locally recharged monsoon floodwater comprises 60 to 85% of riparian groundwater in losing reaches whereas that of gaining reaches contains only 10% to 40%. Baseflow, sampled year round, also contains a significant component of monsoon floodwater ranging from 80% on the upstream end and decreasing to 55% after passing though several gaining reaches. These results highlight the significance of local recharge during monsoon flood events as a water source for desert riparian systems, a fact that should be addressed when constructing and calibrating hydrologic models used to evaluate these future water management decisions.

Isotopic paleoecology of Clovis mammoths from Arizona

“…For comparison, the δ 18 O sc values expected for mammoths consuming water with the same isotopic composition as modern SPV precipitation/ runoff (mean ± 1σ = −6.3 ± 1.0‰ in summer and −11.2 ± 2.8‰ in winter) (20) were calculated using the reverse of the above equations. These give δ 18 O sc values of 26.2‰ (summer) and 21.5‰ (winter) (Fig.…”

“…Clovis mammoths consumed diets high in C 4 plants and drank water with Table S3). The δ 18 O values of meteoric water (and river, lake, or groundwater with meteoric water inputs) in most continental locations, including the modern SPV, are higher in summer and lower in winter (20,30,32,33). Thus, the peaks in the δ 18 O and δ 13 C curves in Clovis mammoths almost certainly represent summer, and the troughs, winter.…”

“…Since the last glacial-interglacial transition, precipitation in the region has occurred primarily in winter and summer (13,20). However, little else is known about seasonality in the Late Pleistocene SPV or how it affected mammoth ecology.…”

Land cover controls on summer discharge and runoff solution chemistry of semi-arid urban catchments

“…In contrast, winter precipitation events are longer in duration, lower in intensity, spatially widespread, and evenly distributed. Winter rainfall accounts for most mountain front recharge in non-urban settings (Coes and Pool, 2007;Eastoe et al, 2004); however, a significant proportion of recharge occurs via stream channel infiltration of runoff generated in response to monsoonal rainfall (Baillie et al, 2007;Goodrich et al, 2004). Therefore, urban rainfall-runoff responses may significantly impact ephemeral channel recharge.…”

Investigation of geochemical indicators to evaluate the connection between inland and coastal groundwater systems near Kaloko-Honokōhau National Historical Park, Hawai‘i

“…Where hydrogeologic information is insufficient to establish the degree of connection between adjacent groundwater systems, geochemical indicators can be used to evaluate the connection (for example, see Baillie et al, 2007;Wahi et al, 2008;Manning, 2009;Musgrove et al, 2010;Gardner and Kirby, 2011).…”