Geology topics

Kevin Hultine

Publications and source records attributed to Kevin Hultine.

3 recordsLinked to original sources

USGS2013

Phreatophytes under stress: transpiration and stomatal conductance of saltcedar ( Tamarix spp.) in a high-salinity environment

Background and aims: We sought to understand the environmental constraints on an arid-zone riparian phreatophtye, saltcedar (Tamarix ramosissima and related species and hybrids), growing over a brackish aquifer along the Colorado River in the western U.S. Depth to groundwater, meteorological factors, salinity and soil hydraulic properties were compared at stress and non-stressed sites that differed in salinity of the aquifer, soil properties and water use characteristics, to identify the factors depressing water use at the stress site. Methods: Saltcedar leaf-level transpiration (EL), LAI, and stomatal conductance (GS) were measured over a growing season (June–September) with Granier and stem heat balance sensors and were compared to those for saltcedar at the non-stress site determined in a previous study. Transpiration on a ground-area basis (EG) was calculated as EL × LAI. Environmental factors were regressed against hourly and daily EL and GS at each site to determine the main factors controlling water use at each site. Results: At the stress site, mean EG over the summer was only 30 % of potential evapotranspiration (ETo). GS and EG peaked between 8 and 9 am then decreased over the daylight hours. Daytime GS was negatively correlated with vapor pressure deficit (VPD) (P < 0.05). By contrast, EG at the non-stress site tracked the daily radiation curve, was positively correlated with VPD and was nearly equal to ETo on a daily basis. Depth to groundwater increased over the growing season at both sites and resulted in decreasing EG but could not explain the difference between sites. Both sites had high soil moisture levels throughout the vadose zone with high calculated unsaturated conductivity. However, salinity in the aquifer and vadose zone was three times higher at the stress site than at the non-stress site and could explain differences in plant EG and GS. Conclusions: Salts accumulated in the vadose zone at both sites so usable water was confined to the saturated capillary fringe above the aquifer. Existence of a saline aquifer imposes several types of constraints on phreatophyte EG, which need to be considered in models of plant water uptake. The heterogeneous nature of saltcedar EG over river terraces introduces potential errors into estimates of ET by wide-area methods.

Colorado River↗

USGS2013

Detection of tamarisk defoliation by the northern tamarisk beetle based on multitemporal Landsat 5 thematic mapper imagery.

The spread of tamarisk ( Tamarix spp., also known as saltcedar) is a significant ecological disturbance in western North America and has long been targeted for control, leading to the importation of the northern tamarisk beetle ( Diorhabda carinulata ) as a biological control agent. Following its initial release along the Colorado River near Moab, Utah in 2004, the beetle has successfully established and defoliated tamarisk across much of the upper Colorado River Basin. However, the spatial distribution and seasonal timing of defoliation are complex and difficult to quantify over large areas. To address this challenge, we tested and compared two remote sensing approaches to mapping tamarisk defoliation: Disturbance Index (DI) and a decision tree method called Random Forest (RF). Based on multitemporal Landsat 5 TM imagery for 2006-2010, changes in DI and defoliation probability from RF were calculated to detect tamarisk defoliation along the banks of Green, Colorado, Dolores and San Juan rivers within the Colorado Plateau area. Defoliation mapping accuracy was assessed based on field surveys partitioned into 10 km sections of river and on regions of interest created for continuous riparian vegetation. The DI method detected 3711 ha of defoliated area in 2007, 7350 ha in 2008, 10,457 ha in 2009 and 5898 ha in 2010. The RF method detected much smaller areas of defoliation but proved to have higher accuracy, as demonstrated by accuracy assessment and sensitivity analysis, with 784 ha in 2007, 960 ha in 2008, 934 ha in 2009, and 1008 ha in 2010. Results indicate that remote sensing approaches are likely to be useful for studying spatiotemporal patterns of tamarisk defoliation as the tamarisk leaf beetle spreads throughout the western United States.

Arizona, Colorado, New Mexico, Utah, Wyoming↗

USGS2009

Tamarisk biocontrol in the western United States: Ecological and societal implications

Tamarisk species (genus Tamarix), also commonly known as saltcedar, are among the most successful plant invaders in the western United States. At the same time, tamarisk has been cited as having enormous economic costs. Accordingly, local, state, and federal agencies have undertaken considerable efforts to eradicate this invasive plant and restore riparian habitats to pre-invasion status. Traditional eradication methods, including herbicide treatments, are now considered undesirable, because they are costly and often have unintended negative impacts on native species. A new biological control agent, the saltcedar leaf beetle (Diorhabda elongata), has been released along many watersheds in the western US, to reduce the extent of tamarisk cover in riparian areas. However, the use of this insect as a biological control agent may have unintended ecological, hydrological, and socioeconomic consequences that need to be anticipated by land managers and stakeholders undertaking restoration efforts. Here, we examine the possible ramifications of tamarisk control and offer recommendations to reduce potential negative impacts on valued riparian systems in the western US.

Frontiers in Ecology and the Environment↗